Recycling metal bv membrane distillation

The invention relates to a method of and an apparatus for recovering metal from a chemical bath for chemically treating a structure with metal, and to a method of use.

In the context of growing product functionalities of component carriers equipped with one or more electronic components and increasing miniaturization of such components as well as a rising number of components to be mounted on the component carriers such as printed circuit boards, increasingly more powerful array-like components or packages having several components are being employed, which have a plurality of contacts or connections, with ever smaller spacing between these contacts. Removal of heat generated by such components and the component carrier itself during operation becomes an increasing issue. At the same time, component carriers shall be mechanically robust and electrically reliable so as to be operable even under harsh conditions.

During manufacturing component carriers and other products using conventional manufacturing technology, a considerable amount of waste may occur.

There may be a need to manufacture metal-coated structures with a reduced amount of waste.

According to an exemplary embodiment of the invention, a method of recovering metal (in particular a heavy metal) from a chemical bath for chemically treating a structure (for instance a component carrier structure) with metal (in particular during manufacturing component carriers) is provided, wherein the method comprises supplying a chemical composition comprising metal from the chemical bath to a membrane distillation device, separating at least part of the metal in the membrane distillation device, and reintroducing the separated metal into the chemical bath.

According to another exemplary embodiment of the invention, an apparatus for recovering metal from a chemical bath for chemically treating a structure (for instance a component carrier structure) with metal (for instance during manufacturing component carriers) is provided, wherein the apparatus comprises a supply unit configured for supplying a chemical composition comprising metal from the chemical bath to a membrane distillation device, the membrane distillation device configured for separating at least part of the metal by membrane distillation, and a reintroduction unit configured for reintroducing the separated metal into the chemical bath.

According to yet another exemplary embodiment of the invention, membrane distillation is used (for instance in a component carrier manufacture plant) for separating metal from a chemical bath and for reintroducing the separated metal into the chemical bath, preferably in a controlled way so as to keep a metal concentration in the chemical bath constant.

In the context of the present application, the term "structure" may particularly denote any physical body, in particular plate-shaped body, to be subjected to a metal treatment.

In the context of the present application, the term "component carrier" may particularly denote any support structure which is capable of accommodating one or more components thereon and/or therein for providing mechanical support and/or electrical connectivity. In other words, a component carrier may be configured as a mechanical and/or electronic carrier for components. In particular, a component carrier may be one of a printed circuit board, an organic interposer, and an IC (integrated circuit) substrate. A component carrier may also be a hybrid board combining different ones of the above mentioned types of component carriers.

In the context of the present application, the term "component carrier structure" may particularly denote a preform of component carriers being presently manufactured. In particular, the component carrier structure may comprise a plurality of still integrally connected component carriers or preforms thereof which may be manufactured in a batch process before being singularized. In particular, a component carrier structure may be a panel (for example having a dimension of 18 inch x 24 inch, or larger), or an array (of for instance six component carriers being presently manufactured). For example, the manufactured component carriers may be printed circuit boards or IC substrates. In the context of the present application, the term "component carrier manufacture plant" may particularly denote a plant or factory in which components carriers such as PCBs or IC substrates are manufactured.

In the context of the present application, the term "chemical bath" may particularly denote a chemical composition in a container and comprising different chemicals, including a metal (for instance metal in elementary form and/or a dissolved metal) and a solvent such as water. One or more further chemicals may be included in the chemical composition, such as one or more additives. The chemical bath may be configured for carrying out a predefined chemical treatment (for instance of a component carrier structure), in particular plating. In such an embodiment, the chemical bath may also be denoted as plating bath or plating unit. For instance, the chemical bath may be adapted for electroplating. Electroplating is a process that uses an electric current to reduce dissolved metal cations so that they form a thin coherent metal coating on an electrode, in particular a component carrier structure. In one technique, the anode is made of the metal to be plated on the (for instance component carrier) structure. Both the anode and the (for instance component carrier) structure may be immersed in an electrolyte solution containing one or more dissolved metal salts as well as other ions that permit the flow of electricity. A power supply supplies a direct current to the anode, oxidizing the metal atoms that it comprises and allowing them to dissolve in the solution. At the cathode, the dissolved metal ions in the electrolyte solution are reduced at the interface between the solution and the cathode, such that they plate out onto the cathode, for instance the component carrier structure. Other electroplating processes may use a non-consumable anode, and ions of the metal to be plated can be replenished and/or reintroduced in the chemical bath as they are drawn out of the solution.

In the context of the present application, the term "chemical fluid" may particularly denote a liquid and/or gaseous solvent or solvent composition, optionally comprising solid particles and/or one or more additives.

In the context of the present application, the term "membrane distillation" may particularly denote a thermally driven separation process in which separation is driven by a phase change. A hydrophobic membrane may be provided as a barrier for a liquid and/or solid phase, allowing a vapor or gaseous phase (for example water vapor) to selectively pass through pores of the membrane. A driving force of the separation process may be a partial vapor pressure difference which may be triggered by a temperature difference.

According to an exemplary embodiment of the invention, a metal recycling and/or metal control system for a plant (such as a component carrier manufacture plant) is provided, in which a metal from a chemical bath for treating (for instance component carrier) structures is separated by membrane distillation. The separated metal can then be fed back into the chemical bath for use in the next iteration, cycle, or phase of a chemical treatment of (for instance component carrier) structures in the chemical bath. By taking this measure, substantially the entire metal content can be maintained within a closed system rather than disposing large amounts of residual metal. Consequently, exemplary embodiments of the invention may ensure an efficient use of metallic resources and keep the ecological footprint during manufacturing products such as component carriers small. Advantageously, it may be possible to control the metal recycling and metal feedback into the chemical bath to avoid undesired dilution of the chemical bath and keep preferably the metal concentration in the chemical bath substantially constant. Advantageously, membrane distillation may be used as a concentration technology to concentrate and reintroduce metal, for instance to avoid a water excess due to a rinsing process, for example to keep a metal concentration in a chemical bath stable over time. Besides the recovery of valuable resources like metals, exemplary embodiments may contribute to waste prevention, since, as a consequence of the recovery of resources, waste may be avoided. For instance, only a solvent such as water may be removed by membrane distillation separation from the chemical bath, while other substances (like acids and additives used for proper plating) may all be recovered. Therefore, a significant amount of hazard waste may be avoided.

Another advantageous effect of embodiments of the invention is that the temperature may be kept constant in the chemical bath. Additives present in the chemical bath may be highly sensitive to temperature fluctuations and may be even damaged once a certain temperature threshold is exceeded (for instance 40°C). Therefore, membrane distillation is a perfect tool in order to recover metal (optionally including plating additives) and solvent (such as water) on the one hand, and to control the temperature of the chemical bath on the other hand. Hence, the concentrated metal solution may already be at a target temperature once it is supplied to the chemical bath.

More specifically, exemplary embodiments of the invention may ensure a significant reduction of a chemical drag-out by implementing membrane distillation in a process of manufacturing structures such as component carriers. In particular, a membrane distillation process may be used to control the concentration of a chemical bath, in particular electroplating liquids of a chemical bath. Advantageously, recovered metal (in particular electroplating substances) may be concentrated and returned to the chemical bath. However, other products than components carriers may be treated in the mentioned way as well. Examples are for instance structures or products treated by gold plating, zinc plating, nickel plating, etc. Generally, embodiments may refer to surface treatment as for instance electro-plating and corresponding applications.

In the following, further exemplary embodiments of the methods and the apparatus will be explained.

In an embodiment, the metal comprises at least one of the group consisting of gold, palladium, tin, silver, iron, nickel, cobalt, lead, iridium, zinc, and copper. The metal may be present in dissolved form and/or as elemental metal. In particular, any kind of heavy metal processed in surface metallization processes (example in terms of component carrier manufacture) may be recovered by exemplary embodiments. In the context of the present application, the term "heavy metals" may particularly denote metals having a density of more than 5 g/cm ³ . In particular, heavy metals may encompass iron, copper, nickel, tin, silver, gold, palladium, and platinum. However, recycling of gold and palladium may be of utmost importance in view of their limited availability.

In an embodiment, the method comprises separating a solvent or chemical fluid, in particular water, from the metal in the membrane distillation device, and reintroducing the separated solvent or chemical fluid into a rinsing system. In addition to the concentration of the metal on one side of the distillation membrane, the accumulated solvent (in particular water) on the opposing side can be fed back as well into a manufacturing process, preferably as rinsing fluid into a rinsing system. Advantageously, an additionally separated chemical fluid such as water can be recycled by membrane distillation as well, and may for instance be fed back to a rinsing system for a subsequent rinsing process. Said rinsing process may be carried out after the chemical treatment of the structure (in particular component carrier structure) in the chemical bath. For instance, the structure which may be provided with metal in the chemical treatment may be rinsed after the chemical treatment to remove excessive amount of metal, and the rinsing fluid including the removed metal may then be supplied into the chemical bath. Medium from this diluted chemical bath may then be supplied to the membrane distillation device for separation of metal against water. By keeping the solvent such as water in the manufacturing process as well, the resources may be used even more efficiently.

In an embodiment, the method comprises separating at least one further substance of the chemical composition in the membrane distillation device, and in particular reintroducing the separated at least one further substance into the chemical bath. For instance, the method comprises concentrating the at least one further substance before reintroducing the concentrated at least one further substance into the chemical bath. In particular, the at least one further substance comprises at least one of the group consisting of at least one plating additive, an acid, and a base. Recycling such substances used during a manufacturing process (for instance for manufacturing component carriers) may avoid waste, reduce the ecological footprint and may save resources.

In an embodiment, the method comprises rinsing chemically treated structures (in particular component carrier structures) by the rinsing system, in particular using the reintroduced solvent. After a plating process, which may be executed with the structure (in particular component carrier structure) in the chemical bath, excessive metallic contaminants of the structure may be removed by rinsing. The required rinsing fluid may be returned from the distillation membrane.

In an embodiment, the method comprises rinsing the structure (in particular component carrier structure) with rinsing fluid directly in or above the chemical bath. In particular, rinsing fluid may be supplied, before, during and/or after rinsing, from a rinsing system to the chemical bath. As a result, the chemical bath may be diluted with rinsing fluid. A diluted solution of a chemical fluid with dissolved metal may then be supplied for metal reconcentration to the membrane distillation device, and the re-concentrated dissolved metal may be supplied back to the chemical bath.

In an embodiment, the method comprises reintroducing the separated solvent into the rinsing system with a flow rate in a range from 5 l/h to 50 l/h in particular in a range from 10 l/h to 30 l/h. Thus, already relatively small flow rates may be sufficient for operating the rinsing system with recovered fluid. These moderate flow rates reflect the fact that the focus of exemplary embodiments of the invention may be on concentrating metal for chemical bath maintenance purposes, and the recycling of chemical fluid such as water is a by-product.

In an embodiment, the method comprises plating plate-shaped structures, in particular panels for manufacturing component carriers, in the chemical bath. The method may also comprise rinsing plate-shaped structures, in particular panels for manufacturing component carriers, in a rinsing system. In particular, the method may comprise plating and/or rinsing the plateshaped structures in a horizontal orientation or in a vertical orientation. Advantageously, it may be possible to implement the membrane distillation in a horizontal plating line. According to such an embodiment, it may be advantageous to mount the rinsing system above an initial rinsing cascade. This method may be used in particular when the panels are plated in a horizontal plating line. Such an embodiment may refer to a scenario in which there is only limited space to install the rinsing system above the chemical bath. More generally, exemplary embodiments of the invention are advantageously compatible both with a horizontal or a vertical alignment of plate-shaped structures during plating and/or rinsing. This increases the freedom of design of a manufacturing architecture.

In an embodiment, the method comprises supplying waste heat from a manufacture plant (in particular a component carrier manufacture plant) to a hot side (which may correspond to the recovered metal side) of the membrane distillation device. By taking this measure, the energy consumption of the recycling process may be reduced.

In an embodiment, the method comprises supplying waste heat from an etching process and/or from a plating process of the manufacture plant (in particular component carrier manufacture plant) to the hot side of the membrane distillation device. In an etching stage of the manufacturing plant, a significant amount of waste heat may occur which is conventionally lost to the environment. By selectively redirecting such waste heat from an etching stage or any other appropriate stage of the manufacturing process to the membrane distillation device, the energy efficiency may be improved. Correspondingly, also a plating process of plating structures (such as component carrier structures) during manufacture of products (such as component carriers), for instance a plating process carried out in the chemical bath, may generate considerable amount of heat. Highly advantageously, the chemical bath when embodied as plating stage may be spatially very close to the membrane distillation device, so that redirection of waste heat from plating to membrane distillation may be energetically highly efficient. However, it should be said that exemplary embodiments of the invention can also be applied to other manufacturing processes than those for component carriers, for instance in terms of plating or surface metallization in any other appropriate industrial branch. In such a scenario, also waste heat created in other manufacturing stages may be applied to the membrane distillation device for heating or preheating.

In an embodiment, the method comprises supplying cooling energy from a manufacture plant (in particular a component carrier manufacture plant) to a cold side (which may correspond to the recovered solvent or water side) of the membrane distillation device. By taking this measure, the energy consumption of the recycling process may be reduced.

In an embodiment, the method comprises supplying cooling energy from a cool rinsing fluid supply (such as an industrial water supply) of the manufacture plant (in particular the component carrier manufacture plant) to the cold side of the membrane distillation device. For example, rinsing fluid is provided in a component carrier factory as part of an industrial water supply system at a temperature typically in a range from 6°C to 14°C, in many cases in a range from 8°C to 12°C. Thus, the temperature of the water supply can be significantly below room or lab temperature. The freshwater supply can thus be used as a heat sink which may cool the solvent side of the membrane distillation device efficiently and will only moderately heat up the freshwater by a few degree Celsius, which will not negatively impact the freshwater supply within the framework of the PCB factory.

In an embodiment, the method comprises concentrating the metal in the membrane distillation device, i.e. accumulating (for instance dissolved and/or elemental) metal on one side of the membrane. Thereafter, it is possible to reintroduce the concentrated metal into the chemical bath. Such a metal concentration approach is a paradigm shift in membrane distillation when being implemented in a PCB manufacturing environment. Usually, membrane distillation is used for large volumes of an aqueous solution it in an attempt to recover water or the like. According to an exemplary embodiment of the invention, this logic is inverted, and the increased concentration of the metal on the hot side of the distillation membrane is the primary goal of the integration of membrane distillation in PCB manufacture. By taking this measure, membrane distillation contributes to keep the chemical bath and in particular its metallic concentration within a target range, and to prevent in particular excessive dilution in the chemical bath.

In an embodiment, the method comprises controlling (in particular regulating, for instance based on a measurement of a metal concentration in the chemical bath) the supplying and/or the separating and/or the reintroducing so that a concentration of the metal in the chemical bath remains constant. In particular, the apparatus may comprise a control unit (such as a processor, multiple processors or part of the processor) configured for controlling (in particular regulating) the apparatus (in particular at least one of the supply unit, the membrane distillation device and the reintroduction unit). More particularly, said control unit may be configured for controlling or regulating the apparatus so that a concentration of the metal in the chemical bath remains constant. Highly advantageously, the metal recovery process may be carried out in a controlled way for the maintenance of the chemical bath, in particular for avoiding excessive dilution thereof. For instance, the control unit may control the apparatus so that a concentration of the metal dissolved in the chemical bath constantly stays at a target concentration. Hence, operation of the membrane distillation device may be adjusted so that the amount of metal supplied back from the membrane distillation device to the chemical bath corresponds to the metal lost in the chemical bath, so that the concentration of the metal in the chemical bath is constant.

In an embodiment, the apparatus comprises a user interface configured for enabling a user to control operation of the apparatus, in particular to control a process of recovering metal from the chemical bath carried out by the apparatus. For example, a user may select, via the user interface, a manual operation mode or an automatic operation mode of the apparatus. In particular, the user interface may be configured for operating the control unit for controlling the process carried out by the apparatus. This may allow for an automation of the operation of the membrane distillation device. A software- assisted control unit may be implemented for enabling a fully automated process-control. Thus, a software-assisted controlling of the membrane distillation may be realized. This may involve one or more process controlling sensors, for instance pressure sensors, flow-rate sensors, etc. The software may receive the information from the sensor(s) and compare these values with predefined nominal values. If these two values do not match, an action may be triggered, for example a flow rate will be increased or decreased.

In the following, details of a user-adjustable control of the apparatus according to an exemplary embodiment of the invention, for instance carried out by a control unit such as a software- based processor, will be explained:

Control components and sensors may be implemented for the control of the process. Such an implementation may enable pressure measurements, flow rate measurements, the provision of frequency inverters for pumps, conductivity measurements, pH measurements, the provision of level adjustment units and/or level indicators, temperature measurements, the provision of valves (such as magnetic valves, motor valves, etc.), the provision of heat volume meters, the provision of leakage sensors, etc.

The apparatus can be controlled in a manual mode or in an automatic mode.

In the manual mode, it is for instance possible to control the pumps, valves, motor valves (to be heated or cooled) manually. Setpoints may be prevented from being automatically regulated in this operation mode. The manual mode may be used when testing adjustments (for example in the event of module changes, during maintenance, etc.). Safety parameters, such as over temperature, may be also active in the manual mode and may lead to a safety stop of the apparatus if a threshold value is exceeded.

In the automatic mode, operation of the apparatus can be carried out as follows. As long as the membrane distillation device of the apparatus is cold, the membrane may be bypassed by a bypass line. A feed circuit may be heated to a target temperature, and a permeate circuit may be cooled to another target temperature. The pumps may run up to the target tempera- ture(s) at a minimum power, for instance by using frequency inverters which may be controlled to a predetermined flow in a parameter management. At the same time, the membrane may be pre-heated to a target temperature. Bypass valves may then be closed, and a flow-through the membrane may be triggered. At the beginning, a flow-through of the membrane may be triggered with a limited ratio between feed and permeate (for example in a ratio 1 :6). When the components of the apparatus have reached the target temperatures, the pump performance may be gradually increased. Feed and permeate flow may be operated on the maximum power specified in the parameters, for instance the ratio may change to 1 : 10. The apparatus may automatically switch between different operation modes via the relationship between filling level and flow rate. This may correspond to a need for rinsing water. The removal of rinsing water may be registered via a sensor in the permeate tank, which measures the filling level. The level at which the next operating mode is to be changed may be specified in a set point (for instance related to a parameter set "minimum", "set point", "maximum"). Even for an absolute minimum, a value is to be entered. If the system falls below said value, the system may stop (for instance a safety stop to avoid a dry running of the pumps, too little separation, etc.). Based on the level, two pumps may regulate the flow rates. If a lot of rinsing water is taken (i.e. in a scenario of high utilization), the level in the permeate tank may decrease and the flow rate (feed and permeate) may be increased to produce more rinsing water.

If the system runs in a maximum operating mode for a certain period of time, i.e. no flushing water is required for a long period of time (for example in a scenario of low load), an automatic change to standby mode may take place (i.e. a mode with minimum separation power). In a setpoint management, a time delay can be set for activating the standby mode.

In the automatic mode, the system may run with temperature values pre-defined in the parameter set. The feed temperature is a relevant parameter in this context, which is the temperature of the process fluid. The maximum value should not be exceeded (since this may destroy the process chemistry). Minimum and maximum values for the temperatures can also be entered in the setpoint management. If the maximum values are exceeded, the system may stop (as a safety stop protecting against overheating). In an embodiment, temperatures are not changed in the standby mode. The system may always remain at a set temperature in an automatic operation in full capacity as well as in standby mode at minimum capacity.

A maximum permitted input and differential pressures on the module may be constantly monitored. If these maximum values are exceeded, the system stops automatically (in automatic mode and manual operation), i.e. a safety stop may be made. The conductivity of the feed and permeate may be constantly monitored. If there is a sharp drop in the conductive value of the feed or a sharp increase in the conductive value of the permeate, the apparatus may go into a safety stop. Disproportionate changes in the conductivity may indicate a membrane breakage or other critical problems in the process. The pH value of the feed and permeate may be also constantly detected. Maximum and minimum limits can also be stored for the pH value in order to force an emergency stop of the system. Feed and permeate flows may be permanently monitored by flow measurements. If there is a significant deviation from the flow defined in the parameter set, the cause may be for example a pipe breakage or an incorrectly switched valve. The apparatus may go back to emergency stop. The apparatus may stand on a drip cup. A leakage sensor may be installed in the drip cup. If the leakage sensor responds, an appropriate alarm may be issued so that an operator can perform a leakage check. If the alarm is not acknowledged for a defined time, the system goes into safety stop.

In an embodiment, the membrane distillation device is configured for providing the separated metal at a heatable or heated side of the membrane distillation device or the membrane thereof. Correspondingly, the membrane distillation device may be configured for providing a chemical fluid or solvent, in particular water, separated from the metal in the membrane distillation device at a coolable or cooled side of the membrane distillation device or the membrane thereof. Due to the temperature gradient applied across the membrane and according to the functioning principle of membrane distillation, metal will accumulate on the hotter side and water will accumulate on the cooler side. After that, the respective separated medium may be supplied back to the chemical bath (i.e. a metallic medium) or to the rinsing system (i.e. the water).

In an embodiment, the apparatus comprises a heating unit configured for heating a metal side of the membrane distillation device. For instance, such a heating unit may be a heating aggregate. Even more preferably, the heating unit may be configured for heating the metal side using waste heat of the (in particular component carrier) manufacture plant. Consequently, the energy efficiency may be increased by using low-temperature waste heat as energy source.

In an embodiment, the apparatus comprises a cooling unit configured for cooling a solvent side of the membrane distillation device. For instance, such a cooling unit may be a cooling aggregate. Even more preferably, the cooling unit may be configured for cooling the solvent side using waste cooling energy of the (for example component carrier) manufacture plant. Hence, the energy efficiency of apparatus and method may be further improved by using a heat sink of the manufacturing apparatus for cooling the solvent side of the membrane distillation device without the need of spending additional energy for cooling.

In an embodiment, the apparatus comprises a closed metal loop for circulating (dissolved and/or elemental) metal within a manufacture plant (in particular a component carrier manufacture plant). Thus, substantially no metal is lost, which reduces the effort for disposing metal which may occur conventionally. Furthermore, the metallic resources consumed by the manufacturing plant may be used more efficiently.

In an embodiment, the apparatus comprises a closed solvent loop for circulating solvent within a manufacture plant (in particular a component carrier manufacture plant). Thus, the water circle may be closed for rinsing applications. A rinsing water demand may thus be reduced.

In an embodiment, the method comprises temporarily bypassing the membrane distillation device with regard to a flow of the chemical composition. In particular, said bypassing may be carried out when, until, or as long as a temperature difference between a hot side and a cool side of the membrane distillation device is below a predefined threshold value. Another challenge arising from the application of a membrane distillation device is that, in the beginning, the necessarily applied temperature gradient may not be obtainable immediately. Accordingly, a metal drag-out (to the water-side) may occur as long as the temperature gradient is not yet reached. In order to efficiently suppress this undesired drag-out it may be possible to implement a bypass function, during the warm-up of the membrane distillation device. Until the temperature difference between the hot side and the cool side of the membrane distillation device is not sufficiently large, the chemical composition from the chemical bath will not be supplied to the membrane distillation device for separation, but will be redirected or guided around the membrane distillation device along a bypass line.

In an embodiment, the method comprises temporarily reducing a ratio between a flow of the chemical composition to the membrane distillation device and a flow of the solvent away from the membrane distillation device. In particular, said reducing of the ratio may be carried out when, until, or as long as a temperature difference between a hot side and a cool side of the membrane distillation device is below a predefined threshold value. Until the temperature difference (and consequently the partial pressure difference) between the hot side and the cool side of the membrane distillation device has become sufficiently large for executing membrane distillation without significant amount of metal moving unintentionally towards a water side, the amount of chemical composition supplied from the chemical bath to the membrane distillation device may be reduced and/or the amount of water drawn at the cool side of the membrane may be increased. Descriptively speaking, this may result in a more favourable adjustment of the partial pressure conditions. In an embodiment, the method comprises pre-heating the membrane distillation device before starting to supply the chemical composition to the membrane distillation device. In particular, said pre-heating without supplying the chemical composition for membrane distillation may be carried out when, until, or as long as a temperature difference between a hot side and a cool side of the membrane distillation device is below a predefined threshold value. For instance simultaneously with the above described bypassing, the membrane can be pre-heated to decrease the time until proper function of the membrane distillation is ensured. This may result in a quicker adjustment of the partial pressure values at the membrane of the membrane distillation device.

In an embodiment, the chemical bath is a plating unit or forms part of a plating unit which is configured for plating, in particular for galvanically plating, a structure (in particular component carriers of the component carrier structure). During plating of gold, palladium, or copper material, a chemical plating bath may be implemented for plating the structure with gold, palladium, or copper material. Such a plating process may result in a contamination of the structure (and/or of a handling unit for handling such a structure) with gold, palladium, or copper in unwanted areas, so that excessive gold, palladium, or copper material may be removed by rinsing. Thereafter, gold, palladium or copper may be recovered from the chemical plating bath and/or from the rinsing system.

In an embodiment, the apparatus comprises a rinsing system for rinsing structures by a treatment with a humid gas beam, in particular with a water- saturated humid air beam. More specifically, water-saturated pressurized gas may be directed onto surfaces of the structure (in particular onto main surfaces of a plate-shaped structure, more particularly component carrier structure) for removing chemicals from said surfaces for cleaning the structure. Descriptively speaking, pressurized gas with high amount of water vapor may function as a gas knife for efficiently cleaning the surfaces of the structure with an advantageously low amount of rinsing liquid (in particular water) being necessary. At the same time, such a humid gas beam may efficiently clean the surface without the risk of solidified chemicals remaining attached to the surface of the structure, thanks to the water content of the human gas beam. Further advantageously, a medium in form of the liquefied former human gas beam may be accumulated in a container or the like and may include a relatively high amount of chemicals. The latter may be recycled, in particular by the membrane distillation device.

In an embodiment, the rinsing system is configured for supplying a medium, collected during rinsing the structures by the treatment with the humid gas beam, to the chemical bath or to the membrane distillation device. Said medium constituting fluidic residues of the described rinsing process using a humid gas knife may have a very high concentration of chemicals (and in particular metallic chemicals) to be recycled. Thus, it is highly appropriate to supply this medium to the chemical bath (or directly to the membrane distillation device) for recycling of metal, plating additives, acid, base, etc.

In an embodiment, the apparatus is configured for supplying water from the membrane distillation device to the rinsing system. More specifically, water collected at the cool side of the membrane distillation device may be supplied to the rinsing system for providing humidity needed for creating a humid gas beam. Such a recovery or feedback of water to a rinsing system using a gas knife may additionally reduce waste and may use resources more efficiently.

In an embodiment, the rinsing system comprises at least one additional rinsing stage for rinsing the structure(s) after rinsing by an initial rinsing stage configured for rinsing the structure(s) by the treatment with the humid gas beam. Hence, a multi-stage rinsing system may be provided, wherein an initial or first stage may be constituted by a humid gas beam directed onto the structure to be rinsed, for instance as described above. Thereafter, the precleaned structure may be cleaned or rinsed additionally in one or more additional rinsing stages. For example, each of said additional rinsing stages may include a sprinkler system sprinkling rinsing liquid such as water onto the structure to be rinsed. Alternatively, any additional rinsing stage may be constituted by a further humid gas beam directed onto the structure to be additionally rinsed (as described above for the initial rinsing stage). Since the gas knife-based initial rinsing stage provides a specifically small amount of residue medium with a specifically high concentration of chemicals to be recycled, and liquid sprinkler-based additional rinsing stages provide a much higher amount of liquid residue medium with significantly lower concentration of chemicals, it may be possible to use only the medium output by the initial rinsing stage for recycling.

In an embodiment, the membrane distillation device comprises a heatable side, a coolable side and an air gap between the heatable side and the coolable side, wherein a first membrane is placed between the heatable side and the air gap and a second membrane is placed between the air gap and the coolable side. In this case, a direct contact between the heatable side, where the chemical concentration is concentrated, and the coolable side, in which the separated solvent is concentrated, is avoided. This makes it possible to avoid contamination of the separated solvent due to leakage of the membrane. It is also possible, in this configuration, to contrast dilution of the separated metal during standstill of the membrane distillation device due to osmotic pressure across the membrane. Any leakage of the separated metal within the air gap can be drained out from the air gap. Also, by applying a moderate vacuum to the air gap it is also possible to remove non condensable gases that might be trapped inside the air gap or within the membrane. The first and the second membrane are preferably hydrophobic PTFE membranes.

According to a further embodiment, the membrane distillation device further comprises a heat exchanger thermally coupled with the heatable side. In this case it is therefore possible to pre-heat the heatable side, thus increasing the temperature difference between the heatable and the coolable side and, as a consequence, to have a more efficient functioning of the membrane distillation device. In this context, the heat exchanger may allow to utilize (otherwise not utilized) waste heat originating from another process and/or from a sub process of the above described method.

According to a further embodiment, the heat exchanger comprises a channel for guiding a flow of hot distillate, wherein the channel is separated from the heatable side through a thermally conductive material layer, preferably through a polymer film. According to this embodiment, it is therefore possible to use waste heat originating from the hot distillate using during the manufacturing process to heat up the heatable side. The thermally conductive material layer is impermeable and is preferably a polymer film, such as Polyvinyl alcohol. It is also possible to use other sources of waste heat present in the manufacturing process.

According to a further embodiment, the membrane distillation device comprises a further heatable side and a further air gap. The coolable side is placed between the air gap and the further air gap and the further air gap is placed between the coolable side and the further heatable side. Hence, the described membrane distillation device can be realized in a modular construction, which may be particularly advantageous for saving space by providing a compact assembly. Also, it may be possible to use a single coolable side to recover solvent from two heatable sides.

According to a further embodiment, the supply unit comprises an evaporator. In particular, the supply unit may comprise an evaporator which can perform flash evaporation of the chemical composition which is to be supplied to the membrane evaporation device. Hence, the evaporation device is a flash evaporation device. During evaporation, only a part of the solvent of the chemical composition present in the evaporator is evaporated.

In a further embodiment, the membrane distillation device comprises a heatable side, a coolable side, a vapor side, a membrane and a thermally conductive layer. The heatable side is placed between the vapor side and the coolable side, the membrane is placed between the heatable side and the coolable side, and the thermally conductive layer is placed between the vapor side and the heatable side. In this embodiment, the apparatus further comprises vapor supply means for supplying vapor from the evaporator to the vapor side, and a concentrate supply means for supplying the chemical composition in a liquid form from the evaporator to the heatable side. In this particular configuration, the vapor generated by the evaporator may be used to heat the heatable side of the membrane distillation device. The vapor may contain the solvent of the chemical composition. The vapor in the vapor side may condensate due to the thermal exchange with the heatable side at the thermally conductive layer and may be collected to be reused as solvent. The solvent in the chemical composition present in the heatable side may partially evaporate and the generated vapor may pass through the membrane, where the vapor may condensate as a solvent and may be collected for further use. The non-evaporated part of the chemical composition may have a higher concentration of the metal element to be recovered and may be collected to be reused. The thermally conductive layer may preferably be a polymeric film.

According to another embodiment, the membrane distillation device further comprises a further heatable side, a further coolable side, a further membrane, and a further thermally conductive layer. The further heatable side is placed between the coolable side and the further coolable side, the further membrane is placed between the further heatable side and the further coolable side, and the further thermally conductive layer is placed between the further heatable side and the coolable side. The apparatus further comprises a further concentrate supply means for supplying the chemical composition in a liquid form from the heatable side to the further heatable side, wherein, during operation, a pressure in the heatable side is bigger than a further pressure in the further heatable side. It may therefore be possible to build the membrane distillation device in a modular way, in which the heatable sides and coolable sides spatially alternate each other and in which the pressure in the system decreases along with the number of modules comprised in the system. By using a decreasing pressure along the modules, it is possible to decrease the temperature needed for the solvent to evaporate, thus using a previous coolable side as waste heat source for the successive heatable side of the system. Hence, the overall efficiency, in particular the energy efficiency of the membrane distillation device may be further increased.

In an embodiment, the manufactured component carriers may comprise a stack of at least one electrically insulating layer structure and/or at least one electrically conductive layer structure. For example, the component carrier may be a laminate of the mentioned electrically insulating layer structure(s) and electrically conductive layer structure(s), in particular formed by applying mechanical pressure and/or thermal energy. The mentioned stack may provide a plate-shaped component carrier capable of providing a large mounting surface for further components and being nevertheless very thin and compact. The term "layer structure" may particularly denote a continuous layer, a patterned layer, or a plurality of non-consecutive islands within a common plane. In an embodiment, the component carrier is shaped as a plate. This contributes to the compact design, wherein the component carrier nevertheless provides a large basis for mounting components thereon. Furthermore, in particular a naked die as example for an embedded electronic component, can be conveniently embedded, thanks to its small thickness, into a thin plate such as a printed circuit board.

In an embodiment, the component carrier is configured as one of the group consisting of a printed circuit board, a substrate (in particular an IC substrate), and an interposer.

In the context of the present application, the term "printed circuit board" (PCB) may particularly denote a plate-shaped component carrier which is formed by laminating several electrically conductive layer structures with several electrically insulating layer structures, for instance by applying pressure and/or by the supply of thermal energy. As preferred materials for PCB technology, the electrically conductive layer structures are made of copper, whereas the electrically insulating layer structures may comprise resin and/or glass fibers, so-called prepreg or FR.4 material. The various electrically conductive layer structures may be connected to one another in a desired way by forming through holes through the laminate, for instance by laser drilling or mechanical drilling, and by filling them with electrically conductive material (in particular copper), thereby forming vias as through hole connections. Apart from one or more components which may be embedded in a printed circuit board, a printed circuit board is usually configured for accommodating one or more components on one or both opposing surfaces of the plate-shaped printed circuit board. They may be connected to the respective main surface by soldering. A dielectric part of a PCB may be composed of resin with reinforcing fibers (such as glass fibers).

In the context of the present application, the term "substrate" may particularly denote a small component carrier. A substrate may be a, in relation to a PCB, comparably small component carrier onto which one or more components may be mounted and that may act as a connection medium between one or more chip(s) and a further PCB. For instance, a substrate may have substantially the same size as a component (in particular an electronic component) to be mounted thereon (for instance in case of a Chip Scale Package (CSP)). More specifically, a substrate can be understood as a carrier for electrical connections or electrical networks as well as component carrier comparable to a printed circuit board (PCB), however with a considerably higher density of laterally and/or vertically arranged connections. Lateral connections are for example conductive paths, whereas vertical connections may be for example drill holes. These lateral and/or vertical connections are arranged within the substrate and can be used to provide electrical, thermal, and/or mechanical connections of housed components or unhoused components (such as bare dies), particularly of IC chips, with a printed circuit board or intermediate printed circuit board. Thus, the term "substrate" also includes "IC substrates". A dielectric part of a substrate may be composed of resin with reinforcing particles (such as reinforcing spheres, in particular glass spheres).

The substrate or interposer may comprise or consist of at least a layer of glass, silicon (Si) or a photoimageable or dry-etchable organic material like epoxy-based build-up material (such as epoxy-based build-up film) or polymer compounds like polyimide, polybenzoxazole, or benzocyclobutene- functionalized polymers.

In an embodiment, the at least one electrically insulating layer structure comprises at least one of the group consisting of resin (such as reinforced or non-reinforced resins, for instance epoxy resin or bismaleimide-triazine resin), cyanate ester resin, polyphenylene derivate, glass (in particular glass fibers, multi-layer glass, glass-like materials), prepreg material (such as FR-4 or FR- 5), polyimide, polyamide, liquid crystal polymer (LCP), epoxy-based build-up film, polytetrafluoroethylene (PTFE, Teflon), a ceramic, and a metal oxide. Reinforcing structures such as webs, fibers, or spheres, for example made of glass (multilayer glass) may be used as well. Although prepreg particularly FR4 are usually preferred for rigid PCBs, other materials in particular epoxybased build-up film or photoimageable dielectric material may be used as well. For high frequency applications, high-frequency materials such as polytetrafluoroethylene, liquid crystal polymer and/or cyanate ester resins, low temperature cofired ceramics (LTCC) or other low, very low or ultra-low DK materials may be implemented in the component carrier as electrically insulating layer structure. In an embodiment, the at least one electrically conductive layer structures comprises at least one of the group consisting of copper, aluminum, nickel, silver, gold, palladium, and tungsten. Although copper is usually preferred, other materials or coated versions thereof are possible as well, in particular coated with supra-conductive material such as graphene.

At least one component, which can be embedded in and/or surface mounted on the stack, can be selected from a group consisting of an electrically non-conductive inlay (such as a ceramic inlay, preferable comprising aluminium nitride or aluminium oxide), an electrically conductive inlay (such as a metal inlay, preferably comprising copper or aluminum), a heat transfer unit (for example a heat pipe), a light guiding element (for example an optical waveguide or a light conductor connection), an optical element (for instance a lens), an electronic component, or combinations thereof. For example, the component can be an active electronic component, a passive electronic component, an electronic chip, a storage device (for instance a DRAM or another data memory), a filter, an integrated circuit, a signal processing component, a power management component, an optoelectronic interface element, a light emitting diode, a photocoupler, a voltage converter (for example a DC/DC converter or an AC/DC converter), a cryptographic component, a transmitter and/or receiver, an electromechanical transducer, a sensor, an actuator, a microelectromechanical system (MEMS), a microprocessor, a capacitor, a resistor, an inductance, a battery, a switch, a camera, an antenna, a logic chip, and an energy harvesting unit. However, other components may be embedded in the component carrier. For example, a magnetic element can be used as a component. Such a magnetic element may be a permanent magnetic element (such as a ferromagnetic element, an antiferromagnetic element, a multiferroic element or a ferrimagnetic element, for instance a ferrite core) or may be a paramagnetic element. However, the component may also be a substrate, an interposer, or a further component carrier, for example in a board-in-board configuration. The component may be surface mounted on the component carrier and/or may be embedded in an interior thereof. Moreover, also other components, may be used as component. In an embodiment, the component carrier is a laminate-type component carrier. In such an embodiment, the component carrier is a compound of multiple layer structures which are stacked and connected together by applying a pressing force and/or heat.

After processing interior layer structures of the component carrier, it is possible to cover (in particular by lamination) one or both opposing main surfaces of the processed layer structures symmetrically or asymmetrically with one or more further electrically insulating layer structures and/or electrically conductive layer structures. In other words, a build-up may be continued until a desired number of layers is obtained.

After having completed formation of a stack of electrically insulating layer structures and electrically conductive layer structures, it is possible to proceed with a surface treatment of the obtained layers structures or component carrier.

In particular, an electrically insulating solder resist may be applied to one or both opposing main surfaces of the layer stack or component carrier in terms of surface treatment. For instance, it is possible to form such as solder resist on an entire main surface and to subsequently pattern the layer of solder resist so as to expose one or more electrically conductive surface portions which shall be used for electrically coupling the component carrier to an electronic periphery. The surface portions of the component carrier remaining covered with solder resist may be efficiently protected against oxidation or corrosion, in particular surface portions containing copper.

It is also possible to apply a surface finish selectively to exposed electrically conductive surface portions of the component carrier in terms of surface treatment. Such a surface finish may be an electrically conductive cover material on exposed electrically conductive layer structures (such as pads, conductive tracks, etc., in particular comprising or consisting of copper) on a surface of a component carrier. If such exposed electrically conductive layer structures are left unprotected, then the exposed electrically conductive component carrier material (in particular copper) might oxidize, making the component carrier less reliable. A surface finish may then be formed for instance as an interface between a surface mounted component and the component carrier. The surface finish has the function to protect the exposed electrically conductive layer structures (in particular copper circuitry) and enable a joining process with one or more components, for instance by soldering. Examples for appropriate materials for a surface finish are Organic Solderability Preservative (OSP), Electroless Nickel Immersion Gold (ENIG), gold (in particular Hard Gold), chemical tin, nickel-gold, nickel-palladium, Electroless Nickel Immersion Palladium Immersion Gold (ENIPIG), etc.

The aspects defined above and further aspects of the invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to these examples of embodiment.

Figure 1 illustrates a schematic view of an apparatus for recovering gold from a chemical bath for chemically treating a component carrier structure with gold in a component carrier manufacture plant according to an exemplary embodiment of the invention.

Figure 2 illustrates a membrane distillation device for an apparatus and a method according to an exemplary embodiment of the invention.

Figure 3 illustrates a schematic view of an apparatus for recovering gold from a chemical bath for chemically treating a component carrier structure with gold in a component carrier manufacture plant according to an exemplary embodiment of the invention.

Figure 4 illustrates a schematic view of an apparatus for recovering palladium from a chemical bath for chemically treating a component carrier structure with palladium in a component carrier manufacture plant according to an exemplary embodiment of the invention.

Figure 5 illustrates elements of a membrane distillation device for an apparatus and to be used in a method according to an exemplary embodiment of the invention.

Figure 6 illustrates an apparatus for recovering metal from a chemical bath for chemically treating a component carrier structure with metal in a component carrier manufacture plant according to another exemplary embodiment of the invention, in which a membrane distillation device may be bypassed, pre-heated, and/or subjected to a variable feed/permeate ratio.

Figure 7 illustrates an apparatus for recovering metal from a chemical bath for chemically treating a component carrier structure with metal in a component carrier manufacture plant according to still another exemplary embodiment of the invention, in which a multi-stage rinsing system comprises an initial stage which is based on a treatment of plate-shaped component carrier structures with a humid gas beam, followed by subsequent stages based on sprinkling the plate-shaped component carrier structures with rinsing liquid.

Figure 8 and Figure 9 illustrate apparatuses for recovering metal from a chemical bath for chemically treating a component carrier structure with metal in a component carrier manufacture plant according to still another exemplary embodiment of the invention implementing different multi-stage rinsing systems.

Figure 10 illustrates an apparatus for recovering metal from a chemical bath for chemically treating a component carrier structure with metal in a component carrier manufacture plant according to yet another exemplary embodiment of the invention.

Figure 11 illustrates a membrane distillation device according to a further embodiment of the invention.

Figure 12 illustrates an apparatus for recovering metal from a chemical bath for chemically treating a component carrier structure with metal in a component carrier manufacture plant according to a further embodiment of the invention, wherein the apparatus comprises a supply unit with an evaporator.

Figure 13 illustrates a membrane distillation device according to a further embodiment of the invention.

The illustrations in the drawings are schematic. In different drawings, similar or identical elements are provided with the same reference signs.

Before, referring to the drawings, exemplary embodiments will be described in further detail, some basic considerations will be summarized based on which exemplary embodiments of the invention have been developed.

In particular, the following description focuses on the application of membrane distillation in terms of a manufacturing process for manufacturing component carriers such as printed circuit boards (PCBs). However, it should be said that exemplary embodiments are not limited to such a technology, but can be broadly applied to the manufacture of other products or structures, in particular for the metallization of surfaces of such products or structures.

In conventional chemical wet processes, products may be rinsed in a rinsing bath followed by a subsequent cascade of rinsing stages. Rinsing with conventional rinsing systems leads to the removal of process liquid from an active bath on the one hand and to large amounts of wastewater contaminated by bath components on the other hand.

Conventionally, membrane distillation is often used to try to recover water from strongly diluted solutions, for instance to desalinate saltwater. Because of the high flows that were attempted to treat, membrane distillation systems have been considered as being too expensive, too big and having a too high-energy consumption.

According to an exemplary embodiment of the invention, membrane distillation may be implemented for recovering metal from an outlet of a chemical bath which is used for treating component carrier structures, wherein metal recovered by membrane distillation may be fed back into the chemical bath for preventing undesired metal depletion or dilution of the chemical bath.

In particular, an exemplary embodiment of the invention may use membrane distillation for separating small amounts of water from an active chemical bath. This concept according to an exemplary embodiment of the invention is a paradigm shift compared with conventional approaches (the latter intending to purify huge amounts of lightly contaminated rinsing water). In contrast to this, an exemplary embodiment of the invention may adapt a rinsing process in order to carry it out directly in or above the chemical bath(s). Since this may lead to a dilution of the chemical bath by contaminated rinsing fluid supplied by the rinsing system, membrane distillation may be implemented as a concentrating technology for concentrating (in particular dissolved and/or elemental) metal to be recovered. By separating an appropriate amount of a chemical fluid or solvent (such as water) from the metal in the membrane distillation device, the metal concentration in the chemical bath (for instance a gold bath used for plating printed circuit boards) can be kept constant or can be kept sufficiently high. In particular, the concentration can be regulated by the amount of recovered dissolved metal or by the addition of (in particular rinsing) water. Corresponding adjustments, which may be made according to exemplary embodiments of the invention, may lead to the fact that only very small quantities of water have to be separated instead of large quantities of highly diluted rinse water having to be reprocessed. The combination of process adaptation and membrane distillation allows the technology to be operated very efficiently with low energy consumption (for example low temperature waste heat). Advantageously, membrane distillation devices may namely be operated with relatively low amount of heat.

According to an exemplary embodiment of the invention, membrane distillation may be implemented in a component carrier manufacture plant for enriching heavy metal from a rinsing bath and for reintroducing the enriched heavy metal into a chemical bath for treatment. More specifically, a membrane distillation process may be employed for an energy-efficient treatment of electroplating liquids. The rinsing process may be done above an etching bath or above a separate basin, leading to dilution of the bath. Therefore, the membrane distillation may be used to control the concentration of the electroplating substance in the etching bath. On the one hand, electroplating substances (including the metal in dissolved and/or elemental form) may be concentrated and returned to the chemical bath and on the other hand a chemical fluid or solvent such as water can be recycled for a next rinsing process. The rinsing process may be done above the chemical bath (in particular an etching bath) or above a separate basin, leading to dilution of the chemical bath. Advantageously, membrane distillation may be used to control the concentration of the metal and/or another electroplating substance in the etching bath.

Advantageously, the described process control may render membrane distillation highly efficient and therefore usable on an industrial scale. Furthermore, exemplary embodiments of the invention may make it possible to close the water circle in rinsing applications. Apart from this, the rinsing water demand may be reduced due to an at least partial recycling of rinsing fluid. Furthermore, the energy efficiency may be improved because low temperature waste heat, created elsewhere in the component carrier manufacturing plant, can be used as energy source for heating a warm side of the membrane distillation device. Advantageously, an apparatus and a method according to an exemplary embodiment of the invention can be used for all processes that work with a chemical bath followed by a rinsing unit. Such embodiments may overcome conventional issues with drag-out metal and/or other electroplating substances by implementing membrane distillation in a production process on industrial scale. Both the manufacturing effort and the environmental impact may be significantly reduced. Moreover, process stability may be enhanced, and resource consumption may be reduced. Apart from this, the energy efficiency and the safety at work may be increased.

In particular, exemplary embodiments of the invention may reduce energy consumption and the demand of chemicals. This may lead to a cleaner and safer production. Additionally, by using membrane distillation, energy and operating efforts of manufacturing component carriers can be reduced. There is no longer a need for operators to add or replenish chemicals so frequently. Therefore, operators come into less contact with hazardous substances. This may significantly increase the safety of the manufacturing process.

Advantageously, membrane distillation may be used as concentrating technology to remove a water excess coming from a rinsing process to keep the metal concentration of the chemical bath stable.

According to exemplary embodiments of the invention, galvanically active agents such as gold and/or palladium, which are conventionally lost with rinsing fluid, can be recovered, or recycled partially or entirely. Such a process may involve the concentration of the metallic medium in the waste solution by membrane distillation, which can be executed advantageously at relatively low temperature. Thus, the described process is energy efficient and saves resources in a process for manufacturing printed circuit boards.

Figure 1 illustrates a schematic view of an apparatus 120 for recovering gold from a chemical bath 100 according to an exemplary embodiment of the invention. The chemical bath 100 is provided for electroplating component carrier structures, for instance panels for manufacturing printed circuit board (PCB), with gold in a component carrier manufacture plant 104.

The illustrated apparatus 120 is configured for recovering gold, as an example for a heavy metal, from chemical bath 100 such as a plating bath. Thus, the chemical bath 100 may be or may form part of a plating unit configured for galvanically plating still integrally connected component carriers of the component carrier structure with gold on panel level. During plating component carrier structures, metal (in the present example gold) from the chemical bath 100 is consumed by being deposited on the component carrier structure. As shown as well in Figure 1 and as indicated by reference sign 145, a chemical fluid (such as water) and chemicals (such as plating metal) may be supplied as rinsing water plus gold from a rinsing system 102 to the chemical bath 100. In the context of a plating process, the chemical bath 100 (functioning as a metal source during plating of the component carrier structure) may be used in combination with one or more rinse baths of the rinsing system 102. The rinsing system 102 may be used for cleaning the component carrier structure and correlated handling tools after plating. During such as a cleaning or rinsing process, plating metal such as gold may be introduced into the rinsing fluid. More specifically, the component carrier structures may be galvanically coated with gold in the galvanic plating bath constituting chemical bath 100. Thereby, the component carrier structure as well as a handling tool for handling the component carrier structures may be contaminated with gold. By the rinsing system 102, the handling tool and the component carrier structures may be cleaned. Advantageously, a previously gold plated component carrier structure may be rinsed directly above the active chemical bath 100 (i.e. gold bath). The contaminated rinsing fluid which may flow into the chemical bath 100 may then be separated.

As shown, the chemical bath 100 is fluidically connected via a supply unit 122 with a membrane distillation device 106, which is here used and configured for concentrating metal. The supply unit 122, which may for instance comprise a pump and a valve (not shown), may control a fluid flow from the chemical bath 100 to the membrane distillation device 106. More specifically, supply unit 122 may be configured for supplying a chemical fluid (such as water) comprising heavy metal (such as gold) from the chemical bath 100 to membrane distillation device 106. The medium supplied by the supply unit 122 to the membrane distillation device 106 may be a diluted chemical. Said dilution may be the result of the supply of rinsing fluid to the chemical bath 100 and/or of the consumption of metallic material in the chemical bath 100 due to plating of component carrier structures therein.

The membrane distillation device 106 is configured for separating the heavy metal from the supplied chemical composition by membrane distillation. Descriptively speaking, a vapor pressure gradient at the membrane distillation device 106 may allow the separation of water from the rest of the chemical composition supplied from the chemical bath 100 to the membrane distillation device 106. More specifically, due to the functionality of membrane distillation in combination with the formation of a temperature gradient between the left hand side and the right hand side of a preferably hydrophobic membrane (see reference sign 140 in Figure 2) of the membrane distillation device 106, (dissolved and/or elemental) gold may accumulate on the left hand side and water may accumulate on the right-hand side of the membrane distillation device 106 of Figure 1. Hence, the gold may be concentrated by the membrane distillation device 106. Descriptively speaking, hydrophobic membrane 140 predominantly only allows water vapor to pass the membrane 140, which removes water from the gold.

Furthermore, apparatus 120 comprises a reintroduction unit 124 configured for reintroducing the separated gold back into the chemical bath 100 (see loop 132 on the left hand side of Figure 1) and for reintroducing separated water back into the rinsing system 102 (see loop 130 on the right hand side of Figure 1). Consequently, closed heavy metal loop 132 is thus provided for circulating gold within the component carrier manufacture plant 104, and closed solvent loop 130 is thus provided for circulating water within the component carrier manufacture plant 104.

More specifically, the membrane distillation device 106 is configured for providing the separated gold at a heated side 108 of the membrane 140. The warmer or heated side 108 is heated by a heating unit 126. Advantageously, the heating unit 126 is configured for heating the heated side 108 using waste heat created elsewhere in the component carrier manufacture plant 104. Preferably, waste heat from an etching process and/or from a plating process (for instance a galvanic plating process for depositing copper on the component carrier structures) of the component carrier manufacture plant 104 may be provided for heating the heated side 108 of the membrane distillation device 106. Consequently, an energy efficient operation of the apparatus 120 is possible. Additionally or alternatively, it is possible to heat side 108 of the membrane 140 with an active heating source 142, such as an electric heating source.

Correspondingly, the membrane distillation device 106 is configured for providing the water, which has been separated from the gold in the membrane distillation device 106, at a cooler or cooled side 110 of the membrane distillation device 106. A cooling unit 128 is provided and configured for cooling the cooled side 110 of the membrane distillation device 106. Preferably, the cooling unit 128 is configured for cooling the cooled side 110 using waste cooling energy of the component carrier manufacture plant 104. Advantageously, cooling energy may be supplied from a cool rinsing fluid supply of the component carrier manufacture plant 104 to the cold side 110 of the membrane distillation device 106. For instance, a rinse water supply may provide rinse water to various consumers of the component carrier manufacturing plant 104 at a relatively low temperature of for example 8°C or 12°C. After cooling the cool side 110, the slightly warmed rinse water may still be used at the various consumers of the component carrier manufacture plant 104, for instance by rinsing system 102. Also cooling the cool side 110 promotes an energy efficient operation of the apparatus 120. Additionally or alternatively, it is possible to cool side 110 of the membrane 140 with an active cooling source 144, such as one or more cooling aggregates.

As already mentioned, a closed solvent loop 130 is provided for circulating solvent within the component carrier manufacture plant 104. The solvent, for instance water, is separated from the gold in the membrane distillation device 106 and is reintroduced into rinsing system 102 for use in subsequent rinsing processes for rinsing component carrier structures treated in the chemical bath 100. Hence, the chemically treated component carrier structures may be rinsed by the rinsing system 102 using the reintroduced water. For instance, separated water may be fed back into the rinsing system 102 with a flow rate of 15 l/h, which may be sufficient for a PCB manufacturing process.

Highly advantageously, a control unit 134 is provided which is configured for controlling or even regulating one or more of the supply unit 122, the membrane distillation device 106, the reintroduction unit 124, the chemical bath 100, and the rinsing system 102 so that a concentration of the gold in the chemical bath 100 remains constant. Therefore, membrane distillation may be used in the component carrier manufacture plant 104 for separating gold from chemical bath 100 and for reintroducing the separated gold into the chemical bath 100 in a controlled way so as to keep the gold concentration in the chemical bath 100 constant. The system of Figure 1 may just be used advantageously for maintenance of the chemical bath 100.

The apparatus 120 comprises a user interface 150 (for instance a graphic user interface, GUI) configured for enabling a user to control operation of the apparatus 120, in particular to control a process of recovering metal from the chemical bath 100 carried out by the apparatus 120. The user interface 150 may be configured for operating the control unit 134 (which may be a processor, part of a processor or a plurality of processors) for controlling the process carried out by the apparatus 120. Such a control architecture may allow an automation of the operation of the membrane distillation device 106 by software-assisted control unit 134, which may enable a fully automated process-control. With the user interface 150 and the control unit 134 configured according to an embodiment of the invention, a software-supported process control for membrane distillation plants may be made possible. For example, the user interface 150 may comprise an input unit (for instance a keypad, a joystick, a touchscreen and/or a voice recognition system) by which a user can input control commands for controlling the control unit 134. Furthermore, the user interface 150 may comprise an output unit (for instance a liquid crystal display, a touchscreen, etc.) outputting results of the operation of the apparatus 120.

In conventional membrane distillation plants, operation and troubleshooting is coordinated and carried out manually by a technician. Especially when the system is started up, manual intervention is mandatory in such conventional systems. In particular during heating or cooling a membrane distillation device, errors often occur due to highly fluctuating temperatures.

In order to obtain a stable controller concept, the functionality of the user interface 150 according to an exemplary embodiment of the invention may be limited to the most important functions, which enables to achieve a high degree of automation when operating apparatus 120 under control of control unit 134. Both a start and a stop of the apparatus 120 can take place in automatic mode, i.e. exclusively controlled by the control unit 134. Both a stand-by operation and an emergency stop of the apparatus 120 can be specified selectively on the user side via user interface 150 or automatically by control unit 134. Advantageously, an error memory can be implemented, which can preferably output a corresponding message text and action specifications. Both activating and deactivating a rinsing process can be specified on the user side via user interface 150 or automatically by control unit 134.

The user interface 150 to be operated by an operator can also allow a setting of all functions of the apparatus 120, such as a parameter adjustment and/or an adjustment of a control of the apparatus 120. Preferably, a controller concept can be implemented, which can handle fluctuations in the heat management as well as the cooling management. For example, a cascade control with several controllers and different guide types can be provided. Due to its high degree of automation, a corresponding apparatus 120 can be user- friendly and enable stable process management by control unit 134. The membrane distillation process can be significantly improved with regard to the operation of the apparatus 120 and may enable the operation of the plant by a user without the support of an expert.

In the embodiment of Figure 1, membrane distillation may thus be used to control the concentration of gold in the chemical bath 100 during the gold plating process. Therefore, water from the chemical bath 100 may be partially separated and purified using membrane distillation. The separation is driven by the difference of the partial vapor pressure of water on both sides of the membrane 140. As water is continuously removed from the chemical bath 100, the concentration of gold increases and the highly concentrated gold solution is supplied back to the chemical bath 100. By this procedure it is possible to keep the gold concentration in the chemical bath 100 constant.

Advantages of the implementation of membrane distillation in the apparatus 120 are its capability of efficiently recycling metallic and aqueous media, a proper matching into the PCB manufacturing process (also in view of required gold concentrations), an advantageously high robustness of the distillation membrane 140 against carry-over during PCB processing compared to other separation techniques, and the unusual implementation of membrane distillation for concentrating gold.

Additionally or alternatively to the recycling of gold, apparatus 120 may also be used for recycling other metals such as copper and/or palladium during a component carrier manufacturing process. A significant advantage of apparatus 120 is its capability of keeping heavy metals in a closed loop during manufacturing component carriers.

Although not explicitly illustrated in Figure 1, operation of the apparatus 120 may comprise recovery of at least one further substance (i.e. another substance than the metal) for instance using the membrane distillation device 106 and/or further recovery entities and reintroducing the concentrated further substance into the chemical bath 100. For instance, such a further substance to be recycled may be a plating additive, an acid, a base, etc. This may allow to further reduce waste and may allow to use resources more efficiently.

Figure 2 illustrates a membrane distillation device 106 for an apparatus 120 and for a method according to an exemplary embodiment of the invention.

Figure 2 illustrates that, between the heated side 108 (feeding metal to be recovered) and the cooled side 110 of a hydrophobic membrane 140 of the membrane distillation device 106, vapor 146 moves substantially only in one direction across the membrane 140. Thus, membrane distillation is implemented as a thermally driven separation or concentration process, in which feed (on heated side 108) and permeate or condensate (on cooled side 110) are separated by hydrophobic membrane 140. Driving force of the separation is a vapor pressure difference, i.e. a temperature difference between feed and permeate. Evaporation may occur already at a relatively low temperature of for example 80°C. Implementation of the membrane distillation device 106 of Figure 2 in the apparatus 120 of Figure 1 may close the water cycle and may reduce the amount of gold needed in the system.

Figure 3 illustrates a schematic view of an apparatus 120 for recovering gold from a chemical bath 100 for chemically treating a component carrier structure with gold in a component carrier manufacture plant 104 according to an exemplary embodiment of the invention.

Figure 3 shows a process flow 160 during PCB manufacture. Before a preceding manufacturing stage 162 and after a succeeding manufacturing stage 164, gold plating of component carrier structures is accomplished in a chemical bath 100, followed by a rinsing of the contaminated component carrier structures by rinsing system 102. Within the process flow 160, a membrane distillation device 106 is used for separating a medium (such as water) supplied from chemical bath 100 including rinsing fluid from rinsing system 102 into gold and water. Concentrated gold is guided back into the chemical bath 100 for use in a subsequent plating process. Separated water is guided back into the rinsing system 102 for use in a subsequent rinsing process.

Advantageously, a component carrier structure is rinsed after treatment by electroplating or in an etching bath, i.e. after treatment in chemical bath 100. This can be done directly above (or even in) the chemical bath 100 or above a separate basin. The rinsing leads to the necessity of concentrating the electroplating or etching bath or the rinsing water has to be treated in a way that, on the one hand electroplating substances are concentrated and can be returned to the chemical bath 100 and on the other hand that the rinsing water has to be cleaned of the electroplating substances and can be recycled as water.

Figure 4 illustrates a schematic view of an apparatus 120 for recovering palladium from a chemical bath 100 (not shown in Figure 4) for chemically treating a component carrier structure with palladium in a component carrier manufacture plant 104 according to an exemplary embodiment of the invention.

During manufacturing component carriers in a manufacturing process 190, various manufacturing stages 180, 182, 184 are carried out. After palladium plating in a chemical bath (not shown in Figure 4, but for instance carried out in one of the manufacturing stages shown in Figure 4), component carrier structures are treated in a conductor bath 192 and later in a selector bath 194. Two rinsing systems 102 are implemented in between in which rinsing of the palladium-treated component carrier structures may be carried out. The palladium-contaminated rinsing fluids from rinsing systems 102 are supplied to a membrane distillation unit 106 for separation of palladium with respect to water. The recovered clean water is guided back to the rinsing systems 102 in a closed loop water cycle, see reference sign 130. The recovered palladium is guided to a palladium precipitation unit 196 for precipitating palladium. For precipitating palladium in an efficient way, the palladium may be concentrated to 50 mg/l or more in membrane distillation unit 106. The recovered palladium may then be used again for palladium plating of component carrier structures. More generally, the recovered palladium may be reintroduced in the manufacturing process, for instance after being conditioned in a conditioning unit 198.

Figure 5 illustrates elements of a membrane distillation device 106 for an apparatus 120 and a method according to an exemplary embodiment of the invention.

Figure 5 illustrates that membrane distillation devices 106 according to exemplary embodiments of the invention can be used with single membrane blocks 166, stacked membrane blocks 168, or even larger modules 170 with multiple stacked membrane blocks 168. Hence, the recovery system according to exemplary embodiments of the invention is properly scalable.

Figure 6 illustrates an apparatus 120 for recovering metal from a chemical bath 100 (such as a plating bath) for chemically treating a component carrier structure (such as a panel for manufacturing printed circuit boards, PCBs) with metal in a component carrier manufacture plant according to another exemplary embodiment of the invention. According to Figure 6, membrane distillation device 106 may be temporarily bypassed, pre-heated and/or subjected to a variable feed/permeate ratio for suppressing undesired switch-on effects (such as chemical leakage).

In particular, it may be possible to temporarily bypass the membrane distillation device 106 with regard to a flow of the chemical composition from the chemical bath 100 when a temperature difference between a hot side 108 and a cool side 110 of the membrane distillation device 106 is below a predefined threshold value. When said temperature difference is too small, the partial pressure difference between hot side 108 and cool side 110 may be too small as well so that membrane distillation does not yet work properly. In particular, it may happen that metal (to be collected at hot side 108) moves to water on the cold side 110. This may result in an undesired carryover of chemicals within apparatus 120. In order to suppress such undesired arte- facts, a chemical composition pumped by a pump 152 from the chemical bath 100 may be directed by a fluid valve 151 (for instance a three-way valve) towards a bypass path 133 to thereby bypass the chemical composition with respect to the membrane distillation device 106. After a proper temperature difference (and consequently a proper partial pressure) has been established between the hot side 108 and the cool side 110 (which may be detected by corresponding sensors, not shown, for instance temperature sensors and/or pressure sensors), fluid valve 151 may be switched (for instance by turning it by 90° in a counter clockwise direction) so that the chemical composition from chemical bath 100 is introduced in the membrane distillation device 106 for separation, as described above referring to Figure 1. Reference sign 155 denotes an evaporator and reference sign 156 denotes a condenser of the membrane distillation device 106.

In order to avoid chemical leakage and/or other disadvantageous phenomena due to an insufficient temperature difference between the hot side 108 and the cool side 110, it may also be possible to temporarily reduce a ratio between a flow of the chemical composition from the chemical bath 100 to the membrane distillation device 106 on the one hand, and a flow of the separated solvent (in particular water) away from the cool side 110 on the other hand. Descriptively speaking, a lower amount of chemical composition may be supplied to and a larger amount of water may be removed from the membrane distillation device 106. This may be accomplished by adjusting operation of pump 152 pumping the chemical composition between chemical bath 100 and membrane distillation unit 106 and of a further pump 154 pumping medium (predominantly water) from the cool side 110 to the rinsing system 102 for use as rinsing fluid. Pump 152 (and/or another pump downstream of membrane distillation unit 106, not shown) may also pump separated metallic medium from the hot side 108 to the chemical bath 100. After a sufficient temperature profile has been established between the hot side 108 and the cool side 110, the amount of transported chemical composition may be again increased and/or the amount of removed water may be again reduced.

Although not shown in Figure 6, three heat exchangers may be implemented additionally in the process. One heat exchanger may be used to cool and heat the membrane distillation device 106. The other two heat exchangers may be used to keep the temperature constant.

Additionally or alternatively, it may be possible to pre-heat the membrane distillation device 106 before starting to supply the chemical composition to the membrane distillation device 106 when a temperature difference between the hot side 108 and the cool side 110 of the membrane distillation device 106 is still below a predefined threshold value. For this purpose, a heating unit 126 may be implemented on the evaporator-side of the membrane distillation device 106. Pre-heating may increase the temperature difference between hot side 108 and cool side 110 and may thereby suppress carryover.

By the described measures, an improvement of the mixing of permeate and feed can be achieved advantageously during the process of membrane distillation. Membrane distillation is a thermally driven separation process and requires a defined temperature difference between the two main volume flows (i.e. feed and permeate). To achieve this temperature difference, the permeate circuit should be cooled before entering the condenser 156 and on the other hand, the feed circuit should be pre-heated.

During this warm-up phase, feed (i.e. medium from the chemical bath 100) and permeate (i.e. solvent such as water) may be subject to chemical leakage. This issue may severely limit the application possibilities of membrane distillation in wet chemical processes. The process or chemical bath 100 may be diluted during start-up, so that the membrane distillation then has to run for a significant time (for example several hours) in order to reach a target concentration. This may significantly limit the use of membrane distillation in production processes to be carried out on an industrial scale with sufficiently high and constant throughput.

In order to overcome this shortcoming, an exemplary embodiment may shorten the start-up time and thus the mixing of the phases with one or more of the following process modifications: In one embodiment, the ratio between feed and permeate can be modified, for instance set to 1 :6 (i.e. 1 part feed and 6 parts permeate). This measure may already significantly reduce mixing. In other embodiments (which can be also combined with the previously described embodiment), it may be possible to decouple the membrane during a start-up phase. More specifically, the membrane distillation device 106 may be bypassed by bypass line 133 during a heat-up phase. This allows the heating or cooling of the feed and permeate circuit without touching the membrane. In addition, the membrane itself may be pre-heated by heating unit 126. The described modifications of the process management may shorten the start-up time which makes the apparatus 120 ready for use more quickly. In addition, the dilution effect may be efficiently suppressed.

Thus, an improved process control (in terms of hydraulics and parameters) can be achieved. Pre-heating of the membrane modules may also be advantageous. This leads advantageously to a strongly reduced undesired mixing of feed and permeate. In addition, these measures may enable the integration and operation of membrane distillation directly into a production process. This prevents longer production downtimes due to dilution of process baths caused by the membrane distillation process.

Figure 7 illustrates an apparatus 120 for recovering metal from a chemical bath 100 for chemically treating a component carrier structure 135 (for instance a plate-shaped panel for manufacturing printed circuit boards) with metal in a component carrier manufacture plant according to still another exemplary embodiment of the invention.

In the shown embodiment, a multi-stage rinsing system 102 is provided which comprises an initial stage 157 which is based on a treatment of the plate-shaped component carrier structure 135 with a humid gas beam, followed by subsequent stages 158, 159, etc., carrying out additional rinsing based on sprinkling the plate-shaped component carrier structure 135 with a liquid such as water. Referring to Figure 7, component carrier structure 135 may be oriented horizontally (rather than vertically) during plating and/or rinsing. This may be advantageous in particular when only limited space is available. Hence, exemplary embodiments of the invention may implement the membrane distillation in a horizontal plating line.

As shown, the initial stage 157 of the rinsing system 102 for rinsing the horizontally oriented component carrier structure 135 may be configured for a treatment with a humid gas beam 139, more precisely with a water-saturated humid air beam to be directed on one or both main surfaces of the component carrier structure 135. Descriptively speaking, the initial stage 157 may form a gas knife 137. The pressurized gas will clean the surfaces of the component carrier structure 135. The water saturation of the gas beam 139 will prevent chemicals from solidifying on the surfaces of the component carrier structure 135, and may thereby avoid contamination of the component carrier structure 135. An aqueous contaminated medium 167 dropping down from the component carrier structure 135 during rinsing the component carrier structure 135 by the treatment with the humid gas beam may be collected, for example in a container 141. Said medium 167, which may include significant amount of chemicals to be recycled, may be supplied to the chemical bath 100 and thereafter to the membrane distillation device 106 (or directly to the membrane distillation device 106). As illustrated by reference sign 138, water being separated in the membrane distillation device 106 based on the medium 167 may be supplied back to the initial stage 157 as a basis for the water content of the humid gas beam 139 to be generated for rinsing.

As shown in Figure 7 as well, the rinsing system 102 comprises one or more additional rinsing stages 158, 159, ..., for rinsing the component carrier structure 135 after rinsing by the initial rinsing stage 157. The one or more additional rinsing stages 158, 159, etc., may be configured for rinsing the component carrier structure 135 using sprinkling devices 139 (or any other rinsing device) or (as in the initial rinsing stage 157) the treatment with a further humid gas beam. Since residues of the additional rinsing stages 158, 159, etc., usually contain significantly smaller amounts of chemicals to be recycled, such residues may be supplied to a drain 143. Alternatively, they may also be supplied to the chemical bath 100.

Referring to Figure 8 and Figure 9, two possibilities will be explained of how to implement the membrane distillation within a horizontal plating line, for example with a panel for manufacturing printed circuit boards being oriented horizontally during plating. It may be preferred to place the membrane distillation device 106 in between the chemical bath 100 and the first rinsing cascade of the rinsing system 102.

Figure 8 illustrates an apparatus 120 for recovering metal from a chemical bath 100 for chemically treating a component carrier structure with metal in a component carrier manufacture plant according to still another exemplary embodiment of the invention implementing a (for instance three- fold) cascaded multi-stage rinsing system 102. Figure 8 shows the initial stage 157 of the rinsing system 102 above additional stages 158, 159, etc., of the rinsing system 102. Figure 9 illustrates an apparatus 120 for recovering metal from a chemical bath 100 for chemically treating a component carrier structure with metal in a component carrier manufacture plant according to yet another exemplary embodiment of the invention implementing a (for example four-fold) cascaded multi-stage rinsing system 102. In the embodiment of Figure 9, it may be possible to implement the initial stage 157 of the rinsing system 102 directly above the chemical bath 100 (as it may also be done for a vertical plating line).

Highly advantageously, the initial stage 157 of the rinsing system 102 may be based on an air-knife, see reference sign 137. The air-knife uses pressure in order to get rid of remaining process liquids. While dry air may be used by the air-knife, a preferred embodiment of the present invention may use saturated air in order to clean the panel surface. When saturated air is used, remaining process liquid may be sufficiently removed from the surface of the component carrier structure, whereas dry pressurized air may lead to undesired residues on the panel surface when the surface is drying. The water content present in the saturated air may be provided from the membrane distillation, see reference sign 138.

Advantageously, the embodiments of Figure 8 and Figure 9 enable a significant reduction of carry-over of chemicals in horizontal wet chemical processes in combination with membrane distillation.

Conventionally, a horizontal wet chemical process uses a rinsing system that requires a very high amount of fresh water to prevent the carry-over of chemicals to the subsequent bath or to clean the product from contaminants. Large amounts of waste water have to be processed extensively, which involves a high effort and is energy consuming. The high dilution of the chemicals with rinsing water usually makes recovery cumbersome or even impossible.

In contrast to this, the exemplary embodiments of Figure 8 and Figure 9 implement a cascaded rinse system 102 in which the first stage 157 is separated from the rest of the cascaded system. In the first stage 157, the air knife 137 may be installed above and below the movement of component carrier structures, which removes chemicals from the component carrier structures using an air jet. In a supply air pipe, humidity of the air may be raised to preferably at least 50%, for example 99%, by using a water atomizer. This may avoid dry chemical residues on the rinsed structure and thereby suppresses quality issues. The compressed air can be produced with low effort by a side channel compressor. A re-circulation of air may be realized in order to strongly reduce an influence of the air balance in the rinse system 102. In addition, this may save large amounts of water during humidification. The diluted chemical concentrate, which accumulates in the first stage 157 of the rinse system 102, is returned to the active module, i.e. to the chemical bath 100.

The slightly diluted chemical bath 100 is concentrated and returned to the desired concentration by membrane distillation. The resulting rinsing water may be returned directly to the water atomizer.

Advantageously, the membrane distillation plant may be primarily operated with low-temperature waste heat from the processes.

The remaining cascades of the rinsing system 102 may be embodied as sprinkler devices. Since the rinsed structure may hardly be contaminated in these cascades, the amount of fresh water needed can be significantly reduced.

A loss of unused chemicals due to carryover in the rinsing system 102 can be greatly reduced by the embodiments of Figure 8 and Figure 9. Large amounts of fresh water and waste water may be saved. The efficiency of production may be increased, as conventionally unusable low-temperature waste heat can be used, to additionally save resources. The fluctuations of the process parameters may be reduced, as fewer bath corrections are sufficient.

Figure 10 illustrates an apparatus 120 for recovering metal from a chemical bath 100 for chemically treating a component carrier structure with metal in a component carrier manufacture plant according to yet another exemplary embodiment of the invention. The embodiment of Figure 10 is similar to the embodiment of Figure 6, but a supplementary description will be provided in the following specifically for the embodiment of Figure 10.

Descriptively speaking, the membrane distillation has three channels 200, 202, and 204. Two pumps may be implemented for the circuits, in the shown embodiment pump 206 for channel 204 (permeate and rinsing water) and pump 208 for channel 202 (feed).

Next, circulation of permeate according to channel 204 will be explained: Permeate may be fed from a permeate tank 210 into the condenser 156 corresponding to the cooled side 110. The permeate flow can be additionally passed through a heat exchanger 212. Heat exchanger 212 may also be thermally coupled with an external cooling source 220. After leaving the condenser 156, the permeate flow is passed through another heat exchanger 214. In this heat exchanger 214, the permeate is heated. Descriptively speaking, said permeate may indirectly become a sort of feed. The hot permeate flow may then heat the evaporator 155 which corresponds to the heated side 108. This means that the permeate flow may be used for cooling and heating. The permeate may then be fed back into the permeate tank 210 to thereby close channel 204.

In the following, feed flow according to channel 202 will be explained: Feed from the chemical bath 100 is guided via the membrane distillation device 106 to a heat exchanger 216 in a closed loop as soon as a sufficient temperature gradient has been reached. Before that, the membrane distillation device 106 may be completely bypassed (see bypass path 133).

Next, channel 200 will be explained: Channel 200 is not a separate flow path, as it is linked to the permeate flow. In the shown embodiment, rinsing water comes from the permeate tank 210, which is continuously filled with the separated water from the membrane distillation device 106. In addition, rinsing water can also be discharged directly into the chemical bath 100, for instance when it is desired to dilute the chemical bath 100. Figure 10 shows a further heat exchanger 222 which is arranged in channel 200 and which may be thermally coupled with an external heat source 224.

Figure 11 illustrates a membrane distillation device according to an exemplary embodiment of the apparatus of the present invention. In Figure 11 a membrane distillation device 1106 is shown. The membrane distillation device 1106 comprises a heat exchanger 1112, a heatable side 1108, an air gap 1122 and a coolable side 1110. The heat exchanger 1112 is a channel through which hot distillate hD flows in the direction shown by the left arrow. The hot distillate hD is, for example, a non-contaminated distillate which was used to rinse components during the manufacturing process of the structure.

A polymeric film layer 1128 is placed between the channel 1112 and the heatable side 1108. The polymeric film 1128 is impermeable and thermally conductive, so that the channel 1112 is thermally coupled with the heatable side 1108, thus providing heat to heat up the chemical composition cC flowing through the heatable side 1108. As a result, the solvent present in the chemical composition cC partially evaporates.

A first membrane 1126, for example a PTFE membrane, separates the heatable side 1108 from the air gap 1122. A second membrane 1130, which can also be a PTFE membrane, separates the air gap 1122 from the coolable side 1110.

In this way, it is therefore possible for vapor to pass from the heatable side 1108 through the first membrane 1126, the air gap 1122 and the second membrane 1130 and to condensate on a side of the second membrane 1130 directed towards to the coolable side 1110. The vapor in the coolable side 1110 condensates as cold distillate cD and is then recovered as a distillate for further use. The chemical composition cC has now a higher concentration of the metal element. This concentrated chemical solution is recovered and reused.

According to the embodiment of Figure 11, the membrane distillation device 1106 further comprises a further air gap 1124, a further heatable side 1118, a further heat exchanger 1120, a third membrane 1134, a fourth membrane 1138 and a further polymeric film layer 1136.

The third membrane 1134 separates the further air gap 1124 from the coolable side 1110. The fourth membrane 1138 separates the further air gap 1124 from the further heatable side 1118.

The further air gap 1124, the further heatable side 1118 and the further heat exchanger 1120 are arranged in a mirrored way with respect to the air gap 1122, the heatable side 1108 and the heat exchanger 1112 about the coolable side 1110.

The membrane distillation device 1106 according to Figure 11 is therefore built in a modular way, in which a single coolable side 1110 is used for condensing distillate vapor provided by two heatable sides 1108 and 1118.

Figure 12 illustrates an apparatus 1200 for recovering metal from a chemical bath for chemically treating a component carrier structure with metal in a component carrier manufacture plant.

The apparatus 1200 of Figure 12 comprises a membrane distillation device 1206, a supply unit 1202 with an evaporator 1212 and a distillate collector unit 1246 with a condenser 1236.

In the evaporator 1212 of the supply unit 1202, a chemical composition 1232 consisting of a solvent 1232 and of metal elements is present. The chemical composition 1232 is provided by the chemical bath for chemically treating a component carrier structure.

The membrane distillation device 1206 comprises a vapor side 1204, a heatable side 1208 and a coolable side 1210. A thin thermally conductive layer 1226, which preferably is a polymeric film, is placed between the vapor side 1204 and the heatable side 1208. The thermally conductive layer 1226 is impermeable. A membrane, preferably a hydrophobic PTFE membrane, 1222 is placed between the heatable side 1208 and the coolable side 1210.

The evaporator 1212 evaporates a part of a solvent 1238 present in the chemical composition 1232. The evaporator 1212 can be a flash evaporator.

The vapor is supplied via a vapor supply means 1214 to the vapor side 1204 and the chemical composition 1232 is supplied to the heatable side 1208 via a concentrate supply means 1216. According to the embodiment described here, the vapor supply means is realized with or comprises a pipe.

The chemical composition 1232 in the heatable side 1208 is heated up by the vapor present in the vapor side 1204. Thereby, the vapor present in the vapor side 1204 cools down and condensates at the thermally conductive layer 1226. The resulting condensate is collected as solvent 1238 inside the condenses 1236.

Part of the solvent 1238 present in the chemical composition 1232 in the heatable side 1208 evaporates due a temperature rise caused by the heat exchange with the vapor in the vapor side 1204. The vapor in the heatable side 1208 is filtered by the membrane 1222 and led to the coolable side 1210.

The coolable side 1210 is thermally coupled, via a further thermally conductive layer 1228 with a further heatable side 1218, in which the chemical composition 1232 coming out from the heatable side 1208 is fed through a further concentrate supply means 1230. A further coolable side 1220 is also present. A further membrane 1224 is placed between the further heatable side 1218 and the further coolable side 1220. According to the embodiment described here the further concentrate supply means 1230 is realized with or comprises a pipe.

The chemical composition 1232 in the further heatable side 1218 is heated up by the vapor present in the coolable side 1210, so that a part of the solvent 1238 in the chemical composition 1232 is vaporized and the vapor in the coolable side 1210 is cooled down and condensates at the further thermally conductive layer 1228. The condensate is collected as solvent 1238 inside the condenser 1236.

The further membrane 1224 filters the vapor produced during the heating of the chemical composition 1232 and feeds it the further heatable side 1218. The vapor reaching the second coolable side condensates and is collected as solvent 1238 in the condenser 1236.

The concentrated chemical composition 1232 is collected at the end of the further heatable side 1218 as a concentrate and recycled for reuse via a concentrate collecting means 1234.

The condenser 1236 cools down the solvent 128 collected from the vapor side 1204, the coolable side 1210 and the further coolable side 1220. The condenser 1236 also collects the remaining, uncondensed vapor present in the further coolable side 1220 via further vapor conducting means 1240. The vapor collected in the condenser 1236 is then condensed and recycled as solvent 1238. The recycled solvent is fed to the system via a solvent feeding means 1244.

Figure 12 shows a modular construction of the membrane distillation system 1206, in which heat produced a partial vaporization of the chemical composition 1232 is used to heat the same in the membrane distillation device 1206. Furthermore, the vapor pressure produced in a previous stage of the membrane distillation device 1206 is used to heat the chemical composition 1232 in a further stage of the membrane distillation device 1206. Also advantageous in this configuration is the use of the decreasing vapor pressure across the stages, thanks to which the vaporization point for the solvent 1238 in the chemical composition 1232 decreases along the stages.

Figure 13 illustrates a membrane distillation device 1306, which is built in a modular way.

Each module comprises a vapor side, a heatable side and a coolable side, wherein a thermally conductive layer is provided between the vapor side and the heatable side and a membrane is provided between the heatable side and the coolable side.

As can be taken from Figure 13, a first module comprises a vapor side 1304, a heatable side 1308, a coolable side 1310, a thermally conductive layer 1312 and a membrane 1340. The thermally conductive layer 1312 is provided between the vapor side 1304 and the heatable side 1308. The membrane 1340 is provided between the heatable side 1308 and the coolable side 1310.

Hot vaporized solvent is supplied to the vapor side 1304 via a vapor supply means 1350, 1352 and a chemical concentration is provided to the heatable side 1308 via a chemical concentration supply means 1360, 1362.

The hot vaporized solvent in the vapor side 1304 heats up the chemical composition in the heatable side 1308 and, due to the heat exchange effect at the thermally conductive layer 1312, it condensates at the thermally conductive layer 1312. The condensate is collected and recirculated outside of the membrane distillation device.

On the other hand, the solvent present in the chemical concentration in the heatable side 1360 partially evaporates due to the heat exchange at the thermally conductive layer 1312. The evaporated solvent is filtered through the membrane 1340 and condensates in the coolable side 1310, where it is collected via a solvent collecting means 1374, 1370. The chemical composition in the heatable side 1308 at the end of the process has a higher concentration of the metal elements to be recovered and is collected via chemical concentration collecting means for further use.

In the embodiment of Figure 13, a second module comprises a further heatable side 1318, a further vapor side 1314, a further membrane 1342 and a further thermally conductive layer 1322. The coolable side 1310 serves as a further coolable side for the second module. A further vapor supply means 1350, 1354 supplies hot vaporized solvent from an evaporator and a further chemical concentration supply means 1360, 1364 supplies the chemical concentration the further heatable side 1318.

As shown in Figure 13, the second module is mirrored, with respect to the first one, about the coolable side 1310. Therefore, the coolable side 1310 is used for concentrating the chemical composition within two heatable sides, namely the heatable side 1308 and the further heatable side 1318.

A third module of the membrane distillation device 1306 of Figure 13 comprises yet a third heatable side 1328, a third coolable side 1320, a third membrane 1344 and a third thermally conductive layer 1332. The further vapor side 1314 serves as a third vapor side for the third module. A third chemical concentration supply means 1360, 1366 supplies the chemical concentration to the third heatable side 1328. A further solvent collecting means 1372, 1374 collects the solvent from the third coolable side 1328.

The third module is mirrored with respect to the second one about the second vapor side 1314.

Lastly, a fourth heatable side 1338 and a fourth membrane 1346, which are part of a fourth module, are also shown in Figure 13, along with a fourth chemical concentration supply means 1360, 1360, supplying the chemical concentration to the fourth heatable side 1338.

For the purpose of the present invention, the term "heatable side" used in connection with the described apparatus is equivalent to the term "heat side" used in connection with the described method. Correspondingly, the term "coolable side" is equivalent to the term "cool side".

It should be noted that the term "comprising" does not exclude other elements or steps and the "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined.

It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims.

Implementation of the invention is not limited to the preferred embodiments shown in the figures and described above. Instead, a multiplicity of variants are possible which use the solutions shown and the principle according to the invention even in the case of fundamentally different embodiments.