PLATING USING AN INSOLUBLE ANODE AND SEPARATELY SUPPLIED PLATING MATERIAL FIELD OF THE INVENTION The present invention relates to dissolving a material to be used in plating and, in particular, to copper plating a circuit board in a plating system having an insoluble anode using a separately produced copper plating material.

BACKGROUND OF THE INVENTION The plating of an item or article immersed in a plating system solution with plating material is commonly practiced. In certain applications, the plating material is copper and it is dissolved into this solution using oxygen as a reaction agent at high temperatures. The dissolved copper acts as the plating material that is applied to the desired item. When the items or articles to be plated are printed circuit boards, the plating solutions are generally operated at lower temperatures. The most common practice of depositing copper on printed circuit boards, as part of the electroplating processes, uses a soluble anode of copper metal in the solution tank. The circuit board acts as the cathode in the solution tank. The soluble anode dissolves into the plating solution contained in the plating system by way of an electro- chemical reaction. This replenishes the copper in the solution at the same time that there is electro-deposition of copper on the circuit board, which is depleting copper in the solution.

It is also known to use an insoluble anode, rather than a soluble anode in the plating system.

In one patented system in which circuit boards can be plated with copper, an insoluble anode is utilized. This system requires circulation of plating solution between the plating system and an ion generator. Brief information is provided related to the process for dissolving the copper that is part of the plating solution. Regarding the copper dissolution, at lower temperatures of the solution in the range of 50-100°F, dissolution of copper in an acid bath to achieve a consistency normally found in circuit board manufacturing facilities is a slow process that requires relatively large reaction vessels in order to dissolve sufficient quantities of material which are required for normal production processes.

It would be beneficial, therefore, to provide a material (e. g. copper) plating process that takes advantage of an insoluble anode, while facilitating and/or enhancing the generation of plating material in a relatively low volume reaction vessel, particularly the dissolution of the material to be plated, such as copper.

SUMMARY OF THE INVENTION In accordance with the present invention, method and apparatus are provided for chemically dissolving a material, such as copper metal. The material to be dissolved can be in a sulfuric-acid-based or other acidic solution at relatively low temperatures. The material to be dissolved (e. g. copper) can be immersed in a sulfuric-acid-based solution or the material to be dissolved can be subject to a material that is sprayed or sprinkled onto the material to be dissolved.

The apparatus includes a reaction tank that receives material to be dissolved. In a preferred embodiment, the material to be dissolved that is located in the reaction tank is copper. The copper is preferably in the form of particles of small size. In one embodiment, when the particles are first placed in the reaction tank, each particle of at least a majority of the placed particles weighs less than about two ounces. Relatedly, each particle of at least a majority of the particles when first placed in the reaction tank has a weight no greater than . 001 of the total weight of the to-be-dissolved plating material. In these embodiments, the weight or mass of the material that can be ionized per cubic volume of reaction tank is optimized or substantially increased so that the reaction tank is practically implemented for use in production facilities.

With respect to controlling the reaction in the reaction tank related to the production of plating material that is to be supplied to the plating tank, fluid, preferably air, that includes oxygen is delivered to the reaction tank where it can come into contact with the material to be dissolved, particularly copper particles. In one embodiment, the delivery of the air involves use of an air compressor, together with a regulator and a filter through which the compressed air passes. A rotometer can be located such that the compressed air passes through it. The rotometer is able to indicate or display data or other information related to the airflow rate. A valve receives the air and is used in controlling air output to the reaction tank. In one embodiment, manual control of the valve is employed whereby an operator can manually regulate the airflow rate based on desired or observed information, including that from the rotometer. In another embodiment, an automatically controlled valve, such as an electronically controlled motorized valve, is utilized. A controller communicates with the automatic valve to regulate its opening/closing. The controller can provide an output control signal to the automatic valve. The control signal can be a function of one or more parameters

or factors relevant to the detennination of valve opening/closing. In one embodiment, this control signal is a function of an amount of current being supplied to the plating tank. In another embodiment, the control signal can be a function of an amount of plating material being sensed.

The apparatus also includes a plating material filter that communicates with the dissolved plating material output by the reaction tank. Such plating material passes through this filter before it can be received by the plating tank. The plating material filter removes any constituents greater than a desired size including insufficiently dissolved particles that may be copper particles.

The reaction tank can also include a number of structures or features that enhance the operation of the reaction tank. In one embodiment, the reaction tank has a sub-floor structure that can include two or more layers. A first layer can have a number of holes and the second layer is at least air permeable for use in generating air bubbles of a desired smaller size. The sub-floor structure preferably includes a third layer, with the second layer being positioned between the first and third layers. The third layer also has a number of holes and is more similar in size and shape to the first layer than to the second layer.

The reaction tank can also have an inclined floor member located in its lower half for use in controlling movement of liquid towards a reaction tank outlet. The reaction tank can have a lid with an internal volume that is in the range of. 01-5 times the volume of the entire reaction tank. The lid can be comprised of two parts, namely, a flat piece or cover and a vertical collar joined thereto so that the flat cover can be removed by itself. Substantially all the volume is defined by the collar. The reaction tank can also be divided or formed into two or more partitions in order to equally distribute and proportion airflow through the cross- section of the material to be dissolved. These vertical partitions can also facilitate periodic maintenance of the particles to be dissolved.

The reaction tank can also include a trough-shaped protuberance attached to its sidewall. The trough can have a number of shapes including a half-pipe shape. This protuberance can be employed for removing fluid from the reaction tank anywhere above its sub-floor. The protuberance is used to reduce cavitation of any pump that is connected to a suction portal, with the lowest point of the protuberance interior being located immediately below this suction portal. Cavitation can occur due to bubbles that would normally pass into

the suction portal. The reaction tank can also house one or more wedges useful in preventing unwanted formation of a single mass of particles to be dissolved.

The apparatus can include different plumbing or fluid carrying hardware useful in providing air to the reaction tank and plating material between the reaction tank and the plating system. Important to the present invention is the generation of plating material separately from the plating system that has the cathode, insoluble anode and solution bath for plating the cathode or other article in the plating system.

With respect to the operation of copper plating a circuit board in the plating system, after the small sized copper particles have been placed in the reaction tank, the copper can be dissolved pursuant to the reaction involving the controlled air being input. The copper particles can be immersed in a solution or be sprayed with a reaction enhancing solution. A less enriched plating material returned or fed back from the plating system can be used to spray the copper particles or, alternatively, maintain the immersion level. The copper plating material comprised of dissolved copper particles is pumped from the reaction tank, preferably from above the bed of copper particles. The copper plating material is carried through the plating material filter so that only desired plating material is supplied to the plating tank.

Regulation of oxygen input to control the reaction in the reaction tank can be automatically controlled using the controller. Alternatively, regulation of the airflow with the oxygen can be manually controlled. The copper plating material plates the cathode, which can be a circuit board, to a desired plating thickness, while the insoluble anode maintains its configuration or size and shape.

Based on the foregoing summary, a number of important features of the present invention are readily discerned. A material for plating is produced separately from a plating system in which an article is being plated. The plating system has an insoluble anode and the solution bath in this system can operate at relatively low temperatures. The plating material can be copper for plating a circuit board that constitutes the cathode in the plating system.

The material that is dissolved to produce the plating material can be comprised of small particles when placed in the reaction tank. The reaction tank can have a small volume. The bed of particles can be immersed in solution or have solution sprayed thereagainst. To ensure that only desired plating material with sufficiently dissolved copper is supplied to the plating system, a filter is employed between the reaction tank and the plating system. Control of

airflow can be automatically or manually controlled. When automatic control is utilized, one or more predetermined parameters are relied on in controlling airflow. The present invention can have a number of significant, secondary aspects associated with the reaction tank including: partitioning the reaction tank to achieve airflow uniformity relative to the particles to be dissolved, a sub-floor structure facilitating desired air bubble generation and passage, preventing formation of a single mass of particles, an inclined floor that directs desired movement towards a reaction tank outlet, and a preferred size lid to make easier placement of particles in the reaction tank.

Additional advantages of the present invention will become readily apparent from the following discussion, particularly when taken together with accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of the apparatus of the present invention, including a reaction tank for supplying plating material to a plating system; Fig. 2 schematically illustrates a side view of a reaction tank illustrating a sub-floor structure; Fig. 3 schematically illustrates a top view of the reaction tank of Fig. 2; Fig. 4 schematically illustrates a side view of three layers that constitute a sub-floor structure involved with supporting the bed of particles ; Fig. 5 schematically illustrates a top view based on Fig. 4 ; Fig. 6 schematically illustrates a reaction tank having a preferred lid where its two parts are joined together; Fig. 7 schematically illustrates a top view based on Fig. 6; Fig. 8 schematically illustrates a reaction tank having a number of vertical partitions; Fig. 9 schematically illustrates a top view based on Fig. 8; Fig. 10 schematically illustrates a reaction tank having a number of wedges useful in preventing unwanted combining of particles in the reaction tank; Fig. 11 schematically illustrates a top view based on Fig. 10; Fig. 12 schematically illustrates an end view of a reaction tank that includes a trough- shaped protuberance; and Fig. 13 schematically illustrates a top view based on Fig. 12.

DETAILED DESCRIPTION With reference to Fig. 1, an apparatus 20 is depicted for separately producing a plating material that is to be supplied to a plating system 24, which contains a solution or bath together with an insoluble anode and a cathode. The plating system 24 can include a vertically standing plating tank or a vessel other than a vertical one, such as a horizontally extending unit or container. In one embodiment, the cathode includes a circuit board to be plated with a copper material. In this embodiment, the plating material from the apparatus 20 that is being supplied to the plating system 24 is a copper material.

The apparatus 20 includes a vertical reaction tank 30, within which is placed a bed 34 of copper metal particles of small size, which bed is normally 12-18 inches thick, but may be of any thickness, and which normally occupies approximately one-third of the volume of the reaction tank 30, but may occupy any portion thereof. In one embodiment of the apparatus 20, the reaction tank 30 is partially filled with sulfuric-acid based copper plating solution to a level that covers the bed of copper particles. As schematically noted in Fig. 1, clean compressed air is injected into the reaction tank 30 at a level below the bed 34 of copper particles and can be forced upward through a perforated floor 38, which is described in more detail later herein, supporting the copper particles or granules, and then through the copper particles themselves. During this process, oxygen is allowed to interact with the copper and sulfuric acid to form copper sulfate in the solution. Plating solution is circulated through the apparatus in a closed loop with the plating system 24 that it serves. The plating system plating solution flows from the plating system 24 using a plating system pump 40 into the apparatus 20 at a point below the bed of copper particles, then through the bed 34 of copper particles, and returning to the plating system 24 via a suitable reaction tank pump 42 and filter 46. In another embodiment, this flow pattern through the apparatus 20 may be reversed, with solution flowing by gravity from the plating system 24 into the apparatus 20 at a point above the bed 34 of copper particles, then moving downwardly through the perforated floor 3 8 and the copper particles, before being removed from the reaction tank 30 at a point below the copper particles and pumped back to the plating system 24 via a suitable filter 46.

In one embodiment, the air injected into the reaction tank 30 is output to the apparatus 20 by a compressor 50. The compressed air is received by a regulator 54 of the apparatus 20.

The regulator 54 ensures that the air being supplied is continuously at a desired pressure. The regulated air is applied to a filter 58 that prevents unwanted particles including fluid particles, such as oil from the air compressor 50, that might be present in the air from passing to the reaction tank 30. In this embodiment, the output of the filter 58 communicates with a rotometer 62 which can be beneficial in monitoring airflow. The output from the rotometer 62 is received by a valve 66. Depending on the state of opening/closing of the valve 66, a desired or predetermined airflow rate is produced for input to the reaction tank 30. As will be described later, the valve 66 can be automatically or manually controlled and thereby control the airflow rate.

In one embodiment of the apparatus 20, solution flow is induced by spraying, sprinkling or otherwise distributing plating solution above the copper particles and allowing the liquid to trickle down through the bed 34 of copper particles, while air flows upwardly past the solution-coated particles, with solution being collected at a point below the particles and pumped back to the plating system 24 via the filter 46. When utilizing this embodiment, it becomes more crucial to properly and accurately control the flow rate associated with the spraying, sprinkling or otherwise distributing plating solution on to the copper particles or other material. Such control is necessary to achieve the required material dissolution for acceptable plating. Other embodiments of the apparatus which bring about copper-solution- oxygen interface could also be used.

In that embodiment of the apparatus 20 where copper metal is submerged in a bath of plating solution, the rate at which copper in the reaction tank 30 is converted to copper sulfate is controlled by the flow rate of air through the apparatus 20, with increased airflow rates inducing greater conversion, and decreased airflow rates inducing lesser conversion.

Without a continuous supply of oxygen, the reaction combining copper and sulfate will virtually cease. In the manual model of that embodiment of the apparatus 20, it is incumbent upon the operator of the apparatus 20 to determine the mass of copper that is required to replenish the copper that has been removed from the plating system 24 through plating and/or other losses such as chemical dragout, and then adjust airflow through the apparatus 20 to increase or decrease the copper conversion process as appropriate. The rotometer 62 can be viewed by the operator in ascertaining a desired airflow since the rotometer 62 provides a visual indication of airflow rate. In an automated model of that embodiment of the apparatus

20, the process of adjusting the airflow to achieve the appropriate level of copper conversion can be automatically controlled through any one of several feedback mechanisms in communication with the plating system 24 and/or its subsystems. Two examples of such feedback mechanisms would be (1) monitoring the amperage (e. g. using an ammeter 70) from the plating tank rectifier 74 to proportionately adjust airflow through the apparatus 20 using a controller 78 such as including a PLC to control the motorized valve 66, and (2) determining copper concentrations in the plating tank solution using a chemical sampling device (e. g. copper sensor 82) and using electronic signals from that device 82 to proportionately adjust airflow through the apparatus 20 using the controller 78 to control the motorized valve 66.

In that embodiment of the apparatus 20 where solution is sprayed, sprinkled or otherwise distributed over the copper particles, rather than submerging the particles in a bath of the solution, the rate at which copper is converted to copper sulfate may be best controlled by establishing a constant airflow rate, and varying the flow rate of plating solution over the copper particles. Such an embodiment could likewise be automated by controlling the solution flow rate by any one of several feedback mechanisms which are in communication with the plating system 24 and/or its subsystems, while maintaining a constant airflow rate.

Two examples of such feedback mechanisms would be (1) monitoring the amperage from the plating rectifier 74 to proportionately adjust the flow rate of solution through the apparatus 20 using the controller 78 to control the motorized valve 66, and (2) determining copper concentrations in the plating system 24 solution using a chemical sampling device 82, and using electronic signals from that device to proportionately adjust the solution flow rate through the apparatus 20 using the controller 78 to control the motorized valve 66.

The flow of plating solution between the apparatus 20 and its related plating system 24 provides a means of conveying the newly formed copper sulfate from the reaction tank 30 to the plating system 24, while at the same time replacing the enriched solution which has been pumped from the reaction tank 30 to the plating system 24, with relatively weaker or less enriched solution from the plating system 24. The rate of flow of solution between the apparatus 20 and the plating system 24 is important within a relatively wide range of flow rates, in that embodiment in which the copper metal is submerged in a bath of plating solution, with slower flow rates producing a more highly enriched solution returning to the

plating system 24 for any given airflow, and faster solution flow rates producing a less highly enriched solution returning to the plating system 24 for any given airflow. However, the mass of copper metal converted and transferred would be the same under both scenarios, as long as the airflow rate was the same in both scenarios.

Periodically, the removal of copper from the apparatus 20 to the plating system 24 will require the recharging of the apparatus 20 with a fresh supply of copper particles. This is accomplished by removing the lid 86 (e. g. cover 124 of the lid 86) from the reaction tank 30, pumping solution from the reaction tank 30 (without allowing the normal return flow from the plating system 24) until the solution level is below the top surface of the bed 34 of copper particles, physically pouring additional particles onto the top of the copper particle bed 34, and returning the apparatus 20 to normal run mode. The design of the apparatus 20 facilitates this process by reducing the requirement for lifting the heavy copper material beyond waist level, and reducing the safety hazard that could result from dropping metal particles into potentially dangerous sulfuric acid. Certain ergonomic design elements of the apparatus, in particular the low-profile reaction tank 30 in conjunction with the high-volume lid 86, increase the safety of this procedure while maximizing the production capabilities of the apparatus 20.

Although the apparatus 20 shown in Fig. 1 has a particular configuration for connection and/or communication with the plating system 249 various other embodiments could be employed to carry the reaction tank solution (the plating solution in the reaction tank 30) to the plating system 24. Likewise, different connections or communication paths could be utilized for carrying less enriched plating solution with copper from the plating system 24 to the reaction tank 30. By way of example, one or more additional tanks or vessels, such as other plating systems and/or reaction tanks could be employed by which plating solution communicates between reaction tank and plating system 30, 24 differently from that of Fig.

1. One or more holding tanks or vessels could also be provided intermediate the plating system 24 and the reaction tank 30. The important and necessary aspect is that reaction tank solution or the more enriched copper solution in the reaction tank 30 be separate from, and eventually communicate with, the plating system 24 having the anode and cathode.

Similarly, it is desirable and beneficial for less enriched copper solution in the plating system 24 be returned to the reaction tank 30 where it is used to maintain solution that covers or

surrounds the copper bed or, alternatively, is sprayed or sprinkled on the copper particles as previously noted.

A process is provided for converting copper into copper sulfate using copper metal, sulfuric acid, or other acid-based material, and airflow, and specificallythe oxygen contained therein, as a reaction agent in the reaction tank 30. The reaction tank 30 induces intimate contact between particles of copper metal, sulfuric acid and oxygen. The acid is to be no cooler than 40 °F and no warmer than 100°F. The solution flow rate is in the range of infinitesimally greater than zero GPM (gallons per minute) to no more than 1.0 GPM per pound of copper metal contained in the reaction tank 30. The copper metal includes particles of copper metal less than two ounces each, on average, and preferably a minor fraction of a gram each. In a preferred embodiment, when the particles of copper metal are first placed into the reaction tank 30, at least a majority of each of the particles weighs less than two ounces. Preferably also, each of the particles of copper metal of a majority of the copper metal particles when first placed in the reaction tank 30 weighs no greater than. 001 of the total weight of all copper metal particles that are then being placed into the reaction tank 30.

The airflow is in the range of infinitesimally greater than zero SCFM (standard cubic feet per minute) to no more than 1.0 SCFM per pound of copper metal contained in the reaction tank.

The copper metal is at least 50% copper by weight and preferably substantially all copper by weight.

A design is provided to automatically control the production rate of the apparatus 20 by the use of (1) a signal generating device which derives its electrical signal from one or more sensors (e. g. copper sensor 82) which monitor somesubsystem or the contents of the plating system 24 which is served by the apparatus 20, in communication with (2) a signal processing device (e. g. including the controller 78) which is capable of receiving and processing the signal from the signal generating device in (1) above and producing an electrical signal recognizable by a mechanical control device capable of proportional adjustment of flow rates, in communication with a (3) mechanical control device, such as the motorized valve 66, which is capable of receiving signals from a signal processing device and acting to proportionally adjust flow rates through the mechanical control device.

With reference to Figs. 2-5, an embodiment is provided of the two-part sub-floor 38 in the reaction tank 30 of the apparatus 20 including : (1) a support structure 100 which, in

conjunction with the sub-floor construction 104, isolates the bottom of the reaction tank 30 from the copper particles in the reaction tank 30, controls airflow below the sub-floor construction 104 to assure proportional distribution of air across the horizontal bottom of the sub-floor construction 104, and supports the weight of the copper particles in the reaction tank 30, and (2) the sub-floor construction 104 including two perforated sheets 108,112 (Fig.

4) with regular perforations 122 (Fig. 5) of less than two square inches in size, ideally less than 0.2 square inch in size, of virtually identical size and shape to a horizontal cross section of the reaction tank 30 of the apparatus 20, of thickness less than two inches each, ideally less than 1/2 inch each, between which is located a section of fabric 116, which fabric is woven to provide average openings between the fibers of between 0. 001 inches and 0.25 inches, which fabric is of substantially the same shape and size as the perforated sheets. This three- part construction acts to (1) assure proportional distribution of air moving from below the sub-floor construction 104 toward the copper particles in the reaction tank 30, (2) progressively reduce the size of air bubbles moving through the sub-floor construction 104, first by forcing them through perforations in the perforated sheets 108, 112 and secondly by forcing them through the woven fiber 116, (3) isolate the copper particles in the reaction tank 30 from the bottom portion of the reaction tank 30, where they would interfere with fluid and air injection/removal and (4) seal the top of the reaction tank 30 from the bottom, thereby forcing all air to flow through the bed 34 of copper particles, instead of around it at the edges.

Referring to Figs. 6 and 7, the high volume lid 86 for the reaction tank 30 is further illustrated. The lid 86 has an internal volume of not less than 0. 01 of the volume of the reaction tank 30, nor more than 5 times the volume of the reaction tank 30, being of any shape and containing an opening 126 for the purpose of allowing the lid 86 to communicate with an external ventilation system. The lid 86 is preferably made up of at least two parts : a collar 128 and the cover 124. Substantially all the lid 86 volume is defined by the collar 128.

As illustrated in Figs. 8 and 9, vertical partitions 130 are provided within the reaction tank 30 for the purpose of equally distributing and proportioning fluid flow and airflow throughout the cross section of the bed 34 of copper particles in the reaction tank 30, and for the purpose of facilitating maintenance of the reaction tank 30, specifically for periodic maintenance of the bed 34 of copper particles in the reaction tank 30. These vertical

partitions 130 can be spaced in such a manner that the area of the horizontal cross section delineated by these barriers is no less than. 5 square foot and no greater than 50 square feet, and preferably about 2-3 square feet in size.

Referring to Figs. 10 and 11, vertical wedges 140 of suitable material can be inserted in the bed 34 of copper particles in such a way that the wedge 140 points downward and its tip rests on the top of the sub-floor construction 104 which supports the copper bed 34. Such wedges 140 should form a cross at 90° angles, run continuously from one side of the reaction tank 30 to the other, and have a vertical height of at least one inch about the sub-floor construction 104, but no more than three feet greater than the depth of the bed 34 of copper particles in which it is inserted. The wedges 140 may be beneficial in removing copper particles from the reaction tank 30 when and if desired. In particular, it can happen over time that the copper particles join together to form essentially one large mass of combined particles. If this should occur, it is more difficult to remove the particles as a combined mass because of the resulting size. The wedges 140 function to prevent the particles from becoming only one large mass in the reaction tank 30. Instead, if the particles should combine or join together, the wedges 140 control the formation of masses of particles to four separate masses defined by the four sections formed by the crossing wedges at 90° angles.

To remove any such masses of copper particles, the wedges are first removed. Then, the separated and non-joined four masses of particles can next be removed.

As also seen in Fig. 10, a horizontally sloping floor 144 can be provided in the reaction tank 30 of the apparatus 20, in the wall abutting the lower end of which is situated a valve 150 for the purpose of draining fluid and possibly debris from the bottom of the reaction tank 30.

With reference to Figs. 12 and 13, a horizontally situated trough-shaped protuberance 160 can be attached to the side wall 164 of the reaction tank 30 such that the lowest point of its interior is located immediately below the suction portal 168 for any pump which removes fluid from the reaction tank 30 anywhere above the sub-floor construction 104 of the reaction tank 30, which protuberance 160 is at least 1/2 inch long, at least 1/2 inch wide, and at least 1/8 inch deep. This protuberance 160 is used to reduce cavitation of any pump that is connected to the suction portal 168. Such cavitation can occur due to bubbles that would normally pass into the suction portal 168, in the absence of the trough-shaped protuberance

160. The protuberance 160 functions to cause liquid to flow to the bottom 172 of the trough and move towards the suction portal 168. This path results in bubbles not passing into the suction portal 168, but moving above and away from the portal whereby bubbles sufficient to cause cavitation do not pass into the suction portal 168.

The foregoing discussion has been presented for purposes of illustration and description. The description is not intended to one or more of the forms disclosed herein.

Consequently, variations and modifications commensurate with the above teachings, within the skill or knowledge of the relevant art, are within the scope of the present invention. The embodiments discussed hereinabove are further intended to explain the best mode known of the invention and to enable others skilled in the art to utilize the inventions in such, or in other, embodiments and with the various modifications required bytheir applications or uses.

It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.