FIELD OF THE INVENTION

The present invention relates to a method and apparatus for imaging a substrate. More particularly, the present invention relates to a method and apparatus for directly imaging a substrate covered with a wet curable photopolymer, wherein a wet photopolymer pouch is subjected directly to UV radiation such as laser or LED to directly form images without the use of a photo-mask suitable for forming electrical circuits such as for printed circuit boards (PCBs), flat panel displays and flexible circuits or for the Photo Chemical Machining (PCM) of metals and glass or other materials suitable for PCM.

BACKGROUND OF THE INVENTION

Although prior techniques exist in the art for producing thin lines suitable for forming electrical circuits such as PCBs or for imaging in the Photo Chemical Machining Industry (PCMI), many of these techniques suffer from a number of significant disadvantages. For example, many previous techniques suffer from poor resolution. Moreover, techniques which do provide high resolution usually requires complex apparatus. A further problem is that previous techniques have required the use of solvent based material which is pre-dried to form a film of photopolymer which are usually supported on a polyester (e.g. Mylar) film. The thickness of these dry films has a detrimental effect on the resolution and/or definition of photoimaged surfaces as this allows unwanted undercutting (i.e. light shadowing) to occur during the photoimaging process. There are also problems in adhering solvent based material which is pre-dried to form a film to substrates and contamination problems which once again causes problems in the photoimaging process. Solvent based material which is pre-dried to form a film is also expensive when used in large quantities. Such systems are described in US 4,888,270 and US 4,954,421 , which are incorporated herein by reference.

At the present time the market for printed circuit imaging and PCM may be identified as having two separate types of resist:

(1) Wet resist which is coated on a panel by a variety of means and then pre-dried with hot air to drive off the solvents. This leaves a 'dry' surface which is photo-imageable using UV light. The raw materials for wet resist are inexpensive but processing costs (heat etc) add substantially to the overall cost of a wet resist.

(2) Dry film resist which starts out as a liquid coating that is pre-dried and supplied sandwiched between two layers of protective film. The user laminates the dry film to a copper panel using heat and pressure. In the process the protective films are removed which requires labour and presents a landfill issue at disposal.

In the prior art both wet resist and dry film resist are exposed using UV light, either by photolithography or by laser direct imaging (LDI).

We also hereby refer to WO2010/007405, incorporated herein by reference, which refers to using a resist that is different to pre-dated prior art in that it is made up of 100% solids so has no solvents involved in the related processing. In this process, the photopolymer is either

(a) coated on a panel but is not pre-dried prior to imaging but is sandwiched under a layer of developable/soluble film such as PVOH or biodegradable starch or cellulose acetate or PVDC or PVDC/PVC blends or other soluble filmic material, the film being soluble in water or water containing dissolved salts or solvent which could include materials such as isopropyl alcohol or methanol or acetone or dichloromethane or other developing solution. During exposure to UV light the photopolymer hardens in the exposed areas only. After imaging, the protective developable/soluble film is dissolved/developed and the unexposed (liquid) photopolymer is washed off the panel;

OR

(b) coated on a layer or reel of developable/soluble film such as PVOH or biodegradable starch or cellulose acetate or PVDC or PVDC/PVC blends or other soluble filmic material, but is not pre-dried (nor pre-cured) prior to imaging but is sandwiched over a panel or the film being developable/soluble in water or water containing dissolved salts or solvent which could include materials such as isopropyl alcohol or methanol or acetone or dichloromethane or other developing solution. During exposure to UV light the photopolymer hardens in the exposed areas only. After imaging, the protective soluble film is dissolved/developed and the unexposed (liquid) photopolymer is washed off the panel. The photopolymer in WO2010/007405 can also be exposed using either photolithography or laser direct imaging (LDI). WO2010/007405 also solely relates to the exposure of the photopolymer using a phototool.

It is an object of at least one aspect of the present invention to obviate or mitigate at least one or more of the aforementioned problems.

It is a further object of at least one aspect of the present invention to provide an improved method for imaging surfaces.

It is a yet further object of at least one aspect of the present invention to provide a cost efficient method for producing electrical circuits with high resolution and small track widths (i.e. fine lines).

It is a further object of at least one aspect of the present invention to provide a cost efficient method for producing high density electrical circuits suitable for PCBs, flat panel displays and flexible circuits or for use in the PCMI.

It is a further object of at least one aspect of the present invention to provide an improved method for imaging surfaces with high resolution and small track widths over a large area.

It is a further object of at least one aspect of the present invention to replace the Mylar protective layer used with current technology with a developable/soluble film and prevent the waste Mylar going to landfill. SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a method for creating a sealed pouch of wet photopolymer, said method comprising:

providing a substrate;

providing a developable/soluble film;

depositing a liquid wet photopolymer onto at least part of the substrate or onto the developable/soluble film to form a layer of liquid wet film of photopolymer on the substrate or the developable soluble film;

applying a developable/soluble film onto the layer of liquid wet film of photopolymer on the substrate or applying the developable soluble film with a wet layer of photopolymer onto a substrate;

providing a cured frame around a sealed area of photopolymer forming a sealed pouch of photopolymer;

providing a direct imaging unit; and directly applying radiation from the direct imaging unit onto the liquid wet photopolymer through the developable/soluble film;

wherein an imaged pattern of cured photopolymer is formed on the substrate.

The present invention therefore relates to a method of photoimaging a sandwich comprising a developable soluble film, a substrate, a wet curable photopolymer (i.e. a wet resist), wherein the photoimaged substrate may be used to form electrical circuits such as PCBs, flat panel displays and flexible circuits or used in PCMI. The present invention may also relate to forming dielectric images on dielectrics. In contrast to many prior art techniques, the present invention therefore relates to the use of 100% solids wet films rather than expensive dry films such as Riston™ (Trade Mark). Dry films are considerably more expensive than the use of wet films. The use of 100% solids wet films also overcomes the need for pre-drying of the wet films and therefore leads to a very controllable process.

In the present invention there is no pre-drying step before the film of wet photopolymer is imaged and irradiated with, for example, UV radiation. This is in complete contrast to prior art techniques which pre-dry a wet film before irradiation occurs.

Typically, the present invention resides in the provision of an improved photoimaging process wherein direct imaging is used and where no phototool is required. There is also no pre-drying step prior to the actual imaging process which occurs on the liquid wet photopolymer (i.e. printable ink which can be imaged and cured).

The substrate may be of any flexible or sheet material and may be made from a conductive material such as copper, silver, gold and the like, or conductive polymers such as PEDOT, ITO or Graphene. Alternatively, the substrate may be made from non- metallic material or dielectric material or any material suitable for use within PCMI.

In optional embodiments, the substrate may comprise a cladding which may comprise or consist of conductive material.

The substrate may have a liquid wet photopolymer deposited onto one or both sides of the substrate or on the developable/soluble film. In embodiments where there is a liquid wet photopolymer on both sides of the substrate then a developable/soluble film is also deposited onto both layers of liquid wet photopolymer. The liquid wet photopolymer is deposited and remains in a wet form (i.e. in a flowable form) until imaging. The chemical properties of the liquid photopolymer may be matched to the required curing properties.

The liquid wet photopolymer on one or both sides of the substrate or on the developable/soluble film is imaged directly with one or two direct imaging units i.e. no phototool is used. The liquid wet photopolymer is therefore imaged using a direct writing process using any suitable light imaging device e.g. a laser direct imaging (LDI) unit or any other suitable digital light imaging device. Typically, UV light may be used.

The parts of the liquid wet photopolymer which are imaged are hardened and may then be used to form, for example, electrical circuitry or used to Photo Chemically Machine a material.

Once the imaging has occurred, the developable/soluble film on one or both sides of the substrate will be washed or developed off the substrate. The photopolymer which is unexposed remains in liquid form and will be washed off in a washing process. One or both sides of a substrate are therefore capable of being simultaneously imaged using this process.

Prior to the imaging of the liquid wet photopolymer in the direct writing process and after the deposition of the developable/soluble film or films onto the liquid wet photopolymer there may be an intermediate process where a curing process occurs which forms a frame, border and/or perimeter of cured photopolymer around a region of uncured liquid wet photopolymer. The uncured liquid wet photopolymer may therefore be sealed within the frame (e.g. similar to a picture frame) of outer cured photopolymer to form sealed panels. During the sealing process the developable/soluble film may be sealed to the cured photopolymer and be adjacent to and abut against the uncured liquid wet photopolymer. This prevents any air and oxygen between the liquid wet photopolymer and the developable/soluble film. The sealed region may be about 1 - 15 mm or more preferably 5 - 10 mm. The sealed panels may be single discrete units such as a single mobile panel (e.g. a packet) or a series of sealed panels which can be formed using a continuous reel of clear film (e.g. polyester film) which provides a sealed packet and a method of moving the panel along - conveyor style or even a sandwich of films in a reel to reel formation.

The sealed frame, border and/or perimeter of cured photopolymer may therefore be formed during a pre-exposure stage using any suitable radiation source (e.g. a UV radiation source) that is capable of curing the liquid wet photopolymer and forming a pocket of uncured liquid wet photopolymer. Light emitting diodes (LEDs) may be used to form the sealed frame, border and/or perimeter of cured photopolymer. During this preexposure stage the substrate may be supported on both upper and lower surfaces by a soluble/developable film or possibly by a clear (or substantially clear) film layer of, for example, polyester on one of the surfaces.

The uncured wet liquid photopolymer in the central area of the panel may be imaged with a low power of about 0.5 - 2 mJ and typically about 1 - 2 mJ or more particularly about 1.8 mJ but a higher power of 1 - 10 mJ or even higher power of 10 - 100mJ or 100mJ - 1000mJ may be utilised. The use of thin wet liquid photopolymer films allows low intensity radiation (e.g. UV light) to be used in the photoimaging process.

The radiation used to cure the wet liquid photopolymer may be any suitable radiation which cures the liquid photopolymer. In particular embodiments, UV radiation may be used to polymerise and/or harden and/or set the exposed liquid (e.g. wet) photopolymer. The UV radiation may have a wavelength of about 200 - 400 nm and may have an intensity matched to cure the photopolymer being used (e.g. about 355 nm or 365 nm or 375 nm or 385 nm or 395 nm or 405 nm or 415 nm). A particularly preferred UV light source may be UV LEDs as they produce very small amounts of heat, have a long lamp life, start up immediately, have substantially no fall-off in power output, are low maintenance and can produce high levels of light intensity. LEDs may therefore be used to print fine lines in an inexpensive photoimaging process according to the present invention. An alternative light source may be a laser light source.

In particular embodiments of the present invention, the radiation may be collimated to improve the quality and/or resolution and/or definition of the photoimaging process.

After imaging the developable/soluble film and the unreacted liquid wet photopolymer may be developed/washed off using water or water containing dissolved salts or solvent which could include materials such as isopropyl alcohol or methanol or acetone or dichloromethane or other developing solution.

The wet liquid photopolymer may be deposited using any suitable technique to only one or both first and second sides of the substrate or to one side of the developable/soluble film. The present invention may therefore relate to a single-sided or a double-sided exposure in, for example, a front to back registration.

The wet liquid photopolymer may be deposited in a substantially even and continuous manner using any suitable technique. For example, the wet liquid photopolymer layer may be deposited using a spray, a brush, a roller and/or a dip coating system. Preferably, the wet liquid photopolymer may be deposited using a series of rollers and optionally a doctor blade to control the thickness of the deposited wet liquid photopolymer layer.

Prior to application of the wet liquid photopolymer or sandwiching to the coated developable/soluble film, the substrate may be cleaned using a contact cleaning process to remove debris and/or contamination from the surface of the substrate.

The wet liquid photopolymer may be made up of 100% solids and contain no solvent.

Typically, the wet liquid photopolymer may be deposited with a thickness according to any of the following: less than or equal to about 150 μηη; less than or equal to about 125 μηη; less than or equal to about 100 μηη; less than or equal to about 75 μηη; less than or equal to about 50 μηη; less than or equal to about 25 μηη; less than or equal to about 10 μηη; less than or equal to about 5 μηη; less than or equal to about 1 μηη; less than or equal to about 0.5 μηη or less than or equal to about 0.1 μηη. Alternatively, the liquid photopolymer may be deposited with a thickness ranging from any of the following: about 177 μηη to about 0.1 μηη; about 125 μηη to about 0.1 μηη; about 100 μηη to about 0.1 μηη; about 75 μηη to about 0.1 μηη; about 50 μηη to about 0.1 μηη; about 25 μηη to about 0.1 μηη or about 10 μηη to about 0.1 μηη. Preferably, the wet liquid photopolymer may have a thickness of about 5 microns.

The use of thin liquid photopolymer films allows low intensity radiation (e.g. UV light) to be used in the photoimaging process.

The developable/soluble film may be of any suitable UV transparent material but particularly may be made such as PVOH or biodegradable starch or cellulose acetate or PVDC or PVDC/PVC blends which may be optically or substantially optically clear.

The process in the present invention may be used to form a variety of electronic components including that of printed circuit boards (PCBs), flat panel displays and flexible circuits or used within the PCM I.

The direct imaging process of the present invention may therefore use a UV transparent optically clear developable/soluble film to locate uncured liquid wet photopolymer within a cured frame over a panel to be imaged. The cured frame may be of any suitable shape and size and may form a continuous perimeter around the area of sealed liquid wet photopolymer. For example, the cured frame may have a size of up to about 1 m X 1 m. The exposure in the present invention is remarkably quick and uses low levels of UV energy compared with standard photopolymers. Prior art standard resists (including other imageable layers like solder mask) require exposure of typically 50 - 80 mJ of energy to complete the cure (cross-linking). Some expensive dry films have been developed with exposure requirements as low as 8 mJ. By contrast the liquid wet photopolymer of the present invention can be exposed with preferably only about 1.8 mJ of UV energy but higher energies from 10 - 1000 mJ may also be used. The significance of this needs to be understood in terms of the improved productivity from direct imaging units (e.g. laser direct imaging units). The use of a direct imaging process also allows for small adjustments of the panel intended to be imaged to be moved slightly so that all imaged panels are exactly the same with no distortions caused by the stretching of the base substrate in a phototool. This cannot be achieved with standard lithographic systems.

The method of the present invention may also be self-contained in a mini-clean room which therefore provides significant cost savings in the photoimaging process as large industrial clean rooms are not required.

Using the method as described in the present invention, high definition fine lines suitable for electrical circuitry or PCM may be obtained. The fine lines may have a width of any of the following: less than or equal to about 200 μηη; less than or equal to about 150 μηη; less than or equal to about 140 μηη; less than or equal to about 130 μηη; less than or equal to about 120 μηη; less than or equal to about 1 10 μηη; less than or equal to about 100 μηη; less than or equal to about 90 μηη; less than or equal to about 80 μηη; less than or equal to about 75 μηη; less than or equal to about 70 μηη; less than or equal to about 60 μηη; less than or equal to about 50 μηη; less than or equal to about 40 μηη; less than or equal to about 30 μηη; less than or equal to about 20 μηη; less than or equal to about 10 μηη; or less than or equal to about 5 μηη. Alternatively the fine lines may have a width of any of the following: about 0.1 - 200 μηη; about 1 - 150 μηη; about 1 - 100 μηη; about 20 - 100 μηη or about 5 - 75 μηη. The fine lines may be used in PCBs and other electrical components such as flat screen displays or within the PCM I.

The method of the present invention may have the added advantage in that all steps such as the deposition of the liquid photopolymer and the deposition and dissolution of the film may occur in a single pass through the apparatus. For example, the depositing of a liquid photopolymer on at least one or both sides of the substrate using a series of rollers, the deposition and dissolution of the film using a developing station and the application of radiation to the liquid photopolymer to cure the photopolymer layer may all occur in a single pass through photoimaging apparatus of the present invention. This one-step process therefore increases the throughput of photoimaged substrates through the apparatus and also provides an apparatus which is easy to control and monitor.

The present invention is therefore based on a number of unique features:

1. Exposing wet photopolymer under a developable/soluble clear overlay (e.g. film).

2. Using a sealed border created using the same wet photopolymer as will later be used for imaging.

3. Transporting a panel by means of a developable/soluble film carrier (e.g.

PVOH film) which also doubles as part of the package being exposed.

The process of the present invention also allows for continuous processing (desirable for efficiency) whereas existing approaches comprise of fragmented manufacturing steps.

The present invention also has a number of advantages:

1. Big energy savings as no heat used to pre-dry the photopolymer.

2. Exposure is much faster due to exclusion of oxygen at the surface of the photopolymer because of the developable/soluble film protection. This results in very rapid throughput in a normally slow cycle direct imaging unit e.g. laser direct imaging (LDI) units. Laser direct imaging (LDI) units cost about £500k - £1 m and time on them is costly.

3. Cost savings using liquid photopolymer compared to expensive dry films.

4. Due to thinness of liquid photopolymer (approx 5 microns) extremely fine detail can be printed. This favours laser imaging since operating at lower power (but quicker speeds) increases the accuracy of the image.

According to a second aspect of the present invention there is provided photoimaged substrates formed according to the first aspect.

The photoimaged substrates may be used to form photoimaged circuits.

Typically, the photoimaged circuits may be electrical circuits which may be used in the manufacture of, for example, PCBs, flat panel displays and flexible circuits. The present invention may also be used for imaging within the PCMI.

According to a third aspect of the present invention there is an apparatus for photoimaging a substrate, said apparatus comprising: a device capable of depositing liquid wet photopolymer onto a surface of the substrate to form a film of liquid wet photopolymer;

a means capable of delivering a developable/soluble film onto the film of liquid wet photopolymer;

a means capable of depositing liquid wet photopolymer onto a surface of a developable/soluble film to form a film of wet liquid photopolymer

a means of delivering a substrate on to the surface of the wet liquid photopolymer layer; and

a direct imaging unit capable of applying radiation onto the liquid wet photopolymer through the developable/soluble film and forming an imaged pattern of cured photopolymer on the substrate.

The photoimaging process may be as defined in the first aspect.

The device capable of depositing liquid wet photopolymer onto a surface of the substrate or developable/soluble film to form a film of liquid wet photopolymer may be in the form of a series of rollers with optional doctor blades to control the rate of photopolymer deposition.

The film of wet liquid may be deposited via a series of rollers, a screen, a flexible unit, a spray head or any other suitable application equipment.

The direct imaging unit may be a laser direct imaging (LDI) unit or any other suitable digital light imaging device.

After exposure the developable/soluble may be removed washing or developing using water or water containing dissolved salts or solvent which could include materials such as isopropyl alcohol or methanol or acetone or dichloromethane or other developing solution.

The apparatus may also comprise pre-exposure radiation unit to perform a curing step which forms a frame, border and/or perimeter of cured photopolymer around a region of uncured liquid wet photopolymer. The pre-exposure radiation unit may comprise light emitting diodes (LEDs) or any suitable actinic radiation exposure unit.

The apparatus may also be in the form of a reel to reel process where the developable/soluble film is delivered in a reel form, unwound to create a web onto which the liquid wet photopolymer is deposited then imaged using UV radiation. The web is then continued to a developing unit to wash off the developable/soluble film and the uncured wet photopolymer then to a rinse station before being dried. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is sectional side view of a substrate in a pre-exposed mode and ready to be imaged according to an embodiment of the present invention;

Figure 2 is a top plan view of the substrate shown in Figure 1 in a pre-exposed mode and ready to be imaged;

Figure 3 is a further top plan view of the substrate shown in Figures 1 and 2 illustrating where imaging by direct laser imaging will occur;

Figure 4 is a yet further top plan view of the substrate shown in Figures 1 to 3 and a further stage in the process where the directly written image is developed in carbonate solution;

Figure 5 is a representational side view of a reel to pouch imaging apparatus according to an embodiment of the present invention;

Figure 6 is a top plan view of two substrates ready to be imaged and which are formed using the reel to pouch imaging apparatus shown in Figure 5;

Figure 7 is a representational view of discrete pouches of wet liquid photopolymer according to a further embodiment of the present invention; and

Figure 8 represents a further alternative coating approach wherein discrete pouches of wet liquid photopolymer are formed according to a further embodiment of the present invention.

BRIEF DESCRIPTION

Generally speaking, the present invention resides in the provision of an improved imaging process wherein direct imaging is used and where no phototool is required. In the present imaging process there is also no pre-drying process prior to the actual imaging process - this is in contrast to prior art processes. The improved imaging process is based on the principle that liquid wet photopolymer (i.e. printable ink which can be imaged and cured) is not pre-dried prior to imaging and is located (i.e. sandwiched) between an upper and lower UV transparent (or substantially UV transparent) developable/soluble film. The liquid wet photopolymer is imaged using a direct writing process such as any suitable light imaging device e.g. a laser direct imaging (LDI) unit or any other suitable digital light imaging device. The parts of the photopolymer which are imaged are hardened and can then be used (e.g. as an etch resist) or seeding layer) to form electrical circuitry or be used to machine parts within the PCM I. The film is then dissolved and washed away during the developing process along with any photopolymer which is unexposed. One or both sides of a substrate are capable of being imaged using this process. This process will now be described in more detail below and referring to Figures 1 to 8.

Figure 1 is a representation of the wet photopolymer pouch of the present invention generally designated 100. The wet photopolymer pouch 100 has a wet liquid photopolymer layer 110 on one or both sides. The wet liquid photopolymer is preferably made up of 100% solids and contains no solvents. The thickness of the wet liquid photopolymer layer 110 may, for example, be less than about 178 μηη (0.007 inch) and in this particular embodiment is about 5 microns. The wet liquid photopolymer layer 110 is not pre-dried prior to photoimaging. There is also shown a layer 1 12 which extends below or between the wet liquid photopolymer layer or layers 110. The layer 112 is a substrate material capable of being imaged and, for example, is made of conductive material such as copper, silver, gold and the like, or non metallic conductors such as PEDOT, ITO or Graphene or even dielectric material or any material suitable for use within the PCMI.

Above the wet liquid photopolymer layer 1 10 there is a clear UV transparent developable/soluble filmic material layer 1 16 which is, for example, PVOH . The films used in the present invention may be coated with a protective coating to aid chemical resistance, release from cured photopolymer and dimensional changes caused by excess humidity levels. Located below the layer 1 12 there is another wet liquid photopolymer layer 1 10 laminated with a clear UV transparent developable/soluble filmic layer 1 18 which is, for example, PVOH . As shown at both ends of the wet photopolymer pouch 100 there are areas of sealed cured photopolymer 1 13, 1 14 which have been exposed to radiation and cured resulting in some regions of film to film lamination 120, 122.

Figure 2 is a top view of the wet photopolymer pouch 100. Located in the middle of the wet photopolymer pouch there is the wet liquid photopolymer layer 1 10 which is not cured. Around the edges of the wet photopolymer pouch 100 there is shown sealed edges 120, 122, 124, 126 i.e. borders. The edges have a sealed width of about 8 - 10 mm. The wet liquid photopolymer layer 1 10 may therefore be seen as being enclosed and sealed in a pouch or envelope ready for photoimaging at a later stage of the process. The wet liquid photopolymer layer 110 is therefore sandwiched between the layers 116, 118. The sealed edges 120, 122, 124, 126 are created in a pre-exposure stage with the wet photopolymer pouch 100 being supported on both upper and lower surfaces by a clear (or substantially clear) developable/soluble film layer of, for example, PVOH. As the uncured wet liquid photopolymer layer 1 10 is sealed this has the advantage of keeping the uncured wet liquid photopolymer protected and clean. As the photopolymer is wet this also allows for quicker exposure as wet photopolymer images faster than dry film. The developable/soluble film which forms the layers 116, 1 18 also has the advantage in that it as it is laid down onto the wet photopolymer it contacts intimately against the wet photopolymer and therefore removes (i.e. squeezes out) any air (including oxygen) adjacent the photopolymer which can be detrimental to the photoimaging process. Obviously, during the deposition of the layers 116, 118 onto the wet photopolymer there should be no air bubbles formed. The developable/soluble film forming the layers 1 16, 118 will be dissolved or washed of completely in the developing process.

Figure 3 is a view of the wet photopolymer pouch 100 showing where the imaging (i.e. writing) may occur in the wet liquid photopolymer layer 1 10. The wet liquid photopolymer layer 110 may be photo-imaged to any suitable or required pattern. As shown in Figure 3 the image writing may occur through about 5 - 6 microns of wet photopolymer with a low power of about 1.8 mJ which allows for a faster writing speed and greater detail as compared with prior art processes but may also be cured with higher energy if required.

Figure 4 is a view of the next stage in the photoimaging process where after imaging the image can be developed in developing solution such as water or a carbonate solution or a suitable solvent. The layers of film 116, 1 18 have been developed along with any wet photopolymer which has not been imaged and hardened in a suitable developing station.

Figure 5 is a representation of reel to pouch imaging apparatus according to the present invention generally designated 200. On the right-hand side of the apparatus there is a series of rollers 210, 212, 220, 226 which are capable of moving a substrate 214 along the length of the apparatus 200. The substrate 214 has first of all been cleaned in a cleaner unit (not shown). The rollers 210, 212 deposit wet liquid photopolymer onto a substrate 214, for example, a copper panel. Doctor blades 21 1 , 213 may be used to control the feed and thickness of deposited wet liquid photopolymer. The rollers 220, 226 are used to deposit film layers 218, 224 (e.g. developable/soluble film) onto the liquid wet photopolymer. Other rollers 216, 222 are used to feed the film 218, 224 onto rollers 220, 226. At the point 238 shown in Figure 5 the substrate panel 214 therefore has an uncured wet liquid photopolymer layer sandwiched between two developable/soluble film layers 218, 224. There is then shown a border exposure unit with two radiation sources 230, 232 which forms the sealed borders around an uncured wet photopolymer layer to create a wet photopolymer pouch. Figure 6 shows that this can form a series of sealed wet photopolymer pouches 214, 228. Pouch 214 has sealed edges 286, 287, 288, 289 along with sealed film areas 282, 284. Pouch 228 has sealed edges 291 , 293, 294, 298 along with sealed film areas 292, 296. Each of the wet photopolymer pouches 278, 279 also has an uncured central region 280, 290, respectively. Figure 6 also shows that there are unexposed regions 310 and 312 in the substrates 214, 228, respectively. These unexposed regions 310 and 312 (sometimes referred to as 'mouse' bites) may be used to form electrical connections.

Returning to Figure 5 wet pouch 228 with its cured edges 291 , 293, 294, 298 is then passed into an exposure apparatus which has an upper exposure unit 240 and a lower exposure unit 242. The upper and lower exposure units 240, 242 are direct imaging units meaning that there is no photoimaging mask (i.e. the imaging is maskless). The exposure units 240, 242 may be laser direct imaging units that write directly onto the unexposed regions 310 and 312 in the wet photopolymer pouches 214, 228, respectively.

The exposed wet photopolymer pouch 228 then moves along to area 234 in the apparatus 200 away from the exposure apparatus. There is then a series of further rollers 250, 256, 258, 260, which transport the packet through the developer station to remove the films 218, 224 and any remaining wet ink left after exposure. Finally, the exposed and imaged and developed substrate 270 is then passed to an etching or other processing unit (not shown).

The process in the present invention may be used to form a variety of electronic components including that of printed circuit boards (PCBs), flat panel displays and flexible circuits are parts required by the PCM I.

The present direct imaging process therefore uses an optically UV transparent clear developable/soluble film to locate uncured liquid wet photopolymer within a cured frame over a substrate (e.g. panel) to be imaged. The exposure in the present invention is remarkably quick and uses low levels of UV energy compared with standard resists. In prior art standard resists (including other imageable layers like solder mask) require typically 50 - 80 mJ of energy to complete the exposure (cross-linking). Some expensive dry films have been developed with exposure requirements as low as 8 mJ. By contrast the liquid wet photopolymer of the present invention can be exposed with only about 1.8 mJ of UV energy. The significance of this needs to be understood in terms of the improved productivity from direct imaging units (e.g. laser direct imaging units). The use of a direct imaging process also allows for small adjustments of the panel intended to be imaged to be moved slightly so that all imaged panels are exactly the same with no distortions caused by the stretching of the base substrate in a phototool. This cannot be achieved with standard lithographic systems.

Figure 7 represents a further embodiment of the invention wherein discrete pouches of wet liquid photopolymer are produced which can be used in LDI or DMD devices not built in line as part of the process but are in themselves discrete processing units already in the field supplied by companies such as Orbotech, Miva, Kleo, Hitachi to name but a few and according to the present invention generally designated 300. On the right-hand side of the apparatus there is a series of rollers 310, 312, 320, 326 which are capable of moving a substrate 314 along the length of the apparatus 300. The substrate 314 has first of all been cleaned in a cleaner unit (not shown). The rollers 310, 312 deposit wet liquid photopolymer onto a substrate 314, for example, a copper panel. Doctor blades 311 , 313 may be used to control the feed and thickness of deposited wet liquid photopolymer. The rollers 320, 326 are used to deposit developable/soluble film layers 318, 324 (e.g. developable/soluble film) onto the liquid wet photopolymer. Other rollers 316, 322 are used to feed the film 318, 324 onto rollers 320, 326. At the point 338 shown in Figure 7 the substrate panel 314 therefore has an uncured wet liquid photopolymer layer sandwiched between two developable/soluble film layers 318, 324. There is then shown a border exposure unit with two radiation sources 330, 332 which forms the sealed borders around an uncured wet photopolymer layer to create a wet photopolymer pouch as described in figure 6. The wet pouch 328 with its cured edges is then passed into a trimming unit with upper blade 340 and a lower blade unit 342. The upper and lower trimming units 340, 342 can cut the developable soluble film from butt ending to leave a flap which could be utilized for handling purposes.

The trimmed wet photopolymer pouch 328 then moves along to area 350 in the apparatus 300 away from the trimming apparatus to a yellow light area to prevent initiation of the photopolymer in the pouch. This pouch can then be stacked or subsequently transported onward for further processing (not shown). such as LDI or DMD imaging units where the pouch may be used to form a variety of electronic components including that of printed circuit boards (PCBs), flat panel displays and flexible circuits are parts required by the PCM I.

Figure 8 represents an alternative coating approach wherein discrete pouches of wet liquid photopolymer are produced which can be used in LDI or DMD devices not built in line as part of the process but are in themselves discrete processing units already in the field supplied by companies such as Orbotech, Miva, Kleo, Hitachi to name but a few and according to the present invention generally designated 400. On the right-hand side of the apparatus there is a series of rollers 410, 412, 420, 426 which are capable of moving a substrate 414 along the length of the apparatus 400. The substrate 414 has first of all been cleaned in a cleaner unit (not shown). The rollers 410, 412 deposit wet liquid photopolymer onto the film 424, for example, a PVOH soluble film. Doctor blades 41 1 , 413 may be used to control the feed and thickness of deposited wet liquid photopolymer. The rollers 420, 426 are used to deposit developable/soluble film layers 318, 324 (e.g. developable/soluble film) with the liquid wet photopolymer on to a suitable substrate such as a copper panel. Other rollers 416, 422 are used to feed the film 418, 424 onto rollers 420, 426. At the point 438 shown in Figure 8 the substrate panel 414 therefore has an uncured wet liquid photopolymer layer sandwiched between two developable/soluble film layers 418, 424. There is then shown a border exposure unit with two radiation sources 430, 432 which forms the sealed borders around an uncured wet photopolymer layer to create a wet photopolymer pouch as described in figure 6. The wet pouch 428 with its cured edges is then passed into a trimming unit with upper blade 440 and a lower blade unit 442. The upper and lower trimming units 440, 442 can cut the developable soluble film from butt ending to leave a flap which could be utilized for handling purposes

The trimmed wet photopolymer pouch 428 then moves along to area 450 in the apparatus 400 away from the trimming apparatus to a yellow light area to prevent initiation of the photopolymer in the pouch which can can then be stacked or subsequently transported onward to another processing unit (not shown). such as LDI or DMD imaging units where the pouch may be used to form a variety of electronic components including that of printed circuit boards (PCBs), flat panel displays and flexible circuits are parts required by the PCMI.

Whilst specific embodiments of the present invention have been described above, it will be appreciated that departures from the described embodiments may still fall within the scope of the present invention. For example, any suitable type of imageable substrate may be used. Moreover, any suitable wet liquid photopolymer or combinations thereof may be used and further any type of soluble developable film may be used. The curing radiation used may be of any appropriate wavelength which is capable of curing the wet liquid photopolymer.