WO2000052975A1

WO2000052975A1 - Circuit board printer

Info

Publication number: WO2000052975A1
Application number: PCT/GB2000/000776
Authority: WO
Inventors: Godwin Okechukwu Osigwe; Robert William Charles Gusthart
Original assignee: Sigtronics Limited
Priority date: 1999-03-04
Filing date: 2000-03-06
Publication date: 2000-09-08
Also published as: GB9905031D0; EP1163826A1; AU3173600A; CA2366927A1

Abstract

A CAD controlled circuit board printer for the in-house production of prototype PCBs. The printer (2) includes pneumatically controlled drilling means (12) for cutting grooves and holes in a substrate (8); a deposition system (10) for filling the grooves and holes with a curable polymeric, conductive ink and an oven for curing the conductive material. A pressing means (16) is also provided for the production of multilayer boards. Substrates are cut and filled with conductive ink which are then cured. For multilayer boards, after lamination by the pressing means, holes are redrilled and refilled to enable the formation of continuous conductive pathways between layers. The printer can be used to provide a single board or multiple boards. Various embodiments of the invention are described.

Description

CIRCUTT BOARD PKTNTKR

This invention relates to a circuit board printer, and in particular although not exclusively to an in-house printer controlled by a computer to produce prototype circuit boards according to a computer aided design (CAD) . This invention also extends to a deposition means for printing circuit boards, and a method of printing circuit boards (PCBs) .

PCBs are increasingly used in a wide range of electrical equipment . PCBs provide a basis for and connection between a variety of discrete components such as resistors, capacitors and microprocessors. Typically, a PCB comprises a substrate of electrically insulating material, such as epoxy glass (FR-4) , upon which is formed a circuit pattern of electrically conducting material such as copper. Circuits can be printed on both sides of a PCB, with two sides being electrically connected by "through-holes".

With a rise in demand for PCBs, the need to produce prototypes to test possible designs has become of considerable importance. Prototypes need to be produced rapidly and cost effectively to enable fast release of the related products on to the market place. Conventional apparatus and methods for the production of PCB prototypes closely correspond to those used by large- scale manufacturers. In most instances, prototype production is carried out by those large-scale manufacturers at their premises. Typical conventional PCB manufacturing techniques involve industrial-size equipment centering on the use of wet chemistry. An example of a conventional PCB production method is a "subtractive" method that includes precoating a substance with a conductive material, printing a circuit pattern on to this using a chemically resistant material, etching away unwanted conductive material, and then removing the chemically resistant material. Such a method is expensive for the comparatively low volume of prototype production, is time consuming and inefficient. The printing on of a circuit pattern usually requires the use of a combination of photo-imaging techniques and wet chemistry. This further adds to the machinery required, and also to the cost of waste processing since stringent environmental laws require adequate handling of these wastes .

A second example of a PCB production method uses an "additive" technique in which a circuit pattern is formed by an initial use of electroless plating of copper followed by electroplating to achieve the required copper thickness. The method is controlled so that plating coats only where required. Again, this method is both inefficient in terms of chemicals and materials required, and is particularly time consuming. These factors make it unsuitable for prototype production, particularly when a large number of prototypes need to be rapidly produced and tested. It can take several days to order a prototype made by such a conventional PCB production method, which may constitute significant lost lead time.

The aim of the present invention is to at least alleviate some of the problems associated with the prior art . According to a first aspect of the present invention there is provided a circuit board printer comprising a housing and, within the housing:

(a) cutting means arranged to cut a groove or a hole in a substrate; (b) deposition means for depositing a curable conductive material onto the groove or hole;

(c) a curing means for curing the conductive material ;

(d) pressing means arranged to laminate the substrate within an insulating layer; and

(e) a transport mechanism for positioning the substrate prior to lamination. The circuit board printer according to the present invention offers several advantages over prior art apparatus for the production of PCBs. Firstly, the number of components required to produce the PCB is reduced compared to examples in the prior art which require numerous equipment associated with extra mechanical and chemical processing of the board. The components themselves are all adaptable to be of a size which can fit within an enclosure comparable in size to a photocopying machine. This enables prototypes to be produced "in-house" rather than ordering the production of prototypes from a large-scale PCB manufacturer. Reduction in the complexity of the apparatus results in a concomitant reduction in the speed and cost of production, vital to the production of prototypes.

The use of a curable conductive material (preferably polymeric) means that electrical pathways can be formed on a board without the need for additional materials. The curable polymeric conductive material is particularly versatile, and can be applied in the polymeric state or substantially so. The flow characteristics of the material are adaptable by addition of certain additives or by partial polymerisation. In addition, the material can normally be applied in a cold state thereby avoiding problems associated with the handling of heated metal- based materials as typically found in the prior art . The material has especially strong adhesive properties . Furthermore, the material is not prone to clogging of holes or "bridging" between holes as is a problem with many prior art materials. Deposition of the material can be extremely accurate. Previously, it has been difficult or impossible to fill holes with a diameter less than approximately 50 micrometers, with holes averaging in size between 250 to 100 microns. Use of the polymeric conductive material according to the present invention alleviates these problems.

Preferably, the circuit board printer is controlled by a computer program operating in relation to computer aided design. This option offers considerable flexibility, accuracy and speed; particularly important for prototype production. In addition, computer control results in a high degree of reproductivity in relation to the prototypes themselves and also the relocation of previously drilled holes.

Preferably, there is included a substrate loader, a substrate unloader and a insulating layer loader for the storing of uncut substrates, cut substrates and insulating layers; respectively. Again, all these components can be dimensioned to fit within a comparatively small enclosure.

Preferably, the cutting means includes a laser, a drill, and/or a milling device. A cleaning means is preferably included for cleaning debris from the groove or hole. This cleaning means has the advantage that it does not necessarily have to be a chemical-based cleaning means that introduces waste as in the prior art; it could simply be of a suction type such as a conventional vacuum cleaner.

The circuit board printer preferably further includes a vacuum table in proximity to the cutting means and the deposition means, the vacuum table being arranged to hold the substrate stationary. The use of a vacuum table has the advantage that it is not necessary to introduce any further mechanical means for holding the substrate in position.

Preferably the deposition means includes a pneumatic control, the pneumatic control including a solenoid or an air-controlled valve. Use of a pneumatic control rather than, say, a hydraulic -based control as is common in the prior art, diminishes the need for lubricants associated with use of hydraulic machinery. It is also possible to easily manufacture a compact pneumatic control that can be cheaper than conventional hydraulic controls.

The deposition means preferably includes a syringe. The syringe enables precise deposition of very small quantities of deposition material which may be necessary when filling small diameter holes on a reduced size prototype board. Precise deposition ensures there is a minimum amount of waste. In the prior art it is common to spot deposition material onto boards and then use additional machinery, such as a squeegy, to spread out the deposited material. Such extra machinery is not needed when a syringe is used. The syringe can also be made compact in size to fit into the confines of an in- house circuit board printer. A plurality of dispensers may be held by the deposition system. A motorised mechanism controlled by the CAD/CAE software positions the required pre-packaged dispenser so as to dispense the required amount of ink into the grooves.

Preferably the oven is a vacuum batch oven including infrared, convection or microwave heating sources. Use of a batch oven enables several substrates to be cured at once. In addition, a batch oven can be made particularly compact in contrast to conveyorised ovens typically employed in the prior art . The advantage of using a vacuum oven is that the environment for curing is optimum for producing high quality PCBs. The combination of infrared and also convection heating elements is ideally matched to a predrying phase and second stage phase of the conductive material curing process.

Preferably, the oven includes a microfilter. Inclusion of the latter ensures that the oven is safe to use within an in-house circuit board printer, in addition to being an oven that can be made compactly and cost effectively.

Preferably, the transport mechanism is rotating. This enables the components of the printer to be arranged around the transport mechanism, thereby minimising the total size of the printer.

The cutting means is preferably arranged to redrill a hole filled with cured conductive material. Since the cutting means is arranged to drill the hole originally, it is not necessary to use extra equipment such as optical aligning equipment, to relocate the hole's position: the position may simply be recalled from the computer memory.

The substrate material is preferably of insulating type and is made of epoxy glass popularly known as FR-4. Any other substrate material used in the industry could also be utilised. In the embodiments, the holes and grooves are drilled/milled directly into the FR-4 substrate. The substrate is not provided with any coating or dielectric layer, prior to grooving, as is conventional^' in the prior art. In conventional PCB manufacture, a groove is made in the dielectric coating, and not into the underlying substrate itself.

According to a second aspect of the present invention there is provided a circuit board printer comprising: (a) cutting means arranged to cut grooves in the surface of a substrate; and

(b) a deposition means for depositing a conductive material into the grooves to form conductive tracks, the deposition means including a syringe arranged to follow the line of the grooves and to deposit conductive material therein.

The curable polymeric conductive material can be applied in monomer or substantially monomer state, and has flow characteristics suitable for use with such a syringe-based deposition means. The syringe enables clean, efficient and accurate deposition of the material. The accuracy of the deposition minimises waste and the need for chemicals to clean away unwanted spillage,- and also further reduces any risk of bridging between deposited areas of material. The syringe can be made efficiently and compactly compared to prior art examples which have adopted more complex techniques requiring extra machinery. For example, it is not necessary to use a squeegy roller to redeposit the material once it has been initially "spot pasted" onto the board.

Preferably, the deposition means includes a pneumatic control, the pneumatic control including a solenoid or an air-controlled valve. Use of a pneumatic control is more cost effective and compact than many typical prior art controls, such as a hydraulic control. The deposition means preferably includes means to suck the conductive material through the hole. This offers the advantage of being able to fill holes that are much smaller in size than would be possible to fill using conventional hole filling methods . A computer program is preferably used to control the deposition means, the computer program operating in relation to a computer aided design.

According to a third aspect of the present invention there is provided a circuit board printing method comprising: (a) drilling a first hole in a first substrate;

(b) depositing a curable conductive material into the first hole;

(c) curing the conductive material;

(d) forming a multilayer board comprising a layer of insulating material between the first substrate and a second substrate;

(e) redrilling the first hole;

(f) depositing further conductive material into the redrilled first hole; and (g) curing the further conductive material.

The invention additionally extends to:

(a) drilling a first hole in a first substrate;

(b) depositing a curable conductive material into the first hole; (c) curing the conductive material;

(d) redrilling the first hole;

(e) forming a multilayer board comprising a layer of insulating material between the first substrate and a second substrate;

(f) redrilling the first hole;

(g) depositing further conductive material into the redrilled first hole; and

(h) curing the further conductive material. The invention further extends to:

(a) cutting grooves on the first face of the first substrate and drilling holes for vias and through-holes therein;

(b) repeat the same on the second face of the substrate if required;

(c) depositing a curable conductive material onto the grooves on both faces of the board and filling the holes and vias also with conductive materials;

(d) repeat on the second face of the first substrate;

(e) curing the conductive materials;

(f) redrilling the first holes for through-hole components and connecting vias;

(g) cutting grooves on the first face of the second substrate and drilling holes for vias and through holes therein;

(h) repeat same on the second face of the second substrate if required;

(i) depositing a curable conductive material onto the grooves on both faces of the board and filling the holes and vias also with conductive materials; (j) curing the conductive materials; (k) redrilling the second holes for through-hole components and connecting vias,-

(1) forming a multilayer board comprising a layer of insulating pre-preg material between the first and second substrates using a mini-press. (m) redrilling the through-holes and vias to remove any clogging by the pre-preg materials;

(n) depositing further conductive materials this time into the connecting via holes to form a continuous connector between the first and second substrates; and

(o) curing the further conductive materials .

The invention also extends to: (a) drilling a first hole and cutting a first groove in the first face of first substrate;

(b) turning over to the second face of first substrate to reveal the second face, cutting grooves and drilling holes on this face; (c) depositing a curable conductive material into the first holes and grooves in the first face;

(d) turning over to the second face of the first substrate and depositing conductive material on this second face; (e) curing both faces of the first substrate;

(f) repeat (a) - (e) for second substrate;

(g) redrill appropriate via and through-holes in both substrate ;

(h) forming a multilayer board comprising a layer of insulating material between the first and second substrate using a mini-press;

(i) redrill the holes in the first and second substrate where required to remove any pre-preg clogging the holes. This method offers a range of advantages over prior art methods, most notably arising from the simplicity of a method that involves a significantly reduced number of procedural steps . Use of the curable polymeric conductive material offers advantages of flexibility, including the possibility of applying the material in a non-molten state in addition to a reduced need for cleaning materials due to its high adhesive properties. The drilling then redrilling of the hole ensures that it is not necessary to use additional apparatus to relocate the hole on redrilling, as is commonly used in the prior art. Preparing the boards prior to making the multilayer also ensures that no problems arise due to dry joints. Preferably the method includes, in order, drilling a first hole in a first substrate; depositing a curable conductive material in the first hole; curing the conductive material, redrilling the first hole, forming a multilayer board comprising a layer of insulating material between the first substrate and a second substrate, redrilling the first hole; depositing further conductive material into the redrilled first hole; and curing the further conductive material . Preferably the redrilling includes removing any insulating material from the hole. The method of redrilling avoids the expensive and timely procedure of removing the insulating material by chemical means. Preferably, redrilling the hole includes drilling through the hole in the first substrate, the insulating layer and a corresponding hole in the second substrate. Again, the advantage of predrilling holes in the first and second substrate prior to laminating means that re-registration of the drilling means at the holes' position does not require additional equipment. The method constitutes a simple, rapid way involving a minimum number of steps to produce a hole from a substrate layer to another.

Drilling the hole preferably includes drilling using a laser or a milling device. Preferably the conductive material is deposited by a syringe. This offers the possibility of an accurate deposition with minimum waste from an apparatus that can be made compactly and cost effectively. Accurate deposition by a syringe eliminates the necessity for further deposition apparatus, such as a squeegy roller.

Preferably the conductive material is cured in a vacuum batch oven including infrared, microwave or convection heat sources . This batch oven can be made compactly and cheaply compared with a conveyorised oven, whilst the use of a vacuum offers an optimum environment for curing. Furthermore the conductive material could be cured by using a combination of infra red heat from the heated platens of a mini-press for pre-dry, a hot air gun or a hot air curtain air process heater for reflow. The airflow and temperature to the air gun or hot air curtain may be controlled by a controller connected to a computer via a variable voltage source (variac) .

The method preferably further includes sucking the conductive material through the hole. Previous methods, such as electroplating, have limited the minimum size of the hole to be above 50 microns. Sucking the material through the hole means holes of less than 50 microns diameter can be filled. This offers the advantage that it enables boards to be produced with a high density of hole as may be required for a prototype board, particularly one that is reduced in size. Preferably the method includes cleaning debris away from the hole.

Preferably the method further includes cutting a groove in the first substrate and depositing the curable polymeric conductive material into the groove. The method is preferably controlled by a computer program operating in relation to a computer aided design.

The redrilled hole is preferably about _y. or ²/₅ the diameter of the original hole.

The invention further extends to a circuit board printer comprising a housing and, within the housing:

(a) a milling and drilling means arranged to cut a groove and drill a hole directly in a give substrate ;

(b) deposition means for depositing curable conductive material onto the groove and hole;

(c) an air gun, or hot air curtain preferably incorporating a negative pressure skirt (to assist with the removal of solvents and re-circulation used gases) with its associated heating elements coupled to a variable voltage source (VARIAC) controlled by a computer for curing the conductive material;

(d) pressing means arranged to laminate the substrates with an insulating layer, the mini-press also doubling as an infra red source for pre-drying and post-curing of the conductive material; and (e) a transport mechanism for positioning the substrate prior to lamination.

With such an arrangement, the oven may optionally be dispensed with. Preferably, the air gun or the hot curtain is moved across the substrate to follow the circuit pattern, with the substrate remaining stationary on a vacuum table. Instead of an air gun, it would be possible to use a moving laser, especially an infra-red laser. Such a laser could either remain stationary, with the beam being optically directed to follow the circuit pattern, or alternatively, the laser could be moved bodily across the substrate.

The present invention can be carried into practice in a number of ways. Specific embodiments will now be described by way of example, with reference to the accompanying drawings in which: Fig. 1 illustrates the components of the machine enclosure of the circuit board printer according to an embodiment of the present invention,-

Fig. 2 is a plane view of the milling and drilling mechanism and the deposition means; Fig. 3 shows the deposition means and associated pneumatic control;

Fig. 4 is a sectional view of the oven; Fig. 5 is a side view of the oven; Fig. 6 is a part-sectional view of the pressing means and associated pneumatic control;

Figs. 7 and 8 illustrate the various stages involved in the manufacture of a multilayer printed circuit board; Fig. 9 is a top view of a printed circuit board with cut grooves and holes ; Fig. 10 is a top view of a printed circuit board with grooves and holes filled with conductive material; Fig. 11 illustrates an alternative embodiment in which the oven is dispensed with showing a side view of the minipress, milling and drilling mechanism and substrate loader mounted on a common platform;

Fig. 12 illustrates a front view of the minipress with the milling and drilling mechanism moved into the minipress;

Fig. 13 illustrates a side view of the minipress in which is positioned the milling and drilling mechanism and associated hot air curtain; Fig. 14 shows a rear view of the minipress, illustrating in more detail the hot air curtain;

Fig. 15 is a more detailed illustration of the hot air curtain of the Figure 11 embodiment;

Fig. 16 shows further details of the hot air curtain;

Fig. 17 shows an air gun for yet another embodiment; Fig. 18 illustrates a side view of the components of the circuit board printer according to a further embodiment of the present invention; Fig. 19 is an enlarged and more detailed reverse side view of the ink roller deposition station shown in Fig. 18;

Fig. 20 is a cross-section of the oven of Fig. 18 in the open position; Fig. 21 is a cross-sectional view of the oven in the closed position, and

Fig. 22 is a cross-sectional view of the oven taken on the lines A-A of Fig. 20.

Fig. 1 illustrates the main components comprising a machine enclosure 2 of a circuit board printer according to a first embodiment of the present invention. The components can be adapted to fit within a machine enclosure 2 that is typically generally rectangular in shape and occupies a volume of approximately lm³ or less. The components of the circuit board printer are preferably controlled by a computer program in order to produce a printed circuit board (PCB) according to a computer aided design (CAD) . In particular, the printer is used to produce prototype PCBs rapidly and cost effectively whilst employing a minimum number of components and procedural steps . In outline, the production of a PCB is typically indicated by the computer program instigating release of a substrate 8 from a substrate loader 24. A transport mechanism 6 moves the substrate to a milling and drilling means 12 which cuts grooves and drills holes in the substrate according to a circuit pattern to be produced. A deposition means 10 inserts a conductive material onto the grooves and holes, with the conductive material subsequently cured in an oven 14. Optionally, multilayer boards can be formed by laminating two or more substrates prepared in this way with separating insulating layers by pressing the layers together in a pressing means 16. Following lamination, the multilayer board is returned to the milling and drilling mechanism 12 and deposition means 10 for redrilling and filling of holes, before being cured for a second time. Finished boards can be stored in a substrate unloader 20, before removal via an access door 4.

In one embodiment of the present invention, the substrate loader, which can be accessed through its own access door 4, will automatically release a bare substrate upon demand. Optionally, this release is computer controlled, with the computer program operating in accordance with instructions to produce a PCB according to a CAD. The CAD software employed is preferably capable of directly converting conventional Gerber output files into DXF or any similar CNC data required to operate, in particular, the milling and drilling mechanism 12.

The substrate 8 that is released may be formed from any suitable insulating material such as polyamide , polyimide, reinforced polypropylene or epoxy glass (FR- 4) . The substrate is released to the transport mechanism 6. This mechanism may be rotating or may alternatively by a linear x-y transport; it is used to move the substrate and insulating layers between the components in the machine enclosure 2.

The transport mechanism 6 first moves the substrate 8 to the milling and drilling mechanism 12. The substrate 8 is held in fixed relation to the milling and drilling mechanism 12 on a vacuum table 26, as illustrated in Fig. 2. The vacuum table 26 is arranged to operate effectively, even when the substrate 8 is subsequently drilled with holes and grooves. The milling and drilling mechanism 12 is positioned on a servo-motor controlled CNC router system with associated x,y,z controllers; and includes a high speed router head.

Optionally, the milling and drilling mechanism could be replaced by a laser. The choice of laser depends in general upon the substrate material used. Typically, the laser is a Nd:YAG laser, with a wavelength of emission in the region of 532 nm.

The milling and drilling mechanism 12 is arranged to cut grooves in the surface of the substrate enhancing the adhesion of the conductive unit to the substrate. The depth of the grooves is perfectly below 50 micrometres because cutting into the glass fibre region of a typical substrate material such as epoxy glass may reduce the lifetime of the drilling means. The grooves when filled with cured conductive material form the basis of the conductive tracks that are used for carrying electric currents on the completed PCB. The width of a groove as opposed to its depth will in general determine the amount of current to be carried by the groove. In addition, the milling and drilling mechanism 12 is arranged to drill holes in the substrate material. These holes later serve as either "vias" (electrical connectors between one face of the substrate and the other) or as through holes (a hole designed to hold the pins of an electrical component onto the substrate prior to being secured in place) . Possible electrical components include resistors, capacitors or memory chips.

The diameter of the holes drilled depends upon their intended function, and the design of the PCB to be produced. In general, holes to function as through holes are drilled to be two and a half times the diameter of the pin of any through component to be inserted into the hole. Holes to be used as blind or buried vias are generally drilled to be twice the normal size. However, PCBs are sometimes required in which the size of the vias must be restricted to less than approximately 50 micrometres. This may be owing to a need for a high density of components, or because some prototype boards are manufactured to be a reduced size. In the case of these through holes, the holes are drilled to be the exact size required for the intended component.

Subsequent to the cutting of the grooves and holes, the grooves of the substrate are optionally vacuum- cleaned by an attached vacuum cleaner (not shown) .

Optionally, the transport mechanism 6 will turn the board over to enable grooves and holes to be cut on the second side of the board if a double-sided board is to be produced. Pads required for holding surface-mounted components can also be cut during the milling process, and can subsequently be filled with conductive material, if required, by the deposition means 10.

The deposition means 10 is typically positioned in close proximity to the milling and drilling mechanism 12, as shown in Fig. 2, possibly mounted on the same serv- motor controlled system. In one embodiment of the present invention, the deposition means comprises a syringe with a needle 30. Fig. 3 illustrates the deposition means 10 and associated pneumatic control means. The deposition means 10 includes a dispenser head 29; piston 33; shut-off valve 32 with associated shut- off valve detector 31; and needle 30. When the substrate 8 is ready for deposition of the conductive material, a computer 35 running a CAD-related program automatically actuates an air pressure regulator 36 and a solenoid valve 34 to supply pressure from an air supply 37 to the piston 33 part of the dispenser head 29. Optionally, air-controlled valves may be used instead of solenoid valves 34. The deposition means 10 deposits conductive material onto the grooves and holes. The actual size of the dispenser chosen is dependent on the width of the groove to be filled. This choice of dispenser is controlled by a computer via a motorized mechanism within the deposition head. The shut-off valve actuator 31 is arranged to ensure that only the required amount of conductive material is allowed to pass through the needle 30 within a given time span. The amount of conductive material deposited per given cross-sectional area is determined by the speed of the dispenser head 29 relative to the substrate 8 and the time interval during which the shut-off valve actuator 31 is open.

The size of the needle 30 may be altered depending upon the amount of conductive material to be dispensed. Preferably a 100 micrometre needle bore is used for deposition of conductive material onto a groove of 100 micrometre width.

When the grooves and have been filled, the transport mechanism 6 may turn the substrate 8 over so as to allow deposition of conductive material onto its other side. The conductive material itself is a curable polymeric conductive material, and when cured constitutes the electrical pathways on the circuit board and the connection between components either mounted on the board or otherwise. Any form of conductive material can in general be used provided that it is compatible with the choice of substrate material and does not exhibit an unacceptable high level of hydrophobic behaviour. An example of suitable polymeric conductive material includes a curable polymeric matrix combined with a metallic additive. Polymeric based inks or compounds which undergo a change in electrical nature when exposed to an influence such as laser or ultra-violet light can also be used in conjunction with the present invention.

Optionally, an enhancing conducting material can be added to the polymeric material.

Upon completion of the deposition of the conductive material, the transport mechanism 6 removes the substrate 8 and transports it to the oven 14, as shown in Fig. 4. The oven can be any means that will cure the polymeric conductive material such as a lamp, heat source or vapour-phase device. Optionally, the oven is a batch oven of a size suitable to fit into the machine enclosure 2. The oven may be a vacuum oven in which the vacuum provides an optimum environment for curing and also facilitates the extraction of the solvent. The heating elements are enclosed within an oven casing 40 to ensure the oven is safe to use within an in-house printer. There may be a combination of infrared heating elements

39 and convection heating elements 45 inside of the outer casing of the oven 40.

Optionally, the oven 14 includes a microwave source. As illustrated in Fig. 4, the oven 14 includes an oven door 38 through which the substrate is inserted; and also a substrate support tray 46. The infrared heating elements dry off any solvent used in the conductive material during a pre-drying process. The pre-drying period, if required, varies depending upon the conductive material used.

Fig. 5 shows a side view of the oven, with oven inner vacuum casing 470 included in particular to promote efficient curing. As illustrated in this figure, the oven includes a vacuum outlet 480 through which the dried off solvents are extracted from the oven. The solvents also preferably pass through a micro filter 471 to ensure that all the exhaust gasses are free from harmful chemicals .

After the "drying" of the solvents, the conductive material is allowed to reflow in the presence of nitrogen gas in a second stage in order to avoid oxidation. Nitrogen gas is introduced into a convection part of the oven comprising convection heating elements 45, a convention fan 44 and a fan motor 41, a nitrogen inlet 490, and the heating elements 45 are then actuated to cause the re-flow to occur. The rate of flow of nitrogen gas into the oven and the rise and fall of temperature within the oven is controlled by a microprocessor profile control system 43. A connection 42 typically RS 232 provides external communication with a controlling PC (not shown) . When the curing process is complete, the conductive material cured in the grooves forms conductive tracks on the substrate; with the substrate including through holes for components and vias connecting the two faces of the substrate. The embodiment shown in Fig. 1 is suitable for the production of multilayer as well as single-layer boards .- Such multilayer boards comprise two or more printed circuit boards or substrates that have been laminated together with separating insulating layers. The multilayer boards typically require vias that connect the various layers together.

The main enclosure 2 illustrated in Fig. 1 includes a multilayer staging area 18 where prepared substrates are stored, before the laminating process. Also illustrated is an insulating layer or "pre-preg" loader 22 which stores layers of insulating material to be used as a separation between the prepared substrates comprising the multilayer.

The termination of a multilayer board is carried out by the "minipress" pressing means 16 illustrated in Fig. 1, and in detail in Fig. 6. This pressing means is operated using an air cylinder 54, a pneumatic pump 53 and a pneumatic ram 55. Typically, the pneumatic control is capable of generating up to 2.1 MPa . A main frame 50 of the pressing means 16 encloses insulating layers 49, heated platens 47 and heating elements 46. A temperature control system 51 is usually included external to the main frame 50. Under the control of the computer program via a connection 52 (preferably RS232) the heating elements are capable of generating up to 300°C. The pressing means 16 is compact compared with most conventionally laminating devices, in addition to being simpler and cheaper owing in particular to the inclusion of a pneumatic control .

An example of a multilayer board comprises three substrate layers. The substrate layers are prepared as described above and are illustrated in Fig. 7 and Fig. 8. In Fig. 7a, three such substrates are represented by the hashed rectangles punctuated by gaps which represent predrilled holes. In Fig. 7b, the holes have been filled with conductive material; whilst in Fig. 7c the conductive material has been cured. The unhashed rectangles common to Figs. 7a, 7b and 7c represent two insulating layers. These insulating layers are optionally transported to the drilling means 12 for drilling of holes prior to laminating. The transport mechanism 6 may transport the substrates to the drilling means 12 for portions of the cured inks to be drilled out to reveal through-holes as shown in Fig. 7d. These through holes when filled with conductive inks and cured after lamination form blind and buried vias. The substrates can be transported to a cassette holder (not shown) which is arranged to align the three substrates and two insulating layers, board-insulation- board-insulation-board on the pressing means 16. The pressing means 16 presses the layers together as shown in Fig. 8e . The holes may become clogged with excess insulating pre-preg material. The multilayer is then transported back to the drilling and deposition means where the excess material is drilled out of the holes leaving an inner wall comprising mainly of cured conductive material as shown in Fig. 8f. The redrilling connects different faces of the substrate material. The redrilling of holes is preferably computer controlled. Since the original holes have already been drilled, a record can be kept of the location of the holes and it is not necessary to use additional equipment to relocate the position of the holes. The original hole is typically twice as wide as the redrilled hole. Fig. 8g illustrates holes that have been filled with fresh conductive material so as to form a continuous electrical connection between the faces when subsequently cured.

Figs. 7 and 8 also illustrate the manufacturing of a via that connects the bottom layer of one board, through an intermediate substrate, to the bottom layer of a further board. The production of this continuous productive path could alternatively be achieved by terminating two substrates; redrilling, filling and curing the holes and then adding a third layer. Blind vias, which connect inner substrate layers with outer substrate layers, can also be created by the printer drilling through the vias that connect two sides of two different substrates (four layers) and thereafter filling the hole created on the vias with conductive material, ensuring that the conductive material connecting the two vias together is in its liquid state.

The multilayer boards that can be produced by this method can have any number of comprising substrate layers. Optionally, several such boards may be in production in the printer simultaneously.

Fig. 9 illustrates a single substrate layer upon which has been drilled grooves 56 and holes 57. Fig. 10 illustrates the same board with the grooves 56 and the holes 47 filled with cured conductive material. An alternative embodiment is illustrated schematically in Figs. 11 to 16. In this embodiment, the oven 14 (Fig. 1) is dispensed with and curing is carried out using an infra-red source, such as the platens of the minipress 16, along with one or more hot air cushions. Except where mentioned otherwise, this embodiment is identical with the embodiment previously described, and the same reference numerals will be used to label similar or identical parts.

As shown in Fig. 11, in this embodiment the milling and drilling mechanism 12 is mounted onto a common platform 100 with the pressing means or mini-press 16.

The milling and drilling mechanism 12 may be moved on the stand toward or away from the mini-press 16 in the direction of the arrows 102. Also illustrated in Fig. 11 is a hot air curtain 120 which may be attached to the milling and drilling mechanism 12, or the deposition means 10.

Fig. 12 is a further side view on which the milling and drilling mechanism 12 and associated hot air curtain 102 have been moved into the mini-press 16. The milling and drilling mechanism 12 includes a router-spindle 104 and a dispenser carriage 106.

Fig. 13 shows a front view of the mini-press 16 into which the milling and drilling mechanism and associated hot air curtain have been translated. A CNC gantry system 108 is shown.

Once the deposition of the conductive material onto the substrate 8 has been completed, the milling and drilling mechanism 12 is moved away from the mini-press 16. The substrate 8 is then positioned between the platens 47 and pre-dried. This is achieved by heating the platens by means of the heating elements 46 so that they act as infra-red sources.

Once pre-drying is complete, the upper platen is retracted and the hot air curtain is introduced, as shown in Fig. 14. Fig. 14 also illustrates an inlet 110 for nitrogen and an outlet 112 to the vacuum.

Activation of the hot air curtain 120 along with their associated air and nitrogen supplies causes reflow of the conductive material on the substrate 8. The hot air curtain 120 is moved across the substrate as curing proceeds. During this operation, the board remains stationary held in place by the lower platen 47 which acts as a vacuum table. The speed of the hot air curtain 120 relative to the board 8 is the factor which determines the flow profile of the board.

Fig. 15 is a further more detailed illustration of the hot air curtain. Fig. 15(a) shows the nitrogen inlets 112 of the hot air curtain 120 in relation to the hot air curtain heaters or coils 116. Fig. 15(b) illustrates a negative pressure skirt of the hot air curtain arranged to move across the substrate, in addition to the return of the nitrogen supply 122.

Fig. 16 further illustrates the hot air curtain 120. Fig. 16(a) is a top view showing the nitrogen inlet 110 and the electrical connection 118. Fig. 16(b) shows a plan view of one of the heating elements 116, with an outer tube 114 optionally made from stainless steel. Once reflow has been completed, the conductive material is post-cured, if required, by moving the milling and drilling mechanism 12 away from the mini- press 16, and relowering the upper platen so as to cause lamination.

In yet a further embodiment the hot air curtain could be replaced by a hot air gun as shown generally at 125 in Fig. 17. The hot air gun comprises a nitrogen inlet 128, a heating element or coil (not shown) and a downwardly-directed nozzle 130. Heated nitrogen 132 issuing from the nozzle 130 is directed onto the material to be cured. The air gun 125 is attached to the milling heat, and can thus be moved in the xy plane across the substrate . In the first embodiment, the deposition of the ink is carried out first, in the channels, and the gun is then moved back along those same channels, curing the ink as it goes. The same software may be used to position the deposition head and the gun. Alternatively, the gun may follow the deposition head, curing the ink as deposition proceeds. Reference is now made to Fig. 18 of the drawings which depicts the components of a circuit board printer in accordance with a further embodiment of the present invention. It will be seen that the components are arranged linearly on a bench 100 and they may be surrounded by a hood or enclosure 102, shown in broken outline. As with the first embodiment shown in Fig. 1, the circuit board printer includes a milling and drilling mechanism 104 for creating grooves and holes in a circuit board substrate 106 (shown in broken outline) , a conductive ink deposition station, generally indicated by reference numeral 108, for depositing conductive ink onto both sides of the printed circuit board 106, an oven 110 for receiving the printed circuit board with the conductive ink deposited in the grooves and holes and for curing the conductive ink. The printed circuit board

106 may be provided as a finished single layer board with cured ink or it can be used in the formation of a multilayer board which comprises two or more printed circuit boards which have been laminated together with separate insulating layers. A mini-press 112 may be used to laminate such printed circuit boards and insulating layers together to create a multilayer board.

The printed circuit board 106 may be moved along the work bench 100 using a transport mechanism which includes rollers 114 which may be actuated under the control of a computer to move the circuit board from the cutting and drilling mechanism 104 to the oven 110 at a controlled speed.

The milling and cutting head 104 operates in substantially the same as the milling and drilling mechanism 12 described with reference to the first embodiment. The milled and drilled board 106 is then conveyed by the mechanism to the ink deposition station 108 which will be better described with reference to Fig. 19 of the drawings. The ink deposition station consists of two opposed ink roller applicators, generally indicated by reference number 118a and 118b. Each respective roller applicator 118a, 118b has an associated pre-filled ink cartridge 120a, 120b. The pre-filled ink cartridge has an associated plunge 122a, 122b which are coupled via an interface adaptor 124 to a computer 126. The computer 126 sends control signals to the plungers to apply pressure to the ink so that the conductive ink is deposited on the circuit board 106 at a controlled rate. The viscosity of the ink enables the ink to stick to the rollers which drag the ink from the cartridge and apply the ink to the surfaces of the board 106 to deposit a uniform ink film of about lOOμm on the board surfaces. It will be seen that the rollers 118a, 118b rotate in opposite directions so as to apply a conductive ink 128 on either side of the printed circuit board 108 in a layer 128 of uniform thickness.

After the ink is applied, the deposited ink is then forced into the grooves 130 and holes 132 by polyurethane blades 134a, 134b. The grooves are about 150μm deep. However, the ink also lies on top of the circuit board surface 106a. This ink must be removed and this is also achieved by using the moveable polyurethane wiper blade 134a and a fixed polyurethane wiper blade 134b. The moveable wiper blade 134a is coupled to a pneumatic actuator 136 which again is coupled to the computer 126 and which can adjust the distance of the moveable wiper blade 134a from the circuit board surface 106a so as to define a gap between the moveable wiper blade 130a and the fixed blade 130b to accommodate circuit boards of different thickness and apply pressure between blades 130a, 130b. The circuit boards are typically 500μm to 1.26 mm thick. The wiper blade portions substantially in contact with the circuit board surfaces are not opposed across the circuit board; they are slightly offset to facilitate removing the ink from the board surface . The wiper blades remove ink from the surface 106 and leave the circuit board with filled grooves 130 and filled holes 132. The ink which is removed from the circuit board surfaces wells up to create reservoir portions 138a, 138b and these reservoir portions are connected by respective conduits 139a, 139b to the ink cartridges 120a, 120b respectively and the excess wiped ink pumped by virtue of pumps 140a, 140b back into the cartridges to provide an ink recovery system. This particular deposition apparatus has an advantage over the syringe in that it provides a uniform ink thickness in all grooves and also facilitates the recovery of excess ink. In use, the circuit board 106 is passed through between the roller applicators 118a, 118b at a controlled speed in the direction of arrow A so that the ink is uniformly deposited on either side of the circuit board 106 and any excess ink is removed by the wiper blades 134a, 134b to leave ink in the grooves and holes 130,132 as shown. It will be understood that suction is provided to the reservoirs 138a, 138b far enough away from the circuit board so as to have no effect on the ink in the grooves. It will also be understood that the pneumatic piston 136 is controlled to apply pressure to the upper wiper blade 134a to maintain sufficient pressure on the board to provide an effective wiping action to facilitate ink recovery.

Reference is now made to Figs. 20 to 22 of the drawings which depicts a more detailed view of the over 110 shown in Fig. 18. It will be seen that the oven consists of upper and lower heating plates, generally indicated by reference numeral 144a, 144b. Fig. 20 shows the oven in the open position with a printed circuit board 106 with grooves and holes filled with conductive ink to be cured. The upper and lower heating stations 144a, 144b are substantially identical but only one will be described in detail. In upper station 144a, four spaced infra-red heating elements 146a are shown. The heating elements are disposed in a chamber 148 and radiation from the elements 146 passes through a ceramic glass plate 150 to heat the printed circuit board 108. This occurs when the oven is in the closed position as shown in Fig. 21. A heat seal 152 is disposed on the periphery of the ceramic glass 150 to effectively provide a seal around the printed circuit board. To facilitate fume removal, apertures 154,156 are disposed at either end of the oven between the seals 154,156. In the closed position, an extractor fan 158 is coupled to the oven and is actuated to force air through the oven and through the apertures 154,156 to remove fumes as the conductive ink cures. The removed fumes are fed to conduits 158 which are coupled to a filter 160, as best seen in Fig. 21 for filtering fumes removed from the curing of the conductive ink. Fig. 22 depicts a sectional view on the line A-A of Fig. 20 and shows that the infra-red heating elements 146 are provided by elongate infra-red bulbs.

Various modifications may be made to the embodiments hereinbefore described without departing from the scope of the invention. For example, when conductive ink is deposited by a syringe, an infra-red laser may be used to cure ink in the grooves and the holes . The laser may be coupled to a computer to be driven in the same path as the syringe so as to allow the laser beam to track the filled ink grooves and holes and thereby facilitate curing. The ink roller applicator deposition apparatus may be provided with a single roller and a single wiper for a single-sided board instead of the double roller applicator arrangement shown in Fig. 19. The location of the extractor conduits in Fig. 19 need not be exactly as shown but should be sufficiently far away from the surface of the board so as to have no effect on the ink in the grooves. The pneumatic piston for moving the moveable wiper head 132a may be replaced by any other suitable movement actuator, such as a solenoid or other electrical or hydraulic actuator. The oven shown in Figs. 20 to 22 may have any suitable number of heating elements. Indeed, different types of heating elements may be used in order to cure or dry the ink. This could be a suitable heating element or coil or hot air applied to the ceramic glass.

Any of the previously-described embodiments may also be used to produce discrete components such as resistors, capacitors, diodes and inductors; these components being directly printed onto the substrate. To achieve this, a modified curable material is used (preferably polymeric) , this material being applied to the substrate in the areas where conventional components would normally be employed. Conveniently, the drilling means is used to provide appropriate grooves, channels or areas for receipt of the modified material, applied as discussed above by means of the deposition means. The modified material is then cured as usual, thereby forming discrete electronic components which are electrically coupled by the conductive polymeric materials making up the PCB circuits .

Claims

1. A circuit board printer comprising:

(a) cutting means arranged to cut a groove or a hole in a substrate;

(b) deposition means for depositing a curable conductive material onto the groove or hole, and

(c) curing means for curing the conductive material .

2. A circuit board printer as claimed in claim 1 including pressing means arranged to laminate the substrate with an insulating layer.

3. A circuit board as claimed in claim 2 including a transport mechanism for positioning the substrate prior to lamination in an automated manufacturing process.

4. A circuit board printer as claimed in any one of claims 1 to 3 including a housing for enclosing the cutting means, deposition means, curing means and pressing means.

5. A circuit board printer as claimed in any preceding claim controlled by a computer program operating in relation to a computer aided design .

6. A circuit board printer as claimed in any preceding claim further including a substrate loader for storing uncut substrates.

7. A circuit board printer as claimed in any one of the preceding claims further including a substrate unloader for storing cut substrates .

8. A circuit board printer as claimed in any one of the preceding claims further including an insulating layer loader for storing insulating layers.

9. A circuit board printer as claimed in any one of the preceding claims in which the cutting means includes a laser.

10. A circuit board printer as claimed in any one of claims 1 to 8 in which the cutting means comprises a milling and drilling device.

11. A circuit board printer as claimed in any of the preceding claims further including cleaning means for cleaning debris from the groove or hole.

12. A circuit board printer as claimed in any one of the preceding claims further including a vacuum table in proximity to the cutting means and the deposition means, the vacuum table arranged to hold the substrate stationary.

13. A circuit board printer as claimed in any one of the preceding claims in which the deposition means includes a pneumatic control, the pneumatic control including a solenoid or an air-controlled valve.

14. A circuit board printer as claimed in any preceding claims in which the deposition means includes a syringe.

15. A circuit board printed as claimed in any preceding claim wherein the deposition includes a roller applicator.

16. A circuit board printer as claimed in claim 15 wherein said applicator includes a pair of opposed roller applicators for applying ink to both sides of said substrate .

17. A circuit board printer as claimed in any one of the preceding claims in which the curing means includes an oven .

18. A circuit board printer as claimed in any one of the preceding claims in which the curing means includes a heated platen.

19. A circuit board printer as claimed in any one of the preceding claims includes an air gun, a hot air curtain, or a laser.

20. A circuit board printer as claimed in claim 17, in which the oven comprises a vacuum bath oven including infra-red, convention or microwave heating sources.

21. A circuit board printer as claimed in any one of claims 17 to 20 wherein said oven includes extractor means for extracting fumes from said substrate as the ink cures .

22. A circuit board printer as claimed in claim 21 wherein a filter is coupled to said extraction means for filtering fumes extracted by said extraction means.

23. A circuit board printer as claimed in any one of the preceding claims including a variable voltage source for controlling the curing means.

24. A circuit board printer as claimed in claim 17 further including a microfilter.

25. A circuit board printer as claimed in any one of the preceding claims in which the transport mechanism is rotating; and is optionally arranged for translational movement .

26. A circuit board printer as claimed in any one of the preceding claims in which the cutting means is further arranged to redrill a hole filled with cured conductive material.

27. A circuit board printer as claimed in any one of the preceding claims arranged to apply a semi-conductive curable material into the groove or hole to form, when cured, a semi-conductor device on the substrate.

28. A circuit board printer comprising: (a) cutting means arranged to cut grooves in the surface of a substrate; and

29. A circuit board printer as claimed in claim 28 further including a pneumatic control, the pneumatic control including a solenoid or an air-controlled valve, for controlling deposition from the syringe onto the substrate .

30. A circuit board printer as claimed in claim 28 or claim 29 in which there is further included means to suck the conductive material through the hole.

31. A circuit board printer as claimed in any one of claims 28 to 30 in which the syringe follows the line of the grooves under computer control.

32. A circuit board printing method comprising:

(a) drilling holes and cutting grooves in a first substrate; (b) depositing a curable conductive material into the holes and grooves;

(c) curing the conductive material; (d) and forming at least a single layer board.

33. A circuit board printing method as claimed in claim 32 including forming a multilayer board by providing a second substrate and providing a layer of insulating material between the first substrate and the second substrate .

34. A circuit board printing method as claimed in claim 32 or 33 including the steps of e) redrilling said holes before lamination; f) depositing further conductive material into the redrilled first hole, and g) curing said further conductive material.

35. A circuit board printing method as claimed in claim 34 in which redrilling the first hole includes drilling through the insulating layer so as to form a continuous passage through the first substrate and the insulating layer.

36. A circuit board printing method as claimed in claim 34 or 35 including:

(h) drilling a second hole in the second substrate; (I) depositing a curable conductive material into the second hole;

(j) curing the conductive material in the second hole;

(k) forming the multilayer board by aligning the first and second holes, with the layer of insulating material between them;

(1) drilling through the conductive material in the first hole, through the insulating material and through the conductive material in the second hole to form a via or through hole; and

(m) depositing the further conductive material into the via or through -hole .

37. A circuit board printing method as claimed in any one of claims 34 to 36 in which the further conductive material, once cured, forms an electrical connection between an upper surface and a lower surface of the first substrate; or between an upper or lower surface of the second substrate and a lower surface of the first substrate;

38. A circuit board printing method as claimed in any one of claims 32 to 37 including depositing the conductive material using a syringe.

39. A circuit board printing method as claimed in any one of claims 32 to 37 including depositing the conductive material using a roller applicator.

40. A circuit board printing method as claimed in any of claims 32 to 39 in which the conductive material is cured in a vacuum batch oven, the vacuum batch oven including infrared, microwave or convection heat sources.

41. A circuit board printing method as claimed in any one of claims 32 to 40 further including sucking the conductive material through the hole.

42. A circuit board printing method as claimed in any one of claims 32 to 41 in which the first hole has a diameter of approximately twice, or approximately 2.5 times, that of the redrilled hole.

43. A circuit board printing method as claimed in any one of claims 32 to 42 further including cleaning debris away from the hole.

44. A circuit board printing method as claimed in any one of claims 32 to 43 controlled by a computer program operating in relation to a computer aided design.

45. A circuit board when manufactured according to the method of any one of claims 32 to 44.

46. A circuit board printer comprising: a cutting station having a board cutter for cutting grooves and holes in a circuit board substrate; a conductive material deposition station for depositing a curable conductive material into the grooves and holes, and a curing station having a radiation source for curing said conductive material.

47. A circuit board printer as claimed in claim 46 wherein said conductive material deposition station includes a roller applicator for applying said conductive material to said circuit board substrate.

48. A circuit board printer as claimed in claim 46 or 47 wherein said conductive material is a conductive ink.

49. A circuit board printer as claimed in claim 47 or 48 wherein said roller applicator includes a pair of opposed rollers for applying conductive material to both sides of said circuit board substrate.

50. A circuit board printer as claimed in claim 48 or 49 wherein said conductive ink is provided in a prefilled ink cartridge coupled to a respective roller.

51. A circuit board printer as claimed in claim 50 wherein said prefilled ink cartridge includes a moveable plunger adapted to be coupled to a computer controller for controlling the deposition of said ink onto said substrate .

52. A circuit board printer as claimed in any one of claims 47 to 51 including conductive ink recovery means for removing excess conductive ink from said circuit board substrate after deposition by said roller applicator.

53. A circuit board printer as claimed in claim 52 wherein said conductive ink recovery means comprises a wiper blade disposed in proximity to each substrate surface for wiping said surface to leave conductive material in said grooves and holes and create a reservoir of excess conductive ink, and conductive ink extraction means coupled to said reservoir of excess conductive material .

54. A circuit board printer as claimed in claim 53 wherein said extraction means is coupled to the ink cartridge of said respective roller applicator, and includes a pump for pumping said wiped conductive material from said reservoir to said cartridge.

55. A circuit board printer as claimed in claim 53 or 54 wherein said wiper blades having wiping edges for being disposed in contact with, or in close proximity with said respective substrate surface which are offset across the circuit board substrate.

56. A circuit board printer as claimed in any one of claims 53 to 55 wherein at least one of said wiper blades is mounted on a moveable element, said blade being moveable with respect to said board surface to define a variable gap with said other wiper blade.

57. A circuit board printer as claimed in claim 56 wherein said moveable element is a pneumatic piston.

58. A circuit board printer as claimed in any one of claims 46 to 57 wherein said curing .station is an oven with at least one infra-red radiation source.

59. A circuit board printer as claimed in claim 58 wherein said over has top and bottom heating plates, for receiving radiation from respective infra-red heating sources which are arranged so that the oven is open for receiving a board substrate with ink to be cured and closed for heating the board substrate and curing the ink.

60. A circuit board printer as claimed in claim 59 wherein the top and bottom heating plates have surrounding heat seals for mutual engagement when said oven is closed, and said heat seals deforming apertures therein and said apertures being coupled to an extractor for extracting fumes from said closed oven as said ink is being cured.

61. A circuit board printer as claimed in claim 60 including a filter coupled to said extractor for filtering fumes removed from said oven.

62. A circuit board printer as claimed in any one of claims 59 to 61 wherein a plurality of infra-red heating sources are provided for heating said top and bottom plates .

63. A circuit board printer as claimed in any one of claims 59 to 62 wherein said plates are ceramic glass.

64. A circuit board printer deposition station for depositing conductive material on a circuit board substrate comprising at least one roller applicator for applying said conductive material to said board substrate .

65. A circuit board printer as claimed in claim 64 wherein said conductive material is a conductive ink.

66. A circuit board printer as claimed in claim 64 or 65 wherein said roller applicator includes a pair of opposed rollers for applying conductive material to both sides of said circuit board substrate.

67. A circuit board printer as claimed in claim 65 or 66 wherein said conductive ink is provided in a prefilled ink cartridge coupled to a respective roller.

68. A circuit board as claimed in claim 67 wherein said prefilled ink cartridge includes a moveable plunger adapted to be coupled to a computer controller for controlling the deposition of said ink into said substrate.

69. A circuit board printer as claimed in any one of claims 64 to 68 including conductive ink recovery means for removing excess conductive ink from said circuit board substrate after deposition by said roller applicator.

70. A circuit board printer as claimed in claim 69 wherein said conductive ink recovery means comprises a wiper blade disposed in proximity to each substrate surface for wiping said surface to leave conductive ink in said grooves and holes and create a reservoir of excess conductive ink, and conductive material extraction means coupled to said reservoir of excess conductive material .

71. A circuit board printer as claimed in claim 70 wherein said extractor means is coupled to the ink cartridge of said respective roller applicator, and includes a pump for pumping said wiped conductive material from said reservoir to said cartridge.

72. A circuit board printer as claimed in claim 70 or 71 wherein said wiper blades having wiping edges for being disposed in contact with, or in close proximity with said respective substrate surfaces which are offset across the circuit board substrate.

73. A circuit board printer as claimed in any one of claims 70 to 72 wherein at least one of said wipe blades is mounted on a moveable element, said blade being moveable with respect to said board surface to define a variable gap with said other wiper blade.

74. A circuit board printer as claimed in claim 73 wherein said moveable element is a pneumatic piston.

75. A method of depositing a curable conductive material on a circuit board substrate for filling holes and grooves therein, said method comprising the step of applying said curable conductive material to said substrate by a roller applicator.

76. A method as claimed in claim 75 including the step of applying said curable conductive medium to both sides of said substrate.

77. A method as claimed in claim 75 or 76 including the step of removing excess conductive material from said board by wiping said conductive material from the substrate surface.

78. A method as claimed in claim 77 including the step of recovering said removed material and supplying said recovered material to a respective roller applicator for subsequent deposition.

79. A method as claimed in any one of claims 75 to 78 including controlling the rate of deposition of said curable conductive material onto said substrate, by coupling said roller applicator to a computer and using said computer to generate deposition rate control signals to said roller applicator.

80. A circuit board printer substantially as hereinbefore described with reference to Figs. 1 to 17 or to Figs. 18 to 23 of the accompanying drawings.

81. A circuit board printer deposition station substantially as hereinbefore described with reference to Figs. 18 to 23 of the accompanying drawings.

82. A method of depositing a curable conductive material on a circuit board substrate substantially as hereinbefore described with reference to Figs. 18 to 23 of the accompanying drawings .