Patent Description:
The present invention relates to systems and methods for printing a printed circuit board (PCB) or a flexible PCB from substrate to full integration.

Surface Mount Technology (SMT) is an area of electronic assembly used to mount electronic components to the surface of a PCB as opposed to inserting components through holes in the PCB as in conventional assembly. SMT was developed to reduce manufacturing costs and allow efficient use of PCB space. As a result of the introduction of SMT and ever-increasing levels of automation, it is now possible to build highly complex electronic circuits into smaller and smaller assemblies with good repeatability.

The recent trend toward miniaturization creates a need for the fabrication of highly integrated PCBs. Printed circuit boards are generally fabricated by lithography using extractive methods, for example etching. Such a fabrication method provides formation of conductive lines by placing a conductive film on a substrate and etching away unnecessary portions of the conductive film to dissolution-remove a portion of the conductive film, where there are no circuits, with a corrosive solution and thereby to leave only necessary conductive lines. In addition, to improve integration, multi-layered printed circuit boards and double-sided printed circuit boards are required. Current fabrication of multi-layered printed circuit boards requires complicated processes including drilling to form through or via holes in order to enable conduction between multilayer boards, laminating the boards and soldering to adhere elements to the printed circuit board. When soldering is performed to adhere elements to the printed circuit board, a region, where a solder is melted and spread, is further required and the elements are thus located in an area wider than the size of elements themselves, which limits miniaturization. Therefore, there is a need for devices and methods enabling efficient and precise fabrication of complex circuit boards.

Flexible-rigid composite electronics represent a new generation of electronics, which can exhibit properties of both stretching as well as bending flexibility. These properties will afford electronic devices with conformity to bending and twisting as well as the capability to stretch and compress over a large strain scale. Because of their soft and conformable nature, stretchable electronics have shown great potential in biomedical engineering, e.g., epidermal electronic devices and implantable devices. As well as in the growing demand for wearable electronics, and other industries such as sensors, antennas with complex geometry, or radio frequency identification (RFID) tags to be placed on curved objects.

Progress in the field of flexible electronics is expected to play a critical role in a number of important emerging technologies. For example, flexible sensor arrays, electronic paper, wearable electronic devices, and large area flexible active matrix displays. In addition, development of flexible integrated electronic systems and processing methods is also expected to significantly impact several other important technologies including micro- and nano-fluidics, sensors and smart skins, RFID, information storage, and micro- and nanoelectromechanical systems.

Flexible electronics refers currently to a technology for building electronic circuits by depositing electronic devices onto flexible substrates. Fabricating flexible electronics with performance that is equal to conventional (rigid) microelectronics built on brittle semiconductor wafers, but capable of optical transparency, being lightweight, stretchable/bendable formats, and being easy to print rapidly over large areas has been shown to enable diverse applications, such as flexible displays, thin film solar cells, and large area sensors and actuators. In all of these applications, the flexibility of both the circuits and the components incorporated on them represents important differences from typically rigid circuits. To date, it has proven to be a challenge to design a bendable (governed by Young's modulus, a modulus of elasticity describing a material property or parameter which is equal to a ratio between a mechanical tension and a corresponding elongation and thus a measure of the stiffness of a material) and stretchable (governed by Poisson's ratio, referring to the measurement of the relative change in width with a change in length, or the tendency of the component to "neck in" during stretching) electronics based on inorganic materials due to their small fracture strain (high Young's modulus and Poisson ratio of <NUM>). A typical embodiment of flexible electronics are thin film inorganics adopted as semiconductors, conductors, and/or insulators on substrates to minimize strains induced by bending or stretching. Another embodiment is represented by circuits in wavy patterns, which can offer fully reversible stretchability/compressibility without substantial strains in the circuit materials themselves.

<CIT> describes a method for fabricating a three-dimensional (3D) electronic device. A liquid support material (e.g., an epoxy acrylate with a photoinitiator) is applied by a laser-induced forward transfer (LIFT) process to a printed circuit board (PCB) having one or more connectors and one or more electronic components thereon, and then cured to solid form by cooling and/or exposure to ultraviolet (UV) radiation. A layer of conductive material (e.g., a metal) is printed on the solidified support material by LIFT to electrically connect the one or more electronic components to respective ones of the connectors on the PCB. Subsequently, the layer of conductive material is dried by heating and metal particles in the conductive layer sintered using a laser beam. The assembly may then be encapsulated in an encapsulant.

<CIT> describes package substrates and methods to fabricate the package substrates. A package substrate may include conductive layers, vias, dielectric layers and traces fabricated therein, all patterned on one or two sides of a core embedded within a package substrate. For an embodiment, vias and traces may be formed by an ablation process and a subsequent ink printing process. For other embodiments, vias and traces may be formed by various combinations of other processes such as, but not limited to, ablation, ink printing, paste deposition, and laser assisted deposition. For various embodiments, the traces may have aspect ratios greater than <NUM>.

<CIT> describes a method for depositing a transfer material onto a receiving substrate, the method using a source of laser energy, a receiving substrate, and a target substrate. The target substrate comprises a laser-transparent support having a laser-facing surface and a support surface. The target substrate also comprises a composite material having a back surface in contact with the support surface and a front surface. The composite material comprises a mixture of the transfer material to be deposited and a matrix material. The matrix material is a material that has the property that, when it is exposed to laser energy, it desorbs from the laser-transparent support. The source of laser energy is positioned in relation to the target substrate so that laser energy is directed through the laser-facing surface of the target substrate and through the laser-transparent support to strike the composite material at a defined target location. The receiving substrate is positioned in a spaced relation to the target substrate. The source of laser energy has sufficient energy to desorb the composite material at the defined target location, causing the composite material to desorb from the defined target location and be lifted from the support surface of the laser-transparent support. The composite material is deposited at a defined receiving location on the receiving substrate. The method is useful for creating a pattern of biomaterial on the receiving substrate.

<CIT> describes a device, system, and method of three-dimensional printing. A device includes: a first 3D-printing head to selectively discharge conductive 3D-printing material; a second 3D-printing head to selectively discharge insulating 3D-printing material; and a processor to control operations of the first and second 3D-printing heads based on a computer-aided design (CAD) scheme describing a printed circuit board (PCB) intended for 3D-printing. A 3D-printer device utilizes 3D-printing methods, in order to 3D-print: (a) a functional multi-layer PCB; or (b) a functional stand-alone electric component; or (c) a functional PCB having an embedded or integrated electric component, both of them 3D-printed in a unified 3D-printing process.

<CIT> describes systems and methods for using additive manufacturing (AM) to fabricate printed circuits having side-mounted components and contacts. More specifically, the disclosure is directed to additive manufacturing methods for fabricating electronic components (AME), for example; printed circuit board (PCB), flexible printed circuit (FPC) and high-density interconnect printed circuit board (HDIPCB) (the PCBs, FPCs, and HDIPCB's together referred to as AMEs, or AME circuits), having conductive contacts and/or components along the Z axis of side walls or facets of the each of the printed AMEs.

<CIT> describes a printed 3D functional part that includes a 3D structure comprising a structural material. At least one functional electronic device is at least partially embedded in the 3D structure. The functional electronic device has a base secured against an interior surface of the 3D structure. One or more conductive filaments are at least partially embedded in the 3D structure and electrically connected to the at least one functional electronic device.

The present inventors have recognized that it is desirable to have a "one stop shop" for the production of PCBs; replacing a highly complex technology that presently utilizes approximately <NUM> stages to produce a single PCB board, not including electronic component placement on the board, by a machine that performs all the production stages and can even effect electronic component placement on the board.

Accordingly, the present invention relates to methods for printing a PCB (rigid or flexible) from substrate to full integration. Various embodiments of the invention utilize a laser-assisted deposition (LAD) system to print a flowable material on top of a substrate by laser jetting to create a PCB structure to be used as an electronic device in a production line. A system for PCB printing includes a jet printing unit, an imaging unit, curing units, and a drilling unit that print directly on a board substrate such as a glass-reinforced epoxy laminate material (e.g., FR4) or others. The jet printing unit can also be used for sintering and/or ablation of materials. Such a system can print copper and gold pastes, epoxies, and solder masks and cure them by heating or by ultraviolet (UV) radiation. Such a system can also print epoxy in joints of copper lines, e.g., where the epoxy layer is printed as a bridge on top of copper line on the PCB board. PCB boards produced according to the present systems and methods may be one-sided or double-sided.

The present invention provides a method of fabricating ef a PCB assembly as defined in claim <NUM>. In the method a metal layer is deposited on a PCB substrate by LAD in which metal droplets from a donor substrate are jetted onto the PCB substrate and/or into one or more holes therein using a laser to form a layer of metal on the PCB substrate. The layer of metal is subsequently dried and sintered, and the jetting, drying, and sintering are repeated until the layer of metal reaches a desired thickness. Thereafter at least one passivation layer is formed over the layer of metal. If needed, the layer of metal may be ablated (e.g., using the same laser as was used for the deposition) if it exceeds the desired thickness. The passivation layer may be a layer of epoxy that is deposited or coated over the metal layer using a roller or blade. Or the passivation layer may be a layer of epoxy printed over the metal layer from an epoxy coat on a donor substrate by LAD. If needed, one or more additional metal layers and epoxy layers may be likewise printed using LAD. The layer of epoxy may be cured by hot air and/or infrared (IR) irradiation.

In some instances, the layer of metal will include a first metal trace, and the epoxy layer will include at least a first portion of epoxy that covers at least a first portion of the first metal trace. Additional metal layers printed over the epoxy layer may thus include a second metal trace having at least a portion disposed over the first portion of the epoxy layer that covers the first portion of the first metal trace. That is, the epoxy layer may form a bridge over which the second metal trace can cross the first metal trace on the same dies of the PCB substrate without causing a short circuit.

In some cases, the one or more holes in the PCB substrate will be formed in a first side of the PCB substrate by drilling or laser engraving the first side of the PCB substrate, but those holes will not pass through an entire thickness of the PCB substrate. Then, the layer of metal may be formed in the one or more holes by LAD from the first side of the PCB substrate; that is, the side on which the holes are present. Subsequently, the PCB substrate may be flipped and the one or more holes completed through the thickness of the PCB substrate by drilling or laser engraving through the second (reverse) side of PCB substrate. Thereafter, remining portions of the one or more holes exposed by the drilling or laser engraving through the second (reverse) side of PCB substrate may be metalized by LAD in the fashion discussed above.

Where desired or needed, a solder mask layer is printed, e.g., by LAD, over the passivation layer and any intervening layers and/or components of the PCB assembly. Also, a label may be printed, e.g., by LAD, over the solder mask. As needed, holes and vias in the various layers, including the solder mask, are formed and metalized by LAD so as to provide electrical connections to the metal layers in the PCB assembly and to provide attachment points for electronic components.

In an example a system for fabricating a PCB assembly is described in which a substrate holder, configured to hold a PCB substrate, is translatable between a plurality of processing stations, including a printing station configured for LAD of one or more materials (e.g., copper and gold pastes, epoxy, and solder mask material, etc.) by jetting respective ones of the materials individually from respective donor substrates on which the respective ones of said materials are coated or otherwise disposed, a curing station configured to cure by heating, IR irradiation, or UV irradiation, deposited ones of the materials on the PCB substrate, and a drilling station configured to drill or engrave through holes and/or vias in the PCB substrate and/or layers of ones of the materials disposed thereon. The printing station may also be configured for laser sintering and/or laser ablation of the respective ones of the materials printed on the PCB substrate and/or additional layers of said PCB assembly. A unit configured to flip the PCB substrate to allow access to both sides of the PCB substrate by the printing station, curing station, and/or drilling station may also be provided.

In yet another embodiment, the present invention provides a method for fabricating a printed circuit board (PCB) assembly in which one or more vias are drilled or laser engraved in a PCB substrate from a first side of the PCB substrate. The vias do not extend through an entire thickness of the PCB substrate. A metal paste is deposited, by LAD, over at least a first portion of the PCB substrate and into one or more of the vias to a first thickness. The depositing is performed by jetting small volumes of metal paste from a donor film on a first carrier substrate by an incident laser beam onto the PCB substrate and into the one or more vias, curing the metal paste deposited on the PCB substrate and into the one or more vias, sintering the deposited and cured metal paste using a same laser that was used for depositing the metal paste, and repeating the depositing, curing and sintering of the metal paste, thereby forming successive thicknesses thereof on the PCB substrate and in the one or more vias, until a desired thickness of the metal paste on the PCB substrate and in the one or more vias is reached. Then a passivation layer is printed by LAD on the desired thickness of metal paste on the PCB substrate and in the one or more vias; the printing being performed by jetting small volumes of epoxy from a second carrier substrate using the same laser that was used for depositing the metal paste, and curing the passivation layer. Finally, a solder mask is formed by LAD over the passivation layer, with the formation involving jetting of small volumes of solder mask material from a third carrier substrate using the same laser that was used for depositing the metal paste, and curing the solder mask. The solder mask layer, passivation layer, and metal paste layer(s) may be cured using heat, or IR or UV radiation.

In various instances, the PCB substrate is moved between the drilling, the depositing, the printing, and the forming processes on a stage that is translatable between positions at which the drilling, the depositing, the printing, and the forming processes take place. Also, the processes of depositing the metal paste and printing the passivation layer may be performed multiple times prior to forming the solder mask so as to produce a PCB assembly having multiple layers of both metal paste and epoxy between the PCB substrate and the solder mask (e.g., on one or both sides of the PCB substrate). Metal electrical connectors for an electronic component may be formed within the passivation layer and/or the solder mask and the metal electrical connectors may be formed from different metals (e.g., Cu, Au, Ag, etc.). One or more electronic components may be attached to the metal electrical connectors, e.g., by one or more solder joints and in some instances one or more additional passivation layers and/or solder mask layers may be formed over the electronic component. Where needed, support structures for the electronic components may be formed by LAD prior to attaching the electronic components. Also, as discussed above, epoxy bridges may be used to avoid short circuits between different layers of electrical traces.

These and further embodiments of the invention are described in greater detail below.

The present invention is illustrated by way of example, and not limitation, in the figures of the accompanying drawings, in which:.

PCB production is a highly developed field with a significant number of stages. The current invention is aiming at simplifying the production process through provision and use of a single system with several sub modules that can construct a PCB from the prepreg and laminate level up to a fully developed board with embedded electronics as a one-shop-stop. Methods in accordance with the present invention need not necessarily employ different materials that are used today for conventional PCB production (although such new materials may be used), but may instead use those same materials in new and different ways. Hence, in various embodiments the present invention relates to methods for printing PCB or a flexible PCB, from substrate level to full integration. As described below, embodiments of the invention may utilize LAD systems to print any flowable material on top of a substrate by laser jetting to create a PCB structure to be used as an electronic device in a production line.

The first stage in the PCB production involves drilling vias in the board substrate. As illustrated in <FIG>, any of several approaches can be taken. For example, and referring to <FIG>, in a PCB board production system 100a a CNC machine <NUM> may be used for drilling into a PCB core substrate board <NUM>. As indicated, the PCB core substrate board <NUM> may be made of a glass-reinforced epoxy laminate such as FR4. Modules of this kind, including those with an additional cleaning unit for removal of drilling waste, are used widely today. The CNC head <NUM> is mounted on a stage (not shown) that is moveable in three dimensions, and the substrate board <NUM> is held flat from its sides or on a sacrificial substrate (not shown in this view). The drilling head <NUM> creates holes <NUM>, optionally with different diameters, at desired locations on the board <NUM>. In the current system it is beneficial to drill only vias and not through holes because a laser can be used to remove extra material after the board is flipped, simplifying the placement of copper paste in the holes and keeping the substrate holder clean (through holes can contaminate the holder surface).

As explained below, other aspects of the PCB board production system are laser-based. Therefore, rather than using a CNC drill head, all of the engraving or cutting involved in the production of a PCB, including the formation of vias, can be done using the laser. To that end, <FIG> illustrates an embodiment of a PCB board production system 100b that engraves the vias using a laser system <NUM>. When laser <NUM> is used, a power or light intensity meter <NUM> can be used to evaluate the hole depth. By measuring the light intensity at the location of a via during laser drilling, the via hole depth can be evaluated (e.g., by table lookup or other means) so that the drilling is stopped before the hole passes through the entire thickness of the board substrate <NUM> (e.g., so that a thickness "z" of the substrate remains). The light intensity measured may be that of the cutting laser beam <NUM> itself or of a separate light source (e.g., one positioned above the cutting position).

As mentioned, drilling/cutting only vias and not through holes simplifies the cleaning of a substrate holder. However, referring to the PCB board production system 100c shown in <FIG>, another solution that may be employed is the addition of a peelable substrate <NUM> beneath the PCB substrate <NUM>. For example, the peelable substrate <NUM> may be added to one side of the PCB substrate <NUM> and, after drilling and cleaning the opposite side, the peelable substrate <NUM> may be removed to allow for drilling of the side of PCB substrate <NUM> on which it was originally placed. Where the peelable substrate <NUM> is used, an appropriate coating and peeling unit is added to the system to enable these operations.

Referring now to <FIG>, still another way to keep a sample holder <NUM> of a PCB board production system 100d clean is to use a sacrificial layer <NUM> (e.g., made of plastic or a similar material) between the sample holder <NUM> and the PCB substrate <NUM>. In this case, the sacrificial layer <NUM> should be able to hold the PCB substrate <NUM> flat. Typically, the sample holder <NUM> is a vacuum holder that keeps the PCB substrate <NUM> flat with the holder surface, but if a sacrificial layer <NUM> is added it should be able to maintain the vacuum on the PCB substrate <NUM>. Accordingly, some holes <NUM> must be added in the sacrificial layer <NUM> so that vacuum is maintained against the PCB substrate <NUM>, and these holes should be located away from the drilling hole <NUM> positions. For each application, a new sacrificial layer <NUM> must be designed (to account for the locations of the drilling holes), and it can be used many times.

Turning now to the metallization process, in embodiments of the present invention this may be performed by paste printing. <FIG> illustrates how, in a PCB board production system <NUM>, a non-flat surface, such as a PCB substrate <NUM> in which vias <NUM> have been engraved/drilled, is covered by a metal paste <NUM> by laser induced jetting. Laser induced jetting is a form of LAD in which a laser beam <NUM> is used to create a patterned surface by controlled material deposition. In particular, laser photons provide the driving force to catapult a small volume of material <NUM> from a donor film <NUM> toward an acceptor substrate such as PCB substrate <NUM>. Typically, the laser beam <NUM> interacts with an inner side of the donor film <NUM>, which is coated onto a non-absorbing carrier substrate <NUM>. The incident laser beam <NUM>, in other words, propagates through the transparent carrier substrate <NUM> before the photons are absorbed by the inner surface of the film <NUM>. Above a certain energy threshold, material <NUM> is ejected from the donor film <NUM> toward the surface of the PCB substrate <NUM> which is situated on a stage (not shown in this view) in a work area.

Once deposited on the PCB substrate <NUM>, including in vias <NUM>, the metal paste <NUM> is dried by hot air <NUM>, see <FIG>, or by heating using an infra-red (IR) lamp or similar arrangement and the resulting metal film <NUM> can be sintered using a laser beam <NUM> that is passed over the deposited metal paste to produce a highly conductive metal (e.g., copper) film as shown in <FIG>. The same laser that was used for the paste deposition may be used for the sintering and can be used also for ablating deposited material that was not placed correctly-an inline repair to increase robustness.

Because the printing of the conductive film is an intermediate step, it is desirable that the formation of this layer does not take a long period of time. Accordingly, the material from which the conductive film is formed should take only a short time to cure (whether by IR irradiation, hot air, or both) and should not shrink much (if at all) during the curing process. Materials that take an excessive time to cure will impede the overall speed of the process, and those that shrink (at least more than a little bit) during curing will impart mechanical stress on the PCB substrate, which may lead to failure.

The active or conductive material used for the conductive film may comprise one or more metals. Metals that are contemplated include pure metals, metal alloys, and refractory metals. Copper is a common choice for PCB metallization, and may be used in embodiments of the present invention. The active material may be applied (printed) using LAD either from a solid state, e.g., small metal particles that are deposited on a plastic film can be used in the LAD process to generate a conductive layer, or in the form of a paste carried on a donor film as described above. The conductive film should be applied in an amount sufficient to fully support the subsequent electronic connections. This may mean applying several layers of paste, one atop the other, with curing steps after each application of a layer. As shown in <FIG>, the laser jetting process is highly accurate and so can be used to print the metal paste <NUM> directly on edges <NUM> of the vias <NUM>, enabling a way to coat only the vias holes and not to fill them. This approach may be of some importance in the case of large and/or deep vias.

One embodiment of the metallization process is illustrated schematically in <FIG>. First, a hole or track is printed (i.e., in the case of a hole, it is filled, and in the case of a track or trace, it is deposited on the PCB substrate or other layer) by laser jetting of a metal (e.g., Cu) (or otherwise) <NUM>, then the solvent is dried <NUM>, and the metal is sintered <NUM>. At this stage, the board can be taken to an imaging unit to verify that the desired hole or track thickness (e.g., in the case of a hole, the fill level) was reached <NUM>. If so, the board is passed to the next stage; otherwise, it is returned for additional printing/deposition and the process repeats until the desired amount of metal has been printed (i.e., a desired thickness reached). As shown in <FIG>, in other embodiments an additional ablation step to remove excess deposited material may be added before (or after) the sintering step.

At any layer, after metallization, a dielectric layer may be added to the board to reduce capacitance and avoid short circuits. There are several ways to add the dielectric layer, for example, by coating a liquid material and curing it or by hot pressing of a prepreg. Examples of such processes will now be explained.

Referring to <FIG> and <FIG>, a dielectric layer <NUM>, which may be an epoxy and act as a passivation layer, may be deposited or coated over the metal (or other) layer and/or the PCB substrate with the aid of a roller or blade, see <FIG>, or by printing the dielectric layer from a donor film using the laser jetting system as shown in <FIG>. In the case of coating a liquid epoxy <NUM> using a roller <NUM> or blade, the epoxy may be a viscous liquid that includes a filler, such as silica balls. An amount of epoxy <NUM> is applied to one end of the board and the roller <NUM>, which may be made of or coated with an anti-sticking material such as polytetrafluoroethylene, ceramic, silicone, or other material, is placed at a desired height over the metal layer <NUM> and moved transversely over the board to spread the epoxy <NUM> into a layer <NUM> in a uniform manner at a desired thickness "h". In some cases, the roller <NUM> may be fixed in position, and the board moved underneath it to cause the epoxy to spread. Where a blade applicator is used instead of a roller, the blade angle with respect to the board will affect the vertical force applied on the epoxy. If the angle is too small, the epoxy may not be squeezed into small apertures between portions of the metal layer. At the same time, if the blade pressure is too small, it may prevent the epoxy from being cleanly applied to the board and if it is too high, it may result in epoxy leakage outside the desired coverage area. Accordingly, adjustment means for the blade angle should be provided and the blade angle adjusted according to the epoxy viscosity and other characteristics.

Alternatively, as shown in <FIG>, the epoxy <NUM> may be applied in a thin layer to a substrate or foil <NUM>, and then deposited in small amounts <NUM> (e.g., droplets) onto the metal layer <NUM> and/or PCB substrate <NUM> by laser jetting using the same laser that produced beam <NUM> that was also used for jetting the metal layer. The epoxy <NUM> may be applied to the substrate <NUM>, which is transparent or nearly so at the wavelengths of laser beam <NUM>, by a roller system in which the substrate is passed between a pair of rollers or a single roller and a fixed surface separated by a well-defined gap so as to ensure the resulting coating of epoxy <NUM> is of uniform thickness. For example, such a coating system may include a syringe of the epoxy and an air or mechanical pump that drives the epoxy onto the substrate <NUM>. The substrate <NUM> may then be moved towards the well-defined gap to create the uniform layer of epoxy <NUM> with a thickness that is defined by the gap. In some embodiments of the invention, the substrate <NUM> can translated bidirectionally in a controlled manner, while opening the gap between the coater rollers, creating the possibility for recoating the same area of the substrate <NUM> with the epoxy without contamination to the rollers and reducing or eliminating the amount of substrate <NUM> consumed during the coating process, thereby preventing waste.

Once coated, the substrate <NUM> with the layer of epoxy <NUM> thereon is positioned in the laser jetting system and dots <NUM> of the epoxy <NUM> are jetted onto the metal layer <NUM> and/or PCB substrate <NUM> using laser beam <NUM>. In one example, the laser beam <NUM> is focused onto the interface between the layer of epoxy <NUM> and the substrate <NUM> causing local heating followed by a phase change and high local pressure which drives jetting of the epoxy onto the metal layer and/or PCB substrate. After printing the epoxy to the metal layer and/or PCB substrate, the substrate <NUM> can be returned for a second (or additional) coating of epoxy <NUM> by reversing the direction of a transport mechanism or, where substrate <NUM> is a continuous film, be moving substrate <NUM> through the coating system in a loop-like process.

In still further embodiments, the substrate <NUM> may be a screen or grid in which the epoxy <NUM> is introduced into holes of the screen by a coater, which may be a roller or blade, and the incident laser beam <NUM> used to displace the epoxy from the holes in the screen onto the metal layer and/or PCB substrate.

Referring to <FIG>, after printing or coating the epoxy layer <NUM>, heat is applied to the layer by hot air, IR irradiation, and/or other heating method(s) and the epoxy layer is cured.

Yet another approach for passivation is to use a laminate to create a passivation layer. The use of laminate reduces height differences in a surface and creates a much more uniform height PCB surface. A laminate passivation layer can be formed in either of two different ways: printing the metal (e.g., Cu) onto the laminate and attaching the resulting structure to the surface (<FIG>) or attaching the laminate to the surface of the PCB and printing metal (e.g., Cu) into open vias (<FIG>).

In the first process, and referring to <FIG>, a laminate film <NUM> is attached to a liner <NUM> and a laser beam <NUM> is used to engrave/cut the laminate into a desired configuration, e.g., by creating through holes <NUM> and/or channels <NUM> in the laminate. The engraved areas are filled with metal (e.g., Cu) <NUM> using the laser beam <NUM> to deposit the metal from a film <NUM> coated on substrate <NUM>, and only then is the laminate <NUM> attached (e.g., by hot pressing) to the PCB substrate <NUM> (or a previously formed laminate layer) to create the layer of both metal and passivation. This approach can enhance the efficiency of the PCB build cycle significantly since the build of the layer and the attachment of the layer can be done as two independent stages, allowing serialization thereof.

Other advantages can be achieved from attachment of a laminate layer <NUM> (e.g., an epoxy laminate) to the PCB substrate <NUM> and subsequently engraving the laminate layer using a laser beam <NUM>, as shown in <FIG>. This approach is more stable to thermal effect at the hot pressing stage when the laminate is attached to the PCB substrate. After engraving, the vias and holes are filled with metal in the fashion described above (<FIG>) and hot air <NUM> is applied to the surface of the board to dry the metal (<FIG>). Additional laser sintering can be added to enhance the conductivity of the metal particles.

In the final part of the PCB production the board is coated by a layer of solder mask. By acting as a protectant for underlying layers, the solder mask layer enables the soldering of electronic components to the board using high temperature without damaging the board's inner layers. As shown in <FIG>, one method for printing a solder mask <NUM> is by laser jetting. Similar to the manner in which an epoxy layer was printed, the solder mask material <NUM> may be applied in a thin layer to a substrate or foil <NUM>, and then deposited in small amounts <NUM> (e.g., droplets) onto the metal layer <NUM> and/or PCB substrate <NUM> by laser jetting using a laser beam <NUM>. Laser beam <NUM> may be produced by the same laser that was also used for jetting the metal layer and/or the epoxy layer. The solder mask material <NUM> may be applied to the substrate <NUM>, which is transparent or nearly so at the wavelengths of laser beam <NUM>, by a roller system in which the substrate is passed between a pair of rollers or a single roller and a fixed surface separated by a well-defined gap so as to ensure the resulting coating of solder mask material <NUM> is of uniform thickness. For example, such a coating system may include a syringe of the solder mask material and an air or mechanical pump that drives the solder mask material onto the substrate <NUM>. The substrate <NUM> may then be moved towards the well-defined gap to create the uniform layer of solder mask material <NUM> with a thickness that is defined by the gap. In some embodiments of the invention, the substrate <NUM> can translated bidirectionally in a controlled manner, while opening the gap between the coater rollers, creating the possibility for recoating the same area of the substrate <NUM> with the solder mask material without contamination to the rollers and reducing or eliminating the amount of substrate <NUM> consumed during the coating process, thereby preventing waste.

Once coated, the substrate <NUM> with the layer of solder mask material <NUM> thereon is positioned in the laser jetting system and dots <NUM> of the solder mask material <NUM> are jetted onto the metal layer <NUM> and/or PCB substrate <NUM> using laser beam <NUM>. In one example, the laser beam <NUM> is focused onto the interface between the layer of solder mask material <NUM> and the substrate <NUM> causing local heating followed by a phase change and high local pressure which drives jetting of the solder mask material onto the metal layer and/or PCB substrate. After printing the solder mask <NUM> to the metal layer and/or PCB substrate, the substrate <NUM> can be returned for a second (or additional) coating of solder mask material <NUM> by reversing the direction of a transport mechanism or, where substrate <NUM> is a continuous film, be moving substrate <NUM> through the coating system in a loop-like process.

Once the solder mask <NUM> has been printed, see <FIG>, it is cured, as shown in <FIG>, using UV light <NUM> and/or heat to create a mask layer that is open only in the soldering areas <NUM>.

It is often useful to have a label on top of the PCB board to help a technician understand the purpose of each component and to point the technician to areas on the PCB board. To that end, an additional label layer <NUM> may be added on top of the solder mask layer <NUM>. The label layer <NUM> can be printed by inkjet, screen printing, or other printing methods, and in one embodiment it is printed by the same laser jetting system used for printing the solder mask layer.

As shown in <FIG>, the label material <NUM> may be applied in a thin layer to a substrate or foil <NUM>, and then deposited in small amounts <NUM> (e.g., droplets) onto the solder mask layer <NUM> by laser jetting using a laser beam <NUM>. Laser beam <NUM> may be produced by the same laser that was also used for jetting the metal layer, epoxy layer, and/or solder mask layer. The label material <NUM> may be applied to the substrate <NUM>, which is transparent or nearly so at the wavelengths of laser beam <NUM>, by a roller system in which the substrate is passed between a pair of rollers or a single roller and a fixed surface separated by a well-defined gap so as to ensure the resulting coating of label material <NUM> is of uniform thickness. For example, such a coating system may include a syringe of the label material and an air or mechanical pump that drives the label material onto the substrate <NUM>. The substrate <NUM> may then be moved towards the well-defined gap to create the uniform layer of label material <NUM> with a thickness that is defined by the gap. In some embodiments of the invention, the substrate <NUM> can translated bidirectionally in a controlled manner, while opening the gap between the coater rollers, creating the possibility for recoating the same area of the substrate <NUM> with the label material without contamination to the rollers and reducing or eliminating the amount of substrate <NUM> consumed during the coating process, thereby preventing waste.

Once coated, the substrate <NUM> with the layer of label material <NUM> thereon is positioned in the laser jetting system and dots <NUM> of the label material <NUM> are jetted onto the solder mask layer <NUM> using laser beam <NUM>. In one example, the laser beam <NUM> is focused onto the interface between the layer of label material <NUM> and the substrate <NUM> causing local heating followed by a phase change and high local pressure which drives jetting of the label material onto the solder mask layer <NUM>. After printing the label layer <NUM>, the substrate <NUM> can be returned for a second (or additional) coating of label material <NUM> by reversing the direction of a transport mechanism or, where substrate <NUM> is a continuous film, be moving substrate <NUM> through the coating system in a loop-like process.

Once the label layer <NUM> has been printed, it is cured, as shown in <FIG>, using UV light <NUM> and/or heat. The curing station may be the same one used for curing the solder mask layer.

One of the advantages of a PCB production system configured as described is its ability to reduce the costs and production times associated with multi-layer PCB boards. Current productions processes for boards that use more than one metal layer are complex. The present invention offers methods which incorporate a wide range of applications that allow for straightforward and fast productions of boards with more than one metal layer. For example, while conventional PCB production processes do not accommodate the fabrications of a simple bridge between metal lines, such a bridge is something that can be very easily done with methods in accordance with the invention.

<FIG> illustrates an example of a PCB <NUM> that includes crossed metal (e.g., Cu) lines <NUM>, <NUM>, <NUM>. Using conventional PCB production processes, fashioning PCB <NUM>, if even possible, would entail several productions stages, consuming significant production time. It may even require the use of a double-sided PCB. In a PCB production system employing the methods of the present invention, however, production complexity and time are significantly reduced. For example, using one or more of the above-described techniques, epoxy patches <NUM>, <NUM> may be printed using laser jetting, allowing the printing of metal lines <NUM>, <NUM>, <NUM> on a single side of PCB <NUM> and, optionally, using the same laser jetting apparatus as is used to print the epoxy patches. <FIG> provides a close-up three-dimensional view of one of the wire crossings on PCB <NUM> illustrated in <FIG>. After printing metal line <NUM>, the epoxy patch <NUM> can be printed so that subsequent metal line <NUM> passes over line <NUM> on the same side of PCB <NUM>, without creating a short circuit. This simple example illustrates how complex double-sided boards of the past can be fashioned in a relatively straightforward manner using the laser jetting techniques for different materials as discussed above. Of course, the present systems and methods may also be used to fashion double-sided PCBs, with or without bridging structures such as epoxy patch <NUM>, thereby facilitating the production of single and double-sided boards, with bridged and non-bridged areas.

Turning now to <FIG> and <FIG>, examples of a PCB processing systems 1000a and 1000b are illustrated. <FIG> illustrates system 100a, composed of individual sub-units, while <FIG> illustrates system 1000b, in which the sub-systems are arranged into various modules. In these example, PCB processing systems 1000a and 1000b include an imaging sub-system <NUM> and a laser sub-system <NUM>, which together may be organized into a printing unit <NUM>, which may include. A UV light sub-system <NUM> may be included in a UV curing unit <NUM>, although this is an optional component. A heating sub-system <NUM> may be a component of a heating unit <NUM>. Further, a drilling unit <NUM>, which includes the CNC drilling head <NUM> described above and a three-dimensional translation sub-system <NUM> for maneuvering the drilling head may be provided as a module, or the components provided separately. Optionally included in the drilling unit <NUM> or elsewhere may be a PCB flipping sub-system <NUM> which is configured to flip the PCB during processing so as to allow for drilling, printing, etc. on both sides of the PCB. Where laminates are used, an optional hot press sub-system <NUM> is available. Associated provided with the printing unit <NUM> are various materials <NUM> for the LAD procedures discussed above. These include the metal used for conductive traces (e.g., Cu), solder mask material, epoxy(ies), etc. as well as the donor substrate(s) on which these materials are coated for deposition onto the PCB. Although not shown in the diagrams, while the printing unit <NUM> can include only a laser sub-system that is for all the laser deposition processes, it may also include an inkjet head or screen printer for printing labels or solder mask materials.

Although not discussed in detail above, imaging sub-system <NUM> may be employed in connection with any or all of the above-described etching and deposition procedures. For example, the imaging sub-system may include one or more two-dimensional and/or three-dimensional imaging units (e.g., cameras, scanning laser arrangements, etc.) that image the PCB or portions thereof at various stages during the production process. Vias and holes or features may be imaged so as to ensure they are free from debris and regular in shape. Deposited layers may be imaged so as to ensure they are uniform in coverage and/or accurately positioned. This may be especially important where layers are printed through successive jetting of small droplets of material. The imaging may also be used to ensure accurate registration of the PCB substrate <NUM> on a holder <NUM>. Imaging in this fashion can allow for in-line repair of a process step, such as additional or re-coating of a layer, or rejection of an in-process PCB when necessary. Stage <NUM> which can translate in two dimensions and, where necessary, raise and lowed PCB <NUM>, facilitates movement of the PCB between the various units of system <NUM> and the sub-systems within those units during processing.

As mentioned, the UV light sub-system <NUM>, whether modularized or not, is optional. As all of the deposited layers can be heat-cured, the use of UV curing is not mandatory, hence, the need for the UV light sub-system is only in cases where UV curing is preferred. When modularized, the UV light sub-system <NUM> can be included in the overall system or removed therefrom as desired.

The heating sub-system <NUM> is used for curing heat sensitive materials and/or for drying solvent base materials. It can be a part of an overall system 1000a, but it preferably is modularized <NUM> so that it can be easily replaced, if necessary, in a system 1000b.

The drilling unit <NUM> is used to create holes and vias in the laminates as discussed above. As previously noted, the drilling unit <NUM> can be a CNC head <NUM>, or a laser based cutting and engraving unit or a combination of both. While the CNC head and/or laser cutting tool can be incorporated in a larger system such as 100a, it is preferable that a modular drilling unit <NUM> be used so as to compartmentalize the debris generated during the drilling process. After drilling a cleaning procedure is applied to the PCB board either by adding a protective film prior to drilling, by cleaning the surface with air pressure and suction, or by another cleaning process.

In cases where a solid laminate is used as a base for the PCB, the additional hot press sub-system <NUM> is used for attachment of the laminate to the PCB substrate <NUM>.

<FIG> illustrate aspects of a production cycle of a single-sided, multilayer PCB, and <FIG> illustrate aspects of a production cycle of a double-sided, multilayer PCB, each from substrate to a final board in accordance with embodiments of the present invention. Beginning with the single-sided, multilayer PCB <NUM> illustrated in <FIG>, the PCB substrate <NUM> may be an FR4 board or a flexible board. A first copper (or other) cladding layer <NUM> is formed on top of PCB substrate <NUM>, and is covered by an epoxy layer <NUM>. One or more through holes <NUM> may be proved in the epoxy layer 1106a to electrically connect copper cladding layer <NUM> to a second copper (or other metal) structured layer <NUM> disposed on the upper side of epoxy layer 1106a. The through holes may be formed by a drilling process and copper or other metal connectors deposited therein as described above. The upper copper structured layer <NUM> is also covered by an epoxy layer 1106b. This structure may be repeated for as many copper (or other metal) layers as are needed, with through holes <NUM> having copper or other metal connectors provided as required. Ultimately, the top-most copper layer is covered by a solder mask layer <NUM> and gold, silver, or other metal connectors <NUM> may be added to allow electrical connections to the various copper lines <NUM>, <NUM> via the metalized through holes <NUM>, <NUM>. Gold, silver, or other metal connectors <NUM> enable the soldering of electrical components to the PCB board. Examples of processes for forming the single-sided, multilayer PCB <NUM> and components thereof will be discussed with reference to <FIG>.

As shown in <FIG>, fabrication of the single-sided, multilayer PCB begins with obtaining a PCB substrate (FR4 or other) <NUM> having a copper (or other metal) cladding layer <NUM> disposed on one side thereof. It is possible to purchase PCB substrates with a copper cladding layer and, in one embodiment of the invention, these may be used as a starting material and the copper cladding layer etched by laser to remove excess material, leaving the desired Cu line forms on the PCB substrate. Alternatively, as shown in the illustration, a bare substrate (FR4 or other) <NUM> may be provided to a laser jetting station such as one described above, and copper (or other metal) lines created on one side thereof through laser jetting of a copper layer <NUM> coated on a donor substrate <NUM> using a laser beam <NUM>. Once any solvent has dried, the copper layer <NUM> jetted onto the surface of the PCB substrate <NUM> is sintered and excess copper removed through ablation. The sintering and ablation processes may be performed using the same laser <NUM>, albeit at different energy than is used for the jetting process. Alternatively, a different laser may be used for sintering and ablation.

After the first copper layer has been formed, a second layer is added to form connectors to additional layers. <FIG> illustrates one example for printing copper connectors <NUM> on top of a first copper layer <NUM> on a PCB substrate <NUM>. In this example, printing is by laser jetting of copper droplets from a copper film or coating <NUM> carried on a donor substrate <NUM>, in the fashion described above. A sufficient number of droplets are jetted for each connector <NUM> using a laser <NUM>. Thereafter, the connectors <NUM> are sintered and, if necessary, ablated to form precise shapes having desired dimensions. As before, the sintering and ablation may make use of the same laser <NUM> used for printing the connectors, at different energies, if needed. Following sintering and ablation of the copper connectors, an epoxy layer <NUM> is added by laser jetting of an epoxy coating <NUM> carried on a donor substrate <NUM>. The same laser <NUM> may be used to print the epoxy layer <NUM> and subsequently, the epoxy layer <NUM> is heated <NUM> in order to cure the layer.

In an alternative process, illustrated in <FIG>, the epoxy layer <NUM> is printed by laser jetting onto the first copper layer <NUM>, cured, and then holes/vias <NUM> are ablated in the epoxy layer in locations at which connectors will ultimately be formed. Thereafter, the copper connectors <NUM> are printed by laser jetting in the holes/vias <NUM> that were created in the epoxy layer. The structure is completed with additional drying and sintering. The processes presented in <FIG> and/or 11d may be repeated multiple times to create a multilayered structure <NUM>, illustrated in <FIG>.

Once a desired number of metal (e.g., copper) and epoxy layers have been formed, electrical connectors and a solder mask layer may be printed. <FIG> illustrates one example of such procedures. First, gold connectors <NUM> are printed by laser jetting on top of the copper connectors <NUM> to create a conductive connection. The laser jetting process uses a laser beam <NUM> to jet gold droplets from a gold film or paste <NUM> coated on a donor film or substrate <NUM> as described above. Then, the gold connectors <NUM> are dried and sintered, and ablated if needed, and a solder mask layer <NUM> is jet printed on the surface epoxy layer and cured either heat and/or UV light <NUM>. The laser used for the sintering, ablation (if needed), and printing of the solder mask layer may be the same as is used for printing the gold connectors and/or used for printing the copper connectors, with energies adjusted accordingly.

As shown in <FIG>, the same result may be achieved by first jet printing the solder mask layer <NUM>, curing it by heating or UV irradiation <NUM>, and then ablating the solder mask layer <NUM> to create holes <NUM> for placing the gold connectors <NUM>. The gold connectors <NUM> are printed and sintered as described above.

The process for forming a double-sided, multilayer PCB is similar to that as described above for creating a single-sided, multilayer PCB, except that some accommodations are needed due to the need for drilling from both sides. Referring to <FIG>, a double-sided, multilayer PCB <NUM> includes a PCB substrate <NUM> on each side of which are one or more metal (e.g., copper) layers (traces) <NUM>, each separated by a layer of epoxy <NUM>. On each side, the final epoxy payers are covered by a solder mask layer <NUM> and gold (or other metal) connectors <NUM> are added at positions at which electrical components will be connected. The gold connectors <NUM> are electrically connected to lower copper layers by copper- (or other metal-) filled vias and holes <NUM> in the epoxy layers.

There are different available alternatives for providing the holes on each side of the PCB substrate <NUM>. Referring to <FIG>, in one embodiment, one or more through holes <NUM> may be drilled in PCB substrate <NUM>, with the drilling tool passing through the entire thickness of the PCB substrate. In such a case, it is preferable to subsequently provide a peelable substrate <NUM> beneath the PCB substrate <NUM> after the drilling is complete in order to accommodate the jet printing of the copper (or other metal) filler into the hole, without contaminating the sample holder. Also, a sample holder <NUM> that secures the PCB substrate from its edges should be used. Using a laser <NUM>, copper (or other metal) is jet printed from a film or paste <NUM> on a donor substrate <NUM> in the fashion described above so as to fill the hole <NUM>. Subsequently, the copper fill <NUM> is sintered (e.g., using the same laser <NUM>) in place in the hole. Thereafter, the peelable substrate <NUM> and sample holder <NUM> may be removed.

Referring to <FIG> and <FIG>, another option is to drill a hole <NUM> in one side of the PCB substrate <NUM>, taking care that the hole <NUM> does not pass all the way through the entire thickness of the PCB substrate. As before, the hole <NUM> is filled with copper <NUM> from a Cu film <NUM> carried on a donor substrate <NUM> by jet printing, and the Cu fill is subsequently dried, sintered, and ablated (if necessary). Thereafter, referring to <FIG>, the PCB substrate <NUM> is flipped, and the laser <NUM> is used to complete the through hole by removing the remaining portion <NUM> of the PCB substrate opposite the Cu fill <NUM>. This leave a small hole <NUM> to be filled with copper by jet printing, as above, and the printed copper <NUM> is again dried and sintered as discussed above.

It is also possible to add a pick and place machine to the system so as to provide for full assembly of the PCB with electronic components. <FIG> illustrate several examples of the inclusion of embedded and other electronic components facilitated through the use of such a machine. In these examples, a single-sided, multi-layer PCB is discussed. This is primarily for ease of illustration; however, it should be appreciated that the discussion applies equally to double-sided, multilayer PCBs. In the case of double-sided PCBs, the board may be flipped when working on a reverse side, or pick and place apparatus may be provided on both sides of a PCB supported at its edges so as to allow component situation and mounting on both sides simultaneously or nearly so.

<FIG> illustrates a PCB assembly <NUM>, which includes a PCB substrate <NUM> made of, for example, FR4 or a flexible board, on which is disposed a plurality of metal (e.g., copper) layers <NUM> separated by epoxy layers <NUM>. The top-most epoxy layer is covered by a solder mask layer <NUM> in which are located a plurality of gold (or other metal) connectors <NUM>, which are electrically coupled to metal (e.g., copper) connectors <NUM>. PCB assembly <NUM> may be fabricated using the above-described PCB production systems and methods.

Also included in PCB assembly <NUM> are a plurality of electronic components 1316a-1316c. Components 1316a-1316c may be integrated circuits (ICs) or other electronic components and are assembled into PCB assembly <NUM> using a pick and place machine or similar system. In particular, components 1316a-1316c are situated so that leads associated therewith make electrical connections to connectors <NUM>, <NUM>, e.g., at solder pads <NUM> or elsewhere. Solder pads <NUM> may be deposited by LAD in a manner similar to the deposition of copper traces, solder masks, and/or connectors, as described above.

As shown, electronic components 1316a-1316c may be added to the PCB assembly at the top or sides of the structure and/or embedded within it. When added from the or sides, the electronic components may be electrically connected to the metal layers by connectors, as discussed above, or directly, as is the case with electronic component 1316c in the illustration. It is also possible to encapsulate an electronic component 1316b within the PCB assembly <NUM>. <FIG> further illustrate aspects of these various procedures for electrically connecting the electronic components.

In <FIG>, a PCB substrate <NUM> has been printed with a metal (e.g., copper) layer <NUM> and one or more epoxy layers <NUM> in the manner discussed above. Metal (e.g., copper) connectors <NUM> have been printed in through holes in the epoxy layer(s) according to the processes described above. The connectors <NUM> have been positioned to accommodate the placement of an electronic component. In one embodiment, the structure shown in <FIG> may be fashioned by selectively depositing epoxy by jetting so as to leave an open area <NUM> for placement of the electronic component. Alternatively, the open area <NUM> may be created through laser engraving (e.g., etching or ablation) of a layer of epoxy.

<FIG> shows a next step in paring the structure to receive an electronic component. A solder mask layer <NUM> has been deposited by LAD in the open area <NUM> on top of the epoxy layer, and gold connectors <NUM> have been fashioned therein so as to provide electrical coupling to the copper connectors <NUM> below. Then, as shown in <FIG>, solder paste <NUM> is jet printed onto the gold connectors <NUM>. The solder paste is printed by laser jetting using a laser <NUM> and a donor substrate <NUM> with solder <NUM> coated thereon in the manner discussed above. An electronic component 1316d is then placed in the open area <NUM> with its leads electrically connected to the solder paste areas <NUM>, for example using a conventional pick and place machine, as shown in <FIG>. Placement of the electronic component in this fashion may be observed using one or more imaging stations so as to ensure correct alignment of the leads with the solder paste locations.

Through the printing of additional epoxy layers <NUM>', copper connectors <NUM>', gold connectors <NUM>', solder paste areas <NUM>', and (optionally) solder mask areas), additional electrical components 1316e may be added to the PCB assembly, as shown in <FIG>. As shown, electrical connections may be made to multiple sides of an electronic component 1316d, and in some cases additional metal (e.g., CU) layers, labels, etc. may be added as described above. During fabrication of this PCB assembly, support structures <NUM> made of resin or other material may be added to provide temporary or permanent support for layers overlying open areas <NUM>. The support structures may be added by LAD in the manner discussed above for the printing of other layers.

The assembly of a PCB structure is not limited to the placement of electronic components. Other structural components may be included in such a structure. <FIG> illustrates an example in which a heat dissipation element <NUM> has been added by adhering the heat dissipation element (e.g., a metal plate or other thermal conductor) to electronic component 1316d by a layer of thermal conductive glue <NUM>. The thermal conductive glue may be printed by LAD in a fashion similar to that described above for the printing of metal layer or connectors, or solder masks or epoxies. The heat dissipation element may be placed by a pick and place machine or, in some cases, may be a printed structure formed by LAD.

Nor is the assembly of a PCB structure is not limited to placement of electronic components in layer arrangement with other elements of the PCB structure. <FIG> illustrates placement of an electronic component 1316f such that its electrical leads are orthogonal to the plane of the PCB substrate <NUM> and its overlying metal, epoxy, and other layers, and which are electrically connected via metal (e.g., Cu) connectors <NUM>, gold connectors <NUM>, and solder paste areas <NUM> that are printed so as to accommodate this orientation. As shown, a temporary or permanent support structure <NUM> may be printed so as to be used as a support for the electronic component when placed in this fashion. The printing of the various epoxy layers <NUM>, connectors <NUM>, <NUM>, and solder paste <NUM> may be done in the manners discussed above using LAD. It may be necessary to maintain a portion of an epoxy layer in place while printing the solder paste, for example, so as not to contaminate structures and/or assemblies below. Although not shown, a solder mask layer may be printed, if needed.

And still another example of a PCB assembly accommodating embedded electronic components is illustrated in <FIG>. In this case, a coil <NUM> is embedded in an epoxy layer <NUM>. The coil may be an existing component that is placed by a pick and place machine and electrically connected to another electronic component 1316d via metal (e.g., Cu) connectors <NUM>", gold connectors <NUM>", and solder joints <NUM>", which themselves are printed in the fashions discussed above, or the coil <NUM> itself may be printed by LAD, for example as described in the present assignee's <CIT>. For example, the coil may be printed by jetting metal from a coating or foil on a donor substrate, similar to the method discussed above for printing metal layers, with the jetted material printed in successive layers so as to partially overlap a most-recently printed element and thereby define a helical pattern of coil elements that collectively make up the coil <NUM>. The coil elements may be printed within the supporting epoxy <NUM> and/or about an inner core (not shown), which act (singularly or collectively) as scaffolds to keep the coil under construction intact as the coil elements fuse with one another. Alternatively, the coil <NUM> may be printed by LAD as a plurality of partially complete rounds, each in a respective layer, with pillars interconnecting successive ones of the partially complete rounds in different ones of the respective layers. The pillars may be vertical, or near-vertical and positions of the pillars between successive ones of the plurality of partially complete rounds may be staggered across the circumference of the partially complete rounds. Following printing of one of the plurality of partially complete rounds in a respective layer, for a number of successive layers of metal corresponding to a desired pillar height, only a connecting pillar is printed. Epoxy scaffolding elements may be printed as part of each respective layer of material concurrently with printing the plurality of partially complete rounds. Embedding coils in this fashion may provide for embedded radio frequency identification (RFID) tags within the PCB assembly.

<FIG> illustrate aspects of a production cycle of a PCB in which laser assisted deposition or another laser-based printing process is used for some aspects of PCB fabrication. In <FIG>, metal layers (e.g., Cu) <NUM>, <NUM> are printed on both sides of a PCB substrate <NUM> using LAD or another laser-based printing process, as described above. In <FIG>, the double-sided PCB from <FIG> is stacked with a similarly fabricated double-sided PCB consisting of metal layers (e.g., Cu) <NUM>, <NUM> printed on both sides of a PCB substrate <NUM> with a prepeg layer <NUM> between them. The prepeg layer <NUM> may be a conventional resin-based prepeg (and may be made of the same material as the PCB core substrate), and the stacking process may be performed by conventional means used in the PCB fabrication industry. The result is an assembly <NUM>.

As shown in <FIG>, the stacking process may be repeated with additional double-sided PCBs <NUM>, <NUM>, etc., each time including a prepeg layer <NUM> between the new double sided PCB and the previous assembly. When the assembly includes two or more double-sided PCBs with interdigitated prepegs, as shown in the illustration, it is subjected to a lamination process using a conventional hot pressing process and a photosensitive dry resist. The result is a multi-board stack <NUM>. Then, as shown in Figure 4d, solder mask layers <NUM> may be printed on each side of the multi-board stack using LAD or another laser-based printing process, as described above. Although not shown in detail, gold, silver, or other pads, and solder as well as labels may also be printed on each side of the multi-board stack using LAD or another laser-based printing process, as described above. Drilling of the PCBs and/or copper plating following drilling may be performed using conventional processes for such activities.

Claim 1:
A method of fabricating a printed circuit board, PCB, assembly (<NUM>), comprising:
depositing a metal layer (<NUM>) on a PCB substrate (<NUM>, <NUM>, <NUM>) by laser-assisted deposition, LAD, in which jetting of metal droplets (<NUM>) from a first donor substrate (<NUM>) onto the PCB substrate (<NUM>, <NUM>, <NUM>) and into one or more holes (<NUM>) therein is effected using a laser (<NUM>, <NUM>, <NUM>) to form the metal layer (<NUM>) on the PCB substrate (<NUM>, <NUM>, <NUM>), the metal layer (<NUM>) being subsequently dried and sintered;
imaging, with an imaging unit (<NUM>), the metal layer (<NUM>) so as to determine whether a desired thickness of the metal layer (<NUM>) has been reached;
repeating the jetting, drying, sintering, and imaging until the metal layer (<NUM>) reaches the desired thickness; and
thereafter forming at least one passivation layer (<NUM>, <NUM>, <NUM>) over the metal layer (<NUM>).