Abstract:
A method of making a printed circuit board includes providing a substrate; providing a circuit design; determining non-conducting intersections between each of a plurality of conductive traces; forming a first set of conductive traces on the substrate; applying insulation material on the first set of traces at each of the non-conducting intersections; and forming a second set of conductive traces over the first set of traces and insulating material.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to methods and apparatus for printing electronic circuitry by deposition of conductive ink on a substrate. 
       BACKGROUND OF THE INVENTION 
       [0002]    Most electronic devices comprise a printed circuit board (PCB) bare-board and the electronic components assembled on it. The term “PCB bare-board” refers to the substrates materials, the conductive traces and the coated or uncoated vias. 
         [0003]    To prevent unwanted electrical contact between conductors on the board, they are placed on different electrically-insulating layers. Electrical contact between conductors on different layers is achieved with vias drilled through the layers by mechanical means or plasma-processes. These vias are then coated with copper or other electrically conductive materials. 
         [0004]    Each insulating layer is a laminate panel, an epoxy resin, and glass-fiber core with copper foil pre-bonded onto each side. The copper foil is covered with a resist layer, a pattern is imaged on the layer and the resist is further developed. At this stage the resist protects certain copper areas. The panel undergoes several chemical processes, such as etching of unprotected copper areas and stripping of the remaining resist. 
         [0005]    The technology currently in use in the industry is complicated and expensive, requires: 
         [0006]    1. Expensive metallic copper; 
         [0007]    2. use of hazardous chemicals which must be disposed of in an environmentally safe manner; 
         [0008]    3. extensive equipment which must be operated in a clean room environment; and 
         [0009]    4. materials must be manufactured to precise dimensions to ensure registration between layers. 
         [0010]    After the layer is prepared, panels are superimposed and laminated. Usually internal-panels are thin and flexible while outer-panels are thicker and less flexible. Electronic components are attached to the outer panels. 
         [0011]    U.S. Pat. No. 7,903,428 (Liu et al.) discloses an intra-connection layout with an alterable area disposed between the devices of an array. The alterable area includes an insulation layer, a first group of conductive wires and a second group of conductive wires. The first conductive wires are disposed within the alterable area along a first direction for selectively connecting electrical paths in a first direction between different devices. The second conductive wires are disposed within the alterable area along a second direction for selectively connecting electrical paths in the second direction between different devices. The insulation layer is disposed within the alterable area and between the first conductive wires and second conductive wires. The insulation layer has an opening to allow one of the conductive wires in the first group and one of the conductive wires in the second group to be connected to each other. 
         [0012]    U.S. Pat. No. 7,903,428 discloses openings  217  and  218  in the insulation layer which are placed according to the design of the circuit. The second conductive wires are disposed over the insulation layer on previously exposed openings in accordance with a circuit design. In addition, the openings  217 ,  218  are formed by cutting off parts of the previously disposed insulation layer. 
         [0013]    There is a long felt need in the industry to reduce the use of expensive copper, reduce the use of hazardous chemicals and eliminate the need for operating in a clean room. 
       SUMMARY OF THE INVENTION 
       [0014]    Briefly, according to one aspect of the present invention a method of making a printed circuit board includes providing a substrate; providing a circuit design; determining non-conducting intersections between each of a plurality of conductive traces; forming a first set of conductive traces on the substrate; applying insulation material on the first set of traces at each of the non-conducting intersections; and forming a second set of conductive traces over the first set of traces and insulating material. 
         [0015]    The conductive wires are printed with plurality of pads and the insulation areas are printed on the non-conducting intersections before the second conductive wires are printed. 
         [0016]    These and other objects, features, and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1 a    shows a schematic exploded view of printed conductive traces with the layers separated (prior art); 
           [0018]      FIG. 1 b    shows a schematic of the assembled PCB with the substrate transparent for clarity (prior art); 
           [0019]      FIG. 2  shows a schematic representation of printed conductive traces and insulation areas; 
           [0020]      FIG. 3  shows a schematic representation of printed conductive traces and insulation paths following the conductive traces; 
           [0021]      FIG. 4 a    shows a schematic representation of printed conductive traces and insulation areas implemented in printing of fixed number of layers; 
           [0022]      FIG. 4 b    shows conductive traces broken into segments in the crossover between two conductive traces; 
           [0023]      FIG. 4 c    shows insulation patches printed over broken segments of conductive traces at crossover between pairs of conductive traces; 
           [0024]      FIG. 4 d    shows conductive traces printed over insulation patches to connect segments of conductive traces; and 
           [0025]      FIG. 5  shows a roll to roll printing system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the disclosure. However, it will be understood by those skilled in the art that the teachings of the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the teachings of the present disclosure. 
         [0027]    While the present invention is described in connection with one of the embodiments, it will be understood that it is not intended to limit the invention to this embodiment. On the contrary, it is intended to cover alternatives, modifications, and equivalents as covered by the appended claims. 
         [0028]    The present invention suggests using roll-to-roll printing devices  500  as is shown in  FIG. 5 , to print circuit board (PCB) bare-boards. This is accomplished using concepts from the printing industry rather than from the traditional PCB industry. PCB bare-board elements are formed by printing a succession of single layers using a combination of printing ink comprised of conducting and dielectric materials. 
         [0029]      FIG. 1 a    and  FIG. 1 b    show a schematic layer configuration with conductor traces  107 ,  111 , and  115  printed using traditional PCB manufacturing means. Conducting layers  108 ,  112 , and  116  are isolated from each other by insulating substrates  101 . The connection between selected layers is achieved by using vias  104 . Vias are vertical holes drilled into the PCB boards, which are filled with conductive material to connect conducting lines from layers  108 ,  112 , and  116  to components, not shown, on the PCB boards. 
         [0030]    In the present invention, traditional PCB conductors  108 ,  112  and  116  are replaced by conductive traces  208 ,  216 , and  224  made of conductive ink, as shown in  FIG. 2  and  FIG. 3 , on a single substrate  201 . The traditional PCB insulation substrate layers are replaced by printed insulation areas  212 ,  220 ,  304 , and  308  made of printed, insulating dielectric ink. The traditional PCB vias are replaced by conducting connection dots  204  made of conductive printed material. The present invention thus eliminates using three separate substrates, which must be individually printed, aligned, and assembled; and therefore reduces cost and assembly time. Three different insulation methods, embodiments, are described in more detail below. 
         [0031]    In  FIG. 2  insulator areas  212  and  220  are formed in the intersection between conductive traces  208 ,  216  and between  216 ,  224  respectively. Forming insulation areas such as  212  and  220  rather than full length insulating traces as is shown in  FIG. 3 , which will be explained in more detail below, carries advantages due to the relatively small quantity of insulating ink needed. The disadvantage is that it requires thorough analysis and calculation to find the cross over locations between each pair of conductors crossing each other. 
         [0032]    The “layers” are printed as follows. It should be noted that the order in which the layers are printed may be varied.
       ‘Layer D’: Conductive dots  204 . Intersections created between two or more conductors will not require printing of conductive dots  204  to connect between those conductors.   ‘Layer 1 conductive’: conductive trace  208 .   ‘Layer 2 insulation’: insulation layer  212 .   ‘Layer 2 conductive’: conductive trace  216 .   ‘Layer 3 insulation’: insulation layer  220 .   ‘Layer 3 conductive’: conductive trace  224 .
 
In an embodiment wherein the substrate is made of dielectric material, the first layer printed on the substrate will be a conductive layer. Alternatively, if certain areas of the substrate are made of conductive material then the first layer printed on the substrate is a dielectric layer.
       
 
         [0039]      FIG. 3  shows printing insulators  304  and  308  following the same path as the conductive traces  216  and  224 . The only difference between the insulators and the conductive trace is that the insulators are shorter and wider than the conductive traces. In addition, the advantage of following the conductive traces for forming insulation paths does not require complicated geometrical calculation between the layers. The path of the insulation can be calculated directly from the path of the conductive, but requires larger quantities of insulation inks compared to the method demonstrated in  FIG. 2 . 
         [0040]    The geometry of the conductive traces as well the insulation paths or insulation areas, are processed and are separated into distinctive layers. Each layer will include relevant geometry representing only the conductive traces and insulation paths that belong to it. For better understanding of the process refer to  FIG. 3 . The layers that are printed in one embodiment is as follows:
       ‘Layer D’: Conductive dots  204 . Intersections created between two or more conductors will not require printing of conductive dots  204  to connect between those conductors.   ‘Layer 1 conductive’: conductive trace  208 .   ‘Layer 2 insulation’: insulation layer  304 .   ‘Layer 2 conductive’: conductive trace  216 .   ‘Layer 3 insulation’: insulation layer  308 .   ‘Layer 3 conductive’: conductive trace  224 .       
 
         [0047]      FIG. 4 a    shows the final results of printing in three steps only. In the first step, all conductive traces  404  of a PCB are printed. Only regions where there is a crossover between two conductive traces with no contact  416  are not printed, as is shown in  FIG. 4 b   . In which case, conductors  404  will be broken into parts or segments. In the second step, the dielectric material  408  is printed over crossover regions  416  as is shown in  FIG. 4 c   . In the third step, the broken conductors are restored by printing a new conductive layer  412  over insulating area  408 , as is shown in  FIG. 4   d.    
         [0048]    This embodiment requires also geometrical calculation between the layers. The advantage of this embodiment is that it requires a fixed number of printing layers, in this case just three layers. In this case there is no one-to-one mapping of the layers as in standard PCB printing. 
         [0049]    For better understanding the process, reference is made to  FIGS. 4 a   - 4   d.  The layers will be as follows:
       ‘Layer 1 conductive’: conductive traces  404 . All  404  traces are printed, those that are printed with crossover regions broken into few segments, as well as complete traces printed in a single segment.   ‘Layer 2 insulation’: print insulation patches  408  for insulating areas of broken conductors  416 .   ‘Layer 3 conductive’: conductive traces  412  are printed over insulation patches  408  to connect broken segments  416 .
 
Using the embodiment shown, a fixed number of layers almost every multi-layer PCB can be printed with three layers, two for conductive traces and one for insulation. In cases where shielded signals are required, i.e. surrounded by GND (ground) signals, the number of layers may rise. Additional advantage of printing conductors and insulators is that the paths of the conductors can be shorter.
       
 
         [0053]      FIG. 5  illustrates a commercial method of implementing the invention. For each layer, a printing plate  508  will be created. The printing plates  508  are installed on separate rotating drums in a roll-to-roll printing system  500 . 
         [0054]    Each plate will be coated with relevant ink material during operation of the system  500 . Plates representing layers, ‘1 conductive’, ‘2 conductive’ and ‘3 conductive’ will be immersed with conductive ink material, while plates representing layers ‘2 insulation’ and ‘3 insulation’ will be coated with insulation material ink. The final printed circuit will be accumulated on roll  504 . In certain cases where inks require longer time to dry, special drying stations (not shown) may be deployed between printing of consecutive printing layers. 
         [0055]    Utilizing printing technology in the PCB industry enables printing multiple crossings of conductors or insulators on a single substrate and replaces the plurality of substrates used in the present PCB industry. Printing allows also deposition of the following electronic components  230 .
       resistors,   capacitors,   inductors,   light-emitting elements,   thermo-chromic elements,   labels   protective and shield layers and more.
 
Eventually transistors and batteries could be added to the list.
       
 
         [0063]    A list of materials for the various parts of the invention is shown below. The material is illustrative, but is not intended to limit the invention. Polyester PET SH31, ITO (Indium Tin Oxide) may be used for the substrate. FTO Sigma-Aldrich, Polymer Heraeus, carbon nanotubes and grapheme may be used for the transparent conductive film coated on the substrate. Silver screen printing ink C2131014D3 Gwent Group, 125-28 flexographic ink Creative 
         [0064]    Materials, 9145 and 5000 Silver conductors, manufactured by Dupont, may be used for the conductive material. D2070209P6 and D2090130P5 Gwent group, Dupont may be used for the insulating material. 
         [0065]    While the invention has been described with respect to a limited number of embodiments, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of some of the preferred embodiments. For example, the order of steps for printing conductive traces and insulating areas may be varied. Other possible variations, modifications, and applications are also within the scope of the invention. Accordingly, the scope of the invention should not be limited by what has thus far been described, but by the appended claims and their legal equivalents. 
       PARTS LIST 
       [0000]    
       
           101  insulating substrates 
           104  conductive vias that pass through the layers 
           107  conductive traces of layer 2 
           108  conductive layer 2 
           111  conductive traces of layer 1 
           112  conductive layer 1 
           115  conductive traces of layer 3 
           116  conductive layer 3 
           201  insulating substrates 
           204  conductive connection dots 
           208  conductive traces of layer 1 
           212  insulation area 
           216  conductive traces of layer 2 
           220  insulation area 
           224  conductive traces of layer 3 
           230  electronic component 
           304  insulation trace between layer 1 and layer 2 
           308  insulation trace between layer 2 and layer 3 
           404  entire and broken conductive traces 
           408  insulation that covers the areas where conductors are broken 
           412  conductors that restore the broken conductors 
           416  crossover between two conductive traces with no contact 
           500  roll-to-roll printing system 
           504  printed electronics roll 
           508  printing plates representing separate printed electronics layers