WO1998020715A1

WO1998020715A1 - Interconnected multi-layer circuit boards

Info

Publication number: WO1998020715A1
Application number: PCT/US1997/018992
Authority: WO
Inventors: Carmine G. Meola; Deanna M. Suilmann
Original assignee: W.L. Gore & Associates, Inc.
Priority date: 1996-11-08
Filing date: 1997-10-22
Publication date: 1998-05-14
Also published as: AU4911397A

Abstract

A printed circuit board assembly and process for assembling such a board involving interconnecting multi-layer printed circuit or printed wiring boards by simultaneously making eletrical interconnects and filling interstitial void spaces. A plurality of printed circuits boards (102, 104) to be interconnected are provided. Each board has conductive pads (106, 108) which are to be interconnected. The boards (102, 104) are aligned so that the conductive pads (106, 108) to be interconnected are opposite each other. A z-axis conductive member (110) is provided between opposing faces of the printed circuit boards (102, 104). The printed circuit boards (102, 104) are laminated with the z-axis conductive member (110), whereby the conductive pads (106, 108) are interconnected by the z-axis conductive member (110). The z-axis conductive member (110) comprises a planar, open cell, porous material having an x, y and z-axis with a series of electrically isolated, vertically defined cross section areas that extend from one side of the material to another side of the material and are covered with conductive metal, and contains a bonding adhesive in the porous material. Electronic devices may be attached to the printed circuit board assembly.

Description

TITLE OF THE INVENTION

INTERCONNECTED MULTI-LAYER CIRCUIT BOARDS

FIELD OF THE INVENTION

The present invention relates to interconnected multi-layer circuit boards in which electrical interconnections are made simultaneously with filling interstitial void spaces, and methods of manufacture

BACKGROUND OF THE INVENTION

It has been a goal in the electronics industry to replace soldering and welding as a means of providing an electrical connection between two opposing rows of conductive elements Connection is needed to connect the traces of one flexible circuit to another flexible circuit or to a printed circuit board, connect a nbbonized flat cable to a printed circuit board, connect a packaged integrated circuit to a printed circuit board, interconnect layers of printed circuit board, or the like Moreover, there is a trend to make more efficient use of board space by decreasing the spacing between leads or traces, and by generally diminishing component size and circuitry Soldering is problematic in that solder connections, if not complete, must be reflowed, which can damage electrical components The usual connectors, e g , spring, finger or pin contacts, are not amenable to the diminished sized components that are common today Two alternative techniques for providing electrical connection between components have been proposed to overcome these problems One technique uses substrates which employ conductive bands of metal particle filled elastomers disposed between bands of non-conductive elastomeπc material These bands form a bar or strip that has alternating conductive and non-conductive regions The strip is used to make an electrical connection between two electrical components by placing it between the row of conductive elements on one electrical component and the opposing row of conductive elements on the other electrical component and applying a normal force, usually by means of a clamp to laminate the electrical components In the laminated form, the bands of conductive elastomer make an electrical connection between the conductive elements on one electrical component and the opposing conductive elements on the other electrical component Generally, the width of each conductive elastomer band is less than the spacing between the individual conductive elements on each electrical component, so the conductive bands make an electrical connection between the opposing elements but not between the individual conductive elements on each electrical component Under ideal conditions, a row of copper lines on one printed circuit board can be electrically connected to a row of copper nes on another printed circuit board without causing an electrical short within the row of copper lines on the printed circuit board themselves, using the conductive particle filled substrate

If the electrical connection between two opposing parts needs to be more permanent, or a constant normal force cannot be exerted to fix the electrical components to one another, then the other technique, which uses a z-axis conductive particle adhesive, is utilized z-axis plane conductive particle adhesives are non-conductive resins filled with conductive particles z-axis conductive particle adhesives come as either liquids, pastes, or cast films The z-axis conductive particle adhesive is used to mechanically bond and electrically connect the respective components and generally require some type of lamination cycle, depending upon the adhesive type In these z-axis materials, conductive particles are suspended and isolated in the non-conductive resin so as to provide conductivity through the axis plane from one side of the connection to the other The diameter of each conductive particle is substantially less than the spacing of the conductive elements, therefore, there is no shorting between the individual elements Conversely, the conductive particles have a sufficiently large diameter so they can electrically bridge between the opposing rows of conductive elements to be connected

Both methods of connection have their limitations The density of the connection that can be attained by the elastomenc connectors is limited by the spacing of the conductive and non-conductive elements in the elastomenc strip The connection requires that a high normal force be exerted, necessitating mechanical fixtunng, such as a clamp, to provide the required high pressure The use of a clamp typically means that low profile connections are not available The z-axis conductive particle adhesive has several limitations based on its ability to keep the conductive particles suspended and isolated in the adhesive If the particles are not evenly dispersed, they can cause shorting between the conductive elements If they are not large enough or are not in sufficient concentration, there will not be sufficient conductivity between the conductive elements to be connected Also, if the adhesive flows or is smeared during processing, the conductive adhesive may cause shorting of other components Another problem with the z-axis conductive particle adhesive is achieving the right balance of adhesion, conductivity, repairabihty, and compliance

In the embodiment described in U S Patent No 5,502,889, a single conductive particle is used to provide the electrical path between two opposing conductive elements In this type of connector, uniformity of particle size is critical to ensure adequate contact, since the degree to which two opposing conductive elements can be pressed together will depend on the diameter of the larger size particles in the elastomenc connector SUMMARY OF THE INVENTION

The present invention relates to a printed circuit board assembly and process for assembling such a board involving interconnecting multi-layer printed circuit or printed wiring boards by simultaneously making electrical interconnects and filling interstitial void spaces A printed circuit board assembly comprises a plurality of interconnected printed circuit boards The assembly is made by aligning the boards so that conductive pads to be interconnected are opposite each other A z-axis conductive member having conductive pathways extending from one side of the member to the other is provided between opposing faces of the printed circuit boards The printed circuit boards are laminated with the z-axis conductive member, whereby the conductive pads are interconnected by the z-axis conductive member

The z-axis conductive member comprises a planar, open cell, porous material having an x, y and z-axis with a series of electrically isolated, vertically defined cross-section areas that extend from one side of the material to another side of the material and are covered with conductive metal, and containing a permanent adhesive in the porous material

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of a preferred embodiment of the invention, will be better understood when read in conjunction with the appended drawings For purposes of illustrating the invention, there is shown in the drawings an embodiment which is presently preferred It should be understood, however, that the invention is not limited to the precise arrangement and instrumentality shown In the drawings Fig 1 is a cross sectional schematic view of a planar, open cell, porous member containing layer having a nodes-fibril scaffold, prior to conversion to a z-axis conductive composite,

Fig 2 is a view of a planar, open cell, porous member having opaque masking,

Fig 3 is a view of an open cell, planar porous member showing designated areas for UV light exposure,

Fig 4 is a view of a planar, selectively conductive z-axis material containing an imbibed adhesive and/or tacky elastomer according to the present invention,

Fig 5 is a scanning electron micro-graph (SEM) of the polytetra-fluoroethylene layer used to prepare a z-axis material, Fig. 6 is a scanning electron micro-graph (SEM) of the polytetra-fluoroethylene layer used to prepare a z-axis material,

Fig 7 is a scanning electron micro-graph (SEM) of the polytetra-fluoroethylene layer used to prepare a z-axis material, Fig. 8 is a scanning electron micro-graph (SEM) of the polytetra-fluoroethylene layer used to prepare a z-axis material,

Fig 9 is a cross-sectional view of two multi-layer printed circuit boards 102 and 104 with a z-axis conductive member 110 of the present invention interposed between the two printed circuit boards, before lamination, Fig. 10 is a cross-sectional view of a printed circuit board assembly comprising two multi-layer printed circuit boards 102 and 104 with a z-axis conductive member 110 of the present invention interposed between the two printed circuit boards, after lamination,

Fig 11 is a cross-sectional view of a printed circuit board assembly comprising two multi-layer printed circuit boards 302 and 304 having recessed conductive pads, with a z-axis conductive member 110 of the present invention interposed between the two printed circuit boards, after lamination, and

Fig 12 is a flow diagram of a lamination process, in accordance with the present invention

DETAILED DESCRIPTION OF THE INVENTION

A printed circuit board assembly, according to the present invention, comprises a plurality of interconnected pπnted circuit boards aligned so that interconnected conductive pads are opposite each other A z-axis conductive member having conductive pathways extending from one side of the member to the other provides the interconnection between opposite conductive pads

The z-axis conductive member comprises a planar, open cell, porous material having an x, y and z-axis with a series of electrically isolated, vertically defined cross-section areas that extend from one side of the material to another side of the material and are covered with conductive metal, and containing a permanent adhesive in the porous material A selectively conductive z-axis material, which may be used as the planar conductive member of the present invention, is described in U S Patent No 5,498,467 In general, the planar, open cell, porous member used in the present invention can be any material having continuous pores from one side to the other The porous planar member must have an internal morphology in which the material defining the pores forms an irregular path through the z-axis direction within a vertically defined cross section through the z-axis plane, as shown

Suitable materials for the z-axis member have a thickness on the order of 5x10⁶m and

5x10⁴m (5 and 500 μm or 2 and 20 mils), and include porous fabrics, which may be woven or non-woven fabric, such as a nylon, glass fiber or polyester fabric or cotton, or the like The member can also be a porous polymeric layer, such as a film, membrane, or thicker material, that is flexible, such as porous polyolefins, e g , porous polyethylene, porous polypropylene, porous fluoropolymers, or open cell, porous polyurethanes Additionally, open cell, porous inorganic materials that have continuous pores from one side to the other can be used Porous fluoropolymers include, but are not limited to, porous polytetrafluoroethylene

(PTFE), porous expanded polytetrafluoroethylene (ePTFE), porous copolymers of polytetrafluoroethylene and polyesters or polystyrenes, copolymers of tetrafluoroethylene and fluoπnated ethylene-propylene (FEP) or perfluoroalkoxy-tetrafluoroethylene (PFA) with a C, - C₄ alkoxy group Preferred porous materials include expanded polypropylene, porous polyethylene and porous polytetrafluoroethylene Most preferably, the material is expanded polytetrafluoroethylene having a microstructure of nodes inter-connected with fibrils, a void volume of about 20 to 90%, such as the material prepared in accordance with the teachings of U S Patent No 3,953,566, incorporated herein by reference

In a preferred embodiment, the planar porous material generally will have a thickness of between about 5 and 500 μm, preferably between about 50 and 125 μm for interconnection of printed circuit boards The ultra-violet light transmission of the material must be greater than or equal to 10% to allow sufficient ultraviolet light to penetrate the sample

When the material 10 for forming the z-axis member is microporous PTFE (expanded polytetrafluoroethylene), the pores 20 are defined as the space between nodes 11 interconnected with fibrils 12, as shown in Fig 1 In this case, the internal structure of nodes interconnected with fibrils is of a material density that results in an irregular continuous path 22 through the z-axis 10 within a vertically defined cross section of the z-axis from one side of the planar member to the other (see Fig 4)

The z-axis material is capable of being compressed from 25% to 75% of its uncompressed dimension The pores size of the material for forming the z-axis conductive pathways is selected so that the irregularly shaped z-axis metal conductive pathways are electrically isolated from each other in the x and y axes directions

In U S Patent No 5,498,467, a planar, open cell, porous member made of a material having pores through it in the z-axis direction is selectively treated to form a series of conductive paths through the thickness of the z-axis direction from one side of the member to the other The paths are irregular in shape and are made receptive to deposition of a metal salt, which metal salt on exposure to radiant energy is converted to nonconductive metal nuclei which then act to catalyze deposition of a conductive metal from an electroless metal deposition solution The open cell material is made receptive to metal deposition by treating it in selected areas with a liquid, ultraviolet radiation sensitive composition comprising a solution of a light sensitive reducing agent, a metal salt, a source of halide ions, and a second reducing agent

The material is in contact with the radiation sensitive composition for a time sufficient, usually

5 to 15 minutes, for the composition to permeate or penetrate through the pores of the material and form a coating on the material along the material defining the pores from one side of the porous planar material to the other

The member is then dried and the surfaces of both sides are masked in selected areas with an opaque cover so that subsequent radiation will not strike the covered area Thereafter, the treated member is exposed to radiation, usually ultraviolet radiation, for a time and at a power sufficient to reduce the metallic cations in the metal salt to metal nuclei throughout the thickness of the member The member is then unmasked and washed with an acidic or alkaline washing solution to wash off the radiation sensitive composition that had been protected by the opaque cover The acidic or alkaline washing (or fixing) solution does not affect the areas where the radiation had reduced the metal cations to metal nuclei, if the solution is not left in contact with the areas for more than a few minutes, e g , 5 minutes or less

The member is next subjected to a reactive metallic cation replacement solution to replace the metal nuclei and provide a suitable stabilized area to receive a conductive metal The metal nuclei from the reducing composition is not stable enough to directly deposit conductive metal on because of the tendency of the metal to be oxidized The metallic cation provides greater stability, and is preferably a noble metal, such as, palladium or gold

Once the metallic cations are deposited, the member is then plated electrolessly by subjecting it to a solution of a conductive metal salt and dried, resulting in a scaffold member, containing pores, that is selectively conductive throughout the z-axis direction in those selected areas that had not been covered by the masking The metal salt may be any conductive metal, such as nickel, gold, copper or any combination thereof

The pores of the material are filled with a bonding adhesive for use as a connector interface between two other conductive materials The adhesive provides a physical bond between the materials which are being connected, while the conductive pathways provide electrical connections Suitable adhesives include epoxy resin, acrylic resin, urethane resin, si cone resin, polimide resin, cyanate ester resin, or the like The adhesive is conveniently imbibed into the pores by immersing the member in a solution of the adhesive For an epoxy resin, a suitable solvent is methylethylketone

In Examples 1-5 below, the z-axis material is impregnated with a bonding adhesive Example 1

A layer formed from a stretched porous polytetrafluoroethylene membrane having the node fibril structure shown in Fig 5 (1000x magnification) is 76 μm thick with a density of 0 22 gm/cm³ and an air volume of 70% at 25°C, and is available from W L Gore & Associates, was prepared to form a z-axis membrane, except that the masking strips were 2 mil pads with a 5 mil pitch The z-axis layer was impregnated with a bonding adhesive such as that described above

Example 2

A polytetrafluoroethylene layer similar to that of Example 1 having the node-fibril structure in Fig 5 (1000x magnification), was prepared as in Example 1 to form a z-axis layer, except that the masking strips were 8 mils with a 15 mil pitch The z-axis layer was impregnated with a bonding adhesive such as that described above

Example 3 A stretched porous polytetrafluoroethylene layer the node-fibril structure shown in Fig

6 (1500x magnification) that is 40 μm thick, with a density of 0 4 gm/cm³ and an air volume of 20% at 25°C, available from W L Gore & Associates, was prepared as in Example 1 to form a z-axis layer, except that the masking strips were 8 mil pads with a 15 mil pitch The z-axis layer was impregnated with a bonding adhesive such as that described above

Example 4

A stretched porous polytetrafluoroethylene membrane with the node-fibril structure shown in Fig 7 (1000x magnification) that is 100 μm thick, with a density of 0 35 gm/cm³ and an air volume of 70% at 25°C, available from W L Gore & Associates, was prepared as in Example 1 to form a z-axis layer, except that the masking strips were 8 mil pads with a 15 mil pitch The z-axis layer was impregnated with a bonding adhesive such as that described above Example 5

A stretched porous polytetrafluoroethylene membrane with the node-fibril structure shown in Fig 8 (1000x magnification) that is 150 μm thick, with a density of 0 20 gm/cm³ and an air volume of 70% at 25°C, available from W L Gore & Associates, was prepared as in Example 1 to form a z-axis layer, except that the masking strips were 8 mil pads with a 15 mil pitch The z-axis layer was impregnated with a bonding adhesive such as that described above

According to the invention, there is provided a process for interconnecting multi-layer circuit boards by simultaneously making electrical interconnects and filling interstitial void spaces As shown in Fig 9, two multi-layer circuit boards 102 and 104, which are to be interconnected, are provided Although two circuit boards are shown as an example, the present invention is equally applicable to the interconnection of more than two circuit boards Each circuit board typically has from 4 to 30 layers On at least one face of each circuit board are conductive pads, such as pads 106 and 108 Each pad is typically made of copper and projects 0 7 to 2 mils from the surface of its respective circuit board Pads can also be formed from other metals or coated with non-oxidative metals, such as gold, platinum, palladium, etc Circuit boards 102 and 104 are arranged so that the faces to be interconnected are opposing each other and the pads to be interconnected are aligned opposite each other Interstitial spaces 112 exist in the gaps between adjacent pads A planar z-axis conductive member 110 is interposed between the two circuit boards The two circuit boards are then laminated with the conductive member

The resulting printed circuit board assembly comprises two circuit boards, as shown in Fig 10, and which has 8 to 60 layers After lamination, connections between the two circuit boards are made through the conductive member Conductive member 110 contains a plurality of z-axis conductive paths 1 14, extending from one side of the member to the other which provide the electrical interconnection between pads, such as 106 and 108 The z-axis conductive member contains a permanent adhesive which provides a physical bond between the two laminated circuit boards

As shown in Fig 1 1 , boards with recessed pads can also be interconnected by the present invention Two multi-layer circuit boards 302 and 304, have recessed pads, such as 306 and 308, as would occur in solder-masked printed circuit boards The pads are interconnected by laminated conductive member 310 and the interstitial gaps 312 are filled The z-axis conductive material of the present invention conforms to the circuit boards and provides interconnection of the recessed pads The present invention also provides successful interconnection of printed circuit boards having projecting pads with printed circuit boards having recessed pads Again, the permanent adhesive which is contained by the z- axis conductive member provides a physical bond between the two laminated circuit boards

A lamination process according to the present invention is shown in Fig 12 In step

402, the multi-layer boards which are to be interconnected are chemically cleaned using a conventional cleaning process In step 404, a first board is pin registered to a tooling fixture, which is used to hold and register all the layers of board Use of the tooling fixture ensures that the pads which are to be interconnected are properly aligned opposite each other In step 406, a layer of z-axis material is placed on the board in the tooling fixture An advantage of the present invention is that it is not necessary to align or register the layer of z-axis material Therefore, the layer of z-axis material may be placed by hand or by any equivalent automated technique In step 408, additional layers of board are placed in the tooling fixture by repeating steps 404 and 406 For each additional layer, a board is pin registered to the tooling fixture and placed over the z-axis material of the previous layer Then, another layer of z-axis material is placed over the newly placed board This is repeated until the stack has reached desired number of layers has been placed Of course, the last layer of board is not covered with z-axis material Thus, a z-axis member is interposed between opposing faces of printed circuit boards In step 410, the top part of the tooling fixture is placed over the stack In step 412, the stack and tooling fixture are placed in a conventional lamination press Heat and pressure are then applied, which produces lamination of the boards with the layers of z- axis material in the stack

The lamination process results in a printed circuit board assembly comprising a stack of boards, interconnected as shown in Figs 10 and 11 During lamination, temperatures are applied which are typically in the range of 250 to 500 degrees Fahrenheit Likewise, pressures are applied which are typically in the range of 200 to 400 pounds per square inch These temperatures and pressures cause metallurgical bonds to be made between the pads of the boards and the conductive channels of the z-axis material The permanent adhesive contained in the z-axis material provides a physical bond between the interconnected boards In addition, the z-axis material has conformed to the surfaces of the boards, providing a gas- free seal In order to provide proper conformance, the thickness of the z-axis material use is typically in the range of 2 to 5 mils, depending on the surface features of the board

After lamination, electronic devices may be attached to a printed circuit board assembly by any well-known technique For example, electronic devices may be attached by hand soldering, wave soldering, infrared reflow soldering, vapor phase reflow soldering, laser soldering, etc Typical electronic devices which may be attached include, for example, resistors, capacitors, inductors, and semiconductors including transistors diodes, and integrated circuits, such as microprocessors, memories, logic devices, analog-to-digital converters, digital-to-analog converters, amplifiers, filters, modulators, demodulators, peak detectors, etc

The present invention is also applicable to the interconnection of printed circuit boards of different sizes and shapes This may easily be accomplished by modifying the tooling fixture used during lamination in a well-known manner to add pins which would register boards in more than one location Smaller boards may be laminated to larger boards to produce a printed circuit board assembly of varying thickness Such an assembly is useful in situations where tight clearances require an assembly which is thinner is some areas and thicker in others Such an assembly would also reduce cost because additional layers of printed circuit board would be laminated to only those areas of the assembly which require additional circuit connections An assembly could be produced using the present invention in which the constituent printed circuit boards only partially overlap This is useful in situations where one board must extend farther, or less far, than another Use of the described materials, such as ePTFE as the conductive member provides a number of advantages For example, a conductive layer may be used which is thick enough to conform to the board profile, filling the gaps 1 12 between adjacent pads This eliminates air and void spaces where process chemicals could become trapped, thus preventing a possible source of corrosion and improving the reliability of the interconnection In the prior art, there is a tradeoff between material thickness and particle diameter Conductive particle size (diameter) typically limits the thickness of z-axis material As a result, the prior art materials cannot be used in thicknesses which provide filling of the interstitial gaps In the described materials, the compressibility and compliancy of the material allows greater thicknesses to be used In addition, the metallization becomes an integral part of the structure of the material The metalized structure is continuous through the layer along the nodes and fibrils and provides lower contact resistance and better uniformity of signal quality than materials that use conductive particles Thus, the described materials avoid the particle to particle resistance problems found in some conductive particle materials using multiple stacked particles to make interconnects Use of described materials, such as ePTFE as the conductive member provides the ability to interconnect finer pitch circuit boards than was feasible in the prior art For example, boards having 4-5 mil diameter pads on 8-10 mil centers may be interconnected using the present invention In addition, many of the described materials, such as ePTFE, have relatively low moduli, which provides stress decoupling between the interconnected boards Although the invention has been described in conjunction with the specific embodiments, it is evident that many alternatives and variations will be apparent to those skilled in the art in light of the foregoing description Accordingly, the invention is intended to embrace all of the alternatives and variations that fall within the spirit and scope of the appended claims

Claims

What is claimed is

1 A method of interconnecting printed circuit boards, comprising the steps of providing a first and a second printed circuit board having a face with conductive pads, aligning the conductive pads to be interconnected opposite each other, providing a z-axis conductive member between opposing faces of first and the second printed circuit boards, the z-axis conductive member comprising a planar, open cell, porous material having an x, y and z-axis with a series of electrically isolated, vertically defined cross- section areas that extend from one side of the material to another side of the material and being covered with conductive metal, and containing an adhesive in the porous material, and laminating the first and the second printed circuit boards with the z-axis conductive member, whereby the conductive pads are electrically connected by the z-axis conductive member

2 The method according to claim 1 , wherein at least three printed circuit boards are provided

3 The method according to claim 1 , wherein the conductive pads project from the face of a printed circuit board

4 The method according to claim 1 , wherein the conductive pads are recessed from the face of a printed circuit board

5 The method according to claim 1 , wherein at least one printed circuit board has conductive pads which project from the face of the board and at least one printed circuit board has conductive pads which are recessed from the face of the board

6 The method according to claim 1 , wherein the first printed circuit board is smaller than the second printed circuit board

7 The method according to claim 1 , wherein the first printed circuit partially overlaps the second printed circuit board

8 The method of claim 1 , wherein the planar, open cell, porous material is a polymer The method according to claim 8, wherein the polymer is a polyolefin

10 The method according to claim 9, wherein the polyolefin is porous polypropylene or porous polyethylene

1 1 The method according to claim 8, wherein the polymer is a fluoropolymer

12 The method according to claim 11 , wherein the fluoropolymer is porous polytetrafluoroethylene (PTFE)

13 The method according to claim 1 1 , wherein the fluoropolymer is porous expanded polytetrafluoroethylene (ePTFE)

14 The method according to claim 1 1 , wherein the fluoropolymer is a porous copolymer of polytetrafluoroethylene

15 The method according to claim 14, wherein the copolymer includes polyesters

16 The method according to claim 14, wherein the copolymer includes polystyrenes

17 The method according to claim 1 1 , wherein the fluoropolymer is a porous copolymer of fluoπnated ethylene-propylene (FEP)

18 The method according to claim 1 1 , wherein the fluoropolymer is a porous copolymer of perfluoroalkoxy tetrafluoroethylene (PFA) with a C -C₄ alkoxy group

19 The method according to claim 1 , wherein the conductive metal is copper

20 The method according to claim 1 , wherein the conductive metal is nickel

21 The method according to claim 1 , wherein the conductive metal is gold

22 The method according to claim 1 , wherein the conductive metal is selected from a group consisting of copper, nickel, gold, and any combination thereof 23 The method according to claim 1 , wherein the adhesive is an epoxy resin

24 The method according to claim 1 , wherein the adhesive is an acrylic resin

25 The method according to claim 1 , wherein the adhesive is a urethane resin

26 The method according to claim 1 , wherein the adhesive is a silicone resin

27 The method according to claim 1 , wherein the adhesive is a polimide resin

28 The method according to claim 1 , wherein the adhesive is a cyanate ester resin

29 A printed circuit board assembly comprising a first and a second printed circuit board having conductive pads which are interconnected and aligned so that the conductive pads which are interconnected are opposite each other, and a z-axis conductive member comprising a planar, open cell, porous material having an x, y and z-axis with a series of electrically isolated, vertically defined cross-section areas that extend from one side of the material to another side of the material and being covered with conductive metal, and containing an adhesive in the porous material, the z axis conductive member between the first and the second printed circuit boards, the first and the second printed circuit boards being laminated so that the conductive pads are interconnected by the z-axis conductive member

30 The printed circuit board assembly according to claim 29, wherein at least three printed circuit boards are provided

31 The printed circuit board assembly according to claim 29, wherein the conductive pads project from the face of a printed circuit board

32 The printed circuit board assembly according to claim 29, wherein the conductive pads are recessed from the face of a printed circuit board 33 The printed circuit board assembly according to claim 29, wherein at least one printed circuit board has conductive pads which project from the face of the board and at least one printed circuit board has conductive pads which are recessed from the face of the board

34 The printed circuit board assembly according to claim 29, wherein the first printed circuit board is smaller than the second printed circuit board

35 The printed circuit board assembly according to claim 29, wherein the first printed circuit partially overlaps the second printed circuit board

36 The printed circuit board assembly of claim 29, wherein the planar, open cell, porous material is a polymer

37 The printed circuit board assembly according to claim 36, wherein the polymer is a polyolefin

38 The printed circuit board assembly according to claim 37, wherein the polyolefin is porous polypropylene or porous polyethylene

39 The printed circuit board assembly according to claim 36, wherein the polymer is a fluoropolymer

40 The printed circuit board assembly according to claim 39, wherein the fluoropolymer is porous polytetrafluoroethylene (PTFE)

41 The printed circuit board assembly according to claim 39, wherein the fluoropolymer is porous expanded polytetrafluoroethylene

42 The printed circuit board assembly according to claim 39, wherein the fluoropolymer is a porous copolymer of polytetrafluoroethylene

43 The printed circuit board assembly according to claim 42, wherein the copolymer includes polyesters 44 The printed circuit board assembly according to claim 42, wherein the copolymer includes polystyrenes

45 The printed circuit board assembly according to claim 39, wherein the fluoropolymer is a porous copolymer of fluoπnated ethylene-propylene (FEP)

46 The printed circuit board assembly according to claim 39, wherein the fluoropolymer is a porous copolymer of perfluoroalkoxy tetrafluoroethylene (PFA) with a C, -C₄ alkoxy group

47 The method according to claim 29, wherein the conductive metal is copper

48 The method according to claim 29, wherein the conductive metal is nickel

49 The method according to claim 29, wherein the conductive metal is gold

50 The method according to claim 29, wherein the conductive metal is selected from a group consisting of copper nickel, gold, and any combination thereof

51 The printed circuit board assembly according to claim 29, wherein the adhesive is an epoxy resin

52 The printed circuit board assembly according to claim 29, wherein the adhesive is an acrylic resin

53 The printed circuit board assembly according to claim 29, wherein the adhesive is a urethane resin

54 The printed circuit board assembly according to claim 29, wherein the adhesive is a silicone resin

55 The printed circuit board assembly according to claim 29, wherein the adhesive is a polimide resin

56 The printed circuit board assembly according to claim 29, wherein the adhesive is a cyanate ester resin 57 The printed circuit board assembly of claim 29, further comprising an electronic device attached to the printed circuit board assembly

58 The printed circuit board assembly of claim 57, wherein the electronic device is a resistor

59 The printed circuit board assembly of claim 57, wherein the electronic device is a capacitor

60 The printed circuit board assembly of claim 57, wherein the electronic device is an inductor

61 The printed circuit board assembly of claim 57, wherein the electronic device is a semiconductor

62 The printed circuit board assembly of claim 57, wherein the electronic device is a transistor

63 The printed circuit board assembly of claim 57, wherein the electronic device is a diode

64 The printed circuit board assembly of claim 57, wherein the electronic device is an integrated circuit

65 The printed circuit board assembly of claim 57, wherein the electronic device is a microprocessor

66 The printed circuit board assembly of claim 57, wherein the electronic device is a memory

67 The printed circuit board assembly of claim 57, wherein the electronic device is a logic device

68 The printed circuit board assembly of claim 57, wherein the electronic device is an analog-to-digital converter 69 The printed circuit board assembly of claim 57, wherein the electronic device is a digital-to-analog converter

70 The printed circuit board assembly of claim 57, wherein the electronic device is an amplifier

71 The printed circuit board assembly of claim 57, wherein the electronic device is a filter

72 The printed circuit board assembly of claim 57, wherein the electronic device is a modulator

73 The printed circuit board assembly of claim 57, wherein the electronic device is a demodulator

74 The printed circuit board assembly of claim 57, wherein the electronic device is a peak detector