FLEXIBLE ELECTRICAL JUMPER CABLE AND ASSEMBLY

Abstract: A flexible flat cable assembly, which is adapted to form a low profile interconnection between two electrical circuit members, each having a row of closely spaced apart conductive traces (18). The cable (2) comprises a row of traces (18), with an insulating polymeric film (20) overlying each side of the row. Also, the row is exposed at each end of the jumper cable, and the exposed end portion is covered by a layer of an anisotropically conductive adhesive (22). The cable is adapted to electrically join a flat display panel (220) to a printed circuit board (222), with the jumper cable (210) forming the interconnection between the conductors (221) on the display panel with the conductors on the circuit board. A jumper cable assembly is also disclosed, which includes surface mountable electrical components (224) which are electrically connected and mechanically secured to the traces (230) of the jumper cable assembly by means of an anisotropically conductive adhesive (22). A cable assembly especially adapted for tapping is also disclosed.

Description: FLEX I BLE ELECTRICAL JUMPER CABLE AND ASSEMB LY The present invention relates to electrical cables adapted for electrically interconnecting a plurality of circuit members , such as a printed circuit board and a flat panel of the type having an addressable matrix display , or a plurality of tap cables . Flexible flat cable is employed in electrical and electronic equipment such as business machines , industrial controls , communication systems and computers . For example, flexible flat cable jumper assemblies constituting insulated flat conductors having terminals or connectors attached at one or both ends , comprise a common method of interconnecting separate components or separate circuits in assemblies such as printed circuit boards . These cable interconnections can be made by employing crimp-type contacts which eliminate flat cable preparation , stripping and conductor plating . Solder tab contacts can also be employed. Conventional flat cable comprises a laminated assembly . having an insulating material on opposite sides of conductors disposed therebetween . Such flat cable assemblies commonly employ polyester , polyvinyl , polyimide, polyetherimide, or polycarbonate insulating films . The conductors are sandwiched therebetween in the laminate and comprise flat metallic conductors , such as flat copper. Etched conductors deposited on one substrate of the flat cable can also be employed . Such conventional cables commonly employ an adhesive to bond the two insulating layers together . Conventional multiconductor flat cables permit interconnection between separate electrical components within a small space, since the conductors can be positioned on the flat cable at a relatively close centerline spacing . For example such multiconductor cables are commonly available on .050 inch center line spacings . Conventional electrical connectors are available for use in interconnecting such conventional cables on these centerline spacings , but the tap connectors have a relatively high profile when compared to the cables . Thus the connectors limit the density of the package, by adding to the thickness of the assembled configuration . Cables of this type have been used to interconnect circuit members such as printed circuit boards or flat panel displays. Furthermore, there is often a need to form interconnections between cables or to form a tap interconnection to cables. Interconnections to flat panels are becoming increasingly significant and more difficult as the centerline spacings between flat panels decrease. Several different types of flat display panels are presently known , including liquid crystal displays , electroluminescent displays , vacuum fluorescent displays , alternating current gas plasma displays , and direct current gas plasma displays . All of these display panels require a large number of electrical interconnections between the substrate of the panel , which is usually glass , and associated driver circuitry. Also, most of these panel displays require a relatively high signal current level through the interconnections , and the displays often require an extremely dense arrangement of the conductors , nominal ly 30 mils with a projected need of 3 mils between centerlines . It has been conventional to form the connections between display panels and the associated circuitry by soldering techniques , which of course is time consuming and expensive. Also, the soldered connections are subject to separation by " reason of the different coefficients of thermal expansion between the members being joined . More recently , mechanical clips or layered elastomeric strips have been employed , as described for example in U . S . Patent Nos . 3 , 998 ,512 and 4,202 ,588. However, these prior devices can be relatively expensive, and many are not able to meet the relatively high current and density requirements of present day display panels . Furthermore, there are problems with the reliability of these devices . The elastomeric strips are subject to compression set and to contamination from the environment. The mechanical pressure needed to maintain electrical contact with the clips can damage the panels . The cable depicted in the preferred embodiments of this invention comprises a multiconductor flat cable having a single flexible insulating substrate with a plurality of conductors disposed side by side thereon . A dielectric coating which in one embodiment of the invention can comprise a dielectric ink comprising a photopolymer can be disposed along the surface of the conductors . The conductors can comprise separate etched or formed metal conductors , such as discrete copper conductors or the conductors can comprise a conductive ink formed from a solidified polymer having conductive material freely dispersed therein . Conventional substrates such as polyester film , polyetherimide, polyvinyl , polyimide film and. polycarbonate film can be employed in such cable. The conductive and dielectric inks employed in one embodiment of this invention are screen printable and the dielectric ink can be curable upon the application of ultraviolet light. I n this one embodiment of the invention the conductive ink can be formed of a conductive material containing a solvated polyester resin . A tap connection to corresponding conductors in a separate flat cable or other conductor array can be established by using a conductive adhesive which is screen printable on one or both of the cables . In this tap configuration openings in the dielectric covering can be positioned in registry with selected conductors . A conductive adhesive located at these tap locations can then be used to establish the interconnection . Both pressure sensitive and heat activated conductive adhesives can be employed for this purpose. When a dielectric ink is used to establish the dielectric cover, the coverlayer can be screen printed with the openings in registry with conductors at desired locations along the length of the cable. Thus this invention permits an adhesive solderless tap connection to be established between two flat cables or between a cable and a conductor array without the use of separate terminals and connectors , thus precluding the dimensional restrictions inherent in solder or solderiess connector interconnection techniques . Furthermore , the cable in accordance with this invention can be easily and efficiently manufactured . Circuit assemblies employing cable to interconnect plural electrical circuit members such as printed circuit board to flat panel or cable to cable can also be constructed . An assembly comprising one or more cables and an intermediate jumper panel can be used to establish an interconnection to an electroluminescent display. The cable can be attached to edges of the jumper panel and electrical components , such as surface mounted integrated circuit packages can be attached intermediate the ends of the conductive traces on the jumper panels . Figure 1 is a top plan view of a cable with conductive ink traces and embodying the principles of this invention . Figure 2 is a sectional view taken along section lines 2-2 of Figure 1 . Figure 3 is a sectional view taken along the section lines 3-3 of Figure 1 . Figure 4 is a sectional view taken along the section lines 4-4 of Figure 1 . Figure 5 is a sectional view taken along section lines 5-5 of Figure 1 . Figure 6 is an exploded sectional view showing two similarly constructed cables prior to mating . Figure 7 is a view similar to Figure 6 but showing two cables interconnected by a pressure-sensitive conductive adhesive. Figure 8 is an exploded cross-sectional view showing the cable of Figure 1 ready to be mated to a conductor array comprising only a substrate and conductor traces disposed thereon . Figure 9 is a fragmentary cross-sectional view showing an exposed conductor at a tap location. Figure 1 0 is a fragmentary top plan view of a segment of the cable in which a conductive pad has been established to enlarge the tap area for a single trace. Figure 11 is a sectional view taken along section lines 1 1 -1 1 of Figure 10. Figure 12 is a perspective view of a flexible flat jumper cable, which embodies the features of the present invention . Figure 13 is a sectional view taken substantially along the line 13-13 of Figure 1 2. Figure 14 is an exploded perspective view of an electrical circuit assembly which includes a jumper cable , and in accordance with the present invention . Figure 15 is a view similar to Figure 14, but illustrating the components in an assembled relationship. Figure 16 is a perspective , partly exploded view illustrating another embodiment of an electrical circuit assembly in accordance with the present invention . Figure 17 is a fragmentary enlarged perspective and partly exploded view of a portion of the jumper cable assembly shown in Figure 16. Figure 18 is an enlarged sectional view taken substantially along the line 18-18 of Figure 17. Figure 19 is a sectional view taken substantially along the line 1 9-19 of Figure 17 and further illustrating a portion of the associated jumper cable; and Figure 20 is a sectional view taken substantially along the 20-20 of Figure 17. Figure 1 shows a pair of multiconductor flat cables 2a and 2b containing flat conductors , each attached to a common electrical connector 4 of conventional construction . A third or tap cable 2c extends at right angles to cable 2b . I nterconnections with individual corresponding conductors in cables 2b and 2c are made at a plurality of predisposed tap locations 6 in the cable. Figures 6 and 7 depict the interconnection of a preferred cable 2 with an essentially identical cable 102. Figure 8 depicts the manner of establishing an interconnection between a cable of the preferred embodiment 2 and a separate conductor array 302 which could comprise a conventional flat cable or an array of conductors disposed upon either a flexible or a rigid substrate. The conductor array 302 in Figure 8 is characterized in that the individual conductors 310 disposed on one surface of an insulating substrate 31 1 are exposed . The construction of the embodiment of Figures 1 -7 can be understood by one skilled in the art from an examination of a plurality of sectional views shown in Figure 2 through 5 in conjunction with reference to the plan view shown in Figure 1 . Cable 2 as shown in Figure 1 comprises a plurality of longitudinally distinct segments . A section adjacent the end of the cable shown in Figure 2 shows that the cable is formed from an insulating substrate 16 having a plurality of conductive traces 18 spaced apart and disposed on one surface thereof. In this embodiment of this invention these conductive traces 18 comprise conductive ink traces having a conductive material interspersed in a solidified polymer . The conductors 18 in the embodiment of Figures 1 -7 extend in parallel and are spaced apart by a distance sufficient to maintain electrical integrity . These conductive ink traces 18 may be disposed upon the upper surface of insulating film 16 by a conventional silk screen or screen printing operation . The insulating film 16 can comprise a conventional dielectric film such as a polyester film , a polyvinyl , a polyetherimide, a polyimide film or a polycarbonate film . The exposed conductors 18 adjacent one end only of the film would normal ly be provided for test purposed during the manufacture of the cable. It should be understood that the exposed conductors in the vicinity of the section shown in Fig . 2 would be terminated to a separate electrical connector or would be severed in actual use. Figure 3 shows a sectional view along a portion of the cable spaced from both ends . The construction of the cable as shown by section 3 would constitute the construction of the cable over the majority of its length provided that a tap interconnection is not desired along the majority of the length of the cable. A tap interconnection in accordance with this invention cannot be made to the cable at locations in which the cable has a construction such as that shown in Figure 3. The conductive traces 1 8 shown in Figure 3 are the same as the conductive traces 18 shown in Figure 2 and are disposed on a surface of an identical insulating film 16. A dielectric coverlayer 20 extends along the upper surface of film 16 and encapsulates the individual conductive traces between film 16 and the dielectric coverlayer 20. In the preferred embodiment of this invention , the dielectric cover 20 comprises a dielectric coating comprising a dielectric ink formed of a photopolymer and having desirable insulating properties. Coverlayer 20 is sufficiently flexible to maintain electrical integrity as the flat cable including film 16 is flexed during actual use. Dielectric coverlayer 20 can be screen printed on film 16 in essentially the same manner as the conductive ink traces 18 , and dielectric coverlayer 20 can be cured to provide a solid film coating for the cable. In those areas where an electrical interconnection is desirable to a separate conductor array such as a similar flat cable having a plurality of conductors , a conductive film 22 may be deposited on the surface of the dielectric coverlayer 20. For example in the area 12 of cable 2 the three-layer cable of Figure 3 is covered by a continuous layer 22 of conductive adhesive. This conductive adhesive 22 is also screen printable and in the preferred embodiment is an anisotropically conductive adhesive such as that described more fully below . Although the sectional view shown in Figure 4 is taken within an area 12 in which a tap interconnection to a separate conductor array is desired , Figure 4 is not taken along a tap location where an interconnection can be made to a corresponding conductor array . Figure 4 also shows a silicone coated slip sheet or release liner 24 which can be placed along the non-tacky , dry conductive adhesive 22. The silicone coated slip sheet or release line can be peeled from the interconnection area 12 when it is desired to make a tap • interconnection . A separate insulating screen printed coverlayer can also be provided over the conductive adhesive, provided the conductive media is exposed when the tap interconnection is completed by application of heat and/or pressure. Figure 5 is a section view taken along one of the predetermined tap locations 6 where a conductor 18 can be exposed both to the conductive adhesive 22 and ultimately to a conductive array to be interconnected thereto. Tap locations 6 are predetermined and in the preferred embodiment of this invention , a staggered row of conductive traces 6 is chosen which can in turn be positioned in registry with a separate set of staggered tap locations 6 and a right angle tap cable 2c shown in Figure 1 . In this embodiment of the invention a conductor pad 26 , is formed over a conductor 18 at a tap location 6. Conductor pad 26 can comprise a conductive ink similar to the conductive ink forming the trace conductors 18 and provides an enlarged area in which to make an interconnection through the anisotropically conductive adhesive 22. Since the dielectric film 20 can be screen printed onto substrate 16 and over conductors 18 , the predetermined tap locations 6 can be easily defined during the screen printing operation and comprise those exposed locations at which a dielectric ink coating 20 is not deposited . Conductive pads 26 extend along the upper surface of the coating 20 both to provide additional surface area in which the connection can be made to the anisotropically conductive adhesive 22 and to provide a section in the conductive adhesive having a smaller thickness . The enlarged conductive pad also provides for a greater target area , thus facilitating a registration between tap locations on separate interconnected conductors . Figures 6 and 7 demonstrate the manner in which a solderiess tap interconnection can be established between two identical cables 2 and 102 at prescribed tap locations 6 and 106 through conductor pads 26 and 126 and through layers of conductive adhesive 22 and 122. First the release liners 24 and 124 are removed from the surface of the cable in the region 12 where a tap interconnection is to be made. As shown in Figure 7 , a pressure sensitive adhesive interconnection can be made by placing conductive pads 26 and 126 in registry and merely applying pressure to fuse the conductive adhesive layers 22' and 1 22' which comprise a pressure sensitive conductive adhesive. A suitable pressure sensitive conductive adhesive is described more fully below. Use of an anisotropically conductive adhesive which establishes electrical continuity perpendicular to the plane of the cable but does not establish electrical continuity in a lateral direction , is the. preferred form of conductive adhesive for use in the instant application . When an anisotropically conductive adhesive is employed , the conductive adhesive can merely be screen printed on the surface of the cable throughout the location 12 to which electrical continuity is to be established . If a biaxial conductive adhesive were employed , deposition of the conductive adhesive would be limited to areas of individual tap locations 6; and unless a bridging interconnection were to be established , separate dots of conductive adhesive must be deposited on each individual tap location . Use of an anisotropically adhesive obviates the necessity of depositing the conductive adhesive only in dots on the film independently in registry with individual tap locations. Of course, if a bridged interconnection between a plurality of tap locations were desired when an anisotropically conductive adhesive was employed , suitable printing of the dielectric coating , leaving the prescribed tap locations commonly exposed , could be established; and a commoning conductive pad formed with a conductive ink could be screen printed to join the connectors . Indeed , non-adjacent connectors could be commoned by depositing a conductive ink over the surface of a layer of dielectric coating covering the intermediate conductors . Figure 8 shows the manner in which a single flat cable 2 in accordance with this invention can be attached to a dissimilar conductor array 302 which could be formed by an insulating substrate 316 having a plurality of conductors , one of which 310 is shown herein. Such a dissimilar conductor array could comprise a printed circuit board , a flat cable without a dielectric coating , or with the dielectric coating removed , or an insulating substrate having a conductive ink pattern formed thereon . Figures 9 through 11 demonstrate the versatility of the preferred embodiment of this invention . For example, Figure 9 illustrates a tap location 6 in which interconnection is made directly between the conductive adhesive 22 in the underlying but exposed conductor 18. No conductive pad is depicted in Figure 9. Figures 10 and 11 however, disclose a separate configuration in which the conductive pad 26 is positioned not only between conductor 18 and conductive adhesive 22 but in which the conductive pad 26 overlies the diejectric 20 covering adjacent connectors , thus greatly enlarging the area in which registration can be established . Reference is now made to Figure 12 illustrating a flexible flat jumper cable 210 which is adapted to form a low profile interconnection between two electrical circuit members , each having a row of closely spaced apart conductive traces . The jumper cable 210 comprises a row of coplanar, and laterally spaced apart electrically conductive traces 21 2. For purposes of illustration , the traces are shown to be parallel to each other. It is to be understood that the traces may be arranged in any desired pattern . An insulating polymeric film 214 overlies each side of the row of traces , with the film on one side of the row (bottom side as seen in Figure 13) being foreshortened at each end of the cable, to define a mounting edge portion 216 which extends laterally across the full width of the row at each end thereof. Thus portions of the traces 212 are effectively exposed on one side of the jumper cable in each mounting edge portion 16. The jumper cable of Figure 12 further includes a layer of an anisotropically conductive adhesive 218 overlying each of the edge portions 216 so as to cover the exposed portions of the traces 212. The coating of adhesive serves to protectively cover the otherwide exposed traces of the cable during shipment and storage, and to electrically and mechanically join the cable to associated electrical circuit members in the manner further described below . Figures 14 and 15 illustrate an electrical circuit assembly in accordance with the present invention , and which comprises a flat display panel 220 having a row of closely spaced apart electrically conductive traces 221 , and a circuit board 222 having a row of a corresponding number of closely spaced apart electrically conductive traces 223 and a number of conventional circuit components 224. Also, the row of electrical conductive traces on each of the flat panel 220 and the circuit board 222 extend perpendicularly to one side edge of the member.-. The flexible jumper cable 210 is employed to electrically interconnect respective ones of the conductive traces of the flat panel and the conductive traces of the circuit board . More particularly , on mounting edge portion 216 of the jumper cable 210 is joined to the side edge of the flat panel 220 bv positioning the side of the mounting edge portion of the cable having the coating of anisotropically conductive adhesive 218 thereon in contact with the side edge of the flat panel , with the respective traces in registry . Heat and pressure may then be applied , so that the coating of anisotropically conductive adhesive 218 electrically interconnects the respective traces and mechanically secures the cable to the surface of the flat panel . Similarly , the jumper cable may be joined to the side edge of the circuit board 22 to form the interconnected assembly. The flat display panel 220 may for example comprise a rigid transparent sheet, such as glass , having an addressable matrix display operatively connected to the associated row of conductive traces 21 , is as well known in the art. In the illustrated embodiment, the jumper cable 210 is composed of two laminated thin plastic films 214, such as laminated polyimide, polycarbonate, polyvinyl , polyetherimide or polyester film, with each layer having a thickness of about 2-5 mils prior to lamination . The electrically conductive traces 212 preferably comprise a solidified electrically conductive polymer which has been deposited on the substrate as a fluid ink and then dried . Typically , the fluid ink comprises silver dispersed in a solvated polyester resin , which dries to form a dried resin binder. Also, it is preferred that the fluid ink is deposited utilizing a screen printing operation . As an alternative construction , the jumper cable may comprise a film substrate, upon which the traces are deposited by screen printing or the like, and with the outer side of the traces being covered by a layer of a dielectric material which may also be screen printed upon the substrate. Also, the traces for the j-umper cable may alternatively be formed by discrete metal wires , or by a metal sheet which has been etched to form the desired pattern of traces by the procedure well known in the art. Figure 16 illustrates a circuit assembly which includes a flat display panel 226 of the type described above , a total of four jumper cables 210 as described above, and a total of four jumper panels 228 joined between each of the jumper cables 210 and the display panel 226. Each jumper panel 228 comprises a substrate 229 , ( Figure 17) , which may for example comprise a sheet of polyester, polyetherimide, polycarbonate, polyvinyl or polyimide film , having a thickness in the range of between about 1 to 1 0 mils , preferably 2-5 mils . A plurality of electrically conductive traces 230 are disposed on one or both surfaces of the substrate, and define a plurality of component connecting areas 232 , with the conductive traces including component lead traces 233 which extend into respective connector areas . Also, portions of the traces are disposed in at least two rows of closely spaced apart traces which extend to a respective side edge of the substrate to define mounting edge portions 234 , 235 which are each adapted to be adhesively joined to a mating edge portion of either the display panel 226 or the associated jumper cable. The electrically conductive traces 230 preferably comprise a solidified electrically conductive polymer which has been deposited on the substrate as a fluid ink and then dried in the manner described above. The portions of the substrate which mount the electrically conductive traces , but which are not within one of the component connecting areas 232 , or the mounting edge portions 234, 235 are covered with a dielectric cover layer 238 , note for example Figures 19 and 20. The dielectric cover layer 238 thus covers and protects the conductive traces of the circuitry , and specifically 14 the traces are thereby sealed from moisture and most other environmental contamination . A surface mounted electrical component 240 such as a resistor or an integrated circuit, overlies a portion of each of the component connecting areas 232 , and each such electrical component includes a plurality of electrical contact members 41 overlying respective ones of the component contact member mounting pads 233. A layer of an anisotropicallv conductive adhesive 242 as described above overlies each of the component connecting areas 232 , with the anisotropically conductive adhesive layer mechanically securing the component to the substrate and electrically interconnecting each of the contact members 241 to its associated component contact member mounting pad 233. The mounting edge portion 235 of the circuit assembly , which is to be joined to the display panel 226 , is also covered with a layer of an anisotropically conductive adhesive 242. The mounting edge portion 234 along the opposite side of the assembly , and which is designed for attachment to the jumper cable 210 , is shown as also being covered with a layer of the anisotropically conductive adhesive. However, this mounting edge portion 234 may remain free of the anisotropically conductive adhesive if desired , in which event the anisotropically conductive adhesive on the jumper cable 210 would provide the interconnection . Alternatively the mounting edge portions 234, 235 of the jumper cable 210 may have a layer of nonconductive adhesive 244 applied over the layer of anisotropically conductive adhesive 218. The nonconductive adhesive provides insulation for the anisotropically conductive adhesivef layer from contact which could cause a short through the anisotropically conductive adhesive. Furthermore, the nonconductive layer provides additional adhesive for mechanically securing the jumper cable to the circuit assembly. Preferably, the nonconductive adhesive is comprised of the same resin binder as the anisotropically conductive adhesive. . Upon assembly of the components in the manner illustrated in Figure 216, the traces along the mounting edge portion 235 of the circuit assembly are electrically connected to the associated traces of the display panel 226 by the layer of anisotropically conductive adhesive 242 , and the jumper cable 210 is similarly joined to the jumper cable assembly 228 by the layer of anisotropically conductive adhesive 242 on the mounting edge portion of the jumper cable assembly and/or on the jumper cable. These interconnections are preferably made with the application of heat and pressure so as to soften the layer of anisotropically conductive adhesive, and so that upon cooling , a secure interconnection is achieved. The temperature typically used to achieve the interconnection is 125°C , well below the temperature of 200°C usually associated with soldering components to a panel . The jumper cable assembly of Figure 16 further comprises nonconductive adhesive layer 244 (note Figure 18) overlying the layer of anisotropically conductive adhesive 242 on those portions of the component connecting areas 232 not covered by an electrical component or the electrical contact members thereof, so as to electrically insulate the layer of anisotropically conductive adhesive from contact with external members which could cause a short through the anisotropically conductive adhesive. Several specific non-limiting examples of the various inks applied to the substrate of the jumper cable 210 and jumper cable assembly 228 will now be described . As noted above , the conductive traces 212 ,230 are preferably applied on the substrate in the form of a polymeric conductive ink , and specifically a silver-containing solvated polyester resin , which is then dried . In addition to polyester , the polymer may comprise an epoxy , acrylic , polycarbonate, polyimide, polyurethane , or polyvinyl resin . The solvent serves to dissolve the polymer, and may be dried by the application of heat to remove the solvent and bond the polymer to the substrate. Butyl cellesolve acetate, and glycol ethers and their derivatives are commonly used solvents . As a specific example of a suitable ink , the conductor ink may be formulated as follows : I ngredient Percentage (by weight) Silver ■ 60% ' Polyester resin 15% Butyl Cellosolve acetate 25% Cellosolve is a trademark of Union Carbide Corporation , Danbury, Connecticut. The conductor ink sold under the designation ,, 5007 π by E. I . Du Pont de Nemours & Co. , I nc. , Wilmington , Delaware, is suitable for use with the present invention . Also, the above inks are adapted to be applied to the substrate by screen printing , which is the preferred method of application . Thermoset or crosslinkable conductive inks may also be used . The conductive ink sold under the designation "CT 5030" by Amicon , Lexington , Massachusetts , is one such ink suitable for use with the invention . It is a screenable epoxy resin based silver ink . The composition of the dielectric coating 38 of the jumper cable assembly 28 also preferably has a formulation which permits it to be applied by a screen printing operation , and in addition , it should have a desirable degree of flexibility and the ability to adhere to the material of the substrate. One particularly suitable formulation for a dielectric coating is as follows : I ngredient Percentage (by weight) FLEXCOAT (W. R . Grace) 68.38% Diallyl phthalate 5.47% Photoinitiator 1 .37% N-vinyl pyrrolidone 8.21 % Acrylated urethane prepolymer 16.47% Additive-adhesion promotor 0.10% 100% FLEXCOAT is a trademark of W. R . Grace Co. , New York , New York , for a screen printable photopolymer solder resist which rapidly cures through the apDlication of ultraviolet light , and which forms a tough protective film over the circuitry. The added ingredients provide improved printability , flexibility and adhesion properties . The plasticizer, diallyl phthalate is added to increase the flexibility of the dielectric coating so that the coating will not crack or craze when the substrate to which it is applied is flexed or is subject to thermal expansion . One source for dial lyl phthalate is Fisher Scientific Co. , Pittsburgh , Pennsylvania . N-vinyl pyrrolidone is a monofunctional acrylate monomer added to control shrinkage of the cured dielectric coating 24. This monomer is available under the trade name V-PYROL from GAF Corporation , New York , New York . The acrylated urethane prepolymer used in the above example is available under the trade name PURELAST 169 , from Polymer Systems Corporation , New Brunswick , New Jersey. This polymer was added to increase the flexibility of the coating . I RGACURE 651 , available from Ciba Geigy Corporation , Ardsley , New York , was used as the photoinitiator. The adhesion promotor was A186 available from Union Carbide Corporation , Danburv , Connecticut. Generally , the adhesive may be made by mixing electrically conductive particles with a non-conductive adhesive binder . The percent by volume and size of the particles are selected so that the particles are dispersed randomly throughout the mixture as non-contiguous conductive units , with each unit being comprised of one or a plurality of individual particles . Preferably the percent by volume of the conductive particles is less than twenty percent and volumetric ratios of fϊ^teen percent or less are desired . The units are sufficiently spaced apart to preclude electrical conductivity between two or more adjacent conductive areas on the same substrate, but the number of particles is sufficient so that the conductive units provide an electrical contact between the conductive areas on two mating substrates. The following example illustrates one method of preparing an anisotropically conductive adhesive which is suitable for use with the present invention . In this preferred example, 15.82 grams of silver coated nickel spheroids (8 micron diameter , 15% by weight silver) were mixed with 100 grams of a soivated polyester resin blend (33% by weight sol ids) . This resulted in a hot melt anisotropically conductive adhesive composition having 5% by volume of silver coated spheroids . Mixing may be accomplished with a propeller type stirrer at moderate rotations per minute for approximately 15 minutes . Immediately after stirring , the mixture may be screen printed using a 105 mesh stainless steel screen , and the unwanted solvents may be driven off by heating at 125°C for 30 minutes . The resulting adhesive film is substantially dry and non-tacky at room temperature. Also, the resulting dry layer of adhesive possesses a relatively high degree of compliance, which is important in permitting accommodation of different coefficients of thermal expansion between the substrate and components , as well as flexure of the substrate. A suitable soivated polyester resin blend for use in the above example may be obtained from KC Coatings , Inc. of Lenexa , Kansas , and is sold under their designation "9627 MYLAR Clear. " MYLAR is a trademark of E. I . Du Pone de Nemours & Co. , I nc. , Wilmington , Delaware. More particularly, "9627 MYLAR Clear" comprises 29% by weight of a polyester resin , and the solvent comprises 59% butyrolactone and 41% of an aromatic solvent blend SC 150. The dielectric cover layer 244 of the jumper cable assembly 228 preferably comprises a thermoplastic resin , and preferably is the same soivated polyester resin blend employed in the adhesive layer.

Claims: What is Claimed is : 1 . An electric circuit assembly comprising circuit members interconnected by flexible flat cable ( 2) , the cable being comprised of a flexible insulative substrate ( 16 ) , a plurality of adjacent conductors ( 18) dispersed on the substrate ( 1 6) and an insulating cover layer overlying the conductors and adhered to the insulating substrate , the circuit members each have a plurality of adjacent conductive traces on at least one surface thereof, positioned in registry with the conductors of the flat cable, the assembly being characterized in that the cable insulating cover layer (20) is selectively discontinuous , an anisotropical ly conductive adhesive (22) being disposed in a thin film overlying adjacent conductors where the insulating cover layer ( 20) is discontinuous , the anisotropically conductive adhesive (22) being conductive normal to the conductors ( 18) and being nonconductive between adjacent conductors ( 18) , the anisotropically conductive adhesive (22) mechanically securing and .electrically connecting the circuit members to the cable. 2. The electrical circuit assembly as described in claim 1 wherein the conductors ( 18 ) , the insulating cover layer ( 20) and the anisotropically conductive adhesive (22) are screen printable. 3. The electrical circuit assembly as described in claim 1 wherein the conductors (1 8) comprise a conductive ink comprising a solidified polymer having conductive material disposed therein . 4. The electrical circuit assembly as described in claim 1 wherein at least one circuit member comprises a second cable (102) . 5. The electrical circuit assembly as described in claim 4 wherein the selectively discontinuous insulating cover layer (20) defines exposed tap locations (6) intermediate the ends of the cable, the cover layer extending between adjacent tap locations , the second cable conductive traces ( 1 8 ) being electrically connected to the conductors of the tap locations (6) . 6. The electrical circuit assembly as described in claim 5 wherein the conductors ( 18 ) are disposed in laterally adjacent relationship , one conductor laterally adjacent another conductor (18) extending through the tap location , being covered by the insulating cover layer (20) ; conductive ink which forms a conductive pad (26) , being disposed over and extending laterally beyond the other conductor (18) . 7. The electrical circuit assembly as described in claim 1 wherein at least one of the circuit members is a flexible member . 8. The electrical circuit assembly as described in claim 7 wherein the flexible member has an insulating cover (214) , selectively discontinuous along edges overlying adjacent conductive traces (212) . 9. The electrical circuit assembly as described in claim 8 wherein the insulating cover (214) is further discontinuous at selected locations intermediate the edges thereof, the selected locations intermediate the edges thereof, the selected locations overlying adjacent conductive traces (212) . 1 0. The electrical circuit assembly as described in claim 9 wherein anisotripically conductive adhesive (218) is disposed over the selected locations and along the edges . 11 . The electrical circuit assembly as described in claim 10 wherein electrical components are mounted mechanically secured and electrically connected to the circuit assembly at the selected locations intermediate the edges . 12. The electrical circuit assembly as described in claim 11 wherein the electrical components (224) are surface mounted to the circuit assembly. 13. The electrical circuit assembly as described in claims 7 , 10 or 11 wherein the circuit member is a jumper panel attached along one edge of an electroluminescent display, such that the conductive traces of the panel are positioned in registry with corresponding conductors of the display and electrically connected and mechanically secured thereto by means of the anisotropically conductive adhesive (218) . 14. The electrical circuit assembly as described in claims 8 or 11 wherein the circuit member is a jumper panel having a plurality of cables ( 228) attached along a first edge of the panel . 15. The electrical circuit assembly as described in claim 14 wherein a second edge of the jumper panel is attached to an electroluminescent display (226) such that the conductive traces of the panel are positioned in registry with corresponding -) conductors of the display and electrical ly connected and mechanically secured thereto by means of the anisotropically conductive adhesive (218) .

Inventors: DERY RONALD ALLEN, GENTRY WILLIAM GRAY, JONES WARREN CHARLIE, MAY CLIFTON CARL JR, WENTINK STEVEN GEORGE, DERY, RONALD, ALLEN, GENTRY, WILLIAM, GRAY, JONES, WARREN, CHARLIE, MAY, CLIFTON, CARL, JR., WENTINK, STEVEN, GEORGE
Applicants: AMP INC, AMP INCORPORATED
Application year: 1986
Main classification: H01R4
IPC codes: H01R4, H05K1, H05K3