PRESSURE CONNECTOR FOR FLEXIBLE CABLES AND THE LIKE

Abstract: A flex harness (20) and a printed wiring board are provided (18) with a plurality of bumps (66) on each line (62) so that, upon mating between the flex harness and the printed wiring board, the bumps provide redundant connections therebetween.

Description: PRESSURE CONNECTOR FOR FLEXIBLE CABLES AND THE LIKE BACKGROUND OF THE INVENTION The present invention relates to an electrical connector for coupling flexible flat cables and the like to like devices, such as other flat cables and printed wiring boards and, in particular, for ensuring electrical continuity between their mating electrical leads . Electrical connectors of this type are well known, and are typified by those described in United States Patents 4,453,795 and 4,125,310 and the patents cited therein. It has been found that, in some, when the contact between leads or traces on mating cables/printed wiring boards utilize soft metal bumps or protuberances, the protuberances compress and deform on the mating surface. In order not to press the metal of the contacts beyond its elastic yield point and to ensure mating despite irregularities in flatness of the mating surfaces, pressure to make and retain the contact must be controlled within narrow limits. This pressure also varies depending upon the number of contacts mating at one time; therefore, the unit load per contact must be carefully regulated. Resilient pads or springs are used to alleviate these problems. The size of the contacts is also generally limited to a minimum 25 mil centerline. l SUMMARY OF THE INVENTION The present invention constitutes an improvement over the prior art by utilizing a redundancy of protuberances or bumps on each circuit line, rather 5 than a single bump, and the bumps are made relatively rigid to avoid problems where too great a pressure thereon will flatten the bumps to preclude repeated mating and demating cycling. Several aims and advantages result from such 0 redundancy. The bumps can be formed by several conven¬ tional processing operations. Harder metals, such as of nickel and beryllium copper, may be used because resiliency in the bumps is not needed. A wide range of unit pressures is allowable, up to near their yield 5 points, both to achieve gas-tight joints and to minimize contact discontinuities due to high vibration and shock environments. Because more than one bump contacts each circuit line, any open circuit, which might result from dirt or other contamination on one bump, is 0 avoided. The presence of redundant bumps assures the likelihood of electrical contact of at least one bump. Opens or discontinuties under severe vibration shock are also effectively eliminated. The redundant contacts can be placed on 8 mil centers or smaller. Their 5 smaller size also permits the weight and volume of the system in which they are used to be greatly reduced and/or permits an increase in the number of functions to be interconnected and in a smaller volume. Backup pressurization hardware can be made of less expensive Q materials and processes, such as from injection-molded plastic parts. Other aims and advantages, as well as a more complete understanding of the present invention, will appear from the following explanation of exemplary 5 embodiments and the accompanying drawings thereof. DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of an illustrative connector assembly embodying the present invention for coupling of a flexible flat cable to a printed wiring board, with FIG. la being an enlarged view of one bump in contact with a mating lead; FIG. 2 is a plan view of a flexible cable secured in the assembly shown in FIG. 1; FIG. 2a is an equivalent representation of an en¬ larged view of one end of the flexible cable depicted in FIG. 2; FIG. 3 is a side view in cross-section showing a modification of the present invention for doubling the interconnection capability of that depicted in FIG. 2; and FIG. 4 is a top view of the modification illus¬ trated in FIG. 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG: 1, a connector assembly 10 com¬ prises a pair of pressure plates 14 and 16 for coupling therebetween a printed wiring board 18 and a flexible cable 20. While illustrated as a printed wiring board, printed wiring board 18 may comprise a similar flexible cable as cable 20 (e.g., cable 21 shown in FIG. 5). Pres¬ sure plates 14 and 16 are provided with aligned openings 22 and 24, respectively, numbering four in total, for example. Placed within each of these openings is an align¬ ment pin 26 having a head 28 at one end, a split dowel 30 at its other end, and a connecting shank 32 therebetween. SUBSTITUTE SHEET Opening 24 is provided with a shoulder 34 onto which head 28 itself, or through the intermediary of a rubber spacer 36, rests. Thus, opening 24 narrows to a smaller sized opening 38, and opening 38 and opening 22 are approximately of the same dimension. Screws 40, for example four in number, pass through an opening 42 in plate 16 and threadedly engage threaded holes 44 in plate 14. Each screw 40 is provided with a head 46 which bears against a surface 48 of plate 16 through the intermediary of a lock, washer 49 so that, by turning of the screw, plates 16 and 14 are drawn together, and press cable 20 and printed wiring board 18 into secure contact with one another. To provide an even pressure between the cable and the printed wiring board, a spring 50 is disposed between one of the plates and one of the cable and the printed wiring board. As illustrated, plate 16 is pro¬ vided with a cavity 52 which may include a spacer plate 54. Cavity 52 has a walled enclosure and is thereby adapted to receive and retain spring 50 so that the spring will not fall out of its retainment within plate 16. A second plate 56 is placed on the side of spring 50 opposite from plate 54 so that the pressure of the spring will be applied through plate 56 and, if desired, a conforming silicon rubber pad 58 against cable 20. Spring 50 may comprise a wave spring or an angled helical spring, and there may be a plurality of such springs placed in side by side relationship with one another and retained within cavity 52. As best shown in FIGS. 2 and 2a, flexible cable 20 is formed from a dielectric substrate 60 and electrical traces, leads or lines 62. SUBSTITUTE SHEET The construction of flexible cable 20 and its traces, leads or lines 62 and printed wiring board 18 and its traces, leads or lines 64 is conventional for such combinations as 5 mil lines on 10 mil centers. Placed on each trace 62 of flexible cable 20 (see FIG. 2a) are a plurality of redundant bumps 66, e.g. 3 x 5 mils and 1 to 2 mils in height. Thus, for a trace 62a, a plurality of bumps 66a, illustrated to be six in number, while for any other specific trace, denoted by indicium 62n, six redundant bumps 66n exist thereon. Bumps 66 are formed from an essentially incompressible metal, such as nickel and beryllium copper. To enable proper registration of cable 20 with printed wiring board 18, each is provided with regis- tration holes 70 and 72. For reinforcement, rings of circuitry metal or bushings surround the holes. These are precisely formed in their respective components and are sized to be slightly smaller than split dowels 30 of registration pins 26. The precision in sizing the openings and the dowels are made commensurate with the size of the traces and the bumps. A modification of cable 20 is shown in FIGS. 3 and 4 as a double sided flexible cable 78, in which conductors or leads 80 and 82 are formed on opposite sides of a dielectric substract 84. Here, leads 82 are formed in two segments 82a and 82b with bumps 86a and 86b thereon. As shown, it may be desirable to SUBSTITUTE SHEET electrically couple one or more conductors 80 and 82 and, to this end, feedthrough vias 88 extend from conductor 80 to conductor 82b. Bumps 66 may be formed in any convenient manner, such as by a "plated-up" or an "etched bump" process. For the "plated-up" process, a 2 mil substrate of any suitable polymer, such as of polyimide, has copper, nickel, beryllium copper, etc., cladding on one or both sides. The metal cladding may be deposited as a sheet, a vacuum deposit or sputtered film, etc. Use of resist materials such as a dry film or liquid film resist may be utilized as conventional in the art. Suitable artwork for the leads and bumps is used. The following steps are employed. The metal surfaces are cleaned in preparation for application of the resist. They are then coated with a dry or liquid resist which is then exposed through the line pattern artwork. The line pattern on the resist is then developed and, after removal of portions thereof, the line pattern is etched into the metal by a suitable etchant. The resist is then stripped from the cladding and the line pattern metal is then cleansed, followed by drying and preheating of the thus far processed material. A further coating of resist is applied and a "bump" pattern artwork is aligned on the etched copper line pattern and exposed to form where the bump areas are to be placed. The resist is then developed and the bump areas are cleaned. It is important that the bump areas to be plated are completely clean of resist residue. The metal bumps are then plated to the desired height of the bump, typically 1 - 2 mils. The resist is then stripped from the cable. The bump and line dimensions are measured and adhesion of the bumps is tested. If adhesion is as desired, the bumps may be plated with a gold or other desired finish. The part is then trimmed. In the "etched bump" process, a polymer, such as a polyimide, with metal cladding is cleaned, dried and coated with a resist. The resist is exposed under film artwork of the bump pattern and developed so that the remaining resist protects the bumps while leaving the remainder of the metal cladding exposed. The exposed metal cladding is then etched to leave the bumps at the desired height. The resist is stripped off, the metal surfaces are cleaned and the substrate is dried. Further resist, preferably liquid to ensure a conformance to the surface, is coated over the thus processed assembly, and artwork for the line pattern is placed thereover. The resist is developed and the line pattern is etched to the remaining sheet thickness of the metal. The resist is stripped, all important dimensions are measured and, if acceptable, gold or other metal is plated to form a finish, followed by trimming the part. Although the invention has been described with respect to particular embodiments thereof, it should be realized that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

Claims: CLAIMS What is Claimed is: 1. An electrical connector for ensuring secure electrical contact between a pair of electrical leads respectively on matable surfaces of supports of dielectric material, comprising a plurality of bumps of electrically conductive material positioned between the leads. 2. An electrical connector according to Claim 1 in which each of said bumps is 3 by 5 mils and 1 to 2 mils in height. 3. An electrical connector according to Claim 1 in which said bumps are essentially incompressible, and further comprising means for resiliently clamping said supports and said surfaces thereon together. 4. An electrical connector according to Claim 1 in which said bumps are integral with a first of said leads and pressed into contact with a second of said leads. 5. An electrical connector according to Claim 4 further comprising a pair of rigid plates placed against said support for pressing said surfaces together. 6. An electrical connector according to Claim 5 further comprising means in said plates and in said supports for registering said supports and thereby said leads in alignment. 7. An electrical connector according to Claim 6 further including resilient means positioned between one of said plates and one of said supports for resiliently pressing said bumps against said second lead. 8. An electrical connector according to Claim 7 in which one of said plates includes means defining a cavity for receipt and retention of said resilient means. 9. An electrical connector according to Claim 8 in which said resilient means comprises at least one wave spring. 10. An electrical connector according to Claim 8 in which said resilient means comprises at least one angled helical spring. 11. An electrical connector according to Claim 10 in which said registration means comprises pairs of openings respectively in said supports and said plates and at least two dowel spring pins extending respectively through said openings. 12. An electrical connector according to Claim 11 wherein said dowel pins respectively have a portion which is partially split and whose diameter is slightly larger than that of said openings. 13. An electrical connector according to Claim 12 further including screw means extending from one of said plates into threaded engagement with the other of said plates for affixing said plates together. 14. An electrical connector according to Claim 6 in which said registration means comprises pairs of openings respectively in said supports and said plates and at least two dowel spring pins extending respectively through said openings. 15. An electrical connector according to Claim 14 wherein said dowel pins respectively have a portion which is partially split and whose diameter is slightly larger than that of said openings. 16. An electrical connector according to Claim 15 further including screw means extending from one of said plates into threaded engagement with the other of said plates for affixing said plates together. 17. An electrical connector according to Claim 1 in which said supports both comprise flexible flat cables. 18. An electrical connector according to Claim 1 in which said support respectively comprise a flexible flat cable and a printed wiring board. 19. An electrical connector according to Claim 1 in which said supports include a plurality of said pairs of leads, with a plurality of said bumps formed on a first of said leads of said pairs of leads, having a plurality of said first leads on one surface thereof and a plurality of leads on a second surface thereof, and at least one feedthrough via electrically and mechanically coupling leads on opposite sides of said flat cable. 20. An electrical connector according to Claim 1 in which said bumps comprise a substantially rigid metal formed integrally with said leads of one of said pair of leads and protruding therefrom. 21. An electrical connector according to Claim 20 in which said bumps comprise one of nickel and beryllium copper plated with gold.

Inventors: LAWRENCE ROBERT, PATEL ASHOK B, LAWRENCE, ROBERT, PATEL, ASHOK, B.
Applicants: HUGHES AIRCRAFT CO, HUGHES AIRCRAFT COMPANY
Application year: 1987
Main classification: H01R9
IPC codes: H01R12, H01R13, H05K3