Electrical connector assembly

Abstract: An electrical connector assembly (10) for connecting two circuit members (23, 17) (e.g., printed circuit board, flexible cable) each including a plurality of electrical connectors (15, 19) thereon. The assembly includes a pressure exertion member (21) having a substantially rigid (e.g., metallic) base plate (31), a plurality of compressible, silicone rubber elements (33) attached to one surface of the base plate to provide the desired pressure when compressed, and a resilient member (37) attached to an opposing side of the base plate such that compensation is provided for surface elevation variations in the first and/or second circuit members upon compression of the exertion member. The assembly includes a means (51) (e.g., clamp) for retaining the invention's exertion member against one (e.g., the second) of the circuit members in final assembly. The invention is able to provide sound electrical connection over prolonged periods of time and during exposure to relatively harsh environ­ mental conditions (e.g., high heat and moisture).

Description: The invention relates to electrical connector assemblies and particularly to such assemblies wherein at least two circuits are electrically connected. Even more particularly, the invention relates to such assemblies wherein external pressure is applied to one or both of the circuit components (e.g., printed circuit, flexible cable) to effect the connection. Utilization of electrical connector assemblies for the purpose of electrically coupling various circuit devices is, of course, well known, with several examples being shown and described in the following patents and publications: US-A-3 861 135, US-A-3 883 213, US-A-3 971 610, US-A-4 184 729, US-A-4,602,317 IBM Technical Disclosure Bulletins: Vol. 18, No. 2 (7/75), p. 340; Vol. 22, No. 2 (7/79), pp. 444,445; and Vol. 25, No. 7A (12/82), pp. 3438-3441 In the design of connector assemblies wherein direct contact is desired between the individual electrical conductors (e.g., printed circuit lines, contact pins, etc.) which constitute part of the circuit devices being coupled, as in the case of the instant invention, application of a reliable contact pressure of sufficient duration and capable of withstanding possibly adverse environmental conditions (e.g., heat, moisture) is considered essential. Excessive pressure can result in damage to various components of the assembly (particularly the conductors) during both assembly and/or operation. Additionally, the provision of such pressure has heretofore typically been accomplished through the utilization of relatively large components (e.g., connector housings) needed to produce these assemblies, thus also adding unnecessarily to the cost thereof. In those assemblies subjected to adverse environmental conditions such as mentioned above, failure to withstand same has also resulted in such problems as contact corrosion, reduced contact pressure, increased maintenance costs, etc. The invention as claimed solves the problem of enhancement of the art of electrical connector assemblies and to provide an electrical connector assembly which provides a sound, effective contact pressure in a reliable manner and which is operable in relatively adverse environmental conditions such a high heat and moisture. These and other objects are achieved according to one aspect of the invention through the provision of an electrical connector assembly comprising a first circuit member having a plurality of electrical conductors thereon, a second circuit member also having a plurality of electrical conductors thereon, a pressure exertion member for exerting a predetermined pressure against the second circuit member to thereby cause electrical contact between respective conductors of the two circuit members, and means for retaining the pressure exertion member against the second circuit member to cause exertion of said force. The pressure exertion member includes a substantially rigid base plate, a plurality of compressible elements located on a first side of the base plate to provide the desired contact force when compressed, and a resilient member located on a second side of the base plate for compensating for variations in the surface elevations of the first and/or second circuit members (e.g., the conductors thereon). In accordance with another aspect of the invention there is provided an electrical connector assembly including similar components as the aforementioned assembly except that the assembly's second circuit member includes but a singular conductor (e.g., a ground path) and the corresponding pressure exertion member thus serves to exert its pressure such that this singular conductor effects contact with the defined plurality of conductors of the first member. The connector assembly of the invention provides a sound, reliable contact pressure of relatively low magnitude through the utilization of effective materials which are relatively inexpensive and which can withstand adverse environmental conditions such as excessive heat and moisture. It is believed that such a connector assembly would constitute a significant advancement in the art. It is a still further advantage of the invention to provide a connector assembly possessing, among others, the several features described herein and yet which can be produced on a relatively large scale (e.g., mass production), thus reducing the overall cost thereof in comparison to many known connector assemblies of the prior art. For a better understanding of the invention, together with other objects and advantages in the following disclosure preferred embodiments are described in connection with the drawings in which: FIG. 1 is a side elevational view, in exploded format, of an electrical connector assembly in accordance with one embodiment of the invention, excluding the defined means for retaining the pressure exertion member against the invention's second circuit member (said assembly including the pressure exertion and housing members of FIGS. 3 and 4, respectively); FIG. 2 is a side elevational view of the assembly of FIG. 1, as assembled, further including the aforementioned retaining means; FIG. 3 is a front perspective view of a pressure exertion member in accordance with one embodiment of the invention; FIG. 4 is a perspective view of a housing member which may be utilized with the pressure exertion member illustrated in FIG. 3; FIG. 5 is a side elevational view, in section, of a pressure exertion member in accordance with another embodiment of the invention; FIG. 6 is a partial view, in section, illustrating the expansion of one of the compressible elements of the invention during compression thereof; FIG. 7 is a partial view, in section, illustrating an alternate form of conductors for use with the invention's first (or second) circuit member; FIG. 8 is a partial view, in section, illustrating another embodiment of a second circuit member capable of being used in the instant invention, said second circuit member having a singular conductor adapted for simultaneously contacting the plurality of electrical conductors of the first circuit member; and FIG. 9 is a graph illustrating compressive stress measurements over time and at different temperature levels for compressible elements comprised of a preferred material (silicone rubber), as taught herein, said elements being measured at approximately thirty (30) percent compression. In FIG. 1, there is shown an electrical connector assembly 10 in accordance with a preferred embodiment of the invention, excluding the defined means for retaining the assembly in compression. This means is illustrated in FIG. 2 and will be further described hereinbelow. Assembly 10 includes a first circuit member 13 with a plurality of electrical conductors 15 thereon, a second circuit member 17 including a plurality of conductors 19 thereon, and a pressure (or force) exertion member 21 for providing a predetermined pressure (or force) of relatively low magnitude against one of the circuit members (in FIG. 1, circuit member 17) sufficient to cause the respective conductors 15 and 19 of circuit members 13 and 17, respectively, to contact each other in a sound, effective manner. As understood herein, member 21 assures a sound electrical connection between each of the respective conductors while at the same time uniquely compensating for surface elevation variations in either/both of the circuit members 13 and 17. Specifically, the invention assures sound connection between the conductors thereof despite differences in thickness of such conductors and/or the substrate upon which these are positioned. As further understood, the invention is able to provide this predetermined pressure over a relatively prolonged period of time, despite deleterious conditions such as relatively high heat and/or moisture to which the invention may be subjected. In a preferred embodiment, first circuit member 13 comprises a printed circuit board having a relatively rigid insulative substrate 23. Substrate 23 is preferably of a known material (e.g., epoxy) and includes the defined conductors 15 located along a first surface 25 thereof. Each conductor 15, as shown, is preferably of flat configuration and comprised of a sound metallic conductive material (e.g., copper). Each conductor 15 is positioned on the epoxy substrate 23 using techniques known in the printed circuit art and further description is thus not believed necessary. In one example of the invention, substrate 23 possessed a thickness of about 1,58 mm (0.062 inch) while each of the copper conductive members 15 possessed an average thickness of about 25,4 µm (0.001 inch). As defined, each conductor 15 is substantially flat in configuration and thus constitutes a "metallic pad" to which connection is made. As defined below, such a configuration (flat) is also preferred for the conductors 19 of the invention's second circuit member. Accordingly, the invention provides for sound connection between opposing, relatively flat metallic conductors in the manner depicted herein. It is understood, however, that alternative designs for the described conductors (15, 19) may be utilized, with one such example being a conductive pin (e.g., as shown in FIG. 7 and described hereinbelow). Circuit member 17 preferably comprises a flexible substrate 27 having the described conductors 19 located on an upper surface 29 thereof. As stated, conductors 19 are also preferably of substantially flat configuration and, in one embodiment of the invention were comprised of copper and deposited on substrate 27 using known printed circuit technology. The corresponding flexible substrate in this example was comprised of electrically insulative material (polyimide) and possessed a thickness within the range of about 50,8 µm (0.002 inch) to about 127 µm (0.005 inch), thus assuring the flexibility desired for this component. As stated, connector assembly 10 further includes the aforementioned pressure (or force) exertion member 21 which, as shown in the orientation depicted in FIG. 1, is located substantially below the flexible circuit 17 and, in accordance with a preferred embodiment of the invention, is designed for physically engaging circuit 17 to force it uniformly against the rigid first circuit member 13 when assembly 10 is fully assembled (FIG. 2). Member 21, as also shown in FIG. 3 (the member in FIG. 3 being inverted for illustrative purposes), includes a substantially rigid base plate 31, a plurality of compressible elements 33 located on a first side 35 of plate 31, and a resilient member 37 located substantially on the opposite side of base 31 from element 33. In a preferred embodiment, rigid base plate 31 was comprised of aluminum and possessed a thickness of about 1,27 mm (0.050 inch). Being metallic and of such thickness, plate 31 thus provides the substantial rigidity needed for the invention, but is also uniquely capable of slight bowing (or bending) during operation thereof. Specifically, plate 31 functions to provide distribution thereacross of the individual pressures exerted by each of the compressible elements 33 when said elements are compressed (as in FIG. 2) to exert a combined, uniform pressure against the flexible circuit 17. During this compression, resilient member 37 functions to compensate for any variations in surface elevations for the described circuit members 13 and/or 17. For example, it is also possible to utilize a material other than aluminum as the invention's base plate 31. Other possible materials include plastic and steel. In a preferred embodiment of the invention, assembly 10 also includes an electrically insulative (e.g., plastic) housing 41 (see also FIG. 4) designed for accommodating member 21. As shown, housing 41 includes a plurality of apertures 43 therein each designed for having a respective one of compressible elements 33 positioned therein. Member 21, as illustrated in FIG. 3, is inverted (see arrow) to achieve this positioning. In non-compressed form (prior to such positioning), each of the compressible elements 33 is shown as being substantially smaller than the corresponding aperture 43 into which it will be positioned, thus allowing for necessary expansion (FIG. 6) of each such element during assembly. Such expansion is also illustrated in the sectional view of FIG. 2. With particular attention to FIG. 6, this outward expansion results in a substantially total occupation of a respective aperture 43 by the respective element. Assembly of the invention (and resulting compression of elements 33 to provide the exertion pressures necessary) can be accomplished using any of several techniques, with one representative example being a clamping member 51 (FIG. 2) designed for specifically engaging the outer surfaces of the rigid circuit member 13 and housing 41. Clamp 51 thus serves to contain the first and second circuit members, the compressed exertion member and the insulative housing therebetween. As stated, clamp 51 is only representative of one of several methods for containing the aforementioned four elements. Other techniques, including simple placement of first circuit member 13 upon a surface within a suitable housing or the like and application of a downward or similar pressure or force against the outer surface of housing 41, are readily possible using the teachings of the invention and the invention is thus not limited to the example illustrated. Further description is thus not believed necessary. As shown in the drawings, each of the compressible elements 33 is of a cylindrical configuration. As understood herein, the shape and selection of material for each such element constitute significant aspects of the invention in order to attain the results defined herein. Using a cylindrical configuration, a resulting shape factor is defined as the ratio of the area of one loaded surface (i.e., 61 in FIG. 3) to the element's free surface area (that not subjected to load). In the embodiment represented in FIG. 3, the area of the cylindrical sides of each element represents the free surface area, the load being applied to surface 61. Shape factor is considered significant in that a higher shape factor will result in exertion of higher reactive forces under equivalent compression. In a preferred embodiment, each of the compressible elements 33 possessed an overall height (H in FIG. 3) within the range from about 2,54 mm (0.100 inch) to about 10,16 mm (0.400 inch) and an outer diameter of about 0,635 mm (0.250 inch). In one example, compression of a total number of four elements 33 to an extent of about fifteen percent to about thirty-five percent of the original height thereof resulted in a combined pressure from exertion member 21 within the range of from about 0,69 (ten) to about 2,07 bar (thirty PSI). In a specific example, a total of eighty-eight conductors 19 on flexible circuit 17 was utilized to contact a respective, similar number of conductors on the rigid circuit member 13. In this example, each of twelve elements 33 were compressed about twenty-four percent of its original height and the resulting combined pressure was about 3,04 bar (forty-four PSI) on conductors 19. It is understood that the number of compressible elements 33 required to produce the desired exertion pressure is substantially less than the corresponding number of contacts on each of the described circuit members. It was also determined, from testing and using the shape factors and particular material defined herein, that optimum performance was attained at about twenty percent to thirty percent compression of elements 33, although these elements, as stated, are capable of exerting a combined pressure greater than about 3,04 bar (forty-four PSI) (e.g., 3,45 bar (fifty PSI)) on resilient member 37. The above numbers are representative only and thus not meant to limit the invention. Specifically, additional combinations are possible depending on the overall system requirements. To determine the appropriate number of compressible elements and corresponding characteristics for member 21, a review of the sizes of the contact area (field), the total number of contacts required (and their individual spacing), the necessary contact pressure (or force) required, and the actuation tolerance allowed is made. Applying this information, the contact area is divided into a grid and a determination made of the number of spaces required along the X and Y axis with each such space designed to accommodate one of the compressible elements 33. Each element is thus designed to provide the defined force for the corresponding plurality of contacts within the defined field. From this number of contacts and the required contact normal force, the total force for each element is determined. From the data of the preferred material for the invention (as defined hereinbelow, and having an preferred operating range at about twenty percent to thirty percent compression), including the defined system tolerance, the overall height and compressive distance for each element 33 is ascertained. Knowing the aforementioned information, the equation below, derived from a curve fit and transformations of the below-defined material data (i.e., at twenty-five percent compression), is employed: Element Force = R² (120.5 R H + 430), wherein element force is the required force (pounds), R is the radius of the cylindrical element (inches) and H is the height thereof (inches). From this formula, the element radius (R) is determined. From this result, and knowing the desired element spacing, size, applied force and the assumed or allowed deflection, the overall size for the force distribution base plate 31 is determined. This is essentially a strength of material solution, depending on the desired material (e.g., aluminum or steel) for plate 31, and can be determined using known beam formulations or the like. The size of the resilient, elevation-compensating member 37 can be determined next by applying a predetermined out-of-flat tolerance (e.g, twenty-five percent) of this member's overall thickness. As stated, proper selection of an appropriate resilient material for the invention's compressible elements 33 is essential to achieve the desired results of long term stress retention, relatively low magnitude pressure (as defined herein), and operability at relatively high temperatures and humidity. A preferred material selected for use in the instant invention is a low compression set polysiloxane rubber available from the Dow Corning Corporation and sold under the name Silastic LCS-745U (Silastic is a registered trademark of the Dow Corning Corporation). This clean, low modulous elastomer demonstrates a seventy-five to eighty-five percent retention of residual compressive stress when loaded in constant deflection at an elevated temperature (e.g., 100 °C) for a prolonged period. These results, in addition to those obtained for other measurements taken at different temperatures, are further illustrated in FIG. 9. FIG. 9 represents this data as obtained from cylindrical compressible elements possessing the aforementioned dimensions and compressed at about thirty percent of original height. The aforementioned silicone rubber used for each of the compressible elements 33 is available from the Dow Corning Corporation in stock form. After being press vulcanized, such parts are serviceable (operable) over a temperature range of from about -73° Celsius (C) to +250 °C and possess the highly desired features of good reversion (heat resistance), low compression set and good resistance to hot oils, water and steam. The described silicone rubber, as molded, possesses a durometer hardness (Shore A) of 52, a tensile strength of about 57,2 bar (830 PSI) and an elongation of about 260 percent. In the embodiment of FIG. 3, each silicone rubber element 33 is shown as being attached to the aluminum base plate 35 (e.g., using a suitable (e.g., silicone based) adhesive). Alternatively, elements 33 and the invention's resilient member 37 may be vulcanized to plate 35 during molding. This alternative embodiment is shown in FIG. 5. The preferred resilient material for member 37 in FIG. 3 is also the aforementioned silicone rubber, said material being attached to the other side of plate 31 using the aforementioned adhesive. In the embodiment depicted in FIG. 5, both elements 33 and member 37 are of the same material (preferably silicone rubber) and molded as one integral unit which encases the aluminum plate 35. It is also within the scope of the invention to attach member 33 to plate 31, as described above, and thereafter mold resilient member 37 about the plate and attached members. The total encasement of plate 31 as shown in FIG. 5 is desirable from an operational and/or manufacturing standpoint. In FIG. 7 there is shown an alternate embodiment for the conductors for use with first circuit member 13. Specifically, these conductors are illustrated as comprising metallic pins 71, each including a head portion 73 to which contact is made with the corresponding conductor from the flexible substrate 17 and a protruding portion 75 which extends within the insulative substrate 23 (e.g., to make contact with a respective internal or external circuit path 77). The head portion 73 of each pin may be of substantially flat configuration (as shown) to thus provide a similar shape to that of the "metallic pads" described above. Other configurations for head portion 73 are also possible including those having protrusions, etc. The preferred metallic material for each pin 71 is copper or an alloy thereof (e.g., beryllium copper or phosphor bronze). In FIG. 8, there is shown an alternate embodiment of the invention wherein the described second circuit member 17′ includes but a singular, elongated electrical conductor 19′ as opposed to individual conductors as illustrated in the embodiment of FIGS. 1 and 2. The embodiment of FIG. 8 provides for electrical connection between the individual conductors 15 of a first circuit member such as described herein with a common, singular conductive path (e.g., ground). As in the embodiment of FIG. 1, the insulative (e.g., polyimide) substrate 27 of the flexible circuit 17′ may be attached (e.g., using a suitable adhesive) to the outer surface of resilient member 37. Singular conductor 19′ may be of known conductive material (e.g, copper, chrome-copper-chrome) and formed on substrate 27 using techniques known in the art. In the embodiment of FIG. 8, member 21 serves to exert its combined force against the singular conductor to assure contact with each of the defined metallic pads 15. Thus there has been shown and described an electrical connector assembly wherein sound effective contact is made between pluralities of electrical conductors therein using a pressure exertion member which includes as part thereof a plurality of compressible, silicone rubber elements able to withstand relatively high temperatures and adverse operating conditions to still assure an effective, low magnitude, uniform predetermined pressure. This is achieved by the invention in a facile, relatively inexpensive manner. The defined preferred silicone rubber material is a molded elastomer, and is also readily adaptable for use as the resilient portion of the invention's pressure exertion member to even further facilitate assembly and operation of the invention. As understood herein, it is also within the scope of the invention to employ more than one exertion member in combination with singular, significantly larger first and/or second circuit members, to thus comprise a larger overall structure wherein several conductor members are connected. It is even further within the scope of the invention to utilize such exertion members in such a larger, overall structure wherein circuit members of several different types are employed.

Claims: An electrical connector assembly (10) comprising: a first circuit member (13) including a plurality of electrical conductors (15); a second circuit member (17) including a plurality of electrical conductors (19) or a singular, elongated electrical conductor (19′); a pressure exertion member (21) for exerting a predetermined pressure against said second circuit member to cause each of said electrical conductors or said singular elongated electrical conductor, respectively, or said second circuit member to electrically contact a respective one of said electrical conductors of said first circuit member, said pressure exertion member including a substantially rigid base plate (31), a plurality of compressible elements (33) located on a first side (35) of said base plate for providing said predetermined pressure when compressed, and a resilient member (37) located on a second side of said base plate for compensating for variations in surface elevations in said first and/or second circuit members during exertion of said predetermined pressure against said second circuit member; and means (51) for retaining said pressure exertion member against said second circuit member to cause said compression of said compressible elements and said exertion of said predetermined pressure. The electrical connector assembly according to Claim 1 wherein said first circuit member includes a substantially rigid substrate (23), said plurality of said electrical conductors (15) of said first circuit member being located on said substrate. The electrical connector assembly according to Claim 1 or 2 wherein each of said electrical conductors of said first circuit member comprises a conductive pin having a portion thereof positioned within said substantially rigid substrate. The electrical connector assembly according to any one of the preceding Claims wherein said second circuit member (17) comprises a flexible substrate (27), each of said electrical conductors (19) or said singular elongated electrical conductor, respectively, of said second circuit member being located on said flexible substrate. The electrical connector assembly according to any one of the preceding Claims wherein each of said electrical conductors of said first and/or said second circuit member comprises a metallic pad. The electrical connector assembly according to any one of the preceding Claims wherein said pressure exertion member (21) substantially distributes thereacross the pressure exerted by each of said compressible elements, said compressible elements (33) exerting said pressure against said base plate (31) when said elements are compressed. The electrical connector assembly according to Claim 6 wherein said base plate is comprised of aluminum. The electrical connector assembly according to any one of the preceding Claims wherein said compressible elements are spacedly located on said first side of said base plate. The electrical connector assembly according to any one of the preceding Claims wherein each of said compressible elements is comprised of a resilient, electrically insulative material, preferably silicone rubber. The electrical connector assembly according to any one of the preceding Claims wherein each of said compressible elements is of substantially cylindrical configuration. The electrical connector assembly according to any one of the preceding Claims wherein said predetermined pressure provided by said compressible elements is within the range of from about 0,69 (10) to about 3,45 bar (50 PSI). The electrical connector assembly according to Claim 11 wherein said compressible elements provide said pressure when compressed within the range of from about fifteen to about thirty-five percent of the original height thereof. The electrical connector assembly according to any one of the preceding Claims further including a housing member (41), each of said compressible elements located on said base plate being positioned within said housing. The electrical connector assembly according to Claim 13 wherein said housing includes a plurality of apertures (43) therein, each of said compressible elements being positioned within a respective one of said apertures within said housing. The electrical connector assembly according to Claim 14 wherein each of said apertures is substantially larger than each respective compressible element when said elements are in a non-compressed state, said elements substantially totally occupying said respective apertures when compressed. The electrical connector assembly according to Claim 15 wherein said means for retaining said pressure exertion member against said second circuit member comprises clamping means engaging said housing member and said first circuit member to clamp said second circuit member therebetween.

Inventors: BRODSKY WILLIAM LOUIS, BUYCK WESLEY JOHN, KNIGHT ALAN DOUGLAS, BRODSKY, WILLIAM LOUIS, BUYCK, WESLEY JOHN, KNIGHT, ALAN DOUGLAS
Applicants: IBM, INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1989
Main classification: H01R9
IPC codes: H05K3, H01R12