Abstract:
A connector for board-to-board and board-to-device interconnect applications includes a plurality of conductive elastomeric columnar contacts arranged in a contact array and retained in a first plurality of openings in an insulative substrate and a plurality of stops retained in a second plurality of openings in the insulative substrate. The stops are dispersed among the contacts of the contact array or positioned on the periphery of the contact array and located in non-abutting relation with respect to adjacent contacts. The contacts and the stops have opposing end surfaces and the end surfaces of the contacts are located a greater distance from the substrate than the end surfaces of the stops such that the stops limit the compression of the elastomeric contacts when the connector is disposed in its intended mounting orientation.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. patent application Ser. No. 10/315,298 filed Dec. 10, 2002, now U.S. Pat. No. 6,669,490. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     N/A 
     BACKGROUND OF THE INVENTION 
     The present invention relates to connectors and more specifically to an interconnect system that utilizes conductive elastomeric columnar contacts to achieve conductive interconnection between opposing arrays of conductive contact pads. 
     Interconnect devices using elastomeric conductive members are known. One such interconnect device is disclosed in U.S. Pat. No. 6,056,557. In this interconnect device, conductive resilient members are disposed in holes in a substrate on a predetermined grid array and the assembly is positioned between adjacent printed circuit boards so as to make conductive contact between conductive pads on opposing boards. 
     Other connectors employing conductive elastomeric columns are disclosed in U.S. Pat. Nos. 5,599,193, 5,624,268, 6,271,482 and 6,348,659. 
     In board to device interconnect applications, such as board to Land Grid Array (LGA) or Ball Grid Array (BGA) devices it is important to maintain accurate positioning of the respective columnar contacts while avoiding distortion of the conductive elements that can result from the application of axial compressive forces to the contacts of the connector. 
     Accordingly, it would be desirable to have a connector system that employs conductive elastomeric columnar contacts that permit board to board or board to device interconnections and that maintain accurate alignment of the contacts in a predetermined array pattern. It would further be desirable for the contact positioning and shape to be resistant to distortion due to applied compressive forces that might adversely affect either the conductivity or positional accuracy of the contacts. 
     BRIEF SUMMARY OF THE INVENTION 
     A connector for use in interconnect applications comprises a plurality of conductive elastomeric columnar contacts retained in an insulating substrate and arranged in a predetermined pattern. The elastomeric columnar contacts are each surrounded by a support column molded of an insulative polymer, such as silicone. In one embodiment, the support columns have a generally cylindral outer surface. The support columns provide mechanical support for and tend to reduce the deformation of the conductive elastomeric columnar contacts when the columnar contacts are subjected to compressive axial forces. Additionally, intermediate columns are formed between at least some of the support columns. The intermediate columns serve as mechanical stops and resist further compression of the connector in response to the application of excessive axial compressive forces to the contacts and the support columns. The location of the intermediate columns corresponds to the location of injection ports used in the molding of the intermediate columns and the support columns. Passageways are provided in the mold that allow for the flow of material from the point of injection at the respective intermediate column to one or more adjacent support columns. Insulative bridges are thus formed between the intermediate columns and the support columns in the location of such passageways. The height of the bridges above the substrate is equal to or less than the height of the intermediate columns above the substrate. 
     In one embodiment of the invention, a plurality of conductive elastomeric columnar contacts are supported by and retained in a substrate, such as a polyimide sheet, to form a contact assembly. The contact assembly is positioned in a mold and an insulative polymer, such as silicon, is injected into the mold to form the support columns and the intermediate columns. The columnar contacts have opposing tips that protrude slightly beyond the respective opposing end surfaces of the support columns to allow the tips of the columnar contacts to make conductive contact with corresponding pads located on printed circuit boards, an LGA device or a BGA device, as applicable. The height of the end surfaces of the intermediate columns is specified to serve as a mechanical stop so as to resist further compression of the connector in response to the application of excessive axial compressive forces on the contacts and the support columns. 
     A connector in accordance with the present invention may be produced by molding the conductive elastomeric columnar contacts in a first molding operation and by molding the support columns, the intermediate columns and the insulative bridges as an integral structure in a second molding operation. 
     In another embodiment of the invention an insulative substrate such as a polyimide sheet is provided having first and second pluralities of openings arranged in first and second hole patterns. Conductive elastomeric contact members are provided that extend through the first plurality of openings to form a contact member array, and insulative polymer columns or stops are provided that extend through the second plurality of openings. The contact members extend from the substrate a greater distance than the stops. The stops serve to limit the compression on the conductive elastomeric contact members when the connector is disposed between opposed contacting surfaces. In this manner, overstress on the conductive elastomeric contact members is avoided. The stops are located in non-abutting relation with respect to the contact members and may be selectively positioned within the array of contact members or on the periphery of the contact member array. The contact members and stops include a generally circumferential recess defining opposing shoulders, and the substrate is captured between the opposing shoulders of the recesses in the contact members and the stops to retain the contact members and the stops in position within the substrate. 
     The contact members and stops may be formed in first and second molding operations as discussed above. 
     Other features, aspects and advantages of the above described connector and methods of making the same will be apparent to those of ordinary skill in the art from the detailed description of the invention that follows. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The invention will be more fully understood by reference to the following Detailed Description of the Invention in conjunction with the drawing of which: 
     FIG. 1 is a perspective view of a connector in accordance with the present invention; 
     FIG. 2 is a perspective view of a contact assembly employed in the connector of FIG. 1; 
     FIG. 3 is a top plan view of the connector of FIG. 1; 
     FIG. 4 is a cross-sectional view of the connector of FIG. 3 along a portion of section ZZ; 
     FIG. 5 is perspective view of an enlarged portion of the connector depicted in FIG. 2; 
     FIG. 6A is a perspective view of a connector depicting another embodiment of the invention; 
     FIG. 6B is a side cross-sectional view of the substrate depicted in FIG. 6 a  without the contacts or stops in place; and 
     FIG. 6C is a side cross-sectional view of the connector of FIG.  6 A. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A connector for making a board-to-board or board to device electrical interconnection and a method for making the connector is disclosed. Referring to FIGS. 1-5, the connector  10  includes an insulative substrate  12  such as a polyimide sheet (e.g. Kapton(™)), and a plurality of conductive elastomeric columnar contacts  14  retained within the substrate  12 . The columnar contacts  14  and the substrate  12  form a contact assembly  16  that is subsequently discussed in greater detail. The connector  10  includes generally cylindrical insulative support columns  18  that surround and abut the columnar contacts  14 . Additionally the connector  10  includes insulative intermediate columns  20 . Each of the intermediate columns  20  is disposed adjacent to selected group of one or more support columns  18 . Each support column  20  surrounds a single elastomeric columnar contact  14  and provides mechanical support for the respective contact. Insulative bridges  22  extend between each intermediate column  20  and at least one adjacent support columns  18  within the respective selected group of support columns  18 . The insulative bridges  22  are the by product of passageways within a mold that allow for molding of the support columns  18  by the injection of fluid insulative material via ports that are located at the respective sites of the intermediate columns  20 . The injected insulative material flows through the passageways into the mold areas that define the intermediate columns, the support columns  18  and the bridges  22  and remain in the passageways that define the bridges following the curing of the insulative material. 
     The columnar contacts  14  are retained within the substrate  12  in a predetermined array and, in one embodiment the support columns  18 , the intermediate columns  20  and the bridges  22  are molded as an integral structure out of an insulative polymer, such as silicone. 
     The insulative substrate  12  includes first and second pluralities of holes arranged in first and second respective hole arrays. Except for holes at the edge of the array, each of the holes in the second plurality of holes is surrounded by holes within the first hole array. The size of the substrate may vary based on the particular application. For example, alignment holes may be provided in the substrate  12  outboard of the first and second pluralities of holes. The contact assembly  16  is formed by molding conductive elastomeric contacts  14  in a predetermined array such that the contacts  14  extend through selected ones of said first plurality of holes and are captively retained within the substrate  12 . The conductive elastomeric contacts  14  may be formed via any process known in the art. In the illustrative embodiment, the portion of the columnar contact  14  extending from the substrate  12  is in the form of a frustum with the largest diameter of the frustrum adjacent the substrate  12 . It should be appreciated however, that any suitable columnar shape may be employed for the columnar contacts  14 . 
     In a first molding operation, the substrate  12  is inserted into a first mold and a conductive elastomeric material is injected into the mold to form the plurality of integral columnar contacts  14  so that the columnar contacts  14  extend from either side of the substrate  12 . The diameter of the contacts  14  at the point at which the contacts abut the substrate  12  is greater than the diameter of the corresponding hole in the substrate  12  through which the columnar contact  14  extends. Consequently, following curing of the conductive elastomeric material to form the conductive contacts  14 , the contacts  14  extend outward from opposing sides of the substrate  12  and are captively retained within the substrate  12 . The first plurality of holes in the substrate  14  may be provided on a first predetermined grid, and the columnar contacts  14  may be molded so as to produce a contact assembly  16  having columnar contacts  14  captively retained in the substrate on the first predetermined grid. 
     The insulative support columns  18  and the insulative intermediate columns  20  connected by the insulative bridges  22  may be formed as an integral structure in a second molding operation. In the second molding operation, the contact assembly  16  is aligned within a mold and an insulative polymer is injected into the mold at the site of the intermediate columns  20  to form the support columns  18 , the intermediate columns  20  and the bridges  22  as a unitary integral structure. The intermediate columns  20  extend through selected ones of the second plurality holes in the substrate  12 . 
     The support columns  18  generally have a cylindrical outer surface, as indicated above, and surround and abut the respective columnar contacts  14 . Except for the insulative bridges, the support columns  18  and the intermediate columns are generally free standing cylindrical columnar structures in the illustrated embodiment although other cross-sections may be fabricated. The contacts  14  have opposing contact tips  24  that protrude slightly beyond the respective end surfaces  26  of support columns  18 . The support columns  18  provide support for the conductive columnar contacts  14  and resist deformation of the contacts  14  when the connector  10  is mounted between two printed circuit boards or between a printed circuit board and a BGA or LGA device and is subjected to axial compressive forces. 
     To further resist deformation of the contacts  14  the intermediate columns  20  are formed between groups of support columns  18  and corresponding contacts  14 . The opposing ends of the intermediate columns  20  are generally planar and serve as stops that resist compression of the connector in response to the application of excessive axial compressive forces on the columnar contacts  14  and the support columns  18 . The outer surface of at least a portion of each intermediate column  20  is spaced equidistant from the outer surfaces of adjacent support columns  18  in one embodiment. Any desired number of intermediate columns  20  may be employed and the intermediate columns  20  may be interspersed within the array of support columns  18 . 
     The intermediate columns  20  extend above and below opposing sides of the substrate  12  and through selected ones of the second plurality of holes in the substrate  12 . The intermediate columns  20  have generally planar opposing end surfaces  28  that are spaced from the surface of the respective substrate  12  by a first predetermined distance. The support columns  18  have opposing end surfaces  26  that are spaced from the respective surface of the substrate  12  by a second predetermined distance. The first predetermined distance is less than the second predetermined distance in the presently disclosed embodiment. Accordingly, the intermediate columns  20  serve as stop flanges that effectively limit the amount of vertical compression of the columnar contacts  14  and the support columns  18  that can occur before the surface of the applicable printed circuit board, LGA or BGA device bottoms out on the end surfaces  28  of the intermediate columns  20 . 
     While the tips of the columnar contacts  14  are depicted as being generally planar at the tip ends, the tips may be hemispherical, conical or of any other suitable shape to engage a mating contact pad. 
     Another embodiment of a connector in accordance with the present invention is depicted in FIGS. 6A-6C. The connector  40  includes an insulative substrate  42  such as a polyimide sheet, and a plurality of conductive elastomeric columnar contacts  44  retained in openings  46  (see FIG. 6B) arranged in a predetermined array within the substrate  42 . The columnar contacts  44  include a circular recess  48  (see FIG. 6C) around the circumference of the contacts  44  sized to capture the substrate  42  between opposing shoulders  50  of the recess  48 . The contacts  44  have opposing ends  54   a ,  54   b  that define a contact height  52 . One end  54   a  of each contact  44  extends above a first surface  42   a  of the substrate  42  by a first height  58   a  and the opposing end  54   b  of the contact extends below the opposing surface  42   b  of the substrate  42  by a second height  58   b , which is equal to the first height  58   a  in the illustrated embodiment. It is recognized however, that the first and second heights  58   a ,  58   b  need not be equal. The portions of the columnar contacts  44  extending from the substrate  42  may be frustums, generally cylindrical, or any other suitable shape. 
     The substrate  42  further includes a second plurality of openings  60  (see FIG. 6B) selectively positioned within the array formed by the first plurality of openings  46  for the contacts  44 . As illustrated in FIG. 6C, insulative polymer columns or stops  62  are mounted within the second plurality of openings  60 . The stops  62  are spaced from the columnar contacts  44 . The polymer stops  62  serve to limit the compression of the contacts  44  when the connector  40  is disposed in a mounting position between opposing contact surfaces. More specifically, the polymer stops  62  each have a recess  64  around the circumference of the stops  62 . The stops  62  capture the substrate  42  between opposing shoulders  66  of the recesses  64  to securely mount the stops  62  within the openings  60  through the substrate  42 . 
     The polymer stops  62  may be fabricated of silicone or any other suitable insulative material. Additionally, in certain applications, it may be preferable to fabricate the stops from a conductive material. The portions of the polymer stops extending from the substrate  42  may be frustums, generally cylindrical, or any other suitable shape. 
     The polymer stops  62  extend above the first surface  42   a  of the insulative substrate  42  by a height  68   a  that is less than the height  58   a , and the polymer stops  62  extend below the second surface  42   b  of the insulative substrate  42  by a height  68   b  that is less that the second height  58   b . Thus, when the connector  40  is disposed in a mounting position and compressed between surfaces having electrical contacts disposed thereon, the conductive elastomeric contacts  44  compress until the polymer stops  62  limit further compression of the contacts  44 . In this manner, the desired amount of compression may be obtained and overstress on the columnar contacts  44  is avoided. 
     In the embodiment depicted in FIG. 6A, the stops  62  are positioned within the array of columnar contacts  44 . It should be noted however, that some or all of the stops  62  may be located outside the perimeter of the columnar contact array. When the stops  62  are located on the periphery of the array of columnar contacts  44 , rectangular shaped stops may be employed in addition to the stop shapes previously described. 
     It will be appreciated by those of ordinary skill in the art that modifications to and variations of the above described connectors and methods of producing the same may be made without departing from the inventive concepts disclosed herein. Accordingly, the invention should not be viewed as limited except as by the scope and spirit of the appended claims.