Patent Publication Number: US-7585173-B2

Title: Elastomeric electrical contact

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to electrical contacts, and more particularly, to elastomeric electrical contacts. 
     Interconnect devices are sometimes used to provide electrical connection between different electrical components, such as, but not limited to, integrated circuits and printed circuit boards, for example when removal, replacement, and/or testing of the electrical components is desired. Many of these electrical components have electrical contacts arranged in a “land grid array” (LGA) which is a two-dimensional array of contact pads. One type of interconnect device, known as an “interposer”, has an array of compressible contacts which is placed between the two opposing arrays of the electrical components to provide an electrical connection between the electrical contacts of the opposing arrays. 
     Establishing reliable contact between the electrical contacts of the opposing electrical component arrays and the electrical contacts of the interposer may sometimes be difficult due to, for example, height variations between electrical contacts of the opposing electrical component arrays and/or the electrical contacts of the interposer. Variations in thickness and/or warping of any of the substrates supporting the opposing electrical contact arrays and the interposer may also cause difficulty establishing reliable contact. Many interconnect devices use elastomeric electrical contacts that are compressed between the electrical contacts of the opposing electrical component arrays such that the elastomeric electrical contacts apply a mechanical force to the electrical contacts to facilitate establishing and maintaining reliable electrical contact between the opposing electrical component arrays. Compression of the elastomeric electrical contacts also allows for some degree of nonplanarity between, and/or misalignment of, the electrical contacts of the opposing electrical component arrays that may be caused by the warping, variations of height, and/or variations of thickness described above. 
     Elastomeric electrical contacts typically include an elastomeric body and electrically conducting pathway. Some known elastomeric electrical contacts, sometimes referred to as “filled elastomers”, include an elastomeric body having an interior that is filled with one or more electrically conducting materials. However, filled elastomers may have a limited elastic working range because of the amount of conducting filler needed to reach the percolation threshold and conduct a predetermined amount of electrical current, which may increase contact forces above desired levels. Other known elastomeric electrical contacts include an elastomeric body that includes an electrically conductive pathway formed on an exterior of the elastomeric body. Elastomeric electrical contacts having an electrically conductive pathway on an exterior thereof may have a higher elastic working range than filled elastomeric electrical contacts. However, the electrically conductive pathway may have a lower current carrying capability than filled elastomeric electrical contacts. For example, the dimensions of the electrically conductive pathway may be limited by the desired elastic working range of the elastomeric body. Specifically, if the electrically conductive pathway is formed too large, it may limit the elastic working range of the elastomeric body or the electrically conductive pathway. However, if the conductive pathway is formed too small, it may not carry a desired level of electrical current. Moreover, if formed too small, the conductive pathway may crack and/or fracture during compression of the elastomeric body such that the electrical circuit is broken. 
     What is needed therefore is an elastomeric electrical contact that has a higher current carrying capability than known elastomeric electrical contacts having exterior electrically conductive pathways while maintaining a predetermined elastic working range without cracking and/or fracture of the pathway. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one embodiment, an electrical contact is provided that includes an elastomeric body extending between a base portion and a mating end portion. The elastomeric body includes a ledge extending from the mating end portion to the base portion of the elastomeric body. The ledge is defined by a portion of the elastomeric body. An electrically conductive pad extends over at least a portion of the mating end portion. An electrically conductive trace is formed on a surface of the ledge. The electrically conductive trace extends from the mating end portion to the base portion of the elastomeric body. The electrically conductive trace is in electrical contact with the electrically conductive pad for electrically connecting the electrically conductive pad with an electrically conductive element engaging the base portion of the elastomeric body. 
     In another embodiment, an interposer for electrically connecting a pair of electrical components is provided. The interposer includes a substrate including an electrically conductive element, and an electrical contact mounted on the substrate. The electrical contact includes a first elastomeric portion having a first mating end portion and a first ledge. The first ledge is defined by a portion of the first elastomeric portion. A second elastomeric portion has a second mating end portion and a second ledge. The second ledge is defined by a portion of the second elastomeric portion. First and second electrically conductive pads extend over at least a portion of the first and second mating end portions, respectively. First and second electrically conductive traces are formed on a surface of the first and second ledges, respectively. The first electrically conductive trace is in electrical contact with the first electrically conductive pad and the electrically conductive element. The second electrically conductive trace is in electrical contact with the second electrically conductive pad and the electrically conductive element such that the first and second electrically conductive pads are electrically connected. 
     In another embodiment, an electrical contact is provided that includes an elastomeric body extending between a base portion and a mating end portion, an electrically conductive pad extending over at least a portion of the mating end portion, the electrically conductive pad comprising a generally planar portion, and an electrically conductive trace formed on an exterior surface of the elastomeric body. The electrically conductive trace extends from the mating end portion to the base portion of the elastomeric body. An exposed surface of the electrically conductive trace faces in a direction generally toward the plane of the generally planar portion of the electrically conductive pad. The electrically conductive trace being in electrical contact with the electrically conductive pad for electrically connecting the electrically conductive pad with a conductive element engaging the base portion of the elastomeric body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front elevation exploded view of an electrical component assembly formed in accordance with an embodiment of the present invention. 
         FIG. 2  is a cross-sectional view of a portion of an interposer shown in  FIG. 1  formed in accordance with an embodiment of the present invention. 
         FIG. 3  is a perspective view of a portion of an elastomeric electrical contact shown in  FIGS. 1 and 2  formed in accordance with an embodiment of the present invention. 
         FIG. 4  is a front elevation view of the electrical component assembly shown in  FIG. 1 . 
         FIG. 5  is a perspective view of an electrical component assembly formed in accordance with an alternative embodiment of the present invention. 
         FIG. 6  is a front elevation view of an electrical component assembly formed in accordance with another alternative embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a front elevation exploded view of an electrical component assembly  10  formed in accordance with an embodiment of the present invention. The assembly  10  includes a pair of electrical components  12 ,  14 , and an interposer  16  for electrically connecting the electrical components  12 ,  14 . The electrical components  12 ,  14  each include a respective array  18 ,  20  of a plurality of electrical contacts  22 ,  24  on opposing surfaces  26 ,  28  thereof, respectively. The array  18  of the electrical component  12  substantially matches the pattern of the array  20  of the electrical component  14 . The interposer  16  includes an array  30  of a plurality of elastomeric electrical contacts  32  for electrically connecting the arrays  18 ,  20  of the electrical components  12 ,  14 . The array  30  of the interposer  16  substantially matches the pattern of the arrays  18 ,  20  of the electrical components  12 ,  14 , respectively. 
     The electrical components  12 ,  14  may each be any suitable type of electrical component, such as, but not limited to, printed circuit boards, integrated circuits, electrical modules, and/or other electrical devices. The arrays  18 ,  20  may each be any suitable type of array of electrical contacts that enables operative electrical connection between the electrical components  12 ,  14 , such as, but not limited to, Pin Grid Arrays (PGAs), Land Grid Arrays (LGAs), and/or Ball Grid Arrays (BGAs). Moreover, the arrays  18 ,  20  may have any suitable configuration, arrangement, and/or pattern of electrical contacts that enables operative electrical connection between the electrical components  12 ,  14 . 
       FIG. 2  is a cross-sectional view of a portion of the interposer  16  formed in accordance with an embodiment of the present invention. The interposer  16  includes a substrate  34  that supports the elastomeric electrical contacts  32  and includes opposite surfaces  36 ,  38 . The elastomeric electrical contacts  32  each include two substantially identical portions  40  each located on one of the opposite surfaces  36 ,  38  of the substrate  34 . As will be described in more detail below, the two portions  40  of each electrical contact  32  are electrically connected via a conducting element  44 . In the exemplary embodiment, the substrate  34  includes a plurality of through holes  46  that are each coated with the conductive element  44  such that the conductive element  44  extends about at least a portion of a circumference of the corresponding through hole  46 . Optionally, some or all of the coated through holes  46  are grounded using any suitable means, such as, but not limited to, ground traces  48  on the substrate  34 . The holes  46  are arranged in a pattern that substantially matches the pattern of each of the electrical contact arrays  18 ,  20  (shown in  FIG. 1 ) of the electrical components  12 ,  14  (shown in  FIG. 1 ), respectively. In the exemplary embodiment, the elastomeric electrical contact portions  40  are partially received within the corresponding through holes  46  to facilitate fastening the portions  40  to the substrate  34  and aligning each portion  40  with the pattern of its corresponding array  18 ,  20 . Additionally or alternatively, each elastomeric electrical contact portion  40  may be fastened to the substrate  34  using any suitable fastener, such as, but not limited to, an adhesive. The two substantially identical portions  40  located on the opposite surfaces  36 ,  38  of the substrate  34  may optionally be connected together at base portions  52  (shown in  FIG. 3 ) thereof such that the opposite portions  40  form an integral structure extending completely through the corresponding through hole  46 , whether the portions  40  are formed integrally or attached together. 
     Alternatively, the substrate  34  and the electrically conductive elements  44  may have other arrangements and/or configurations besides coated through holes that enable the conductive elements  44  to electrically connect the portions  40  of each elastomeric electrical contact  32 . Moreover, although shown as extending over the surfaces  36 ,  38 , the conductive elements  44  may only extend over interior surfaces of the substrate that define the through holes  46 . 
     The conductive elements  44  may be fabricated from any suitable material(s) that enable the conductive elements  44  to function as described herein, such as, but not limited to, copper, aluminum, silver, nickel, palladium, platinum, rhodium, rhenium, tin, and/or gold. Non-noble metals covered with a conductive layer may be used as a base material(s) to provide strength and/or rigidity. Such non-noble metals may be covered with a barrier metal that is covered with a surface structure of a noble metal to ensure chemical inertness and provide suitable asperity distribution to facilitate good metal-to-metal contact. The substrate  34  may be fabricated from any suitable material(s) that enables the substrate  34  to function as described herein, such as, but not limited to polyimide, polyester, epoxy, other materials having a low and uniform dielectric constant, and/or electrically conductive materials, such as, but not limited to, stainless steel. In some embodiments, the substrate  34  is fabricated entirely from one or more materials having a low and uniform dielectric constant (excluding any conducting elements, traces, and the like, e.g., the elements  44  and the traces  48 ). Alternatively, the substrate  34  is fabricated from one or more conductive materials, such as, but not limited to, stainless steel, that is at least partially covered with one or more materials having a low and uniform dielectric constant. The dielectric properties of the substrate  34  facilitate shielding the electrical contacts  32  from each other. Additionally or alternatively, each electrical contact portion  40  may be at least partially covered by one or more shielding layers of any suitable material(s). 
       FIG. 3  is a perspective view of a portion  40  of an elastomeric electrical contact  32  formed in accordance with an embodiment of the present invention. Each portion  40  of each elastomeric electrical contact  32  is substantially identical, except for their locations on the corresponding surface  36 ,  38  (shown in  FIG. 2 ) of the substrate  34  (shown in  FIG. 2 ). For clarity, only one portion  40  of an elastomeric electrical contact  32  is shown in  FIG. 3 . The elastomeric electrical contact portion  40  includes an elastomeric body  50  extending from a base portion  52  to a mating end portion  54 . Each base portion  52  engages a corresponding conductive element  44  on the substrate  34 , as is shown in  FIG. 2 . In the exemplary embodiment, each base portion  52  is partially received in a corresponding through hole  46  (shown in  FIG. 2 ) of the substrate  34 . The elastomeric bodies  50  are compressible such that they apply a mechanical force to the electrical contacts  22 ,  24  (shown in  FIG. 1 ) of the arrays  18 ,  20  (shown in  FIG. 1 ), respectively, when the electrical components  12 ,  14  are mechanically connected together. 
     An electrically conductive pad  56  extends over the mating end portion  54  of the elastomeric body  50 . The pad  56  engages a corresponding electrical contact  22 ,  24  of the corresponding array  18 ,  20 , respectively, to electrically connect the electrical contacts  22 ,  24  with the corresponding electrical contact  32 , as will be described below in more detail. The electrically conductive pad  56  may also facilitate preventing siloxane contamination at the interface of the pad  56  and the corresponding electrical contact  22 ,  24 . Although shown as generally planar, the electrically conductive pad  56  may have any suitable shape, whether completely or partially planar, and may cover any portion of the mating end portion  54  of the elastomeric body  50  that enables the conductive pad  56  to function as described herein. 
     The elastomeric body  50  includes a ledge  58  extending about an exterior thereof. The ledge  58  extends from the mating end portion  54  to the base portion  52  of the elastomeric body  50 . An electrically conductive trace  60  is formed on a surface  62  of the ledge  58 . The electrically conductive trace  60  extends from the mating end portion  54  to the base portion  52  of the elastomeric body  50 . The electrically conductive trace  60  is in electrical contact with the electrically conductive pad  56  at an end  64  thereof. An opposite end  66  of the electrically conductive trace  60  is positioned such that when the base portion  52  of the elastomeric body  50  is engaged with the corresponding conductive element  44 , the conductive trace  60  is in electrical contact with the corresponding conductive element  44 . Accordingly, when the base portion  52  is engaged with the corresponding conductive element  44 , the electrically conductive pad  56  is electrically connected to its corresponding conductive element  44  via the electrically conductive trace  60 . The size of the electrically conductive trace  60  may be selected to provide a predetermined current carrying capability as well as provide sufficient support for the trace  60  such that the trace  60  does not crack and/or fracture for a predetermined elastic working range of the elastomeric body  50 . 
     The ledge  58  and the electrically conductive trace  60  may each have any suitable shape and follow any suitable path about the elastomeric body  50  that enables them to function as described herein. In the exemplary embodiment, the ledge  58  and the trace  60  each extend in a generally helical path about the elastomeric body  50 . Moreover, in the exemplary embodiment, an exposed surface  68  of the trace  60  faces in a direction generally toward a plane  70  of the generally planar electrically conductive pad  56 . The plane  70  of the electrically conductive pad  56  extends, in the exemplary embodiment, generally perpendicularly to a longitudinal axis  72  of the elastomeric body  50 . However, in embodiments where the electrically conductive pad  56  does not define a plane that extends generally perpendicularly to the longitudinal axis  72 , the trace  60  may face in a direction generally toward a plane (not shown) that extends generally perpendicularly to the longitudinal axis  72 . 
     The electrically conductive trace  60  may be formed on the ledge  58  using any suitable means, method(s), and/or process(es), such as, but not limited to, electroplating, physical vapor deposition, evaporation, sputtering, chemical vapor deposition, and/or direct metal printing. The electrically conductive trace  60  may be fabricated from any suitable material(s) that enable the trace  60  to function as described herein, such as, but not limited to, copper, aluminum, silver, nickel, palladium, platinum, rhodium, rhenium, tin, and/or gold. Non-noble metals covered with a conductive layer may be used as a base material(s) to provide strength and/or rigidity. Such non-noble metals may be covered with a barrier metal that is covered with a surface structure of a noble metal to ensure chemical inertness and provide suitable asperity distribution to facilitate good metal-to-metal contact. 
     The conductive pad  56  may be fabricated from any suitable material(s) that enable the conductive pad  56  to function as described herein, such as, but not limited to, copper, aluminum, silver, nickel, palladium, platinum, rhodium, rhenium, tin, and/or gold. Non-noble metals covered with a conductive layer may be used as a base material(s) to provide strength and/or rigidity. Such non-noble metals may be covered with a barrier metal that is covered with a surface structure of a noble metal to ensure chemical inertness and provide suitable asperity distribution to facilitate good metal-to-metal contact. 
     The elastomeric body  50  may be fabricated from any suitable material(s) that enable the elastomeric body  50  to function as described herein, such as, but not limited to, silicone rubber, fluorosilicone rubber, polyepoxide, polyimide, polybutadiene, neoprene, ethylene propylene diene monomer (EPDM), a thermoplastic elastomer, and/or polystyrene. The elastomeric body  50  may have any suitable shape that enables the elastomeric body  50  to function as described herein, such as, but not limited to, a cone, a truncated cone (a frustoconical shape), a pyramid, a truncated pyramid, a prism, and/or a hemisphere. In the exemplary embodiment, the elastomeric body  50  includes a frustoconical shape extending between the mating end portion  54  and the base portion  52 . 
       FIG. 4  is a front elevation view of the electrical component assembly  10 . In operation, the interposer  16  is positioned between, and aligned with the electrical components  12 ,  14 . When the electrical components  12 ,  14  are mechanically connected together, the elastomeric electrical contacts  32  of the interposer  16  electrically connect each electrical contact  22  of the array  18  with its corresponding electrical contact  24  of the array  20 . Specifically, each electrically conductive pad  56  of the elastomeric electrical contact portions  40  located on the surface  36  of the interposer substrate  34  is in electrical contact with its corresponding electrical contact  22  of the array  18  of the electrical component  12 . Each electrically conductive trace  60  of the elastomeric electrical contact portions  40  located on the substrate surface  36  electrically connects its corresponding pad  56  to the corresponding conductive element  44 . The conductive elements  44  are also electrically connected to the electrically conductive traces  60  of the elastomeric electrical contact portions  40  located on the substrate surface  38 . The elastomeric electrical contact portions  40  located on the substrate surface  38  are electrically connected to their corresponding electrically conductive pads  56 , which are engaged with, and therefore electrically connected to, the corresponding electrical contact  24  of the array  20  of the electrical component  14  to complete the electrical connection between the electrical components  12 ,  14 . When the electrical components  12 ,  14  are mechanically connected together as shown in  FIG. 4 , the elastomeric electrical contacts  32  of the interposer  16  are compressed between the opposing arrays  18 ,  20  and therefore apply a mechanical force to the electrical contacts  22 ,  24  of the arrays  18 ,  20 , respectively, to facilitate establishing and maintaining reliable electrical contact between the arrays  18 ,  20 . The elastomeric properties of the electrical contacts  32  also allow for some degree of nonplanarity between, and/or misalignment of, the electrical components  12 ,  14 . 
       FIG. 5  is a perspective view of a portion of an electrical component assembly  100  formed in accordance with an alternative embodiment of the present invention. Although the elastomeric electrical contacts  32  are shown in  FIGS. 1-4  as including two identical portions  40  (shown in  FIGS. 1 ,  2 , and  4 ) on opposite sides of an interposer substrate  34  (shown in  FIGS. 1 ,  2 , and  4 ), embodiments of the elastomeric electrical contacts of the present invention are not limited to such an arrangement. Rather, embodiments of elastomeric electrical contacts formed in accordance with the present invention may be used without an interposer, and/or with only one or more than two portions. For example,  FIG. 5  illustrates an alternative embodiment of an elastomeric electrical contact  132  for electrically connecting an electrical component  112  with another electrical component (not shown). The elastomeric electrical contact  132  is substantially similar to the contacts  32  except the contact  132  includes only one portion  140  and is not configured for use as a portion of an interposer. Specifically, the contact  132  is mounted directly on the electrical component  112  such that an electrically conductive trace  160  is in electrical contact with an electrical contact  124  of the electrical component  112 . The trace  160  is also electrically connected to an electrically conductive pad  156  that is configured to engage and electrically connect to an electrical contact (not shown) on the other electrical component. 
       FIG. 6  is a front elevation view of an electrical component assembly  210  formed in accordance with another alternative embodiment of the present invention. The assembly  210  includes an electrical component  212 , a circuit board  216 , and a plurality of elastomeric electrical contacts  232  that electrically connect the electrical component  212  to the circuit board  216 . The electrical component  212  and the circuit board  216  each include a respective array  218 ,  220  of a plurality of respective electrical contacts  222 ,  224 . The arrays  218 ,  220  may each be any suitable type of array of electrical contacts that enables operative electrical connection between the electrical component  212  and the circuit board  216 , such as, but not limited to, Pin Grid Arrays (PGAs), Land Grid Arrays (LGAs), and/or Ball Grid Arrays (BGAs). Moreover, the arrays  218 ,  220  may have any suitable configuration, arrangement, and/or pattern of electrical contacts that enables operative electrical connection between the electrical component  212  and the circuit board  216 . 
     In the exemplary embodiment, each of the electrical contacts  224  of the circuit board  216  extends through a corresponding through hole  247  within the circuit board  216  such that each contact  224  includes a portion  225  extending along a surface  236  of the circuit board and a portion  227  extending along an opposite surface  238  of the circuit board  216 . The elastomeric electrical contacts  232  are mounted directly on the circuit board  216  such that an electrically conductive trace  260  of each contact  232  is in electrical contact with the portion  225  of a corresponding one of the electrical contacts  224  of the circuit board  216 . Each trace  260  is also electrically connected to an electrically conductive pad  256  of the contact  232  that is engaged with, and therefore electrically connected to, a corresponding one of the electrical contacts  222  of the electrical component  212 . The portions  227  of each of the electrical contacts  224  of the circuit board  216  may be electrically connected to corresponding electrical contacts (not shown) of any other suitable electrical component (not shown), such as, but not limited to, another circuit board, integrated circuits, electrical modules, and/or other electrical devices. Optionally, the elastomeric electrical contacts  232  may each extend through a through hole  246  within the circuit board  216  and include a base portion  252  extending along the surface  238  of the circuit board  216 . The base portion  252  may facilitate stabilizing and/or facilitate holding the elastomeric electrical contacts  232  on the circuit board  216 . 
     The embodiments described herein provide an elastomeric electrical contact that may reduce a stress applied to an electrically conductive trace during compression of an elastomeric body of the contact. 
     Exemplary embodiments are described and/or illustrated herein in detail. The embodiments are not limited to the specific embodiments described herein, but rather, components and/or steps of each embodiment may be utilized independently and separately from other components and/or steps described herein. Each component, and/or each step of one embodiment, can also be used in combination with other components and/or steps of other embodiments. For example, although specific sensor elements are described and/or illustrated with specific attachment devices, each described and/or illustrated sensor element may be used with any of the described and/or illustrated attachment devices as is appropriate. When introducing elements/components/etc. described and/or illustrated herein, the articles “a”, “an”, “the”, “said”, and “at least one” are intended to mean that there are one or more of the element(s)/component(s)/etc. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional element(s)/component(s)/etc. other than the listed element(s)/component(s)/etc. Moreover, the terms “first,” “second,” and “third,” etc. in the claims are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means—plus-function format and are not intended to be interpreted based on 35 U.S.C. § 112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.