Patent Publication Number: US-2021184385-A1

Title: Compressible conductive elastomer for electrical connection of orthogonal substrates

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of provisional application 62/947,440 filed Dec. 12, 2019. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to a grounding connection for a pressure sensor assembly, which includes at least one conductive elastomer plug as the grounding connection between a piezoresistive pressure cell and a housing. 
     BACKGROUND OF THE INVENTION 
     Pressure sensor elements typically require electrical grounding to reduce or eliminate electromagnetic interference (EMI). Several different types of solutions have been developed, but these solutions have included conductive elastomers which are typically used to make electrical or thermal contact between parallel substrates, as flexible EMI shielding gaskets, or are adhesively bonded to one or more flexible substrates such as in a form-in-place operation. 
     However, these solutions are not cost effective, and are not sufficient for providing an electrical connection between two rigid, substantially orthogonal opposed substrates. 
     Accordingly, there exists a need for a conductor which may be economically installed without any secondary processes or additional materials, and functions as a stand-alone component between two substrates which achieves a desired electrical connection. 
     SUMMARY OF THE INVENTION 
     In one embodiment, the present invention is a pressure sensor assembly which includes an electrical connection between two substantially orthogonal rigid substrates by using a compressible electrically conductive elastomer. 
     The compressible electrically conductive elastomer provides a sufficiently low resistance electrical connection between two rigid, substantially orthogonally opposed substrates without the need for additional manufacturing processes such as soldering, applying conductive adhesive, or attaching a flexible circuit connection. No additional joining materials are necessary to create the electrical connection; the deformation of the conductive elastomer results in an application of force against the surfaces of the two substrates. 
     In an embodiment, a conductive elastomer is extruded, die cut or molded to a specific shape, such as a plug, allowing simultaneous compression in two substantially orthogonal directions, creating a low resistance electrical connection between the two substantially orthogonally opposed rigid substrates. 
     In an embodiment, the conductive elastomer is generally cylindrical with additional optional geometric features aiding in compression and surface contact, such as a hollow core and external ribs or teeth, creating a gear-like shape. Radial compression of the generally cylindrical conductive elastomer is achieved by installation of the elastomer with an interference fit against a first conductive substrate, with the first conductive substrate positioned substantially tangential to the generally cylindrical shape, using a portion of the outer surface of the cylindrical elastomer shape as the contact area. Biaxial compression of the elastomer then occurs when a second conductive substrate is assembled against one flat end of the generally cylindrical shape. 
     In an embodiment, the pressure sensor assembly includes an electronics housing, and a non-conductive cavity in the electronics housing is used to secure the conductive elastomer in place by an interference fit, allowing for compression in the radial direction against a vertically opposed rigid substrate (or, alternately, a conductive contact area on the vertically opposed rigid substrate) and for compression in the axial direction against a horizontally opposed rigid conductive substrate (or, alternately, a conductive contact area on the horizontally opposed rigid conductive substrate). 
     The two substrates independently create compression upon the elastomer in generally orthogonal directions. As such, the amount of compression in each direction—which may affect the function of a low resistance electrical connection—may be tailored by simply adjusting the dimensions of the generally cylindrically shaped elastomer rather than modifying the mating components. 
     A conductive elastomer material that is generally electrically isotropic is used, allowing for conductivity in orthogonal directions simultaneously, thus creating a sufficiently low resistance electrical connection between the two substantially orthogonal substrates. 
     Multiple raw material combinations are possible to achieve an effective solution depending on the substrates used in the application and the environment to which the assembly is exposed. 
     In an embodiment, the present invention is an electronics assembly which includes a grounding connection, having a housing, a connector, a portion of the connector formed around the housing, a recess portion integrally formed as part of the connector, a substrate located in proximity to the connector, and circuitry mounted to the substrate such that the circuitry is at least partially disposed in a cavity formed as part of the connector. A conductor is mounted to the connector such that the conductor is located in the recess, and the conductor is in contact with the housing and the substrate. A grounding connection is formed between the circuitry and the housing when the conductor is in contact with the housing and the substrate. 
     In an embodiment, the conductor is made of an elastomeric material, and the conductor deforms when the substrate is placed in proximity to the connector. In an embodiment, the elastomeric material is isotropic. 
     In an embodiment, the conductor is a plug, and the plug includes a body portion, and a plurality of ribs integrally formed as part of the body portion. The plug is deformed when the plug is in contact with the connector and the pressure cell, and a first portion of the plurality of ribs is in contact with the connector, and a second portion of the plurality of ribs is in contact with the housing. 
     In an embodiment, the plug includes a first outer surface on one side of the body portion and each of the plurality of ribs, and a second outer surface on another side of the body portion and each of the plurality of ribs. The substrate is in contact with the first outer surface, and a lower surface and the cavity is in contact with the second outer surface. 
     In an embodiment, the substrate and the housing are orthogonal to one another. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is perspective view of a pressure sensor assembly having at least one grounding connection, according to embodiments of the present invention; 
         FIG. 2  is a first exploded view of a pressure sensor assembly having at least one grounding connection, according to embodiments of the present invention; 
         FIG. 3  is a second exploded view of a pressure sensor assembly having at least one grounding connection, according to embodiments of the present invention; 
         FIG. 4  is an enlarged perspective view of part of a pressure sensor assembly during the assembly of at least one conductive elastomer plug used for at least one grounding connection, according to embodiments of the present invention; 
         FIG. 5  is a perspective view of part of a pressure sensor assembly after the assembly of at least one conductive elastomer plug used for at least one grounding connection, according to embodiments of the present invention; 
         FIG. 6  is a sectional view of part of a pressure sensor assembly having at least one grounding connection, according to embodiments of the present invention; 
         FIG. 7  is a top view of a conductive elastomer plug, used for at least one grounding connection, which is part of a pressure sensor assembly, according to embodiments of the present invention; 
         FIG. 8  is a top view of a conductive elastomer plug that has been compressed, used for at least one grounding connection, where the conductive elastomer plug is part of a pressure sensor assembly, according to embodiments of the present invention; and 
         FIG. 9  a sectional view of a pressure sensor assembly having at least one grounding connection, according to embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     An embodiment of a pressure sensor assembly according to the present invention is shown in  FIG. 1 , generally at  10 . Referring to the Figures generally, the assembly  10  is an absolute pressure sensor, and includes a connector  12  which is molded around part of an aluminum housing  14 . Integrally formed as part of the connector  12  are several apertures  16 , and a portion of a corresponding spring  18  is located in each aperture  16 . Also formed as part of the connector  12  is a cavity, shown generally at  20 . Disposed in the cavity  20  is circuitry, which is part of a signal conditioning Application Specific Integrated Circuit (ASIC), shown generally at  22 , mounted to a support substrate  24 , which together form a pressure cell, shown generally at  26 . The substrate  24  is supported by the springs  18 , and the use of the springs  18  allows for the location of the pressure cell  26  to have various tolerances, and still maintain proper electrical connections, and for the circuitry  22  to be properly located in the cavity  20 . 
     In contact with the back surface of the substrate  24  is an O-ring  28 , and the O-ring  28  is partially disposed in a recess  30  formed as part of a port  32 . Integrally formed as part of the port  32  is a threaded portion  34 . A second O-ring  36 , which is located on a back surface of the port  32  such that the threaded portion  34  extends through the O-ring  36 , provides sealing between the port  32  and another component. 
     Referring to  FIGS. 4-6 and 9 , also formed as part of the connector  12  is a recess portion, shown generally at  38 , and the recess portion  38  has an inner sidewall  38   a . A conductive plug, shown generally at  40 , is located in the recess portion  38 , such that the plug  40  is partially surrounded by the inner sidewall  38   a , and the plug  40  is in contact with the substrate  24  and an inner surface  14   a  of the housing  14 . In this embodiment, the conductive plug  40  is made of a conductive elastomeric material, but it is within the scope of the invention that the plug  40  may be made of other materials as well. In an embodiment, the plug  40  may be made of an elastomer material which is isotropic. The plug  40  is disposed in the recess portion  38  such that there is an interference fit between the plug  40  and inner sidewall  38   a  of the recess portion  38 , and an interference fit between the plug  40  and the inner surface  14   a  of the housing  14 , such that the plug  40  is compressed by the sidewall  38   a  and the inner surface  14   a  in a first orthogonal direction, which results in a deformation of the plug  40 . When pressure cell  26  is placed in proximity to the connector  12  such that the pressure cell  26  is supported by the springs  18 , there is also an interference fit between the plug  40  and a lower surface  38   b  of the recess portion  38 , and an interference fit between the plug  40  and the substrate  24 , such that the plug  40  is compressed by the lower surface  38   b  and the substrate  24  in a second orthogonal direction and there is additional deformation of the plug  40 . An example of the plug  40  being in a relaxed position is shown in  FIG. 7 , and an example of the plug  40  being in a deformed position is shown in  FIG. 8 . 
     The plug  40  being in contact with the housing  14  and the substrate  24  results in a grounding of the circuitry  22  of the pressure cell  26 . The ability for the plug  40  to deform allows for an electrical connection between the pressure cell  26  and the housing  14  without the need for additional manufacturing processes, and no additional joining materials are required to create the electrical connection. 
     In the embodiment shown, the plug  40  includes a body portion  42 , and several geometric features, which in this embodiment are external ribs  44 . The body portion  42  is generally circular, and has an aperture  46 , as well a first outer surface  48   a  and a second outer surface  48   b . When assembled, a portion of the external ribs  44  are in contact with the inner sidewall  38   a , and another portion of the external ribs  44  are in contact with the inner surface  14   a . Also, when assembled, a portion of the support substrate  24  is in contact with the first outer surface  48   a , and the lower surface  38   b  of the recess portion  38  is in contact with the second outer surface  48   b . While one embodiment of the shape of the plug  40  has been described, it is within the scope of the invention that other shapes may be used. The shape of the plug  40  may be changed depending upon the shape and space between the surrounding substrates the plug  40  is connecting. The plug  40  may be shaped to accommodate the housing  14 , the recess portion  38 , or the support substrate  24  having different shapes. For example, the plug  40  may or may not have the geometric features, and shapes of the plug  40  may include, but are not limited to, round, square, rectangle, oval, trapezoid, a hollow shape, or irregular shape. The uncompressed or undeformed shape of the plug  40  is designed to be larger than the as-assembled shape of the plug  40 , such that the plug  40  is compressed in two orthogonal directions, to facilitate the conductive connection between the two orthogonal substrates. 
     In the embodiment shown, the inner surface  14   a  and the surface of the substrate  24  in contact with the plug  40  are orthogonal to one another. Therefore, the plug  40  provides an electrical connection between two orthogonal surfaces. 
     The shape of the plug  40  in conducive to elastic deformation. Referring again to  FIGS. 7 and 8 , the plug  40  is shown being uncompressed in  FIG. 7  and compressed in the radial direction in  FIG. 8 . 
     While the present invention has been described for use with a pressure sensor assembly, it is within the scope of the invention that the present invention may be used with any type of electronics assembly requiring two orthogonal substrates to have a ground connection with floating mechanical tolerances. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.