Abstract:
A resilient electrical connector assembly includes a base PCB and stacked layers of interconnected resilient conductive structures where each structure has at least two resilient conductive strips and at least two conductive contacts. One contact is integrated with a conductive path on the base PCB and another contact pad is positioned to establish a conductive path with a target PCB when the latter is mounted parallel to the base PCB. The resilient conductive strips flex due to a compressive force exerted between the base PCB and target PCB on the stacked layers. The resilient conductive structures are formed by depositing metal to sequentially form each of the stacked layers with one contact being initially formed in engagement with the conductive path on the base PCB.

Description:
BACKGROUND 
       [0001]    This invention relates to establishing an electrical connection between two substrates or printed circuit boards. 
         [0002]    Modern electronics often contain circuitry formed on a plurality of stacked layers/boards, e.g. between two parallel printed circuit boards (PCB), between two parallel substrates with patterned metallization, between a multi-element antenna array and an interconnection board, or between two layers of a microwave module or integrated circuit. Where multiple stacked surfaces are used, there exists a need to provide electrical interconnections and for some applications a resilient electrical interconnection is advantageous where the distances between the surfaces may change or may not be uniform. One approach for coupling electrical signals is to use a solderball between the respective conductive pads on the two adjacent layers. In another approach, a fuzz button can be placed between the two adjacent layers. However, fuzz buttons are normally time-consuming and/or tedious to install. Solder bumps require subsequent heating and if several such connections are required, uneven heating or differences in characteristics among the solder bumps may yield unreliable or inconsistent connections. The solder balls or fuzz buttons are additional parts that must be attached to the layers of the circuit and increase the “touch labor”. The disassembly of layers connected using either of these techniques for maintenance or repair of the circuitry may result in even greater difficulties where such interconnections are required to be manually reestablished during reassembly of the respective layers. Additionally, the minimum practical size of fuzz buttons may negatively impact the performance of RF circuits above a frequency, e.g. above 20 GHz. Thus, there exists a need for an improved resilient interconnector that minimizes such difficulties. 
       SUMMARY 
       [0003]    It is an object of the present invention to satisfy this need. 
         [0004]    A resilient electrical connector assembly includes a base PCB and stacked layers of interconnected resilient conductive structures where each structure has at least two resilient conductive strips and at least two conductive contacts. One contact is integrated with one surface and engages a conductive path on the base PCB and another contact is positioned to establish a conductive path with a target PCB when the latter is mounted parallel to the base PCB. The integrated resilient conductive strips flex due to a compressive force exerted between the base PCB and target PCB on the stacked layers. The resilient conductive structures are additively manufactured by depositing metal to sequentially form each of the stacked layers with one contact being initially formed in engagement with the conductive path on the base PCB. 
         [0005]    Another embodiment of the invention includes the use of a spacer board between the base PCB and target PCB with two sets of stacked layers forming the resilient conductive structures. One of the sets is disposed between the base PCB and the spacer board and the other set is disposed between the spacer board and the target PCB. A conductive Via traversing the spacer board connects the two sets and the connections provide a conductive path from the base PCB to the target PCB. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0006]    Features of exemplary implementations of the invention will become apparent from the description, the claims, and the accompanying drawings in which: 
           [0007]      FIG. 1  is a perspective view of an exemplary embodiment of a resilient interconnector in accordance with the present invention. 
           [0008]      FIG. 2  shows a front elevational view of the embodiment of  FIG. 1 . 
           [0009]      FIG. 3  shows a side elevational view of the embodiment of  FIG. 1 . 
           [0010]      FIG. 4  is a partial view illustrating an application of embodiments utilized to form a coaxial-type connection for a high frequency RF signal. 
           [0011]      FIG. 5  is a representative cross-sectional view of exemplary connectors providing an electrical connection between adjacent layers/boards via an intermediate spacer/board. 
           [0012]      FIG. 6  is a perspective view of an alternate embodiment of an electrical connector of the present invention. 
           [0013]      FIG. 7  is a representative cross-sectional view of exemplary connectors providing an electrical connection between adjacent layers/boards. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]      FIGS. 1, 2 and 3  show an exemplary embodiment of a miniature resilient interconnector  100  having an “X” general shape. As used herein, “miniature” refers to a structure having a maximum strip length of 10 mils (250 um) The top surface of the conductive base connection blocks  105  and  110  support a conductive, resilient, elongated strip  115 . As used herein, the referenced “strip(s)” means generally thin planar layers that could have shapes other than rectangular, e.g. oval, circular, etc. The bottom surfaces of the conductive base connection blocks  105  and  110  are integrated onto the PCB to engage and make electrical connection with a planar conductive element such as an area of copper on an adjacent printed circuit board (PCB). As used herein, a PCB includes all forms of structures having at least one generally planar surface. The bottom surface of conductive block  120  engages the middle of strip  115 . The top surface of conductive block  120  engages the bottom surface of conductive block  125  which has a top surface that engages the middle of elongated strip  130 . Another elongated conductive strip  145  is mounted above strip  130  in a plane parallel to strip  130  and is supported by conductive blocks  135  and  150  at one end and conductive blocks  140  and  155  at the other end. The ends of conductive strip  130  engage and provide support for conductive blocks  135 ,  150 ,  140  and  155 . Mounted near the middle of conductive strip  145  is conductive block  160  which has mounted thereto conductive block  165 . The conductive strips  115 ,  130  and  145  are each a conductive, resilient, elongated strip. The top surface of conductive block  165  is disposed to engage and establish an electrical connection with another conductive element such as an area of copper on another PCB that is spaced apart from the PCB that engages conductive blocks  105  and  110 . 
         [0015]    Because all of the described elements provide electrical conductivity and engage adjacent elements, an electrical connection is established between the bottom surfaces of conductive blocks  105 / 110  and the top surface of conductive block  165 . The thickness of conductive blocks  135 ,  150  and  140 ,  155  establishes a spacing between conductive strips  130  and  145  that permits strip  145  to be resiliently deflected downward at its middle due to a compressive force applied to the top surface of block  165  relative to blocks  105 ,  110 . Additionally, due to the same compressive force, elongated strip  115  may be resiliently deflected downward and may engage the same conductive surface engaged by the bottom surfaces of blocks  105 ,  110 . Without the application of a compressive force, each of the strips  115 ,  130  and  145  preferably lies within a plane, i.e. is relatively straight. Strip  115  is substantially transverse to strips  130 ,  145 . As will be appreciated, the maximum possible deflection upon the application of a compressive force would be the sum of the distances of the thickness of block  105  (assuming block  110  is the same thickness), the thickness of block  135 , and the thickness of block  150  (assuming blocks  140 ,  155  have the same corresponding thicknesses). Preferably, the two surfaces to be connected by connector  100  have a final mounted position relative to each other in which the distance between the two surfaces supplies some amount of compressive force to connector  100  which is utilized to provide an electrical interconnection between first and second locations of engagement on the two surfaces, respectively. 
         [0016]    Exemplary dimensions are 10 um to 100 um for the width of  130  and 100 um to 1000 um for the length of  115  of  FIG. 3 . Due to the precision of the manufacturing process the minimum spacing between parts can be as small as 10 um and as great as the size of the substrate. This will enable 5-wire coaxial RF structures that are typically 25 to 500 um apart. By using different metals, the stiffness of the structure can be adjusted to range from an easier to compress structure using Au, to a stiffer structure using Ti and Ni, that will approach the rigidity of a fuzz button. 
         [0017]    Microelectronics fabrication builds up patterned layers of dielectric and metal materials. Dielectrics typically include “hard” dielectrics such as silicon nitride and “soft” dielectrics such as BCB (benzocyclobutane). Metals can be plated or evaporated and commonly plated metals are nickel which can add strength, e.g. adding strength to the embodiments of the invention, and gold, which forms excellent contacts and does not develop highly resistive oxide layers. The interconnector  100  is preferably made by patterning photoresist 7 times (7 different masks), with a metal plating step for each mask layer concurrent with the manufacture of a parent PCB for which connections are required with another PCB. Thus, the metal surface of the blocks of the interconnector  100  that engage the parent PCB are deposited directly on the conductive path of the PCB for which a connection with another PCB is needed. 
         [0018]      FIG. 4  is a partial view of a quartz (or other substrate) PCB illustrating an application of embodiments of the use of the X structures utilized to form a coaxial-type connection for a high frequency RF signal. As used herein, a radio frequency (RF) signal refers to signals having frequency less than 20 GHz and a high frequency RF signal refers to signals having a frequency greater than 20 GHz. A nonconductive substrate  405  of the PCB supports a conductive surface  410  that in the illustrative example surrounds an interior conductive pad  415  separated by a surrounding nonconductive area from the conductive surface  410 . A contact  420  in accordance with an embodiment of the present invention conductively engages pad  415 . Four contacts  425  are conductively mounted to conductive surface  410  preferably in a symmetrical spaced apart relationship to pad  415 . The contacts  420  and  425  form what is referred to as a “5 wire” connection that provides a piecewise linear representation of a cylindrical coaxial cable where contact/connector  420  supplies a connection for the center conductor of the simulated coaxial cable and the contacts/connectors  425  supply a connection representing the outer braid of the simulated coaxial cable. The spacing between pad  415  and the surrounding surface  410  as well as the spacing between connector  420  and the surrounding connectors  425  can be varied to provide different impedance characteristics of the simulated coaxial cable in order to match a corresponding desired impedance and minimize an impedance discontinuity due to the interconnections provided by the connectors. Another PCB (not shown which could be an organic material or a hard substrate like quartz) would be mounted parallel to surface  410  in a final assembled position and would have an aligned conductive pad opposing pad  415  and aligned conductive surfaces opposing each of connectors  425 . Preferably the another PCB will be mounted so that its facing surface will have a substantially uniform distance from surface  410  and will have a spacing such that a desired amount of compressive force is supplied to the connectors  420 ,  425 . Thus, in a final mounted position, the connectors  420 ,  425  will provide a 5 wire connection supporting the coupling of a high frequency RF signal between two PCBs. Although a 5 wire connection is illustrated, it will be apparent that single independent connections can be made utilizing the connectors to support the transmission of lower frequency signals and/or DC signals between the two respective PCBs. Various conventional nonconductive spacers disposed between the two PCBs can be used to establish and maintain a desired spacing therebetween in order to control the amount of compressive force applied to the respective connectors. 
         [0019]      FIG. 5  illustrates an application of exemplary connectors in accordance with the present invention. A PCB  505  is connected to a PCB  510  through an intermediate PCB  515  and connectors  520 ,  525 ,  530  and  535  such as previously described. The top surface of PCB  505  has a conductive path  540  coupled to a conductive pad  547  on the bottom surface of PCB  550  by Via  545 . The bottom surface of PCB  505  has a conductive path  550 . The conductive path  540  is connected by Via  545 , pad  547 , connector  520 , pad  553  on the top surface of PCB  515 , Via  555  of PCB  515 , pad  557  on the bottom of PCB  515 , connector  530 , pad  563  on the top surface of PCB  510 , Via  565  of PCB  510  to the conductive path  570  on the bottom surface of PCB  510 . The conductive path  550  is connected by connector  525 , pad  554  on the top surface of PCB  515 , Via  560  of PCB  515 , pad  564  on the bottom surface of PCB  515 , connector  535 , pad  573  on the top surface of PCB  510  and Via  575  of PCB  510  to conductive path  580  on the bottom surface of PCB  510 . The spacing between the bottom surface of PCB  505  and the top surface of PCB  515 , and the spacing between the bottom surface of PCB  515  and the top surface of PCB  510  are dimensioned to provide the desired amount of compressive force to the respective connectors  520 ,  525 ,  530  and  535 . Should there be a need to space PCB  505  and  510  an even greater distance apart, the thickness of PCB  515  can be selected to have an increased thickness to maintain the desired compressive force on the connectors. 
         [0020]      FIG. 6  shows a perspective view of an alternate embodiment of another connector  600  in accordance with the present invention. Connector  600  includes five stacked layers of interconnecting elements. A first, base element  605  includes conductive blocks  610  and  615  connected to the respective ends of resilient conductive strip  620 . The other base element  625  is substantially identical to element  605  with the respective conductive strips being parallel to each other and spaced apart. Intermediate elements  630  and  635  are substantially identical to element  605 . Elements  630  and  635  have spaced apart parallel resilient conductive strips supported at the respective ends by conductive blocks that are supported by intermediate positions along the respective conductive strips of base elements  605  and  625 . Elements  640  and  645  have spaced apart parallel conductive strips each supported by two blocks having upward facing ends engaging intermediate portions of the strips and downward facing ends that rest on intermediate portions of the strips of elements  630  and  635 . Each of the distal ends on the top surface of the strips of elements  640  and  645  support upward projecting blocks that engage and support intermediate portions of the spaced apart parallel conductive strips of top elements  650  and  655 . Upward projecting conductive blocks are disposed near the distal ends and on the top surface of the respective strips of top elements  650  and  655 ; the top ends of these blocks are disposed to engage an upper surface to which a conductive path is to be established. The bottom ends of the blocks associated with base elements  605  and  625  are disposed to engage a lower surface to which the conductive path is to be established. In accordance with the subject connector  600 , resilient conductive strips are disposed in four parallel spaced apart planes, e.g. stacked, in order to accommodate a substantial amount of compression and span a greater distance. It will be apparent that the blocks and resilient strips must each be conductive, or at least contain a conductive path, in order to establish an electrical connection between two spaced apart parallel surfaces. In order to facilitate ease of assembly and reassembly, the connector  600  is preferably fabricated as an integrated part of one of the surfaces to be connected, i.e. part of one of the PCBs, so that it is permanently attached to that board and does not have to be independently placed between the surfaces requiring interconnection. 
         [0021]      FIG. 7  illustrates another application of exemplary connectors in accordance with the present invention. A conductive path  705  of PCB  715  is connected by connector  720  with the conductive path  730  of PCB  740 . More specifically, the conductive path  705  is connected through Via  745  to a pad  750  on the bottom surface of PCB  715 , connector  720  that is under compression between pad  750  on the bottom surface of PCB  715  and pad  755  on the top surface of PCB  740 , Via  760  which is connected to conductive path  730 . Conductive path  710  on the bottom surface of PCB  715  is connected by connector  725  which is under compression between conductive path  710  and conductive path  735  of the top surface of PCB  740 . The spacing between the bottom surface of PCB  715  and the top surface of PCB  740  is dimensioned to provide the desired amount of compressive force to the respective connectors  720 ,  725 . This may, for example, be accomplished by the use of appropriately dimension spacers disposed at various locations between PCB  715  and PCB  740  to establish and control the assembled PCB spacing. 
         [0022]    Although exemplary implementations of the invention have been depicted and described in detail herein, it will be apparent to those skilled in the art that various modifications, additions, substitutions, and the like can be made without departing from the spirit of the invention. 
         [0023]    The scope of the invention is defined in the following claims.