Abstract:
A connector assembly includes a substrate assembly and a receptacle. The substrate assembly includes a first substrate layer having a conductive trace that is accessible for direct electrical interconnection with a first conductor associated with another device. A second substrate layer on the assembly includes an electrical contact for electrical interconnection with a second conductor associated with the other device. The electrical contact on the second substrate layer is disposed such that when the substrate assembly is inserted into the receptacle, the electrical contact is electrically connected with the second conductor, a direct electrical interconnection between the conductive trace and the first conductor is maintained. The arrangement is advantageous in that the connector assembly is capable of transmitting low frequency signals through electrical connections that also serve to maintain a high frequency direct electrical interconnection.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     A claim of priority is made to U.S. Provisional Patent Application No. 60/324,328, entitled “Small Form-Factor Pluggable Connection of High Frequency and Low Frequency Signals between Substrates”, by Martin R. Handforth, et al., filed Sep. 24, 2001, which is incorporated by reference. 
     This patent application may be related to the following commonly-owned United States patent application, which is incorporated in its entirety by reference: 
     U.S. patent application entitled SIGNAL LAYER INTERCONNECTS, Ser. No. 09/821,722, by Martin R. Handforth et al., filed Mar. 29, 2001. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to electrical connectors, and more particularly to electrical interconnect technology for providing high and low frequency electrical interconnections. 
     BACKGROUND OF THE INVENTION 
     Many signal interconnect applications require the transmission of both high frequency and low frequency signals. It is known in the art to use different types of connectors to transmit high frequency and low frequency signals, however, this disadvantageously contributes to high cost and complexity in module design. It would be desirable to provide an interconnect technology whereby both high frequency and low frequency signals are efficiently transmitted. 
     SUMMARY OF THE INVENTION 
     In accordance with the principles of the invention, a substrate assembly is provided which includes a first substrate layer having a conductive trace that is accessible for direct electrical interconnection with a first conductor associated with another device. A second substrate layer on the assembly includes an electrical contact for electrical interconnection with a second conductor associated with the other device. The electrical contact on the second substrate layer is disposed such that when the electrical contact is electrically connected with the second conductor, a direct electrical interconnection between the conductive trace and the first conductor is maintained. The direct electrical interconnection is advantageously employed for the transmission of a high frequency signal, while the electrical contact is conveniently used to transmit a lower frequency signal. 
     The substrate assembly can further include a third substrate layer having an electrical contact for electrical interconnection with a third conductor associated with the other device. The second and third substrate layers then define a protrusion from the substrate assembly, such that when the electrical contacts are electrically connected with the respective second and third conductors, the connection forms an overlapping joint which serves to maintain the direct electrical connection between the conductive trace and the first conductor. 
     Alternatively, the substrate assembly may be configured such that the second substrate layer protrudes from the substrate assembly. When the electrical contact is electrically connected with the second conductor, the connection forms an overlapping joint which serves to maintain the direct electrical connection between the conductive trace and the first conductor. 
     The substrate assembly can also be arranged such that the first substrate layer and the second substrate layer define a protrusion from the substrate assembly. When the electrical contact is electrically connected with the second conductor, the connection causes pressure to be applied between the substrate assembly and the other device which serves to maintain the direct electrical connection between the conductive trace and the first conductor. 
     According to a further aspect of the invention, a connector assembly is provided. The connector assembly includes a substrate assembly having a first substrate layer with a conductive trace. The conductive trace is accessible for direct electrical interconnection with a first conductor associated with another device. The substrate assembly has a second substrate layer including an electrical contact for electrical interconnection with a second conductor associated with the other device. The connector assembly further includes a receptacle for disposal on the other device. A conductive contacting member is provided, such that when the substrate assembly is inserted into the receptacle, the electrical contact is electrically connected with the second conductor via the contacting member, and the contacting member serves to maintain a direct electrical interconnection between the conductive trace and the first conductor. The contacting member may be located on the substrate assembly or on the receptacle. 
     Further provided in accordance with the invention is a connector assembly which includes a substrate assembly and a receptacle. The substrate assembly includes a first substrate layer having a conductive trace that is accessible for direct electrical interconnection with a first conductor associated with another device. The substrate assembly further includes a second substrate layer having an electrical contact for electrical interconnection with a second conductor associated with the other device. The receptacle is for disposal on the other device. The electrical contact on the second substrate layer is disposed such that when the substrate assembly is inserted into the receptacle, the electrical contact is electrically connected with the second conductor, and a direct electrical interconnection between the conductive trace and the first conductor is maintained. 
     A third substrate layer may be provided, including an electrical contact for electrical interconnection with a third conductor associated with the other device. The second and third substrate layers define a protrusion from the substrate assembly, such that when the substrate assembly is inserted into the receptacle, the electrical contacts are electrically connected with the respective second and third conductors, and the connection between the electrical contacts and second and third conductors form an overlapping joint which serves to maintain the direct electrical connection between the conductive trace and the first conductor. 
     Alternately, the connector assembly may include a substrate assembly wherein the second substrate layer protrudes from the substrate assembly such that when the substrate assembly is inserted into the receptacle, the electrical contact is electrically connected with the second conductor, and the connection between the electrical contact and the second conductor form an overlapping joint which serves to maintain the direct electrical connection between the conductive trace and the first conductor. 
     According to another alternative, the connector assembly may include a substrate assembly wherein the first substrate layer and the second substrate layer define a protrusion from the substrate assembly such that when the substrate assembly is inserted into the receptacle, the electrical contact is electrically connected with the second conductor, and pressure is applied between the substrate assembly and the receptacle which serves to maintain the direct electrical connection between the conductive trace and the first conductor. 
     The various aspects of the invention are advantageous in that a connector assembly is provided that is capable of transmitting low frequency signals through electrical connections that also serve to maintain a high frequency direct electrical interconnection. 
     The present invention will now be described in more detail with reference to exemplary embodiments thereof as shown in the appended drawings. While the present invention is described below with reference to preferred embodiments, it should be understood that the present invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present invention as disclosed and claimed herein, and with respect to which the present invention could be of significant utility. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to facilitate a fuller understanding of the present invention, reference is now made to the appended drawings. These drawings should not be construed as limiting the present invention, but are intended to be exemplary only. 
         FIG. 1  is a side view of a connector assembly providing a high frequency direct electrical interconnection and a low frequency electrical interconnection in accordance with the present invention. 
         FIG. 2  is a side view of a preferred embodiment of the connector assembly of  FIG. 1 . 
         FIG. 3  is a side view of an alternate version of the preferred embodiment of the connector assembly shown in  FIG. 2 . 
         FIG. 4  is a perspective view of the substrate assembly of  FIG. 2 . 
         FIG. 5  is a perspective view of the receptacle portion of the connector assembly shown in  FIG. 2 . 
         FIG. 6  is a side view of an alternate embodiment of the connector assembly of  FIG. 1 . 
         FIG. 7  is a perspective view of the substrate assembly of  FIG. 6 . 
         FIG. 8  is a side view of an alternate embodiment of the connector assembly shown in  FIG. 1 . 
         FIG. 9  is a side view of another embodiment of the connector assembly of  FIG. 1 . 
         FIG. 10  is a perspective view of the substrate assembly of  FIG. 9 . 
         FIG. 11  is a side view of another embodiment of the connector assembly of  FIG. 1 . 
         FIG. 12  is a perspective view of the substrate assembly of  FIG. 11 . 
         FIG. 13  is a perspective view of a substrate assembly including a compliant layer. 
         FIG. 14  is a perspective view of a substrate assembly including bending beams supporting high frequency traces. 
         FIG. 15  is an overhead view of the bending beams of  FIG. 13 . 
         FIG. 16  is a perspective view of the substrate assembly of  FIG. 14  including an elastomer material supporting the bending beams. 
         FIG. 17  is a perspective view of the substrate assembly wherein protrusions are disposed upon the signal traces. 
         FIG. 18  is a perspective view of another aspect of the invention wherein the signal traces are disposed within channels on the substrate. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Co-pending patent application Ser. No. 09/821,722, incorporated by reference herein, describes an interconnect technology that is advantageously used for the transmission of high frequency electrical signals. High frequency signal traces are exposed on their respective substrates, and a direct electrical connection is provided when the traces are placed in direct contact with one another. Various problems associated with known interconnect technologies, such as impedance mismatches and cross-talk, are thereby minimized. 
     Referring to  FIG. 1 , there is shown a preferred embodiment of a connector assembly  10  with direct signal layer interconnect capability. The connector assembly  10  is shown to include a substrate assembly  12  and receptacle  14 . Note that in  FIG. 1 , only an side view of one wall of the receptacle is shown. The substrate assembly  12  is shown disposed within the receptacle  14  such that a high frequency direct electrical connection is maintained at interface  16 . Exposed signal traces on the substrate assembly  12  are brought into direct electrical contact with exposed signal traces on the receptacle  14  at the interface  16 , thus providing a reliable high frequency connection. At the interface  18 , an electrical connection is made between a conductive contacting member  20  and electrical contacts on the surface  22  of the substrate assembly  12 . The conductive contacting member  20  provides an electrical connection between the electrical contacts on the surface  22  and corresponding electrical contacts on the receptacle  14 . The conductive contacting member  20  also serves to maintain the high frequency direct electrical connection at the interface  16  due, in this example, to the pressure that is provided by the contacting member  20  against the substrate assembly  12 . 
     The preferred embodiment is shown in more detail in  FIG. 2 . The substrate assembly  12  has multiple layers, including outer layer  24  and inner layers  26 ,  28 , and  30 . Each layer includes a dielectric portion and a conductive portion. For example, layer  30  includes substantially flat conductive traces  32  (shown in  FIG. 4 ) disposed on dielectric substrate material  34 , such as FR4, ceramic, or other materials. Each inner layer is generally dedicated to a single function, such as carrying ground, power or signals. The receptacle  14  also includes a substrate material  36 , such as FR4, ceramic, or other materials. The receptacle  14  further includes electrical conductors  38  and  40  through which low frequency electrical connections and high frequency electrical connections will respectively be made. 
     Portions of selected signal layer traces  32  are made directly accessible in order to facilitate electrical connection. As shown for instance in  FIG. 4 , one end of substrate material  34  containing some of the signal layer traces  32  is exposed so that traces  32  are accessible for direct electrical connection with corresponding exposed conductors  40  on the receptacle. The direct electrical connection between the traces  32  and the conductors  40  is particularly advantageous for the transmission of high frequency signals as described in the co-pending patent application Ser. No. 09/821,722. 
     The outer layer  24  on the substrate assembly  12  includes electrical contacts  42  ( FIG. 4 ) for the transmission of low frequency signals such as power, ground, or certain control signals. The conductive contacting member  20  contacts the electrical contacts  42  to establish an electrical connection between the electrical contacts  42  and corresponding low frequency conductors  38  on the receptacle  14 . The contacting member  20  may be for example a leaf spring, a coil spring, a bending beam, or a ball contact, and may be attached either to the surface  44  of the receptacle  14  (as shown) or to the top of the outer layer  24  of the substrate assembly  12 . The contacting member  20  conveniently serves to maintain the high frequency electrical interconnection  46  at interface  48  in this particular embodiment due to the pressure provided between the substrate assembly  12  and the receptacle  14 . The pressure in this embodiment is due to the spring force between the conductors  38  of the receptacle and the electrical contacts  42  of the substrate assembly  12  provided by the contacting member  20 . Alternatively, the contacting member may be an inflexible member like a ball contact, in which case the pressure provided between the substrate assembly  12  and the receptacle  14  could be provided by a flexible member located in another place. 
     In  FIG. 3  there is shown an alternate embodiment of the connector assembly  10  of  FIG. 2 . This embodiment does not include substrate layers below the layer  30 . 
     In  FIG. 5  there is shown a perspective view of the receptacle  14 , showing the contacting member  20  as a series of leaf springs. This receptacle  14  is placed on a substrate  36 , and the high frequency interconnection is made between signal traces on a substrate assembly  12  and signal traces on the substrate  36 . The high frequency interconnection would be maintained via the spring force provided by the leaf spring contacting members  20 . The leaf spring contacting members  20  are bonded, for example by soldering or welding, to low frequency signal contacts  38 . The leaf spring contacting members  20  contact low frequency signal traces  42  on the substrate assembly  12 . 
     In an alternate embodiment as shown in  FIG. 6 , the high frequency direct electrical interconnection is maintained via a tunnel joint  50  that conducts low frequency signals between the substrate assembly  12  and the receptacle  14 . As further seen in  FIG. 7 , layer  52  of the substrate assembly  12  includes high frequency signal traces  32 , which are exposed for direct electrical interconnection with corresponding conductors on the receptacle  14  when the substrate assembly  12  is inserted into the receptacle  14 . The substrate assembly  12  also includes electrical contacts  42  on layers  54  and  56 . The substrate layers above layer  56  have been cut away such that the electrical contacts on layer  56  are exposed, and such that the layers  54 – 56  form a protrusion  57  for insertion between low frequency contact surfaces  58  and  60  disposed on the receptacle  14 . When the substrate assembly  12  is inserted into the receptacle  14 , the electrical contacts  42  on layer  54  of the substrate assembly  12  electrically contact corresponding low frequency conductors  38  on surface  60  of the receptacle  14  for transmission of low frequency signals between the contacts  42  and the conductors  38 , while the electrical contacts on layer  56  of the substrate assembly  12  electrically contact corresponding low frequency conductors  38  on surface  58  of the receptacle  14  for transmission of low frequency signals between the contacts  42  and the conductors  38 . The protrusion  57  as inserted between the surfaces  58  and  60  acts as a tunnel joint  50  for securing the substrate assembly  12  within the receptacle  14  and maintaining via pressure the high frequency electrical interconnection  46  between the signal traces  32  and corresponding conductors  40  on receptacle surface  62 . 
     According to another embodiment as shown in  FIG. 8 , the positions of the tunnel joint  50  and low frequency surfaces  58  and  60  are reversed relative to the position of the high frequency interconnection  46  as was shown in  FIG. 6 . Here, the tunnel joint  50  is positioned above the layer  52  on the substrate assembly  12  upon which the high frequency signal traces  32  are exposed. Electrical contacts  42  on layers  54  and  56  contact low frequency conductors  38  on the receptacle  14  for transmission of low frequency signals between the contacts  42  and the conductors  38 . The layers  54 – 56  are disposed between the surfaces  58  and  60  on receptacle  14  to form the tunnel joint  50  for securing the substrate assembly  12  within the receptacle  14  and maintaining the high frequency electrical interconnection  46  between the signal traces  32  and conductors  40  on the receptacle surface  62 . 
     According to another embodiment as shown in  FIGS. 9 and 10 , the tunnel joint  50  is now disposed between the high frequency interconnection  46  and one of the low frequency connections  64 . Layers  66  through  68  of the substrate assembly  12  form a protrusion  69  beyond the other layers of the substrate assembly  12 . High frequency signal traces  32  are exposed on the edge  70  of layer  68  for direct interconnection with conductors  40  on the surface  72  of the receptacle  14 . Electrical contacts  42  are disposed on the edge  74  of layer  66  for electrical connection with corresponding low frequency conductors  38  on surface  76  on the receptacle  14 . Further electrical contacts  42  are disposed on the edge  78  of layer  80  for electrical connection with conductors  38  on surface  82  on the receptacle  14 . When the substrate assembly  12  is inserted into the receptacle  14 , the protrusion  69  forms a tunnel joint  50  between the high frequency interconnection  46  and the low frequency connection  64 . The high frequency direct interconnection  46  is thereby maintained due to the pressure applied by the tunnel joint  50 . The “stairstep” nature of the low frequency connections can be advantageous in that several wide track low frequency connections can be provided without requiring an excessively wide form factor. 
     According to the embodiment shown in  FIGS. 11 and 12 , layers  84  and  86  of the substrate assembly  12  include electrical contacts  42  for establishing low frequency connections with corresponding conductors  38  on surfaces  88  and  90  on the receptacle  14 . High frequency signal traces  32  are exposed along the edge of Layer  92  of the substrate assembly  12 . When substrate assembly  12  is inserted into receptacle  14 , the pressure provided between the low frequency interconnections  94  and  96  maintains the high frequency direct interconnection  46 . As seen in  FIG. 11 , a row of low frequency electrical contacts  42  ( 10  are shown) are disposed along the bottom of layer  84  of the substrate assembly  12 , for contact with corresponding conductors  38  on the surface  88  of the receptacle. Further low frequency electrical contacts  42  are disposed on layer  86 , for contact with corresponding conductors  38  on the surface  90  of the receptacle. High frequency signal traces  32  are disposed on layer  92  for contact with conductors  40  on the receptacle  14 . 
     In all of the embodiments shown in  FIGS. 6–12 , it is noted that two different low frequency connection paths are provided. Several different low frequency electrical connections can thereby be advantageously provided while the high frequency direct electrical connection is maintained. 
     Though the various embodiments described herein are directed to the use of a low frequency interconnection to maintain a high frequency direct electrical interconnection, a skilled artisan will realize that signals of various frequencies may be transmitted via the electrical connections that serve to provide pressure to maintain the high frequency direct electrical connection  46 . The frequencies of these signals may vary as long as they are compatible with the properties associated with standard electrical interconnects and with the electrical properties associated with their trace lengths and widths. 
     In accordance with further principles of the invention, it has been found convenient to provide some compliance in the substrate upon which the high frequency signal traces  32  are exposed, in order to improve the quality of the direct electrical connection formed by the contact of the exposed signal traces  32  with corresponding conductors  40  on the receptacle  14 . In  FIG. 13 , the substrate assembly  12  is shown to include a layer of polymeric material  100 , for example Kapton® polyimide film. The Kapton layer provides flexibility to the layer  102  upon which the exposed traces  32  are disposed, allowing the traces  32  to be positioned with uniform pressure against the corresponding exposed traces  40  on the receptacle when the substrate assembly  12  is inserted into the receptacle  14 . 
       FIG. 14  shows further mechanisms for improving the quality of the direct electrical connection. The exposed signal traces  32  are here shown to include differential pair  104 , and ground traces  106 . Longitudinal cuts  108  have been made in the top three substrate layers  110 , between the ground traces  106  and differential pair traces  104 . The bottom seven substrate layers  112  have been removed below the exposed traces  32 . Each ground trace  106  and the differential pair traces  104  are now supported on a bending beam  114 . Each ground trace  106  and the differential pair traces  104  can thereby move laterally relative to each other. When the substrate assembly  12  is inserted into the receptacle  14 , contact of uniform pressure is made between the exposed traces  32  and corresponding conductors  40  on the receptacle  14  even if there is slight lateral misalignment of any of the exposed traces  32  or  40 . 
     Though the current example shows the exposed traces  32  being supported by three substrate layers, a skilled artisan will realize that any number of substrate layers can provide a reasonably performing bending beam  114 . 
     In  FIG. 15  there is shown a top view of the substrate assembly  12  of  FIG. 13 . In this example, differential signal traces  104  are typically 3 to 8 mils (hundredths of an inch) wide, and spaced about 5 to 8 mils apart. The ground traces  106  are typically 3 to 8 mils wide. The ground traces  106  are typically spaced about 55 mils from the center of the differential traces  104 . For these dimensions, well performing bending beams  114  are produced by providing longitudinal cuts  108  that are typically about 20 to 30 mils wide, and about 100 to 150 mils deep. The skilled artisan will of course realize that reasonably performing bending beams  114  may be provided through cuts of different dimensions. 
       FIG. 16  shows the addition of an elastomer material  116  below the bending beams  114 , disposed within the area from which the substrate section  112  has been removed. The material may be for example one of the following: Poly(ethylene-co-propylene), commonly know as EPR, Poly(tetrafluoroethylene-co-perfluoropropylene), commonly known as Viton A, Poly(butadiene-co-styrene), commonly known as SBR, Poly(butadiene-co-aclonitrile), commonly known as Hycar, Poly(cis-1,4-butadiene), commonly known as Budene, Poly(cis-isoprene), which is natural rubber, Poly(2-hydroxypropyl acrylate), Poly(isobutylacrylate), or Poly(isobutylmethacrylate). 
     The addition of elastomer material  116  can provide additional elasticity to the bending beams  114 , particularly as the substrate that comprises the bending beams  114  loses flexibility over time. The elastomer material  116  flexibly supports the bending beams  114  as the substrate assembly  12  is inserted into the receptacle  14 , further facilitating a fit of uniform pressure between the exposed traces  32  and  40 . 
     In  FIG. 17 , there is shown another mechanism for improving the quality of the direct electrical interconnection. Traces  104  and  106  on a substrate assembly  12  are shown to have protrusions  120  disposed thereon, which may be for example welded gold ball contacts. These small protrusions  120  facilitate establishment of the direct electrical interconnection by deforming slightly against the corresponding trace when the substrate assembly  12  is inserted into the receptacle  14 . Nickel and gold protrusions, for example, may be formed on copper traces by pre-cleaning the copper surface, applying at least 0.120″ of electroless nickel on the copper, and then applying approximately 0.030″ electroless gold on the nickel surface. Embodiments of protrusions are described in U.S. Pat. No. 5,101,553, entitled “Method of making a metal-on-elastomer pressure contact connector,” which is incorporated by reference. The protrusions  120  may be disposed upon the traces  104  and  106  on the substrate assembly  12 , or on the corresponding traces on the receptacle  14 , or on both sets of traces. 
     In  FIG. 18 , there is shown another mechanism for improving the quality of the direct electrical interconnection. As shown herein, the high frequency signal traces  104  and  106  reside within channels  122 . The signal traces  104  and  106  reside on an exposed substrate layer  124 , while material has been removed from the substrate layer  126  above the layer  124  such that channels  122  are formed and such that the signal traces  104  and  106  reside on the floors of the channels. The upper substrate layers  128  have been removed above the channels  122  such that the signal traces  104  and  106  within the channels  122  are exposed for direct electrical interconnection with corresponding signal traces on a receptacle  14 . The channels  122  may be formed such that the channels are the same width as the signal traces  104  and  106 , or are wider than the signal traces  104  and  106 . The walls of the channels may be perpendicular to the plane of the substrate layer  124  or may be disposed at an angle, and may be straight or curved. 
     Also shown are resilient conductive members  130 , herein embodied as leaf springs. The resilient conductive members  130  are bonded to the exposed signal traces  104  and  106 , for example by soldering or welding. The resilient conductive members  130  may initially be part of a busbar assembly. The busbar assembly is aligned with the subtstrate assembly  12  such that the resilient conductive members  130  are aligned with the signal traces  104  and  106 . The resilient conductive members  130  are then welded or soldered to the traces  104  and  106 , preferably in a single operation, and then the busbar is cut off, leaving an individual resilient conductive member  130  on each trace  104  and  106 . Alternatively, individual resilient contact members  130  can be placed on each trace  104  and  106 , for example by hand or by pick-and-place machine. 
     Once attached to the signal traces  104  and  106 , the resilient conductors  130  protrude slightly above the top surface  132  of the layer  126 , for example by about 5 mils. When the substrate assembly  12  is inserted into the receptacle  14 , the resilient conductive members  130  will resiliently contact exposed signal traces on the receptacle  14  to form the direct electrical interconnection. The resiliency of the conductive members provides reliable electrical interconnections between each corresponding signal trace despite any warping or deformations that may exist in the substrate assembly  12  or the receptacle  14 . 
     The present invention is not to be limited in scope by the specific embodiments described herein. Indeed, various modifications of the present invention, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such modifications are intended to fall within the scope of the following appended claims. Further, although the present invention has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present invention can be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present invention as disclosed herein.