Patent Publication Number: US-6984156-B2

Title: Connector for surface mounting subassemblies vertically on a mother board and assemblies comprising the same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 60/500,405, “Connector For Surface Mounting Subassemblies Vertically On A Mother Board And Assemblies Comprising The Same”, filed Sep. 5, 2003. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to devices for mounting electrical devices, such as printed circuit subassemblies, to other electrical devices, such as printed circuit mother boards. 
     BACKGROUND OF THE INVENTION 
     Electronic systems are becoming faster, denser in the number of components, and increasingly complex. Increasing density typically requires greater current which, in turn, requires low resistance interconnection and effective heat dissipation. Higher speed and larger currents require low inductance. Increasing complexity often requires that subassemblies be mounted and connected onto system boards (“mother boards”). 
     Both the subassemblies and the mother boards are typically printed circuit boards comprised of insulating substrates supporting patterns of conductive leads, mounting pads and circuit components. Such assemblies are now quickly manufactured by a surface mount technology that can precisely place components on mounting pads and efficiently connect them by solder reflow. 
     Surface mount assembly works well with small components. However subassemblies can be relatively large in area compared with individual components, and in connecting one printed circuit board (e.g. a subassembly) to another (e.g. the mother board) can present issues of co-planarity. If the two printed circuit boards are not sufficiently co-planar, mounting pads may not touch and solder reflow will not connect. 
     Accordingly, there is a need for a mounting and connection system for providing high density, low resistance, low inductance connections using surface mount technology. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention a surface mount connector is provided for vertically mounting one circuit device on another. By “vertically mounting” is meant that a circuit device with a major surface is mounted perpendicular to the major surface of another circuit device. The connector is a conductive body comprising a base section and a transverse section, the base section having a width greater than the transverse section and a length which extends beyond the transverse section. Advantageously, the base section extends beyond the transverse section in front, behind and on both sides. In typical use, a major surface of a subassembly can be connected to the transverse section and an edge of the subassembly can be connected to the base extensions. The base can then be connected to the mother board. With this mounting, problems of co-plurality are substantially eliminated, higher densities in the use of subassemblies can be achieved and low resistance, low inductance connection can be provided along with effective heat dissipation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages, nature and various additional features of the invention will appear more fully upon consideration of the illustrative embodiments now to be described in detail in connection with the accompanying drawings. In the drawings: 
         FIG. 1  is a perspective view showing a first circuit device having a second circuit device vertically connected to it; and 
         FIG. 2  is a perspective view of a connector useful for vertically connecting the second circuit device to the first. 
     
    
    
     It is to be understood that these drawings are for purposes of illustrating the concepts of the invention and are not to scale. 
     DETAILED DESCRIPTION 
     Referring to the drawings,  FIG. 1  is a perspective view of a connected circuit assembly  10  comprising a first circuit device  11  having a generally planar major surface  12  and a second circuit device  13  having a major surface  14  and edges  15 . The first circuit device  11  can for example, be the system board (mother board) of the assembly, and the second circuit device  13  can be a subassembly board. Each device  11 ,  13  will typically comprise a printed circuit board having substantially planar major surfaces that bear mounting pads (e.g.  19 A,  19 B), adherent conductive leads (not shown) and a plurality of electrical components  16  such as integrated circuits, resistors, capacitors or inductors. The circuit devices are typically comprised of insulating PC boards that may include one or more internal conductive layers  17 . 
     If the second circuit device  13  were connected to the first circuit device  11  with the major surfaces parallel, the second device  13  would occupy a relatively large area on the surface of device  11 . Moreover, if the devices were printed circuit boards and were to be connected using conventional surface mount technology, co-planarity would be an issue, as mounting pads must be in contact for reliable connection by solder reflow. 
     Rather than connecting the devices with their major surfaces parallel, the present inventors contemplate that the second device  13  will be connected with its major surface(s) perpendicular to the major surface of device  11 , and they provide connectors  20  to facilitate such perpendicular (vertical) connection compatible with surface mount fabrication of the assembly  10 . 
       FIG. 2  is an enlarged perspective view of the surface mount connector  20  useful for vertically connecting the second circuit device to the first. The connector  20  is composed of a conductive body  21  comprising a base section  22  and a transverse section  23 . 
     With reference to the coordinate system shown in  FIG. 2 , the base section  22  can be a sheet of conductive material that is essentially planar in the xy-plane. The transverse section  23  is essentially planar in the y-z plane, substantially perpendicular to the base section. The base section  22  advantageously has a width W in the y-direction greater than the extent w of the transverse section in the y-direction so that one or more arm portions  24  of the base section extend beyond the transverse section in the x-direction. Thus the base section advantageously extends beyond the transverse section in front, behind (via arms  24 ) and on both sides, providing the transverse section with a firm foundation for mounting. 
     The connector  20  can be readily fabricated from a rectangular sheet of conductive material such as copper or copper alloy. A pair of cuts in the sheet separates the portion to become the transverse section  23  from the arms  24 , and the transverse section can then be bent perpendicular to the sheet, leaving the remainder of the sheet as the base section  22 . The resulting connector has arms  24  extending beyond the transverse section by a length that, in this instance, equals the height of the transverse section. 
     The connector is preferably provided with solderable surfaces. Copper alloys such as phosphor bronze, beryllium copper or brass are advantageously plated with a thin layer of copper, nickel or gold, followed by solder, to enhance solderability. Alternatively, the connector can be provided with a surface finish appropriate for adhesion by a thermally and electrically conductive epoxy. 
     The large form factors of the base and transverse sections provide paths with low inductance and low electrical and thermal resistance. Making the sections relatively thin with relatively large areas minimizes inductance and resistance. 
     A convenient way to fabricate the assembly of  FIG. 2  is to apply one or more connectors  20  to the subassembly  13  and then to surface mount the connectors on subassembly  13  to the system board  11 . The subassembly  13  can be provided with mounting pads  19 A on the major surface  12  and optional mounting pads  19 B on an adjacent edge  15 . The connectors can be picked up and placed on the subassembly as conventional surface mount components, the transverse section serving as a vacuum nozzle pick-up point. During reflow soldering, the surface tension of the solder will draw the connectors toward the mounting pads so that the transverse section and the arms are flush with the subassembly board. Assuming the edge of the subassembly is properly finished (&lt;0.1 mm), the subassembly  13  can then be surface mounted on the mother board by placing the connector bases onto aligned mounting pads on the system pad  11  and reflow soldering. 
     It is understood that the above-described embodiments are illustrative of only a few of the many possible specific embodiments, which can represent applications of the invention. Numerous and varied other arrangements can be made by those skilled in the art without departing from the spirit and scope of the invention.