Abstract:
An area array connector for providing a thermal and an electrical interconnection between a first circuit element and a second circuit element is described. The area array connector includes at least one electrically conductive interconnector adapted to provide an electrical interconnection between the first circuit element and the second circuit element. The area array connector also includes at least one thermally conductive member adapted to provide thermal interconnection between the first circuit element and the second circuit element.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This Application claims the benefit under 35 USC 119(e) of U.S. Provisional Application No. 60/494,013, filed on Aug. 7, 2003. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to interposers, such as area array connectors adapted for connecting the contact pads of one generally planar circuit element, such as a printed circuit board, to corresponding contact pads on another generally planar circuit element, such as an integrated circuit or multichip module, and more particularly, but not by way of limitation, to an interposer adapted for both electrical and thermal energy transfer therethrough. 
   DESCRIPTION OF RELATED ART 
   The manufacture of printed circuit boards, and more particularly, circuit board connectors, has expanded greatly over the past several decades. Both designs and fabrication techniques have improved to the point that ease in assembly and reliability of connection can almost be guaranteed. Not the least of these developments is the advent of the printed circuit board connector and its assembly to the printed circuit board itself. For example, U.S. Pat. No. 3,671,917 teaches a printed circuit board connector of the “edge connector” variety wherein the contact terminals are first inserted into a substrate and an insulative housing snapped thereover. This particular technology addresses the basic underlying structure of a printed circuit board which includes a mounting board having a plurality of contact terminals mounted therein and insulative housing covering the terminals. In this particular embodiment, the housing comprises an outer shell open at the bottom to permit it to fit down over and enclose the contact terminals and has U-shaped edges at the top to define a printed circuit board receiving opening. The advantages of such assemblies were well known in the &#39;70s when edge connectors were in widespread use. As space became a design criteria, however, the type of connectors and the spacing of such connectors received intense focus. 
   As referenced above, in many electronic applications, compactness of the electronic assembly is one of the more critical goals. Several approaches have been used for increasing compactness, particularly within the utilization of semiconductor chip assemblies. For example, U.S. Pat. No. 5,367,764 teaches a method of making a multi-layer circuit assembly formed by laminating circuit panels with interposers incorporating flowable conductive material at interconnect locations and a flowable dielectric material at locations other than the interconnect locations. In this way, the flowable materials of the interposers, together with a reservoir, allow the interposers to compress and take up tolerances in the components. The flowable dielectric material encapsulates conductors on the surface of the circuit panels. Similarly, U.S. Pat. No. 5,570,504 teaches a multilayer circuit construction, method and structure made by stacking circuit panels having contacts on their top surface through conductors extending between top and bottom surfaces and terminals connected to the bottom end of each through conductor. These and other interconnecting systems and devices facilitate the aforesaid compactness in the electronic assembly. 
   Another approach to achieving compactness is to stack circuit cards, such as printed circuit boards, one upon another as referenced above for electrically connecting the circuit cards together. There are many advantages in this approach. In order to make use of such a compact arrangement, it is, however, necessary that the face-to-face connection of circuit cards be made assuredly both electrically and mechanically. Interposers, such as area array connectors, are often used to connect corresponding contact pads on adjacent circuit cards for this purpose. 
   One interposer design addressing many of these issues is set forth and shown in U.S. Pat. No. 6,220,869, (the &#39;869 patent) assigned the assignee of the present invention and incorporated herein by reference. As shown in the &#39;869 patent, an array connector is adapted to connect contact pads on one generally planar circuit element to corresponding contact pads on another generally planar circuit element. The connector has an insulated contact mounting sheet having a plurality of contact mounting apertures therein. A plurality of electrically conducting contacts are mounted in the contact mounting apertures, each contact having contact pad engaging legs resiliently projecting away from opposite faces of the contact mounting sheet. 
   Another interposer design address additional design issues is set forth and shown in U.S. patent application Ser. No. 10/285,777 (hereinafter the &#39;777 application) filed Nov. 1, 2002 and assigned to the assignee of the present invention and incorporated herein by reference. As shown in the &#39;777 application, an array connector is shown to be adapted to connect contact pads on a first generally planar circuit element to corresponding contact pads on a second generally planar circuit element by the use of an interposer housing. The interposer housing includes a plurality of electrical contacts strapped in a substantially parallel relationship to one another and wherein in one embodiment, the at least one electrical interconnector is a power interconnector. 
   It may thus be seen that various enhancements to and advantages for array connectors can be provided by innovations in the design of interposers and the use of such interposers relative to printed circuit boards. 
   Another design criteria that is often a major consideration in printed circuit board designs is that of heat transfer and/or heat dissipation, relative to various printed circuit board components mounted thereon. The necessity to remove heat from heat generating components has found wide spread focus and innovation. For example, U.S. Pat. No. 6,452,804 describes an assembly for supplying power and removing heat from a microprocessor while controlling electro magnetic emissions. U.S. Pat. No. 6,459,582 and U.S. Pat. No. 6,483,708 teach the use of a heat sink clamping assembly including an electrical circuit assembly, printed circuit board, a backing plate, a clamp plate, a thermal interposer and a heat sink. This assembly is set forth to provide a thermal conducting connection for removing heat from the electrical circuit. Likewise, U.S. Pat. No. 5,158,912 teaches the use of a semiconductor package having an integral heat sink. U.S. Pat. No. 6,449,155 teaches a land grid array subassembly including a stacked assembly of a heat sink, a thermal interface, a multi-chip module, a land grid array interposer, and a protective cover. 
   An important component of many interposer designs for electrically connecting circuit cards is that of providing power interconnection. In some conventional interposer designs power interconnection is provided through separate, large, discrete power contacts that have to be physically separated from the interposer. In other conventional interposer designs, a number of single electrical contacts are scattered around the interposer and connected electrically in parallel via the power and ground plane circuitry on the circuit card. This interposer design wastes a large amount of valuable circuit card area and creates a problem with what is commonly called “current sharing”, i.e., the need to split the current nearly equally between all of the parallel electrical contacts. 
   These and other designs have been suggested for use in heat dissipation and power interconnection between and/or among the multiple components and assembly members. It would be a distinct advantage therefore to incorporate an improved thermal conductive member in direct association with an interposer permitting the advantage of the interposer as described above in the &#39;777 application and the &#39;869 patent while affording enhanced thermal conductivity in a manner improving the operational efficiency in the structure. The present invention provides such an assembly by the use of an interposer in direct association with the a heat sink assembled therewith. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention relates to interposers adapted to allow both electrical and thermal energy transfer therethrough. More particularly, one aspect of the invention is directed to a connector assembly for providing an electrical interconnection between a first circuit element and a second circuit element. The connector assembly may include an interposer and at least one electrically conductive interconnector disposed within the interposer. The at least one electrically conductive interconnector is adapted to provide an electrical interconnection between the first circuit element and the second circuit element. The assembly may also include at least one thermally conductive member in association with the interposer. The at least one thermally conductive member is adapted to provide thermal interconnection between the first circuit element and the second circuit element. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings wherein: 
       FIG. 1  is an exploded view of a system in accordance with aspects of the present invention; 
       FIG. 2  is an enlarged view of the system of  FIG. 1 ; 
       FIG. 3  is an exploded view of a bottom surface of the interposer, IC package, and cover of  FIG. 1 ; 
       FIG. 4  is a top view of the interposer of  FIG. 1  with several layers of the laminated housing and a large fraction of the individual contacts hidden from view in order to make the internal structure of the interposer more readily visible; 
       FIG. 5  is an unexploded cross-sectional view of the system of  FIG. 1 ; 
       FIG. 6  is a perspective view of an integrated heat sink and interposer according to an aspect of the present invention; 
       FIG. 7  is a perspective view of the heat sink of  FIG. 6 ; 
       FIG. 8  is a perspective view of the interposer of  FIG. 6  with the heat sink hidden from view; 
       FIG. 9  is a perspective view of the heat sink of  FIG. 7  and a portion of the interposer of  FIG. 8 ; 
       FIG. 10  is a perspective view of the heat sink of  FIG. 7  and a portion of the interposer of  FIG. 8 ; 
       FIG. 11  is a flow diagram of a method of manufacturing the integral heat sink and interposer of  FIG. 1 ; and 
       FIG. 12  is a flow diagram of a method of manufacturing the integral heat sink and interposer of  FIG. 6 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   To improve the heat transfer from heat emitting elements, such as integrated circuits (ICs), a variety of heat dissipation techniques may be applied. In accordance with one embodiment of the present invention, as shown in  FIG. 1 , a system  100  may implement an integrated heat sink  102  and interposer  104 . By including the heat sink  102  at a central portion of the interposer  104 , the heat sink  102  improves the heat conduction from an IC package  106  through the system  100 . The path of the heat flow from the heat emitting element (IC package  106 ) maximizes the conductivity of the conduction path and improves heat transfer. 
   The IC package  106  typically includes an outer ceramic shell  110  and an IC chip  112 . The IC package  106  may be protected by a cover  108 . The IC package  106  is connected electrically and thermally through the interposer  104  and the heat sink  102  to a printed wiring board (PWB)  114  which may then be integrated within an electronic device such as a flight control computer in a jet fighter or missile. The PWB  114  may include one or more circuitry layers  118  and at least one thermal plane  116 . The thermal plane  116  may extend beyond the outside edges of the circuitry layers  118  to contact another system component or a chassis (not shown) of the electronic device. The thermal plane  116  is typically formed of a thermally conductive material and fastened to the chassis by a metal fastener in order to provide a heat conduction path from the thermal plane  116  to the chassis. Also shown on the surface of the PWB  114  near the interposer  104  is a pattern of electrical contact pads  120 . The electrical contact pads  120  are typically gold plated and correspond to the signal contact location in the interposer  104 , however other materials and orientations are possible. In a central portion of the pattern of electrical contact pads  120  is a large pad  122  which, in this embodiment, is fashioned as a solid metal plug directly connected to the thermal plane  116 . 
   When active, the IC chip  112  emits heat that is transferred to surrounding components. To prevent the heat from destroying the IC chip  112 , the heat is transferred from the IC chip  112 , through the thermally conductive ceramic IC package, to the large pad  122  via the heat sink  102 . The large pad  122  dissipates the heat through the thermal plane  116  to another system component or the chassis (not shown). 
   Referring now to  FIG. 2 , an enlarged view of the system  100  of  FIG. 1  is illustrated. As shown more clearly in  FIG. 2 , the interposer  104  includes five layers, although other configurations are possible. The heat sink  102  is located under the IC chip  112  and above the large pad  122  to allow a direct conduction path for the heat to flow from the IC chip  112  to the thermal plane  116 . A contact pattern  124  is located on an upper surface of the interposer  104 . In one embodiment, the contact pattern  124  may include a 20×20 array of contacts  126 , however, the contact pattern  124  may include a variety of shapes and sizes depending on the IC package  106  to be connected to the PWB  114 . 
   Referring now to  FIG. 3 , an exploded view of a bottom surface of the interposer  104 , IC package  106 , and cover  108  of an embodiment of the present invention is illustrated. The bottom surface of the IC package  106  includes pads  130  which are typically gold plated. The locations of the pads  130  correspond to the locations of the contacts  126  on the upper surface of the interposer  104 . The IC chip  112  (not shown) is situated on the upper surface of the ceramic shell  110  and a layer of heat conductive ceramic separates the IC chip  112  from the interposer  104 . The heat of the IC chip  112  is conducted through the conductive ceramic to the heat sink  102  of the interposer  104 . 
   Referring now to  FIG. 4 , a top view of the interposer  104  of an embodiment of the present invention is illustrated. At least one upper layer of the interposer  104  is hidden from view to show an intermediate layer  140  of the interposer  104 . The heat sink  102  may include a lip  142  for retaining the heat sink  102  within the interposer  104 . In this embodiment, the lip  142  extends slightly beyond the inner perimeter of the central cut-outs in the layers immediately above and below the intermediate layer  140  so that when the at least one upper layer is placed on the upper surface of the intermediate layer  140 , the upper and lower layers overlap the extensions on the perimeter of the heat sink thus holding the heat sink  102  in place. Although the present embodiment illustrates the heat sink  102  as including a lip  142  for placement between layers of the interposer  104 , the heat sink  102  may be formed so that the lip  142  extends along an upper surface or lower surface of any of the layers of the interposer  104 , including the uppermost and lowermost layers. In addition, the heat sink  102  may be held in place by means other than a lip  142 . For example, the heat sink  102  may be bonded to the interposer  104 . The heat sink  102  shown is a substantially square shape, however other configurations are possible such as a rectangular, pentagonal, or circular shape. 
   Referring now to  FIG. 5 , a cross-sectional view of the system of  FIG. 1  is illustrated. The cover  108  is placed on an upper surface of the IC package  106 . The IC package includes the IC chip  112  that is set in the ceramic shell  110 . The bottom surface of the IC package  106  rests on a top surface of the interposer  104 . The contacts  126  meet the pads  130  of the IC package  106 . The heat sink  102  is oriented within the interposer  104  and in a region near the IC chip  112 . The interposer  104  and heat sink  102  are oriented above the PWB  114  which includes the thermal plane  116 . The thermal plane  116  extends to form the large pad  122  in direct contact with the heat sink  102 . 
   The heat flow begins at the IC chip  112  and is conducted directly through the ceramic shell  110  of the IC package  106  to the heat sink  102 . The heat sink  102  allows conduction of the heat to the thermal plane  116  via the large pad  122  (if present). The thermal plane  116  disperses the heat to another system component or the chassis. 
   Now referring to  FIG. 6 , an alternate embodiment of the integrated heat sink  602  and interposer  604  in accordance with an aspect of the present invention is illustrated. In this embodiment, the heat sink  602  is oriented in a ring-type fashion to form an outer border around the interposer  604 . The contact pattern  624  is arranged in a central portion of the integrated heat sink  602  and interposer  604 . An IC chip (not shown) emits heat that is transferred to the ceramic shell (not shown) and is absorbed by the heat sink  602  at an outer portion of the ceramic shell. 
   Referring now to  FIG. 7 , a perspective view of the heat sink  602  of  FIG. 6  is illustrated. As shown, the heat sink  602  includes a top face  700 , a bottom face  702 , a front exterior face  704 , two side exterior faces  706 ,  710 , and a back exterior face  708 . The heat sink  602  also includes a front interior face  712 , two side interior faces  714 ,  718 , and a back interior face  716 . Along the front, back, and side interior faces  712 ,  714 ,  716 , and  718 , a lip  642  extends into a void  720  into which the interposer  604  is positioned. When the interposer is fully assembled, the lip  642  is sandwiched between the center layer and the two layers above and below the center layer thus holding the interposer  604  and heat sink  602  together securely. The lip  642  may be placed anywhere along the interior faces  712 ,  714 ,  716 , and  718 . In addition, the lip  642  may be located on only a portion of the interior faces or may not be present on all or some of the interior faces  712 ,  714 ,  716 , and  718 . Alternatively, the heat sink  602  may be fastened to the interposer  604  by other means such as bonding. 
   Referring now to  FIG. 8 , a perspective view of the interposer  604  of  FIG. 6  is illustrated. A top face  810  of the interposer includes apertures through which the contacts  626  extend. The interposer  604  may include a front face  802 , two side faces  804 ,  808 , and a back face  806 . Along the faces  802 ,  804 ,  806 , and  808  a notch  800  is configured to receive the lip  642  of the heat sink  602 . In a manner similar to that of the lip  642  of the heat sink  602 , the notch  800  may be oriented on only a portion of the faces or may not be present on all or some of the faces  802 ,  804 ,  806 , and  808 . Alternatively, the heat sink  602  may be fastened to the interposer  604  by other means such as bonding and therefore, the notch  800  may not be necessary. 
   Referring now to  FIGS. 9 and 10 , an integration of the interposer  604  to the heat sink  602  is illustrated. To laminate the heat sink  602  to the interposer  604 , a lower layer of the interposer  604  is positioned in the void  720  created by the heat sink  602 . The lower layer of the interposer  604  is positioned below the lip  642 . The upper surface  900  of the lower layer of the interposer  604  may abut a lower surface of the lip  642 . As shown in  FIG. 10 , an intermediate layer  902  of the interposer  604  is placed in the void  720  above the lower portion of the interposer  604 . The intermediate layer  902  is configured to accommodate the lip  642  of the heat sink  602 . An upper layer (not shown) is added on top of the intermediate layer  902  in order to lock the heat sink  602  into the interposer assembly. 
   As previously mentioned, the notch  800  may not be necessary in some applications, and therefore, the intermediate layer  902  may be formed in a similar configuration as the upper and lower layers. Furthermore, the interposer  604  may not be composed of layers and the configuration of the faces  802 ,  804 ,  806 , and  808  may be made on a single piece interposer. 
   Referring now to  FIG. 11 , a method  1100  of forming the integral heat sink and interposer of an aspect of the present invention is illustrated. At step  1102 , an interposer is formed to include a central void. The interposer may have a variety of shapes, thereby affecting the shape of the void defined by the interposer. At step  1104 , a heat sink is formed to fit substantially in the void defined by the interposer. The heat sink may extend above or below the edges of the interposer, depending on the requirements of the system. At step  1106 , the heat sink may be fastened to the interposer. The heat sink and interposer may be bonded or laminated together. 
   Referring now to  FIG. 12 , an alternate method  1200  of forming the integral heat sink and interposer of an aspect of the present invention is illustrated. At step  1202 , a heat sink is formed with a central void. As noted above, the heat sink, and the void, may be configured in a variety of shapes and sizes. At step  1204  an interposer is configured to be substantially positioned in the void created by the heat sink. The heat sink and interposer are fastened together by a suitable means at step  1206 . For example, the heat sink and interposer may be bonded or laminated together. 
   Although the above embodiments have shown the heat emitting element as an IC chip, it would be readily apparent to one skilled in the art that other heat emitting elements, such as a multichip module, may be utilized in accordance with the present invention. In addition, the PWB has been shown with a large pad to conduct heat from the heat sink to the thermal plane. However, the PWB may have a cutout along the top surface to allow a heat sink formed with a protrusion to directly contact the thermal plane. The protrusion of the heat sink may extend beyond the bottom surface of the interposer and fit through the PWB cutout in order to contact the thermal plane. 
   It should be understood that the heat sink and interposer of the present invention may be constructed of a number of suitable materials. In one aspect of the present invention, the heat sink may be constructed of copper, which provides for a very high thermal conductivity. In another aspect of the present invention, the heat sink may be constructed of aluminum which includes the properties of high thermal conductivity as well as low material density. In another aspect of the present invention, the layers of the interposer may be constructed from printed circuit board material. Examples of suitable printed circuit board construction materials include non-woven aramid fiber filled epoxy materials, such as those manufactured by Arlon. In still another aspect of the present invention, the interposer may be of a molded construction using glass filled polyphenylene sulfide (PPS) material, such as that manufactured under the tradename Fortron by Ticona. In still another aspect of the present invention, the interposer may be of a molded construction using a liquid crystal polymer (LCP) material. 
   Although a preferred embodiment of the method and apparatus of the present invention has been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it is understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications, and substitutions without departing from the spirit of the invention as set forth and defined by the following claims.