Abstract:
An enclosure or containment system for expansion cards includes first and second sub-enclosures that interengage to form an enclosure assembly that substantially surrounds the major surface areas of the expansion card while providing support along some of the edges thereof to provide a protected volume that physically protects and shields the electronic and electrical components on the expansion card while providing enhanced heat transfer therefrom.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of commonly owned U.S. Provisional Patent Application 60/987,177 filed Nov. 12, 2007 by the inventor herein, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to printed circuit board systems of the type having a mainboard (also known as a motherboard) into which one or more printed circuit boards (known as expansion cards or daughterboards) are connected via connector arrangements and, more particularly, to an enclosure system for the expansion cards that provides a ruggedized containment for each expansion card and which maximizes the opportunity for heat transfer from the expansion card to the external environment and which also provides improved EMI shielding. 
     In the packaging of electronic systems using a plurality of printed circuit boards, one common architecture involves a primary printed circuit board, variously referred to as a backplane, a baseboard, a mainboard, or, more commonly, as a motherboard, that includes a plurality of connectors for receiving subsidiary printed circuit boards, commonly referred as expansion cards or daughterboards. With this type of system, currently used in personal computers, function-specific expansion cards can be easily removed and replaced with different expansion cards having improved functionality or different functions. Typically, the expansion cards correspond to one of several form factors and have standardized edge connectors: expansion cards in common usage can conform to the ISA, EISA, AGP, PCI, PCIe standards and variants thereof with the expectation that expansion card form-factors and connector arrangements will continue to evolve. 
     In the motherboard/expansion card architecture discussed above and as used in many computer architectures, the expansion cards are typically held in place by a single threaded fastener at one end of the expansion card, and/or, in some cases, by claw-like clamp at the opposite ends of each expansion card that interengages with the connector. While these board-retaining arrangements are adequate for stationary applications with a minimum of vibration, the generic motherboard/expansion card architecture is not well suited for mobile applications where the system will be exposed to vibrations, shock forces, jolts, and other accelerations or G-forces. Additionally, the individual expansion cards in the generic motherboard/expansion card architecture are exposed to EMI radiated from adjacent expansion cards and from other EMI sources. 
     The heat generated by the electronic components in the motherboard/expansion card architecture is typically transferred from the boards by forced air cooling by which fan-forced ambient air passes over the boards to remove heat with the now-heated air exhausted from the enclosure. Typically, some types of enclosures contain the motherboard/expansion card assembly with one or more axial-flow fans mounted in the enclosure and, in many cases, smaller axial-flow fans and fan/heat sink combinations are attached to selected integrated circuits on the boards, these integrated circuits typically providing microprocessor, graphical, or video processing functionality. 
     SUMMARY 
     The present invention provides an encasement for each expansion card or daughterboard in a protective enclosure that provides a measure of physical protection and EMI shielding of the expansion card while providing effective conductive and convective thermal coupling between the expansion card and the ambient environment to efficiently remove heat therefrom. 
     In a preferred embodiment, first and second sub-enclosures interengage to form an enclosure assembly that substantially surrounds the major surface areas of the expansion card while providing support along at least some of the edges thereof. Additional components then substantially fully enclose the expansion card to provide a protected volume that provides both physical protection and EMI shielding for the electronic and electrical components on the expansion card while providing enhanced heat transfer therefrom. 
     If desired, the various so-enclosed expansion cards can be mechanically interengaged to form a connected group of so-enclosed expansion cards to provide an structurally integrated and ruggedized system with an additional level of EMI shielding. 
     In another embodiment, a unitary sub-enclosure substantially surrounds the major surface areas of the expansion card while providing support along at least some of the edges thereof. 
     The embodiments provide two primary thermal paths from the electronic components via direct conductive heat transfer from at least some of the edges of the expansion cards and convective heat transfer from the electrical components to the enclosure itself. If desired, various of the integrated circuits can also be directly thermally coupled to their enclosure by using a thermally conductive interface material or a thermally conductive gap filler. The convective thermal paths and the various thermal conductive paths keep the temperature differential between the electronic components and the enclosure to a minimum to ensure efficient heat transfer. 
     The convective heat transfer path between the enclosure and the external environment is optimized because of the relatively large surface area provided for each expansion card with in its enclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is plan view of a representative or example daughterboard or expansion card showing electrically conductive traces along one side thereof that define an edge connector and also showing a representative integrated circuit thereon; 
         FIG. 2  is an isometric view of the expansion card shown in  FIG. 1 ; 
         FIG. 3  is an isometric view of the expansion card of  FIGS. 1 and 2  contained within an enclosure assembly; 
         FIG. 4  is an isometric view of the expansion card of  FIGS. 1 and 2  contained within the enclosure of  FIG. 3  taken from the edge-connector side of the expansion card; 
         FIGS. 5 and 6  are end views of the enclosure of  FIGS. 1 and 2  with an end plate removed to reveal interior components; 
         FIG. 7  is an enlarged detail of selected structures of first and second sub-housings; 
         FIG. 8  is an enlarged detail of the structures of  FIG. 7  interengaged with one another; 
         FIG. 9  illustrates the manner by which the first and second sub-housings interconnect to constrain an expansion card therebetween; 
         FIG. 10  illustrates a motherboard arrangement for accepting enclosures of the type shown in  FIGS. 2 and 3 ; 
         FIG. 10   a  is an enlarged detail of interengaged flanges for connecting adjacent enclosures together to form a connected group of enclosures; 
         FIG. 11  illustrates the system of  FIG. 10  fully populated with enclosures of the type illustrated in  FIGS. 2 and 3 ; and 
         FIG. 12  illustrates a variant of the enclosure housing structure in which the housing is a one-piece structure. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a plan view and  FIG. 2  is an isometric view of a representative or example expansion card  20  having an edge connector  22  on a forward or connector-side of the expansion card  20  and defined by a plurality of spaced parallel conductive traces (unnumbered) and a rear edge  24  on the side opposite the front or connector side. The expansion card  20  shown is representative of a contemporary PCI architecture; however, the invention is suitable for use with any type of known interface board including the ISA, AT, EISA, AGP, and current and proposed PCI variants as well as any other board configurations that may or may not correspond to an industry-accepted standard. As shown, the board is populated with electronic components as symbolically represented at  26 , and, while not shown, can include one or more subsidiary boards, currently known a “mezzanine” boards. For those components that require augmented heat removal, a heat sink and/or fan can be mounted upon or associated with the component, as is known. In a typical configuration and as explained below, the edge connector  22  of the various expansion boards/cards is designed to be received by respective socket, socket-like receptacle, or similar connectors on a motherboard, baseboard, backplane, mainboard, systemboard, etc. 
       FIGS. 3 and 4  show the expansion card  20  of  FIGS. 1 and 2  mounted in a protective enclosure, generally designed by the reference character  30 . The enclosure  30  is defined by first sub-housing  32  and a second sub-housing  34  (described in more detail below) that cooperate with end plates  36  ( FIG. 3  only) to define a protected volume for the expansion card  20 ; in the preferred embodiment, the end plates  36  are fabricated from flat sheet stock. The protective containment defined by first sub-housing  32  and the second sub-housing  34  provides a measure of physical protection and EMI shielding for the so-enclosed expansion card  20  as well as plural heat transfer paths for transferring heat therefrom. 
       FIGS. 5 and 6  show the opposite ends of the enclosure  30  with the end plates  36  removed for reasons of clarity. As shown, the first sub-housing  32  and the second sub-housing  34  are designed to interengage around the expansion card  20  to provide support therefor along the rear edge  24  and an area  38  spaced from the edge connector end at the forward or connector end of the expansion card  20 . Both the first sub-housing  32  and the second sub-housing  34  are preferably fabricated as an extrusion from a heat-conducting metal (i.e., aluminum or aluminum alloy or equivalent metal or metal alloy) or a non-metallic material have sufficient thermal conductivity; the sub-housings are at least as long as the end-to-end dimension of the expansion card to fully contain the expansion card therein. The first sub-housing  32  and the second sub-housing  34  include respective fins,  40  and  42 ; while fins are preferred, other heat-radiating structures, such as slotted fins or spines, or some combination thereof, are also suitable. Additionally, the first and second sub-housings,  32  and  34 , are provided with screw-accepting formations, generally indicated at  44 , for accepting self-tapping screws to secure the end plates  36  to the opposite ends of the enclosure  30 . While the use of self-tapping screws is preferred, conventionally threaded bores for accepting machine screws are also suitable. As shown in the lower part of  FIGS. 5 and 6 , the second sub-housing  34  includes a flange  64  that is spaced by one flange thickness from the back surface  66  of the sub-housing  32 . Additionally, the sub-housings  32  and  34  include a fin or fins  68  that extend rearwardly of the sub-housings  32  and  34 . 
       FIG. 7  illustrates the formations on the first sub-housing  32  that interengage with complementary formations on the second housing  34  to embrace the rear edge or rear margin of the expansion card  20 . As shown, the first sub-housing  32  includes a forwardly facing cleat  46  that, along with a raised ridge  48   a  formed on a fin  48 , defines a slot  50 . In a similar manner, the second sub-housing  34  includes a rearward facing cleat  52  that also defines a slot  54 . 
     As shown in  FIG. 8 , the cleats  46  and  52  interengage with one another with the cleat  46  received in the slot  54  and the cleat  52  received in the slot  50  while the ridge  48   a  defines a backstop for the rear edge  24  of the expansion card  24 . As shown, the spacing between the cleat  52  and the fin  48  is sufficient to accommodate the thickness of the expansion card  20  and hold the rears portion  24  in a channel, groove, or slot (unnumbered) defined between the cleat  52 , the fin  48 , and the ridge  48   a . While not shown in the figures, a heat transfer gel or an elastomeric heat-transfer material (not shown) can be interposed between the two sides of the expansion card  20  and the corresponding surfaces of the first and second sub-housings  32  and  34  to enhance conductive thermal transfer from the expansion card  20  to the first and second sub-housings  32  and  34 . 
       FIG. 9  illustrates the expansion card  20  mounted between the first and second sub-housings  32  and  34  with forward end of the expansion card  20  constrained between surfaces of the first and second sub-housings  32  and  34  as shown at  38 . Since most expansion cards  20  have conductive traces at or adjacent the area  38 , various types of electrically insulating materials, layers, tapes, sheets, gaskets, etc, are interposed between the surface of the expansion card  20  the sub-housings to preserve electrical integrity. If desired, a heat transfer gel or an elastomeric heat-transfer material (not shown) can be interposed between the two sides of the expansion card  20  and the corresponding surfaces of the first and second sub-housings  32  and  34  to enhance conductive thermal transfer from the expansion card  20  to the first and second sub-housings  32  and  34 . 
     The assembly of  FIG. 9  is completed by installation of an end plate  36  ( FIG. 3 ) on opposite ends of the assembly of  FIG. 9  to connect the first and second sub-housings  32  and  34  together to define the protected enclosure  20 . In the preferred embodiment, the end plates  36  are held in place by threaded fasteners; however, other attachment arrangements, including spring clips are suitable. The protected volume defined by the enclosure shown in  FIG. 9  provides a measure of physical protection and EMI shielding for the so-enclosed expansion card  20  and both conductive and convective heat transfer paths for transferring heat therefrom. 
     In general and as shown in  FIG. 10 , expansion cards  20  of the type described are designed to “plug-in” to socket-type strip connectors on a motherboard (also known as the system board, mainboard, and/or baseboard).  FIG. 10  shows a representative motherboard system  100  in which a single enclosure  30  (without its end plate  36 ) is installed immediately adjacent a thicker enclosure  30 ′ (also without its end plate  36 ). Enclosures of different thicknesses are contemplated and, in the case of the enclosure  30 ′, the additional interior volume can accommodate an additional sub-board (i.e., a “mezzanine” board) connected to the board  20  as well as a heat sink and/or cooling fan(s) (not shown) that are often mounted on expansion cards. 
     The structure of  FIG. 10  includes a motherboard  102  having spaced socket-like connectors  104  designed to receive the edge connector  22  extending from each enclosures  30 . While not shown in the figures, cable trays or conduits are provided for any cabling that enters/exits the motherboard system  100 . 
     As shown in the enlarged detail of  FIG. 10   a , each of first and second sub-housings  32  and  34  include interengaging flanges  64  and  66  at the back ends of the respective sub-housing with one of the flanges offset from the other by approximately the thickness of one flange so that the two flanges overlap with the overlapping flanges secured together by removable screws or similar fasteners (not shown). The overlapping flanges  64  and  66  thus allow the adjacent enclosures  30  to be secured to one another to define a connected set of enclosures  30  that increases the overall structural sturdiness of the system. 
       FIG. 11  illustrates the motherboard system  100  of  FIG. 10  fully “populated” by enclosures  30  with their end plates  36  and increased thickness enclosure  30 ′ and its endplate  36 ′ in place and secured to one another as described in relationship to  FIG. 10   a.    
     The system shown in  FIG. 11  thus provides a physical and EMI protected volume for each expansion card  20  with enhanced thermal paths from the expansion card  20  to address heat transfer concerns and with the various enclosures  30  mechanically connected or “ganged” together to provide an additional level of structural and EMI protection. 
     As shown in  FIGS. 10 and 11 , the cooling fins  40  of the sub-housing  32  and the cooling fins  42  of the sub-housing  34  are located on their respective sub-housings so that they occupy different ‘staggered’ or interdigitated planes “A” and “B” as best shown in  FIG. 11 ; this staggered relationship allows for increased convective heat flow. 
     In the preferred embodiment described above, the enclosure  30  is defined by first and second sub-housings  32  and  34  to thus define a two-piece arrangement for the enclosure  30 . As can be appreciated and as shown in  FIG. 12 , a one piece housing is contemplated in which the housing is extruded as a one piece component. In the arrangement of  FIG. 12 , the expansion card  20  is slid into the housing from one end or the other with the end plates  36  thereafter assembled to the one-piece housing to thereby create the enclosure  30 . 
     As will be apparent to those skilled in the art, various changes and modifications may be made to the illustrated embodiment of the present invention without departing from the spirit and scope of the invention as determined in the appended claims and their legal equivalent.