Abstract:
A computing system includes a number of circuit cards fastened by brackets to a slotted panel, which has slots allowing the attachment of external cables to the circuit cards. Electrical grounding between the slotted panel and the brackets is achieved through the use of a conductive gasket extending along an inner surface of the slotted panel. The conductive gasket includes a central web, a number of contact bumps extending from the central web to the slotted panel, and a number of contact bumps extending from the central web to the brackets. Contact bumps thus extending in opposite directions are placed in alternating positions along the central web, so that the central web is deflected as the contact gasket is compressed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a conductive gasket for improving electrical grounding between adjacent conductive parts, and, more particularly, to a gasket for improving electrical grounding within a computing system between a slotted panel through which connectors of circuit cards extend for the attachment of external cables and brackets mounting such circuit cards. 
     2. Background Information 
     FIGS. 1 and 2 are fragmentary elevations of a conventional computing system  8  including a mother board  10  and a conventional circuit card  12  having a tab  14  inserted within a card edge connector  16  of the mother board  10 . FIG. 1 is a fragmentary vertical cross-sectional elevation of the computing system  8 , while FIG. 2 is a fragmentary rear elevation thereof. 
     The rear end  18  of the circuit card  12  includes a card bracket  20  attached to a slotted panel  22 , forming part of the computing system, by means of a screw  24 . An individual slot  26  within the slotted panel  22  provides a space through which an I/O connector  28  extends for attachment to an external cable (not shown). Thus the card  12  is rigidly held in place by the screw  24  near its top edge  30  and by the engagement of its tab  14  with the card edge connector  16  near its lower edge  32 . The mother board  10  may be a relatively large system (or planar) board extending inwardly adjacent a cover  36  of the computing system. Alternately, the mother board  10  may be a riser board extending perpendicularly from the system (or planer) board to provide for the attachment of one or more circuit cards  12 . Typically, the computing system  8  includes a number of card edge connectors  16  and a number of slots  26 , each of which is located in a standard way relative to a connector  16  to provide for the installation of a standard type of circuit card  12 . While each circuit card  12  has a card bracket  20 , not all cards  12  have I/O connectors  28 . Cards  12  without I/O connectors, which are not configured for attachment to external cables, include brackets  20  which are used to close an associated slot  26  within the slotted panel  22 . When a circuit card  12  is not placed in one of the card edge connectors  16 , the associated slot  26  is closed by a filler bracket  38 , which is not attached to a circuit card  12 . Like the card brackets  20 , each filler bracket  38  is fastened in place using a screw  24 . 
     Electrical contact between the card bracket  20  and the slotted panel  22  is typically used to provide for electrical grounding of circuits within the circuit card  12  and within an external cable (not shown) connected to the I/O connector  28 . This contact may form a portion of multiple grounding points. Electrical contact between the card bracket  20  and the slotted panel  22  is also used to close a slot through which radio-frequency electromagnetic noise could otherwise be radiated to interfere with electronic communications. 
     A problem with this conventional approach arises from the uncertain nature of the electrical contact established between the card bracket  20  and the slotted panel  22 . While specific contact pressure between the card bracket  20  and the slotted panel  22  is established adjacent the head of screw  24 , the contact pressure at other locations between these parts depends on the slightly variable dimensions of parts, including their flatness. 
     A card bracket formed from a thin metal sheet, having a number of individual formed cantilevers to provide specific points for contact with a slotted panel, has been used in a number of circuit cards developed particularly for use with the IBM MICRO CHANNEL architecture. An example of this type of card bracket, configured particularly for use with a daughter card attached to the circuit card, is shown in U.S. Pat. No. 5,980,275. However, this type of card bracket must be used with a much different type of slotted panel having wide edges along which the contact cantilevers slide, and with cards not having formed brackets of the standard types used with the Industry Standard Architecture (ISA) and the Peripheral Card Interconnect (PCI) architecture. What is needed is a gasket providing specific contact locations which may be used with cards having such standard brackets, since such cards are widely available. 
     A number of conductive gaskets for various applications, other than the grounding of card brackets of slotted panels, are also formed to include a number of cantilevers providing specific points of contact. Such gaskets have a disadvantage of nesting together when they are shipped or otherwise handled in quantities, with the cantilevers of different gaskets interlocking so that the gaskets cannot easily be separated without damage. What is needed is a gasket configuration producing parts which can be handled and shipped together without this kind of nesting. Furthermore, such gaskets are often easily damaged during the handling and installation of associated parts, since the easily-twisted cantilevers may become snagged on other surfaces. 
     Conductive gaskets formed of fine-diameter woven conductive fibers or conductive fibers compressed into a matted, felt-like material have also been used for various applications other than the grounding of such card brackets. Gaskets formed in this way have disadvantages of a difficult fabrication process and of attendant relatively high costs. 
     U.S. Pat. No. 5,825,634 describes the use of an undulating or serpentine spring gasket in an assembly including a shielding cover fastened in place to extend along a portion of a surface of a circuit board. The spring extends between a peripheral edge of the cover and an electrical contact extending along the surface of the circuit board adjacent the peripheral edge. The relatively long and gentle undulations of the spring material produce alternating high and low areas. While a spring of this type can undergo relatively large deflections to provide a mechanically flexible interface between the mating parts, the resulting deflections of the spring, which cause each leg of the spring to lengthen as the spring is compressed between mating parts make it difficult to control the overall dimensions of the spring gasket in use. In the application of the present invention, i.e. in the grounding of card brackets to a slotted panel, overall dimensions must be carefully controlled, since a number of parts have to fit together in a small area. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a first objective of the present invention to provide a spring gasket causing electrical contact to be made at particular locations between a card bracket in a computing system and a slotted panel providing access to a circuit card I/O connector for external cables. 
     It is a second objective of the present invention to provide a spring gasket which is flexible, allowing electrical contact to occur despite variations in the dimensional configurations of adjacent parts. 
     It is a third objective of the present invention to provide a spring gasket in which the length of various legs within the gasket does not substantially change as the spring gasket is compressed. 
     It is a fourth objective of the present invention to provide a spring gasket which does not nest with other similar parts during storage or shipment. 
     It is a fifth objective of the present invention to provide a spring gasket which is not easily damaged by contact with adjacent parts during installation and handling. 
     According to a first aspect of the present invention, a conductive gasket for providing electrical conductivity between adjacent first and second conductive members separated in a first direction is provided. The conductive gasket includes a central web, a first plurality of contact bumps extending from the central web in the first direction; and a second plurality of contact bumps extending from the central web opposite the first direction, wherein contact bumps in the first and second pluralities of contact bumps are arranged in alternating patterns along the central web to include contact bumps in the first plurality of contact bumps adjacent contact bumps in the second plurality of contact bumps. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary cross-sectional end elevation of a computing system including a mother board and a conventional circuit card having a tab inserted within a card edge connector of the mother board; 
     FIG. 2 is a fragmentary rear elevation of the computing system of FIG. 1, showing a slotted panel and circuit card brackets; 
     FIG. 3 is a fragmentary plan view of the computing system of FIG. 1, showing a spring gasket installed therein in accordance with the present invention; 
     FIG. 4 is a fragmentary cross-sectional elevation of the computing system of FIG. 1, including the spring gasket of FIG. 3, taken as indicated by section lines IV—IV in FIG.  3 . 
     FIG. 5 is a fragmentary cross-sectional plan view of the slotted panel and circuit card brackets of FIG. 2, together with the spring gasket of FIG. 3, taken as indicated by section lines V—V in FIG. 4; 
     FIG. 6 is a fragmentary cross-sectional plan view of the slotted panel and circuit card brackets of FIG. 2, together with the spring gasket of FIG. 3, taken as indicated by section lines VI—VI in FIG. 4; 
     FIG. 6A is a fragmentary vertical cross-sectional elevation of the slotted panel of FIG. 2, together with the spring bracket of FIG. 3, taken as indicated by section lines VIA—VIA in FIG. 4; 
     FIG. 7 is a fragmentary vertical cross-sectional elevation of the slotted panel of FIG. 2, together with the spring gasket of FIG. 3, taken as indicated by section lines VII—VII in FIG. 4; 
     FIG. 8 is a front elevation of a spring gasket built in accordance with a first alternative version of the present invention; and 
     FIG. 9 is a front elevation of a spring gasket built in accordance with a second alternative version of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While FIGS. 1 and 2 have been described as showing the prior art, continued reference will be made to these figures, and reference numerals originally used in reference to these figures will continue to be used, as devices configured in accordance with the present invention are used with the prior art devices of FIGS. 1 and 2. 
     FIG. 3 is a fragmentary top view of the computer system  8 , having installed therein a spring gasket  40  configured in accordance with the present invention, together with a pair of filler brackets  38 . The remaining positions in which filler brackets  38  and card brackets  20  can be installed are shown with such brackets not being installed in order to reveal the structure of the spring gasket  40 . 
     FIG. 4 is a fragmentary cross-sectional front elevation of the computer system  8 , having installed therein the spring gasket  40 . This cross-section view is taken in the direction indicated by section lines IV—IV in FIG. 3 to show a portion of the interior surface  42  of the rear wall  44  of the computer. In the example of this figure, the slotted panel  22  includes seven slots  26 , each of which is to be internally covered by either a card bracket  20  or a filter bracket  38  (as shown in FIG.  2 ). However, in FIG. 3, these brackets  20 ,  26  and the various circuit cards  12  are not shown as installed, in order that the details of the spring gasket  40 , which is shown as installed, may be easily seen. 
     Referring to FIGS. 3 and 4, the spring gasket  40  is installed inside the slotted panel  22  to provide for electrical contact between the slotted panel  22  and any combination of card brackets  20  (shown in FIG. 2) and filler brackets  38  which may be fastened in place with screws  24  extending through holes  46  along a ledge  48  of the slotted panel  22 . The spring gasket  40  includes a slot  50  aligned with each of the slots  26  in the slotted panel  22 , so that each I/O connector  28  extending outward from a card bracket  20 , as shown in FIG. 1, can extend through a slot  50  in the in the spring gasket  40  as well as a slot  26  in the slotted panel  22 . The spring gasket  40  also includes an upper ledge  52 , which is fastened in place to extend along the ledge  48  of the slotted panel  22 . This upper ledge  52  includes a number of clearance holes  54 , which are brought into alignment with the holes  46  extending along the ledge  48  of the slotted panel  22 . When a combination of circuit cards  12 , having card brackets  20 , and filler brackets  38  is installed using screws  24  extending through the clearance holes  54  into the holes  46 , the spring gasket  40  is clamped between the slotted panel  22  and the brackets  20 ,  38 . 
     FIGS. 5,  6 , and  6 A are fragmentay cross-sectional view of the computer system  8 , taken in the direction indicated by section lines V—V, VI—VI, and VIA—VIA, respectively, in FIG. 3, to show contact conditions occuring among the slotted panel  22 , the spring gasket  40 , and a pair of brackets, each of which may be either a card bracket  20  or a blank bracket  38 . These brackets  20  or  38  are shown as installed in FIGS. 5 and 6 but not in FIGS. 3 and 6A. 
     Referring to FIGS. 4-6, the portion of the spring gasket  40  extending downward, in the direction of arrow  56 , between the slotted panel  22  and the brackets  20 ,  38 , includes a central web  58 , a first plurality of contact bumps  60  extending inward, in the direction of arrow  62 , from the central web  58 , and a second plurality of contact bumps  64  extending outward, opposite the direction of arrow  62 , from the central web  58 . Preferably, the spring gasket is stamped and formed from a spring metal sheet, such as a 0.1 mm (0.004 in.) thick sheet of half-hard stainless steel, with the contact bumps  60 ,  64  extending 0.75 mm (0.03 in.) from the center of the central web  58 . Each of the contact bumps  60 ,  64  preferably extends to an edge  66  of the spring gasket  40 . 
     Unlike the cantilevers of various gaskets and brackets described in the prior art, the contact bumps  60 ,  64  are not defined by slots extending into the web  58 , but are rather formed such that the perimeter of the bump is continuous with the central web  58 . Therefore, the contact bumps  60 ,  64  provide a number of contact surfaces which are not easily twisted or otherwise damaged during handling and installation of the spring gasket  40 , or during a subsequent installation of a circuit card  12  having a bracket  20  which is slid along the spring gasket  40  during the installation of the card  12 . Furthermore, this lack of slots extending into the web  58  prevents a number of spring gaskets  40  which are stored or shipped together from nesting in a way preventing the easy separation of the parts without damage. In this way, another advantage over prior-art devices having cantilevers is achieved. 
     The complex curvature  68  forming the contact bumps  60 ,  64  limits the flexibility of each of these bumps  60 ,  64 , causing most of the deflection occurring with the compression of the spring gasket  40  between the slotted panel  22  and the brackets  20 ,  38  to occur within the central web  58 . Preferably, the outward-extending contact bumps  60  and inward-extending contact bumps  64  are arranged in alternating positions, with the outward extending contact bumps  60  being formed at points of a first rectangular array, and with the inward-extending contact bumps  64  being formed at points of a second rectangular array. These arrays extend in the vertical direction indicated by arrow  56  and in the horizontal direction indicated by arrow  70 . In the example of FIG. 4, both the first and second rectangular arrays are divided by intervening slots  50 , having sides also extending in the vertical and horizontal directions indicated by arrows  56  and  70 , respectively. Adjacent outward-extending contact bumps  60  are separated by individual inward-extending contact bumps  64 , and adjacent inward extending contact bumps  64  are separated by individual outward-extending contact bumps  60 , so that compression of the spring gasket  40  results in twisting of the central web  58 . 
     FIG. 7 is a fragmentary vertical cross-sectional view of the spring gasket  40  installed on the slotted panel  22 , taken as indicated by section lines VII—VII in FIG. 4 to show the lower edge of a slot  50 , which is formed by a tab  71  extending outward to prevent the lower end  72  of a card bracket  20  (shown in FIG. 2) from catching on a sharp edge of the spring gasket  40  as a card  12  (shown in FIG. 1) is installed against the spring gasket by sliding dowmward. 
     In accordance with a preferred version of the present invention, the spring gasket  40  and the slotted panel  22  have equal numbers of slots, with the slots  50  of the spring gasket  40  being in alignment with the slots  26  of the slotted panel  22 . To this end, the spring gasket may be formed in a number of different configurations having different numbers of slots  50 . For example, FIG. 8 is a front elevation of a spring gasket  74  having two slots  50 , and FIG. 9 is a front elevation of a spring gasket  76  having only one slot  50 . Alternately, a spring gasket may be placed to ground the bracket  20  of only one card, or of several cards among many, where such grounding is particularly important. 
     While the invention has been described in its preferred forms or embodiments with some degree of particularity, it is understood that this description has been given only by way of example, and that numerous changes in details of construction, fabrication, and use, including changes in the combination and arrangement of parts, may be made without departing from the spirit and scope of the invention.