Abstract:
An assembly for use in providing EMI shielding for a circuit card. The assembly comprises a circuit card; a fastener; and, a shielding apparatus. The shielding apparatus comprises: a body providing EMI shielding and includes an attaching portion extending therefrom, wherein the attaching portion has a segment at a proximal end portion thereof which blocks an opening in the body for controlling EMI leakage and positions the attaching portion so that a fastener can fasten the attaching portion to a circuit card such that a first fastener end portion is engageable in juxtaposed relationship with a first card surface and a second fastener end portion terminates so as not to extend generally beyond a predetermined distance from a second card surface of the card.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to an apparatus, assembly, and system for providing shielding against electromagnetic interference (EMI). In particular, the invention relates to an improved apparatus, assembly, and system that are particularly adapted for shielding a circuit card in an electronic enclosure against the negative consequences of EMI by expeditiously complying with industry accepted standards. 
     Electromagnetic compatibility (EMC) means that electric and electronic devices are compatible with similar devices in their vicinity in terms of shielding against EMI caused by the electromagnetic (EM) energy levels so that EMI does not adversely affect their operations. Because of the faster and more powerful computer systems evolving, EMI levels associated therewith are consequently changing and becoming relatively more difficult to satisfy. Manufacturers seek to achieve EMC to avoid malfunctioning of their systems and for gaining product acceptance. Towards this end, standards and requirements governing EMI have been and are becoming very common since they represent a way of insuring proper operation of electronic equipment. Manufacturers generally desire these standards since they tend to ensure that electronic devices do not interfere with their own operation or the operation of nearby electronic equipment. Furthermore, trade is facilitated by, for example, overcoming technical barriers to products. 
     Many electronic devices, such as computers, are made from a plurality of various electronic components, such as printed circuit boards. The printed circuit boards are typically electrically and mechanically connected to a backplane that is located within the housing. For example, peripheral component interface (PCI) circuit boards or cards are often used to connect computer peripheral devices to, for example, a computer motherboard. In the evolving computer field there is a continuing trend for size reduction of components and increases in their operating capabilities. Moreover, as the capabilities of the electronic devices have increased, the number of electronic components, such as PCI boards, required to be located within a computer has also generally increased. The reduced sizes of the electronic devices coupled with the increased number of electronic components located within the electronic devices has increased the need for improved EMI shielding. The improved shielding requirements present even more problems with PCI boards since the latter generally interface to external peripheral components and accordingly are associated with openings in the electronic housing. These openings are generally detrimental to the EMI requirements of the electronic devices. 
     One known approach for dealing with EMI issues in the context of a computer system using PCI cards is to employ the open industry PCI standards established by and available from the PCI-Special Interest Group (PCI-SIG). The standards available from this group cover several aspects of the PCI cards. For addressing some of these standards, it is well known in the field to use tailstock assemblies that form part of a PCI card assembly and function as an EMI barrier. The tailstock are electrically conductive and act to reduce these EMI issues adjacent the end of the cards that are typically adjacent openings in a computer&#39;s chassis. The tailstocks not only provide desired EMI shielding characteristics, but enhance overall card rigidity, as well as a serve as a convenient installing mechanism. A typical PCI card tailstock includes a unitary bracket comprised of an elongated, flat metallic stamped element that is secured, as by appropriate fasteners, to a card end. Tailstocks are provided with spaced apertures allowing for passage and coupling of electrical connectors to the PCI card as well as for controlling EMI emissions. 
     However, in order to comply with relatively more recent and more rigorous specifications specified in relevant standards for PCI cards (e.g., PCI Local Bus specification version 2.2), it is now recommended that the tailstock be attached to a bottom surface of the card as opposed to the previously recommended top card surface. A reason for the change is that it forces repositioning of the attaching tab to the PCI card, whereby a tailstock notch or opening formed adjacent the tab bend that provides EMI exposure is better shielded. While the tab relocation technique provides an enhanced EMI barrier or shield at this area, there are nevertheless some potential negative tradeoffs when implemented. For example, the relocated tab creates potential tolerance issues for the fastener used for joining the card to the tailstock. In particular, relocation makes it relatively more difficult to retain threaded fasteners within a PCI specification&#39;s bottom or backside form factor. This form factor is intended to restrict board components from exceeding it so as to thereby minimize potential costly physical damage to surrounding components in an electronic enclosure. Moreover, in order to comply with this newer specification, a manufacturer would have to use shorter and relatively more costly specially constructed threaded fasteners. However, the use of shorter and specially constructed fasteners would lead to additional potential problems in that the strength of the threaded attachment is diminished due to fewer engaged threads being employed, thereby compromising the overall structural integrity of the PCI cards as well as being relatively more expensive than conventionally used or so-called off-the-shelf fasteners. It will be appreciated, therefore, that without the ability to provide for effective and reliable EMI shielding for electronic devices, such a PCI cards, in a computer system, especially in the context of satisfying industry accepted standards, the true potential of providing reliable EMI shielding is less than otherwise desired. Accordingly, it would be highly desirable to provide for effective EMC integrity in such systems by providing EMI shielding for such cards which satisfy certain industry accepted standards, whereby such cards can be used in multiple brands of computer systems. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is to provide an apparatus for providing EMC integrity through the provision of EMI shielding of a circuit card. 
     An aspect of the present invention is to provide an apparatus for enhancing EMC integrity by providing EMI shielding of a PCI card so as to expeditiously comply with industry standards governing EMI. 
     An aspect of the present invention is to provide an improved circuit card assembly of the type noted for use in an electronic system that effectively provides EMC integrity for the card assembly and system. 
     Still another aspect of the present invention is to provide an improved PCI card assembly for use in a computer system that effectively provides EMI shielding integrity for the PCI card assembly and system but, in addition, complies with industry accepted standards controlling PCI devices relative to EMI. 
     Still another aspect of the present invention is to provide an apparatus, assembly and system for providing EMI shielding that complies with industry standards in a low-cost and reliable manner. 
     In this regard, the present invention provides an apparatus comprising: a body providing EMI shielding and including an attaching portion extending therefrom, the attaching portion has a segment at a proximal end portion thereof which blocks an opening in the body for controlling EMI leakage and positions the attaching portion so that a fastener can fasten the attaching portion to a circuit card such that a first fastener end is engageable in juxtaposed relationship with a first card surface and a second fastener end terminates so as not to extend generally beyond a predetermined distance from a second card surface of the card. 
     In an illustrated embodiment, the circuit card is a PCI card and the predetermined distance is defined as a form factor dimension established by a PCI specification. In another illustrated embodiment, the proximal end segment is a folded portion that provides a hem which positions the attaching portion relative to the card without compromising EMI blocking of the opening by the proximal end segment. 
     A tailstock assembly or apparatus comprises an elongated body portion providing EMI shielding and includes an attaching portion extending laterally therefrom. The attaching portion has a segment at a proximal end portion thereof which blocks an opening in a bracket portion for controlling EMI and positions the attaching portion so that a fastener can fasten the attaching portion to the PCI card such that a first fastener end is engageable in juxtaposed relationship with a datum surface of a PCI card surface and a second fastener end terminates so as not to extend generally beyond a predetermined distance from the PCI card surface opposite the datum surface. 
     The present invention also includes a circuit card assembly for use in providing EMI shielding for a circuit card, the circuit card assembly comprising: a circuit card; a fastener; and, a shielding apparatus. The shielding apparatus comprises: a body providing EMI shielding and including an attaching portion extending therefrom. The attaching portion has a segment at a proximal end portion thereof which blocks an opening in the body for controlling EMI leakage and positions the attaching portion so that a fastener can fasten the attaching portion to a circuit card such that a first fastener end is engageable in juxtaposed relationship with a first card surface and a second fastener end terminates so as not to extend generally beyond a predetermined distance from a second card surface of the card. 
     Still another preferred embodiment is directed to a computer system comprising an enclosure, circuit card assembly, and a mounting structure for the circuit card assembly of the type noted above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, reference is now made to the following detailed description of a preferred embodiment of the present invention illustrated in the accompanying drawings in which: 
     FIG. 1 is a perspective view of an interior portion of a computer system embodying one preferred embodiment of the present invention illustrating a PCI card assembly being attached to an EMC supporting structure therefor. 
     FIG. 2 is a fragmentary elevation view illustrating a PCI card assembly in accordance with a preferred embodiment of the present invention. 
     FIG. 3 is an end view of the PCI card assembly of FIG.  2 . 
     FIG. 4 is a fragmentary planar view of the PCI card assembly illustrated in FIG.  2 . 
     FIG. 5 is an enlarged fragmentary view illustrating a portion of a tailstock assembly and a PCI card. 
     FIG. 6 is an enlarged fragmentary view illustrating an attaching portion of the tailstock in relationship with an opening in the tailstock. 
    
    
     DETAILED DESCRIPTION 
     Reference is made initially to FIGS. 1-6 for illustrating one preferred embodiment of a computer system  10  including an electronic enclosure or housing assembly  12  for enclosing a plurality of printed circuit boards or cards, such as peripheral component interface (PCI) card assemblies  14 ; only one of which is depicted. The PCI card assembly  14  is directed to providing EMI shielding by attenuating EMI between the interior and exterior of the housing assembly as well as attenuating EMI to the PCI card assembly itself so as to comply with certain industry accepted PCI specifications; such as PCI Local Bus specification (version 2.2). The computer system  10  may be implemented utilizing a computer, such as IBM iSeries®, a product of International Business Machines Corporation, Armonk, N.Y. It will also be appreciated that the principles of the invention apply to such kinds of cards not only in a computer system, but also other electronic devices or systems providing EMI shielding. The housing assembly  12  includes a known cover or casing  16  exterior of a faceplate  18 . The faceplate  18  is affixed to a chassis (not shown). The faceplate  18  defines a plurality of spaced apart PCI slots  20 . Each of the slots  20  is adapted to slidably receive in a known manner a respective PCI card assembly  14 . It will be appreciated that the slots  20  are exposed to the exterior of the casing  16  for allowing cables and/or connectors (not shown) to pass therethrough to the PCI card assembly  14  mounted interiorly of the housing assembly. The faceplate  18  is provided with EMC gaskets  22  in a known manner. Such a faceplate serves as an EMC shielding member. While the preferred embodiment is in the context of a computer system, it will be appreciated that the principles of the present invention apply to other electronic systems enclosing PCI cards or the like. 
     FIGS. 2-6 illustrate one preferred embodiment of a PCI card assembly  14  which includes a conventional kind of circuit board or card  30  that has attached at each longitudinal end thereof an internal shield apparatus  32  for providing EMI shielding at the PCI slots. In this preferred embodiment, the shielding apparatus is defined by a tailstock apparatus or assembly  32  (only one of which is shown). The tailstock assembly  32  includes a pair of laterally extending and spaced bent or folded attaching portions or tabs  34  that are fastened to the printed circuit card  30  as by fasteners  36  and are bent generally perpendicularly relative to the plane of the longitudinal extent of the tailstock as illustrated. The fasteners  36  are threaded, such as screws or the like, but can include rivets or other similar fastening elements. In a preferred embodiment, the threaded fastener  36  is a screw having the following specifications 4-40 thread, 6-12 mm long. The tailstock assemblies  32  serve to mount and easily install the PCI card assemblies  14  to an EMC faceplate  18  that is mounted interiorly of the housing, whereby the card assemblies are positioned in juxtaposed relationship with an opening (not shown) in the casing  16  for reducing EMI and for allowing the connectors and/or wiring to be joined to the computer system. 
     Each of the tailstock assemblies  32  includes ideally an elongated body or bracket portion  40  made of, for example, a generally flat metal stamping, such as of steel having a plurality of openings  42   a, b  for allowing the connectors and/or other wiring to pass therethrough in a known manner. The bracket portion  40 , as is known, is electrically connected to the housing assembly at a plurality of locations to reduce EMI. Although steel is described as an electrically conductive material for providing the EMI, other materials are contemplated. Moreover, the tailstock assembly  32  need not have the size and shape as illustrated in this embodiment, but can also have a wide variety of shapes and sizes so long as they are consistent with the functioning as described herein. In addition, instead of the bracket being a single structure, it can be made of several integrated components. It will be appreciated, therefore, that the term tailstock as used herein is not limited to a tailstock as illustrated and described, but includes other structures. 
     FIGS. 2-6 depict the attaching portions  34  being bent or folded generally perpendicularly from a plane of the bracket portion  40  in a region or opening  44 . As shown in FIG. 6, the opening  44  is a cutout area or notch that allows the attaching portion  34  to be bent as noted. As noted earlier, the PCI Local Bus specification (version 2.2), suggests that the bent attaching portion  34  be attached to a first or bottom surface  46  of the card  30 ; as opposed to the opposing top or datum surface  48 . However, the present invention provides for the attaching portion  34  having a proximal end portion  50  with a folded segment  52  or hem  52  that serves to allow repositioning of the attaching portion  34 . The proximal end portion  50  has a planar segment  54  extending outwardly into the plane of the opening  44  by a distance that restricts the size of such opening to thereby comply with the noted PCI specification. It will be appreciated that the folded hem portion  52  repositions the attaching portion  34 , whereby it can engage the datum or top surface  48 . As a result, the threaded fastener  36  can have its head portion  55  directly engaging the circuit board  30 . Moreover, a terminal end portion  56  of the fastener is threaded through apertures  58   a, b  in the card and the attaching portion. In this embodiment, the threaded fastener  36  has a length in a range of about 6 to about 12 mm. Such fasteners are common and provide adequate strength between the card and the attaching portion. In addition, the fastener head portion  55  remains within the maximum PCI height form factor specification for the backside is generally indicated by a distance or height “A”; which according to this embodiment is 2.67 mm (FIG. 4) as measured from the bottom planar bottom surface  46 . As a result, not only is the PCI height specification complied with because the threaded member does not extend beyond it, but also the folded segment effectively reduces the size of opening  44  by approximately the same amount as would be the case if the tab were attached to the bottom surface; thereby providing the desired EMI shielding complying with the noted PCI specification. Another advantage of the foregoing arrangement is that a threaded fastener can be used which does not have to be especially made shorter then those currently used (e.g., 6.4 mm) with current PCI card assemblies. 
     As noted earlier, this is important because a threaded fastener shorter than that currently used poses a problem in that the threaded connection between the card and the attaching portion might be less than otherwise thought desirable thereby resulting in a weakened connection between the components that might be relatively more prone to failure. Furthermore, by having the fastener remain within the backside form factor height specification there is less of a tendency for a fastener damaging other juxtaposed components in the computer system. The present invention, envisions that the folded portion need not be folded as illustrated but can have other configurations as well so long as the opening  44  is reduced by approximately the same amount as would be the case if the attaching portion were connected directly to the bottom surface as suggested by the new PCI Local Bus specification (version 2.2) and the threaded member does not extend beyond the noted backside form factor height specification. Advantageously, a relatively less expensive and relatively more robust threaded connection may be maintained without the necessity to resort to shorter screws resulting in tolerance, thread engagement, and assembly concerns that could also lessen the integrity of the threaded connection. 
     The embodiments and examples set forth herein were presented to best explain the present invention and its practical application and to thereby enable those skilled in the art to make and use the invention. However, those skilled in the art will recognize that the foregoing description and examples have been presented for purposes of illustration and example only. The description set forth is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teachings without departing from the spirit and scope of the appended claims.