Abstract:
A snap-fit shield is provided which fits securely within a frame opening, and which shields and grounds the opening while eliminating a need for a complementary connector portion. The shield has an insulative inner housing having a first base wall and a first pair of side walls and end walls extending therefrom defining a first cavity. The shield includes a conductive shell having a second base wall and a second pair of side walls and end walls extending therefrom defining a second cavity. The second pair of side walls and end walls have at least one outward bias positioned thereon. The shield also has an insulative outer housing having a third base wall and a third pair of side walls and end walls extending therefrom defining a third cavity. The outer housing is configured to snap-fit within an opening in a frame so as to shield circuitry internal thereto. The third cavity of the outer housing is configured to receive at least a portion of the conductive shield therein, while the second cavity of the conductive shield is configured to receive the inner housing therein.

Description:
BACKGROUND OF INVENTION 
   The present invention relates generally to the shielding of electromagnetic radiation in order to minimize electromagnetic coupling, and to the prevention of electrostatic discharge. More specifically, the present invention provides improved shielding and grounding of the openings in shielded equipment cages, e.g., in computer equipment, telecommunications equipment, and the like. 
   Two problems that have long plagued electrical equipment designers are electromagnetic coupling (EMC) and electrostatic discharge (ESD). EMC is the unintentional transfer of electromagnetic radiation from one or more electrical components to another electrical component. EMC produces undesirable noise in and/or interferes with the normal operation of the receiving electrical component. EMC can occur any time an electrical component is located within an electromagnetic radiation rich environment, such as proximate other electrical components. To prevent EMC, a system of electrical components, e.g., the various interconnected circuit boards of a computer, is often contained within a metal cage, e.g., a processor cage, that blocks out, i.e., “shields” the system from most electromagnetic radiation existing outside the metal cage, and that likewise prevents electromagnetic radiation produced within the cage from affecting equipment external to the cage. 
   ESD is the discharge of static electrical charge that occurs when two objects having different static charge states, e.g., different amounts of charge, opposite polarity charge, etc., are closely proximate. Because ESD can result in large, although short duration, voltages which can interfere with the operation of or damage electrical devices, ESD must be avoided whenever possible. To prevent static charge buildup that can cause ESD, the cage, electrical components therewithin, and any connections thereto share the same ground, i.e., are commonly grounded. For instance, a computer may have a processor cage shielding the computer&#39;s main circuit boards, and a frame surrounding and supporting a hard drive, power supply, the processor cage, etc. To prevent ESD between the frame and processor cage, the frame and processor cage should be commonly grounded whenever a connection is made therebetween. 
   While a properly grounded cage may protect electrical circuitry within the cage from EMC and ESD, often the electrical circuitry within the cage must connect to external circuitry/equipment. To allow for such connections, openings are provided in the cage. These openings form an EMC path into the cage, and if not properly grounded, form a conduit or “situs” for ESD. 
   One approach for reducing EMC and ESD through a shielded cage opening while shielding against dust is to plug the opening with a shielded plug. For example, one shielding method mounts a shield resembling a cable connector having an electrical connector configured to operably connect with a complimentary configured card connector extending in a central aperture of the frame. This shielding plug also includes electrically conductive contact tabs adapted to electrically couple with the frame wall defining the central aperture. In order to hold the shield securely in place and thus to avoid the inconsistent shielding caused by shield movement, central aperture type shields are often adhesively mounted or mounted mechanically via screws or the like. Shield mounting thereby becomes time consuming, slows equipment assembly and teardown, and is unacceptable for many applications. Furthermore, the contact tabs are not suitable for repeated teardown and assembly. 
   In addition, there is an ever increasing demand for reducing the physical size and manufacturing cost of such shielding plugs. Such a grounding means is commonly assembled using a diecast shielded connector plug with a cable opening of the card connector plug being plugged since the cable is absent. Accordingly the assembly and manufacturing costs can be high using a shielded connector that resembles the original card connector but for the absence of a cable extending therefrom. 
   Accordingly, a need exists for a method and apparatus for shielding cage openings when they are not in use. The shield must be mechanically stable to ensure a continuous grounding, shielding, and dust protection and must be designed to facilitate assembly and teardown. In addition, it is desired that the assembly and manufacturing costs for a method and apparatus for shielding cage openings be reduced. 
   SUMMARY OF INVENTION 
   The foregoing discussed drawbacks and deficiencies of the prior art are overcome or alleviated by a method and system for a snap-fit shield which fits securely within a frame opening, and which shields and grounds the opening while eliminating a need for a complementary connector portion. The shield has an insulative inner housing having a first base wall and a first pair of side walls and end walls extending therefrom defining a first cavity. The shield includes a conductive shell having a second base wall and a second pair of side walls and end walls extending therefrom defining a second cavity. The second pair of side walls and end walls have at least one outward bias positioned thereon. The shield also has an insulative outer housing having a third base wall and a third pair of side walls and end walls extending therefrom defining a third cavity. The outer housing is configured to snap-fit within an opening in a frame so as to shield circuitry internal thereto. The third cavity of the outer housing is configured to receive at least a portion of the conductive shield therein, while the second cavity of the conductive shield is configured to receive the inner housing therein. 
   An exemplary embodiment of the invention also includes an electrical machine including a frame having an opening and a shield snap-fit within the frame opening so as to shield circuitry internal thereto. The shield includes an insulative inner housing having a first base wall and a first pair of side walls and end walls extending therefrom defining a first cavity. The shield has a conductive shell having a second base wall and a second pair of side walls and end walls extending therefrom defining a second cavity, the second pair of side walls and end walls have at least one outward bias positioned thereon. The shield also has an insulative outer housing having a third base wall and a third pair of side walls and end walls extending therefrom defining a third cavity. The outer housing is configured to snap-fit within an opening in a frame so as to shield circuitry internal thereto. The third cavity of the outer housing is configured to receive at least a portion of the conductive shield therein, while the second cavity of the conductive shield is configured to receive the inner housing therein. The first cavity covers an unused connector port and eliminates a complementary mating terminal connector portion in the shield. 
   The method includes providing electromagnetic shielding for an exposed unused connector port in electrical equipment, the frame having an opening approximately aligned with an exposed unused connector terminal. In particular, the method includes configuring an inner insulative housing having a first base wall and a first pair of side walls and end walls extending therefrom defining a first cavity. The method further includes configuring a conductive shell having a second base wall and a second pair of side walls and end walls extending therefrom defining a second cavity, the second pair of side walls and end walls having at least one outward bias positioned thereon. The method also includes configuring an insulative outer housing having a third base wall and a third pair of side walls and end walls extending therefrom defining a third cavity. The outer housing is configured to snap-fit within the opening of the frame so as to shield circuitry internal thereto. Next the inner housing is inserted into the second cavity defined by the conductive shell and at least a portion of the conductive shell having said inner housing is inserted into the third cavity defining the outer housing. The assembled shield is snap-fit in place by the action of latch features extending into the first cavity mating with corresponding latch features extending from the exposed unused connector port. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     Referring to the exemplary drawings wherein like elements are numbered alike in the several FIGURES: 
       FIG. 1  is a perspective view of a plurality of electrical connectors mounted to corresponding printed circuit boards and extending through respective apertures in a panel, one shield plug is shown operably engaged with one electrical connector and a second shield plug is aligned with another electrical connector in accordance with an exemplary embodiment; 
       FIG. 2  is an exploded view of one of the shield plugs of  FIG. 1  illustrating a handle extending from an outer housing, an EMC gasket, and an inner housing in accordance with an exemplary embodiment; 
       FIG. 3  is a plan view of a sheet of electrically conductive material from which the EMC gasket is fabricated in accordance with an exemplary embodiment; and 
       FIG. 4  is an enlarged reverse perspective view of the shield plug of  FIG. 1  in accordance with an exemplary embodiment. 
   

   DETAILED DESCRIPTION 
   Referring to the drawings in greater detail, and first to  FIG. 1 , a plurality of electrical connectors, generally designated  10 , are mounted to a surface of a printed circuit board (not shown), with an open front mating face  14  of the connector projecting through a respective aperture defined by a panel  16 . Each connector  10  includes a rectangular box-like electrically conductive housing, generally designated  18 , substantially surrounding an electrical terminal connector rectangular box-like shield, generally designated  20 , except for the open front face  14  of the housing. The connector mounts a plurality of contact pins (not shown). The pin terminals are located within housing  18 , and are operably connected to the printed circuit board for establishing electrical connection to appropriate circuit traces on the board. A pair of alignment pins  22  is disposed on either side of the plurality of contact pins defining a male terminal assembly. The pin terminals are adapted for mating with female terminals of a complementary connector (not shown) inserted into the open face of the connector. The complementary connector includes alignment apertures to receive alignment pins  22  and to provide proper mating alignment of mating electrical terminals. Terminal ends defining each alignment pin  22  are adapted for releasable engagement with a latch disposed with the complementary connector or a shield plug. In the embodiment shown, the terminal ends each include a detent or notch  24  adapted to releasably engage a latch of either the complementary connector or a shield plug. 
   The invention herein is directed to the structure and method of fabricating a shield plug  30  ( FIG. 1 ). However, it should be understood that the particular shield plug  30  shown in  FIG. 1 , along with its mounting and application in an exposed terminal connector in panel  16  are for illustration purposes only. The structure and the method of fabricating the shield of the invention are applicable to a variety of other configurations of connectors than the particular system shown in  FIG. 1 . More specifically, a first shield plug  30  is covering a top connector  10 , while a second shield plug  30  is aligned with a contiguous connector  10  to cover the same. With that understanding, reference is made to  FIG. 4  wherein the final structure of shield  20  is also shown in an opposite perspective view, as depicted in conjunction with connector  10  in  FIG. 1 . 
   Referring now to  FIG. 2 , shield plug  30  is illustrated in an exploded view. Shield plug  30  includes an EMC gasket  32 , an inner housing  34 , and an outer housing  36 . Inner housing  34  is configured as an open box structure defining a cavity  37  in which to receive alignment pins  22  and corresponding terminal connector  10  therein. Outer housing  36  includes a handle  38  extending therefrom. EMC gasket  32  is configured as a single one piece open box structure defining a cavity  40  in which to receive inner housing  34 . Outer housing  36  is also configured as an open box structure defining a cavity  42 . Cavity  42  is adapted to receive at least a portion of EMC gasket  32  therein leaving fingers  44  extending from a perimeter of EMC gasket  32  exposed. In this manner, EMC gasket  32  is intermediate inner housing  34  and outer housing  36 . Alternatively, cutouts  48  may be configured in outer housing  36  aligned with a corresponding finger  44  allowing fingers to extend therethrough and remain exposed as illustrated in  FIG. 2 . In this manner, a larger portion of EMC gasket  32  may be receive within cavity  42  of outer housing  36 . 
   Specifically, the EMC gasket  32  is stamped and formed from electrically conductive sheet metal material and includes a base wall  50  integrally joined to a pair of opposite side walls  52  and a pair of opposite end walls  54  to define a generally rectangular box-like structure having an open side defining an opening to cavity  40 . The open side of the shield is coincident with the open mating face  14  of housing  18  of connector  10  as described above in relation to  FIG. 1 . 
   In this manner, connector  10  is enclosed in cavity  40 . Furthermore, a complementary mating terminal is absent in exemplary embodiments compared with prior art shield plugs, therefore, reducing complexity, assembly, and cost of the shield plug. 
   Referring now to  FIG. 3 , EMC gasket  32  is illustrated as a planar sheet of electrically conductive material before it is formed into the open box structure illustrated in  FIG. 2 . A flat blank, generally designated  62 , of sheet metal material is stamped from a larger piece of the material. This blank, in its entirety, is folded as shown in  FIG. 3  to result in the structure of the shield shown in  FIG. 2 . Specifically, blank  62  includes a center section  50 ′ which eventually forms base wall  50  of the shield; side sections  52 ′ which eventually form side walls  52  of the shield; and end sections  54 ′ which eventually form end walls  54  of the shield. 
   During the stamping of blank  62 , a center hole  64  may be cut in center section  50 ′ through which a center post  66  extending from a base wall  68  defining inner housing  34  ( FIG. 2 ) eventually can protrude and be received in complementary aperture  70  configured in a base wall  72  defining cavity  42  of outer housing  36  (e.g., during assembly of the three pieces defining plug  30 ). A pair of apertures  74  are stamped or cut in blank  62  on either side of center hole  64 . Apertures  74  are configured to receive snap-fit features  76  extending from outer housing  36  in cavity  42  to releasably retain outer housing  36  coupled to inner housing  34  with EMC gasket  32  therebetween. A pair of alignment pin apertures  80  are disposed outboard of apertures  74  in base wall  50 ′. Apertures  80  are configured to receive latch features  82  therethrough into cavity  37  for releasable latching engagement with a corresponding notch  24  ( FIG. 1 ). Latch features  82  include inward biasing latches  82 , for example, but are not limited thereto. 
   The plurality of fingers  44  disposed about an entire perimeter defining gasket  32  are configured in each of the side sections  52 ′ and end sections  54 ′. It will be recognized by one skilled in the pertinent art that fingers  44  may also be stamped or cut into blank  62 . Each finger  44  is formed by cutting three sides of a rectangle allowing retention thereof to the remaining sheet blank  62  via the uncut fourth side defining the rectangle. The resulting finger  44  is bent in a middle portion  86  defining each finger  44  to form an outward biasing member  88  as best seen in  FIGS. 2 and 4 . 
   It should be noted in  FIG. 3  that a plurality of dotted lines  90  are shown between center sections  50 ′, side sections  52 ′, and end sections  54 ′ in order to provide a clear and concise understanding of the portions of blank  62  which are used to eventually form the EMC gasket structure shown in  FIG. 2 . In essence, the dotted lines  90  represent fold lines which will be clearly understood with reference to  FIGS. 2 and 3  together. Stamped blank  62  may be fed through appropriate folding or forming machines, or a single forming machine with a plurality of folding stations, to carry out the various folding operations as illustrated in  FIG. 3 . Upon completion of the folding operations, a simple single piece fully containable EMC spring/gasket  32  results. 
   Referring again to  FIGS. 2 and 4 , inner housing  34  and outer housing  36  are each fabricated of an insulative material such as molded plastic, for example, and accordingly dimensioned to sandwich EMC gasket  32  when the two plastic housings  34  and  36  are snapped together. In this manner, housings  34  and  36  provide damage control of EMC gasket  32 , especially during shipping. More specifically, when inner housing  34  is received in cavity  40  of EMC gasket  32 , side walls  92  and end walls  94  defining inner housing  34  are covered via gasket  32 . Exposed terminal ends defining side walls  92  and end walls  94  each include a lip  96  adapted to receive a terminal edge  98  of corresponding gasket walls  54  and  56 . In this manner, lip  96  receives a corresponding terminal edge of gasket  32  to prevent undesired folds in gasket  32  when gasket  32  and inner housing  34  are received in cavity  42  of outer housing  36 . Further, inner housing walls  92  and  94  include cutouts  99  allowing inward flexing of terminal ends of fingers  44  into cavity  37 . 
   It should be noted and will be recognized by one skilled in the pertinent art that base wall  68  defining inner housing  34  includes holes and apertures (not shown) corresponding to and aligned with hole  64 , and apertures  74  and  80  on base wall  30  of gasket  32 . In this manner, snap-fit/latch features  76  and  82  extending from outer housing  36  may extend into cavity  37  of inner housing  34 . 
   Referring now to  FIGS. 1 ,  2 , and  4  a handle assembly  100  including outer housing  36  and handle  38  will now be described. Base wall  72  of outer housing  36  includes slots  102  ( FIG. 1 ) corresponding to and aligned with hole  64 , and apertures  74  and  80  on base wall  30  of gasket  32  and corresponding to apertures on base wall  68  of inner housing  34 . In this manner, snap-fit/latch features  76  and  82  extending from outer housing  36  may extend into cavity  37  of inner housing  34 . A cylinder portion  106  extends from base wall  72  toward handle  38  and defines complementary aperture  70  configured in base wall  72 . Cylinder portion captures center post  66  extending from base wall  68  of inner housing  34 , as best seen in  FIG. 1  during assembly of inner and outer housings  34 ,  36  having EMC gasket  32  therebetween. 
   Handle  38  extends from base wall  72  of outer housing  36  and extends from opposite sides of cylinder portion  106 . Handle  38  terminates in a handle portion  110 . In an exemplary embodiment, handle portion  110  terminates with a lip portion  112  adapted for a finger to pull or push on to facilitate removal and installation of shield  30  from and to a corresponding connector  10 , respectively. 
   Snap-fit features  76  extend from a lower portion of handle  38  proximate outer housing  36  on either side of cylinder portion  106 . In an exemplary embodiment referring to  FIG. 1 , each snap-fit feature  76  terminates in a hook configured to releasably engage base wall  68  through apertures (not shown) therein. For example, a pair of hooks on each shield plug  30  may be oriented in opposite directions to prevent inadvertent disassembly of the plug  30  caused by shipping shock or during assembly and removal of the plug  30 . In this manner, legs  108  extending to the hooks and defining snap-fit features  76  are pushed in opposite directions to release engagement of the hooks from an inside surface  120  ( FIG. 4 ) defining base wall  68  of inner housing  34 . 
   Latch features  82  extend into inner housing  34  via alignment pin guides  122  extending from inside surface  120  of inner housing  34 . Alignment pin guides  122  are configured to facilitate alignment of a corresponding pair of alignment pins  22  upon insertion of plug  30  into a respective connector  10 . 
   Each latch feature  82  defines one terminal end of a corresponding member  128  having an opposite terminal end  130  proximate handle portion  110 . An intermediate portion  132  of member  128  attaches to an intermediate portion of handle  38  via a resilient leg  134 . Each opposite terminal end  130  of each member  128  is configured to be manually biased toward handle  38  (e.g., with a finger) thereby causing latch features  82  to move away from each other. In this manner, a hook feature, for example, defining each latch feature  82  is released from a corresponding notch  24  on pins  22  to allow removal of plug  30  from connector  10 . Each opposite terminal end  130  may be configured with a stop feature  136  to limit a manual bias of member  130  toward handle  38 . It can be seen with reference to  FIGS. 2 and 4  that stop feature  136  may be as simple as a protrusion dimensioned to limit travel of terminal end  130  toward handle  38 . 
   Opposite terminal ends  130 , including handle portion  110 , optionally includes a finger grip profile to facilitate grabbing plug  30  and prevent slipping during manual manipulation of members  128  and handle portion  110 . In an exemplary embodiment, the finger grip profile includes a plurality of parallel spaced apart grooves  140  for example. 
   Resilient legs  134  provide resiliency to allow outward movement of latch features  82 , while also providing an inward bias to releasably engage corresponding notches  24  on alignment pins  22  upon insertion of a plug  30  with connector  10 . 
   In operation, to place the inventive shield plug  30  within the frame opening  14  ( FIG. 1 ), a user simply aligns alignment pins  22  extending therefrom with guides  122  within cavity  37  with one hand. The shield plug  30  is then inserted within the frame opening  14  until the latches features  82  engage notches  24  on respective alignment pins  22 . As the shield plug  30  is inserted within frame opening  14 , fingers  44  of EMC gasket  32  compress against housing  18  defining frame opening  14 . The curved design defining each finger  44  to form an outward biasing member  88  and cutouts  99  in inner housing  34  facilitate their compression. Hooks defining latch features  82  then resiliently engage corresponding notches  24  and releasably lock shield plug  30  with connector  10 . In this manner, fingers  44  of EMC gasket  32  surround an entire perimeter of frame opening  14  and inner housing  34  covers a male or female terminal assembly associated with connector  10 . In this manner both the forward and backward movement of the shield plug  30  is limited. Accordingly the inventive shield plug  30  is securely held in place, and provides excellent shielding of an unused connector port, such as for shielding a plurality of connector pins located within a frame opening, and provides a continuous ground path between the frame  14  and the internal cage. 
   To remove the inventive shield plug  30  from the frame  14  opposite terminal ends  130  of members  128  are deflected inward or toward each other so that the inward biases of latch features  82  are relieved on respective notches  24 . The shield  11  is then pulled from the frame opening  14 . The inventive shield plug  30  is thus quickly and easily snap-fit within, and extracted from, an opening, without requiring the use of screwdrivers or other tools. The snap-fit virtually eliminates movement of the shield plug  30  once the shield plug  30  is in place within the frame opening  14 , ensuring continuous grounding and shielding. Therefore with use of the inventive shield plug  30  the negative effects of EMC and ESD are significantly reduced. 
   Because of its simple design, the inventive shield plug  30  may be inexpensively manufactured from a single sheet of material for the EMC gasket  32  and molding inner and outer housings  34  and  36 . The EMC gasket  32  is preferably made of a single one piece thin sheet, e.g., 0.005 to 0.010 inches thick, of stainless steel or beryllium copper. Other materials may be similarly employed. Fingers  44  are formed surrounding an entire perimeter of cavity  40  defined when the thin sheet is folded. Housings  34  and  36  are molded using an insulative material, and preferably molded plastic, however, other materials may be similarly employed. 
   While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims.