Abstract:
An EMI gasket takes the form of a metal shroud that completely encircles a metal shielding cage. The shroud has an opening that is surrounded by a plurality of sides and each side has first and second flanges, which respectively contact the inner surface of the device faceplate and the exterior surfaces of the shielding cage. A pair of spring arms are provided in order to apply a biasing force against the shroud, thereby forcing it into contact with the faceplate. The spring arms each include a torsion loop, and each loop engages the shielding cage and fixes the rear position of the spring arms.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority from U.S. Provisional Patent Application Ser. No. 60/742,936 filed Dec. 6, 2005, which is hereby incorporated herein by reference.  
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates generally to structures that prevent or retard electromagnetic interference (“EMI”) emissions from connector assemblies, and more particularly to an EMI shroud intended for use on a metal shielding cage for blocking electromagnetic interference emissions.  
         [0003]     It is a common practice in the electronic arts to connect cables to a circuit board by utilizing plug connectors at the ends of the cables which are intended for insertion into an opposing mating connector. The mating connector is typically mounted on a circuit board, which is held within an exterior housing. Such an arrangement is typically found in servers and routers. These devices have multiple connector assemblies that now operate at high speeds, typically 2 gigabits per second and greater. The high speed electrical transmission in these devices can produce electromagnetic emissions, which may leak from the connection between the plug connector and its mating connector. These emissions can cause problems in high speed transmissions in that they can negatively influence signal transmissions between the connectors.  
         [0004]     These types of transmissions are routinely reduced by the use of a metal shielding cage that is also mounted to the circuit board and which surrounds the mating connector in the device. These cages have openings that open to a faceplate, which is commonly referred to as a bezel in the art. These openings define an entrance leading toward the mating connector into which the plug connector is inserted. Testing has determined that despite the metal shielding cages, EMI leakage still occurs in such structure, primarily at the areas where the shielding cages meet the circuit board and around the opening(s) of the faceplate or bezel, into which the cage openings extend. Conductive gaskets have been developed in efforts to address this problem.  
         [0005]     Problems still exist in the use of gaskets, for it is desired that the gaskets be conductive and held in close contact to both the shielding cages and the faceplate. These cages are becoming smaller and smaller in size as the overall size of most electronic devices continues to diminish. The small size of the cages often makes it difficult to develop a structure that will force the EMI gasket into reliable contact with the faceplate and the cage, without detrimentally affecting the strength of the shielding cage.  
         [0006]     Accordingly, the present invention is directed to an improved EMI gasket structure that takes the form of a shroud and which overcomes disadvantages of the prior art. An important problem to be addressed is how to enhance EMI-preventing contact between components of connector assemblies.  
         [0007]     Examples of prior approaches proposed for addressing EMI shielding problems include U.S. Pat. No. 5,204,496 (Boulay, et al.) and No. 6,420,009 (Cheng) that show incorporating a bent flange EMI gasket. U.S. Pat. No. 6,851,978 (Akama, et al) proposes a hook for a shielding cage gasket. Included in U.S. Pat. No. 6,752,663 (Bright, et al) is a shielding gasket assembly having pre-formed slots that fit over and receive mounting feet of the bottom of a cage. The combination of a formed gasket and a backing plate is shown in U.S. Pat. No. 6,878,872 (Lloyd, et al.). These patents, and all other references noted herein, are hereby incorporated hereinto by reference.  
       SUMMARY OF THE INVENTION  
       [0008]     Accordingly, it is a general object or aspect of the present invention to provide an EMI gasket structure for use with a shielding cage that utilizes a metal shroud and a biasing mechanism that engages the shielding cage and applies a biasing force to urge the shroud into close contact with a faceplate of the device in which the gasket structure is used.  
         [0009]     Another object or aspect of the present invention is to provide an EMI gasket assembly in the form of a metal shroud that encircles the opening of a metal shielding cage, the shroud closely fitting against the cage and an interior surface of a faceplate installed over the cage opening, the assembly including means for biasing the shroud into contact with the faceplate interior surface.  
         [0010]     Yet a further object or aspect of an embodiment of the present invention is to provide an EMI shroud for a shielding cage, the shroud having a continuous perimeter with an inner opening that receives the front end of a metal shielding cage therein, the shroud having an inner lip formed thereon that extends along two opposing sides of the shroud, the shroud further having a pair of biasing springs that have a backbone portion with two free ends, the free ends of the biasing springs being received within the shroud inner lips, and the backbone portion of the biasing springs having means for engaging the outer surfaces of the shielding cage.  
         [0011]     A still further object or aspect of an embodiment of the present invention is to provide a biased EMI gasket for a metal shielding cage, the shielding cage having a generally rectangular front end that fits into an opening of a faceplate of an electronic device, the gasket including a metal shroud that encircles the cage front end, the shroud having first and second flanges preferably extending along its entire extent, the first flanges contacting an interior surface of said face plate and the second flanges contacting the exterior surfaces of the shielding cage, the shielding cage having a pair of tabs extending outwardly therefrom on two parallel sidewalls of the shielding cage, and a pair of biasing springs disposed along the two sidewalls of the shielding cage, each of the biasing springs including an end loop with two free ends, the end loops engaging the shielding cage tabs, and the spring free ends engaging the shroud between the first and second flanges, the springs imparting an outward biasing force to the shroud against the faceplate of the device.  
         [0012]     Yet another object or aspect of an embodiment of the present invention is to provide a shielding cage with a pair of springs disposed on opposite sidewalls of the shielding cage, the springs being disposed such that their end loops engage the shielding cage approximately halfway between the top and bottom walls of the shielding cage.  
         [0013]     The present invention accomplishes these and other objects and aspects by virtue of its structure, which in one principal aspect includes a conductive shroud that has a generally rectangular shape, so that it encircles the front end of the shielding cage. Typically, the shroud is stamped and formed from a single piece of conductive material, such as a metal, and it is formed with a central opening so that it extends in a continuous fashion around the entire perimeter of the shielding cage front end.  
         [0014]     The shroud may be formed with first and second flanges, and the flanges meet along a perimeter center line such that the junction area of these two flanges contacts the exterior surfaces of the shielding cage. One of the first and second flanges extends forwardly of the shroud toward the shielding cage front end so that it will make contact with an opposing interior surface of a faceplate, or bezel. Along the two sidewalls of the shielding cage, the junction of the first and second flanges defines an interior lip, or shoulder, which defines a reaction surface against which a biasing means rests. The contact between the one flange and the faceplate may be a flush contact between the shroud flange and a rear, or inner, surface of the faceplate and it may also be a flush contact between the one shroud flange and the inner perimeter of the faceplate opening. In any event, the shroud is fitted to fill any opening that occurs between the shielding cage and the faceplate.  
         [0015]     In another principal aspect of the present invention, the shroud includes an associated means for biasing the shroud in a forward direction against and into contact with the faceplate interior surface. This biasing means, in an embodiment illustrated herein, takes on the form of a torsion-type spring having two spring arms that are joined together by a center engagement loop. The spring arms have free ends that extend forwardly and into contact with the interior lip of the shroud. In order to provide a means for fixing the biasing means to the shielding cage, one or more engagement tabs may be formed as part of the shielding cage itself, and these tabs extend outwardly from the shielding cage exterior surfaces, preferably in directions transverse to the direction of insertion of a plug connector into the shielding cage.  
         [0016]     The center loops of the spring in this embodiment engage these tabs, and the tabs serve to fix the location of the spring relative to the shroud and the shielding cage front end. As such, these tabs define fixed points of engagement. In assembly, the shroud is placed over the shielding cage front end so that its first flange faces up and extends toward the shielding cage front end. The spring loops are placed onto their respective engagement tabs, and the free ends are placed into the interior lips of the shroud. The tabs may have a mushroom-type configuration with an enlarged end so as to retain the biasing spring in place thereon. The lower portion of the shroud may be slotted so as to provide mounting clearance with the mounting legs of the shielding cage.  
         [0017]     These and other objects, aspects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     The invention, together with its objects and the advantage thereof, may be best understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements in the figures and in which:  
         [0019]      FIG. 1  is a perspective view of an electronics assembly that utilizes a shielding cage, internal connector mounted to a circuit board and having a faceplate extending around the shielding cage;  
         [0020]      FIG. 2  is the same view as  FIG. 1 , but illustrated in an exploded fashion;  
         [0021]      FIG. 3  is the same view as  FIG. 1 , but taken from the rear of the assembly;  
         [0022]      FIG. 4  is the same view as  FIG. 3 , but illustrated in an exploded fashion;  
         [0023]      FIG. 5  is an enlarged view of an embodiment of the biasing means used in association with the EMI shroud of the invention;  
         [0024]      FIG. 6  is an enlarged side view of  FIG. 1 , partially in section and cut away, of the interface between the EMI shroud, the top of the shielding cage and the faceplate; and,  
         [0025]      FIG. 7  is an enlarged detail view, taken from the top of the shielding cage in order to show the interface between the shroud and the faceplate in this illustrated embodiment.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]      FIG. 1  illustrates an electronic assembly  10  of the type that would normally be found in a router or server and which is utilized in the transmission of high speed data signals. Such an assembly includes a plurality of receptacle-style connectors (not shown) that are mounted in a stacked configuration, to a circuit board  12 . A metal shielding cage  15  is provided and as, shown the cage  15  includes a base plate, or bottom wall  16 , a body portion  17  (which includes a pair of sidewalls  22 ) and a rear and top plate, or wall,  18  that engages the cage and covers its rear end and part of its top. The cage  15  has a series of openings  19  that lead to respective hollow interior bays, into each of which an electronic module (also not shown) attached to a cable end, may be inserted. Once assembled, the shielding cage  15  has a plurality of exterior surfaces  24 . The metal shielding cage  15  is conductive and the front end of it usually is inserted into a faceplate of an electronic device. Specifically, the front end  21  of the shielding cage assembly is received within an opening  31  ( FIG. 2 ) of the faceplate  30 .  
         [0027]      FIG. 1  shows the assembly as including a shielding cage  15  of the 2×5 style, that is two horizontal rows with five cage openings  19  each extending in a horizontal fashion. The openings  19  are stacked one on top of each another and in order to accommodate this arrangement, the shielding cage  15  illustrated includes interior, or center, wall portion  20  which separates the two bays or openings from each other. Electronic modules, which are connected to wire cables, are inserted into and removed from the cage openings in order to make a connection to the receptacle connectors held in the interior of the shielding cage  15 . The shielding cage  15  has a front end  21  that contains the plurality of openings  19 .  
         [0028]     The shielding cage  15  and its internal connectors and supporting circuit board are held together in a exterior enclosure (not shown) but which includes a faceplate, or bezel  30 . This faceplate  30  sits over the front opening of the exterior enclosure and around the perimeter of the shielding cage as shown. In this regard, the faceplate  30  is typically a continuous member, formed from sheet metal with a desired thickness, and an inner opening  31 . A lip  33  defines the inner surface of the faceplate opening, and the faceplate has a front, or outer, surface  32  and a rear, or inner, surface  34 . The front end  21  of the shielding cage projects slightly past the outer surface  31  of the faceplate  30 . The fit between the shielding cage  15  and the faceplate lip  33  is preferably an interference fit, with the faceplate loose enough to be slid over the cage front end  21 .  
         [0029]     The area between the faceplate and the shielding cage is prone to the discharge, or leakage, of electromagnetic emissions during high speed data transfer that can cause EMI. Accordingly, designers in the electronic arts endeavor to provide some sort of gasket that fits between the shielding cage and the faceplate  15 . Achieving uniform and secure contact that addresses leaking of electromagnetic emissions is problematic. The present invention is directed to problems that arise in the use of such EMI gaskets and difficulties in holding the gasket in uniform and secure contact between the cage and the faceplate. Conductive pliable foams have been used, but they are prone to tearing and other damage, and the degree of EMI protection may be dependent on the amount of conductive material. The foam materials tend to deform over time, and this deformation may weaken the ability of the foam to stay in uniform and secure contact with the shielding cage and the faceplate.  
         [0030]     The present invention utilizes an improved gasket construction. As shown in  FIG. 2 , a conductive gasket  40  is provided in the form of a metal shroud  41 . The shroud  41  includes a plurality of sides, which are preferably interconnected together to form a continuous structure. The shroud  41  has an opening  42  formed therein that is sized and shaped to receive the front end  21  of the shielding cage therein. The shroud  41 , in the embodiment shown, is stamped out of sheet metal, and each side, or leg, thereof can be seen to be bent into a general U- or V-shape, in which first and second flanges  44 ,  45  are defined on opposite sides of a fold, or form, line  46  ( FIGS. 4 and 7 .) As shown, the flanges are bent on opposite sides of the form line  46 . Preferably, each side of the shroud  41  includes both of the two flanges, and more preferably, as shown best in  FIG. 3 , the second flange  45  is placed into contact with the exterior surfaces of the shielding cage, and the first flange  44  is either placed into contact with the interior surface  34  of the faceplate, or into contact with inner lip  33  of the faceplate. Preferably, the contact is a flush contact so that the shroud  41  fills and seals the space between the faceplate opening and the exterior of the shielding cage  15 .  
         [0031]      FIG. 5  illustrates best the manner in which the shroud provides an EMI seal to the structure of this illustrated embodiment. The shroud  41  contacts the exterior surfaces  24  of the shielding cage  15 . This contact is primarily effected by the form line  46  of the shroud  41  and secondarily by the second flange  45  of the shroud. The flange  45  preferably contacts the shielding cage  15  for a preselected distance from the form line  46  rearwardly toward the end of the shielding cage  15 , such that the second flange  45  extends upwardly from the shielding cage exterior surfaces  24  at an slight (acute) angle as illustrated at  2  in  FIG. 5 . The second flange  45  may also lie flush against the exterior surfaces  24  of the shielding cage  15 .  
         [0032]     Likewise, the first flanges  44  contact the inner surface  34  of the faceplate  30  for a short extent and extend at an angle outwardly therefrom either toward the ends  48  of the faceplate  30  or toward the rear of the cage as illustrated in  FIGS. 5 and 6 . As such the first flange  44  of the shroud  41  may lie partially flush against the inner surface of the faceplate  30  and extend away at an angle therefrom as the second flange  45  does with the shielding cage  15 , or as in the embodiment illustrated, the first flange  44  of the shroud  41  contacts the inner lip  33  of the faceplate  30 .  
         [0033]     In any event, it is desirable that the EMI shroud  41  makes contact with the shielding cage at a minimum along its form line  46  in order to provide a base point of contact with the shielding cage  15 , so that the shroud and its flanges  44 ,  45  fill any opening that occurs between the shielding cage and the faceplate opening inner lip  33 . Thus the shroud serves as an EMI barrier that seals the faceplate opening  31 . As shown in  FIG. 2 , the bottom portion of the shroud  41  may be notched, as at  47 , and these notches  47  are aligned with the forward attachment legs  49  that extend through slots formed in the base plate  16  of the shielding cage  15 .  
         [0034]     In order to exert a pressure on the shroud and to keep it in contact with the faceplate  30 , a biasing means is provided. In the illustrated embodiment shown in the Figures a biasing means  50  is shown as a pair of biasing springs  51  that are formed to define a torsion, or coil, loop  52  at one end thereof and a pair of free ends  53  at the other end thereof. In the embodiment illustrated, the torsion loops  52  constitute the rear ends of the biasing springs  51 , and they form what we consider to be backbone portions of the biasing springs  51  while the free ends  53  define the front ends of the biasing springs  51 . The free ends  53  are captured between the two flanges  44 ,  45 , along the sidewalls of the shielding cage  15 , and they preferably make contact with the form line  46  of the shroud  41 . In this fashion, the form line  46  may be considered as forming along an inner lip  59  ( FIG. 7 ) of the shroud  41 . The free ends  53  of the illustrated biasing springs  51  are retained between the flanges  44 ,  45  and make contact with the shroud inner lip  59  so as to provide a forward biasing force against the shroud  41  to urge it into contact with the faceplate  30 , particularly the inner surface  34  thereof.  
         [0035]     The shielding cage  15  may be provided with engagement members, illustrated in the form of tabs  55  that extend outwardly away from the sidewalls of the cage  21 . These tabs  55  are received within the openings of the torsion loops  52  of the biasing springs  51  and so define a fixed reaction, or anchor point, for the biasing springs  51  while attached to the shielding cage  15 . In the illustrated embodiment, the tabs  55  may be formed as part of the shielding cage interior walls  23   a ,  23   b  ( FIG. 1 ) and project through corresponding openings  56  that are formed in the shielding cage sidewalls  22 . The tabs  55  may have an enlarged head portion  57  that prevents the torsion loop  52  from coming out of its engagement with the tab  55 . The illustrated embodiment shows this head portion as a mushroom-style shape. The springs  51  may be easily applied by squeezing the free ends of the spring to enlarge the torsion loop and slip it over the enlarged head portions  57  of the engagement tabs  55 .  
         [0036]     The horizontal interior walls  23   a  shown in the Figures may be easily formed by bending a sheet of sheet metal over upon itself to create a central area  26  between the top and bottom bays and openings  19  of the shielding cage  15  which spaces the bays apart from each other and defines a plurality of openings  19  in the shielding cage  15 . In order to attempt to achieve an even pressure on the shroud against the faceplate  30 , the engagement tabs  55  are preferably located along a line that is aligned with this central area, which lies approximately midway between the top and bottom surfaces of the shielding cage sidewalls  22 . Although described as being made from metal, the shroud  41  may be formed from other materials, such as a plastic, which has either been conductively coated with a metal or which has had conductive material integrated into it such as by molding or filling.  
         [0037]      FIGS. 6 and 7  illustrate the contact that occurs between the shielding cage exterior surfaces  24  and the shroud flanges  44 ,  45 . As shown in  FIG. 6 , the second flanges  45  extend generally parallel, or flush with the exterior surfaces  24  of the shielding cage  15 , with the understanding that as used herein “flush” means that the inner surfaces of the flanges  45  are as close as they can be to the exterior surfaces of the shielding cage yet still permit some movement of the shroud on the shielding cage.  FIG. 7  illustrates one manner in which the first flange  44  contacts the faceplate  30  and forms the inner lip  59  against which the free ends of the torsion springs  51  bear.  
         [0038]     While the preferred embodiment of the invention have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the spirit of the invention, the scope of which is defined by the appended claims, including those combinations of features that are individually disclosed of claimed herein.