FIELD OF THE INVENTION 
     This invention generally relates to the art of electrical connectors and, particularly, to a shielded electrical connector having a new and improved electromagnetic shield. 
     BACKGROUND OF THE INVENTION 
     A wide variety of electrical connectors require protection against the egress or ingress of radio frequency interference (RFI) and/or electromagnetic interference (EMI). This is particularly true in electrical connectors used with high speed electronic equipment. “EMI” has become fairly generic to describe most types of interference caused by electronic waves. 
     EMI protection typically is provided by substantially enclosing a connector, at least about its mating interface, with an electrically conductive shield. Such shielding enclosures typically are stamped and formed from sheet metal material. The shields are grounded, such as to a ground wire of an electrical cable or to a ground circuit trace on a printed circuit board. When two connectors are mated, it is desirable to have the shields of the two connectors in positive engagement to establish a common ground therethrough and to prevent electromagnetic radiation from or to the connectors in the area of the mating interface thereof. 
     Heretofore, EMI protection at the interface of a pair of mating connectors has been accomplished simply by overlapping the two shields of the respective connectors. Although this method is quite effective, it requires additional space in the mating direction of the connectors and this is highly undesirable when space is critical in miniaturized, high speed electronics. The same type of space problem arises when radially extending flaps are used between the shields to establish positive engagement, with the space problem being in the transverse direction rather than the mating direction. 
     In order to solve the space problems described above, positive engagement between a pair of shields of a pair of mating connectors has been accomplished by using flexible, cantilevered ground arms which are stamped directly out of a side wall of at least one of the shields at the mating interface of the connectors. Although such flexible ground arms do not require additional space, they create further problems in creating stamped openings about the arms through which electromagnetic interference can pass. In addition, if the flexible arms are too short, they are susceptible to failure due to stress and strain from numerous mating and unmating cycles of the connectors. In other words, it is desirable to have relatively long cantilevered ground arms, but the size of connectors often do not allow sufficient dimensions to lengthen the arms. The present invention is directed to solving one or more of this myriad of problems in shielded electrical connectors. 
     SUMMARY OF THE INVENTION 
     An object, therefore, of the invention is to provide a new and improved electromagnetic shield for at least one electronic component. 
     Another object of the invention is to provide an electrical connector with a new and improved electrically conductive shield. 
     In the exemplary embodiment of the invention, the electromagnetic shield includes an electrically conductive enclosure having wall means defining an open end at a mating face of the component. A flexible elongated ground arm is integrally formed from the wall means and extends generally parallel to the mating face. The ground arm includes a contact portion for engaging a conductive ground portion of a complementary mating electronic component. A portion of the ground means is folded over in an area in registry with said ground arm to minimize electromagnetic leakage about the ground arm. 
     As disclosed herein, the enclosure is stamped and formed of conductive sheet metal material. The ground arm is stamped from the wall means leaving an opening about the ground arm. The folded over portion of the wall means is in registry with at least a portion of the opening. The ground arm is cantilevered and extends across a substantial portion of the mating face. The contact portion is at a distal end of the cantilevered ground arm. 
     Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of this invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with its objects and the advantages 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: 
     FIG. 1 is a top perspective view of a pair of mating connectors, with one of the connectors embodying the concepts of the invention; 
     FIG. 2 is an enlarged top perspective view looking at the mating face of the one connector; 
     FIG. 3 is a fragmented perspective view of a blank of sheet metal material partially stamped to form two ground arms; 
     FIG. 4 is a view of the blank of FIG. 3 in the process of being folded; 
     FIG. 5 is a bottom perspective view of the mating connectors of FIG. 1; and 
     FIG. 6 is a perspective view similar to that of FIG. 5, but looking at the bottom of the one connector. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings in greater detail, and first to FIG. 1, the invention is embodied in an electrical connector, generally designated  10 , which is adapted for mounting on a surface of a printed circuit board and which mates with a plug connector, generally designated  12 , which is adapted for terminating an electrical cable. In other words, board-mounted connector  10  is a receptacle connector for receiving plug connector  12 . 
     Plug connector  12  is substantially surrounded by a shield of electrically conductive sheet metal material. The shield has a front face  16  which is engageable by a plurality of ground arms of connector  10 , as will be described in greater detail hereinafter. The shield has a rear end  18  which is crimped onto an electrical cable. Actually, rear end  18  is crimped onto the ground foil of the cable to perform a dual function of providing strain relief on the cable as well as grounding shield  14  to the foil. 
     Referring to FIG. 2 in conjunction with FIG. 1, board-mounted connector  10  includes a dielectric housing, generally designated  20 , which defines a mating face  22  of the connector. The housing may be a one-piece stricture unitarily molded of dielectric material such as plastic or the like. The housing has a plurality of through passages  24  which mount a plurality of terminals  26  which have solder tails  28  projecting from a rear of the housing for a solder connection to appropriate signal and power circuit traces on the printed circuit board. 
     The invention is incorporated in an electrically conductive shield, generally designated  30 , which forms an electrically conductive enclosure substantially about housing  20 , leaving an open end  32  at mating face  20  of the connector. The shield is stamped and formed of conductive sheet metal material and includes a plurality of tail portions  34  for solder connection to appropriate ground traces on the printed circuit board. 
     As seen best in FIG. 2, stamped and formed sheet metal shield  30  includes wall means defined by a top wall  36  which forms the major top side of the shield. The top wall is joined perpendicularly to a pair of end walls  38  which form minor ends of the shield. A flap  40  is folded over the top of top wall  36 . A flexible elongated ground arm  42  is stamped out of top wall  36  so the ground arm is integral with and cantilevered from the top wall. A second flexible elongated ground arm  44  is stamped out of flap  40  to be integral therewith and cantilevered therefrom. When the ground arms are stamped, an opening  46  is formed behind ground arm  42 , and an opening  48  is formed behind ground arm  44 . By criss-crossing the arms as seen in FIG. 2, each arm closes a good portion of the opening behind the other arm to minimize the escape of electromagnetic interference therethrough and provides an additional pathway for high frequency currents through capacitative coupling. Each flexible ground arm  42  and  44  has a rounded contact portion  50  at the distal end thereof for resiliently engaging front face  16  of shield  14  of plug connector  12  as seen clearly in FIG.  1 . Therefore, upon mating of connectors  10  and  12 , flexible cantilevered ground arms  42  and  44  become spring loaded to establish good grounding connections between shields  30  and  14  of connectors  10  and  12 , respectively. 
     It should be understood that the use of two overlapping ground arms  42  and  44  is a preferred embodiment of the invention. However, by folding flap  40  over top wall  36 , only one ground arm could be stamped out of either the flap or the top wall, with the other of the flap or top wall completely blocking any opening formed behind the single ground arm and through which electromagnetic interference could pass. 
     FIGS. 3 and 4 simply show a portion of the stamping and forming process for ground arms  42  and  44  and folding flap  40  over top wall  36  of shield  30 . In particularly, FIG. 3 shows ground arm  42  having been stamped out of top wall  36  leaving opening  46  therebehind. Ground arm  44  is seen stamped out of what will become flap  40 , leaving opening  48  therebehind. FIG. 4 shows flap  40  being folded at  52  in the direction of arrow “A” whereupon the flap eventually will be folded onto top wall  36  as seen in FIG.  2 . Of course, if only one ground arm  42  or  44  is stamped out of top wall  36  or flap  40 , the other of the top wall or flap will substantially entirely close the opening about the single ground arm to completely eliminate or at least minimize electromagnetic leakage about the ground arm. 
     FIGS. 5 and 6 show the bottom of board-mounted connector  10  and a second pair of ground arms, generally designated  56 , having contact portions  50  for engaging front face  16  of shield  14  of plug connector  12 . Ground arms  56  are effective in connectors where it is found undesirable or impossible to provide a sufficiently long ground arm out of a single wall or side of the connector. In other words, it can be seen most clearly in FIG. 6 that each ground arm  56  has a right-angular configuration. Each arm  56  has a first portion  58  contiguous with one of the end walls  38  of shield  30 . Each arm is bent to form a second portion  60  which extends at a right angle to portion  58  and across the bottom side of the housing  20 . Although board-mounted connector  10  does not have a bottom wall, effective shielding is achieved by using two ground arms  56 . The two ground arms  56  represent multiple contacts which provide a lower impedance between the printed circuit board and the cable attached to the plug connector  12 , a more balanced current flow through the shield and a balanced mechanical force completely around the contact edge of the shield. When the ground arms  56  are combined with the copper grounding plate at the bottom of the printed circuit board, adequate electromechanical leakage is substantially reduced. 
     The advantages of providing right-angled ground arms  56  are not limited to board-mounted connectors. The right-angled ground arms could be placed at the top wall of the shield, or on a plug shield at the intersection of any transverse walls of any shield or on a plug shield. The advantages are provided by forming a single ground arm out of two adjacent walls of a given shield, so that the ground arm can be lengthened beyond that which a single wall may possibly afford. In addition, the twisting action of portion  60  of ground arm  56  relative to portion  58  enhances the resiliency of the ground arm. 
     It will be understood that the invention may be embodied in other specific forms without departing from the spirit or central characteristics thereof. The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein.
An electromagnetic shield is provided for at least one electronic component. The shield includes an electrically conductive enclosure having walls defining an open end at a mating face of the component. A flexible elongated ground arm is integrally formed from the walls and extends generally parallel to the mating face. The ground arm includes a contact portion for engaging a conductive ground portion of a complementary mating electronic component. A portion of the walls is folded over in an area in registry with the ground arm to minimize electromagnetic leakage about the ground arm.