Abstract:
The present invention is directed to a gasket for reducing electromagnetic emission from electronic equipment. The gasket is defined by a substantially rectangular body that includes one or more openings through which a portion of a connector, to which the gasket is mounted, may pass. The gasket includes a hook-shaped peripheral edge, a plurality of locating projections, a plurality of retaining clips, and tabs that are formed on opposing sides of the opening(s). The hook-shaped edge, locating projections and retaining clips are adapted to receive and secure a connector to the gasket, and the tabs are provide to make an electrical contact with the connector housing. Additionally, the gasket includes spring fingers for use in mounting the gasket to a bulkhead and for forming an electrical contact with the bulkhead.

Description:
FIELD OF THE INVENTION 
     This invention relates to electromagnetic interference shielding, and more particularly to a gasket for shielding such interference. 
     BACKGROUND OF THE INVENTION 
     Electromagnetic interference (EMI) is a problem that is commonly encountered in the design and operation of electronic equipment. Standards have been set that limit the amount of allowable EMI emissions from electronic devices. To meet the emissions standards it is necessary to seal around doors, panels, and slots that hold expansion cards and connectors. This task is challenging in today&#39;s commercial environment because there is pressure to minimize the spacing between slots and openings in order to increase the density of connection points to a particular piece of electronic equipment. 
     EMI containment problems have been exacerbated as processing speeds of electronic equipment have increased because EMI can cause electronic equipment to malfunction or not function at all. For example, contemporary electronic communications equipment operate at very high frequencies and equipment packaging attempts to concentrate a relatively large amount of circuitry per frame of equipment. Each frame tends to act as a transmitting source of EMI to the environment and more so as frequencies become higher (i.e., wavelengths become smaller). 
     In the majority of cases, the solution to the problem consists of enclosing the frames of equipment in a properly grounded metal box. These metal boxes usually comprise a metal frame on which metal panels may be removably secured to allow access to the equipment on the frame. In order to provide adequate EMI shielding, the mating surfaces of these panels must be electrically connected together. This is usually achieved through the use of an EMI gasket which provides an interface between mating conductive surfaces. The gasket should provide high conductivity to ensure DC continuity between mating surfaces and is usually compressible. 
     One known gasket is made from conductive rubber, which is inserted into a channel between two mating surfaces. Alternatively, the gasket may be glued to the inside of the channel. In such an arrangement, the channel is used to give the gasket lateral stability and to prevent its misalignment which could result through repeated removal and replacement of the panels. Another method of shielding box panels is through the use of a metallized compressible gasket attached to a metal band along its length. The metal band is secured to one of the mating surfaces so that the gasket is sandwiched between the mating surfaces when a panel is attached to the frame. 
     Another example of an EMI shield is illustrated in U.S. Pat. No. 5,161,997, to Defibaugh et al. The Defibaugh et al. EMI shield has opposed edges formed into a pair connector receiving of channels. The lower channel of the shield receives a connector, which is secured to the shield by rotating the connector toward the shield such that a rear face of the shield contacts front face of the connector. Next, an extending upper tab of the shield is bent over an upper edge of the connector, forming an upper channel, to secure the connector to the shield. While the Defibaugh et al. is disclosed as being a “hardwareless” connector (i.e., it may be mounted without additional hardware), it requires secondary tooling to form the upper channel after connector insertion. 
     These methods of EMI control are fully operable for their intended purpose. However, there still remains a need for an improved EMI shield that allows for higher densities of connection points to electronic equipment, and that is capable of providing an adequate level of protection against emissions. Further, there is a need for a shielding gasket that provides for easy mounting to connectors without requiring additional tooling or hardware. The present invention provides such a solution. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a gasket for reducing electromagnetic emission from electronic equipment. The gasket is defined by a substantially rectangular body that includes one or more openings through which a portion of a connector, to which the gasket is mounted, may pass. The gasket includes a hook-shaped peripheral edge, a plurality of projections, a plurality of retaining clips, and tabs that are formed on opposing sides the opening(s). The hook-shaped edge, projections and retaining clips are adapted to receive and secure a connector to the gasket, and the tabs are provide to make an electrical contact with the connector housing. The clips and projections may engage the holes provided in the connector flange to enhance the integrity of the system. Additionally, the gasket includes spring fingers for use in mounting the gasket to a bulkhead and for forming an electrical contact with the bulkhead. The spring fingers provide for additional points of contact. 
     The above-noted structure of the gasket of the present invention further provides for easy attachment of connectors to the gasket without the use of additional mounting hardware. 
     Other features and aspects will be described herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing summary, as well as the following detailed description of the preferred embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings an embodiment that is presently preferred, in which like references numerals represent similar parts throughout the several views of the drawings, it being understood, however, that the invention is not limited to the specific methods and instrumentalities disclosed. In the drawings: 
     FIG. 1 is a front view of an embodiment of an EMI gasket in accordance with the present invention; 
     FIG. 2 is a cross sectional view taken along line II—II of FIG. 1; 
     FIG. 3 is an enlarged cross sectional view of an upper portion of the EMI gasket of FIG. 2; 
     FIG. 4 is an enlarged cross sectional view of a lower portion of the EMI gasket of FIG. 2; 
     FIGS. 5 and 6 are front and side views of an exemplary connector to which the EMI gasket of the present invention may be mounted; and 
     FIG. 7 is a cross section view taken along line VII—VII of FIG. 5, which additionally shows the EMI gasket partially secured to the exemplary connector; 
     FIG. 8 is a cross section view taken along line VII—VII of FIG. 5, which additionally shows the EMI gasket secured to the exemplary connector; and 
     FIG. 9 is a front view of another embodiment of the EMI gasket of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is directed to novel electromagnetic interference (EMI) gasket that may be advantageously mounted to a connector without requiring additional mounting hardware. 
     Referring to FIGS. 1,  2 ,  5  and  6  there is illustrated an exemplary EMI gasket  10  in accordance with a first embodiment of the present invention and a connector  38  to which the EMI gasket  10  of the present invention may be secured. One such connector is part number 73465 available from FCI/Berg Electronics. It is noted that the present invention is in no way limited by the physical and electrical structure and features of connector  38 , as the connector  38  is being presented merely for exemplary purposes. 
     Referring to FIG. 1, the substantially rectangular gasket  10  can include four openings  12 A- 12 D and is preferably comprised of a plated 0.006/0.010 Phros Bronze strip. 
     Each opening  12 A- 12 D has associated therewith locating structure (such as projections or bumps  14 A- 14 D), fingers  15 A- 15 D, retaining clips  16 A- 16 D, and tabs  18 A- 18 D. The openings  12 A- 12 D are provided such that a portion of a connector  38  may be aligned therewith. It is also noted that although four openings  12 A- 12 D are illustrated in the exemplary gasket  10  of FIG. 1, additional or fewer openings may be provided in accordance with the requirements of a particular application. 
     Referring now to FIGS. 2-4, additional details of the gasket  10  will now be described. The gasket  10  includes a hooked end  20 , which forms a channel to engage the connector housing  40  (upper flange  48 ) when the gasket  10  is secured to the connector  38 . The size of the channel formed by the hooked end  20  is preferably such that the upper flange  48  of connector housing  40  may be fitted there between (e.g., approximately 0.76 mm). As shown in FIG. 3, the channel  20  curves outward toward the rear of the gasket  10  such that an end thereof forms an angle β with respect to the horizontal, which is preferably 45°. The curved end acts as a lead-in surface to guide housing  40  into channel  20 . 
     Referring again to FIG. 1, locating projections  14 A- 14 D and retaining clips  16 A- 16 D are associated with each opening  12 A- 12 D. Preferably, each opening  12 A- 12 D has a pair of locating projections  14 A- 14 D and a pair of retaining clips  16 A- 16 D. The locating projections  14 A- 14 D are received within a first pair of circular openings  46  in the connector  38  to position the connector  38  with respect to the opening  12 A- 12 D. The retaining clips  16 A- 16 D are received by a second pair of circular openings  44  in the connector  38  to secure one portion of the connector  38  to the gasket  10 . In order to facilitate assembly of connector  38  and gasket  10 , clips  16 A- 16 D secure the lower portion of connector  38  while channel  20  receives the upper portion of connector  38 . 
     The fingers  15 A- 15 D are provided to form an electrical contact with a bulkhead (not shown) to which the gasket  10  and connector  38  may be mounted. The fingers  15 A- 15 D are provided at the top and bottom of their respective openings  12 A- 12 D, and are angled toward the front of the gasket  10  at an angle α. The angled fingers  15 A- 15 D ensure a good electrical contact between the fingers  15 A- 15 D and the bulkhead. In addition, the fingers  15 A- 15 D create a biasing force when the gasket  10  is mounted to the bulkhead to aid in maintaining the gasket  10  in position. Preferably, the angle a is between approximately 8° and 10°. The openings  12 A- 12 D may optionally allow spring fingers (not shown) provided on the connector  38  to pass therethrough to make contact with a bulkhead (not shown) to which the connectors  38  are to be mounted. 
     The tabs  18 A- 18 D are provided to form an electrical contact with the connector housing  40 . As shown in FIG. 1, the tabs  18 A- 18 D are provided on each side of their respective opening  12 A- 12 D. It is preferable that the tabs  18 A- 18 D on one side of the opening be offset with respect to the tabs  18 A- 18 D other side of the opening and a center line of the opening such that the tabs  18 A- 18 D interdigitate with and contact corresponding tabs  42  provided on the connector housing  40  when the gasket  10  is mounted to the connector  38 . 
     Also shown in FIG. 3 projection  14  has a diameter that is approximately that of the first circular openings  46  in the connector housing  40 . In the exemplary connector  38 , the first circular openings  46  have a diameter of 2.44 mm, thus it is preferable for the diameter of the projection  14  to be approximately 2.4 mm. In addition, the housing  40  preferably has a thickness of 0.305 mm, therefore, it is preferable that the projection  14  extend approximately 0.42 mm from the remainder of the gasket  10 . As such, the projection  14  will seat within the first circular openings  46  of the connector housing  40  to properly align the connector  38  with respect to the opening  12  in the gasket  10 . 
     The retaining clips  16 A- 16 D are shown in greater detail in FIG.  4 . Each retaining clip  16  includes a pair of hooks  24  and  26  that are adapted to engage opposed sides of the second circular openings  44  of the connector  38 . For example, if the exemplary connector  38  has second circular openings  44  having a diameter of 2.44 mm, the retaining clips  16  are preferably formed having an opening height C of approximately 2.1 mm, a radius of curvature of approximately 0.35 mm, and a distance D between hooks  24  and  26  of 2.5 mm. Such dimensions will allow the hooks  24  and  26  to deflect upon insertion into the second openings  44  and to return to their original position to clasp the connector  38  to the gasket  10 . 
     Also shown in FIG. 4, the gasket  10  can have a lower end  28  that is rigified by bending a length B of the gasket material back onto itself, wherein the length B is preferably approximately 1.22 mm. The lower end  28  may be used as a ledge to locate the lower flanges  50  and  52  of the connector  38 , and optionally, locking the gasket  10  to the connector  38 . 
     The attachment of the EMI gasket  10  to the connector  38  will now be described with reference to FIGS. 7 and 8, which illustrate a cross section view taken along line VII—VII of FIG. 5 and a side view of an EMI gasket  10  partially secured thereto (FIG. 7) and completely secured thereto (FIG.  8 ). The present invention provides an advantageous structure and method by which the gasket  10  may be secured to the connector  38  without requiring additional mounting hardware. Also, the connector is typically secured to a printed circuit board P (see FIG. 6) before mounting the gasket  10  thereto. To mount the gasket  10  to the connector  38 , the flange  48  of the connector  38  is first positioned within the gap formed by the channel  20 . Then, the gasket  10  can be slid along the connector  38  to align the projections  14  with the openings  46 . Next, the bottom of the gasket  10  is rotated toward the connector  38  to seat the locating projections  14 A seat within the first circular openings  46  and to position the connector  38  with respect to the gasket  10 . Next, the pair of hooks  24  and  26  of the retaining clips  16 A are inserted into the second circular openings  44  to secure the gasket  10  to the connector  38 . As noted above, once the gasket  10  is mounted to the connector  38 , the tabs  18 A contact the tabs  42 , creating addition points of electrical contact between the gasket  10  and the connector housing  40 . After combining the gasket  10  and the connector  38 , the unit is placed adjacent a bulkhead B′ (see FIG.  7 ). The fingers  15 A are formed such that they create an electrical connection between the bulkhead and the gasket  10 . 
     The above-described gasket of the present invention provides a novel structure by which connectors may be quickly secured thereto, while simultaneously providing effective shielding for high density applications due to the many points of electrical contact between the gasket and the connector, and the gasket and the bulkhead. 
     FIG. 9 illustrates a second embodiment of the EMI gasket  10 ′ of the present invention. Similar elements to those of FIG. 1 are identified by reference numerals have a prime “′” appended thereto. Accordingly, these elements will not be described in detail herein again. In addition, the gasket  10 ′ includes similar structure to that shown in FIGS. 2-4 to provide for connector mounting and electrical contacts. The embodiment of FIG. 9 is preferably used when minimum side-by-side stacking distance is desired. 
     As illustrated in FIG. 9, a single opening  12  is provided to accommodate several of the connectors  38 , rather than the individual openings  12 A- 12 D of FIG.  1 . Connectors mounted to the gasket  10 ′ are aligned between each of the pairs of locating projections  14 A′- 14 C′ and the retaining clips  16 A′- 16 C′. Thus, the gasket  10 ′ provides for an open space between connectors. As is evident from FIG. 9, tabs  18 A′ and  18 C′ will only mate with the tabs  42  of the outmost connectors to which the gasket  10 ′ is mounted (i.e, those connectors  38  mounted to locating projections  14 A′ and the retaining clips  16 A′ and locating projections  14 C′ and the retaining clips  16 C′). The gasket  10 ′ also is provided with extra fingers  30  that create additional points of electrical contact between the gasket  10 ′ and the bulkhead to which the gasket  10 ′ is mounted. The extra fingers  30  may be formed having an angle a (e.g., 8-10°) with respect to the front face of the gasket  10 ′ to ensure a good electrical contact between the fingers  30  and the bulkhead. 
     The gasket  10 ′ advantageously provides a structure such that connectors  38  ay be more closely spaced, as well as a structure that is adaptable to provide mounting positions to accommodate a varying numbers of connectors, e.g, one to eight (or more) positions. A variable number of positions may be provided by varying the dimensions (in mm) such as those labeled “E,” “F,” and “G” in FIG. 9 in accordance with Table 1 below. 
     As seen in FIG. 9, dimension “E” represents the total length of the gasket  10 , dimension “F” represents the length of the opening  12 , and dimension “G” represents the distance between the centerline of the first and last connectors  38  mounted to the gasket  10 . 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Number of Positions 
                 Dimension “E” 
                 Dimension “F” 
                 Dimension “G” 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 One 
                 40.00 
                 15.20 
                 NA 
               
               
                 Two 
                 50.00 
                 35.20 
                 20.00 
               
               
                 Three (e.g., FIG. 9) 
                 80.00 
                 55.20 
                 40.00 
               
               
                 Four 
                 100.00 
                 15.20 
                 60.00 
               
               
                 Five 
                 120.00 
                 95.20 
                 80.00 
               
               
                 Six 
                 140.00 
                 115.20 
                 100.00 
               
               
                 Seven 
                 160.00 
                 135.20 
                 120.00 
               
               
                 Eight 
                 180.00 
                 155.20 
                 140.00 
               
               
                   
               
             
          
         
       
     
     TABLE 1 
     The present invention may be employed in other specific forms without departing from the spirit or essential attributes thereof. For example, the gasket  10 ′ maybe adapted such that connectors may be provided within the space between the connectors mounted between each of the pairs of projections  14 A′- 14 C′ and the retaining clips  16 A′- 16 C′. While the invention has been described and illustrated with reference to specific embodiments, those skilled in the art will recognize that modification and variations may be made without departing from the principles of the invention as described herein above and set forth in the following claims.