Abstract:
A method for mounting a fingerstock EMI shielding gasket on a sheet metal structure includes the steps of forming tabs which protrude from the surface of the sheet metal structure. The shielding gasket, which has a generally D-shaped cross section with at least one mounting tab forming at least part of an upright portion therefor, is inserted into position longitudinally between the tabs.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is based on U.S. patent application Ser. No. 60/503,831, filed Sep. 18, 2003, on which a claim for Convention priority is made in this application. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to the provision of EMI shielding and specifically to the mounting of a fingerstock EMI shielding gasket on a sheet metal structure. 
   2. Description of the Prior Art 
   Fingerstock EMI shielding gaskets are well known in the art. Gaskets of this type are mounted for either wiping or compression closing applications on structures used to house circuit boards, such as those designed to plug into a rack for electronic equipment. 
   In the prior art, fingerstock gaskets have been mounted in a variety of ways. In one method, double-sided, pressure-sensitive adhesive (PSA) tape is used to hold the gasket in a desired position on the structure. Alternatively, rivets or mounting tracks, both of which include fastening means designed to engage into holes drilled or otherwise provided in the structure of interest, may be used. Finally, the gaskets may also be inserted into slots in the structure, clipped onto an edge of the structure, or welded or soldered into the position desired. 
   The present invention provides an alternative to these mounting methods of the prior art. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is a method for mounting a fingerstock EMI shielding gasket on a sheet metal structure. The shielding gasket has a generally D-shaped cross section with at least one mounting tab forming at least part of an upright portion therefor, and is of a variety well known to those of ordinary skill in the art. 
   The method comprises the steps of forming at least one outer tab and at least one inner tab from the sheet metal structure. The inner and outer tabs protrude outwardly from a surface of the sheet metal structure. The inner tabs are oriented generally toward the outer tabs and are laterally separated therefrom. The shielding gasket is slid longitudinally between the inner and outer tabs, one of its two mounting tabs being inserted beneath the inner tabs, to be secured between the inner and outer tabs. 
   In practice, a plurality of outer tabs and a plurality of inner tabs are aligned longitudinally in a direction parallel to an edge of the sheet metal structure. A second mounting tab of the shielding gasket may be directed generally beneath the edge of the sheet metal structure, or may reside on the surface of the sheet metal structure. Alternatively, anti-snag tabs, also protruding outwardly from a surface of the sheet metal structure, may be formed to hold the second mounting tab down on the surface to prevent snagging. 
   Moreover, longitudinal-retention tabs, protruding partially or completely from the surface of the sheet metal structure, may be provided to prevent the shielding gasket from shifting longitudinally out of position once it is slid thereinto between the inner and outer tabs. 
   The present invention will now be described in more complete detail with frequent reference being made to the figures identified below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a gasket mounted on a structure in accordance with the method of the present invention; 
       FIG. 2  is a cross-sectional view showing an alternative mounting method; 
       FIG. 3  is a perspective view in which the gasket is partially cut away; 
       FIGS. 4A through 4D  are views showing the gasket in relation to the outer, inner and anti-snag tabs; 
       FIGS. 5A through 5E  are perspective views showing several schemes by which the structure may be provided with outer, inner and anti-snag tabs; 
       FIGS. 6A and 6B  are perspective views of ends of structures with gaskets held in position by longitudinal-retention tabs; 
       FIGS. 7A and 7B  are side views of the ends shown in  FIGS. 6A and 6B , respectively; 
       FIGS. 8A through 8C  are end views, similar to that of  FIG. 4C , showing the mounting of alternative varieties of fingerstock gaskets in accordance with the present invention; 
       FIGS. 9A and 9B  are perspective and end views, respectively, of a gasket mounted on a structure in an alternate embodiment of the present invention; and 
       FIGS. 10A and 10B  are perspective and end views, respectively, of a gasket mounted on a structure in still another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Turning now to these figures,  FIG. 1  is a perspective view of a fingerstock gasket  10  mounted on a structure  12  designed to hold a circuit board or other component of a piece of electronic equipment. In practice, the fingerstock gasket  10 , which may be made of any of a variety of electrically conducting materials, provides EMI shielding when the structure  12  closely abuts against another component or structure in the piece of electronic equipment, thereby being compressed between the two and closing the gap between them against leakage of electromagnetic fields from within the equipment. This and other figures in the present application are intended to show the mounting of the fingerstock gasket  10  in accordance with the present invention, and not the specifics of every situation in which the gasket  10  may find use. 
   In accordance with the present invention, the fingerstock gasket  10  is mounted using tabs formed from the material from which the structure  12  is made. As shown in  FIG. 1 , as well as in the other figures, fingerstock gasket  10  has a generally D-shaped cross section with two mounting tabs  14 , 16 . Outer tabs  18  and inner tabs  20 , of which one may be seen in  FIG. 1 , are formed from the structure  12  itself. Outer tabs  18  and inner tabs  20  are stamped and formed from structure  12 . Alternatively, tabs  18 , 20  may be produced by casting, for example, by die-casting, or by molding. As will be made more apparent in subsequent figures, fingerstock gasket  10  is mounted into position on structure  12  by sliding longitudinally therealong with mounting tab  14  captured between outer and inner tabs  18 , 20 . The outer tab  18  can also serve as a down stop. 
     FIG. 2  is a cross-sectional view showing an alternative method for mounting the fingerstock gasket  10 . In contrast to the view shown in  FIG. 1 , mounting tab  16  wraps around an edge  22  of the structure  12 , instead of resting on its surface  24 . 
     FIG. 3  is a perspective view, similar to that provided in  FIG. 1 . In  FIG. 3 , gasket  10  is partially cut away to show inner tabs  20  as well as an anti-snag tab  26 . As in  FIG. 1 , mounting tab  14  of gasket  10  is captured between outer and inner tabs  18 , 20 . In addition, mounting tab  16  of gasket  10  is secured under anti-snag tab  26 , which, like tabs  18 , 20 , is formed from the structure  12  itself. That is to say, anti-snag tab  26  is stamped and formed from structure  12 , although it may alternatively be produced by casting, for example, by die-casting, or by molding. Anti-snag tab  26  is so called because it holds mounting tab  16  securely and prevents snagging as structure  12  is being mounted in a piece of electronic equipment. As was the case with the embodiment shown in  FIG. 1 , fingerstock gasket  10  is mounted into position on structure  12  by sliding longitudinally therealong with mounting tab  14  captured between outer and inner tabs  18 , 20  and mounting tab  16  disposed under anti-snag tab or tabs  26 . 
     FIGS. 4A through 4D  are views showing the gasket  10  and mounting tabs  14 , 16  in relation to the outer tab  18 , inner tab  20  and anti-snag tab  26  of the structure  12 .  FIGS. 4A through 4C  shown cross-sectional and end views of the embodiment shown in  FIG. 1 , which lacks anti-snag tabs  26 .  FIG. 4A  is a cross-sectional view taken through one of the outer tabs  18 ;  FIG. 4B  is a cross-sectional view taken through one of the inner tabs  20 ; and  FIG. 4C  is an end view. In  FIGS. 4A through 4C , mounting tab  14  of gasket  10  can be seen to be captured between outer tab  18  and inner tab  20 .  FIG. 4D  is a cross-sectional view of the embodiment shown in  FIG. 3 . It is taken through an anti-snag tab  26 . In addition to showing mounting tab  14  of gasket  10  captured between outer tab  18  and inner tab  20 , it shows mounting tab  16  of gasket  10  held securely by anti-snag tab  26 . 
     FIGS. 5A through 5E  are perspective views showing several schemes by which structure  12  may be provided with outer tabs  18 , inner tabs  20  and anti-snag tabs  26 .  FIG. 5A  shows the basic scheme, which works best for short lengths of gasket  10 . In this basic scheme, each outer tab  18  faces a pair of inner tabs  20 . 
   In  FIG. 5B , the outer tabs  18  and inner tabs  20  are disposed as in the basic scheme shown in  FIG. 5A . An anti-snag tab  26  is also disposed between each pair of inner tabs  20 . 
     FIGS. 5C and 5D  show schemes having the same numbers of outer tabs  18  and inner tabs  20 . In  FIG. 5C , the outer tabs  18  and inner tabs  20  are in staggered positions relative to one another; in  FIG. 5D , the outer tabs  18  and inner tabs  20  are aligned with one another. 
     FIG. 5E  shows a scheme like that of  FIG. 5D  wherein anti-snag tabs  26  are disposed between the inner tabs  20 . This may also be done with the scheme shown in  FIG. 5C . 
   In all of the schemes shown in  FIGS. 5A  though  5 E, it should be understood that the outer tabs  18  are all longitudinally aligned on the structure  12 . The same can be said for the inner tabs  18  and any anti-snag tabs  26  that may be present. This longitudinal alignment ensures that the gasket  10  may be longitudinally slid into position on the structure  12 . 
     FIGS. 6A and 6B  are perspective views of ends of structures  12  with fingerstock gaskets  10  held in position against longitudinal movement by longitudinal-retention tabs  28 , 30 , which are stamped and formed from structure  12 . In  FIG. 6A , longitudinal-retention tab  28  is fully sheared and protrudes completely above the surface  24  of the structure  12 . In  FIG. 6B , longitudinal-retention tab  30  is only partially sheared and protrudes less than its full thickness above the surface  24  of the structure  12 . 
     FIGS. 7A and 7B  are side views of the ends shown in  FIGS. 6A and 6B , respectively. The difference between longitudinal-retention tab  28 , which is fully sheared and protrudes completely above the surface  24  of the structure  12 , and longitudinal-retention tab  30 , which is only partially sheared and protrudes less than its full thickness above the surface  24  of the structure  12 , is readily apparent in  FIGS. 7A and 7B . 
   Alternatively, longitudinal-retention tabs  28 , 30  may be produced by casting, for example, by die-casting, or by molding. 
     FIGS. 8A through 8C  are end views, similar to that of  FIG. 4C , showing the mounting of alternative varieties of fingerstock gaskets in accordance with the present invention. In each of  FIGS. 8A through 8C , structure  12  is again provided with outer tabs  18  and inner tabs  20  as previously described. In  FIG. 8A , gasket  32 , an all-purpose fingerstock gasket available from Laird Technologies, Inc. of Delaware Water Gap, Pa., U.S.A. (Series 97-540), is shown mounted between outer and inner tabs  18 , 20 . Gasket  32  has only one mounting tab  34 , in contrast to the symmetrical design of gasket  10  described above.  FIG. 8B  shows gasket  36 , a no-snag fingerstock gasket also available from Laird Technologies, Inc. Gasket  36  is also shown mounted between outer and inner tabs  18 , 20 , and also has only one mounting tab  38 .  FIG. 8C  shows gasket  40 , a foldover-series fingerstock gasket also available from Laird Technologies, Inc. Gasket  40  has only one mounting tab  42 , which is folded back as shown in  FIG. 8C , and which is captured between outer tab  18  and inner tab  20 . 
     FIGS. 9A and 9B  are perspective and end views, respectively, of a gasket  10  mounted on a structure  42 . Structure  42  has outer tabs  44  and inner tabs  46  which are integrally formed therewith by extrusion or by casting. By producing tabs  44 , 46  by extrusion or by casting, shielding is improved because tabs  44 , 46  do not leave apertures in the structure  42 . 
     FIGS. 10A and 10B  are perspective and end views, respectively, of a gasket  40  mounted on a structure  48 . Outer tabs  50  and inner tabs  52  are not integrally formed with structure  48 , but, rather, are additional pieces attached to structure  48 . Again, shielding is improved because tabs  50 , 52  do not leave apertures in structure  48 . 
   Outer tabs  50  and inner tabs  52  are typically made from sheet metal, and are attached to structure  48  by welding, soldering, adhesives or fasteners, such as screws or rivets. Outer tabs  50  and inner tabs  52  may be full-length, like the extruded tabs  44 , 46  shown in  FIGS. 9A and 9B , or may be segmented like the punched tabs shown in  FIGS. 1 through 8C . Moreover, in this embodiment, outer and inner tabs  50 , 52  need not be of an electrically conductive material, and may be molded from plastic. 
   The present invention has several distinct advantages over the methods of the prior art. No adhesive tape is required to secure the fingerstock gaskets, and, as a consequence, no residue must be removed if they have to be replaced. Further, the positioning of the gaskets is repeatable and accurate and does not depend on operator skill with the present invention. Moreover, the cost of the gasket used in the present invention is less than those used in the track-mounted gaskets of the prior art. Finally, the tabs on the structures used in the practice of the present invention are smaller than the slot-mount openings used in the prior art, and, as a consequence, leak less electromagnetic radiation. In addition, with the present invention, the underside of the structure can be sealed against leakage, for example, with metal foil tape, since mounting tabs do not protrude through them. 
   Modifications to the invention would be obvious to those of ordinary skill in the art, but would not bring the invention so modified beyond the scope of the present invention.