Patent Publication Number: US-2007121307-A1

Title: EMI/RFI shield for electronic device

Description:
TECHNICAL FIELD  
      The present invention relates to shields for shielding electronic components on a printed circuit board, and particularly to an EMI shield easily assembled to and detached from a printed circuit board of an electronic device.  
     BACKGROUND  
      Electronic devices are subject to external EMI (electromagnetic interference) and/or RFI (radio frequency interference) which can result in signal distortion. Thus, EMI sensitive electronic components on a printed circuit board of a electronic device are conventionally protected from EMI by a shield. Referring to  FIG. 5 , an EMI shield in a electronic device (not labeled) comprises a shield  51  soldered onto a printed circuit board (PCB)  52  to shield electronic components (not labeled) on the PCB  52 . An upper cover  50  and a lower cover  53  are assembled together to enclose the PCB  52  and the shield  51  therein. The shield  51  is needs to be fixed on the PCB  52  via a soldering process, which can be difficult. Furthermore, in order to replace or repair the electronic components, the shield must be de-soldered (i.e. the solder must be removed) before the shield can be safely detached from the PCB  52 . This makes any repairs inconvenient and cumbersome.  
      U.S. Pat. No. 5,748,455 disclosed one solution to the problem mentioned above. Referring to  FIG. 6 , a lower cover  67  forms a plurality of posts  69  therein, each post defining a threaded hole (not labeled) therethrough for engaging with a corresponding screw  70 . A PCB  71  defines a plurality of threaded holes  62  corresponding to the posts  69 . A shield  63  defines a plurality of cutouts  66  at edges thereof for fitting the periphery of the posts  69 . A plurality of spring pieces  64  extends out from edges of the shield  63 , and a plurality of retaining pieces  65  perpendicularly project from edges of the shield  63  adjacent to the spring pieces  64 . In assembly, the spring pieces  64  abut the PCB  61 , and the retaining pieces  65  abut an inner wall  68  of the lower cover  67  and the PCB  61 . The screws  70  are extended through the posts  69  and the threaded holes  62  of the PCB  61  and are secured in an upper cover  60 . Therefore, the upper and lower covers  60 ,  67 , the shield  63  and the PCB  61  are fixedly assembled together.  
      However, the above-described art comprising posts, threaded holes, screws, spring pieces, and retaining pieces, is unduly complicated and cumbersome. The shield is designed to shield the entire PCB, whereas only certain components on the PCB need be shielded to obtain the desired protection from external EMI.  
      What is needed, therefore, is an EMI shield which overcomes the above-described shortcomings.  
     SUMMARY  
      In one embodiment thereof, a shield for shielding electronic components mounted on a printed circuit board (PCB) disposed within a housing for an electronic device is provided. The shield includes a top wall and a circumferential sidewall. The circumferential sidewall extends from peripheral edges of the top wall towards a side of the top wall. The circumferential sidewall and the top wall cooperatively form a shield cavity for shielding the electronic components provided on the printed circuit board. The shield is integrally formed with an inner surface of the housing.  
      Other advantages and novel features of the preferred embodiments of the present shield and its applications will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Many aspects of the present EMI shields and their applications can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the EMI shields. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.  
       FIG. 1  is a partially exploded, perspective view illustrating a mobile phone, to which an EMI shield according to a preferred embodiment is applied;  
       FIG. 2  is a perspective view illustrating the mobile phone illustrated in  FIG. 1 ;  
       FIG. 3  is a partially perspective, assembled view of the mobile phone;  
       FIG. 4  is a cross-sectional view taken along VI-VI line of  FIG. 3 ;  
       FIG. 5  is an isometric view of a typical EMI shield; and  
       FIG. 6  is an isometric view of another typical EMI shield. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      An EMI shield according to a preferred embodiment of the present invention is adapted for use in an electronic device such as a mobile phone  100 . Referring to  FIGS. 1 and 2 , the mobile phone  100  includes an upper housing  10 , a printed circuit board (PCB)  20 , and an EMI shield  30 . The PCB  20  has electronic components  22  and, a ground trace  24  surrounding the electronic components  22  and disposed on the PCB  20 . The PCB  20  defines mounting holes  26  adjacent to two ends thereof, for mounting the PCB  20  to the upper housing  10 . The shield  30  is used for providing EMI and/or RFI (radio frequency interference) shielding for electronic and electrical circuitry disposed on a printed circuit board (PCB).  
      The housing  10  could be the outer plastic cover of a radiotelephone, or other such housing. The housing  10  includes an upper surface  12 , and a lower surface  14 . The housing  10  has a compartment  16  defined in upper surface  12  thereof. The housing  10  has a square circumferential protrusion extending from the lower surface  14  thereof.  
      Referring to  FIGS. 3 and 4 , the shield  30  includes a top wall  32 , a circumferential sidewall  34 , and a circumferential flange  36 . The top wall  32  and the circumferential sidewall  34  cooperatively form a shielding cavity  38 . The shield  30  is preferably a conductive sheet. The shield  30  may be integrally formed on the housing  10  and joined with an inner surface of the circumferential protrusion  18  by in-mold laminating. The shield  30  may be formed by means of punching a conductive sheet, then be integrally formed on the housing  10  by means of insert molding. The shield  30  is thus substantially lower in cost, simpler in construction, and light in weight.  
      In assembly, a conductive adhesive such as an electrically conductive rubber  40  is applied on the ground trace  24 . The PCB  20  is assembled on the lower surface  14  of the housing  10  via the mounting holes  26 , with the electronic components  22  facing the lower surface  14  of the housing  10 , and the circumferential flange  36  of the shield  30  compressing on the electrically conductive rubber  40 . The electronic components  22  are received in the shield cavity  38  of the shield  30 .  
      In alternative embodiment, the flange  36  may be omitted. The sidewalls  34  of the shield  30  can directly connect with the conductive rubber  40 . The flange  36  may directly connect with the ground trace  24 , thus the conductive rubber  40  may be omitted.  
      It is believed that the embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.