Abstract:
A construction and method are provided for electronically shielding an electronic component and for removing heat generated by the component. The construction and method involve the use of a shielding can, formed with EMI shielding material that surrounds the electronic component and a lid or cap that both contacts and forms a heat sink with the component and also provides a shielding effect as it acts as the cap for the shielding can.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to shielding devices and more particularly to lids for shielding cans used to shield electronic components from electromagnetic interference (EMI). 
     Many electronic apparatuses, such as computer products, cellular phones and the like, include electronic components, such as printed circuit boards (PCBs) and integrated circuits (ICs). It is often desirable to isolate the electronic component) to prevent the EMI from the component from affecting other electronic components incorporated in the apparatus or for shielding the component from EMI emitted by other sources. 
     Many electronic components generate significant amounts of heat. Excessive heat build up can lead to reduced product life and reliability. Thus, various constructions have been proposed for removing heat generated by electronic components. 
     Existing constructions and methods for simultaneously removing heat from an electronic component and for shielding the component have not always proven to be fully satisfactory, such as in view of the complexity, size, costs or effectiveness of these constructions and methods. Accordingly, it is desirable to provide an improved construction and method for shielding an electronic component and removing heat from the component, which overcomes inadequacies of the prior art. 
     SUMMARY OF THE INVENTION 
     Generally speaking, in accordance with the invention, an improved construction and method are provided for electronically shielding an electronic component and for removing heat generated by the component. The construction and method involves the use of a shielding can, formed with EMI shielding material that surrounds the electronic component and a lid or cap that both contacts and forms a heat sink with the component and also provides a shielding effect as it acts as the cap for the shielding can. 
     The can may be formed with side walls and an opening, such as a window located at the top thereof. The lid can be in the form of a resilient member formed of electrical and heat conductive material and preferably having heat dispersing fins, which snaps in place at the opening in the can, and maintains good contact with the electronic component. In preferred embodiments of the invention, the lid is spring biased against the component. The shielding lid can be formed as a snap in lid that includes a contacting surface to draw heat from the heat producing component and outwardly extending fins which transfer heat drawn from the component to the surrounding environment. 
     The shielding can may be any known electrical housing with any number of sidewalls and with a single or stepped horizontal top surface having one or more openings, each providing shoulder for the snap-in lid. The can may include a window at the top surface thereof and side walls that extend up and then can extend partially into the interior of the can, to provide a shoulder defining the opening. The lid can include a camming surface which snaps under the shoulder and biases the lid down onto the heat producing component, so as to maintain good thermal contact between the lid and the component. In certain embodiments of the invention, heat conductive material, such as electronically insulating heat conductive material, in the form of gels, coatings, paints, rubbers, elastomers, polymers and resins can be disposed at the interface of the lid and the electronic component. 
     Accordingly, it is an object of the invention to provide improved structures for shielding an electronic component and for drawing heat from the component; 
     Another object of the invention is to provide improved methods for shielding an electronic component and for drawing heat from the component. 
     The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the article possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure. The scope of the invention will be indicated in the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention, reference is had to the following description, taken in connection with the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a shielding can for use in accordance with preferred embodiments of the invention; 
     FIG. 2 is a perspective view of a shielding/heat sink lid, constructed in accordance with preferred embodiments of the invention; 
     FIG. 3 is a side view of the lid of FIG. 2; 
     FIG. 4A is a perspective view of the can of FIG.  1  and the lid of FIG. 2, prior to installation; 
     FIG. 4B is a perspective view shows the can and lid of FIG. 4A, during installation; 
     FIG. 4C is a perspective view showing the lid of FIG. 4A installed in the can of FIG. 4B; 
     FIG. 5 is a side cross-sectional view of the installed lid and can of FIG. 4C; and 
     FIG. 6 is a perspective view of a shielding can having multiple snap-in heat sink lids. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A non-limiting example of a shielding can for use in constructions and methods in accordance with preferred embodiments of the invention is shown generally as shielding can  100  in FIG.  1 . Shielding can  100  is of a generally known type and should be formed of EMI shielding material, such as various conductive materials, including brass, copper, aluminum, copper beryllium alloy, phosphor bronze or steel. Shielding can  100  can be formed from a flat sheet of metal having four tabs  110  which are folded down to become the four side walls of can  100 . Shielding can  100  also includes an open window  120  defined by an inner edge  135  of an upper shoulder  130 . As would be apparent to those of ordinary skill in the art, other configurations of a shielding can may be used, as appropriate. 
     In use, shielding can  100  is disposed over an electronic component, for the purpose of shielding the component from EMI emitted from other electronic components or to prevent EMI from the device shielded by the can from interfering with other components. Components which are commonly shielded include ICs, PBCs and the like which can be mounted on a PC board and the shielding can  100  is likewise mounted on the PC board. In preferred embodiments of the invention, shielding can  100  can be grounded in any number of ways, which would be apparent to those of ordinary skill in the art. 
     A non-limiting example of a heat sink shielding lid for use in constructions and methods in accordance with the invention is shown generally as shielding lid  200  in FIGS. 2-5. Shielding lid  200  is preferably formed from a heat conductive and EMI shielding material. Shielding lid  200  is also advantageously formed of a resilient spring-like material. Advantageous materials includes beryllium copper alloys, such as alloy c 17410, aluminum, brass and phosphor bronze. Lid  200  can be bare metal or coated with a suitable electrically conductive plating to provide galvanic compatibility with shielding can  100   
     Shielding lid  200  is advantageously formed from a flat sheet of metal having four tabs, which are bent up to form four spring walls  210  of shielding lid  200 . Spring walls  210  extend upwards from a heat sink wall  220 , the bottom surface of which is intended to contact the heat producing component. In certain preferred embodiments of the invention, at least heat sink wall contact surface  220  is covered with an electrically insulating material and/or a heat conductive material to prevent current from flowing from the component into lid  200  and to enhance the conduction of heat from the component into lid  200 . Preferred materials include ceramic particles, ferrite EMI/RFI absorber particles or metal or fiber glass mesh in a base of rubber, gel, grease or wax. 
     In one preferred embodiment of the invention, shielding can  100  is formed from a 0.015″ thick sheet of brass which can be tin plated. The outside dimensions of each wall  110  are 1.5″ and the inside diameter of window  120  is 1.280″. Walls  110  are 0.5″ high. However, as would be apparent to those of ordinary skill in the art, these dimensions can be varied and modified, based on the size of the component to be shielded, space considerations within the overall apparatus and other factors of design choice. 
     Shielding lid  200  can be formed from a 0.01″ thick beryllium copper alloy. Each spring wall  210  and the sides of contact surface  220  can be slightly under 1″ in width. Each side wall  210  can have a height of 0.904″ and each tab  230  can have a height of 0.36″ and a width of 0.151″. The gap between fins  230  can be 0.06″. 
     Each spring wall  210  includes an insertion wall  236 , at an outside angle A to bottom surface  220 . Angle A should be less than 90°, generally from about 45-85°, preferably 60 to 70° and most preferably about 65°. Insertion wall  236  slides against edge  135 , which deflects spring walls  210  inwards, temporarily increasing angle A. 
     Spring wall  210  also includes a camming shoulder  235  at an angle B to insertion wall  236 , extending from an outside corner  237  to an inside corner  238 . Angle B can be about 80 to 100°, preferably about 90°. Because shoulder  235  will be at an acute angle to the underside of edge  135  and spring wall  210  is biased outwards, the interaction between shoulder  235  and edge  135  causes can  100  to exert a downwards force on lid  200 , which serves to improve the contact heat transfer between bottom surface  220  and the component being shielded and cooled. 
     Spring wall  210  also includes an upper portion, above inner corner  238 , which is advantageously formed with fins  230 , advantageously at an angle C to camming shoulder  235 . Angle C is advantageously less than 115 degrees and may be varied greatly to fit the fins  230  within the space where the component  500  is located. The height of fins  230  will be affected by space and heat transfer considerations. 
     Referring to FIG. 4A, shielding can  100  is shown mounted on a PC board  410  over an electronic component  450 . As shown in FIG. 4B, as shielding lid  200  is pressed into window  120  of can  100 , insertion surfaces  235  impinge on edge  135  and bend spring walls  236  inwardly. As edge  135  clears corner  237  where shoulder  235  meets wall  236 , the springiness of spring wall  210  and the angle of contact with shoulder  235  force lid  200  down onto the top of the electronic device  450 , to yield a snap-in heat sink shielding construction  400  of FIG.  4 C. Accordingly, it is advantageous that in final construction  400 , when lid  200  is in its final position, that edge  135  rests between comers  237  and  238 , advantageously approximately midway between corners  237  and  238 . Reaction force cause by internal stress on lid  200  acts to hold lid  200  down firmly against electronic component  450 , so as to make good thermal contact. In certain preferred embodiments of the invention, a conductive interface material  500  is disposed between lid  200  and component  450  as either a separate layer, on the top surface of component  450  or on the bottom surface  220  of lid  200 . Such materials can include ceramic particles, ferrite EMI/RFI absorber particles, or metal or fiberglass mesh in a base of rubber, gel, grease or wax. 
     As evident of the foregoing, the invention provides a heat sink, advantageously formed of thermally conductive and electronically shielding springy material, but preferably copper beryllium alloy, that makes acceptable thermal contact with a heat producing component, such as an integrated circuit, either directly or through an appropriate layer of thermally conductive interface material, such as thermally conductive elastomer or gel or ferrite loaded elastomer, while electronically shielding the heat producing component. The invention can provide a simple-to-construct single piece snap-in lid that includes a contact surface area to draw heat from the heat producing device and fins to transfer such heat to the surrounding environment. By making the lid of a springy material, it can snap into an aperture, such as a window on the top of an existing shielding can, and thereby electrically shielding the device and provide force between the lid and the device to enhance thermal contact. 
     Lids in accordance with the invention can also be used in shielding cans having multiple apertures which house multiple heat producing components. Referring to FIG. 6, a shielding can  600  is shown mounted on PC board  410  over electronic components not shown. Shielding can  600  is formed with three windows  120  into each of which a shielding lid  200  is inserted. 
     It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes are made in carrying out the above method and in the articles set forth, without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense. 
     It should also be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall there between.