Abstract:
An arrangement for dissipating heat from a circuit element attached to a printed circuit board, comprising: a heatsink having a pair of arms, each one of the arms having tips including bumps, and a structure coupled to the printed circuit board on at least two sides. The structure has holes structured and arranged to allow each of the bumps on the tips of the arms to fit into the holes of the structure.

Description:
FIELD OF THE INVENTION 
     The invention relates to the cooling of a circuit element, and, more particularly, the invention relates to an apparatus for dissipating heat from a circuit element mounted on a printed circuit board. 
     BACKGROUND OF THE DISCLOSURE 
     In general, heatsinks dissipate heat away from integrated circuits (ICs) to the surrounding air. Presently, there are two main approaches to installing such heatsinks. In the first approach, the heatsink is bonded to the top of the IC. In bonding, the bond line between the IC and the heatsink must be sufficiently thin to ensure minimal thermal resistance through the bonding material. 
     Unfortunately, delamination of the heatsink can result if the IC generates too much heat. The loose heatsink could come in contact with other circuitry and cause an electrical short, and the now improperly bonded heatsink will not dissipate heat from the IC. Bonding is thus a poor solution when maximal heat dissipation is required. 
     In the second approach, the heatsink is mechanically mounted to the printed circuit board (PCB) such that the IC is sandwiched between the heatsink and the PCB. Specifically, the heatsink is mounted by either securing the heatsink to the IC via clips that attach to the underside of the IC package (i.e., piggyback mounting), or mounting the heatsink to the PCB using spring clips or screws. Piggyback mounts are typically not used with ICs having a low profile package, such as a quad flat pack (QFP) or a ball grid array (BGA) package, because there is minimal gap between the IC and the PCB for attaching the heatsink. Attaching the heatsink to the PCB using spring clips or screws requires isolating the mounting area from the traces of the PCB thereby reducing the available space for circuit routing. As such, knowledge of heatsink placement is required before design and sometimes results in enlargement of the PCB to accommodate the heatsink. 
     Therefore, a need exists in the art for a heatsink arrangement that provides maximum heat dissipation without being bonded to the IC or being mounted to the PCB or the under edge of the IC package. 
     SUMMARY OF THE INVENTION 
     The disadvantages associated with the prior art are overcome by an apparatus for dissipating heat from a circuit element mounted to a PCB. In an embodiment of the invention, a heatsink for dissipating heat from an (Integrated Circuit) IC mounted to the PCB is coupled to a surrounding structure of the PCB. The surrounding structure is a RF shield. The heatsink comprises a connector for thermal contact with an IC, and a pair of arms for dissipating heat and for coupling the heatsink to the surrounding structure without contacting the PCB. If the ICs have electrically conductive packages, non-electrically conductive thermal spacers are inserted between the connector and the corresponding IC to electrically isolate the heatsink from the IC. Additionally, each arm has a tip extending perpendicularly therefrom, substantially increasing the surface area thereof for increased heat dissipation and for structural stability. 
     The heatsink is mounted to the surrounding structure using bumps attached to the tips of each arm. Holes in the surrounding structure accept the bumps attached to the tips of each arm. In alternative embodiments of the invention, the heatsink is coupled to slots or holes in the surrounding structure via rivets, pin plugs, pegs or screws on the tips of the arms of the heatsink. Because the heatsink does not come into contact with the PCB, the PCB can be made smaller and trace routing is maximized. 
     Further embodiments of the present invention will become apparent from the detailed description contained hereinafter. It should be understood, however, that the detailed description and specific examples are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
     FIG. 1 illustrates an embodiment of a heatsink according to the present invention; 
     FIG. 2 depicts the right tip portion of the heat sink of FIG. 1; 
     FIG. 3 depicts an isometric view of a circuit element mounted to a printed circuit board; and 
     FIG. 4 depicts the heatsink coupled to a structure and in thermal contact with a circuit element. 
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
     DETAILED DESCRIPTION 
     FIG. 1 illustrates an embodiment of a heatsink  10  according to the present invention. Specifically, the heatsink  10  comprises a rectangular left arm  20 , a rectangular connecting member  12 , and a rectangular right arm  24 . It will be appreciated by those skilled in the art that connecting member  12 , left arm  20  and right arm  24  may also be formed using non-rectangular shapes. Moreover, it will be appreciated that while the heatsink  10  of FIG. 1 is described primarily in rectangular and other specific shapes, various modifications to such shapes are contemplated by the inventor and within the scope of the present invention. 
     Rectangular connecting member  12  includes side walls  14 , an open top  16  and an opposing open bottom  18 . Extending perpendicularly from one of said side walls  14  is a left arm  20 . A left tip  22  extends perpendicularly from substantially the majority of the width of the left arm  20 . Extending perpendicularly from one of said side walls  14  opposite the left arm  20  is a right arm  24 . A right tip  26  (FIG. 2) extends perpendicularly from and substantially the majority of the width of right arm  24 . Together left arm  20  and right arm  24  comprise a pair of arms  34 . On the outer surface of each tip is a plurality of bumps  28  and on each side wall is a plurality of holes  32 . 
     Heatsink  10  is made out of a thermally conductive material such as aluminum. Important bends of heatsink  10  include gussets  30 , which provide mechanical strength to avoid deformation and have adequate bend radii so as not to restrict the conductive flow of heat through the metal. 
     Connecting member  12  is designed to mechanically mate with the desired circuit element using an interference or compression fit, whereby adequate pressure can be applied to ensure heat transfer from the circuit element to heatsink  10 . That is, the interference fit provides mechanical support and low thermal resistance by ensuring a minimum “contact patch” between the heatsink  10  and a circuit element producing a great amount of heat dispersion. Heat sink  10  is designed so that connecting member  12  sits on top of the circuit element. Heat is drawn from the circuit element into side walls  14  and dispersed to pair of arms  34  and to the air, for example, via open top  16  and open bottom  18 . 
     Connecting member  12  can be in direct contact with a circuit element having a non-electrically conductive package (e.g., ceramic package), or if the circuit element has a metal package, can be thermally coupled to the circuit element with conductive spacers that are electrical insulators. Although the heatsink  10  of FIG. 1 is made of aluminum, it is understood by those skilled in the art that heatsink  10  can be made of any thermally conductive material (e.g. metal, metal composite, polymer). 
     FIG. 3 depicts an isometric view of a circuit element  36  mounted to a printed circuit board (PCB)  38 . The circuit element  36  comprises, illustratively, an integrated circuit (IC) encapsulated within a package  40  that has a substantially planar top surface  42  and opposing bottom surface  44 , such as a quad flat pack (QFP) or ball grid array (BGA) package. Leads  46  are connected to the IC within the package  40  and extend outward for attachment to PCB  38 . 
     While the present invention has been illustrated for enhanced cooling of a packaged IC, it will be appreciated that the inventive principles can be utilized with any heat generating circuit element. Such element does not necessarily require a planar surface, since a conductive compound can be utilized to ensure good surface contact on non-planar surfaces. Further, while conventional leads  46  have been illustrated for mounting the circuit element  36  to the PCB  38 , it will be appreciated by those skilled in the art that the invention can be practiced with circuit elements having other types of connection elements, such as ball grid solder bumps. 
     FIG. 4 depicts an assembly including a heatsink according to the present invention. Specifically, FIG. 4 depicts an isometric view of an structure or module comprising a heatsink formed according to the present invention cooperating with an structure  48  to contain a PCB  38  including integrated circuits thermally cooperating with the heatsink. The heatsink mechanically cooperates with the structure  48  and the PCB  38  to form a compression fit such that a path of low thermal resistance is formed between the heatsink and integrated circuits on the PC board to be cooled. 
     The structure  48  comprises side walls perpendicularly oriented with respect to the edges of the PCB  38 . Other shapes (e.g., round, oval, etc.) and orientations including portions or the entirety of the PCB  38  are also within the scope of the present invention. 
     FIG. 4 depicts the heatsink  10  of the present invention coupled to structure  48  surrounding the PCB  38 . Structure  48  comprises a side wall  50  on each side of the PCB  38 . Each of the side walls  50  includes a top edge  52  and a bottom edge  54 , where the bottom edge  54  of each of the side walls  50  includes downwardly extending plurality of solder tabs  56 . The plurality of solder tabs  56  are used to attach structure  48  to the PCB  38 . Other devices for connecting the structure  48  to the PCB  38  are also within the scope of the invention. Dispersed throughout each side walls  50  are a plurality of holes  32 . Other types of perforations (i.e. slots and the like) may be used. Structure  48  is any surrounding structure of PCB  38 , for example, an RF shield or chassis. 
     In this illustrative embodiment, the pair of arms  34  of heatsink  10  is depicted as being attached to the structure  48  via the bumps  28  and holes  32  of the respective devices. Although heatsink  10  and structure  48  are depicted as having bumps  28  and holes  32  respectively, other methods of attachment may be used, for example, slots, rivets, pins, plugs, pegs, screws or combinations thereof. Additionally, heatsink  10  is depicted as being removable from structure  48  but it can also be permanently locked into place. 
     Pair of arms  34  also provide a large surface area for dissipating heat away from circuit element  36  when an electronic component  36  is in thermal contact with connecting member  12 . Although it is not depicted, thermally conductive spacers that are electrical insulators can be used with the present invention. The spacers can be used for example when electronic component  36  has a metal structure that is not electrically isolated. Additionally, thermally conductive spacers can also be used where there is an insufficient amount of interference between the heatsink and the electronic component. 
     Thus, as described, the present invention provides for enhanced cooling of a conventional electronic component by making available, on the top surface of the component, an additional surface for heat dissipation. By utilizing an arrangement whereby the present invention is coupled to a chassis structure, heat is dissipated from the electronic component to the surrounding air. This is accomplished without requiring the design of customized components. 
     Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.