Abstract:
A heat sink may transfer heat from electronic devices. A heat conductive base may have integrally attached thereto a plurality of parallel fins. The fins may be made up of two sheets of material. One sheet may be a metal having significant structural integrity and the other sheet of material may be a pyrolytic graphite material having excellent heat transfer characteristics. The two layers may be integrally bonded together.

Description:
BACKGROUND  
       [0001]     This invention relates to removing heat from heat producing electronic devices such as microprocessors.  
         [0002]     In operation, electronic devices, including microprocessors, tend to generate heat. Their performance may be adversely affected by their temperature. Thus, it is advantageous to remove heat from the integrated circuits as effectively as possible.  
         [0003]     To this end, heat sinks are commonly attached to integrated circuit packaging. These heat sinks may include fins and integrated heat spreaders which transfer heat from the integrated circuit packaging to the heat sink.  
         [0004]     Existing heat sinks tend to be heavy, contributing to weight of the overall electronic device. In some electronic devices, including mobile devices, overall weight is an important factor.  
         [0005]     Thus, there is a need for ways to improve the heat transfer from electronic devices. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a partial, front elevational view of one embodiment of the present invention in the course of manufacture;  
         [0007]      FIG. 2  is a partial, front elevational view of the embodiment of  FIG. 1  after further processing; and  
         [0008]      FIG. 3  is a perspective view of one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0009]     Referring to  FIG. 1 , a heat sink base  12  may be formed of copper or other heat conducting material. The base  12  may have a number of closely spaced fin receiving apertures  16 . In one embodiment, the fin receiving apertures  16  may have a downwardly expanding, dovetail shape.  
         [0010]     A heat sink fin  14   b  may include a metallic layer  18  and a graphite or non-metallic layer  16 . The non-metallic layer  16  provides good heat transfer characteristics at relatively lower weight compared to metals. In other words, the layer  16  is lighter than the layer  18  per unit of volume. The layers  16  and  18  may be bonded together along the line  20 .  
         [0011]     In the illustrated embodiment, the layers  16  and  18  are of equal thickness. One of the layers  16  or  18  may be thicker in some embodiments.  
         [0012]     In order to join the fin  14   b  to the base  12 , crimping forces, indicated by the arrows A and B, may be applied in one embodiment. In other words, the heat sink fin  14   b  may be inserted into the slot  16 . Thereafter, the two opposed sides of the base  12  are compressed together causing the edges  17  to cut into and engage the material of the fin  14   b . To this end, it may be advantageous, in some embodiments, that the material of the base  12  is harder than the material used for the layer  16  or  18 .  
         [0013]     Referring to  FIG. 2 , the completed structure may include a fin  14   a  engaged in a dovetail arrangement in the base  12 . Indentations  19  may be formed in the fin  14   a  caused by the base material  12  crimping process.  
         [0014]     The fins  14  may be made of a high conductivity metal and a pyrolytic graphite material in some embodiments. The two material sheets may be compressed together and held in place with a high thermal conductivity adhesive along the bond line  20  to form a laminated fin  14 . The laminated fin  14  may then be permanently attached to the heat sink base  12 , for example, using the crimping process illustrated in  FIGS. 1 and 2 . The laminated fin  14  is used in place of the traditional solid metal fin, achieving improved thermal performance and reduction in weight in some embodiments.  
         [0015]     The metal layer  18  provides structural integrity to the laminated fin  14 . An isotropic metal layer  18  may also act as a medium to transfer heat to the surrounding air via forced convection, as one example. In one embodiment, the layer  18  may be aluminum.  
         [0016]     The layer  16 , which may be graphite, may spread the heat in a more efficient manner than metal since layer  16  may have a thermal conductivity value on the order of three times that of solid metals. Since graphite material is non-isotropic, thermal conductivity in one direction is significantly lower than in the other two directions of heat transfer. As a result, heat may be transferred effectively in the direction of the fin height and length, but not so in the direction of fin thickness. However, this is insignificant since the heat can still easily be transferred through the relatively thin fin thickness.  
         [0017]     The layer  16  may be in intimate contact with the base  12  to improve the heat transfer through the laminated fin  14 . To this end, the laminate fin  14  may be permanently attached to the base  12 .  
         [0018]     In some embodiments of the present invention, graphite material with advantageous heat transfer properties can be used in a fin shape having relatively extended aspect ratios. Normally, graphite material would not be sufficiently tough to be used in such environments. However, the combination of graphite and metal has both advantageous heat transfer properties and sufficient structural integrity.  
         [0019]     Referring to  FIG. 3 , the heat sink fins  14  may be attached to a base  12  so that a large number of fins are arranged in close proximity. The fins  14  may be rectangular in shape, in one embodiment, with the long axis extending along and into the base  12 . An electronic device  20 , such as a microprocessor, may be thermally coupled to the base  12 . In some embodiments, thermal interface materials may be utilized between the device  20  and the base  12 . In addition, an integral heat spreader may be applied between the electronic device  20  and the base  12 . In some embodiments, the electronic device  20  may consist of an integrated circuit enclosed within an integrated heat spreader.  
         [0020]     In one embodiment of the present invention, the aspect (height to thickness) ratio of the fins  14  may be higher than 20:1. In one particularly advantageous embodiment, the aspect ratio may be 60:1.  
         [0021]     While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.