Abstract:
The capability of an assembly to transfer heat from a semiconductor package source is enhanced while a reduction in the space required for effective operation is achieved. Bodies of fins defining tubular channels are affixed to oppositely facing surfaces of a rectilinear body which is adapted to receive heat from a semiconductor package.

Description:
FIELD AND BACKGROUND OF INVENTION  
         [0001]    This invention relates to heat sinks for semiconductor packages and combinations of such a heat sink with devices from which heat must be transferred.  
           [0002]    The generation of heat within semiconductor packages for devices such as microprocessors has long been recognized as requiring heat transfer arrangements to permit satisfactory operation of computer circuits and the like. As the technology has progressed, heat loads imposed have risen which space allowances have compressed. Thus problems arise in effectuating the necessary transfers of heat from increasingly confined spaces. Recently, heat loads from microprocessor have risen to exceed seventy five watts, while space allowances have shrunk to limit the available height for a heat sink to less than forty millimeters.  
         SUMMARY OF THE INVENTION  
         [0003]    With the above problems in mind, it is a purpose of the present invention to enhance the capability of an assembly to transfer heat from a semiconductor package source while enabling reduction in the space required for effective operation. In realizing this purpose of the present invention, bodies of fins are affixed to oppositely facing surfaces of a rectilinear body which is adapted to receive heat from a semiconductor package. In a preferred form of the invention, one body of fins is on the surface which is adapted to engage the semiconductor package. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0004]    Some of the purposes of the invention having been stated, others will appear as the description proceeds, when taken in connection with the accompanying drawings, in which:  
         [0005]    [0005]FIG. 1 is a schematic perspective view of a heat sink in accordance with this invention showing a body of fins affixed to a first broad surface of a heat transferring body;  
         [0006]    [0006]FIG. 2 is a view similar to FIG. 1 of the other side of the heat sink of FIG. 1;  
         [0007]    [0007]FIG. 3 is a schematic perspective view of the heat sink of FIGS. 1 and 2 as assembled with a printed circuit board and a semiconductor package; and  
         [0008]    [0008]FIG. 4 is a schematic sectional view through the assembly of FIG. 3. 
     
    
     DETAILED DESCRIPTION OF INVENTION  
       [0009]    While the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which a preferred embodiment of the present invention is shown, it is to be understood at the outset of the description which follows that persons of skill in the appropriate arts may modify the invention here described while still achieving the favorable results of the invention. Accordingly, the description which follows is to be understood as being a broad, teaching disclosure directed to persons of skill in the appropriate arts, and not as limiting upon the present invention.  
         [0010]    Referring now more particularly to the accompanying drawings, a heat sink in accordance with the present invention is there generally indicated at  10 . The heat sink has a rectilinear body  11  of heat transferring material having opposing first and second broad surfaces, a first body of fins  12  affixed to the first broad surface and defining a first array of a plurality of elongate tubular channels directing heat transfer fluid flow, and a second body  14  of fins affixed to the opposite broad surface and defining a second array of a plurality of elongate tubular channels directing heat transfer fluid flow. In one form the body  11  essentially is a plate or moderately thick sheet of metal such as copper, silver or the like having a relatively high thermal conductivity. Such as material, as is known, is effective to transfer heat efficiently from a high temperature source, such as a microprocessor, to a lower temperature sink, such as a flowing stream of cooling air. In an alternate form contemplated by this invention, the rectilinear body may be a thin capsule heat pipe, formed by a relatively thin walled envelope within which is sealed a medium which transfers heat by phase change across a liquid/gas transition point. The technology of heat pipes is well known and need not be here discussed in detail. In either instance, the body  11  has length and width dimensions significantly greater than the thickness dimension.  
         [0011]    The fin bodies  12  and  14  are affixed to opposite faces of the body  11  for purposes which will become more clear hereinafter. In each instance, the fins are closed one to another at the ends remote from affixation to the body  11 , so that an adjacent pair of fins in the body define a tubular channel through which a cooling air flow is directed by appropriate air handling devices. The fact that the channels are closed, thus defining tubes, is significant in assuring that heat transfer rates desired for the heat sink of this invention are attained.  
         [0012]    As shown more particularly in FIG. 2, the fin body  14  on one surface of the rectilinear body  11  covers less of the area of that surface. This allows provision of an area indicated at  15  for engagement with a semiconductor package, such as a packaged microprocessor, from which heat is to be drawn by the heat sink of this invention.  
         [0013]    While it is only exemplary of this invention, it is noted that in the form shown one fin body  12  covers substantially the entire area of the surface to which it is affixed, while the other fin body  14  covers less than the entire area in order to allow for the contact area  15 .  
         [0014]    [0014]FIG. 3 illustrates a practical embodiment of a product in which two heat sinks in accordance with this invention are employed. The product includes a printed circuit board  16  on which are mounted semiconductor packages, two of which (not visible in FIG. 3) are cooled by use of heat sinks  10  in accordance with this invention.  
         [0015]    [0015]FIG. 4 is a schematic illustration of a section through the circuit board  16 , showing the engagement of the heat sink  10  with a semiconductor package  18 . As will be noted there, the presence of the fin body  14  enables enhanced use of a surface of the rectilinear body  11  which otherwise would have significantly lower heat transfer capability by guiding air flowing immediately adjacent the printed circuit board through the elongate tubes provided by the fin body.  
         [0016]    In the drawings and specifications there has been set forth a preferred embodiment of the invention and, although specific terms are used, the description thus given uses terminology in a generic and descriptive sense only and not for purposes of limitation.