Abstract:
An exemplary heat sink apparatus ( 10 ) includes a base ( 12 ) and a number of fins ( 14 ) extending from an upper external first surface ( 124 ) of the base. The base defines a sealed cavity ( 122 ) therein. Operating fluid ( 18 ) is filled in the cavity. The operating fluid is liquid form. In use, heat produced by a heat source is transferred to the base. Then, the liquid operating fluid in the base absorbs the heat and is vaporized. The vaporized operating fluid is diffused to an upper inner wall ( 126 ) of the base and releases the heat, thereby being transformed back into liquid form. The fins transfer the heat to the ambient environment. The heat sink apparatus can dissipate the heat produced by the heat source to the ambient environment quickly and uniformly by adopting the operating fluid. Thus, the thermal operating efficiency and effect of the heat sink apparatus are enhanced.

Description:
BACKGROUND  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates generally to thermal transmitting structures, and more particularly to a heat sink apparatus utilizing operating fluid and thereby having enhanced heat dissipating efficiency.  
         [0003]     2. Related Art  
         [0004]     Electronic components, such as semiconductor chips, are becoming progressively smaller with each new product release, while at the same time the heat dissipation requirements of these kinds of components are increasing due to their improved ability to provide more functionality. In many contemporary applications, a heat sink apparatus is one of the most efficient systems in use for transmitting heat away from such components.  
         [0005]     Generally, a typical heat sink apparatus includes a base portion, and a predetermined number of parallel fins projecting from an upper section of the base portion. The fins project a predetermined distance or height, and at a predetermined angle, from the upper section. The heat sink apparatus is usually constructed of metals such as aluminum, aluminum alloy, copper, and copper alloy. The base portion includes a base surface. In typical use, the base surface is positioned against a heat transfer surface of an electronic device package, and is firmly held in contact with the heat transfer surface in order to ensure good thermal transfer between the two surfaces.  
         [0006]     The metals including aluminum, aluminum alloy, copper, and copper alloy all have relatively high coefficients of thermal conduction. Thus the heat sink apparatus can readily absorb heat produced by electronic devices contained in the electronic device package, and dissipate such heat to the ambient environment. However, many modern electronic device packages are very compact and generate much heat, and in some cases the above-described heat sink apparatus may not be able to transfer the heat from the electronic device package to the ambient environment quickly enough. This is apt to produce hotspots in the heat sink apparatus, and usually results in nonuniform dissipation of heat from the heat sink apparatus. That is, the thermal operating efficiency of the heat sink apparatus may be unsatisfactory.  
         [0007]     What is needed, therefore, is a heat sink apparatus having enhanced heat dissipating efficiency.  
       SUMMARY  
       [0008]     In one embodiment, a heat sink apparatus includes a base and a plurality of fins extending from one surface of the base. The base defines a hermetically sealed cavity defined therein. Operating fluid is filled in the cavity. The operating fluid is liquid form. In use, heat produced by a heat source is transferred to the base. Then, the liquid operating fluid in the base absorbs the heat and is vaporized. The vaporized operating fluid is diffused to an upper inner wall of the base and releases the heat, thereby being transformed back into liquid form. The fins transfer the heat to the ambient environment.  
         [0009]     Other advantages and novel features of the present heat sink apparatus will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The components in the drawings are not necessarily to scale, the emphasis instead being placed upon clearly illustrating the principles of the present heat sink apparatus. Moreover, in the drawings, all the views are schematic, and like reference numerals designate corresponding parts throughout the several views.  
         [0011]      FIG. 1  is a cross-sectional view of a heat sink apparatus in accordance with a first exemplary embodiment of the present invention.  
         [0012]      FIG. 2  is a cross-sectional view of a heat sink apparatus in accordance with a second exemplary embodiment of the present invention.  
         [0013]      FIG. 3  is a cross-sectional view of a heat sink apparatus in accordance with a third exemplary embodiment of the present invention. 
     
    
       [0014]     The exemplifications set out herein illustrate at least one preferred embodiment of the present heat sink apparatus, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.  
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0015]     Reference will now be made to the drawings to describe embodiments of the present heat sink apparatus in detail.  
         [0016]     Referring to  FIG. 1 , a heat sink apparatus  10  in accordance with a first exemplary embodiment of the present invention includes a base  12 , a plurality of fins  14 , and operating fluid  18 . The base  12  has an upper external first surface  124  and a lower external second surface  128 . The base  12  defines a hermetically sealed cavity  122  therein, which is surrounded by a plurality of inner walls  126 . The inner walls  126  include an upper inner wall  126 , a lower inner wall  126 , and four side inner walls  126 ; however, only one of the side inner walls  126  is labeled in  FIG. 1 . The upper inner wall  126  is nearest to the first surface  124 , and is opposite to the lower inner wall  126 . The side inner walls  126  interconnect the upper and lower inner walls  126 . The fins  14  are substantially parallel to each other, and extend from the first surface  124  of the base  12 . In the art, the operating fluid  18  is also commonly known as working fluid. The operating fluid  18  is filled in the sealed cavity  122  of the base  12 . When the heat sink apparatus  10  is not in use, the operating fluid  18  is in liquid form, and is supported on the lower inner wall  126 . Preferably, a protection layer  16  is coated on the inner walls  126 .  
         [0017]     The base  12  is preferably made of material selected from the group consisting of copper, aluminum, stainless steel, and any suitable alloy thereof. The base  12  can be formed by welding a pair of metal plates together. Each metal plate has a peripheral flange. The metal plates are welded together at the flanges, thereby forming the base  12  having the cavity  122  therein. Then the cavity  122  is vacuumized, and the operating fluid  18  filled in the cavity  122 . Finally, the cavity  122  is sealed. A volume of the operating fluid  18  is in the range of approximately ten percent to approximately ninety percent of a volume of the cavity  122 . The operating fluid  18  is preferably selected from the group consisting of water, ammonia, methanol, ethanol, hexanol, acetone, and heptane. Furthermore, the operating fluid  18  preferably has heat conduction materials (not shown) added therein. The heat conduction materials are preferably selected from the group consisting of copper powder, carbon nanotubes, carbon nanospheres, and carbon nanofibers.  
         [0018]     The fins  14  are preferably made of a material selected from the group consisting of copper, aluminum, stainless steel, and any suitable alloy thereof. The fins  14  can be integrally molded with the base  12 . Alternatively, the fins  14  can be attached on the first surface  124  of the base  12  by means of welding.  
         [0019]     The protection layer  126  has stable chemical and physical properties that are compatible with the operating fluid  18 . That is, no reaction occurs between the protection layer  16  and the operating fluid  18 . In particular, the protection layer  16  is made of material with a high coefficient of thermal conduction, such as graphite, diamond-like carbon material, or nano-scaled carbon material. Preferably, the protection layer  16  is made of nano-scaled carbon material selected from the group consisting of carbon nanotubes, carbon nanospheres, and carbon nanofibers.  
         [0020]     In typical use, the second surface  128  of the base  12  engages with an electronic device (not shown). Heat produced by the electronic device is transferred to the operating fluid  18  by conduction through the base  12 , and the temperature of the operating fluid  18  rises. When the temperature of the operating fluid  18  reaches and passes a vaporization/boiling temperature of the operating fluid  18 , the operating fluid  18  becomes vaporized. Vapor pressure drives the vaporized operating fluid  18  to the upper inner wall  126  of the base  12 . At the upper inner wall  126 , the vaporized operating fluid  18  transmits the heat to the fins  14  by conduction through the base  12 , and the vaporized operating fluid  18  is thereby transformed back into liquid form. The fins  14  dissipate the heat to the external environment. Gravity drives the operating fluid  18  back to the lower inner wall  126 . The heat sink apparatus  10  continues this cyclical process of transmitting heat as long as there is a temperature differential between the heat sink apparatus  10  and the electronic device, and as long as the heat is sufficient to vaporize the operating fluid  18 .  
         [0021]     Compared with a conventional heat sink apparatus, the present heat sink apparatus  10  with the operating fluid  18  can quickly dissipate the heat produced by the electronic device to the ambient environment. Thus, development of hotspots in the heat sink apparatus  10  can be avoided. This helps ensure that the heat sink apparatus  10  dissipates heat uniformly. Therefore, the thermal operating efficiency of the heat sink apparatus  10  is most apt to be satisfactory.  
         [0022]     Referring to  FIG. 2 , a heat sink apparatus  20  in accordance with a second exemplary embodiment of the present invention includes a base  22 , a plurality of fins  24 , operating fluid  28 , and a fan  26 . The base  22  has an upper external first surface  224  and a lower external second surface  228 . The base  22  defines a hermetically sealed cavity  222  therein, which is surrounded by a plurality of inner walls  226 . The inner walls  226  include an upper inner wall  226 , a lower inner wall  226 , and four side inner walls  226 ; however, only one of the side inner walls  226  is labeled in  FIG. 2 . The upper inner wall  226  is nearest to the first surface  224 , and is opposite to the lower inner wall  226 . The side inner walls  226  interconnect the upper and lower inner walls  226 . The fins  24  are substantially parallel to each other, and extend from the first surface  224  of the base  22 . The operating fluid  28  is filled in the sealed cavity  222  of the base  22 . When the heat sink apparatus  20  is not in use, the operating fluid  28  is in liquid form, and is supported on the lower inner wall  226 . Preferably, a protection layer (not shown) is coated on the inner walls  226 . The fan  26  is attached on free ends of the fins  24 , by any of a variety of means as would be known to those of ordinary skill in the art. For example, the fan  26  and the free ends of the fins  24  can be provided with complementary interengaging means. Such complementary interengaging means can for example include resiliently deformable clip portions provided on the fan  26 , and engaging slots provided in selected of the free ends of the fins  24 .  
         [0023]     As seen, the heat sink apparatus  20  is similar to the above-described heat sink apparatus  10 , except that the heat sink apparatus  20  further includes the fan  26  located on the free ends of the fins  24 . In use, the fan  26  can accelerate convection of ambient air near the fins  24 . This can further accelerate dissipation of heat from the fins  24 . Thus, the thermal operating efficiency of the heat sink apparatus  20  is further enhanced.  
         [0024]     Referring to  FIG. 3 , a heat sink apparatus  30  in accordance with a third exemplary embodiment of the present invention includes a base  32 , a plurality of fins  34 , operating fluid  38 , a first fan  362 , and a second fan  364 . The base  32  has an upper external first surface  324  and a lower external second surface  328 . The base  32  defines a hermetically sealed cavity  322  therein, which is surrounded by a plurality of inner walls  326 . The inner walls  326  include an upper inner wall  326 , a lower inner wall  326 , and four side inner walls  326 ; however, only the lower inner wall  326  is labeled in  FIG. 3 . The upper inner wall  326  is nearest to the first surface  324 , and is opposite to the lower inner wall  326 . The side inner walls  326  interconnect the upper and lower inner walls  326 . The fins  34  are substantially parallel to each other, and extend from the first surface  324  of the base  32 . The operating fluid  38  is filled in the sealed cavity  322  of the base  32 . When the heat sink apparatus  30  is not in use, the operating fluid  38  is in liquid form, and is supported on the lower inner wall  326 . Preferably, a protection layer (not shown) is coated on the inner walls  326 . The first fan  362  is located on free ends of the fins  34 . The second fan  364  is substantially located in the cavity  322 . The first and second fans  362 ,  364  commonly use a single axle  36 . That is, the axle  36  extends through the base  32  into the cavity  322 . A sealing material (not shown) is provided between the axle  36  and the base  32 , in order to ensure that the cavity  322  is sealed. The sealing material can be lubricating oil. In use, the axle  36  can rotate smoothly, thereby driving the first and second fans  362 ,  364  to rotate correspondingly.  
         [0025]     As seen, the heat sink apparatus  30  is similar to the above-described heat sink apparatus  20 , except that the heat sink apparatus  30  further includes the second fan  364  located in the cavity  322 . In use, the second fan  364  can accelerate diffusion of vaporized operating fluid  38  and flowing of liquid operating fluid  38 . This can further accelerate eventual dissipation of heat from the fins  34 . Thus, the thermal operating efficiency of the heat sink apparatus  30  is further enhanced.  
         [0026]     Finally, it is to be understood that the above-described embodiments are intended to illustrate rather than limit the invention. Variations may be made to the embodiments without departing from the spirit of the invention as claimed. The above-described embodiments illustrate the scope of the invention but do not restrict the scope of the invention.