Abstract:
Heat dissipation systems and structures which are employed in the cooling of electronic devices and/or semiconductor integrated-circuit chips which are installed in computer and/or communications systems. Moreover, disclosed is a method for implementing the heat dissipation systems and structures.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to heat dissipation systems and structures which are employed in the cooling of electronic devices and/or semiconductor integrated-circuit chips which are installed in computer and/or communications systems. Moreover, the invention discloses a method for implementing the heat dissipation systems and structures. 
     2. Discussion of the Prior Art 
     Murage, et al., U.S. Pat. No. 4,675,783 entitled “Heat Pipe Heat Sink for Semiconductor Devices” teaches a method of arranging heat pipes in a zigzag configuration extending towards the direction of an air flow around the fin section of the heat sink. Furthermore, a semiconductor device is mounted on a block at the heat-inlet section of the heat pipes. 
     Chao et al., U.S. Pat. No. 5,412,535 entitled “Apparatus and Method for Cooling Electronic Devices” discloses a heat transfer assembly which is mounted on a printed-wiring board, and includes mechanical structure adapted to support an electronic device. A heat pipe equipped with fins is mounted so as to extend perpendicularly of the heat transfer assembly. 
     Neither of these above-referenced patents address themselves to the problems encountered with regard to enhanced heat spreading and compliant interfacing of components in order to achieve an improved degree of heat transference. 
     SUMMARY OF THE INVENTION 
     Accordingly, in order to obviate the drawbacks encountered in the prior art, pursuant to the invention there is disclosed a highly efficient heat sink structure which is adapted to improve the cooling capability of electronic and semiconductor devices. The heat sink essentially consists of multiple sets of heat distribution means which are constructed with a plurality of heat pipes adapted to transfer heat directly from the heat generating devices to various locations on the heat sink. The ends of the heat pipes are mounted inside of a heat-transfer block which is located on the surface of the heat generating device through the intermediary of a set of springs. The heat-transfer block is preferably dissected into smaller sections in order to further improve the interfacing compliance and to also reduce any mechanical stresses which may be transferred to the electronic devices. 
     Accordingly, it is an object of the present invention to provide heat sink means which is adapted to improve the cooling capability of electronic and/or semiconductor devices. 
     Another object of the invention is to provide a method for constructing a compliant interface between a heat sink and a heat generating device which will result in an efficient heat transfer between these components. 
     A further object of the invention is the utilization of heat pipes to distribute heat evenly about the heat sink in order to boost the best spreading efficiency thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-listed objects and other advantageous features of the invention become more readily apparent from the following detailed descriptions, taken in conjunction with the accompanying drawings; in which: 
     FIGS. 1 a  and  1   b  illustrate, respectively, an exploded perspective view and a side view of a heat sink assembly with an electronic device; 
     FIGS. 2 a  to  2   c  illustrate, respectively, bottom and cross-sectional views of the detailed structure of an upper portion of the heat sink assembly with heat pipes and an inner heat-transfer block; 
     FIGS. 3 a, b  and  c  illustrate, respectively, bottom, side and sectional views of the detailed structure of a lower portion of the heat assembly with heat pipes and an outer heat transfer block; and 
     FIGS. 4 a  to  4   c  illustrate, respectively, perspective, bottom and sectional views of another embodiment of the heat sink assembly with a therein enclosed cooling fan. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention is directed to the design of an efficient heat sink assembly which is constructed with heat pipes and spring-loaded heat-transfer blocks. An exemplary embodiment of a heat sink assembly is shown in 
     FIGS. 1 a  and  1   b,  in which FIG.  1 ( a ) is an exploded perspective view, and FIG.  1 ( b ) is a side view showing the heat sink as mounted on an electronic device. The heat sink assembly  10  consists of upper and lower portions  12  and  14  which are to be interleaved when the heat sink assembly  10  is mounted on top of an electronic device  16 . 
     The details of the structure of the upper portion  12  of the heat sink assembly  10  is shown in FIGS.  2 ( a ) through  2 ( c ). Referring to the bottom view of the upper heat sink portion  12  as shown in FIG.  2 ( a ), a heat-transfer block  20  is placed at the center of a heat sink base plate  22 . Provided are four heat pipes,  24 ,  26 ,  28 , and  30 , which are connected at one of the ends thereof to the heat-transfer block  20 . The other ends of these four heat pipes are positioned at various locations on the heat sink base plate  22  by means of four separate anchors,  32 ,  34 ,  36  and  38 , respectively. The anchors,  32 ,  34 ,  36  and  38 , are placed generally close to the fins  40  so as not to block the air which flows between the fins. There are represented eight straight fins in the drawing figure; however, the quantity and type of fins are for illustrative purpose only; since they can be any number and types; such as pin fins, and are not limited to those shown in the drawing figure. The heat-transfer block  20  is dissected into four pieces which are separated by two gaps  42  and  44  and are connected together by a thin sheet of material  46 , as shown in FIG.  2 ( b ) which is a cross-sectional view taken along the line A—A in FIG.  2 ( a ). The thin sheet of material  46  can be made from the same material as the heat-transfer block  20 , or from other materials possessing low thermal coefficients of expansion, such as a copper-invar-copper, or copper-tungsten alloys. Each heat pipe is inserted into its designated section in the heat transfer block  20 . The portion of the heat pipe which is located within the block is in a good thermal contact with the heat transfer block  20 . The number of heat pipes and their corresponding sections in the heat transfer block  20  can be varied and should not be limited to four as shown in the drawing figures. The heat transfer block  20  is supported by two plate springs  48  and  50  which are installed in a slot  52  on the fins as shown in the FIG.  2 ( c ) which is a cross-sectional view taken along line B—B in FIG.  2 ( a ). The heat transfer block  20  can be moved slightly up and down along the slot channel  54 . When the heat sink assembly  10  is mounted to the electronic device, the heat transfer block  20  will contact the surface of the electronic device and as a consequence, the plate springs  48  and  50  are compressed. The resulting spring force will then act on the heat transfer block  20  to ensure a good heat conduction from the electronic device to the heat transfer block and the heat pipes. This heat-transfer block is accordingly spring-loaded, and thereby provides a compliant interface with the electronic device. 
     The details of the structure of the lower portion of the heat sink assembly are shown in FIGS.  3 ( a ) to  3 ( c ). The bottom view of the lower heat sink portion  14  is shown in FIG.  3 ( a ), a heat-transfer ring  60  is placed at the center of the heat sink base plate  62 . The ring  60  is located such that the heat transfer block  20  from the upper heat sink portion  12  can be inserted through an opening on the heat sink base plate  62  and the center opening  64  of the ring  60  when the upper and lower portions  12 ,  14  of the heat sink are assembled. 
     There are four heat pipes,  66 ,  68 ,  70  and  72  which are inserted at one of their ends into the heat-transfer ring  60 . The other ends of these four heat pipes are located at various locations on the heat sink base plate  62  by means of four separate anchors,  74 ,  76 ,  78  and  80 , respectively. Provided are seven straight fins  82  on the other side of the heat sink base place  62 , as shown in FIG.  3 ( b ). The quantity and type of fins are for illustrative purpose only; since they can be any number and type, such as pin fins, and are not limited to those shown in the drawing figure. The heat-transfer ring  60  is supported by a set of springs  84  which can be made of metal or elastomers, as shown in FIG.  3 ( c ). The springs  84  are compressed when the heat sink is assembled; whereby the reaction force from the springs  84  will, in turn, force the heat transfer ring  60  to make a good thermal contact with the electronic device. 
     When the upper and lower portions  12  and  14  of the heat sink are interleaved, the heat-transfer block  20  from the upper portion  12  will pass through an opening on the lower heat sink portion base plate  62  and the heat-transfer ring  60 . Both of these components will be in good contact with the surface of the electronic device which is to be cooled. The gaps,  42  and  44  on the heat-transfer block  20  can be used to store some thermally conductive materials, such as thermally conductive grease, or phase-changing materials. When the temperature rises, the thermally conductive materials will flow and wet the surfaces of the block and the electronic device, and hence improve the heat transfer from the electronic device to the heat-transfer block. The heat pipes will distribute the heat to various locations on the heat sink base and eliminate the temperature drop along the heat sink base place. The spring-loaded structure at the heat-transfer block and ring makes the heat sink much more compliant to the surface of the electronic device. Furthermore, the heat transfer rates to the block and the ring can be tailored to different levels. For instance, some electronic device may have higher heat flux at the center of the device and require higher cooling rate. In this case, the heat transfer rate at the heat-transfer block can be raised by using more and/or larger heat pipes. The heat pipes described herein can be of any types and any shapes, such as round, flat, oval or polygonal. 
     The heat sink assembly as disclosed hereinabove can be used as an entirety with the upper and lower portions  12 ,  14  being interleaved as shown in FIGS.  1 ( a ) and  1 ( b ), or the upper or lower portions can be employed individually. If the lower portion  12  is used alone, the shape of the heat transfer ring  60  can be changed to a plate. Furthermore, the tip of the heat transfer block  20  and surface of the heat transfer ring  60  can be either flat or crown-shaped. 
     FIGS.  4 ( a ) to  4 ( c ) show another embodiment of present invention, with a cooling fan  90  being embedded or contained within the heat sink structure. The compactness of the disclosed structure renders this embodiment highly suitable for applications such as laptop computers where available space is at a premium. Referring to FIG.  4 ( a ), the heat sink body  92  has the cooling fan  90  embedded or recessed therein, and includes several mounting holes  94  on the other side for this purpose. The bottom view of the heat sink assembly is shown in FIG.  4 ( b ) in which two heat pipes,  96  and  98  have their own ends inserted into the heat sink body  92  near the fan location. The other ends of the heat pipes are inserted into a heat-transfer block  100  which is dissected partially into four pieces, with the inclusion of two gaps  102  and  104 . The cross-sectional view of the heat sink body  92  is shown in FIG.  4 ( c ), in which a metal spring or thermally conductive elastomer  108  can be ascertained between the heat-transfer block  100  and the heat sink body  92 . A spring  108  is used to bias the heat-transfer block  100  into good contact with an electronic device. Heat is transferred from the electronic device to the block  100  and then to the heat pipes  96  and  98 . The heat is then discharged near the fan  90 . The fan  90  has a motor  110  mounted directly on the heat sink body  92 , and is adapted to drive the fan blades  112 . When the blades  112  rotate, air will be propelled upwardly towards the heat sink body  92  and pushed to the exit  114  on the end of the heat sink body  92 . The heat delivered from the heat pipes will be picked up by the moving air. The gaps  102  and  104  can be used to store a thermally conductive fluid, such as a thermally conductive grease, or phase-changing materials in order to enhance the heat transfer between the electronic device and the heat-transfer block  100 . 
     While there has been shown and described what are considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is, therefore, intended that the invention be not limited to the exact form and detail herein shown and described, nor to anything less than the whole of the invention herein disclosed as hereinafter claimed.