Patent Abstract:
A heat sink includes a first heat pipe having a flat plate-shape and a second heat pipe connected perpendicularly to the first heat pipe. The first heat pipe has a first wick provided along an inner surface thereof. The second heat pipe has a second wick provided along an inner surface thereof. Each of end portions of the first and second wicks in a connecting portion of the first and second heat pipes has a comb-toothed part formed in a convexoconcave form like teeth of a comb so that the first and second wicks are connected by the comb-toothed parts fitting to each other. The comb-toothed parts of the second wick traverses an interior of the first heat pipe and contacts with the first wick on an opposite side.

Full Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to heat sinks and, more particularly, to a heat sink having a heat pipe suitable for cooling a semiconductor device or the like. 
   2. Description of the Related Art 
   In recent years, as a cooling device for cooling a semiconductor device generating a large amount of heat, a heat sink using a heat pipe having an extremely high heat transfer performance. In a conventional heat pipe, heat is absorbed in a heat absorbing part by a cooling medium sealed within a pipe or a flat plate-shaped container being evaporated in the heat absorbing part. The evaporated cooling medium moves to a heat radiating part and cooled so as to be liquefied, resulting in the heat absorbed in the heat absorbing part being radiated. The cooling medium liquefied in the heat radiating part spreads into a mesh or fiberform member referred to as a wick, and moves through the wick according to a capillary phenomenon and returns to the heat absorbing part, and is evaporated again and moves to the heat radiating part. 
   As a cooling medium enclosed in a heat pipe, pure water is used in many cases. In order to lower an evaporation temperature and to make an operation temperature low, the interior of the heat pipe in which a cooling medium is enclosed may be set to a reduce pressure. Moreover, a container of a heat pipe is formed of copper or aluminum, which has a high thermal conductivity, in many cases. 
   When arranging a heat pipe as a heat sink, it is general to increase a heat radiation efficiency by attaching heat radiation fins to a heat radiation part. In order to increase the heat radiation efficiency further, the heat radiation part may be enlarged. For example, there may be a structure in which a heat pipe is formed as a flat plate-shaped container and heat radiation fins are attached to one of flat surfaces. Additionally, there is a structure in which a long heat pipe is accommodated in a small volume by bending the bar-like heat pipe in a U-shape. 
   It is also suggested to acquire a higher heat radiation efficiency by increasing a volume inside a heat pipe by making the heat pipe itself into a three-dimensional construction. In order to increase the volume inside the heat pipe, it is considered to make the heat pipe itself to have a three-dimensional construction. 
   For example, there is suggested a heat sink having a structure in which a rod-like heat pipe is bent in a channel shape so form a three-dimensional construction and opposite ends thereof are inserted into a base member forming heat radiation fins (for example, refer to Patent Document 1). Additionally, there is suggested a heat pipe having a structure in which one heat pipe is connected perpendicular to another heat pipe and interiors of the heat pipes are caused to communicate with each other (for example, refer to Patent Documents 2 and 3). 
   Patent Document 1: Japanese Laid-Open Patent Application No. 6-13511 
   Patent Document 2: Japanese Laid-Open Patent Application No. 7-142652 
   Patent Document 3: Japanese Laid-Open Patent Application No. 7-263601 
   In the heat sink disclosed in the above-mentioned Patent Document 1, a three-dimensional structure is formed by bending a heat pipe. However, since a wick is attached on an inner surface of the heat pipe, the wick may be cut when bending the heat pipe. If the wick is cut, a flow of the cooling medium is blocked, which results in a decrease in the cooling efficiency. Additionally, it is difficult to bend a flat plate-shaped heat pipe unlike rod-like heat pipe. 
   Although the heat sinks disclosed in Patent Documents 2 and 3, have a flat plate-shaped heat pipe connected with a plurality of flat plate-shaped heat pipes perpendicularly, there is no description of a structure of a wick. For example, it is assumed that two flat plate-shaped heat pipes  1 A and  1 B are connected with each other as shown in  FIG. 1 . In this case, it is needed to connect wicks  2 A and  2 B attached to inner surfaces to each other. However, if the wicks  2 A and  2 B are connected at a connecting part of the heat pipes, a liquid transportation path length to a heat receiving part (that is, a cooling part contacting a heat generating member  3 ) becomes long. Thus, there is a problem in that a thermal transportation efficiency is decreased due to a cooling medium returning a heat receiving part along the wick by turning to a liquid. In  FIG. 1 , flows of the cooling medium are indicated by arrows. Additionally, if the wicks are not connected well at the connecting part, and in a top heat in which the heat receiving part is located up or side (that is, an arrangement in which a heat generating member is attached to an upper portion or a side portion of the heat pipe), a flow of the liquid cooling medium is blocked at a cut portion of the wicks, which causes a problem in that the cooling medium cannot be transported to the heat receiving part. 
   As mentioned above, although there were suggestions to connect heat pipes three-dimensionally, they are not a connection structure in which a consideration is given to a flow of a cooling medium inside. There is no consideration of a connection method of wicks in a plurality of heat pipes at all. 
   SUMMARY OF THE INVENTION 
   It is a general object of the present invention to provide a novel and useful heat sink in which the above-mentioned problems are eliminated. 
   A more specific object of the present invention is to provide a heat sink in which wicks are surely connected even if a three-dimensional structure is made by connecting a plurality of heat pipes so that the wicks maintain a cooling performance high even if it is a top heat. 
   In order to achieve the above-mentioned objects, there is provided according to the present invention a heat sink comprising: a first heat pipe having a flat plate-shape; and a second heat pipe connected perpendicularly to the first heat pipe, wherein the first heat pipe has a first wick provided along an inner surface thereof, the second heat pipe has a second wick provided along an inner surface thereof, each of end portions of the first and second wicks in a connecting portion of the first and second heat pipes has a comb-toothed part formed in a convexoconcave form like teeth of a comb so that the first and second wicks are connected by the comb-toothed parts fitting to each other, and the comb-toothed part of the second wick traverses an interior of the first heat pipe and contacts with the first wick on an opposite side. 
   In the heat sink according to the present invention, the first heat pipe may be provided with a heat-receiving part. The first and second wicks may be formed of a porous sintered sheet. The second heat pipe may include two pieces of heat pipes perpendicularly connected to the first heat pipe in parallel to each other, and a heat-receiving part may be provided on an opposite side of a side of the first heat pipe where the second heat pipe is connected. Additionally, the two pieces of heat pipes of the second heat pipe may be connected to the same surface of the first heat pipe, and heat-radiation fins may be provided between the two pieces of heat pipes of the second heat pipe in parallel to the surface of the first heat pipe. The heat sink may further comprise heat-radiation fins provided perpendicular to the surface of the first heat pipe. In the heat sink according to the present invention, the two heat pipes of the second heat pipe may be connected to opposite ends of the same surface of the first heat pipe, respectively, and heat-radiation fins may be provided between the two heat pipes of the second heat pipe in parallel to the surface of the first heat pipe. 
   Additionally, the heat sink according to the present invention may further comprise a third heat pipe connected perpendicular to the two heat pipes of the second heat pipe, wherein the third heat pipe may have a third wick provided along an inner surface thereof, each of end portions of the second and third wicks in a connecting portion of the second and third heat pipes may have a comb-toothed part formed in a convexoconcave form like teeth of a comb so that the second and third wicks are connected by the comb-toothed parts fitting to each other, and the comb-toothed part of the second wick may traverse an interior of the third heat pipe and contacts with the third wick on an opposite side. The first heat pipe and the third heat pipe may be connected to opposite ends of the second heat pipe facing and parallel to each other, and heat radiation fins may be provided parallel to the second heat pipe between the third heat pipe and the first heat pipe. One of the first and third heat pipes may be provided with a heat-receiving part. 
   According to the present invention, wicks attached to inner surfaces of a heat pipe having a three-dimensional structure can be surely connected to each other so that a liquid cooling medium can be transported to a heat-receiving part through the wicks. Accordingly, the liquid cooling medium can be surely transported to the heat-receiving part even in a top-heat use, and a cooling performance can be improved. Additionally, since the comb-toothed part extends and contacts the opposite side wick in the connecting portion of on the end of the wick, the liquid transportation path by the wicks can be shortened. Thereby, the thermal transportation efficiency by the heat pipes can be increased, which results in formation of a heat sink having a three-dimensional structure of a high cooling performance. 
   Other objects, features and advantages of the present invention will become more apparent from the scope of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of heat pipes connected according to a conventional structure of connection; 
       FIG. 2  is a cross-sectional view of a heat pie according to an embodiment of the present invention; 
       FIG. 3A  is a plan view of a part of the heat pipe shown in  FIG. 2 ; 
       FIG. 3B  is a cross-sectional view taken along a line III-III of  FIG. 3A ; 
       FIG. 4A  is a horizontal cross-sectional view of a part of the heat pipe shown in  FIG. 2 ; 
       FIG. 4B  is a cross-sectional view taken along a line III-III of  FIG. 4A ; 
       FIG. 5  is a cross sectional view of a connecting portion of wicks; 
       FIG. 6A  is a plan view of a heat sink according to a first embodiment; 
       FIG. 6B  is a cross-sectional view of the heat sink shown in  FIG. 6A ; 
       FIG. 7  is a cross-sectional view of a heat sink according to a second embodiment; 
       FIG. 8  is a cross-sectional view of a heat sink according to a third embodiment; and 
       FIG. 9  is a cross-sectional view of a heat sink according to a fourth embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A description will now be given, with reference to the drawings, of an embodiment of the present invention. 
     FIG. 2  is a cross-sectional view of a heat pipe having a three-dimensional structure according to an embodiment of the present invention. In  FIG. 2 , a heat pipe  11 A is a plate-shaped heat pipe, and heat pipes  11 B and  11 C are attached perpendicularly to the heat pipe  11 A. The heat pipes  11 B and  11 C may be plate-shaped or rod-shaped. Inner spaces of the heat pipes  11 B and  11 C in which a cooling medium (operation fluid) is charged are communicated with an inner space of the heat pipe  11 A in which the cooling medium (operation fluid) is also charged. 
   Wicks  12 A,  12 B and  12 C are applied onto entire inner surfaces of the heat pipes  11 A,  11 B and  11 C, respectively. The wicks  12 A,  12 B, and  12 C are mesh or fiberform members or porous sheet members formed of a material having a good thermal conductivity, and configured to be capable of transporting a liquefied cooling medium according to a capillary phenomenon. 
   A heat-generating element  3  is attached to the heat pipe  11 A, and a portion to which the heat-generating element  3  is attached serves as a heat-receiving part. The liquefied cooling medium spread into the wick  12 A in the heat-receiving part absorbs heat and evaporates to be turned into gas. A part of the evaporated cooling medium moves in directions toward opposite ends of the heat pipe  11 A, and also a part of the evaporated cooling medium moves to interiors of the heat pipes  11 B and  1 C. The opposite ends of the heat pipe  11 A and the heat pipes  11 B and  11 C together serve as a heat-radiating part. That is, the gasiform cooling medium, which has moved to the opposite end sides of the heat pipe  11 A and the interiors of the heat pipes  11 B and  11 C, is cooled and liquefied by being brought into contact with the wicks  12 A,  12 B and  12 C. The liquid cooling medium spreads into the wicks  12 A,  12 B and  12 C when it is liquefied, and returns to the heat-receiving part of the heat pipe  11 A by moving through the wicks according to a capillary phenomenon. In the above-mentioned cycle of the cooling medium, a pressure is generated in the interiors of the heat pipes  11 A,  11 B and  11 C, and the cooling medium circulates efficiently between the heat-receiving part and the heat-radiating part to transport heat. 
   Here, the liquid cooling medium, which moves inside the wicks  12 B and  12 C, cannot move to the wick  12 A unless the wick  12 A is connected to the wicks  12 B and  12 C, and the cooling medium cannot be circulated efficiently. Moreover, the liquid cooling medium spread into an upper portion of the wick  12 B in  FIG. 2  moves to the heat-receiving part by going through an upper end portion of the heat pipe  11 A (wick  12 A), which results in a long transportation path of the liquid cooling medium. 
   Thus, in the present embodiment, a heat pipe having a three-dimensional structure is configured so that the wick  12 A is connected well to the wicks  12 B and  12 C by providing a special structure to the connection structure between the wick  12 A and the wicks  12 B and  12 C and a distance from each of the wicks  12 B and  12 C to the heat-receiving part is shortened. 
   A description will now be given, with reference to  FIGS. 3 through 5 , of the connection structure of the wicks.  FIG. 3A  is a plan view of the heat pipe  11 A before the heat pipes  11 B and  11 C are attached.  FIG. 3B  is a cross-sectional view taken along a line III-III of  FIG. 3A .  FIG. 4A  is a horizontal cross-sectional view of the heat pipe  11 B before being attached to the heat pipe  11 A.  FIG. 4B  is a cross-sectional view taken along a line IV-IV of  FIG. 4A .  FIG. 5  is a cross-sectional view showing the connecting portion between the wick  12 A and the wick  12 B. It should be noted that the connecting portion between the wick  12 A and the wick  12 C has the same structure as the connecting portion between the wick  12 A and the wick  12 B, and, thus, only the connecting portion between the wick  12 A and the wick  12 B will be explained. 
   As shown in  FIG. 3 , the heat pipe  11 A has an opening  13  in a portion to which the heat pipe  11 B is connected. The heat pipe  11 B is fixed to the heat pipe  11 A in a state where it is inserted into the opening  13 . In the opening  13 , a plurality of comb-tooth portions  12 A 1  of a comb-toothed part formed in the wick  12 A are protruded. 
   As shown in  FIG. 4 , the wick  12 B of the heat pipe  11 B has a plurality of comb-tooth portions  12 B 1  of a comb-toothed part on the side connected to the heat pipe  11 A. Each of the comb-toot portions  12 B 1  is formed in a shape which can be inserted into a space between the adjacent comb-tooth portions  12 A 1  of the wick  12 A of the heat pipe  11 A. That is, the comb-tooth portions  12 A 1  and the comb-tooth portions  12 B 1  are configured and arranged to fit to each other as shown in  FIG. 5 . Additionally, the comb-tooth portions  12 B 1  extend through the inner space of the heat pipe  11 A as shown in  FIG. 5  in the state where the heat pipe  11 B is attached to the heat pipe  11 A. The comb-tooth portions  12 B 1  are formed to have a length with which the ends thereof are in contact with the wick  12 A of the heat pipe  11 A. 
   As mentioned above, since the wick  12 A and the wick  12 B are connected by the comb-tooth portions  12 A 1  and the comb-tooth portions  12 B 1  intruding mutually, the wick  12 A and the wick  12 B can be surely brought into contact with each other. For this reason, the wick  12 A and the wick  12 B are connected surely with each other, and a flow of the liquid cooling medium according to a capillary phenomenon is not cut between the wick  12 A and the wick  12 B. Therefore, the liquid cooling medium can be surely moved from the wick  12 B to the wick  12 A. 
   Moreover, a space is formed between the adjacent comb-tooth portions  12 B 1 , and the gasiform cooling medium can move freely through this space. Accordingly, even in a structure where the wick  12 B is extended through the inner space of the heat pipe  11 A so as to be in contact with the wick  12 A, the inner space of the heat pipe  11 A is not blocked by the wick  12 B, which acquire a sufficient flow path of the gasiform cooling medium. 
   According to the above-mentioned connection structure of the wicks, as indicated by arrows in  FIG. 2 , the circulation path of the cooling medium can be formed in a short path, which improves a thermal transportation efficiency. 
   It should be noted that the wick  12 C of the heat pipe  11 C also has the comb-tooth portions  12 C 1 , and the wick  12 C is connected to the wick  12 A with the same connection structure as the wick  12 B. 
   A description will now be given of a heat sink having the heat pipe of the three-dimensional structure in which the wicks are connected by the above-mentioned connection structure. 
     FIG. 6A  is a plan view of a heat sink according to a first embodiment.  FIG. 6B  is a cross-sectional view of the heat sink shown in  FIG. 6A . The heat sink shown in  FIGS. 6A and 6B  has a three-dimensional structure in which plate-shaped heat pipes  21 B and  21 C are perpendicularly connected to a plate-shaped heat pipe  21 A. A plurality of heat-radiating fins  23  are attached parallel to the heat pipe  21 A so as to bridge between the heat pipes  21 B and  21 C. The wick  22 A in the heat pipe  21 A and the wicks  22 B and  22 C in the heat pipes  21 B and  21 C are connected according to the connection structure explained with reference to  FIG. 2  through  FIG. 5 . In the present embodiment, a center portion serving as a heat-receiving part of the heat pipe  21 A is joined to a semiconductor device  24  as a heat-generating member so that the heat sink  20  serves as a cooling device for cooling the semiconductor device  24 . 
     FIG. 7  is a cross-sectional view of a heat sink according to a second embodiment. The heat sink shown in  FIG. 7  has a three-dimensional structure in which heat pipes  31 B and  31 C are connected to opposite ends of a heat pipe  31 A. A plurality of heat-radiating fins  33  are attached parallel to the heat pipe  31 A to bridge between the heat pipe  31 B and  31 C. A wick  32 A in the heat pipe  31 A and inner-side portions of wicks  32 B and  32 C in the heat pipes  31 B and  31 C are connected according to the connection structure explained with reference to  FIG. 2  through  FIG. 5 . In the present embodiment, a center portion serving as a heat-receiving part of the heat pipe  31 A is joined to a semiconductor device  24  as a heat-generating member so that the heat sink  30  serves as a cooling device for cooling the semiconductor device  24 . 
     FIG. 8  is a cross-sectional view of a heat sink according to a third embodiment. The heat sink  40  shown in  FIG. 8  has the same structure as the heat sink  20  shown in  FIGS. 6A and 6B  except for heat-radiating fins  44  attached perpendicularly to a heat pipe  41 A. That is, the heat sink shown in  FIG. 8  has a three-dimensional structure in which heat pipes  41 B and  41 C are connected to opposite ends of the heat pipe  41 A. A plurality of heat-radiating fins  43  are attached parallel to the heat pipe  41 A to bridge between the heat pipe  41 B and  41 C. A wick  42 A in the heat pipe  41 A and the wicks  42 B and  42 C in the heat pipes  41 B and  41 C are connected according to the connection structure explained with reference to  FIG. 2  through  FIG. 5 . In the present embodiment, a center portion serving as a heat-receiving part of the heat pipe  41 A is joined to a semiconductor device  24  as a heat-generating member so that the heat sink  40  serves as a cooling device for cooling the semiconductor device  24 . 
     FIG. 9  is a cross-sectional view of a heat sink according to a fourth embodiment. The heat sink  50  shown in  FIG. 9  has a three-dimensional structure in which a plate-shaped heat pipe  51 B is perpendicularly connected to an end of a plate-shaped heat pipe  51 A, and a plate-shaped heat pipe  51 C is perpendicularly connected to an end of the heat pipe  51 B. A plurality of heat-radiating fins  53  are attached parallel to the heat pipe  51 B so as to bridge between the heat pipes  51 A and  51 B. A wick  52 B in the heat pipe  51 B and wicks  52 A and  52 C of the heat pipes  51 A and  51 C are connected according to the connection structure explained with reference to  FIG. 2  through  FIG. 5 . In the present embodiment, a center portion serving as a heat-receiving part of the heat pipe  51 A is joined to a semiconductor device  24  as a heat-generating member so that the heat sink  50  serves as a cooling device for cooling the semiconductor device  24 . A center portion of the heat pipe  51 C may be formed as a heat-receiving part and the heat pipe  51  may be joined to the semiconductor device  24 . 
   The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention. 
   Present application is based on Japanese priority application No. 2006-145669 filed May 25, 2006, the entire contents of which are hereby incorporated herein by reference.

Technology Classification (CPC): 5