HEAT SINK

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention deals with a heat sink for cooling an exothermic element using a heat pipe for transporting heat in the form of latent heat of a condensable working fluid encapsulated therein.

2. Discussion of the Related Art

A heat pipe is a generally known heat transfer device for transporting heat in the form of latent heat of a condensable working fluid. A non-condensable gas such as an air is evacuated from a container of the heat pipe, and a condensable fluid such as water or hydrocarbon is encapsulated therein. The container is sealed air-tightly. Therefore, if a part of the heat pipe is heated from outside when another part of the heat pipe is being cooled, the working fluid is vaporized by the heat, and the vapor flows toward a cooled part where a temperature and a pressure are low. The vapor releases the latent heat outside of the container and then liquefies. The resultant liquid phase working fluid flows toward a heated portion where the heat is transmitted from outside.

As explained above, the vaporized working fluid is transmitted to a heat radiating side by a pressure difference in the container arising from the heating and radiation. Meanwhile, a pressure for refluxing the working fluid to the heated portion is required. For this purpose, common heat pipes are adapted to create a capillary pumping. Specifically, thin slits, porous materials or meshes functioning as a wick are arranged in the container. When the working fluid infiltrating in the wick is evaporated, a meniscus of the working fluid infilling pores in the wick comes down. Consequently, a capillary pumping arises from a surface tension. The condensed working fluid infiltrating into the wick is aspirated to be flown back to the heated portion side where evaporation takes place, by the capillary pumping thus created at the heated portion.

The heat pipe of this kind is capable of cooling the exothermic element by a vapor flow and a reflux of the working fluid in the container. Therefore, in these days, the heat pipes are utilized in e.g., artificial satellites and spacecrafts, and widely used for cooling exothermic electron devices such as a central processing unit of an electronic device.

As an example of a conventional heat sink using a heat pipe for cooling an electron devices such as a central processing unit, Japanese Patent Laid-Open No. 2004-111966 (corresponding to U.S. Pat. No. 6,894,900) discloses a heat sink comprising a heat pipe erected vertically on a heat-absorbing base with a bend, and a plurality of horizontal fins arranged at a regular intervals along the vertically erected part of the heat pipe.

As an another example of a conventional heat sink, there has been developed a heat sink comprising a plurality of vertical fins erected on an upper face of a heat-absorbing base at regular intervals, and a plurality of heat pipes extending from a side wall of the base to communicate with the vertical fins.

However, in case of elongating the erected part of the heat pipe lengthwise for the purpose of enhancing heat exchange (or radiating) efficiency of the conventional heat sink disclosed in U.S. Pat. No. 6,894,900, a quantity of the fins has to be increased. Consequently, the size of the heat sink of this kind has to be larger.

On the other hand, according to another example of the conventional heat sink, a plurality of heat pipes penetrates the vertical fins, and the heat pipes are contacted with the vertical fins. Therefore, thermal exchanges (i.e., heat radiation) between the individual heat pipes and the individual vertical fins take place simultaneously. In this case, if the vertical fins are arranged close together, temperatures of the air existing between the vertical fins are raised. As a result, thermal resistance of the vertical fins is increased and this degrades thermal exchange efficiency. Especially, the thermal exchange efficiency is degraded significantly in the direction to radiate the heat laterally from the heat pipes. For this reason, the vertical fins have to be enlarged to enhance the thermal exchange efficiency. That is, the heat sink of this kind also has to be larger as the case of the conventional heat sink of U.S. Pat. No. 6,894,900.

SUMMARY OF THE INVENTION

The present invention has been conceived in view of the aforementioned technical problems, and it is an object of the present invention to improve thermal exchange efficiency, i.e., heat radiation of a heat sink without enlarging the size of the heat sink itself.

In order to achieve the aforementioned objective, a heat sink of the present invention comprises a heat receiving base for receiving heat from an exothermic element, a plurality of fins for radiating heat arranged radially around the heat receiving base at predetermined intervals in a circumferential direction, and one or more heat pipe(s) comprising a curved portion. One of end portions of the curved portion is individually connected to a predetermined portion of the heat receiving base, and a predetermined region of the curved portion is contacted with the fins in a heat transferable manner.

The curved portion of the heat pipe is bent into arcuate and situated inward of an outermost portion of the fins.

According to another aspect of the invention, a heat sink comprises a heat receiving base for receiving heat from an exothermic element, a plurality of fins for radiating heat arranged to enclose the heat receiving base at predetermined interval in a radial direction of the heat receiving base, and a plurality of heat pipes. One of end portions of the heat pipe is individually connected to a predetermined portion of the heat receiving base, and those heat pipes are arranged to extend radially in different directions and to be contacted sequentially with the fins in a heat transferable manner.

The fins enclosing the heat receiving base are divided evenly according to the number of the heat pipes extending radially, and a predetermined clearance exists between abutting sets of the fins belonging individually to one heat pipe.

According to the heat sink of the invention, the heat receiving base is structured as a heat pipe comprising a porous structured wick disposed on an interior bottom face, and porous structured projections formed integrally on an upper face of the wick.

Also, according to the heat sink of the invention, the heat pipe penetrates the fins while contacting sequentially with the fins.

Further, according to the heat sink of invention, the aforementioned heat pipes are arranged not to be overlapped with each other.

According to the present invention, the heat pipe is bent into arcuate and such a curved portion is contacted sequentially with the plurality of fins, and one of the end portions of the heat pipe is connected to the heat receiving base. This structure allows the heat pipe to be contacted with the fins over a long range. For this reason, heat exchange or radiating efficiency of the heat pipe within a limited space can be improved significantly. Meanwhile, the fins mounted on the heat pipe are not shared by another heat pipe. Therefore, heat exchange can be carried out efficiently without enlarging the fins. In other words, this is advantageous to downsize the heat pipe. Thus, the heat pipe of the invention can also comply with a demand of reduction in size and weight of an electronic control unit of various types of equipments. Further, according to the present invention, the heat receiving base as a core of the heat sink is structured as a heat pipe, and one of the end portions of the heat pipes bent into arcuate are connected thereto. This structure also improves heat transfer efficiency and heat exchange efficiency of the heat sink as a whole. Specifically, according to the invention, a porous structured wick is formed on an interior bottom face of the heat receiving base, and porous structured protrusions are formed thereon. Therefore, heat transporting capacity of the heat sink is further enhanced, and heat exchange efficiency between the heat sink and the exothermic element is thereby improved.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and accompanying drawings, which should not be read to limit the invention in any way, in which:

FIG. 1 is a top view showing a first embodiment of a heat sink according to the invention.

FIG. 2 is a perspective view showing an arrangement of an installation base and a heat receiving base according to the first embodiment.

FIG. 3 is a partially omitted cross-sectional view showing a structure of the heat receiving base according to the first embodiment.

FIG. 4 is a perspective view showing an arrangement of the installation base, the heat receiving base and a heat pipe according to the first embodiment.

FIG. 5 is a perspective view showing an arrangement of the installation base, the heat receiving base, the heat pipe and fins according to the first embodiment.

FIG. 6 is a side view showing one of configurations of the fin according to the first embodiment.

FIG. 7 is a perspective view showing an arrangement of the installation base, the heat receiving base, the heat pipe, and two kinds of the fins according to the first embodiment.

FIG. 8 is a side view showing another configuration of the fin according to the first embodiment.

FIG. 9 is an explanatory drawing showing how to join the fins according to the first embodiment.

FIG. 10 is a perspective view showing an arrangement of the installation base, the heat receiving base, the heat pipe, the two kinds of fins, and a bracket according to the first embodiment.

FIG. 11 is a perspective view showing an arrangement of the installation base, the heat receiving base, the heat pipe, the two kinds of fins, the bracket, and an axial fan mounting frame according to the first embodiment.

FIG. 12 is a top view showing a second embodiment of a heat sink according to the invention.

FIG. 13 is a partially omitted perspective view showing an arrangement of an installation base, the heat receiving base, a heat pipe, and fins according to the second embodiment.

FIG. 14 is a perspective view showing an exterior appearance of a main part of the heat sink according to the second embodiment.

FIG. 15 is a top view showing a third embodiment of a heat sink according to the invention.

FIG. 16 is a partially omitted perspective view showing an arrangement of an installation base, a heat receiving base, heat pipes, and fins according to the third embodiment.

FIG. 17 is a perspective view showing an exterior appearance of a main part of the heat sink according to the third embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Here will be described a first exemplary embodiment of the invention. FIG. 1 is a top view showing a first embodiment of a heat sink according to the invention. The heat sink 1 illustrated in FIG. 1 comprises an installation base 5. As illustrated in FIGS. 2 to 4, a heat receiving base 3 is mounted on a center of the installation base 5, and a bottom face of the heat receiving base 3 is aligned to be contacted with at least an upper face of a not-shown electron device as an exothermic element, e.g., a central processing unit.

As illustrated in FIG. 2, the installation base 5 comprises a base plate 7, a circular reinforcement frame 9, linear reinforcement frames 11 and clips 13. The circular reinforcement frame 9 is formed on the base plate 7 at a predetermined height, and the heat receiving base 3 is mounted thereon. The linear reinforcement frames 11 extend from the circular reinforcement frame 9 radially to four corners of the base plate 7, and the end portion thereof is bent downwardly. At the leading end of the linear reinforcement frame 11, there is formed a clip 13.

The heat receiving base 3 is positioned by forming an inner flange along an inner circumference of the circular reinforcement frame 9 on which the heat receiving base 3 is to be placed, or by forming a flange around a lower end of an outer circumference of the heat receiving base 3 by which the heat receiving base 3 is fixed within the circular reinforcement frame 9 at the predetermined height. Alternatively, in case of positioning the heat receiving base 3 without a flange, the heat receiving base 3 may be placed directly on an exothermic element by allowing a vertical movement of the heat receiving base 3 within the inner circumference of the circular reinforcement frame 9, or the heat receiving base 3 may also be positioned by placing a lower end of below-mentioned fins 35 and 41 fixed with the heat receiving base 3 on the circular reinforcement frame 9. In any case, a lower circumference of the heat receiving base 3 is preferable to be soldered with the circular reinforcement frame 9 using a copper or the like having an excellent endothermic characteristics so as to enhance a structural strength.

An illustrated structure of the installation base 5 is an example to carry out the invention and a structure of the installation base 5 should therefore not be limited to the illustrated structure. Another appropriate structure of the installation base 5 may also be applied to the invention.

The heat receiving base 3 is structured as a heat pipe. Specifically, the heat receiving base 3 comprises a column-shaped hollow container 15. Non-condensable gas such as an air is evacuated from the container 15, and the container 15 is filled with a condensable working fluid such as water. An area of an upper face of the container 15 is slightly smaller than that of a bottom face so that a peripheral wall of the container 15 is tapered. Additionally, a nozzle 16 is formed on an upper face the container 15. The condensable working fluid is infused through the nozzle 16 and the nozzle 16 is then closed.

As illustrated in FIG. 3, a wick 17 made of porous material is disposed on an interior bottom face of the container 15, and a plurality of porous structured projections 19 are formed integrally on an upper face of the wick 17. The wick 17 is formed into a flat sheet by binding particles 21. The particle 21 is a material which has an excellent hydrophilicity with the working fluid, and which does not react with the working fluid. For example, a copper particle of several hundred micrometers (e.g., around 200 μm) diameter can be used as the particle 21. Those particles 21 are consolidated by sintering or the like so as to form the wick 17.

According to an exemplary aspect of the present invention, the thickness of the wick 17 is not constant and the upper face thereof is rugged. Specifically, a substantially flat base layer is formed by consolidating the above-mentioned particles 21 into one or more layers. A base layer is attached to the inner bottom face of the container 15. At predetermined portions of the base layer, the particles 21 are heaped up and consolidated integrally with the base layer by a sintering etc. Accordingly, the thickness of the wick 17 is thicker at those portions. The portions where the particles 21 are heaped up correspond to porous projections 19 of the present invention. Those portions may be described as “stacks” or “cones”. The projections 19 may be shaped into an arbitrary shape like a cylinder, cone, or pyramid as would be understood by one of skill in the art. In case of a conical shape, for example, the height of each projection 19 may be around 1.8 mm. Additionally, the projections 19 may be arranged at either regular or irregular intervals. Besides, in FIG. 3, the wick 17 and the projections 19 are illustrated in larger scale than the actual proportion, and the number of the illustrated projections 19 is smaller than the actual number for the convenience of illustration, however, an actual size of the projections 19 is considerably small and the actual number of the projections 19 is significantly large.

A wick may also be formed on an inner circumferential face of the container 15. For example, a plurality of thin slits may be formed as a wick on the inner circumferential face of the container 15 in a vertical direction. Alternatively, a net material formed of extremely thin strings may also be arranged as a wick on the inner circumferential face of the container 15. In this case, meshes of the net material are preferably formed into rhombic wherein an inner angle of vertexes is within the range of 5 to 85 degree for the purpose of reducing a flow resistance.

A bottom face of the heat receiving base 3 is basically formed into a shape congruent with a shape of an upper face of an electron device. However, in order to enhance an endothermic efficiency, the bottom face of the heat receiving base 3 may also be formed into a shape to be contacted partially with side faces of the electron device, or a deformable heat absorbing material may be interposed between the bottom face of the heat receiving base 3 and the upper face of the electron device.

As illustrated in FIG. 1, 4 and 5, each heat pipe 27 comprises a linear portion 31 which is to be inserted into the heat receiving base 3, and an arcuate curved portion 33 which is to be situated concentrically with and outside of the heat receiving base 3. A radial distance from an inner circumference of the curved portion 31 to the outer face of the peripheral wall of the heat receiving base 3 (or the container 15) is substantially constant everywhere in the curved portion 31. A condensable working fluid, whose boiling point is lower than that of the water encapsulated in the container 15, e.g., hydrocarbon or the like, is encapsulated in the heat pipe 27. Specifically, the linear portion 31 inserted into the heat receiving base 3 functions as an evaporating portion (i.e., a heat receiving portion), and the curved portion 33 enclosing the heat receiving base 3 halfway functions as a condensing portion (i.e., a heat radiating portion).

As illustrated in FIG. 2, a plurality of holes 25 into which the linear portion 31 of the heat pipes 27 are to be inserted tightly are formed on the peripheral wall of the heat receiving base 3 (i.e., the container 15). In order to enhance a thermal conductivity, a contour of the holes 25 is preferably congruent with a cross-sectional shape of the heat pipe 27. The linear portion 31 of the heat pipe 27 is inserted into the heat receiving base 3 from one of the holes 25 formed on relatively upper side of the peripheral wall. For the purpose of enhancing a structural strength, the heat pipe 27 is preferably soldered with the hole 25 using an alloy having an excellent thermal conductivity such as a copper. Meanwhile, a leading end of the linear portion 31 is housed in the hole 25 which is situated on a relatively lower portion of the peripheral wall of the heat receiving base 3, in a side diametrically opposite to the hole 25 where the heat pipe 27 is soldered with. Thus, as illustrated in FIGS. 1 and 5, the heat pipes 27 are arranged not to be contacted or overlapped with each other in the heat sink 1.

As illustrated in FIGS. 1 and 5, a plurality of fins 35 for radiating heat is mounted on the curved portion 33 of the heat pipe 27. Specifically, as illustrated in FIG. 6, a circular opening 37 whose diameter is identical to that of the heat pipe 27 is formed in the fin 35. The fins 35 are mounted on the heat pipe 27 by inserting the heat pipe 27 into the opening 37 of the fins 35. The fins 35 are arranged on the heat pipe 27 at regular intervals. A distance from an innermost portion of the opening 37 to an innermost side of the fin 35 is identical to the radial distance from the inner circumference of the curved portion 33 to the peripheral wall of the heat receiving base 3. For this reason, the innermost sides of the fins 35 are contacted with the peripheral wall of the heat receiving base 3 when the fins 35 are mounted on the heat pipe 27. As a result, the fins 35 are arranged radially around the peripheral wall of the heat receiving base 3. In order to enhance a structural strength, contact portions between the innermost side of the fins 35 and the peripheral wall of the heat receiving base 3, and contact portions between the openings 37 and the heat pipe 27 are preferably soldered or brazed using an alloy having an excellent thermal conductivity such as a copper. Here, a reference numeral 36 in FIG. 5 represents soldered portions.

As can be seen from FIG. 5 and 7, the leading end portion of the curved portion 33 is situated near the linear portion 31 of the other heat pipe 27. Therefore, as illustrated in FIGS. 7 and 8, fins 41 comprising an opening 37 as well as a cutout 39 for housing a linear portion 31 of the other heat pipe 27 are used in the leading end area of the curved portion 33. As the case of fins 35, contact portions between an innermost side of the fins 41 and the peripheral wall of the heat receiving base 3, and contact portions between the openings 37 and the heat pipe 27 are preferably soldered using a copper or the like so as to enhance a structural strength.

Here, in FIGS. 5 and 7, although the fins 35 and 41 are mounted only on one of the heat pipe 27 for the convenience of illustration, the fins 35 and 41 are also mounted on the other heat pipe 27.

As explained above, and as evidenced by the structure of the fins 35 and 41 in which only one circular opening 37 is formed therein, the heat pipes 27 are not contacted with each other in the heat sink 1. For this reason, the thermal exchange efficiency of the heat pipes 27 is improved and this eliminates a necessity to enlarge the fins 35 and 41.

Further, the fins 35 and 41 comprise a snap structure as shown in FIG. 9. Specifically, a joint portion 43 is formed by bending an outermost portion of the fins 35 and 41 in a same direction. The joint portion 43 comprises a cutout 45 and a projecting portion 47 on both upper and lower end of the fins 35 and 41 illustrated in FIGS. 6 and 8. The fins 35 and 41 are mounted on the heat pipe 27 by inserting the heat pipe 27 into the hole 37 of the fins 35 and 41 sequentially and pushing the projecting portions 47. As a result, the projecting portions 47 are fitted with the adjacent cutouts 45, and the fins 35 and 41 are arranged at regular intervals by the joint portion 43. The heat pipe 27 and the fins 35 as well as 41 are thereby assembled at a high intensity.

After the fins 35 and 41 are mounted on the heat pipe 27, a bracket 49 is mounted on the heat receiving base 3 for the purpose of an installation of an axial fan, as illustrated in FIG. 10. The bracket 49 is mounted on the heat receiving base 3 by fitting the nozzle 16 into a central opening 51 of the bracket 49 for example. Alternatively, the bracket 49 can also be bonded with the heat receiving base 3. The method for fixing the bracket 49 should not be limited to those methods but the bracket 49 may be fixed on the heat receiving base 3 by other appropriate methods.

The bracket 49 comprises two pairs of foundations 53 on which an after mentioned installation frame 57 for the axial fan is to be mounted, and a fitting portions 55 which is bent generally at a right angle downwardly so as to be fitted with the installation frame 57.

In order to secure a space for the bracket 49, the fins 35 and 41 are not arranged on diametrically opposite two portions of the heat receiving base 3, in other words, in the vicinity of the linear portion 31 of the heat pipe 27.

However, the configuration of the bracket 49 should not be limited to the illustrated configuration but the bracket 49 may be modified appropriately according to need. For example, in case of arranging the fins 35 and 41 all around the heat receiving base 3, the bracket 49 may be modified to meet this requirement.

As illustrated in FIGS. 1 and 11, the axial fan installation frame 57 comprises a ring portion 59 to be mounted on the outer end of the fins 35 and 41 and on the foundations 53. In the ring portion 59, fixing portions 61 extending downwardly are formed on diametrically opposite two portions. The installation frame 57 is fixed with the heat sink 1 by fitting the fixing portion 61 with the fitting portion 55 of the bracket 49. The installation frame 57 further comprises a cable management portion 60.

On the ring portion 59, four columns 63 are erected at regular intervals. From the upper end of the column 63, a support 65 is formed to connect the column 63 and a mounting plate 67 for an axial fan 69 driven by a not shown motor. The supports 65 are situated at a predetermined angle with respect to the mounting plate 67 so as to establish a reaction force against a revolution of the axial fan 69. In FIG. 11, the axial fan 69 is mounted on an upper face of the mounting plate 67 as depicted by a broken line. However, the axial fan 69 may also be mounted on a bottom face of the mounting plate 67 within an inner circumference of the ring 59 in a rotatable condition.

In addition to above, the structure of the axial fan installation frame 57 should not be limited to the illustrated structure but may be modified arbitrarily according to need.

Clips 13 of the installation base 5 are adapted to fix the heat sink 1 with an electronic substrate, a chassis of an electric device or the like by inserting a bolt, screw and etc. into an opening 13a shown in FIG. 1. Alternatively, the clip 13 may also be fixed by soldering or brazing.

According to this embodiment, the heat pipe 27 connected to the heat receiving base 3 is bent into arcuate, and the plurality of fins 35 and 41 are mounted on the curved portion 33 of the heat pipe 27 by inserting the heat pipe 27 into the hole 37. This configuration allows arranging a large number of fins 35 and 41 along almost entire length of the heat radiating portion of one heat pipe 27. For this reason, the heat radiation efficiency of the heat pipe 27 can be improved significantly within a limited space.

For the purpose of facilitating the heat radiation from the heat pipe 27, ambient air is blown into the clearances between the fins by operating the axial fan 69. Therefore, the heat radiation efficiency of the heat pipe 27 can be further improved within a limited space.

Additionally, the fins 35 and 41 mounted on the heat pipe 27 are not shared by another heat pipe. This eliminates a necessity to enlarge the heat radiating area of the fins 35 and 41 for the purpose of improving the heat radiating efficiency, unlike the case in which a fin is shared by a plurality of heat pipes. Therefore, the heat sink 1 of the invention can fulfill the requirement of downsizing of personal computers, laptop computers, a central processing unit of electronic devices and so on.

Furthermore, according to this embodiment, the heat receiving base 3 as a core of the heat sink 1 is also structured as a heat pipe. Specifically, a wick 17 made of porous material is disposed on the interior bottom face of the heat receiving base 3, and a plurality of porous structured projections 19 projecting upwardly are formed integrally on the wick 17. In addition, the linear portion 31, i.e., the heat receiving portion of the heat pipes 27 is connected to the heat receiving base 3 structured as a heat pipe. Therefore, the heat transporting capacity and the heat transporting efficiency of the heat sink 1 are further improved. As a result, the thermal exchange efficiency between the heat sink 1 and an exothermic element is further improved.

Next, a heat sink 71 as a second embodiment of the present invention will be explained with reference to FIGS. 12 to 14. FIG. 12 is a top view showing the heat sink 71.

Differences between the heat sink 71 of the second embodiment and the heat sink 1 of the first embodiment are configurations of a heat receiving base 73, heat radiation fins 81 and heat pipes 85. The remaining elements of the heat sink 71 illustrated in FIGS. 12 to 14 are similar to those of the heat sink 1, so further description will be omitted by allotting common reference numerals.

The heat receiving base 73 is made of a material whose heat conductivity is excellent such as a copper. As illustrated in FIG. 13, the heat receiving base 73 comprises a column shaped heat receiving body 75, and a cylindrical heat exhausting portion 77 which is formed integrally on a circumference of the heat receiving body 75. In heat receiving body 75, there are formed two vertical holes 79 into which an evaporating side of the after mentioned heat pipes 85 are buried tightly.

A plurality of heat radiating fins 81 are arranged around the heat receiving base 73. The fins 81 are preferably fixed to a peripheral wall of the heat receiving base 73 by a soldering or blazing using a copper or the like having an excellent heat conductivity. According to the second embodiment illustrated in FIGS. 12 to 14, all of the fins 81 are formed in the same configuration. Specifically, the fin 81 comprises a cutout 83 in which the heat pipe 85 is housed. The cutout 83 has a contact portion 83a to which the heat pipe 85 is contacted. A curvature of the contact portion 83a is congruent with a sectional curvature of the curved portion (i.e., a heat radiating portion) 89 of the heat pipe 85. Likewise the fins 35 and 41 of the first embodiment, the fins 81 also comprise a snap structure as shown in FIG. 9. Therefore, the fins 81 can be integrated easily at regular intervals.

As illustrated in FIGS. 12 to 14, an end portion of the evaporating side of the heat pipes 58 is inserted into the vertical hole 79 tightly. The heat pipe 85 comprises a bent portion 87 which is bent at the portion above an upper face of the heat receiving body 75 at generally right angle outwardly of the heat exhausting portion 77, and a curved portion 89 which extends half around the heat receiving base 73 from the bent portion 87 clockwise. As the first embodiment, the heat pipes 85 are arranged not to be contacted or overlapped with each other.

The configuration of the fin 81 should not be limited to the above-explained configuration. That is, configuration of the cutout may be modified according to the configuration of the heat pipe.

In addition, an axial fan may also be mounted on the heat sink 71 of the second embodiment. In order to mounting the axial fan on the heat sink 71, for example, an installation frame can be mounted on an appropriate portion in the installation base 5 such as a linear reinforcement frame 11, a clip 13 etc. However, the measure for mounting the axial fan should not be limited to the aforementioned example but detailed explanation about installation of the axial fan is omitted.

According to the second embodiment, the heat radiating portion (i.e., the condensing portion) of the heat pipe 85 connected to the heat receiving base 73 is bent into arcuate, and contacted sequentially with the fins 81 through the contact portion 83a of the cutouts 83. This configuration allows the heat pipe 85 contacting with a large number of fins 81 along almost entire length of the heat radiating portion of one heat pipe 85. For this reason, the heat radiation efficiency of the heat pipe 85 can be improved significantly within a limited space.

In addition to above, since the fins 81 are designed to be contacted with the heat pipe 85 through the cutout 83, the fins 81 can be manufactured easily, and also, the fins 81 can be attached easily to the heat receiving base 73. For this reason, an assembly of the heat sink 71 can be simplified significantly. This is also advantageous for a volume production of the heat sink 71.

Furthermore, the evaporation sides of the heat pipe 85 are inserted tightly, i.e., buried tightly into the vertical holes 79 of the heat receiving base 73. For this reason, the heat generated by the exothermic element can be transmitted efficiently to the evaporation side of the heat pipe 85, and a structural strength of the heat sink 71 is also improved.

Next, a heat sink 91 as a third embodiment of the present invention will be explained with reference to FIGS. 15 to 17. FIG. 15 is a top view showing the heat sink 99 of the third embodiment.

Differences between the heat sink 91 of the third embodiment and the heat sink 1 and 71 are configurations of a heat receiving base 93, heat radiation fins 99a to 99n and heat pipes 97. The remaining elements of the heat sink 91 illustrated in FIGS. 15 to 17 are similar to those of the heat sinks 1 and 71, so further description will be omitted by allotting common reference numerals.

The heat receiving base 93 is made of a material whose heat conductivity is excellent such as a copper. As illustrated in FIG. 16, the heat receiving base 93 also has a column-shaped main body, and comprises vertical holes 93 into which an evaporation side of the after mentioned heat pipes 97 are buried tightly. The heat receiving base 93 further comprises a plurality of protrusions 93b, which are formed around outer circumference at regular intervals, and to which heat radiating fins 99a are contacted.

As illustrated in FIGS. 15 and 16, the heat pipes 97 in which the evaporation side is inserted into the holes 95 are arranged radially at regular intervals. Specifically, an angle between two heat pipes 97 is 72 degrees. On the condensing side of the heat pipes 97, one set of fins 99a to 99n is mounted, and widths of the fins 99a to 99n in the circumferential direction are within a range of approximately 70 degrees. Additionally, a predetermined clearance exists in the radial direction between each two sets of the fins 99a to 99n. In fins 99a to 99n, there is formed a not shown opening into which the condensing side of the heat pipe 97 is inserted. The innermost fin 99a is contacted with protrusions 93b of the heat receiving base 93.

The set of fins 99a to 99n are preferably soldered to the heat pipe 97 using a copper or the like so as to enhance the structural strength.

As illustrated in FIG. 17, clips 13 of the installation base 5 are adapted to fix the heat sink 91 with an electronic substrate or the like by inserting a clip fastener 101 into an opening of the clip 13.

According to the third embodiment, the heat pipes 97 buried tightly into the vertical holes 95 of the heat receiving base 93 are arranged radially, and the condensing portion of the heat pipes 97 are contacted sequentially with the set of fins 99a to 99n. This configuration allows the heat pipe 97 contacting with a large number of fins such as fins 99a to 99n along almost entire length of the heat radiating portion of one heat pipe 97. For this reason, the heat radiation efficiency of the heat pipe 97 can be improved significantly within a limited space.

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