US20110108244A1

US20110108244A1 - Heat sink

Info

Publication number: US20110108244A1
Application number: US12/939,309
Authority: US
Inventors: Hisao Anzai
Original assignee: Fujitsu Ltd
Current assignee: Fujitsu Ltd
Priority date: 2009-11-11
Filing date: 2010-11-04
Publication date: 2011-05-12
Also published as: TW201122788A; JP5333161B2; JP2011103384A; CN102074532A

Abstract

A heat sink includes a base board, a fin group, heat pipes, and a radiation plate. The fin group includes a plurality of fins arranged on the base board at right angles to the base board. Each of the heat pipes has the shape of the letter “U,” is arranged, on the whole, in parallel with each fin, and conducts heat from the base board to the radiation plate placed on the fin group. The base board and the radiation plate are thermally connected to each fin.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2009-257925, filed on Nov. 11, 2009, the entire contents of which are incorporated herein by reference.

FIELD

The embodiment discussed herein is related to a heat sink.

BACKGROUND

Heat sinks for dissipating heat which radiates from heat generation sources (such as CPUs (Central Processing Units) or switching elements) of products are known.
With many products equipped with heat sinks, space for a heat sink is limited. In addition, for example, there has been an increase in CPU speed or the switching speed of switching elements, so the amount of heat which radiates from the heat generation sources is increasing.
Accordingly, various attempts to improve heat radiation efficiency in a limited space are being made.
A heat pipe for efficiently conducting heat to fins is included in a heat sink as one of such attempts.
FIG. 5 illustrates a heat sink including heat pipes.
A heat sink 90 includes two base plates 91 opposite to each other and many plate-like fins 92 arranged between the base plates 91 at right angles with surfaces of the base plates 91 opposite to each other.
Parallel portions 94 of each U-shaped heat pipe 93 illustrated in FIG. 5 are fitted into penetration holes 95. Parallel portions 94 of two heat pipes 93 are fitted into one penetration hole 95 from both sides and the tips of the parallel portions 94 are touching each other in the middle of the penetration hole 95.
Japanese Laid-open Patent Publication No. 11-145354
With the structure illustrated in FIG. 5, connecting portions 96 between the two base plates 91 are sticking out of the main body. However, fins are not arranged around the connecting portions 96, so heat radiation space around these portions is useless.

SUMMARY

According to an aspect of the present invention, there is provided a heat sink including a base, a fin group having a plurality of fins arranged on the base at right angles to the base, at least one U-shaped heat pipe both straight portions of which are arranged in parallel with the plurality of fins and which conducts heat from the base to the plurality of fins, and a radiation plate which is placed on the fin group and which is thermally connected to the plurality of fins.
The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a heat sink according to an embodiment;

FIG. 2 is an exploded perspective view of the heat sink;

FIG. 3 illustrates a modification of the heat sink;

FIG. 4 illustrates an application of the heat sink; and

FIG. 5 illustrates a heat sink including heat pipes.

DESCRIPTION OF EMBODIMENT(S)

An embodiment will now be described in detail with reference to the accompanying drawings.
FIG. 1 is a perspective view of a heat sink according to an embodiment.
A heat sink (radiator) 1 according to an embodiment includes a base board (heating plate) 2, a fin group 3, heat pipes 4 a and 4 b, and a radiation plate 5.
The base board 2 is rectangular.
Two grooves 21 and 22 parallel with a side 2 a of the base board 2 are cut in the base board 2 at determined distance from each other. Part of the heat pipe 4 a is touching the groove 21 with solder therebetween. Part of the heat pipe 4 b is touching the groove 22 with solder therebetween.
In addition, a surface of the base board 2 opposite to a surface over which the fin group 3 is arranged is touching a heat generation source (not illustrated) with a heat conduction member, such as grease or a thermal sheet, therebetween.
For example, a semiconductor chip such as a CPU, a switching element, a resistance element, or a semiconductor package including them is a heat generation source.
In addition, the base board 2 is made of copper, aluminum, or the like.
If the base board 2 is made of aluminum, a heat pipe (other than the heat pipes 4 a and 4 b) may be embedded in the base board 2 for diffusing heat.
The fin group 3 is arranged over the base board 2 with solder therebetween.
The fin group 3 includes a plurality of fins 3 a. Each fin 3 a has a platelike shape. The plurality of fins 3 a are arranged at right angles to the base board 2. There is a determined distance between two adjacent fins 3 a and each fin 3 a is arranged regularly so that it will be parallel to the other fins 3 a.
In addition, each fin 3 a is arranged so that its longitudinal direction will be equal to that of the base board 2.
The length of the fin group 3 (length in the longitudinal direction of each fin 3 a) is longer than its width.
Each fin 3 a is made of aluminum, copper, or the like.
For example, each fin 3 a may have a connecting portion (not illustrated) for connection to another fin 3 a. The fins 3 a may be connected to one another by these connecting portions.
The heat pipes 4 a and 4 b are arranged within the fin group 3.
The radiation plate 5 is placed opposite the base board 2 so that it will cover most of the top of the fin group 3. That is to say, the heat sink 1 has a structure (what is called a sandwich structure) in which the fin group 3 is put between the base board 2 and the radiation plate 5.
In FIG. 1, the length in the longitudinal direction of the radiation plate 5 is slightly shorter than the length in the longitudinal direction of the top of the fin group 3.
The radiation plate 5, the fin group 3, and the heat pipes 4 a and 4 b are thermally connected to one another.
The function of the radiation plate 5 is not only to conduct heat conducted from the heat pipes 4 a and 4 b to each fin 3 a of the fin group 3 but also to directly radiate heat conducted from the heat pipes 4 a and 4 b into the air.
The radiation plate 5 is made of copper, aluminum, or the like.
If the radiation plate 5 is made of aluminum, a heat pipe (other than the heat pipes 4 a and 4 b) may be embedded in the radiation plate 5 for diffusing heat.
FIG. 2 is an exploded perspective view of the heat sink.
Each of the heat pipes 4 a and 4 b has a main body which has the shape of the letter “U” and which is made of metal such as copper. The main body is tubular. The tips of the main body having the shape of the letter “U” are closed and the main body is airtight. Wicks each having porous substances or narrow grooves are arranged on an internal wall of the main body.
A small amount of liquid (working liquid) is sealed within the main body. Pure water, ammonia, a chlorofluorocarbon-replacing material, or the like is used as a working liquid.
There is no special limitation to the shape of a cross section of each of the heat pipes 4 a and 4 b. The shape of a cross section of each of the heat pipes 4 a and 4 b may be round, oval, or flat. If the shape of a cross section of each of the heat pipes 4 a and 4 b is flat, it is easy to work them. In addition, if the shape of a cross section of each of the heat pipes 4 a and 4 b is flat, the base board 2 and the radiation plate 5 can be made thinner. As a result, the heat sink 1 can be miniaturized.
By the way, notches 31 are cut in part of the plurality of fins 3 a included in the fin group 3 according to the shape of a curve 41 in the heat pipe 4 a and a curve 42 in the heat pipe 4 b. In other words, the length in the longitudinal direction of the fins 3 a in which the notches 31 are cut is shorter than the length in the longitudinal direction of the other fins 3 a.
As illustrated in FIG. 1, the heat pipes 4 a and 4 b are arranged so that the curves 41 and 42 will be at right angles to the base board 2 as viewed from the side of the initial point of an arrow A drawn along the side 2 a (as viewed from the front). That is to say, the curve 41 in the heat pipe 4 a and the curve 42 in the heat pipe 4 b are arranged in parallel with each fin 3 a.
In addition, the curve 41 in the heat pipe 4 a and the curve 42 in the heat pipe 4 b are arranged between fins 3 a. There is a space of about 2 millimeters between the curve 41 in the heat pipe 4 a and the fin 3 a adjacent thereto and between the curve 42 in the heat pipe 4 b and the fin 3 a adjacent thereto so that air will flow.
Straight portions 43 and 45 of the heat pipe 4 a and straight portions 44 and 46 of the heat pipe 4 b are arranged in the longitudinal direction of each fin 3 a.
When the above heat sink 1 is assembled, the tips of the straight portions 43 and 45 of the heat pipe 4 a are placed at end portions 32 in the longitudinal direction of the fins 3 a in which the notches 31 are cut.
Furthermore, the tips of the straight portions 44 and 46 of the heat pipe 4 b are placed at end portions 32 in the longitudinal direction of the fins 3 a in which the notches 31 are cut.
A substantial reduction in the number of fins 3 a which results from cutting the notches 31 will now be described.
For example, it is assumed that the thickness of each fin 3 a is 0.5 mm, that the fins 3 a are arranged at intervals of 2 mm, that the diameter of the heat pipes 4 a and 4 b is 6 mm, that the radius of the curvature of the curves 41 and 42 is 15 mm, and that the length of the straight portions 43, 44, 45, and 46 is 60 mm.
As stated above, the internal wall of each heat pipe has a minute structure, so there is a limit to the radius of the curvature. If the diameter of the heat pipes 4 a and 4 b is 6 mm, then the limit of the radius of the curvature is about 15 mm. The radius of the curvature is measured with the center line of each heat pipe as reference.
The number of the fins 3 a in which the notches 31 are cut depends on the diameter of the heat pipes 4 a and 4 b.
If the heat pipes 4 a and 4 b are arranged within the fin group 3, the number of the fins 3 a in which the notches 31 are cut is 5 (=10 mm (=6 mm+2 mm (space)×2)/2 mm) for each of the heat pipes 4 a and 4 b. Therefore, the total number of the fins 3 a in which the notches 31 are cut is 10.
In addition, the area of the notches 31 depends on the radius of the curvature of the curves 41 and 42.
In this example, a notch 31 accounts for about 25 percent of the area of an entire fin 3 a.
Accordingly, a reduction in the number of fins 3 a in the entire fin group 3 which results from cutting the notches 31 in the part of the plurality of fins 3 a is 2.5 (=10×25(%)).
In FIG. 5, on the other hand, the width of the curve 96 is 18 mm (=15 mm (radius of curvature)+6 mm/2). Accordingly, about 7 fins (=18 mm/(2 mm (interval)+0.5 mm (thickness))) cannot be mounted on one side.
That is to say, with the conventional heat sink 7 fins cannot be mounted. With the heat sink according to the present embodiment, however, a reduction in the number of fins is only 2.5.
If the number of heat pipes increases, this difference becomes smaller. However, usually the number of heat pipes used in a heat sink is two.
The mechanism of heat radiation by the heat sink 1 will now be described.
When the heat sink 1 is used, the heat sink 1 is placed so that a heat generation source will be touching a nearly central portion of the base board 2.
First heat is conducted from the heat generation source to the base board 2.
Part of the heat conducted to the base board 2 is conducted from the groove 21 to the straight portion 45 of the heat pipe 4 a. In addition, another part of the heat conducted to the base board 2 is conducted from the groove 22 to the straight portion 46 of the heat pipe 4 b. Still another part of the heat conducted to the base board 2 is conducted directly to the fins 3 a.
When heat is conducted to the working liquid in the heat pipes 4 a and 4 b, the temperature of the working liquid rises and the working liquid vaporizes into vapor. The vapor flows through the curves 41 and 42 and to the straight portion 43 of the heat pipe 4 a and the straight portion 44 of the heat pipe 4 b.
The vapor which flows to the straight portion 43 of the heat pipe 4 a and the straight portion 44 of the heat pipe 4 b is then cooled by the fin group (low temperature member) 3 and is liquefied. To be concrete, heat is conducted from the vapor which flows to the straight portion 43 of the heat pipe 4 a and the straight portion 44 of the heat pipe 4 b to the radiation plate 5 connected to the straight portions 43 and 44 with solder therebetween and the fins 3 a. As a result, the vapor condenses into the working liquid.
The working liquid flows along the internal walls and returns to the straight portions 45 and 46 by capillary action.
An example of a method for fabricating the heat sink 1 will now be described.
First the base board 2 in which the grooves 21 and 22 are cut is prepared.
In addition, the fins 3 a are connected to one another by, for example, the above connecting portions to form the fin group 3.
Cream solder is then applied to the base board 2 and the radiation plate 5 and the base board 2 and the radiation plate 5 are bonded to the fin group 3. At this time cream solder is also applied to the grooves 21 and 22 in the base board 2 and grooves 51 and 52 in the radiation plate 5.
The straight portion 45 of the heat pipe 4 a is then fitted into the groove 21 in the base board 2 so that the end of the straight portion 45 will reach the far side of the groove 21. The straight portion 43 of the heat pipe 4 a is fitted into the groove 51 in the radiation plate 5 so that the end of the straight portion 43 will reach the far side of the groove 51. In addition, the straight portion 46 of the heat pipe 4 b is fitted into the groove in the base board 2 so that the end of the straight portion 46 will reach the far side of the groove 22. The straight portion 44 of the heat pipe 4 b is fitted into the groove 52 in the radiation plate 5 so that the end of the straight portion 44 will reach the far side of the groove 52.
In this state, the base board 2 and the radiation plate 5 are fixed by jigs (not illustrated) so that their positions will not shift.
After that, these members are put into a furnace to melt cream solder. Solder hardens, so the base board 2, the fin group 3, the heat pipes 4 a and 4 b, and the radiation plate 5 adhere to one another.
By doing so, the heat sink 1 can be fabricated.
With the heat sink 1, as has been described, the heat pipes 4 a and 4 b are arranged, on the whole, in parallel with the fins 3 a. As a result, the fin mount efficiency of the heat sink 1 rises and heat radiation efficiency can be improved.
In addition, the notches 31 are cut in the fins 3 a and the curve 41 in the heat pipe 4 a and the curve 42 in the heat pipe 4 b are arranged within the fin group 3.
As a result, the heat pipes 4 a and 4 b can be embedded in the fin group 3 by an easy working. Accordingly, the heat sink 1 can be fabricated easily.
To be concrete, for example, heat pipes are inserted at right angles to fins. In order to arrange fins around curves in the heat pipes, it is necessary to make holes in fins according to the shape of the curves in the heat pipes. In this case, however, it is necessary to make the holes different in shape in the fins.
With the heat sink 1, on the other hand, two kinds of fins 3 a different in length are prepared. In addition, each fin 3 a is rectangular, so it is worked easily.
Furthermore, the curve 41 in the heat pipe 4 a and the curve 42 in the heat pipe 4 b are embedded in the fin group 3, so the heat sink 1 can be miniaturized. For example, if the heat sink 1 is placed in a unit, space can be saved.
Moreover, by arranging the heat pipes 4 a and 4 b, on the whole, in parallel with the fins 3 a, the number of the fins 3 a in which the notches 31 are cut and the area of the notches 31 can be reduced. As a result, heat radiation efficiency can be improved.
In addition, the grooves 21 and 22 are cut in the base board 2. The straight portion 45 of the heat pipe 4 a is fitted into the groove 21 and the straight portion 46 of the heat pipe 4 b is fitted into the groove 22. The grooves 51 and 52 are cut in the radiation plate 5. The straight portion 43 of the heat pipe 4 a is fitted into the groove 51 and the straight portion 44 of the heat pipe 4 b is fitted into the groove 52.
As a result, there is no need to work the straight portions 43 and 45 of the heat pipe 4 a and the straight portions 44 and 46 of the heat pipe 4 b. The heat sink 1 can be fabricated easily. Furthermore, when the heat sink 1 is fabricated, the grooves 21 and 22 in the base board 2 and the grooves 51 and 52 in the radiation plate 5 also function as guides for inserting the heat pipes 4 a and 4 b.
In this embodiment each fin 3 a is arranged in the longitudinal direction of the base board 2. However, each fin 3 a may be arranged in the lateral direction of the base board 2. In this case, the heat pipes 4 a and 4 b are also arranged in parallel with each fin 3 a, that is to say, in the lateral direction of the base board 2.
In this embodiment the number of heat pipes is two. However, the number of heat pipes is not limited to two. The number of heat pipes may be one or three or more.
Furthermore, in this embodiment the heat pipes 4 a and 4 b are arranged so that the curves 41 and 42 will be at right angles to the base board 2 as viewed from the front. However, the heat pipes 4 a and 4 b may be arranged so that the curves 41 and 42 will form a determined angle other than 90° with the base board 2 as viewed from the front.
Moreover, in this embodiment the straight portions 43 and 45 of the heat pipe 4 a and the straight portions 44 and 46 of the heat pipe 4 b are arranged in parallel with each fin 3 a. From the viewpoint of heat diffusion, however, they may be arranged at an angle with each fin 3 a.

(Modification)

FIG. 3 illustrates a modification of the heat sink.
With a heat sink la a straight portion 43 of a heat pipe 4 a and a straight portion 44 of a heat pipe 4 b extend outwardly. As a result, heat diffusion efficiency improves. Each of the straight portions 43 and 44 is arranged at a determined angle with the longitudinal direction of each fin 3 a. As illustrated in FIG. 3, a groove is not cut in a radiation plate 5 a. The straight portions 43 and 44 are touching the top of the radiation plate 5 a. The straight portions 43 and 44 may be soldered further to the radiation plate 5 a.
In this embodiment, the grooves 21 and 22 are cut in the base board 2 and the grooves 51 and 52 are cut in the radiation plate 5. The straight portions 43 and 45 of the heat pipe 4 a are fitted into the grooves 51 and 21, respectively, and the straight portions 44 and 46 of the heat pipe 4 b are fitted into the grooves 52 and 22 respectively. For example, however, the heat pipes 4 a and 4 b may be embedded in penetration holes made in the base board 2 and the radiation plate 5. In this case, the heat pipes 4 a and 4 b may be soldered to the penetration holes.
In addition, it is not necessary to cut a groove or a penetration hole especially in the radiation plate 5. An effect can be obtained only by soldering the straight portions 43 and 44 to the radiation plate 5.
Furthermore, in this embodiment the whole of the curve 41 in the heat pipe 4 a and the curve 42 in the heat pipe 4 b is arranged within the fin group 3. However, part or the whole of the curves 41 and 42 may be arranged outside the fin group 3. By doing so, the area of the notches 31 cut in the fins 3 a decreases.

(Application)

An example in which a fan is used for radiating heat will now be described.
FIG. 4 illustrates an application of the heat sink.
In the application illustrated in FIG. 4, a printed board or a heat generation element is not illustrated.
A cooling system 10 illustrated in FIG. 4 includes a heat sink 1, an enclosure base 11, and a fan 12.
The enclosure base 11 includes a rectangular platelike flat portion 111 and a side portion 112 which bends at right angles from one end of the flat portion 111.
The fan 12 is installed on the side portion 112. In order to send a uniform amount of air, there is a certain space between the heat sink 1 and the fan 12.
The fan 12 takes in air from air intakes (openings) 113 formed in the side portion 112, and sends it in the direction of fins 3 a of the heat sink 1. A space between adjacent fins 3 a forms a ventilation flue. Air sent from the fan 12 flows along the ventilation flue and flows out from a side of a fin group 3 opposite the fan 12.
Even if part or the whole of curves 41 and 42 is arranged outside the fin group 3 by the use of the space between the fan 12 and the heat sink 1 of the cooling system 10, the part or the whole of the curves 41 and 42 is housed in the space between the heat sink 1 and the fan 12. Therefore, it is possible to cut no notches 31 or reduce the area of notches 31.
According to the heat sink disclosed, heat radiation efficiency can be improved in a limited space.
All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment(s) of the present invention has(have) been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.

Claims

1. A heat sink comprising:

a base;

a fin group including a plurality of fins arranged on the base at right angles to the base:

at least one U-shaped heat pipe both straight portions of which are arranged in parallel with the plurality of fins and which conducts heat from the base to the plurality of fins; and

a radiation plate which is placed on the fin group and which is thermally connected to the plurality of fins.

2. The heat sink according to claim 1, wherein:

notches the shape of which corresponds to a curve in the heat pipe are cut in part of the plurality of fins; and

the curve in the heat pipe is placed in the notches.

3. The heat sink according to claim 1, wherein the straight portions of the heat pipe are arranged at a determined angle with a longitudinal direction of each fin.

4. The heat sink according to claim 1, wherein:

the radiation plate has a groove corresponding to a straight portion of the heat pipe; and

the straight portion of the heat pipe is fitted into the groove.

5. The heat sink according to claim 1, wherein:

the base has a groove corresponding to a straight portion of the heat pipe; and

the straight portion of the heat pipe is fitted into the groove.