JP2013148289A - Flat heat pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a flat surface to which a heat-generating body is mounted, from being expanded and curved due to an increase in internal pressure in a flat heat pipe.SOLUTION: A flat heat pipe 2 includes: a pair of flat plates (top plate 3 and bottom plate 4) in which a surface of one of the flat plates is formed into a mounting surface for a heat-generating body; a side plate 5 that surrounds peripheries of the pair of flat plates facing each other and defines a closed space therein; and an elastic body 7 for coupling the pair of flat plates to each other in the closed space 6. In the heat pipe 2, the side plate 5 is expanded and contracted so as to allow a variation in distance between the pair of flat plates. The side plate 5 typically has a bellows structure. When an internal pressure is increased in the heat pipe 2, the bellows structure of the side plate allows the distance between the pair of flat plates to be extended while the pair of flat plates are supported by the elastic body 7, thus the heat pipe 2 can suppress center parts of the plat plates from being curved.

Description

  The technology disclosed in this specification relates to a flat plate heat pipe.

  A flat plate heat pipe may be used to cool the CPU and the semiconductor chip. A heat pipe is a device in which a small amount of hydraulic fluid is sealed in a sealed internal space and transports heat using the heat of vaporization and condensation of the hydraulic fluid. A heating element such as a CPU or a chip is attached to one surface of a flat plate heat pipe, and the other surface is cooled. If it does so, a hydraulic fluid will absorb the heat | fever of a heat generating body and vaporize on one side. The vaporized hydraulic fluid condenses and releases heat on the other side. Thus, heat is transported from one side to the other side. For convenience of explanation, a plate on a side where a heating element such as a CPU is attached to a plane opposite to the flat plate heat pipe may be referred to as a bottom plate, and a plate facing the bottom plate may be referred to as a top plate.

  The heat pipe has a simple structure, but various techniques have been proposed. For example, Patent Document 1 proposes a heat pipe having a bellows structure on the side surface and a shape like a lantern.

  On the other hand, since the flat heat pipe has a flat internal space, there is a possibility that the structural strength is lowered when the plate is thinned. In order to reinforce the structural strength of a flat plate-type heat pipe, techniques for disposing an elastic body inside are disclosed in Patent Document 2 and Patent Document 3, for example.

JP 2006-93700 A (FIG. 18, FIG. 19, paragraph 0068) JP 2011-009720 A JP 2004-077120 A

  It is surmised that the heat pipe having a bellows-structured side surface disclosed in Patent Document 1 has a thickness that is difficult to deform into a top plate and a bottom plate. In order to reduce the weight of the heat pipe, it is preferable to reduce the thickness of the top plate and the bottom plate. However, if the top plate and the bottom plate are thinned, the internal working fluid is vaporized, and if the internal pressure increases, the top plate and the bottom plate may be curved even if the side plate expands and contracts. If the region to which the heating element is attached is curved, the degree of contact with the heating element is lowered and the movement of heat is hindered. The present specification provides a technology for suppressing the expansion and bending of a flat surface on which a heating element is attached due to an increase in internal pressure in a flat plate heat pipe.

  The flat plate heat pipe disclosed in the present specification is a side plate that surrounds a pair of flat plates whose surface of one flat plate is a mounting surface of a heating element and a pair of opposed flat plates and forms a closed space inside. And the elastic body which connects a pair of flat plates in the closed space is provided. The heat pipe has a side plate made of an elastic member, and expands and contracts to allow a change in the distance between the pair of flat plates. The side plate typically has a bellows structure (bellows structure) that expands and contracts the distance between the pair of flat plates. In this flat plate type heat pipe, when the internal pressure increases, the distance between the pair of flat plates increases due to the bellows structure of the side plates, and the inner elastic body connects the pair of flat plates to each other, so that the central portion of the flat plate expands. Suppresses bending. The top plate and the bottom plate correspond to a pair of flat plates. Usually, the surface of the bottom plate (a plate located vertically below) serves as a mounting surface for the heating element (semiconductor element).

  It is the place where the heating element is attached that wants to suppress the curvature of the flat plate. Therefore, it is preferable that the elastic body is disposed so as to overlap with the heating element mounting scheduled position when the mounting surface is viewed in plan. The elastic body also plays a role of transferring heat between a pair of flat plates, like a so-called fin. Therefore, by disposing the elastic body so as to overlap the heating element, the heat transport efficiency between the opposing flat plates is improved.

  The heat pipe disclosed in the present specification is arranged around a plurality of first elastic bodies arranged so as to overlap with a heating element attachment planned position when the attachment surface is viewed in plan view. It is preferable that a plurality of second elastic bodies are provided, the rigidity of the first elastic body is lower than the rigidity of the second elastic body, and the distribution density of the first elastic body is higher than the distribution density of the second elastic body. As described above, the elastic body contributes to heat transfer between the flat plates. Therefore, it is preferable to arrange a plurality of elastic bodies so as to overlap the heating element. However, if a large number of elastic bodies are intensively arranged at a position overlapping with the heating element, there is a disadvantage that a large difference occurs in the stress generated in the plate material between the area where the elastic body is arranged and the surrounding area. Therefore, the first elastic body having low rigidity is disposed at a high density in the vicinity of the heating element, and the second elastic body having high rigidity is disposed at a low density around the first elastic body. By arranging two types of elastic bodies in such a manner, the heat transport force between the flat plates is improved in the vicinity of the heating element, and stress is prevented from being biased.

  Details of the technology disclosed in this specification and further improvements will be described in the embodiments of the present invention.

FIG. 1A is a plan view of the heat pipe of the first embodiment. FIG. 1B is a cross-sectional view taken along line BB in FIG. It is a top view of the heat pipe of 2nd Example.

  (First Embodiment) A heat pipe according to an embodiment will be described with reference to the drawings. FIG. 1 is a plan view and a cross-sectional view of the heat pipe 2. The heat pipe 2 has a casing constituted by a pair of opposing flat plates, a top plate 3 and a bottom plate 4, and a side plate 5 surrounding them. The surface of the bottom plate 4 (the lower surface of the heat pipe 2 in FIG. 1) is a mounting surface for the heating element 90. In FIG. 1, the heating element 90 is drawn with imaginary lines. The heating element 90 is, for example, a package (chip) on which a power semiconductor element such as an IGBT is mounted. In FIG. 1, a cable (lead wire) connecting semiconductor elements is not shown. The side plate 5 connects the opposing top plate 3 and bottom plate 4 and surrounds them to form a closed space 6 therein. The side plate 5 has an expandable / contractible bellows structure so as to allow a change in the distance between the top plate 3 and the bottom plate 4 to be connected. A plurality of springs 7 that connect the top plate 3 and the bottom plate 4 are disposed in the closed space 6. The spring 7 is a coil spring.

  The top plate 3, the bottom plate 4, and the side plate 5 are made of a metal having high thermal conductivity such as copper or aluminum. The bellows-like side plate 5 is made, for example, by press working. The spring 7 is made of a steel material having high rigidity.

  The function of the heat pipe 2 will be described. During production, the closed space 6 is evacuated and a small amount of hydraulic fluid is enclosed. The working fluid is an inert or non-corrosive liquid such as water or ammonia. As described above, the heating element 90 such as a transistor element is attached to the surface of the bottom plate 4. The hydraulic fluid is vaporized by the heat of the heating element 90. The vaporized gas rises and touches the top board 3. The gas touching the top plate 3 is cooled and condensed, returns to the liquid, and returns to the bottom plate 4 by gravity. It absorbs the heat of vaporization when the working fluid vaporizes, and releases the heat of condensation when it returns to the liquid. Thus, heat is transported from the bottom plate 4 to the top plate 3 by the hydraulic fluid. Therefore, although the ceiling plate 3 can be expected to have a certain cooling effect only by touching the outside air, it is preferable that the top plate 3 is in contact with some cooler.

  Further, the spring 7 functions as a heat bridge, and heat is transferred from the bottom plate 4 to the top plate 3. That is, the spring 7 also contributes to heat transport. In particular, as shown in FIG. 1, the spring 7 is arranged so as to overlap with a position where the heating element 90 is to be attached (portion drawn with a virtual line in FIG. 1) when viewed in plan. That is, the spring 7 is disposed at a position where the heat of the heating element 90 is easily received. Such an arrangement increases the contribution of the spring 7 to heat transport as a heat bridge. Note that the spring 7 may be partially overlapped with the heating element mounting scheduled position when viewed in plan. Further, when the heat pipe 2 includes a plurality of springs 7, it is not always necessary that all the springs overlap with the planned mounting positions.

  Another advantage of the heat pipe 2 will be described. The heat pipe 2 includes a side plate 5 having a bellows structure and a spring 7. As well shown in FIG. 1B, the heat pipe 2 has a structure in which the top plate 3 and the bottom plate 4 are connected only by an elastic body. Therefore, when the internal pressure is increased, neither the top plate 3 nor the bottom plate 4 is curved so much that the distance between them increases while maintaining a flat surface. Therefore, since the curvature of the mounting surface of the heating element 90 is suppressed, the degree of adhesion between the heating element 90 and the bottom plate 4 is maintained. As a result, the heat transfer efficiency from the heating element 90 to the bottom plate 4 does not decrease.

  (Second Embodiment) FIG. 2 is a plan view of a heat pipe 2a of the second embodiment. The heat pipe 2a has two types of springs disposed therein. One is the first spring 7a arranged so as to overlap with the mounting position of the heating element 90 when viewed in plan. The first spring 7a is the same as the spring 7 in the heat pipe 2 of the first embodiment. The other one is a second spring 7b disposed around the first spring 7a so as to surround it. Similar to the heat pipe 2 of the first embodiment, the first spring 7a and the second spring 7b connect the top plate 3 and the bottom plate 4 inside the heat pipe. The other structure is the same as that of the heat pipe 2 of the first embodiment. That is, in the heat pipe 2a of the second embodiment, the side plate 5 has a bellows structure and expands and contracts to allow a change in the distance between the top plate 3 and the bottom plate 4.

  The rigidity of the second spring 7b is higher than the rigidity of the first spring 7a. As well shown in FIG. 2, the five first springs 7a are arranged in a region of area S1 = L1 × L2. The four second springs 7b are arranged in a region of area S2 = L3 × L4. Obviously S1 <S2. That is, the distribution density of the first springs 7a is higher than the distribution density of the second springs 7b. Eventually, the first spring 7a is less rigid than the second spring 7b, but has a higher distribution density. Therefore, the total rigidity per unit area of the plurality of first springs 7a is substantially the same as the total rigidity of the plurality of second springs 7b per unit area. Therefore, when the distance between the top plate 3 and the bottom plate 4 expands, each of the top plate 3 and the bottom plate 4 receives a substantially uniform load over the entire surface. Therefore, the top plate 3 and the bottom plate 4 are unlikely to be bent when the distance between the plates increases. As a result, a decrease in adhesion between the heating element 90 and the bottom plate 4 is suppressed. That is, a decrease in cooling capacity is suppressed.

  Points to be noted regarding the technology of the embodiment will be described. The elastic body installed in the housing of the heat pipe is not limited to the coil spring, but may be a leaf spring. Alternatively, the elastic body may be made of a material having elasticity such as rubber. The number of elastic bodies provided inside the heat pipe is not limited to the case of the embodiment. One elastic body may be provided inside. In the drawing of the embodiment, one heating element 90 is illustrated for one heat pipe, but the number of heating elements attached to the heat pipe is not limited to one. The shape of the heat pipe when viewed from above is not limited to a rectangle. It may be circular, elliptical or polygonal.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

2, 2a: Heat pipe 3: Top plate 4: Bottom plate 5: Side plates 7, 7a, 7b: Spring

Claims (4)

A pair of flat plates in which the surface of one flat plate is a mounting surface of the heating element;
A side plate surrounding a pair of opposing flat plates and forming a closed space inside;
An elastic body connecting a pair of flat plates in the closed space;
A flat plate-type heat pipe, wherein the side plate expands and contracts to allow a change in the distance between the pair of flat plates.   The flat plate heat pipe according to claim 1, wherein the side plate has a bellows structure.   The flat plate-type heat pipe according to claim 1 or 2, wherein the elastic body is disposed so as to overlap with a position where the heating element is to be attached when the attachment surface is viewed in plan. A plurality of first elastic bodies arranged so as to overlap with a planned mounting position of the heating element when the mounting surface is viewed in plan;
A plurality of second elastic bodies arranged around the first elastic body;
With
The flat plate type according to claim 1 or 2, wherein the rigidity of the first elastic body is lower than the rigidity of the second elastic body, and the distribution density of the first elastic body is higher than the distribution density of the second elastic body. heat pipe.

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