US20120080171A1

US20120080171A1 - Heat relay mechanism and heat-dissipating fin unit

Info

Publication number: US20120080171A1
Application number: US13/225,883
Authority: US
Inventors: Kenichi Uesugi; Yoshihisa Nakagawa; Toshimitsu Kobayashi; Hideki Sonobe; Atsushi Kaneko
Original assignee: Fujitsu Ltd
Current assignee: Fujitsu Ltd
Priority date: 2010-09-30
Filing date: 2011-09-06
Publication date: 2012-04-05
Also published as: JP2012077988A

Abstract

A heat relay mechanism includes a heat-dissipating member for dissipating heat, a buffer member contacted with the heat-dissipating member at a first surface, a thermally deformable member connected to a second surface of the buffer member and deforms at a high temperature, a heat pipe connected to the thermally deformable member at one end, and a device connected to another end of the heat pipe.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2010-222930 filed on Sep. 30, 2010, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments disclosed herein are related to a heat relay mechanism that relays heat generated inside an apparatus and to a heat-dissipating fin unit provided with the heat relay mechanism.

BACKGROUND

With recent-year demands for higher performance and smaller installation spaces, apparatuses to be installed outdoors, such as a mobile communications base station, have problems relating to heat generated thereinside. If the packing density of a circuit is increased for higher performance and space-saving, the amount of heat generated from devices included in the circuit increases correspondingly. Furthermore, such an apparatus has a reduced space thereinside and easily becomes filled with the heat generated from the devices. Therefore, the devices are provided with heat-dissipating fins as means for dissipating heat generated inside the apparatus to the outside, whereby the heat generated from the devices is dissipated. Some apparatuses include heat pipes functioning as heat-transporting elements through which heat from the heat-dissipating fins is conducted to casings of the apparatuses, and the heat is further dissipated from the casings to the outside.
The amount of heat transportable through a heat pipe is determined by the radius of the pipe. If the radius of the pipe is increased, the size of the apparatus tends to increase correspondingly. Therefore, it is desirable to increase the heat transport capacity without changing the radius of the heat pipe. In this respect, there is a known technique of increasing the heat transport capacity by applying an organic substance to the inner surface of a heat pipe so as to increase the wettability.
Apparatuses to be installed outdoors may be exposed to environments near the equator and in the desert, for example, with large amounts of sunlight and at high ambient temperatures. Therefore, circuits provided in such apparatuses are desired to operate even at, for example, 55° C. In this respect, sunshades or cooling fans may be added to the apparatuses so as to cool the insides of the apparatuses. Nevertheless, the sunshades may prevent smooth dissipation of heat generated from the apparatuses themselves. Meanwhile, the addition of cooling fans leads to additional power consumption. Moreover, there arise problems such as noise generated by the operation of the fans and the warranty periods of bearings of the fans.
The followings are reference documents.

[Document 1] Japanese Laid-open Patent Publication No. 2006-189239.

SUMMARY

According to an aspect of the embodiment, a heat relay mechanism includes a heat-dissipating member for dissipating heat, a buffer member contacted with the heat-dissipating member at a first surface, a thermally deformable member connected to a second surface of the buffer member and deforms at a high temperature, a heat pipe connected to the thermally deformable member at one end, and a device connected to another end of the heat pipe.
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 illustrates a heat relay mechanism;

FIGS. 2A and 2B illustrate the principle of operation of the heat relay mechanism;

FIGS. 3A to 3C illustrate a method of manufacturing a buffer sheet;

FIGS. 4A to 4C illustrate methods of attaching different kinds of buffer sheets, respectively, to a heat relay component;

FIGS. 5A and 5B illustrate an effect provided by the buffer sheet;

FIG. 6 illustrates the heat relay mechanism provided in a mobile communications base station; and

FIGS. 7A and 7B illustrate the state of connection between the heat relay mechanism and a heat-dissipating fin unit.

DESCRIPTION OF EMBODIMENTS

A preferred embodiment of a technique according to the present disclosure will now be described in detail with reference to the accompanying drawings.
FIG. 1 illustrates a heat relay mechanism provided in an apparatus, such as a mobile communications base station, to which the technique according to the present disclosure is applied. An apparatus casing 1 houses a power semiconductor device (not illustrated), such as a laterally diffused metal-oxide semiconductor (LDMOS) or a gallium-nitride (GaN) semiconductor, that is typically employed in power amplifier circuits included in mobile phone base stations based on MOS, and the like. Since the power semiconductor device generates a large amount of heat, the power semiconductor device is provided with a heat-dissipating fin unit 2 with a fin-side heat pipe 20 interposed therebetween. The heat-dissipating fin unit 2 is made of metal, such as copper or aluminum, having a high thermal conductivity. The fin-side heat pipe 20 is in contact with a plate-like thermally deformable component 3 that is deformable with heat. The thermally deformable component 3 is bimetal, shape-memory plastic, or the like.
The thermally deformable component 3 is provided on one side thereof with a buffer sheet 4. The buffer sheet 4 is pasted on a contact portion of the thermally deformable component 3 that is in contact with the fin-side heat pipe 20. Heat of the fin-side heat pipe 20 is temporarily stored in the buffer sheet 4 and is subsequently conducted to the thermally deformable component 3. The buffer sheet 4 is a commercially available thermal sheet or a sheet member made of a polymer material having a higher thermal resistance than the thermal sheet. One end of the thermally deformable component 3 opposite the contact portion is fixed to the apparatus casing 1 with a first block 61. The block 61 functions as a point of support when the thermally deformable component 3 deforms with heat.
The block 61 is provided with a heat pipe 5 fixed to one side thereof opposite the side on which the thermally deformable component 3 is fixed. The heat pipe 5 is filled with a liquid heat carrier and includes thereinside a wick (capillary) structure. In the heat pipe 5, when heat is input to an evaporator portion, the liquid heat carrier evaporates and moves to a condenser portion, where the evaporated heat carrier is condensed and liquefied; the liquefied heat carrier flows back to the evaporator portion by capillary action caused by the wick structure. The heat inputted to the evaporator portion is dissipated as a thermal output from the condenser portion. One end of the heat pipe 5 opposite the end fixed to the block 61 is fixed to the apparatus casing 1 with a second block 62. The block 62 has one side surface thereof being in contact with a device 7.
The device 7 is a memory device or a general-purpose large-scale integrated circuit (LSI) whose guaranteed operating temperature range is 0° C. to 70° C. The device 7 does not operate stably at temperatures below 0° C. The device 7 is the target of the heat relay mechanism. That is, the heat relay mechanism allows the device 7 to operate at a temperature within the guaranteed operating temperature range.
Referring now to FIGS. 2A and 2B, the principle of operation of the technique according to the present disclosure will be described. FIG. 2A illustrates a state of the heat relay mechanism at the time of startup of the apparatus or when there is no temperature rise inside the apparatus casing 1. In this state, the plate-like thermally deformable component 3 has the initial shape; that is, the thermally deformable component 3 is fixed to the block 61 in such a manner as to be parallel to the fin-side heat pipe 20. The buffer sheet 4 at the end of the thermally deformable component 3 is closely in contact with the fin-side heat pipe 20 in such a manner as to be pressed against the fin-side heat pipe 20 by the plate-like thermally deformable component 3. Therefore, the heat of the fin-side heat pipe 20 is efficiently conducted into the buffer sheet 4.
When the entirety of the buffer sheet 4 is warmed up, the heat is conducted to the thermally deformable component 3 that is in contact with one side of the buffer sheet 4 opposite the side that is in contact with the fin-side heat pipe 20. Subsequently, the heat is conducted through the thermally deformable component 3 to the block 61, and is further conducted through the heat pipe 5 to the block 62. Ultimately, the heat generated from the power semiconductor device is conducted to the device 7 that is in contact with the block 62. Thus, even if the apparatus is installed in an environment at a temperature below 0° C. and the device 7 does not operate stably at the time of startup of the apparatus, the heat from the power semiconductor device, such as an amplifier component, that generates a large amount of heat is conducted to the device 7 and warms up the device 7 to a temperature within the guaranteed operating temperature range. Therefore, the time period before the operation of the apparatus is stabilized is shortened.
FIG. 2B illustrates another state of the heat relay mechanism after a certain period of time has elapsed from the startup of the apparatus and the temperature inside the apparatus casing 1 has risen to a sufficient level. When the temperatures of heat-generating components further rise from those in the state illustrated in FIG. 2A and the temperature inside the apparatus casing 1 rises correspondingly, the plate-like thermally deformable component 3 gradually warps toward the right side of FIG. 2B, i.e., in a direction away from the fin-side heat pipe 20.
The thermally deformable component 3 is a bimetal member in which a NiFe member and a NiMnFe member are bonded together, or a trimetal member in which a NiMnFe member, a Cu member, and a NiFe member are bonded together. Since the metal members bonded together have different coefficients of thermal expansion, when the temperature rises, the plate-like thermally deformable component 3 warps. Along with the warping of the thermally deformable component 3, the buffer sheet 4 that has been in surface contact with the fin-side heat pipe 20 is gradually separated from the fin-side heat pipe 20, and the heat conduction to the device 7 is stopped.
Typically, the guaranteed operating temperature ranges of memory devices and general-purpose LSIs range from 0° C. to 70° C. Such devices do not operate at temperatures below 0° C. and do not operate stably at high temperatures. Therefore, the thermally deformable component 3 functions as a switch for cutting off the path for supplying the heat generated from the power semiconductor device to the device 7. Thus, the device 7 is prevented from being excessively heated. Although the heat conduction to the device 7 is cut off halfway, there is no problem because the heat from the power semiconductor device is continued to be dissipated to the outside of the apparatus through the fin-side heat pipe 20 and the heat-dissipating fin unit 2.
Referring now to FIGS. 3A to 3C, a method of manufacturing the buffer sheet 4 will be described. First, a thermal sheet 41 of a predetermined size is prepared. The thermal sheet 41 is made of a material based on acrylic rubber having excellent thermal conductivity. Subsequently, as illustrated in FIG. 3A, a part of the surface of the thermal sheet 41 is scraped off such that a cavity 42 is provided. Subsequently, as illustrated in FIG. 3B, the cavity 42 is filled with a silicon compound 43 that is softer than the thermal sheet 41. Subsequently, as illustrated in FIG. 3C, a thin film 44 is provided on one side of the thermal sheet 41 opposite the side having the silicon compound 43.
The thin film 44 may be formed by vapor deposition or plating of metal, such as Al, having a high heat conductivity. Alternatively, the thin film 44 may be a graphite sheet. To maintain the flexibility, the thin film 44 desirably has a thickness of about 0.5 mm or smaller. If the thin film 44 is not provided, the surface of the thermal sheet 41 having the silicon compound 43 may melt with the high temperature of the fin-side heat pipe 20 and may stick to the fin-side heat pipe 20. The thin film 44 made of metal, graphite, or the like provided on the buffer sheet 4 provides an effect of preventing the buffer sheet 4 from thermally adhering to the fin-side heat pipe 20 and an effect of evening out the heat from the fin-side heat pipe 20 over the entirety of the surface of contact with the fin-side heat pipe 20. As a substitute for the buffer sheet 4, a gel pack filled with a liquid such as Fluorinert (trademark) provides the same effects. Thus, the amount of thermal input to the thermally deformable component 3 is temporarily reduced, and the thermal shock applied to the device 7 to which the heat is relayed is reduced.
Referring now to FIGS. 4A to 4C, a method and effects of pasting the buffer sheet 4 onto the thermally deformable component 3 will be described. FIG. 4A illustrates a case where the thermal sheet 41 having the thin film 44 is pasted onto the thermally deformable component 3 with adhesive or the like. In this case, the thermal sheet 41 does not have the silicon compound 43. Therefore, the thermal sheet 41 having the thin film 44 only provides a physical buffering effect.
FIG. 4B illustrates a case where the buffer sheet 4 including the thermal sheet 41 having the silicon compound 43 and the thin film 44 as illustrated in FIGS. 3A to 3C is pasted onto the thermally deformable component 3 with adhesive or the like. In this case, the buffer sheet 4 provides thermal and physical buffering effects. In addition, a force that deforms the buffer sheet 4 held between the thermally deformable component 3 and the fin-side heat pipe 20 is absorbed by the silicon compound 43.
FIG. 4C illustrates a case where the buffer sheet 4 illustrated in FIG. 4B is pasted onto the thermally deformable component 3 with adhesive or the like while a metal sheet 45 is interposed therebetween. The metal sheet 45 is made of a material having a high thermal conductivity, such as copper. Since the thermally deformable component 3 is also metal, specifically, a bimetal member, the metal sheet 45 and the thermally deformable component 3 are bonded together by soldering or with adhesive or the like. In this case, as in the case illustrated in FIG. 4B, the buffer sheet 4 provides thermal and physical buffering effects, and the force that deforms the buffer sheet 4 held between the thermally deformable component 3 and the fin-side heat pipe 20 is absorbed by the silicon compound 43. The metal sheet 45 is processed after the thermal sheet 41 is pasted onto the thermally deformable component 3. When the silicon compound 43 is supplied into the thermal sheet 41 in obtaining the buffer sheet 4, the metal sheet 45 functions as a base.
Referring now to FIGS. 5A and 5B, the effects provided by the buffer sheet 4 will be described. FIGS. 5A and 5B illustrate the buffer sheet 4 and the fin-side heat pipe 20 in the states illustrated in FIGS. 2A and 2B, respectively, seen from the lower side of FIGS. 2A and 2B. FIG. 2A illustrates the state of the heat relay mechanism at the time of startup of the apparatus or when there is no temperature rise inside the apparatus casing 1. In this state, the plate-like thermally deformable component 3 has the initial shape and is parallel to the fin-side heat pipe 20. In this state, the distance between the thermally deformable component 3 and the fin-side heat pipe 20 is shorter than the original thickness of the buffer sheet 4.
Therefore, as illustrated in FIG. 5A, the buffer sheet 4 is deformed by being squashed between the thermally deformable component 3 and the fin-side heat pipe 20. The surface of the buffer sheet 4 that is in contact with the fin-side heat pipe 20 has an area larger than the original because the buffer sheet 4 is squashed. Therefore, the heat of the fin-side heat pipe 20 rapidly conducts into the buffer sheet 4. Accordingly, the temperature of the buffer sheet 4 itself, which is not so high at this time, rapidly rises. Consequently, the heat is quickly conducted to the device 7 through the heat relay mechanism including the buffer sheet 4, the thermally deformable component 3, the block 61, the heat pipe 5, and the block 62.
As described above referring to FIG. 2B, when the temperature inside the apparatus casing 1 gradually rises after the startup of the apparatus, the plate-like thermally deformable component 3 gradually warps toward the right side of FIG. 2B, i.e., in the direction away from the fin-side heat pipe 20, and the distance between the thermally deformable component 3 and the fin-side heat pipe 20 increases correspondingly.
Consequently, the buffer sheet 4 that has been squashed gradually restores the original shape, and the area of the surface of the buffer sheet 4 that is in contact with the fin-side heat pipe 20 is gradually reduced. Accordingly, the amount of heat conducted from the fin-side heat pipe 20 to the buffer sheet 4 is gradually reduced. Compared with the state at the time of startup, the buffer sheet 4 at this time is sufficiently warmed up. Therefore, the heat continues to be conducted in the heat relay mechanism.
When the heat conduction further continues and the thermally deformable component 3 further warps, the buffer sheet 4 is completely spaced apart from the fin-side heat pipe 20 as illustrated in FIG. 5B. In this state, the buffer sheet 4 still has some heat. Therefore, the buffer sheet 4 is maintained to be spaced apart from the fin-side heat pipe 20. Subsequently, when the temperature of the thermally deformable component 3 drops and the warpage of the thermally deformable component 3 is reduced, the buffer sheet 4 may come into contact with the fin-side heat pipe 20 again. Nevertheless, the buffer sheet 4 exerts the thermal buffering effect and does not repeatedly come into contact with and move away from the fin-side heat pipe 20.
FIG. 6 and FIGS. 7A and 7B illustrate the heat relay mechanism, described above, provided in a mobile communications base station 10. FIG. 6 is a perspective view illustrating the inside of the mobile communications base station 10 seen through from a side on which the heat-dissipating fin unit 2 is provided. The thermally deformable component 3 is fixed to the top of the casing of the mobile communications base station 10 with the block 61. A power semiconductor device (not illustrated), which is a heat-generating component, is in contact with a lower part of the fin-side heat pipe 20 provided on the near side of FIG. 6.
FIG. 7A illustrates the heat-dissipating fin unit 2 seen from a side on which the casing of the mobile communications base station 10 is provided. FIG. 7B is an enlarged view of a part of the heat-dissipating fin unit 2 illustrated in FIG. 7A on which the heat relay mechanism is provided. The heat-dissipating fin unit 2 is provided on one side thereof with a plurality of fin-side heat pipes 20. Heat of the power semiconductor device, which is a heat-generating component, is conducted through the fin-side heat pipes 20 to the heat-dissipating fin unit 2 and is dissipated from the heat-dissipating fin unit 2.
Referring to FIG. 6, the thermally deformable component 3 is provided with the buffer sheet 4 at a part thereof near a bend in one of the fin-side heat pipes 20. The heat pipe 5 extending from the block 61 runs inside the mobile communications base station 10, and the distal end thereof is in contact with the device 7 (not illustrated) that do not operate stably at temperatures below 0° C. Thus, heat generated from the heat-generating component provided in the mobile communications base station 10 is dissipated from the heat-dissipating fin unit 2 while being conducted through the heat relay mechanism to the device 7 that do not operate stably at temperatures below 0° C.
The configuration of the heat relay mechanism has been described as above. Now, a technique of increasing the efficiency of the heat relay mechanism, i.e., a technique of increasing the thermal conductivities of the fin-side heat pipe 20 and the heat pipe 5, will be described. To increase the performance of the heat pipes 20 and 5, it may be considered to change the surface of the wick (capillary) structure provided in each heat pipe to a hydrophilic surface. Specifically, the inner and outer surfaces of the heat pipe is decorated with a self-assembled monolayer (SAM). The SAM may be provided on various kinds of solid surfaces, making the surfaces hydrophilic, hydrophobic, biocompatible, or the like. Exemplary SAMs suitable for decoration for obtaining a hydrophilic surface include 11-mercapto undecanoic acid. By decorating the inner and outer surfaces of the heat pipe, the surface tension of the inner surface of the heat pipe, which is copper or the like, increases, whereby the capillary force of the wick structure increases. Consequently, the heat transport capacity of the heat pipe increases.
By giving the above surface decoration to the heat-dissipating fin unit 2, it is expected that the fin-side heat pipes 20 may be soldered to the heat-dissipating fin unit 2 without performing nickel plating on the heat-dissipating fin unit 2, which is necessary in related-art techniques. By decorating an aluminum member that is to become the heat-dissipating fin unit 2 with the SAM mentioned above, the surface tension of the aluminum member increases, and solder becomes easier to spread over the surface of the aluminum member than on a surface that is not decorated with the SAM. Since the area of contact between the aluminum member and the solder increases, the adhesion therebetween increases correspondingly. Thus, it becomes possible to solder the fin-side heat pipe 20 to the aluminum member without performing the nickel plating.
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 embodiments of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.

Claims

1. A heat relay mechanism comprising:

a heat-dissipating member for dissipating heat;

a buffer member contacted with the heat-dissipating member at a first surface;

a thermally deformable member connected to a second surface of the buffer member and deforms at a high temperature;

a heat pipe connected to the thermally deformable member at one end; and

a device connected to another end of the heat pipe.

2. The heat relay mechanism according to claim 1, wherein the thermally deformable member is a plate-like member that deforms with a rise of temperature in such a manner as to bend toward one side.

3. The heat relay mechanism according to claim 1, wherein the buffer member is a thermal sheet in which silicon rubber is provided, the buffer member being provided with a thin metal film on the first surface thereof.

4. The heat relay mechanism according to claim 1, wherein the heat-dissipating member is a second heat pipe and conducts heat of a heat-generating element.

5. The heat relay mechanism according to claim 1, wherein the thermally deformable member is a bimetal or trimetal member in which plate-like metal members having different coefficients of thermal expansion are bonded together.

6. A heat-dissipating fin unit comprising:

a first heat pipe;

a buffer member contacted with the first heat pipe at a first face;

a thermally deformable member connected to a second surface of the buffer member and deforms at a high temperature; and

a second heat pipe connected to the thermally deformable member at one end.