JP2005077052A - Flat heat pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flat heat pipe capable of efficiently cooling a heating element such as semiconductor chip or integrated circuit board with a reduced thickness. <P>SOLUTION: This flat heat pipe comprises a casing formed of an upper plate and a bottom plate constituted by thin plates of a composite body of graphite and metal, at least one of the upper plate and the bottom plate being grooved, and a working fluid sealed in the grooves within the casing. The upper plate and the bottom plate of the casing are desirably composed of a composite body of graphite and metal having a heat conductivity of 100W/mK or more and a thermal expansion coefficient of 0.1 ppm/K or more and 15 ppm/K or less. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a planar heat pipe used for cooling a heating element such as a semiconductor element or an integrated circuit substrate.

  In recent electronic devices, high output and highly integrated parts such as a microprocessor are incorporated. Microprocessors are highly integrated and emit large amounts of heat for high-speed processing. Therefore, various cooling systems have been proposed to cool high-power, highly integrated chips and the like. One of them is a heat pipe. The heat pipe includes a round pipe-shaped heat pipe and a planar heat pipe. For cooling electronic devices, flat heat pipes are preferably used for convenience of mounting on the parts to be cooled. A space serving as a flow path for the working fluid is provided inside the heat pipe, and the working fluid accommodated in the space undergoes a phase change or movement such as evaporation or condensation, thereby transferring heat.

  The details of the heat pipe including a sealed cavity and in which heat is transferred by the phase transformation and movement of the working fluid contained in the cavity are as follows. On the heat absorption side of the heat pipe, the working fluid evaporates due to the heat generated by the parts to be cooled, such as semiconductor elements and integrated circuit boards, which are conducted through the material of the container constituting the heat pipe, and the vapor is heated. Move to the heat dissipation side of the pipe. On the heat radiating side, the working fluid vapor is cooled and returned to the liquid phase again. The working fluid that has returned to the liquid phase in this way moves (refluxs) again to the heat absorption side. Heat is transferred by such phase transformation and movement of the working fluid. In a gravity heat pipe, the working fluid that has become a liquid phase by phase transformation moves (refluxs) to the heat absorption side by gravity or capillary action.

  Conventional flat heat pipes are generally extruded materials made of aluminum, copper or the like. Further, the working fluid includes water, alternative chlorofluorocarbon, acetone, methanol, and the like, and is selected according to the use temperature. In addition, the heat pipe is usually kept airtight.

  In the conventional flat type heat pipe using extruded material, a wire as a wick is inserted into each hole of the extruded material, and a capillary force is applied to the part where the tube wall and the wire come into contact, so that the heat pipe operates horizontally. And allows reverse operation.

The biggest issue in semiconductor cooling technology using heat pipes is improving the cooling performance. As a means for solving this problem, a device for improving the contact with the semiconductor by taking advantage of the shape of the heat pipe, such as flattening, is used.
Patent Document 1 proposes a planar heat pipe in which two aluminum plates are brazed so as to form a heat transfer circuit between them and sealed with a working fluid.
Patent Document 2 proposes a flat plate heat pipe made of a metal such as aluminum.
Patent Document 3 proposes a small-diameter tunnel plate heat pipe by extrusion molding of an aluminum-based / magnesium-based alloy.
However, in any case, the material constituting the heat pipe is a metal material such as aluminum, magnesium, or copper having a large coefficient of thermal expansion, and it is difficult to directly join the semiconductor element or the ceramic circuit board as the component to be cooled.

Japanese Patent No. 3164518 JP 2000-146470 A JP 2001-241870 A

  Therefore, the conventional flat type heat pipe using the extruded material made of copper, aluminum, magnesium or an alloy thereof has the following problems. That is, the above-described conventional planar heat pipe is made of copper, aluminum, magnesium, or an alloy thereof, and thus has a large coefficient of thermal expansion and a large difference from the coefficient of thermal expansion of a component to be cooled such as a semiconductor element or an integrated circuit board. For this reason, the heat pipe and the component to be cooled perform heat transfer via grease or a graphite sheet. However, the thermal conductivity in the thickness direction of the grease and the graphite sheet is as low as 10 W / mK or less, and in particular, in the case of the graphite sheet, the intervention of the air layer cannot be avoided. Therefore, there has been a fatal problem that good heat transfer from the part to be cooled to the heat pipe is not possible.

  Furthermore, copper, aluminum, etc. are inferior in machinability, and the conventional flat heat pipe is mainly made of an extruded material, and it takes time to perform complicated machining.

  Therefore, an object of the present invention is to efficiently cool a heating element such as a semiconductor chip or an integrated circuit substrate, to perform various machining processes, and to provide a planar heat pipe that is reliable in its operation. It is to provide.

  The present inventor has intensively studied to solve the conventional problems described above. As a result, by using a casing made of a composite of graphite and metal, it is possible to efficiently cool heating elements such as notebook PCs, semiconductor chips incorporated in various electronic devices, integrated circuit boards, etc. It has been found that it is possible to provide a flat heat pipe having a small thickness and a thin thickness that can be easily manufactured by various machining processes.

  In the present invention, a groove is formed on a thin plate constituting at least one of the upper plate and the bottom plate, or a groove is formed on the casing made of a thin plate made of a composite of graphite and metal. A planar heat pipe characterized in that a passage groove is formed in the housing by sandwiching another thin plate made of a composite of graphite and metal, and a working fluid is sealed in the groove of the passage. It is.

  In the planar heat pipe of the present invention, the top plate and the bottom plate of the housing have a thermal conductivity of 5 W / mK or more and 2000 W / mK or less, a thermal expansion coefficient of 0.1 ppm / K or more and 15 ppm / K or less. It consists of a composite of graphite and metal having anisotropy in thermal conductivity and thermal expansion coefficient. Further, it is desirable to use a composite of graphite and metal obtained by heat-treating a high thermal conductivity / low thermal expansion composite material obtained by impregnating a porous graphitized extrudate with metal, and having a thermal conductivity of 250 in the extrusion direction. The coefficient of thermal expansion is 10 ppm / K or less at W / mK or more and 10 ppm / K or less (thinking that it is necessary to narrow at this stage) is less than 4 ppm / K, and the thermal conductivity in the direction perpendicular to the extrusion direction is 150 W / m A composite having a thermal expansion coefficient of 10 ppm / K or less at mK or higher is desirable.

  The flat heat pipe of the present invention is characterized in that a groove formed in at least one of an upper plate and a bottom plate made of a thin plate made of a composite of graphite and metal forms a loop. is there.

  The planar heat pipe of the present invention is characterized in that a groove formed in at least one of an upper plate and a bottom plate made of a thin plate made of the graphite and metal composite has a comb-tooth shape.

  In the planar heat pipe of the present invention, a comb-like groove is formed on the top plate and the bottom plate made of a thin plate made of a composite of graphite and metal, and the comb teeth are alternately combined into a meandering shape. It is a feature.

  The flat heat pipe of the present invention is characterized in that the casing has a thickness of 20 mm or less.

  The flat type heat pipe of the present invention is a case in which a metal layer is formed on at least a joining portion of an upper plate and a bottom plate made of a thin plate made of a composite of graphite and a metal, and the upper plate and the bottom plate are metal-bonded. It is characterized by being.

  The planar heat pipe according to the present invention further includes a heat sink having a required shape outside the casing.

  The planar heat pipe of the present invention is characterized in that the casing and the semiconductor element and / or the integrated circuit board are metal-bonded.

  According to the present invention, it is possible to provide a planar heat pipe with a thin heat pipe having a small coefficient of thermal expansion and a reliable operation, and cooling a heating element such as a semiconductor chip or an integrated circuit board. It is effective to do.

  The aspect of the planar heat pipe of the present invention will be described in detail. In the flat heat pipe according to the present invention, a groove is formed in a casing composed of a top plate and a bottom plate made of a thin plate made of a composite of graphite and metal, and a thin plate constituting at least one of the top plate and the bottom plate. Or by sandwiching another thin plate made of a composite of graphite and metal with a groove formed therein, a passage groove is formed in the housing, and a working fluid is sealed in the groove of the passage. To do.

  At this time, the graphite / metal composite includes a graphite copper composite, a graphite aluminum composite, a graphite brass composite, a graphite copper alloy composite, a graphite aluminum alloy composite, and the like. Among these, a graphite aluminum alloy composite is more preferable. As the working fluid, water, alternative chlorofluorocarbon, acetone, methanol, helium, nitrogen, ammonia and the like can be used as in the conventional case.

  The graphite / metal composite used in the present invention may be any composite having a thermal conductivity of 5 W / mK or more and 2000 W / mK or less and a thermal expansion coefficient of 0.1 ppm / K or more and 15 ppm / K or less. The thermal conductivity is more preferably 150 W / mK or more, still more preferably 200 W / mK or more, and the thermal expansion coefficient is more preferably 1 to 10 ppm / K, still more preferably 3 to 7 ppm / K. This composite desirably has anisotropy in thermal conductivity and thermal expansion coefficient. That is, since it has a structure in which a metal with high thermal conductivity is pressure-infiltrated into the pores of the porous graphitized extruded product, it has a significantly higher thermal conductivity than graphite. Further, the graphite skeleton itself is made of an extruded product and has anisotropy, so that there is a difference in thermal conductivity between the extrusion direction and the orthogonal direction. The thermal conductivity of the porous graphitized extrudate itself is 150 W / mK or more in the extrusion direction and 80 W / mK or more in the orthogonal direction. Therefore, regardless of the type of metal to be impregnated, the thermal conductivity of the composite material is 250 W / mK or more in the extrusion direction, and can exhibit a thermal conductivity of 150 W / mK or more in the orthogonal direction. Furthermore, the thermal conductivity of this composite material is further improved by heat treatment. On the other hand, since the skeleton is made of a porous graphitized extruded product, the overall thermal expansion coefficient is close to that of graphite. Further, since the graphite skeleton is made of an extruded product, there is a difference in the coefficient of thermal expansion between the extrusion direction and the orthogonal direction. The coefficient of thermal expansion of the porous graphitized extruded product itself is 3.0 ppm / K or less in the extrusion direction and 4.0 ppm / K or less in the orthogonal direction. Therefore, although it differs somewhat depending on the type of metal to be impregnated, the thermal expansion coefficient of the composite material can be achieved at 10 ppm / K or less, particularly less than 4.0 ppm / K in the extrusion direction, and in the orthogonal direction, it is 10 ppm / K at all. It is preferable that a low thermal expansion coefficient of K or less can be exhibited. Furthermore, the thermal expansion coefficient of this composite material is further reduced by heat treatment. In this way, anisotropy can be provided in the thermal conductivity and the thermal expansion coefficient.

As described above, the composite of graphite and metal has, for example, a thermal conductivity in the extrusion direction of 200 W / mK or more, more preferably 250 W / mK or more, and a thermal expansion coefficient of less than 4 ppm / K, which is orthogonal to the extrusion direction. A high thermal conductivity / low thermal expansion composite material having a thermal conductivity of 100 W / mK or more, more preferably 150 W / mK or more and a thermal expansion coefficient of 10 ppm / K or less is used. When this composite is subjected to heat treatment, the rate of dimensional change due to thermal history is preferably ± 0.5% or less, more preferably ± 0.3% or less, and even more preferably ± 0.1% or less. This thermal history is below the melting point of the metal or the metal used for the composite material when the flat heat pipe of the present invention is produced or when the flat heat pipe is formed. The process of heating to temperature and then returning to room temperature is shown.
In the flat heat pipe of the present invention, the influence of thermal stress is suppressed by the top plate and the bottom plate excellent in high thermal conductivity and low thermal expansion or the thin plates sandwiched between them, and the heat spreads in the lateral direction and in the thickness direction. A heat pipe that conducts well and can efficiently dissipate heat and is excellent in heat diffusion can be obtained. At the same time, it has a coefficient of thermal expansion close to that of the component to be cooled, such as a semiconductor element or an integrated circuit board, so that the component to be cooled and the heat pipe can be joined well, and the coefficient of thermal expansion in the thickness direction is low When assembled in a housing, the thickness direction accuracy is good and a highly airtight heat pipe can be obtained.

  The planar heat pipe of the present invention is characterized in that it is first constituted by a thin plate made of the above-mentioned composite of graphite and metal. Further, as described below, the groove is formed in at least one of the upper plate and the bottom plate. When this groove forms a loop, when the working fluid receives heat in a part of the loop, the working particles change from the liquid phase to the gas phase, and the liquid is generated by nucleate boiling that transports latent heat using the movement of the gas phase. The phase vibrates, and this vibration can transport sensible heat to cool the heating element.

  The flat type heat pipe according to the present invention is characterized in that a groove formed in at least one of a top plate and a bottom plate made of a thin plate made of a composite of graphite and metal has a comb shape. The comb teeth serve as a wick and can help the working fluid flow back.

  The planar heat pipe of the present invention is characterized in that comb-like grooves are formed in an upper plate and a bottom plate made of a thin plate made of a composite of graphite and metal, and the comb teeth are alternately combined. . By alternately combining, the working fluid can be more easily recirculated. The groove may be formed directly on the thin plate, or may be formed by joining an intermediate plate having a cut-out space forming a space to either the top plate or the bottom plate.

  The planar heat pipe according to the present invention is characterized in that the casing has a thickness of 20 mm or less. By making the total thickness 20 mm or less, it becomes possible to use for cooling of a CPU chip, a laser oscillation part of an optical reading device, a desktop personal computer, a notebook personal computer or the like. More preferably, it is 10 mm or less. More preferably, it is 5 mm or less.

  The flat heat pipe according to the present invention is a casing in which a metal layer is formed on at least a joint portion of a top plate and a bottom plate made of a thin plate made of a composite of graphite and a metal, and the top plate and the bottom plate are metal-bonded. It is characterized by being. The metal layer is preferably copper, aluminum, nickel, or an alloy containing them as a main component. The metal layer is formed by plating, vapor deposition, paste printing / firing.

  The planar heat pipe according to the present invention further includes a heat sink having a required shape outside the casing. It is preferable to provide a comb-like heat sink outside the housing. By providing the comb-shaped heat sink, heat dissipation is promoted. When a comb-shaped heat sink is provided, a separately manufactured one may be installed, or one of the working fluids of the top plate and the bottom plate made of a thin plate made of a composite of graphite and metal is enclosed. The back surface of the surface to be formed may be integrated with comb teeth. In the case of an integrated planar heat pipe with comb-shaped heat sink, the thickness does not depend on 20 mm or less.

  The planar heat pipe according to the present invention is characterized in that the casing and a semiconductor element and / or a component to be cooled such as an integrated circuit board are joined by metal. By metal bonding, the thermal resistance between the heat pipe and the component to be cooled is reduced, and the heat dissipation efficiency is improved. Metal bonding includes, for example, a method of performing soldering after nickel plating is applied to the joint surface between the flat heat pipe and the component to be cooled, and a method of brazing the joint surface between the flat heat pipe and the component to be cooled. is there.

  Furthermore, the planar heat pipe of the present invention is composed of a composite of graphite and metal, and since the easily processable graphite exists in the composite, it is excellent in machinability as a composite. Without being constrained, it is possible to make the shape along the installation space of the parts, and the space can be used effectively. The planar heat pipe of the present invention can be used over a wide range of housings of various electronic circuit boards such as desktop personal computers and notebook personal computers, sealed housings, and electronic circuit boards used in aircraft.

  FIG. 1 shows a first embodiment (a) is a top view of a thin plate, and (b) is a cross-sectional view of an AA portion in an assembled state. As shown in FIG. 1, a flat top plate 1 and a bottom plate 2 of 25 × 40 mm square are produced by a thin plate made of a composite of graphite and aluminum alloy having a thickness of 1 mm, and further a composite of graphite and copper having a thickness of 1 mm. A thin plate 3 made of 25 × 40 mm is prepared by removing it with an end mill so as to form a loop as shown in FIG. 1A, and is removed so as to form the loop between the top plate 1 and the bottom plate 2. 3 was sandwiched and joined. Joining was performed by printing and baking with copper paste, brazing to produce a flat heat pipe container, evacuating, using water as a working fluid, and producing a housing housed in a loop shape. As shown in FIG. 1, a predetermined space 4 having a wick structure serving as a working fluid passage is provided between the top plate 1 and the bottom plate 2. The thickness of the flat heat pipe thus manufactured was 3 mm. The composite of graphite and metal was produced as follows.

(Top plate 1, bottom plate 2: composite of graphite and aluminum alloy)
A porous graphitized extruded product obtained by extruding and graphitizing a melt-kneaded product of coke particles having an average particle diameter of 500 μm and pitch (bulk specific gravity: 1.70, ash content 0.3 mass%, direction of extrusion and direction orthogonal to the direction of extrusion Specific resistance is 5.0 μΩm and 8.5 μΩm, respectively, and the thermal expansion coefficient is 0.6 ppm / K and 2.0 ppm / K in the direction orthogonal to the extrusion direction and the extrusion direction, respectively, and the thermal conductivity in the direction orthogonal to the extrusion direction and the extrusion direction is Porous graphitized extrusion molding first into the cavity of the die unit (kept at 750 ° C) using 230 W / mK and 120 W / mK respectively) and Al-Si alloy containing 12% by mass of Si The body was placed, and the molten Al-Si alloy (750 ° C.) was poured into it, and then the upper punch was pushed down to forge the molten metal at 100 MPa for 5 minutes. After cooling, excess Al-Si alloy was removed by cutting to obtain a composite of graphite and aluminum alloy (Al-Si). This composite was heat-treated at a temperature rising rate of 2 ° C./minute, a holding condition of 500 ° C. × 60 minutes, and a cooling rate of 2 ° C./minute. The composite after heat treatment was cut out to the above size. In addition, the thickness direction of the top plate and the bottom plate was matched with the extrusion direction of the composite material.
When the thermal conductivity and thermal expansion coefficient of the composite after heat treatment were measured, the thermal conductivity was 340 W / mK in the extrusion direction, 250 W / mK in the orthogonal direction, and the thermal expansion coefficient was 3.5 ppm / in the extrusion direction. K and the orthogonal direction were 6.9 ppm / K.

(Thin plate 3: Composite of graphite and copper)
Using the same porous graphitized extrudate as above and pure copper (purity 99.9% or higher), first place the porous graphitized extrudate in the cavity of the mold apparatus (maintained at 1000 ° C). Then, the above pure copper melt (1350 ° C.) was poured, and then the upper punch was pushed down, and the melt was forged at 100 MPa for 5 minutes. After cooling, excess pure copper was removed by cutting to obtain a composite of graphite and copper. This composite was heat-treated at a temperature rising rate of 5 ° C./minute, a holding condition of 900 ° C. × 120 minutes, and a cooling rate of 5 ° C./minute. The composite after heat treatment was cut into the above shape. The thickness direction of the thin plate was matched with the extrusion direction of the composite material.
When the thermal conductivity and thermal expansion coefficient of the composite after heat treatment were measured, the thermal conductivity was 350 W / mK in the extrusion direction, 250 W / mK in the orthogonal direction, and the thermal expansion coefficient was 1.7 ppm / in the extrusion direction. K and the orthogonal direction were 5.8 ppm / K.

  When the flat heat pipe manufactured in this way was applied by brazing to the back surface of the bottom plate of the laser element storage package, heat generation could be effectively dissipated, and a good cooling effect was obtained.

  FIG. 2 is a sectional view showing a second embodiment. As shown in FIG. 2, a flat bottom plate 5 of 25 mm square is produced by a thin plate made of a composite of graphite and copper having a thickness of 4 mm, and a comb having a width of 0.5 mm and a depth of 3 mm is formed on the bottom plate 5. Tooth-shaped grooves were formed and electroless copper plating was applied to the whole. In addition, a thin plate upper plate 1 made of a composite of graphite and copper having a thickness of 1 mm and subjected to electroless copper plating is disposed, and the upper plate 1 and the bottom plate 5 are brazed to form a planar heat pipe. A container was manufactured, evacuated, water was used as a working fluid, and a housing in which comb-like wicks 6 were housed was manufactured. A predetermined space 4 having a wick structure is provided between the comb-like shape 6 and the upper plate 1 as shown in FIG. The thickness of the flat heat pipe thus manufactured was 5 mm. The top plate 1 and the bottom plate 5 used the same composite of graphite and copper as in Example 1.

  When the planar heat pipe produced in this way was applied to a chip of a small CPU, heat generation could be moved effectively and a good cooling effect was obtained. Therefore, it can be seen that a good cooling effect can be obtained by a flat heat pipe having a very thin thickness. The thermal expansion coefficient of the flat type heat pipe is 10ppm / K or less, so the flat type heat pipe can be brought into close contact with the chip of the small CPU, and the thermal conductivity is improved.

  FIG. 3 is a sectional view showing a third embodiment. As shown in FIG. 3, a flat bottom plate 7 of 25 mm square was prepared by a thin plate made of a composite of graphite and aluminum alloy similar to Example 1 having a thickness of 4 mm, and a width of 0.5 mm was formed on the bottom plate. Comb-like grooves having a pitch and a depth of 3 mm were formed, and electroless nickel plating was performed. Furthermore, the upper part which consists of the composite of graphite and copper similar to Example 1 of the edge thickness 1mm by which electroless nickel plating was given, groove width 0.8mm, depth 3mm, and comb-tooth thickness 0.2mm. A plate 8 is arranged, and the top plate 8 and the bottom plate 7 are brazed to produce a flat heat pipe container, evacuated, water is used as a working fluid, and a meandering wick 9 is accommodated therein. A housing was made. A predetermined space was provided between the meandering wick and the upper plate as shown in FIG. The thickness of the flat heat pipe thus manufactured was 5 mm.

  When the flat heat pipe produced in this way is applied to a laser oscillation unit of an optical reading device used in a CD-ROM device, a DVD device, a game machine, etc., heat generation can be moved effectively, A good cooling effect was obtained. Therefore, it can be seen that a good cooling effect can be obtained by a flat heat pipe having a very thin thickness.

  The planar heat pipe of the present invention can be used for cooling a heating element such as a semiconductor element or an integrated circuit substrate.

It is a figure which shows one embodiment of the planar heat pipe of this invention. It is a figure which shows another embodiment of the planar heat pipe of this invention. It is a figure which shows another embodiment of the planar heat pipe of this invention.

Explanation of symbols

1, 8: Upper plate 2, 5, 6, 7: Bottom plate 3: Thin plate 4, 9: Wick

Claims (9)

A casing made of a top plate and a bottom plate made of a thin plate made of a composite of graphite and metal, and a groove formed in the thin plate constituting at least one of the top plate and the bottom plate, or the graphite having a groove formed therein A planar heat pipe characterized in that a passage groove is formed in the housing by sandwiching another thin plate made of a metal composite, and a working fluid is sealed in the groove of the passage. The top plate and the bottom plate of the housing have a thermal conductivity and a thermal expansion coefficient of 5 W / mK or more and 2000 W / mK or less, and a thermal expansion coefficient of 0.1 ppm / K or more and 15 ppm / K or less. 2. The flat heat pipe according to claim 1, comprising a composite of graphite and metal having anisotropy. The planar heat according to claim 1 or 2, wherein a groove formed in at least one of an upper plate and a bottom plate formed of a thin plate made of a composite of graphite and metal forms a loop. pipe. The flat heat pipe according to claim 1 or 2, wherein a groove formed in at least one of an upper plate and a bottom plate made of a thin plate made of a composite of graphite and metal has a comb shape. The plane according to claim 1 or 2, wherein comb-like grooves are formed in an upper plate and a bottom plate made of a thin plate made of a composite of graphite and metal, and the comb teeth are alternately combined. Type heat pipe. The planar heat pipe according to any one of claims 1 to 5, wherein the casing has a thickness of 20 mm or less. The casing is formed by forming a metal layer on at least a joining portion of an upper plate and a bottom plate made of a thin plate made of a composite of graphite and a metal, and metal-joining the upper plate and the bottom plate. The planar heat pipe according to any one of 1 to 6. The planar heat pipe according to any one of claims 1 to 7, further comprising a heat sink having a required shape outside the housing. The planar heat pipe according to any one of claims 1 to 8, wherein the casing, the semiconductor element, and / or the integrated circuit board are metal-bonded.

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