JP2012057841A - Heat pipe, and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of not capable of coping with miniaturization and enhancing of performance, which being requested lately, of a heat pipe, relating to a conventional wick structure for a heat pipe which is composed of a groove about 0.1-1 mm, metal mesh about 50-100 μm, or sintered metal about 25-250 μm.SOLUTION: The inner wall of a lower side container 2 is provided, as a wick structure, with a graphite substrate 4 in which a rough structure having an interval W of 10 μm or less is formed. The rough structure on an evaporation part side 5 is denser than the rough structure on the side of a condensing part 6.

Description

  The present invention relates to a heat pipe, a vapor chamber, and the like that act as a heat transport member of a heat generating electronic device, and more particularly to a capillary structure (hereinafter referred to as a wick structure).

  2. Description of the Related Art In recent years, the amount of heat generated has increased with the enhancement of performance of electronic devices such as light emitting diodes (LEDs), semiconductor elements, and solar cells. On the other hand, there is an increasing demand for smaller and thinner electronic devices. As a result, the heat generation density of the electronic device becomes very high, and the electronic device is forced to be in a severely thermal condition. In order to cool such an electronic device, a heat pipe as a heat transport member has attracted attention.

  The heat pipe is sealed in a vacuum by sealing a condensable working fluid such as water in a hollow sealed container such as copper (hereinafter referred to as container) with non-condensable gas such as air deaerated. A wick structure is provided, and heat is transferred by phase transformation and movement of the working fluid. Specifically, on the evaporation part (also referred to as the heat absorption part) side of the heat pipe, the working fluid in the liquid phase is evaporated by heating and becomes a gas phase state, and moves to the condensation part (also referred to as the heat dissipation part) of the heat pipe. To do. On the other hand, on the condensing part side of the heat pipe, the working fluid that has become vapor is cooled and condensed to change into a working fluid in a liquid phase again, and is returned to the evaporation part by the capillary pressure due to the wick structure.

  Since the wick structure is for generating a capillary pressure, that is, a pumping force for the liquid phase working fluid, the so-called wettability with the working fluid is good and a meniscus formed on the liquid surface of the liquid phase working fluid. It is preferable that the effective capillary radius is as small as possible. Therefore, the conventional heat pipe wick structure has a groove of about 0.1 to 1 mm (Reference: Patent Documents 1 and 2), a metal mesh of about 50 to 100 μm (Reference: Patent Document 2), or a sintered metal of about 25 to 250 μm. (Reference: Patent Document 2).

  It is known that the pumping force for refluxing the liquid-phase working fluid is increased by making the wick structure different between the evaporation section side and the condensation section side (see Patent Document 2). In other words, the evaporation part side has a relatively small capillary structure to reduce the effective capillary radius at the meniscus, while the condensation part side has a relatively large capillary structure to provide an effective capillary radius at the meniscus. By connecting them relatively large, capillary pressure is positively generated on the evaporation side, and fluidization of the liquid phase working fluid is made smooth on the condensation side. For example, when a sintered metal of about 25 to 250 μm is used, this can be achieved by preparing a sintered metal body having a different size as a pretreatment and fixing it on the inner wall of the container.

JP 2000-193385 A Japanese Patent Application Laid-Open No. 2005-180871

  However, in the above-mentioned conventional heat pipe wick structure having a fine structure of 20 μm or more, there is a limit to reducing the effective capillary radius at the meniscus caused by the wick structure. However, there is a problem that it cannot cope with high performance.

  In order to solve the above-mentioned problems, the wick structure for heat-dissipating material heat pipe according to the present invention includes a carbon-based substrate having a concavo-convex structure with a spacing of 10 μm or less, for example, nanometer order on the surface. Thereby, the effective capillary radius at the meniscus formed on the liquid surface of the liquid phase working fluid is reduced.

  The method for manufacturing a wick structure for a heat pipe according to the present invention includes a step of processing a concavo-convex structure of an order of 10 μm or less, for example, nanometer, on the surface of a carbon-based substrate.

  According to the present invention, since the wick is formed using a carbon-based substrate having a concavo-convex structure on the order of nanometers, the effective capillary radius is reduced, so that the capillary pressure is increased and the heat pipe can be improved in performance. . In addition, the heat pipe can be miniaturized as the performance is improved, that is, the heat transport capacity can be increased.

Embodiment of the heat pipe which concerns on this invention is shown, (A) is a top view, (B) is the BB sectional drawing of (A). It is a flowchart which shows the processing flow of the nano uneven structure of the graphite substrate of FIG. It is a scanning electron microscope (SEM) photograph of the surface of the graphite board | substrate before and behind the plasma etching of FIG. It is a table | surface for demonstrating the effect of this invention.

  1A and 1B show an embodiment of a heat pipe according to the present invention, in which FIG. 1A is a plan view and FIG. 1B is a sectional view taken along line BB in FIG.

  Referring to FIG. 1, a heat pipe container 1 includes a lower container 2 made of a metal having good thermal conductivity such as copper, and an upper container 3 as a sealing member for the lower container 2. The container 1 has a rectangular parallelepiped shape, but may be cylindrical.

  The inner walls of the lower container 2 and the upper container 3 are provided with graphite substrates 4 and 4 ′ having a concavo-convex structure with a spacing W of 10 μm or less, and function as a wick structure. For example, the concavo-convex structure of the graphite substrates 4, 4 'is, for example, on the order of nanometers (nm). The nanometer order means a range of about 1 nm to 100 nm.

  When sealing by joining the opening end of the lower container 2 and the opening end of the upper container 3, the condensability of water, alternative chlorofluorocarbon, etc. in a state where non-condensable gas such as air is deaerated. The working fluid is sealed and vacuum-sealed. A region indicated by a dotted line 5 indicates an evaporation portion, and is disposed below a heat generating electronic component such as an LED (not shown). On the other hand, a region indicated by a dotted line 6 indicates a condensing portion and is disposed on a heat radiating member (not shown). The space between the evaporator 5 and the condenser 6 may be covered with a heat insulating member (not shown).

  In FIG. 1, the concavo-convex structure on the evaporation unit 5 side is made denser than the concavo-convex structure on the condensation unit 6 side, and the wick structure is made different between the evaporation unit 5 side and the condensation unit 6 side. As a result, capillary pressure is positively generated on the evaporation section 5 side, while fluidization of the liquid phase working fluid is made smooth on the condensation section 6 side. That is, the internal resistance of the working fluid is reduced and the heat transport performance is improved. In the case where there are a plurality of heat generation sources, a plurality of evaporation sections can be provided, and the uneven structure on the evaporation section side can be selectively made dense.

  FIG. 2 is a flowchart showing a processing flow of the nano uneven structure of the graphite substrate of FIG.

In step 201 of FIG. 2, the graphite substrate having the mirror-like surface shown in FIG. 3A is etched by a plasma etching method using H ₂ gas, and the interval shown in FIG. 3B is on the order of nanometers. A graphite substrate having a concavo-convex structure is obtained. The plasma etching conditions are, for example, as follows.
RF power: 100-1000W
Reaction chamber pressure: 133-13300Pa (1-100Torr)
Hydrogen flow rate: 5-500sccm
Etching time: 1-100 minutes

2 may be any of reactive ion etching (RIE), electron cyclotron resonance (ECR) etching, microwave plasma etching, etc., and the processing gas is H Ar gas other than ₂ gas, O ₂ gas, CF ₄ gas or the like may be used.

  For example, the RIE method is one of microfabrication methods classified as dry etching, in which plasma is generated by applying an electromagnetic wave or the like to a processing gas in a reaction chamber, and a high frequency voltage is applied to a graphite substrate installation electrode. As a result, a bias voltage is generated between the graphite substrate and the plasma, and ions and radicals in the plasma collide with the graphite substrate. At this time, sputtering by ions and chemical reaction of the processing gas occur at the same time, so that highly accurate uneven microfabrication can be performed. Therefore, the RF power, the pressure in the reaction chamber, the gas flow rate, and the etching time can be controlled within the above ranges, and the RIE method can perform anisotropic etching, so that the heat pipe wick structure can be controlled. As a result, the above RIE condition is controlled for the graphite substrate 4 so that the uneven structure on the evaporation unit 5 side is made denser than the uneven structure on the condensation unit 6 side, and the wick structure is formed on the evaporation unit 5 side and the condensation unit 6 side. Make it different. As a result, as described above, capillary pressure is positively generated on the evaporation unit 5 side, and fluidization of the liquid-phase working fluid is made smooth on the condensing unit 6 side. As a result, the heat transport performance is improved. In the case where there are a plurality of heat sources, the concavo-convex structure on the side of the plurality of evaporation units is selectively controlled.

Next, a conventional wick structure made of a sintered copper metal with a thickness of 25 μm and a wick structure made of a graphite substrate having a concavo-convex structure with a spacing of 10 μm according to the present invention will be compared. Here, the wick structure is a 2.5 cm square and 0.6 mm thick flat plate having the same volume (= 0.375 cm ³ ). For convenience, the wick structure on the evaporation side and the condensation side is the same.

As shown in FIG. 4A, the specific gravity is 8.92 in the case of the copper sintered metal, and 1.5 in the case of the concavo-convex structure graphite substrate. Therefore, at the same volume (= 0.375 cm ³ ), the weight is 3.345 g for the copper sintered metal, and 0.5625 g for the concavo-convex structure graphite substrate, 17% for the copper sintered metal. Only. Thus, while the demand for downsizing and thinning of electronic devices is increasing, the weight ratio of the heat radiating member is relatively large. Very effective.

As shown in FIG. 4B, when the microstructure size of the sintered copper metal is 25 μm, the surface area is about 1,000,000 μm ² , and on the other hand, when the microstructure size of the concavo-convex structure graphite substrate is 10 μm, The surface area is about 6,250,000 μm ^2, which is more than six times that of sintered copper metal. As described above, when the surface area is increased, the effective capillary radius at the meniscus is decreased, a strong capillary pressure is exhibited, and a high heat transport capability can be exhibited. In addition, the concavo-convex structure graphite substrate can be miniaturized by the amount equivalent to the high heat transport performance.

  The graphite substrate described above can be a metal-impregnated dense graphite substrate impregnated with metal. Thereby, since the toughness of the dense graphite substrate is large, workability and adhesion to the container are improved, and there is no gap between the container and the container.

  In the above-described embodiment, the graphite substrate is used. However, a carbon-based substrate other than the graphite substrate, for example, a substrate in which a concavo-convex structure is formed by plasma etching the surface of a diamond substrate may be used.

1: Container
2: Lower container
3: Upper container
4, 4 ': Graphite substrate
5: Evaporation part
6: Condensing part
201: Nano uneven structure processing step

Claims (8)

In a heat pipe having a wick structure,
The wick structure is a heat pipe including a carbon-based substrate having a concavo-convex structure with a space of 10 μm or less on the surface.   The heat pipe according to claim 1, wherein the interval between the uneven structures is on the order of nanometers. When both ends of the wick structure are defined as an evaporation part and a condensation part,
The heat pipe according to claim 1, wherein the uneven structure on the evaporation part side is denser than the uneven structure on the condensation part side.   The heat pipe according to claim 1, wherein the carbon-based substrate comprises a graphite substrate.   A method for manufacturing a heat pipe, comprising a concavo-convex structure processing step for forming a wick structure of a heat pipe by processing the surface of a carbon-based substrate into a concavo-convex structure with a spacing of 10 μm or less.   The method for manufacturing a heat pipe according to claim 5, wherein the uneven structure processing step is a plasma etching step. When both ends of the wick structure are defined as an evaporation part and a condensation part,
The method of manufacturing a heat pipe according to claim 6, wherein the uneven structure on the evaporation part side is made denser than the uneven structure on the condensation part side by controlling plasma etching conditions in the plasma etching step.   The method for manufacturing a heat pipe according to claim 5, wherein the carbon-based substrate comprises a graphite substrate.