JP2008222912A - Radiating material and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiating material which has high heat conductivity and excels in flexibility and tensile elongation and its manufacturing method. <P>SOLUTION: The radiating material contains a base at least whose surface portion is Al, Mg or Zn and a composite layer formed on at least one surface of the base, and the composite layer is constituted of a plurality of cylindrical or projecting materials formed from Al<SB>2</SB>O<SB>3</SB>, MgO or ZnO on the surface of the base and a resin packed among the spaces of the above materials. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a heat radiating material, and more particularly to a heat radiating material having high thermal conductivity and excellent flexibility and a method for producing the same.

  As the functions of personal computers and mobile electronic devices become higher, the amount of heat generated by a heat source such as a CPU has increased dramatically, and there is a need for higher performance heat dissipation devices. A simple and effective method for dissipating heat is to dissipate heat by attaching a heat dissipating sheet or adhesive to the surface of the heat source. And in heat dissipation of many electronic devices, non-conductivity is often required for the heat dissipation sheet and the adhesive.

These heat dissipation materials are generally materials in which particles having high thermal conductivity are dispersed in a resin. As the high thermal conductivity particles, a metal particle dispersion type such as Ag or Cu having a thermal conductivity of about 400 W / mK (Patent Document 1) or a ceramic particle dispersion type composite material such as Al ₂ O ₃ or AlN is used. There are many (patent document 2).
Conventional high thermal conductivity particles have the following problems. That is, in order to develop high thermal conductivity in these composite materials, the volume content of dispersed particles having high thermal conductivity must be set high. That is, to some extent, the dispersed particles come into contact with each other to form a metal phase network, so that a certain degree of thermal conductivity is exhibited. For example, when Ag particles are dispersed, about 9 W / mK is obtained. However, there are problems that the thermal conductivity is not satisfactory, the specific gravity is large and heavy, and the conductivity is high.

On the other hand, in the case of a ceramic particle dispersed composite material, the thermal conductivity of the ceramic particles themselves is low. For example, the thermal conductivity of sintered Al ₂ O ₃ and AlN ceramics, which are insulating materials, is about 30 and 170 W / mK, respectively. These values are values for sintered bodies that have been sufficiently sintered to increase crystallinity and reduce impurities in the crystals, and the thermal conductivity when these ceramics are made into particles is these values. Much lower than the value. Therefore, when a structure similar to the metal particle-dispersed composite material is produced, there is a problem that the thermal conductivity is much lower.

JP 2002-003829 A JP-A-2005-139267

  This invention makes it a subject to provide the thermal radiation material which has high thermal conductivity, and was excellent in the softness | flexibility and the tensile elongation rate, and its manufacturing method.

  The present invention has been made to solve this problem, and in a ceramic-resin composite material, the length direction of alumina ceramic is oriented substantially parallel to the direction in which the thermal conductivity is required. It relates to materials, sheets, and their manufacturing methods, and has the following characteristics.

(1) A heat dissipation material including a substrate having at least a surface portion made of Al, Mg, or Zn, and a composite layer formed on at least one surface thereof, wherein the composite layer has Al ₂ O _{3 on} the substrate surface, A heat-dissipating material comprising a plurality of columnar or protrusion-shaped objects formed of MgO or ZnO and a resin filled in the gaps.
(2) The heat radiation material as described in (1) above, wherein a major axis of a tip portion of the columnar or protrusion-shaped object is 50 μm or less.
(3) The heat-dissipating material according to (1) or (2) above, wherein an aspect ratio, which is a ratio of a height to a major axis of the tip of the columnar or protrusion-shaped object, is 3 or more.
(4) The heat dissipation material as described in any one of (1) to (3) above, wherein a volume content of the columnar or protrusion-shaped object in the composite layer is 10 to 60%.
(5) The heat dissipation material as described in (4) above, wherein the Al ₂ O ₃ crystal system is α-type.
(6) The heat dissipation material according to any one of (1) to (5) above, wherein the composite layer has a thermal conductivity of 10 W / mK or more.
(7) The heat dissipation material according to any one of (1) to (6), wherein the substrate is Al.
(8) The material for heat dissipation as described in any one of (1) to (7) above, wherein the thickness of the substrate is 50 μm or less.
(9) The heat dissipation material according to any one of (1) to (8) above, wherein the tensile elongation of the composite layer is 20% or more.

(10) The method for producing a heat-dissipating material according to (1) above, wherein at least a part of the substrate whose surface portion is Al, Mg, or Zn is masked, and the non-masking portion is anodized. A method for producing a heat-dissipating material, comprising a step of forming columnar or protruding alumina on a surface of a substrate, and a step of filling a resin in a gap between the alumina.
(11) The method for manufacturing a heat-dissipating material as described in (10) above, wherein the anodizing treatment includes a sealing treatment.
(12) The method for producing a heat-dissipating material as described in (10) or (11) above, comprising a step of heat-treating at 500 ° C. or higher before the step of filling the resin.
(13) The method for manufacturing a heat radiation material according to any one of (10) to (12), wherein the substrate is Al.

  The heat-dissipating material according to the present invention is a resin-based composite material having high thermal conductivity and high tensile elongation because columnar or projecting shapes having high thermal conductivity are oriented in a specific direction.

Next, an example of the heat-dissipating material of the present invention and its manufacturing method will be described.
The heat-dissipating material according to the present invention has a composite layer having a structure in which a columnar or protrusion-shaped object is formed on the substrate surface, and a resin, particularly a resin excellent in flexibility, is filled in the gap. The composite layer may be formed only on one side of the substrate, or may be formed on both sides. In order to form a columnar or protruding shape, an anodic oxidation process is used in the present invention. The columnar or protruding shape is preferably Al ₂ O ₃ , MgO or ZnO. Hereinafter, a case where alumina ceramics (Al ₂ O ₃ ) is used will be described.

Anodization is a process in which an aluminum plate is transformed into porous alumina by applying an electric field of several tens of volts in an electrolytic solution. As the electrolytic solution, an aqueous solution of oxalic acid, ammonium borate, ammonium phosphate, ammonium adipate or the like is often used.
As shown in FIG. 1, about 1/3 of the alumina pillar formed when anodizing aluminum is formed at a position higher than the original aluminum position, and the remaining 2/3 is formed inside the aluminum base. That is well known. The inventor pays attention to this phenomenon, and by masking a part of the aluminum surface so as not to be oxidized, columnar alumina can be formed, and a resin is filled in the gap between the alumina. The thermal conductivity of alumina formed by anodization is 60 W / m
Since it is as high as about K and excellent in electrical insulation, the present composite material has been found to be a heat dissipation material with excellent insulation, high thermal conductivity and excellent flexibility.

  First, mask the aluminum surface. As the masking shape, for example, a honeycomb shape can be considered. Thereby, each part to be anodized is isolated. Due to the anodic oxidation after masking, only the isolated part is transformed into alumina. At this time, the tip surface converted to alumina is positioned higher than the aluminum surface. Will increase. For anodizing, the usual aluminum anodizing process can be used as it is. Depending on the conditions of the anodizing treatment, alumina may be a column that is substantially perpendicular to the substrate surface, and the tip surface may be a protrusion that is smaller than the bottom. In the case of the latter, in the latter case, when the heat source is brought into contact with the heat source in order to dissipate heat, the area where the resin contacts the heat source increases, so that a gap between the heat source and the heat radiation material is less likely to occur. There is also an advantage that the thermal resistance becomes smaller.

The smaller the major axis of the tip of the columnar or protruding alumina, the easier it is for the composite material to deform when it comes into contact with the heat source, and it comes into firm contact with the uneven heat source member surface. The major axis is preferably 50 μm or less, and the smaller the smaller the diameter, the better the effect. For example, when the masking pattern is formed by screen printing, it is possible to produce alumina having a long diameter of about 30 μm, and when masking is performed by a semiconductor exposure process or the like, about 100 nm.
The larger the aspect ratio, which is the ratio of the height of the tip or columnar alumina to the major axis, the easier it is to deform, and 3 or more is preferred. More preferably, it is 5 or more.
The lower the volume content of alumina in the composite layer, the easier it is to deform. However, the thermal conductivity of the composite layer is small, so 10 to 60% is preferable. When it exceeds 20%, the thermal conductivity of the composite material becomes 10 W / mK or more. The crystal system of anodized alumina is usually amorphous (amorphous), but when heat-treated at 500 ° C. or higher, it begins to convert to α-type, and the thermal conductivity of alumina becomes higher. The thermal conductivity of increases.

  The substrate is not limited to resin, Cu foil, ceramics, glass, or the like, but a material having high electrical conductivity is preferable for the substrate. By forming a thick aluminum film on the surface of these base materials by CVD or other methods, anodization can be performed in the same manner as in the case of an aluminum base material. When the substrate is anodized using an aluminum foil and the treatment is completed in the middle of the thickness direction of the aluminum foil, a structure in which alumina pillars are formed on the surface of the aluminum foil is obtained. In order to promote the crystallization of alumina, the heat treatment temperature may be increased. In this case, ceramics having excellent heat resistance are preferable.

When a metal substrate such as Al or Cu is used, the heat dissipation material becomes more flexible as the thickness of the metal portion after anodization is smaller. In particular, a sheet-like substrate having a thickness of 50 μm or less is preferable because the flexibility of the sheet is high.
The anodizing treatment may be performed on one surface or both surfaces of the substrate. When anodizing both surfaces, it is preferable to mask the masking patterns on the front and back sides that are shifted from each other. When both surfaces are anodized in this way, a composite layer of resin and alumina is formed on both surfaces so as to sandwich the metal (FIG. 2 shows a case where masking patterns on the front and back sides are alternately formed). Between the heat spreader and the heat spreader, the heat of the heat source can be efficiently transmitted to the heat spreader. When processing only one surface, the back surface should be masked.
The masking material may be any material that is resistant to acids and alkalis exposed by a series of anodizing treatments, and may be an epoxy or the like or a ceramic film such as SiO ₂ if it is a resin.

Next, a resin is filled in the gap between the porous layers to form a composite layer, but the method is not particularly limited. For example, when an ultraviolet curable resin is used, a porous resin is impregnated with a liquid resin. The impregnation is facilitated by, for example, dropping the resin onto the surface of the formed porous layer made of a columnar or projecting shape and loading it in a container such as a desiccator and then evacuating the interior of the desiccator. Next, when the impregnated resin is irradiated with ultraviolet rays, the resin is cured to form a composite material.
The resin is preferably a resin having as little hardness as possible and having high flexibility. The flexibility of the resin is generally based on the elongation rate during the tensile test. The elongation is preferably 50% or more. For example, there is a urethane acrylate resin having a main chain made of polyisoprene and acrylic double bonds at both ends of the main chain. Of course, other resins may be used. The tensile elongation when such a resin is used for the composite material is preferably 20% or more. Moreover, it is preferable to fill the adhesive resin because it can be easily attached to a heat source.
After the heat from the heat source is transferred from alumina to the aluminum substrate, infrared radiation and heat transmitted in the in-plane direction of the aluminum substrate are transferred to other members in contact with the aluminum substrate to dissipate heat. Will be.

  In the composite layer made of ceramic-resin, the material for heat dissipation according to the present invention has a columnar or projecting shape (alumina) growing vertically along the thickness direction of the sheet. It exists independently of the shape. Therefore, even after impregnating the resin, there is a feature that resistance to elongation in the in-plane direction of the sheet is small. That is, the sheet has a high tensile elongation rate. On the other hand, since a normal ceramic porous body has a three-dimensionally connected structure, it is difficult to be deformed, and the tensile elongation is reduced when a composite material is used.

  When such a heat-dissipating material is formed into a sheet shape and attached to a heat source, heat is transferred to the Al foil with extremely high thermal conductivity along the thickness direction of the composite material with high thermal conductivity, and then the Al foil In addition to the thickness direction, it is also transmitted in the in-plane direction of the Al foil, so that the heat dissipation effect becomes extremely large.

The metal to be anodized is generally aluminum, but may be magnesium or zinc. Both MgO and ZnO, which are converted by anodizing these, have high thermal conductivity and can be a constituent member of the present invention.
Note that before the resin is filled in the gaps in the porous layer, the columnar or protrusion-shaped object may be subjected to a sealing treatment in order to improve the corrosion resistance. The sealing treatment includes, for example, a method of closing the holes by holding in pure water heated to 95 to 100 ° C., but is not particularly limited thereto.
Of course, in the product of the present invention, the base material may be removed to make only a composite material of ceramics and resin.

<Patterning>
As the substrate, Al foil of 20 × 20 mm and various thicknesses was used.
As shown in FIG. 3, a silica film was coated with a thickness of 0.5 μm as a mask material by photolithography. The size and pitch of the exposed part of aluminum were changed. When anodizing only one side, the entire back side was masked. When both surfaces were anodized, the masking patterns on the front and back sides were masked by shifting the x-axis and y-axis by ½ the pitch length.

<Anodic oxidation>
Anodization was performed using the apparatus shown in FIG. Sulfuric acid and oxalic acid were used as the plating bath. A platinum plate was used for the positive electrode. The temperature was adjusted with a chiller so that the entire system was at a constant temperature.

<Resin impregnation>
Two kinds of resins were used.
i) Showa Polymer vinyl ester resin: Trade name: Lipoxy PH-300A (acrylic)
ii) Showa High Polymer Vinyl Ester Resin: Product Name: Lipoxy PH-300A (Styrene)
A 1 wt% polymerization initiator (IRGACRE184: manufactured by Ciba Specialty Chemicals) of the resin was added to these resins, stirred, and then dropped onto the surface of the first substrate on which whiskers were grown. This was placed in a vacuum oven and impregnated with resin at room temperature while being evacuated with a rotary pump. The ceramic content of the composite material was calculated from the specific gravity of the composite material.

<Curing of resin>
The resin was cured by irradiating ultraviolet rays having a wavelength of 365 nm with a light intensity of 50 mW / cm ² .

<Measurement of thermal conductivity>
a) Measurement of thermal conductivity of resin composite material itself Only the composite material layer was cut out by processing and measured by a periodic heating method.
b) Measurement of tensile elongation rate Only the composite material layer was cut out by processing and measured by a method according to JIS K 6249.
The results are shown in Table 1.

It is a conceptual diagram showing an example in which the alumina was formed in the aluminum substrate by the anodic oxidation. It is a conceptual diagram which shows an example in the state in which the alumina was formed in the front and back of the aluminum substrate by the anodic oxidation. It is a conceptual diagram showing an example of the shape of the mask used when performing anodization. It is a conceptual diagram showing an example of the apparatus which performs anodization.

Claims (13)

A heat dissipation material including a substrate having at least a surface portion made of Al, Mg, or Zn and a composite layer formed on at least one surface of the substrate, wherein the composite layer is formed on the substrate surface with Al ₂ O ₃ , MgO, or ZnO A heat-dissipating material comprising: a plurality of columnar or protrusion-shaped objects formed by the above-mentioned and a resin filled in the gaps.   The material for heat dissipation according to claim 1, wherein a major axis of a tip part of the columnar or projecting shaped object is 50 µm or less.   The heat-dissipating material according to claim 1 or 2, wherein an aspect ratio, which is a ratio of a height to a major axis of a tip portion of the columnar or protrusion-shaped object, is 3 or more.   The material for heat dissipation according to any one of claims 1 to 3, wherein a volume content of the columnar or protrusion-shaped object in the composite layer is 10 to 60%. The heat dissipation material according to claim 4, wherein the crystal system of the Al ₂ O ₃ is α-type.   The heat dissipation material according to any one of claims 1 to 5, wherein the composite layer has a thermal conductivity of 10 W / mK or more.   The heat dissipation material according to any one of claims 1 to 6, wherein the substrate is Al.   The thickness of the said board | substrate is 50 micrometers or less, The heat dissipation material as described in any one of Claims 1-7 characterized by the above-mentioned.   The heat dissipation material according to claim 1, wherein the composite layer has a tensile elongation of 20% or more.   It is a manufacturing method of the material for heat dissipation of Claim 1, Comprising: The process which masks a part of board | substrate whose surface part is Al, Mg, or Zn at least, anodizing a non-masking part, and on the surface of a board | substrate A method for producing a heat-dissipating material, comprising a step of forming columnar or protruding alumina and a step of filling a resin in a gap between the alumina.   The method for manufacturing a heat radiation material according to claim 10, wherein the anodizing treatment includes a sealing treatment.   The method for producing a heat-dissipating material according to claim 10 or 11, further comprising a step of heat-treating at 500 ° C or higher before the step of filling the resin.   The said board | substrate is Al, The manufacturing method of the material for heat dissipation as described in any one of Claims 10-12 characterized by the above-mentioned.

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