JP2008169245A - Heat dissipation material and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-radiating material having high heat conductance and a method for producing the same. <P>SOLUTION: This heat radiating material is provided by consisting of a composite material having a ceramic porous material and a heat-absorbing part and heat-radiating part consisting of a resin or metal as a second component, having a continuous phase of the second component by filling the resin or metal in macro-holes installed so as to orient from the heat-absorbing part to heat-radiating part in the ceramic porous material and micro-holes linking the continuous phase of the oriented other second component, and also having a linking phase obtained by filling the resin or metal in the micro-holes. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a heat radiating material and a manufacturing method thereof, and more particularly to a heat radiating material used for a heat radiating device for an electronic component and the like and a manufacturing method thereof.

As the functions of personal computers and mobile electronic devices increase, the amount of heat generated by a heat source such as a CPU has increased dramatically, and there is a need for higher performance of heat dissipation devices.
A simple and effective method for dissipating heat is a method of dissipating heat by attaching a heat dissipating sheet to the surface of the heat source. The heat radiating sheet is generally a material in which particles having high thermal conductivity are dispersed in a resin (Patent Document 1). As the high thermal conductivity particles, metal particles such as Ag and Cu having a thermal conductivity of about 400 W / mK, and ceramic particles such as Al ₂ O ₃ and AlN are often used, but there are common problems.

In order to develop high thermal conductivity in these composite materials, it is necessary that dispersed particles having high thermal conductivity in the composite material have at least a part of the particles in contact with each other. That is, when the particles do not contact each other and become an isolated particle dispersed structure, the thermal conductivity of the composite material becomes extremely low.
In order to bring the dispersed particles into contact with each other, the volume content of the particles must be increased to 50% or more. In this case, however, the flexibility that is characteristic of the resin is impaired, and the heat dissipation sheet becomes a heat source. It becomes impossible to adhere to the gap without any gap, and the heat dissipation is reduced.
A method of preparing a porous ceramic body with a high porosity by a sintering method in advance and loading a resin into the porous body is also conceivable, but a ceramic porous body with a high porosity is very brittle and has a shape after sintering. It is difficult to maintain.

JP 2005-139267 A Japanese Patent No. 312274

  This invention makes it a subject to provide the thermal radiation material with high heat conductivity, and its manufacturing method in order to solve the said problem.

The present invention has been made to solve this problem, and has the following characteristics regarding a heat radiating material having high thermal conductivity and flexibility even when the resin content is large and a method for producing the same.
(1) A composite material having a ceramic porous body and a heat absorbing portion and a heat radiating portion made of a resin or metal as a second component, the macro provided in the ceramic porous body so as to be oriented from the heat absorbing portion to the heat radiating portion It has micropores that connect the continuous phase of the second component in which the holes are filled with resin or metal and the continuous phase of the other second component that is oriented, and the micropores are filled with resin or metal A heat dissipation material comprising a composite material having a connected phase.
(2) The heat dissipation material as described in (1) above, wherein the second component is a resin.
(3) The heat radiation material according to (1) or (2), wherein the volume content of the second component is 50 to 90% in the heat radiation material.

(4) The heat dissipation material as described in any one of (1) to (3) above, wherein a diameter of a macropore serving as a continuous phase of the second component is 5 to 100 μm.
(5) The heat dissipation material according to any one of (1) to (4), wherein an average pore diameter of the micropores is 0.1 to 5 μm.
(6) The heat dissipation material according to any one of (1) to (5) above, wherein the ceramic porous body has a thermal conductivity of 20 W / mK or more.
(7) The heat dissipation material as described in any one of (1) to (6) above, wherein a resin having a tensile elongation of 50% or more is used as the second component.
(8) The heat radiation material according to any one of (1) to (7), wherein an adhesive layer is formed on at least a part of the surface of the heat radiation material.

(9) Slurry preparation step for dispersing ceramic raw material powder in water, step of freezing the obtained slurry from a specific direction to promote ice growth, vacuum freeze-drying the frozen slurry to sublimate ice, A step of making a molded body having, a step of baking a molded body sublimated with ice by heat treatment to form micropores in the molded body, and a resin or a second component in the macropores and micropores or And a step of filling with a metal.
(10) The method for manufacturing a heat dissipation material as described in (9) above, wherein the second component is a resin.

  Since the heat dissipation material according to the present invention uses a ceramic porous body having macropores oriented in one direction as a starting material, the ceramic porous body is easily impregnated with resin or metal, and as a result, a composite material having high thermal conductivity is obtained. . In particular, when a porous ceramic body is impregnated with a resin, a flexible composite material can be obtained.

  The heat dissipating material according to the present invention is a composite material having a continuous phase and a connected phase. The continuous phase has a structure in which a resin or metal as a second component is filled in macropores that are oriented and penetrated from the heat absorbing portion to the heat radiating portion in the ceramic porous body. Furthermore, the macropores are connected by micropores (connection phase) filled with resin or metal. In the heat dissipation material according to the present invention, the heat absorption part means a part that absorbs heat when the heat dissipation material is attached to the heat generating member, and the heat dissipation part means a part that releases heat from the heat dissipation material. . The heat absorbed from the heat absorbing part is transferred to the heat radiating part through the resin, metal or ceramics and radiated to the outside. Therefore, when the heat dissipating material according to the present invention is formed into a sheet shape, one surface attached to the heat generating portion is a heat absorbing portion, and the opposite surface is a heat dissipating portion.

  It is preferable that the heat radiating portion of the heat radiating material according to the present invention is provided with a second base material made of a metal foil such as Cu foil or Al foil or a resin foil such as polyimide. With such a second base material, the heat transferred from the composite material is also transferred in the in-plane direction in addition to the thickness direction of the second base material, so that the heat dissipation effect becomes extremely large. Furthermore, it is preferable that a heat radiation layer is provided on the outermost surface of the second base material because heat can be radiated by radiation from the surface of the heat radiation layer. The heat radiation layer is not particularly limited as long as it can radiate heat into the atmosphere as infrared rays. Ceramics or the like can also be preferably used. Moreover, when the heat-absorbing part is provided with an adhesive sheet, it can be easily attached to the heat generating part.

Next, an example of the composite material of the present invention and its manufacturing method will be described.
The heat dissipating material of the present invention is obtained by preparing a ceramic porous body having a high porosity in advance and filling a resin inside the pores of the porous body.
The method for producing a ceramic porous body is called a freeze-drying method, a slurry adjustment step of dispersing ceramic raw material powder in water, a step of freezing the obtained slurry from a specific direction to promote ice growth, and a frozen slurry Are formed by vacuum freeze-drying and sublimating ice to form a molded body having macropores, and a process of baking the molded body with ice sublimated by heat treatment to form micropores in the molded body. (See Patent Document 2)
The heat dissipating material of the present invention can be produced by filling a resin in the produced porous body.

  As shown in FIG. 1, the manufacturing method of the ceramic porous body used as the base of the heat dissipating material of the present invention includes a step of adjusting a slurry by dispersing ceramic raw material powder in water (step 1), and the slurry in a specific direction (drawing). The process of freezing from the direction of the arrow) to promote ice growth (process 2), the process of making the formed slurry with macropores by sublimating the frozen slurry by vacuum freeze-drying (process 3), and sublimating the ice The formed body is fired by heat treatment, and is produced by a step (step 4) of forming micropores in the skeleton constituting the formed body.

The ceramic raw material powder used in step 1 is a raw material for forming the skeleton of the porous body, and the material is not particularly limited as long as it contains a sinterable ceramic. A ceramic having a conductivity of 20 W / mK or more. When a ceramic porous body is impregnated with a resin to form a composite material, almost all the thermal conductivity of the composite material is determined by the ceramic. When the thermal conductivity of ceramics is smaller than this, the advantage as a heat dissipation material becomes small. Higher thermal conductivity is preferable, and Al ₂ O ₃ , SiC, ZnO, Si ₃ N ₄ , AlN, and the like are candidates. If necessary, a sintering aid may be added to the ceramic slurry.

  The volume content of ceramics in the slurry is preferably 10 to 50%. If the volume content of the ceramic is less than 10%, the shape-maintaining product of the formed body after sublimation may be damaged, and the ceramic may collapse when the resin is filled. On the other hand, if it exceeds 50%, the porosity of the ceramic porous body becomes small, and the flexibility of the composite material after resin filling is impaired. Therefore, 50-90 volume% resin or metal can be contained in the heat dissipation material which consists of the composite material of the ceramic porous body of this invention and the resin or metal as a 2nd component.

  Next, step 2 will be described. In step 2, the above-described slurry is frozen from one direction, so that the water component is frozen in parallel with the freezing direction, and frost column-shaped ice is formed in the slurry. Specifically, it may be performed as follows. For example, only the bottom surface is immersed in a solution tank containing a refrigerant such as alcohol in which the container into which the slurry is poured is kept at a low temperature and is allowed to stand. As the alcohol, methanol and ethanol are preferable. The temperature of the cooling tank needs to be kept at least below the freezing point of water. Moreover, the container which puts a slurry is produced, for example with a resin-type material etc. with a low heat conductivity in the side surface with a metal with good heat conductivity. When the upper part of the slurry container is released so as to be in contact with the atmosphere, an ice column grows upward in the vertical direction from the bottom of the slurry so that an adjusted frost column is formed.

In step 3, the frozen slurry is freeze-dried together with the container under reduced pressure. By this operation, the ice portion is directly sublimated without passing through the liquid (water), and holes are formed in the molded body as sublimation marks aligned in the above-described freezing direction.
Step 4 is a firing process of the obtained molded body. The formed body formed in step 3 is carefully extracted from the slurry container and fired at a temperature and sintering time suitable for each ceramic. The firing temperature and time are preferably performed under conditions where densification does not proceed much. As a result, a ceramic porous body having columnar ice sublimation marks as macropores is produced. This macro hole is a continuous hole penetrating the sintered body in one direction in accordance with the aforementioned sublimation mark. In step 3, in addition to the columnar ice, ice having an extremely small diameter compared to the columnar ice is also produced in the slurry. Since this ice is also frozen and sublimated in the fourth step, ice is also formed on the wall surface of the macropore and the ceramic skeleton. As a result, fine pores are formed inside the ceramic skeleton, and the porous body has a large specific surface area.

  As shown in FIG. 2, macropores (open pores penetrating in the vertical direction in the drawing) are formed as gaps between ceramic blocks serving as a skeleton. Micropores are formed inside the ceramic structure that serves as the skeleton. The size of the macropores can be controlled by adjusting the amount of water during slurry adjustment. Further, by adjusting the sintering temperature and time, it is possible to finely adjust the size of the macropores and the size of the micropores. Moreover, when making the heat dissipation material which concerns on this invention into a sheet | seat shape as shown in FIG. 2, it is preferable that thickness (length of a direction parallel to a macro hole) is 50 micrometers-200 micrometers.

Finally, the heat radiating material of the present invention is obtained by filling the ceramic porous body with a resin or metal as the second component.
The impregnation of the resin can be performed by various methods, but in order to impregnate the porous layer, a resin having a viscosity as low as possible is preferable. For example, after impregnating a low-viscosity liquid resin among ultraviolet curable resins, there is a method of curing by irradiating ultraviolet rays.

  Among the ultraviolet curable resins, it is preferable to use a soft resin even after curing, because such a heat-dissipating sheet is required to follow the shape of a part that becomes a heat source. That is, the softer the harder is the gap with the surface of the heat-generating component, and the less the heat transport loss due to the air present in the gap. The softness of the resin is generally based on the elongation rate during the tensile test. The elongation percentage of the resin is preferably 50% or more. For example, there is a uretanane 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.

In the ceramic porous body used for the heat dissipating material according to the present invention, the macro holes penetrating in the direction parallel to the heat dissipating are oriented. Furthermore, the macropores are filled with a resin as the second component to form a continuous phase. Further, an appropriate amount of resin is impregnated into the micropores, so that the macropores The columns are joined together with moderate strength. For this reason, when an external force is applied in the direction perpendicular to the length direction of the resin column (in the case of a sheet, the load in the in-plane direction of the sheet), peeling occurs at the interface between the resin column and the ceramic part, The phenomenon that the material is destroyed can be prevented. For this reason, it has a feature of excellent flexibility such as bending, and can be attached to the heat generating member without any gap. Further, the resin impregnated in the macropores has an effect of increasing the heat dissipation of the ceramic portion.
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 the resin is filled, for example, as shown in FIG. 2, it is desirable to impregnate the resin only from one surface of the flat plate-shaped ceramic porous body. This is because impregnation from many surfaces of the ceramic porous body adds processing for removing the resin around the composite material after impregnation and increases the processing cost. When impregnating only from one surface, it is easy because only the upper surface can be removed by grinding or the like, and if the amount of resin impregnated in the ceramic porous body is calculated in advance, it is not necessary to prepare extra resin. In some cases.

  In the case of a ceramic porous body having oriented macropores, the liquid resin is first impregnated along the macropores. While the macropores are being impregnated, the micropores connecting the macropores are simultaneously impregnated. Of the micropores, pores having too small pore diameters are not preferred because resin impregnation does not occur.

  In the production of the ceramic porous body before filling with the resin, it is not preferable that the whole slurry is cooled because ice may grow due to heat transfer from the side surface of the container. That is, it becomes a molded body in which macropores are formed not in one direction but in random directions, and this structure is reflected in the sintered body as it is. The porous body having such a structure cannot be sufficiently impregnated with resin.

  The pore diameter of the ceramic porous body produced by this production method can be controlled by the size of the raw material powder used. In general, the diameter of the macropore is about 5 to 100 μm. The diameter of the micropore is about 0.1 to 5 μm. The macropores are almost completely impregnated with the resin. Micropores having a diameter of 1 μm or less tend not to be impregnated with resin.

The present invention can be used not only for the composite material of ceramics and resin, but also for the production of composite materials of metal and resin. As the metal, for example, Cu alone, Ag alone or the like can be preferably used, but considering the wettability between the metal and ceramic, a metal containing Ti is more preferable. When a Ti alloy is used and wettability with ceramics is sufficiently high, it is not necessary to apply pressure when impregnating the molten metal into the ceramics.
Further, when a resin that is flexible and has a high tensile elongation is used as the resin to be impregnated, the resin can be directly attached to the heat source without using the adhesive layer.

(Example 1)
<Synthesis of porous ceramics>
ZnO, Al ₂ O ₃ , AlN powder and distilled water having various average particle diameters as ceramic raw material powder were mixed so that the volume ratio of the powder was 80-60 vol%. After this mixed powder was ball mill mixed for 10 hours, the resulting slurry was placed in a vacuum defoamer and the bubbles present in the slurry were removed while stirring.
Each slurry was poured into a decomposable container designed to have a diameter of 40 mm shown in FIG. The ethanol temperature was set to −50 ° C. and gently immersed so that only the Cu portion was immersed, and held for about 60 minutes to completely freeze the slurry. The slurry container was taken out and the alcohol content was thoroughly wiped off and placed in a vacuum freeze dryer. After drying for about 20 hours, the compact was carefully extracted from the container and sintered for 2 hours in various atmospheres and various sintering temperatures.

<Resin impregnation>
As the resin, Showa High Polymer vinyl ester resin: Trade name: Lipoxy PH-300A was used. A 1 wt% polymerization initiator (IRGACRE 184: manufactured by Ciba Specialty Chemicals) of the resin was added to this resin, stirred, and then dropped onto the surface of the above various ceramic porous bodies. This was placed in a vacuum oven and impregnated with resin at room temperature while being evacuated with a rotary pump.

<Curing of resin>
Thereafter, the resin was cured by irradiating the ceramic substrate impregnated with the resin with ultraviolet light having a wavelength of 365 nm at a light intensity of 50 mW / cm ² .
<Measurement of thermal conductivity>
The resin-impregnated sample was processed into a diameter of 10 mm, and the thermal conductivity was measured with a laser flash type thermal conductivity measuring device. Tensile specimens were also processed and the tensile elongation was measured.

  As a comparison, a ZnO powder having an average particle size of 8.6 μm was press-molded to produce a compact, and sintered in the atmosphere at a temperature of 800 ° C. for 2 hours to prepare a porous body having a porosity of 50%. This was impregnated with a resin in the same manner to obtain a composite material, and the thermal conductivity and tensile elongation were measured.

The results are shown in Table 1.
The ceramic-resin composite material layer of the present invention exhibits high thermal conductivity and tensile elongation.
The reason why the tensile elongation rate of the comparative product is small is considered that the resin was not sufficiently impregnated.

(Example 2)
<Synthesis of porous ceramics>
The one of Example 1 was used.
<Metal impregnation>
A bulk body of 71 wt% Cu-28 wt% Ag-1 wt% Ti alloy having a purity of 99.9% was placed on a ceramic porous body, placed in a vacuum furnace, and heated at 900 ° C. for 2 hours to impregnate the molten metal. .
<Measurement of thermal conductivity>
The resin-impregnated sample was processed into a diameter of 10 mm, and the thermal conductivity was measured with a laser flash type thermal conductivity measuring device.

As a comparison, a ZnO powder having an average particle size of 8.6 μm was press-molded to produce a compact, and sintered in the atmosphere at a temperature of 800 ° C. for 2 hours to prepare a porous body having a porosity of 50%. This was impregnated with a resin in the same manner to obtain a composite material, and the thermal conductivity was measured.
The results are shown in Table 2.
The ceramic-metal composite material of the present invention exhibits high thermal conductivity.

It is a figure which shows the manufacturing method of the ceramic porous body used as the base of the thermal radiation material of this invention. It is a figure which shows the process of impregnating resin to a ceramic porous body. It is a figure which shows the decomposable container used when manufacturing the thermal radiation material of this invention.

Claims (10)

  A composite material having a ceramic porous body and a heat-absorbing part and a heat-dissipating part made of a resin or metal as a second component, wherein the resin is provided in a macropore provided in the ceramic porous body so as to be oriented from the heat-absorbing part to the heat-dissipating part. Alternatively, a continuous phase of the second component filled with the metal and a continuous phase of the oriented second phase of the other second component, and a connected phase in which the micropore is filled with a resin or a metal, A heat dissipating material comprising a composite material having   The heat dissipation material according to claim 1, wherein the second component is a resin.   The heat dissipation material according to claim 1 or 2, wherein the volume content of the second component is 50 to 90% in the heat dissipation material.   The diameter of the macropore used as the continuous phase of said 2nd component is 5-100 micrometers, The heat radiating material as described in any one of Claims 1-3 characterized by the above-mentioned.   The heat dissipation material according to any one of claims 1 to 4, wherein an average pore diameter of the micropores is 0.1 to 5 µm.   The heat dissipation material according to any one of claims 1 to 5, wherein the ceramic porous body has a thermal conductivity of 20 W / mK or more.   Resin having a tensile elongation of 50% or more is used as the second component, and the heat dissipating material according to any one of claims 1 to 6.   The heat dissipation material according to any one of claims 1 to 7, wherein an adhesive layer is formed on at least a part of the surface of the heat dissipation material.   A slurry preparation step for dispersing ceramic raw material powder in water, a step for freezing the obtained slurry from a specific direction to promote ice growth, a freeze-dried frozen slurry to sublimate ice, and a molded body having macropores A process in which the ice-sublimated molded body is baked by heat treatment to form micropores in the molded body, and a resin or metal as a second component is filled in the macropores and micropores. A process for producing a heat dissipation material.   The method for manufacturing a heat dissipation material according to claim 9, wherein the second component is a resin.

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