JP2010260225A - Thermoconductive molding and use thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoconductive molding which has high thermal conductivity and is suitable particularly as a heat radiating member for electronic components. <P>SOLUTION: The thermoconductive molding is obtained by cutting a silicone laminate from the laminated direction, which laminate is formed by incorporating 50-75 vol.% thermoconductive filler containing the blended boron nitride powder obtained by blending boron nitride powder (A) having 25-45 μm average particle size and 15-100 aspect ratio with boron nitride powder (B) having 0.5-5 μm average particle size and 2-10 aspect ratio by the mass ratio (blending ratio) of 5:5 to 9:1. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a thermally conductive molded article having excellent thermal conductivity and its application, and particularly when used as a heat radiating member for an electronic component, a heat generating electron such as a transistor, a thyristor, or a CPU (central processing unit). The present invention relates to a thermally conductive molded body that can be incorporated into an electronic device without damaging the components.

  In heat-generating electronic components such as transistors, thyristors, and CPUs, it is an important problem how to remove heat generated during use. Conventionally, as such a heat removal method, a heat-generating electronic component is generally attached to a heat-radiating fin or a metal plate via an electrically insulating heat-dissipating sheet, and the heat is released. Uses a silicone rubber with a thermally conductive filler dispersed therein.

In recent years, the amount of heat generated has increased with the high integration of circuits in electronic components, and there has been a demand for a heat dissipating sheet having higher thermal conductivity than before.

Conventional techniques for improving the thermal conductivity of the heat-dissipating sheet include a method of highly filling the thermal conductive filler and a method of aligning and arranging the thermal conductive fillers exhibiting anisotropy. (Patent documents 1-4).

In addition, the conventional laminated heat conductive molded body uses boron nitride powder having an average particle size of 7 μm, and the silicone rubber can be filled with only about 40% by volume of the heat conductive filler. (Patent Document 2).

Furthermore, in the composite material composed of the heat conductive filler and the silicone rubber, heat is easily transmitted especially through contact between the heat conductive fillers. However, when boron nitride powder having an average particle diameter of 7 μm is used, Since the heat conductive fillers have low density and the heat conductive fillers hardly contact each other, the thermal conductivity was about 3 to 5 W / mK (Patent Document 2).

Japanese Patent Laid-Open No. 11-21388 Japanese Patent Laid-Open No. 11-19948 JP 2007-254637 A JP 2007-277406 A

  An object of the present invention is to provide a thermally conductive molded article having high thermal conductivity and particularly suitable as a heat radiating member for electronic parts.

The present invention employs the following means in order to solve the above problems.
(1) The average particle diameter of the boron nitride powder (A) is 25 to 45 μm, the aspect ratio is 15 to 100, the average particle diameter of the boron nitride powder (B) is 0.5 to 5 μm, and the aspect ratio is 2 to 10 And a silicon laminate comprising 50 to 75% by volume of a thermally conductive filler containing boron nitride powder in which the mixing ratio of (A) :( B) in the boron nitride powder is 5: 5 to 9: 1 by mass ratio Is cut from the laminating direction.
(2) The silicone laminate contains a silicone sheet (C) containing 50 to 60% by volume of a heat conductive filler containing boron nitride powder and 65 to 75% by volume of a heat conductive filler containing boron nitride powder. The thermally conductive molded article according to (1), wherein the silicone sheets (D) are alternately laminated.
(3) A heat dissipating member for electronic parts, comprising the heat conductive molded body according to (1) or (2).

  ADVANTAGE OF THE INVENTION According to this invention, the heat conductive molded object which shows high heat conductivity can be provided.

Hereinafter, the present invention will be described in detail.
Examples of the thermally conductive filler used in the present invention include aluminum oxide, magnesium oxide, boron nitride, aluminum nitride, silicon nitride, silicon carbide and the like. Among these, boron nitride has extremely high thermal conductivity in the length direction of the scaly particles, and high thermal conductivity can be imparted if the characteristics are utilized well, and is therefore particularly suitable for the present invention. . The boron nitride powder is preferably highly crystalline with a graphite index (GI) of 2.5 or less by powder X-ray analysis.

Furthermore, in the present invention, conductive powders such as aluminum, copper, silver, carbon fiber, and carbon nanotube can be used in combination as long as the insulating properties are not impaired.

The content of the heat conductive filler in the heat conductive molded body of the present invention is preferably 50 to 75% by volume, particularly 65 to 70% by volume in the entire volume. If the content rate of a heat conductive filler is less than 50 volume%, it exists in the tendency for the heat conductivity of a heat conductive molded object to reduce. If it exceeds 75% by volume, the mechanical strength of the molded product tends to be impaired.

The boron nitride powder (A) of the present invention must have an average particle diameter of 25 to 45 μm, and the average particle diameter is preferably in the range of 30 to 40 μm. When the average particle diameter is larger than 45 μm, it tends to be difficult to densely fill the heat conductive filler. On the other hand, when the average particle size is smaller than 25 μm, the filling property is deteriorated and the thermal conductivity tends to decrease.

The boron nitride powder (B) of the present invention must have an average particle diameter of 0.5 to 5 μm, and the average particle diameter is preferably in the range of 1 to 3 μm. When the average particle diameter is larger than 5 μm, the particle diameter is close to that of the boron nitride powder having an average particle diameter of 25 to 45 μm, so that the filling property tends to deteriorate and the thermal conductivity tends to decrease. On the other hand, when the average particle size is smaller than 0.5 μm, the filling property of the whole heat conductive material tends to deteriorate, and the heat conductivity tends to decrease.

The average particle diameter in the present invention was measured using “Laser diffraction particle size distribution analyzer SALD-200” manufactured by Shimadzu Corporation. As an evaluation sample, 5 g of 50 cc of pure water and a heat conductive powder to be measured were added to a glass beaker, stirred using a spatula, and then subjected to a dispersion treatment for 10 minutes using an ultrasonic cleaner. The solution of the thermally conductive material powder that had been subjected to the dispersion treatment was added drop by drop to the sampler portion of the apparatus using a dropper, and waited until the absorbance became measurable. The measurement is performed when the absorbance becomes stable in this way. In the laser diffraction type particle size distribution measuring device, the particle size distribution is calculated from the data of the light intensity distribution of the diffracted / scattered light by the particles detected by the sensor. The average particle size is obtained by multiplying the value of the measured particle size by the relative particle amount (difference%) and dividing by the total relative particle amount (100%). The average particle diameter is the average diameter of the particles.

The boron nitride powder (A) of the present invention must have an aspect ratio of 15 to 100, and the aspect ratio is preferably in the range of 30 to 80. When the aspect ratio is greater than 100, the filler filling property tends to deteriorate. On the other hand, when the aspect ratio is smaller than 15, it becomes difficult to densely fill the resin, and the thermal conductivity tends to decrease.

The boron nitride powder (B) of the present invention needs to have an aspect ratio of 2 to 10, and the aspect ratio is preferably in the range of 3 to 8. When the aspect ratio is larger than 10, the filling property of the filler tends to deteriorate. On the contrary, when the aspect ratio is smaller than 2, it becomes difficult to densely fill the resin, and the thermal conductivity tends to decrease.

The aspect ratio of boron nitride powder was dispersed on conductive carbon double-sided tape with boron nitride powder affixed on a glass slide, and 200 particles were observed using Keyence's “3D Real Surface View Microscope VE-9800”. Then, the lengths of the major axis and the minor axis are measured and calculated from the calculation formula of aspect ratio = major axis / minor axis.

  The mixing ratio of the boron nitride powder (A) and the boron nitride powder (B) needs to be 5: 5 to 9: 1 by mass ratio, and more preferably 6: 4 to 8: 2 by mass ratio. . When the proportion of the boron nitride powder (A) is less than 5, the filler filling property tends to be poor. On the other hand, when the ratio of the boron nitride powder (A) is greater than 9, the filler becomes difficult to be densely packed, and the thermal conductivity tends to decrease.

  High filling of the thermally conductive filler, which was difficult when using boron nitride powder with an average particle diameter of 7 μm, which is a conventional technique, was filled with boron nitride powder with an average particle diameter of 25 to 45 μm having a large particle diameter. By filling the voids with boron nitride powder having an average particle diameter of 0.5 to 5 μm, it becomes possible to more precisely fill the thermally conductive filler, and the filler filling amount is from 45% by volume to 75% of the conventional amount. It becomes possible to rise to volume%.

  Silicone laminates are made by laminating uncured bodies (hereinafter referred to as green sheets) formed from thin composite materials of heat-conductive filler and silicone rubber, and then curing them by heating to bond the uncured green sheets together. And a cured silicone laminate is obtained.

The silicone laminate includes a green sheet A having a thermal conductive filler content of 50-60% by volume containing boron nitride powder and a green sheet B having a thermal conductive filler content of 65-75% by volume containing boron nitride powder. Are preferably laminated alternately. Further, green sheets A having a thermal conductive filler content of 53 to 58% by volume containing boron nitride powder and green sheets B having a thermal conductive filler content of 68 to 73% by volume containing boron nitride powder are alternately laminated. More preferred is When the content of the thermally conductive filler containing the boron nitride powder of the green sheet A is less than 50% by volume, the amount of the thermally conductive filler filled decreases, and the thermal conductivity tends to decrease. When the content rate of the heat conductive filler containing the boron nitride powder of the green sheet A exceeds 60 volume%, adhesiveness with the green sheet B will deteriorate, and the heat conductivity between the green sheets tends to decrease. Moreover, when the content rate of the heat conductive filler containing the boron nitride powder of the green sheet B is less than 65 volume%, the filling amount of the heat conductive filler decreases, and the heat conductivity tends to decrease. When the content rate of the heat conductive filler containing the boron nitride powder of the green sheet B exceeds 75 volume%, the mechanical strength of the green sheet B tends to be impaired.

  Examples of the rubber used as the matrix of the present invention include silicone rubber, urethane rubber, acrylic rubber, butyl rubber, ethylene propylene copolymer, ethylene vinyl acetate copolymer and the like. Of these, silicone rubber is most suitable because it has excellent flexibility, shape followability, adhesion to a heat generating surface when it is brought into contact with an electronic component, and heat resistance.

As a type of silicone rubber, millable type silicone is representative, but since it is often difficult to express the required flexibility as a whole, addition reaction type silicone is suitable for expressing high flexibility. It is. Specific examples of the addition reaction type liquid silicone include one liquid reaction type organopolysiloxane having both a vinyl group and an H-Si group in one molecule having a molecular weight of tens of thousands, or a vinyl group at a terminal or side chain. A two-part silicone of an organopolysiloxane having two or more H-Si groups at the terminal or side chain. For example, there is a product name “SE-1885A / B” manufactured by Toray Dow Corning Silicone.

In order to improve the moldability of the green sheet, it is preferable to add methyl vinyl silicone raw rubber having a vinyl group having a weight average molecular weight of 300,000 to 800,000. By adding a methyl vinyl silicone raw rubber having a large molecular weight, it is possible to prevent the molecular chain from being cut by filling the filler highly, and to enable the formation of a green sheet with a high filler filling. For example, there is a trade name “SRH-32” manufactured by Momentive Performance Materials.

The addition reaction type liquid silicone used in the present invention includes reaction retarders such as acetyl alcohols and maleates, thickeners such as 10 to several hundred μm aerosil and silicone powder, flame retardants, pigments, etc. Can also be used together.

Thermal conductivity, sandwiched between the TO-3 TO-3 type cut sample was (1mm) built of transistor type copper heater case (effective area 6 cm ²⁾ and copper plates, 10% of the initial thickness compression After setting with a load, the transistor is applied with power 15W and held for 5 minutes, and the thermal resistance calculated by the following equation (1) from the temperature difference (° C.) between the heater case and the radiation fin (° C./W) is converted by equation (2).

Thermal resistance (° C / W) = Temperature difference (° C) / Power (W) (1)

Thermal conductivity (W / mK) = {sample thickness (m) / {thermal resistance (° C./W)×sample area (m ² ) (2)

If an example of the manufacturing method of the heat conductive molded object of this invention is shown, an addition reaction type liquid silicone and boron nitride powder will be mixed at room temperature, and a silicone raw rubber will be added and mixed, and a compound may be adjusted, There is a method of extruding with a piston-type or screw-type extruder to temporarily form a green sheet, laminating and heat-curing it, and then cutting it to a desired width from the laminating direction.

  The heat conductive molded body of the present invention is used by being sandwiched between a heat generating electronic component or a circuit board on which a thermothermal electronic component is mounted and a cooling device. For example, it can be supplied as a heat radiating member for electronic parts. Examples of the cooling device include a heat sink, a heat radiating fin, a metal or ceramic case, and examples of the ceramic include aluminum nitride, boron nitride, silicon carbide, silicon nitride, and aluminum oxide.

  In addition, examples of electronic devices in which the heat dissipating member for electronic parts is used include personal computers, home game machines, power supplies, automobiles, projectors, and the like.

Examples 1-10 Comparative Examples 1-8
Two-component addition reaction type silicone (manufactured by Toray Dow Corning Co., Ltd.) consisting of the thermally conductive filler shown in Table 1, solution A (organopolysiloxane having a vinyl group) and solution B (organopolysiloxane having an H-Si group) , Trade name “SE-1885”) is mixed with the mixing ratio (volume%) shown in Tables 2, 3, and 5 for the mixing ratio of A liquid to B liquid, and further, this is a silicone raw rubber (made by Momentive Performance Materials) , Trade name “SRH-32”) was mixed at room temperature to prepare a compound.

This compound is filled into a cylinder structure die fixed with a die having a slit (1 mm × 60 mm), extruded from the slit while applying pressure with a piston, and an uncured thin plate of a composite material of a heat conductive filler and silicone rubber (Green sheet) was produced.

A green sheet was cut out from 25 green sheets having a thickness of 1 mm, a width of 60 mm, and a length of 120 mm with a cutter so as to form a square having a length and width of 50 mm. And 50 layers were laminated | stacked until it became a height of 50 mm, aligning each corner | angular of square green sheets. Then, it heat-cured for 22 hours at 150 degreeC using the dryer, and produced the silicone laminated body. This silicone layered body which is a cube with a length of 50 mm on one side is perpendicular to the surface on which the green sheets are stacked with a cutter, and is cut while lowering the blade parallel to the side, thereby forming the sheet-like shape of the present invention A thermally conductive molded body (1 mm) was produced.

The green sheets A and B shown in Examples 11 to 13 in Table 4 are the same as in Examples 1 to 10, and the thermally conductive filler, A liquid (organopolysiloxane having a vinyl group), and B liquid (shown in Table 1). A two-component addition reaction type silicone of H-Si group (organopolysiloxane) (trade name “SE-1885”, manufactured by Toray Dow Corning Co., Ltd.) having a mixing ratio of A to B in Table 4 ( In addition, a silicone raw rubber (manufactured by Momentive Performance Materials, trade name “SRH-32”) was mixed at room temperature to prepare a compound.

Each compound is filled into a cylinder structure mold in which a die with a slit (1 mm × 60 mm) is fixed, and is extruded from the slit while applying pressure with a piston, and an uncured composite material of a heat conductive filler and silicone rubber is uncured. Thin plates (green sheets A and B) were prepared.

The green sheets A and B were alternately laminated until reaching a height of 50 mm, and then heat-cured at 150 ° C. for 22 hours using a dryer to produce a silicone laminate. This silicone laminate was cut with a cutter perpendicular to the lamination direction and parallel to the sides to produce a sheet-like thermally conductive molded article (1 mm) of the present invention.

About the sheet-like heat conductive molded object obtained above, it cut | judged to TO-3 type | mold and measured thermal conductivity. The results are shown in Tables 2-5. In Comparative Example 5, a sheet-like thermally conductive molded body could not be produced.

From the Examples and Comparative Examples in Tables 2 to 5, the thermally conductive molded body of the present invention exhibits excellent thermal conductivity.

Claims (3)

The average particle diameter of the boron nitride powder (A) is 25 to 45 μm and the aspect ratio is 15 to 100, the average particle diameter of the boron nitride powder (B) is 0.5 to 5 μm, and the aspect ratio is 2 to 10, A silicone laminate comprising 50 to 75% by volume of a thermally conductive filler containing boron nitride powder having a mass ratio of (A) :( B) of boron nitride powder of 5: 5 to 9: 1 is laminated. The heat conductive molded object characterized by cut | disconnecting from a direction. Silicone sheet (C) containing 50-60% by volume of thermally conductive filler containing boron nitride powder, and 65-75% by volume of silicone sheet containing thermally conductive filler containing boron nitride powder (Silicone laminate) The thermally conductive molded article according to claim 1, wherein D) are alternately laminated. The heat radiating member for electronic components using the heat conductive molded object of Claim 1 or Claim 2.