JP2022191990A - Thermally conductive sheet and thermally conductive sheet production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermally conductive sheet with high thermal conductivity, where a pass/fail evaluation of a desired thermally conductive sheet can be easily made.

SOLUTION: A thermally conductive sheet 1 comprises a cured product of a composition containing a binder resin 2, an anisotropic thermally conductive filler 3, and a thermally conductive filler 4 other than the anisotropic thermally conductive filler 3, and satisfies conditions 1-3 below. [Condition 1] A gloss value measured with a light ray 6 which is incident at a position 60° from a virtual perpendicular line 5 with respect to the surface of the thermally conductive sheet 1 is less than 10. [Condition 2] The average particle size of the anisotropic thermally conductive filler 3 is from 15 μm to 45 μm inclusive. [Condition 3] In the thermally conductive sheet 1, the total content of the anisotropic thermally conductive filler 3, and the other thermally conductive filler 4 exceeds 60 vol.% but is less than 75 vol.%.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2023,JPO&INPIT

Description

The present technology relates to a thermally conductive sheet and a method for manufacturing the thermally conductive sheet.

2. Description of the Related Art As electronic devices become more sophisticated, semiconductor devices are becoming more dense and highly mounted. Along with this, it has become important to more efficiently dissipate the heat generated from the electronic components that make up the electronic equipment. For example, in order to efficiently dissipate heat in a semiconductor device, an electronic component is attached to a heat sink such as a heat dissipating fan or a heat dissipating plate via a heat conductive sheet. As a thermal conductive sheet, a silicone resin containing (dispersing) a filler such as an inorganic filler is widely used.

A further improvement in thermal conductivity is required for a heat dissipating member such as this heat conductive sheet. For example, in order to increase the thermal conductivity of the thermally conductive sheet, it is being studied to increase the filling rate of the inorganic filler blended in the matrix such as the binder resin. However, if the filling rate of the inorganic filler is increased, the flexibility of the thermally conductive sheet may be impaired, or powder of the inorganic filler may fall off. Therefore, there is a limit to increasing the filling rate of the inorganic filler in the heat conductive sheet.

Examples of inorganic fillers include alumina, aluminum nitride, and aluminum hydroxide. For the purpose of high thermal conductivity, the matrix may be filled with scaly particles such as boron nitride or graphite, carbon fibers, or the like. This is due to the anisotropy of thermal conductivity of scale-like particles, carbon fibers, and the like. For example, carbon fibers are known to have a thermal conductivity of about 600-1200 W/m·K in the fiber direction. Boron nitride, which is a scaly particle, has a thermal conductivity of about 110 W/m K in the plane direction, and a thermal conductivity of about 2 W/m K in the direction perpendicular to the plane direction. known to have Thus, carbon fibers and scaly particles are known to have anisotropic thermal conductivity. Making the fiber direction of the carbon fibers and the surface direction of the scale-like particles the same as the thickness direction of the heat conductive sheet, which is the direction of heat transfer, that is, orienting the carbon fibers and the scale-like particles in the thickness direction of the heat conductive sheet. By this, the thermal conductivity of the thermally conductive sheet can be dramatically improved.

By the way, in addition to having high thermal conductivity, the heat conductive sheet is used to judge the quality of the manufactured heat conductive sheet. It is demanded that it is possible to easily determine whether or not a thermally conductive sheet has a predetermined thermal conductivity.

Patent Document 1 discloses a thermally conductive sheet made of a resin composition containing a resin and a scaly thermally conductive filler dispersed in the resin, wherein the scaly thermally conductive filler increases the thickness of the thermally conductive sheet. A thermally conductive sheet is described in which the inclination with respect to the longitudinal direction periodically changes along one direction within the surface direction of the thermally conductive sheet. The heat conductive sheet described in Patent Literature 1 has an insufficient degree of orientation of the scale-like filler and cannot be said to be a high heat conductive sheet having anisotropy, and it is considered difficult to achieve high heat conductivity.

JP 2019-214663 A

The present technology has been proposed in view of such conventional circumstances, and provides a thermally conductive sheet that has a high thermal conductivity and can easily determine the quality of a desired thermally conductive sheet.

A thermally conductive sheet according to the present technology is a thermally conductive sheet made of a cured product of a composition containing a binder resin, an anisotropic thermally conductive filler, and a thermally conductive filler other than the anisotropic thermally conductive filler. and satisfies the following conditions 1 to 3.
[Condition 1] The gloss value is less than 10 as measured by light rays incident at a position of 60° from an imaginary perpendicular to the surface of the heat conductive sheet.
[Condition 2] The average particle size of the anisotropic thermally conductive filler is 15 μm or more and 45 μm or less.
[Condition 3] The total content of the anisotropic thermally conductive filler and other thermally conductive fillers in the thermally conductive sheet is more than 60% by volume and less than 75% by volume.

A method for producing a thermally conductive sheet according to the present technology comprises a thermally conductive composition containing a curable resin composition, an anisotropic thermally conductive filler, and a thermally conductive filler other than the anisotropic thermally conductive filler. a step of extruding and then curing the thermally conductive composition to obtain a columnar cured product; and cutting the columnar cured product into a predetermined thickness in a direction substantially perpendicular to the length direction of the column. and obtaining a heat conductive sheet, and the heat conductive sheet satisfies the conditions 1 to 3 described above.

The present technology can provide a thermally conductive sheet that has high thermal conductivity and can easily determine the quality of a desired thermally conductive sheet.

FIG. 1 is a cross-sectional view showing an example of a heat conductive sheet. FIG. 2 is a diagram for explaining an example of a gloss value measuring method. FIG. 3 is a perspective view schematically showing scale-like boron nitride having a hexagonal crystal shape, which is an example of an anisotropic thermally conductive filler. FIG. 4 is a cross-sectional view showing an example of a semiconductor device to which a heat conductive sheet is applied.

As used herein, the average particle size (D50) of anisotropic thermally conductive fillers and other thermally conductive fillers means that the entire particle size distribution of the anisotropic thermally conductive fillers or other thermally conductive fillers is 100 %, it means the particle diameter when the cumulative value is 50% when the cumulative curve of the particle diameter value is obtained from the small particle diameter side of the particle diameter distribution. In addition, the particle size distribution (particle size distribution) in this specification is determined by volume. Examples of the method for measuring the particle size distribution include a method using a laser diffraction particle size distribution analyzer.

<Thermal conductive sheet>
FIG. 1 is a cross-sectional view showing an example of a heat conductive sheet 1 according to the present technology. The thermally conductive sheet 1 is made of a cured composition containing a binder resin 2 , an anisotropic thermally conductive filler 3 , and a thermally conductive filler 4 other than the anisotropic thermally conductive filler 3 . The thermally conductive sheet 1 has an anisotropic thermally conductive filler 3 and another thermally conductive filler 4 dispersed in a binder resin 2, and the anisotropic thermally conductive filler 3 extends in the thickness direction B of the thermally conductive sheet 1. is oriented.

Here, the orientation of the anisotropic thermally conductive fillers 3 in the thickness direction B of the thermally conductive sheet 1 means, for example, that among all the anisotropic thermally conductive fillers 3 in the thermally conductive sheet 1, The ratio of the anisotropic thermally conductive filler 3 whose long axis is oriented in the thickness direction B of the conductive sheet 1 is 50% or more, may be 55% or more, or may be 60% or more, 65% or more, 70% or more, 80% or more, 90% or more, 95% or more, 99% or more may

The anisotropic thermally conductive filler 3 is a thermally conductive filler having an anisotropic shape. Examples of the anisotropic thermally conductive filler 3 include thermally conductive fillers having a long axis, a short axis, and a thickness (for example, scale-like thermally conductive fillers). The scale-like thermally conductive filler is a thermally conductive filler having a long axis, a short axis, and a thickness, has a high aspect ratio (long axis/thickness), and is isotropic in the plane including the long axis. It has a good thermal conductivity. The short axis of the scaly thermally conductive filler is a direction that intersects through the midpoint of the long axis of the scaly thermally conductive filler in a plane containing the long axis of the scaly thermally conductive filler. , refers to the length of the shortest part of the scale-like thermally conductive filler. The thickness of the scale-like thermally conductive filler refers to the average value obtained by measuring the thickness of the surface including the long axis of the scale-like thermally conductive filler at 10 points. The aspect ratio of the anisotropic thermally conductive filler 3 is not particularly limited, and can be appropriately selected depending on the purpose. For example, the aspect ratio of the anisotropic thermally conductive filler 3 can be in the range of 10-100. The major axis, minor axis and thickness of the anisotropic thermally conductive filler 3 can be measured with, for example, a microscope, scanning electron microscope (SEM), particle size distribution meter, or the like.

Other thermally conductive fillers 4 are thermally conductive fillers other than the anisotropic thermally conductive fillers 3, that is, thermally conductive fillers having no anisotropy in shape.

FIG. 2 is a diagram for explaining an example of a gloss value measuring method. As a result of investigation by the present inventors, the formulation of the thermally conductive sheet 1 (in particular, the orientation of the anisotropic thermally conductive filler 3, the average particle size of the anisotropic thermally conductive filler 3, the anisotropic thermally conductive filler 3 and the total content of other thermally conductive fillers 4, etc.), and the gloss value measured by the light beam 6 incident from the position of 60 ° from the imaginary perpendicular 5 to the surface 1A of the thermally conductive sheet 1 in the thermally conductive sheet 1. It is conceivable that there is the following relationship between

First, as the influence of the orientation of the anisotropic thermally conductive filler 3 in the thermally conductive sheet 1, in the thermally conductive sheet in which the anisotropic thermally conductive filler 3 is not oriented, the anisotropic thermally conductive filler 3 is oriented. Compared to a thermally conductive sheet that has a high gloss value, it tends to have a higher gloss value because the reflected component of incident light increases.

In addition, as the effect of the total content of the anisotropic thermally conductive filler 3 and the other thermally conductive filler 4 in the thermally conductive sheet 1 on the gloss value, the anisotropic thermally conductive filler 3 in the thermally conductive sheet 1 and the When the total content of the other thermally conductive fillers 4 is reduced, the binder existing on the surface of the thermally conductive sheet 1 is more likely to be reflected than the particles (anisotropic thermally conductive fillers 3 and other thermally conductive fillers 4). The effect of the glossiness of the resin 2 tends to increase. For example, when the binder resin 2 is a silicone resin, the luster of the silicone resin flowing out from the thermally conductive sheet 1 becomes stronger than the reflection by the anisotropic thermally conductive filler 3 and other thermally conductive fillers 4, and the anisotropic It is considered that the decrease in the total content of the thermally conductive filler 3 and the other thermally conductive filler 4 increases the effect of the silicone resin on the gloss value.

Moreover, it can be expected that the thermal conductivity of the thermally conductive sheet 1 increases as the particle diameter of the anisotropic thermally conductive filler 3 increases. However, when the particle size of the anisotropic thermally conductive filler 3 exceeds a certain value, it becomes difficult to fill the binder resin 2 with the anisotropic thermally conductive filler 3 due to the effect of the particle size. It tends to be difficult to improve the conductivity. On the other hand, the smaller the particle size of the anisotropic thermally conductive filler 3, the more the anisotropic thermally conductive filler 3, for example, in order to conduct heat from one end to the other end in the thickness direction B of the thermally conductive sheet 1. Therefore, more contact points of the anisotropic thermally conductive filler 3 are required. As described above, when the number of contact points of the anisotropic thermally conductive filler 3 in the heat conductive sheet 1 increases, the thermal resistance between contacts at the contact portion increases, and heat conduction loss is more likely to occur. It tends to be difficult to improve the thermal conductivity in the thickness direction B of the sheet 1 . The same applies to the plane direction A of the heat conductive sheet 1 .

Therefore, the heat conductive sheet 1 satisfies the following conditions 1 to 3.
[Condition 1] The gloss value measured by the light ray 6 incident from the position of 60° from the imaginary perpendicular 5 to the surface 1A of the heat conductive sheet 1 is less than 10.
[Condition 2] The average particle size of the anisotropic thermally conductive filler 3 is 15 μm or more and 45 μm or less.
[Condition 3] The total content of the anisotropic thermally conductive filler 3 and the other thermally conductive filler 4 in the thermally conductive sheet 1 is more than 60% by volume and less than 75% by volume.

Regarding Condition 1, the heat conductive sheet 1 has a gloss value of less than 10, and may be 8 or less, measured with a light ray 6 incident at a position of 60° from an imaginary perpendicular 5 to the surface 1A of the heat conductive sheet 1. , 7 or less, 6.2 or less, 5.4 or less, 5.2 or less, or 3.9 or less. The method for measuring the gloss value of the thermally conductive sheet 1 is the same as the method described in Examples below.

When the thermally conductive sheet 1 satisfies the condition 1, as described above, the ratio of the anisotropic thermally conductive filler 3 in the thermally conductive sheet 1 tends to be high, and the thickness direction of the thermally conductive sheet 1 Good thermal conductivity. Further, when the thermally conductive sheet 1 satisfies the condition 1, the quality of the manufactured thermally conductive sheet is determined, for example, the thermally conductive sheet containing a predetermined amount of thermally conductive filler having a predetermined particle size has a predetermined thermal conductivity. can be easily determined. In other words, in addition to measuring the thermal conductivity of the thermally conductive sheet 1, the gloss value of the thermally conductive sheet 1 can also be measured to obtain a rough estimate of the thermal conductivity of the thermally conductive sheet 1. Furthermore, when the thermally conductive sheet 1 satisfies the condition 1, when using the thermally conductive sheet 1, it is possible to more reliably avoid erroneous image recognition when the thermally conductive sheet 1 is picked up by an automatic machine. It becomes possible to pick up the heat conductive sheet 1 more reliably.

Regarding Condition 2, from the viewpoint of improving the thermal conductivity of the thermally conductive sheet 1, the average particle size of the anisotropic thermally conductive filler 3 in the thermally conductive sheet 1 is 15 μm or more, even if it is 20 μm or more. It may be 25 μm or more, 30 μm or more, 35 μm or more, or 40 μm or more. Moreover, the average particle size of the anisotropic thermally conductive filler 3 in the thermally conductive sheet 1 is preferably in the range of 20 to 40 μm from the viewpoint of improving the thermal conductivity of the thermally conductive sheet 1 .

The thermally conductive sheet 1 may use one kind of anisotropic thermally conductive filler 3 alone, or may use two or more kinds of anisotropic thermally conductive fillers 3 having different particle sizes in combination. When the thermally conductive sheet 1 contains two or more types of anisotropic thermally conductive fillers 3 with different particle sizes, the particle size is 20 μm with respect to the total content of the anisotropic thermally conductive fillers 3 in the thermally conductive sheet 1. The content ratio of the anisotropic thermally conductive filler 3 having a diameter of 40 μm or more may be 50% by volume or more, may be 60% by volume or more, may be 70% by volume or more, or may be 80% by volume or more. It may be vol % or more, 90 vol % or more, or 100 vol %.

From the viewpoint of moldability of the heat conductive sheet 1, the heat conductive sheet 1 preferably contains one type of anisotropic heat conductive filler 3 as the anisotropic heat conductive filler 3 alone. That is, it is preferable not to use two or more anisotropic thermally conductive fillers 3 together in the thermally conductive sheet 1 .

Regarding condition 3, the thermally conductive sheet 1 has a total content of the anisotropic thermally conductive filler 3 and the other thermally conductive filler 4 of 60% by volume from the viewpoint of thermal conductivity and the gloss value of the condition 1 described above. It may exceed 61% by volume, may be 63% by volume or more, may be 66% by volume or more, or may be 67% by volume or more. In addition, from the viewpoint of moldability of the heat conductive sheet 1, the total content of the anisotropic heat conductive filler 3 and the other heat conductive filler 4 is less than 75% by volume, and 74% by volume. 70% by volume or less, 69% by volume or less, or 68% by volume or less. Further, in the thermally conductive sheet 1, the total content of the anisotropic thermally conductive filler 3 and the other thermally conductive filler 4 may be in the range of 63 to 67% by volume.

The content of the anisotropic thermally conductive filler 3 in the thermally conductive sheet 1 is preferably more than 20% by volume from the viewpoint of the thermal conductivity of the thermally conductive sheet 1 and the gloss value of Condition 1 described above, and 23% by volume. % or more, 25 volume % or more, or 26 volume % or more. In addition, the content of the anisotropic thermally conductive filler 3 in the thermally conductive sheet 1 is preferably less than 35% by volume from the viewpoint of moldability of the thermally conductive sheet 1, and even if it is 30% by volume or less. It may be 28% by volume or less, or 27% by volume or less. Also, the content of the anisotropic thermally conductive filler 3 in the thermally conductive sheet 1 may be in the range of 23 to 27% by volume.

In addition, the content of the other thermally conductive filler 4 in the thermally conductive sheet 1 may be 10% by volume or more, may be 15% by volume or more, or may be 20% by volume or more, It may be 25% by volume or more, 30% by volume or more, or 35% by volume or more. In addition, the upper limit of the content of the other thermally conductive filler 4 in the thermally conductive sheet 1 may be 50% by volume or less, may be 45% by volume or less, or may be 40% by volume or less. good too. In addition, the content of the other thermally conductive filler 4 in the thermally conductive sheet 1 may be in the range of 30 to 50% by volume, may be in the range of 35 to 45% by volume, and may be in the range of 37 to 42% by volume. % may be in the range.

A thermally conductive sheet 1, that is, a cured product of a composition containing a binder resin 2, an anisotropic thermally conductive filler 3, and another thermally conductive filler 4, satisfying the conditions 1 to 3 described above. The sheet tends to have more anisotropic thermally conductive fillers 3 oriented along the thickness direction B as the L* value in the L*a*b* color system of the sheet surface increases. The thermal conductivity of is good. Therefore, the heat conductive sheet 1 preferably has an L* value of 70 or more, may be 75 or more, may be 77 or more, or may be 80 in the L*a*b* color system of the sheet surface. It may be 85 or more, 88 or more, or 89 or more. The upper limit of the L* value of the sheet surface in the L*a*b* color system of the heat conductive sheet 1 is preferably 95 or less, and may be 90 or less.

Here, the L*a*b color system is, for example, a color system described in "JIS Z 8781", and is indicated by arranging each color in a spherical color space. In the L*a*b color system, lightness is indicated by the position in the vertical axis (z-axis) direction, hue is indicated by the position in the outer peripheral direction, and saturation is indicated by the distance from the central axis. The position in the vertical axis (z-axis) direction indicating brightness is indicated by L*. The value of lightness L* is a positive number, and the smaller the number, the lower the lightness, which tends to be darker. Specifically, the value of L* varies from 0, which corresponds to black, to 100, which corresponds to white. In a cross-sectional view of the spherical color space horizontally cut at L*=50, the positive direction of the x-axis is the red direction, the positive direction of the y-axis is the yellow direction, the negative direction of the x-axis is the green direction, and the y The negative direction of the axis is the blue direction. Position along the x-axis is represented by a*, which ranges from -60 to +60. Position along the y-axis is represented by b*, which ranges from -60 to +60. Thus, a* and b* are positive and negative numbers representing chromaticity, and the closer they are to 0, the darker they become. Hue and saturation are represented by these a* and b* values.

The thermal conductivity of the thermal conductive sheet 1 is preferably as high as possible from the viewpoint of high thermal conductivity. · K or more, 8.4 W / m · K or more, 8.7 W / m · K or more, 10.3 W / m · K or more . The thermal conductivity of the thermally conductive sheet 1 can be measured by the method described in Examples below.

The thickness of the heat conductive sheet 1 is not particularly limited, and can be appropriately selected according to the purpose. For example, the thickness of the heat conductive sheet can be 0.05 mm or more, and can be 0.1 mm or more. Moreover, the upper limit of the thickness of the heat conductive sheet may be 5 mm or less, may be 4 mm or less, or may be 3 mm or less. From the viewpoint of handleability of the heat conductive sheet 1, the thickness of the heat conductive sheet 1 is preferably 0.1 to 4 mm. The thickness of the thermally conductive sheet 1 can be obtained, for example, by measuring the thickness B of the thermally conductive sheet 1 at five arbitrary points and calculating the arithmetic average value thereof.

Specific examples of the components of the thermally conductive sheet 1 will be described below.

<Binder resin>
The binder resin 2 is for holding the anisotropic thermally conductive filler 3 and other thermally conductive fillers 4 within the thermally conductive sheet 1 . The binder resin 2 is selected according to properties such as mechanical strength, heat resistance, and electrical properties required for the heat conductive sheet 1 . The binder resin 2 can be selected from thermoplastic resins, thermoplastic elastomers, and thermosetting resins.

Examples of thermoplastic resins include polyethylene, polypropylene, ethylene-α-olefin copolymers such as ethylene-propylene copolymers, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymers, Fluorinated polymers such as polyvinyl alcohol, polyvinyl acetal, polyvinylidene fluoride and polytetrafluoroethylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polystyrene, polyacrylonitrile, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer Polymer (ABS) resin, polyphenylene-ether copolymer (PPE) resin, modified PPE resin, aliphatic polyamides, aromatic polyamides, polyimide, polyamideimide, polymethacrylic acid, polymethacrylic acid such as polymethacrylic acid methyl ester acid esters, polyacrylic acids, polycarbonates, polyphenylene sulfides, polysulfones, polyethersulfones, polyethernitrile, polyetherketones, polyketones, liquid crystal polymers, silicone resins, ionomers and the like.

Thermoplastic elastomers include styrene-butadiene block copolymers or hydrogenated products thereof, styrene-isoprene block copolymers or hydrogenated products thereof, styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, and vinyl chloride-based thermoplastic elastomers. , polyester-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, polyamide-based thermoplastic elastomers, and the like.

Thermosetting resins include crosslinked rubbers, epoxy resins, phenol resins, polyimide resins, unsaturated polyester resins, diallyl phthalate resins, and the like. Specific examples of crosslinked rubber include natural rubber, acrylic rubber, butadiene rubber, isoprene rubber, styrene-butadiene copolymer rubber, nitrile rubber, hydrogenated nitrile rubber, chloroprene rubber, ethylene-propylene copolymer rubber, chlorinated polyethylene rubber, Chlorosulfonated polyethylene rubber, butyl rubber, halogenated butyl rubber, fluororubber, urethane rubber, and silicone rubber.

As the binder resin 2, for example, a silicone resin is preferable from the viewpoint of adhesion between the heat generating surface of a heat generating body (for example, an electronic component) and the heat sink surface and from the viewpoint of satisfying Condition 1 described above. As the silicone resin, for example, a two-component addition reaction type silicone resin composed of a silicone having an alkenyl group as a main component, a main agent containing a curing catalyst, and a curing agent having a hydrosilyl group (Si—H group). can be used. As the alkenyl group-containing silicone, for example, a vinyl group-containing polyorganosiloxane can be used. The curing catalyst is a catalyst for promoting the addition reaction between the alkenyl group in the alkenyl group-containing silicone and the hydrosilyl group in the hydrosilyl group-containing curing agent. As the curing catalyst, well-known catalysts used for hydrosilylation reaction can be used. For example, platinum group curing catalysts, such as platinum group metals such as platinum, rhodium and palladium, and platinum chloride can be used. As the curing agent having hydrosilyl groups, for example, polyorganosiloxane having hydrosilyl groups can be used. The binder resin 2 may be used individually by 1 type, and may use 2 or more types together.

The content of the binder resin 2 in the heat conductive sheet 1 is not particularly limited, and can be appropriately selected according to the purpose. For example, the content of the binder resin 2 in the heat conductive sheet 1 may be more than 25% by volume, may be 30% by volume or more, may be 32% by volume or more, or may be 33% by volume or more. may be In addition, the upper limit of the content of the binder resin 2 in the heat conductive sheet 1 can be 60% by volume or less, may be 50% by volume or less, or may be 40% by volume or less. It may be vol% or less. In particular, from the viewpoint of lowering the gloss value of condition 1 described above, the content of the binder resin 2 in the heat conductive sheet 1 is preferably more than 25% by volume and less than 40% by volume, and is 33 to 37% by volume. There may be.

<Anisotropic Thermally Conductive Filler>
The material of the anisotropic thermally conductive filler 3 is not particularly limited, and examples thereof include boron nitride (BN), mica, alumina, aluminum nitride, silicon carbide, silica, zinc oxide, and molybdenum disulfide. Boron nitride is preferable from the viewpoint of the rate and the gloss value of Condition 1 described above. The anisotropic thermally conductive filler 3 may be used singly or in combination of two or more.

FIG. 3 is a perspective view schematically showing scale-like boron nitride 3A having a hexagonal crystal shape, which is an example of the anisotropic thermally conductive filler 3. As shown in FIG. In FIG. 3, a represents the long axis of the scaly boron nitride 3A, b represents the thickness of the scaly boron nitride 3A, and c represents the short axis of the scaly boron nitride 3A. As the anisotropic thermally conductive filler 3, it is possible to use scale-like boron nitride 3A having a hexagonal crystal shape as shown in FIG. preferable. In the present technology, as the anisotropic thermally conductive filler 3, a scaly thermally conductive filler (eg, scaly boron nitride 3A) that is cheaper than a spherical thermally conductive filler (eg, spherical boron nitride) is used. As a result, it is possible to obtain the thermally conductive sheet 1 having both excellent thermal properties (high thermal conductivity) and optical properties (low gloss value) at low cost.

The average particle size of the anisotropic thermally conductive filler 3 can be appropriately selected depending on the purpose within a range that satisfies the condition 2 described above.

The content of the anisotropic thermally conductive filler 3 in the thermally conductive sheet 1 can be appropriately selected according to the purpose within the range that satisfies the condition 2 described above.

<Other Thermally Conductive Fillers>
Other thermally conductive fillers 4 include spherical, powdery, granular, and other thermally conductive fillers. From the viewpoint of the thermal conductivity of the thermally conductive sheet 1, the material of the other thermally conductive filler 4 is preferably, for example, a ceramic filler. Specific examples include aluminum oxide (alumina, sapphire), aluminum nitride, aluminum hydroxide, zinc oxide, boron nitride, zirconia, silicon carbide and the like. Other thermally conductive fillers 4 may be used singly or in combination of two or more.

In particular, as the other thermally conductive filler 4, alumina and It preferably contains at least one of aluminum nitride, zinc oxide and aluminum hydroxide. For example, aluminum nitride and alumina can be used in combination.

The average particle size of aluminum nitride may be less than 30 μm, may be 0.1 to 10 μm, may be 0.5 to 5 μm, may be 0.5 to 5 μm, and may be 1 to 1 μm. It may be 3 μm, or it may be 1 to 2 μm. In addition, the average particle size of alumina can be 0.1 to 10 μm, may be 0.1 to 8 μm, or even be 0.1 to 7 μm from the viewpoint of the specific gravity of the heat conductive sheet 1. Well, it may be 0.1-3 μm.

The content of the other thermally conductive filler 4 in the thermally conductive sheet 1 can be appropriately selected depending on the purpose within the range satisfying the condition 3 described above. For example, when aluminum nitride particles and alumina particles are used together as another thermally conductive filler 4, the content of aluminum nitride particles in the thermally conductive sheet 1 is 10 to 25% by volume (especially 17 to 23% by volume). The content of alumina particles is preferably 10 to 25% by volume (especially 17 to 23% by volume).

Preferred aspects of the heat conductive sheet 1 are as follows. The thermally conductive sheet 1 is a cured product of a composition containing a silicone resin as a binder resin 2, boron nitride as an anisotropic thermally conductive filler 3, and alumina and aluminum nitride as other thermally conductive fillers 4. It is preferable to consist of Moreover, in the heat conductive sheet 1, the content of boron nitride as the anisotropic heat conductive filler 3 is preferably more than 20% by volume and less than 35% by volume.

The heat conductive sheet 1 may further contain components other than the components described above within a range that does not impair the effects of the present technology. Other components include, for example, coupling agents, dispersants, curing accelerators, retarders, tackifiers, plasticizers, flame retardants, antioxidants, stabilizers, colorants, solvents and the like. For example, from the viewpoint of further improving the dispersibility of the anisotropic thermally conductive filler 3 and other thermally conductive fillers 4, the thermally conductive sheet 1 includes the anisotropic thermally conductive filler 3 and/or Alternatively, other thermally conductive fillers 4 treated with a coupling agent may be used.

<Method for manufacturing heat conductive sheet>
The manufacturing method of the thermally conductive sheet 1 has the following process A, process B, and process C.

<Process A>
In step A, by dispersing the anisotropic thermally conductive filler 3 and the other thermally conductive filler 4 in the binder resin 2, the binder resin 2, the anisotropic thermally conductive filler 3, and the other thermally conductive A thermally conductive composition is prepared which contains a conductive filler 4. In addition to the binder resin 2, the anisotropic thermally conductive filler 3, and the other thermally conductive filler 4, the thermally conductive composition contains the above-described other components as necessary, and is uniformly mixed by a known method. It can be prepared by mixing.

<Step B>
In step B, the thermally conductive composition prepared in step A is extruded and then cured to obtain a columnar cured product (molded block). The method of extrusion molding is not particularly limited, and various known extrusion molding methods can be appropriately employed depending on the viscosity of the thermally conductive composition, the properties required for the thermally conductive sheet 1, and the like. In the extrusion molding method, when the thermally conductive composition is extruded through a die, the binder resin 2 in the thermally conductive composition flows, and the anisotropic thermally conductive filler 3 is oriented along the flow direction.

The size and shape of the columnar cured product obtained in step B can be determined according to the required size of the heat conductive sheet 1 . For example, a rectangular parallelepiped having a cross-sectional length of 0.5 to 15 cm and a width of 0.5 to 15 cm can be used. The length of the rectangular parallelepiped may be determined as required.

<Process C>
In step C, the column-shaped cured product obtained in step B is cut into a predetermined thickness in the length direction of the column to obtain the heat conductive sheet 1 . The anisotropic thermally conductive filler 3 is exposed on the surface (cut surface) of the thermally conductive sheet 1 obtained in step C. The cutting method is not particularly limited, and can be appropriately selected from known slicing devices (preferably an ultrasonic cutter) according to the size and mechanical strength of the cured columnar product. When the molding method is extrusion molding, the cutting direction of the columnar cured product is 60 to 120 degrees with respect to the extrusion direction because the anisotropic thermally conductive filler 3 is oriented in the extrusion direction in some cases. , more preferably in a direction of 70 to 100 degrees, and even more preferably in a direction of 90 degrees (substantially perpendicular). The cutting direction of the columnar cured product is not particularly limited except for the above, and can be appropriately selected according to the purpose of use of the heat conductive sheet 1 and the like.

Thus, in the method of manufacturing a thermally conductive sheet having steps A, B, and C, a thermally conductive sheet 1 that satisfies the conditions 1 to 3 described above is obtained.

The method for manufacturing the heat conductive sheet 1 is not limited to the above-described example, and for example, after the step C, the step D of pressing the cut surface may be further included. By further including the step D of pressing, the surface of the heat conductive sheet 1 obtained in the step C is made smoother, and the adhesion with other members can be further improved. As a method of pressing, a pair of pressing devices comprising a flat plate and a press head having a flat surface can be used. Moreover, you may press with a pinch roll. The pressure for pressing can be, for example, 0.1 to 100 MPa. In order to enhance the effect of pressing and shorten the pressing time, it is preferable to press at a temperature higher than the glass transition temperature (Tg) of the binder resin 2 . For example, the pressing temperature can be from 0 to 180.degree. C., can be within the temperature range of room temperature (eg, 25.degree. C.) to 100.degree.

<Electronic equipment>
The thermally conductive sheet 1 is, for example, an electronic device (thermal device) having a structure arranged between a heat generating body and a radiator so that the heat generated by the heat generating body is released to the heat radiator. can be An electronic device has at least a heating element, a radiator, and a thermally conductive sheet 1, and may further have other members as necessary.

The heat generating element is not particularly limited, and includes, for example, CPU, GPU (Graphics Processing Unit), DRAM (Dynamic Random Access Memory), integrated circuit elements such as flash memory, transistors, resistors, and other electronic components that generate heat in electric circuits. etc. The heating element also includes components for receiving optical signals, such as optical transceivers in communication equipment.

The radiator is not particularly limited, and examples thereof include heat sinks, heat spreaders, and the like, which are used in combination with integrated circuit elements, transistors, optical transceiver housings, and the like. Materials for the heat sink and heat spreader include, for example, copper and aluminum. As the radiator, in addition to the heat spreader and the heat sink, any material can be used as long as it conducts the heat generated from the heat source and dissipates it to the outside. Heat pipes, vapor chambers, metal covers, housings, and the like. A heat pipe is, for example, a cylindrical, substantially cylindrical, or flat cylindrical hollow structure.

FIG. 4 is a cross-sectional view showing an example of a semiconductor device to which a heat conductive sheet is applied. For example, as shown in FIG. 4, the heat conductive sheet 1 is mounted on a semiconductor device 50 built in various electronic devices, and sandwiched between a heat generator and a radiator. A semiconductor device 50 shown in FIG. 4 includes an electronic component 51 , a heat spreader 52 , and a heat conductive sheet 1 . By sandwiching the heat conductive sheet 1 between the heat spreader 52 and the heat sink 53 , together with the heat spreader 52 , a heat dissipation member for dissipating the heat of the electronic component 51 is configured. The mounting location of the heat conductive sheet 1 is not limited to between the heat spreader 52 and the electronic component 51 or between the heat spreader 52 and the heat sink 53, but can be appropriately selected according to the configuration of the electronic device or semiconductor device. The heat spreader 52 is formed, for example, in the shape of a square plate, and has a main surface 52a facing the electronic component 51 and side walls 52b erected along the outer circumference of the main surface 52a. The heat spreader 52 is provided with the heat conductive sheet 1 on the principal surface 52a surrounded by the side walls 52b, and is provided with the heat sink 53 via the heat conductive sheet 1 on the other surface 52c opposite to the principal surface 52a.

Examples of the present technology will be described below. Note that the present technology is not limited to these examples.

<Example 1>
33% by volume of silicone resin, 27% by volume of scaly boron nitride (D50 is 40 μm) whose crystal shape is hexagonal, 20% by volume of aluminum nitride (D50 is 1.2 μm), and spherical alumina particles (D50 is A thermally conductive composition was prepared by uniformly mixing 2 μm) with 20% by volume. This thermally conductive composition is poured into a mold (opening: 50 mm × 50 mm) having a rectangular parallelepiped internal space by an extrusion molding method, and heated in an oven at 60 ° C. for 4 hours to form a columnar cured product ( A compact block) was formed. A release polyethylene terephthalate film was attached to the inner surface of the mold so that the release-treated surface faced the inside. By cutting (slicing) the obtained columnar cured product into a sheet having a thickness of 2 mm with an ultrasonic cutter in a direction substantially perpendicular to the length direction of the column, scale-like boron nitride is obtained. A heat conductive sheet oriented in the thickness direction of the sheet was obtained.

<Example 2>
In Example 2, 33% by volume of silicone resin, 27% by volume of scaly boron nitride (D50 is 30 μm) whose crystal shape is hexagonal, 20% by volume of aluminum nitride (D50 is 1.2 μm), and spherical A thermally conductive sheet was obtained in the same manner as in Example 1, except that a thermally conductive composition was prepared by uniformly mixing 20% by volume of alumina particles (D50: 2 μm).

<Example 3>
In Example 3, 37% by volume of silicone resin, 23% by volume of scaly boron nitride (D50 is 30 μm) whose crystal shape is hexagonal, 20% by volume of aluminum nitride (D50 is 1.2 μm), and spherical A thermally conductive sheet was obtained in the same manner as in Example 1, except that a thermally conductive composition was prepared by uniformly mixing 20% by volume of alumina particles (D50: 2 μm).

<Example 4>
In Example 4, 33% by volume of silicone resin, 27% by volume of scaly boron nitride (D50 is 20 μm) whose crystal shape is hexagonal, 20% by volume of aluminum nitride (D50 is 1.2 μm), and spherical A thermally conductive sheet was obtained in the same manner as in Example 1, except that a thermally conductive composition was prepared by uniformly mixing 20% by volume of alumina particles (D50: 2 μm).

<Comparative Example 1>
In Comparative Example 1, 40% by volume of silicone resin, 20% by volume of scaly boron nitride (D50 is 40 μm) having a hexagonal crystal shape, 30% by volume of aluminum nitride (D50 is 1.2 μm), and spherical A thermally conductive sheet was obtained in the same manner as in Example 1, except that a thermally conductive composition was prepared by uniformly mixing 10% by volume of alumina particles (D50: 2 μm).

<Comparative Example 2>
In Comparative Example 2, 40% by volume of silicone resin, 20% by volume of scaly boron nitride (D50 is 40 μm) having a hexagonal crystal shape, 20% by volume of aluminum nitride (D50 is 1.2 μm), and spherical A thermally conductive sheet was obtained in the same manner as in Example 1, except that a thermally conductive composition was prepared by uniformly mixing 20% by volume of alumina particles (D50: 2 μm).

<Comparative Example 3>
In Comparative Example 3, 40% by volume of silicone resin, 20% by volume of scaly boron nitride (D50 is 40 μm) whose crystal shape is hexagonal, 10% by volume of aluminum nitride (D50 is 1.2 μm), and spherical A thermally conductive sheet was obtained in the same manner as in Example 1, except that a thermally conductive composition was prepared by uniformly mixing 30% by volume of alumina particles (D50: 2 μm).

<Comparative Example 4>
In Comparative Example 4, 40% by volume of silicone resin, 20% by volume of scaly boron nitride (D50 is 20 μm) whose crystal shape is hexagonal, 20% by volume of aluminum nitride (D50 is 1.2 μm), and spherical A thermally conductive sheet was obtained in the same manner as in Example 1, except that a thermally conductive composition was prepared by uniformly mixing 20% by volume of alumina particles (D50: 2 μm).

<Comparative Example 5>
In Comparative Example 5, 25% by volume of silicone resin, 35% by volume of scaly boron nitride (D50 is 40 μm) whose crystal shape is hexagonal, 20% by volume of aluminum nitride (D50 is 1.2 μm), and spherical A thermally conductive composition was prepared by uniformly mixing 20% by volume of alumina particles (D50 of 2 μm).

<Comparative Example 6>
In Comparative Example 6, 33% by volume of silicone resin, 27% by volume of scaly boron nitride (D50 is 40 μm) whose crystal shape is hexagonal, 20% by volume of aluminum nitride (D50 is 1.2 μm), and spherical A thermally conductive composition was prepared by uniformly mixing 20% by volume of alumina particles (D50 of 2 μm). This thermally conductive composition was molded with a bar coater to a thickness of 2 mm and heated in an oven at 60° C. for 4 hours to obtain a thermally conductive sheet with a thickness of 2 mm.

<Comparative Example 7>
In Comparative Example 7, 33% by volume of silicone resin, 27% by volume of scaly boron nitride (D50 is 50 μm) whose crystal shape is hexagonal, 20% by volume of aluminum nitride (D50 is 1.2 μm), and spherical A thermally conductive sheet was obtained in the same manner as in Example 1, except that a thermally conductive composition was prepared by uniformly mixing 20% by volume of alumina particles (D50: 2 μm).

<Comparative Example 8>
In Comparative Example 8, 33% by volume of silicone resin, 27% by volume of scaly boron nitride (D50 of 10 μm) having a hexagonal crystal shape, 20% by volume of aluminum nitride (D50 of 1.2 μm), and spherical A thermally conductive sheet was obtained in the same manner as in Example 1, except that a thermally conductive composition was prepared by uniformly mixing 20% by volume of alumina particles (D50: 2 μm).

<L* value>
The L* value in the L*a*b color system of the surface (cross section) of the heat conductive sheet was measured. The L* value was determined according to JIS Z 8781 using a spectrophotometer (product name: CM-700d manufactured by Konica Milnolta). Table 1 shows the results. In Table 1, "-" indicates that the L* value could not be measured because the heat conductive sheet could not be produced.

<Bulk thermal conductivity>
For bulk thermal conductivity, the thermal resistance of each thermal conductive sheet is measured by a method in accordance with ASTM-D5470, the horizontal axis is the thickness (mm) of the thermal conductive sheet at the time of measurement, and the vertical axis is the thermal resistance of the thermal conductive sheet ( °C·cm ² /W) was plotted, and the bulk thermal conductivity (W/m·K) of the thermal conductive sheet was calculated from the slope of the plot. The thermal resistance of the thermally conductive sheet was measured by preparing three types of thermally conductive sheets with different thicknesses and measuring the thermally conductive sheets with different thicknesses. Table 1 shows the results. In Table 1, "-" indicates that the bulk thermal conductivity could not be measured because the thermally conductive sheet could not be produced.

<60° gross value>
The gloss value of the surface of the heat conductive sheet was measured by a method based on ASTM D523 using Micro Trigloss (manufactured by BYK Instruments). Table 1 shows the results. In Table 1, "-" indicates that the gloss value could not be measured because the heat conductive sheet could not be produced.

The thermally conductive sheets obtained in Examples 1 to 4 consist of cured products of compositions containing binder resins, anisotropic thermally conductive fillers, and other thermally conductive fillers, and meet the conditions 1 to 3 described above. It was found that the thermal conductivity is high by satisfying

In addition, since the heat conductive sheets obtained in Examples 1 to 4 satisfy the above-described condition 1, the quality of the manufactured heat conductive sheet can be determined, for example, the heat conductive sheet containing a predetermined amount of heat conductive filler having a predetermined particle size. It becomes possible to easily determine whether the sheet has a predetermined thermal conductivity.

It was found that the thermally conductive sheets obtained in Comparative Examples 1 to 4 did not have good thermal conductivity. This is probably because the heat conductive sheets obtained in Comparative Examples 1 to 4 did not satisfy the conditions 1 and 3 described above.

In Comparative Example 5, a heat conductive sheet could not be produced due to high hardness. The thermally conductive composition used in Comparative Example 5 had a total content of the anisotropic thermally conductive filler and other thermally conductive fillers of 75% by volume, which is considered to be because the above condition 3 was not satisfied.

It was found that the thermally conductive sheet obtained in Comparative Example 6 did not have good thermal conductivity. This is probably because the heat conductive sheet obtained in Comparative Example 6 did not satisfy Condition 1 described above.

It was found that the thermally conductive sheets obtained in Comparative Examples 7 and 8 did not have good thermal conductivity. This is probably because the heat conductive sheets obtained in Comparative Examples 7 and 8 did not satisfy Condition 2 described above.

1 thermally conductive sheet 1A surface 2 binder resin 3 anisotropic thermally conductive filler 4 other thermally conductive filler 5 imaginary perpendicular line 6 light ray 51 electronic component 52 heat spreader 53 heat sink 52a main surface, 52b side wall

Claims (9)

A thermal conductive sheet made of a cured product of a composition containing a binder resin, an anisotropic thermally conductive filler, and a thermally conductive filler other than the anisotropic thermally conductive filler,
A thermal conductive sheet that satisfies the following conditions 1 to 3.
[Condition 1] The gloss value is less than 10 as measured by light rays incident at a position of 60° from an imaginary perpendicular to the surface of the heat conductive sheet.
[Condition 2] The average particle size of the anisotropic thermally conductive filler is 15 μm or more and 45 μm or less.
[Condition 3] In the thermally conductive sheet, the total content of the anisotropic thermally conductive filler and the other thermally conductive filler is more than 60% by volume and less than 75% by volume. The thermally conductive sheet according to claim 1, wherein the content of the anisotropic thermally conductive filler is more than 20% by volume and less than 35% by volume. 3. The thermally conductive sheet according to claim 1, wherein the surface of the thermally conductive sheet has an L* value of 70 or more in the L*a*b color system. The thermally conductive sheet according to any one of claims 1 to 3, which has a bulk thermal conductivity of 8 W/m·K or more. The anisotropic thermally conductive filler is boron nitride,
The thermally conductive sheet according to any one of claims 1 to 4, wherein the other thermally conductive filler contains alumina and at least one of aluminum nitride, zinc oxide and aluminum hydroxide. 6. The thermally conductive sheet according to claim 5, wherein the boron nitride is scaly boron nitride. The thermally conductive sheet according to any one of claims 1 to 6, wherein the anisotropic thermally conductive filler has an average particle size of 20 µm or more and 40 µm or less. Step A of preparing a thermally conductive composition containing a binder resin, an anisotropic thermally conductive filler, and a thermally conductive filler other than the anisotropic thermally conductive filler;
Step B of extruding and then curing the thermally conductive composition to obtain a columnar cured product;
a step C of obtaining a thermally conductive sheet by cutting the columnar cured product into a predetermined thickness in a direction substantially perpendicular to the length direction of the column;
A method for producing a thermally conductive sheet, wherein the thermally conductive sheet satisfies the following conditions 1 to 3.
[Condition 1] The gloss value is less than 10 as measured by a light beam incident at a position of 60° from an imaginary perpendicular to the surface of the heat conductive sheet.
[Condition 2] The average particle size of the anisotropic thermally conductive filler is 15 μm or more and 45 μm or less.
[Condition 3] In the thermally conductive sheet, the total content of the anisotropic thermally conductive filler and the other thermally conductive filler is more than 60% by volume and less than 75% by volume. a heating element;
a radiator;
An electronic device comprising the thermally conductive sheet according to any one of claims 1 to 7 sandwiched between a heating element and a radiator.

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