TWI880093B - Heat conduction sheet and method for manufacturing heat conduction sheet - Google Patents

Abstract

The present invention provides a heat conductive sheet with high thermal conductivity, which can easily determine the quality of the required heat conductive sheet. The thermal conductive sheet 1 contains a cured product of a composition including an adhesive resin 2, an anisotropic thermal conductive filler 3, and other thermal conductive fillers 4 other than the anisotropic thermal conductive filler 3, and satisfies the following conditions 1 to 3: [Condition 1] The gloss value measured by the light 6 incident from a position 60° relative to the imaginary vertical line 5 on the surface of the thermal conductive sheet 1 is less than 10; [Condition 2] The average particle size of the anisotropic thermal conductive filler 3 is greater than 15 μm and less than 45 μm; [Condition 3] The total content of the anisotropic thermal conductive filler 3 and other thermal conductive fillers 4 in the thermal conductive sheet 1 exceeds 60 volume % and does not reach 75 volume %.

Description

Heat conductive sheet and method for producing the same

This technology relates to a heat conductive sheet and a method for manufacturing the heat conductive sheet. This application claims priority based on Japanese Patent Application No. 2021-099910 filed in Japan on June 16, 2021, and the application is incorporated herein by reference.

As electronic devices become more high-performance, semiconductor components are becoming more dense and mounted. It is important to release the heat generated by the electronic components that make up the electronic devices more efficiently. For example, in semiconductor devices, electronic components are mounted on heat sinks such as heat sinks and heat sinks via heat-insulating conductive sheets in order to efficiently dissipate heat. As heat-conductive sheets, silicone resins containing (dispersed with) inorganic fillers and other filling materials are widely used.

For heat dissipation components such as the heat conductive sheet, it is required to further improve the thermal conductivity. For example, research is conducted to increase the filling rate of inorganic fillers mixed in a matrix such as an adhesive resin to achieve high thermal conductivity of the heat conductive sheet. However, if the filling rate of the inorganic filler is increased, there is a risk of damaging the flexibility of the heat conductive sheet or causing the inorganic filler to fall off. Therefore, there is a limit to the improvement of the filling rate of the inorganic filler in the heat conductive sheet.

Examples of inorganic fillers include aluminum oxide, aluminum nitride, aluminum hydroxide, and the like. In addition, for the purpose of high thermal conductivity, there are also cases where scaly particles such as boron nitride and graphite, carbon fibers, and the like are filled in the matrix. The reason for this is the anisotropy of the thermal conductivity possessed by scaly particles, carbon fibers, and the like. For example, it is known that carbon fibers have a thermal conductivity of about 600 to 1200 W/m・K in the fiber direction. In addition, boron nitride as a scaly particle is known to have 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. Thus, it is known that the thermal conductivity of carbon fibers or scaly particles is anisotropic. By aligning the fiber direction of the carbon fibers or the surface direction of the scaly particles with the thickness direction of the heat conductive sheet, that is, aligning the carbon fibers or the scaly particles along the thickness direction of the heat conductive sheet, the thermal conductivity of the heat conductive sheet can be dramatically improved.

In addition, in addition to requiring high thermal conductivity, thermal conductive sheets are also required to be able to easily determine the quality of the manufactured thermal conductive sheets, for example, whether the required thermal conductive sheet (for example, a thermal conductive sheet containing a thermal conductive filler of a specific particle size in a specific amount) has a specific thermal conductivity.

Patent document 1 describes a thermal conductive sheet, which contains a resin composition including a resin and a scaly thermal conductive filler dispersed in the resin, and the slope of the scaly thermal conductive filler relative to the thickness direction of the thermal conductive sheet changes periodically along one direction in the surface direction of the thermal conductive sheet. The scaly filler of the thermal conductive sheet described in Patent document 1 has an insufficient orientation, and it can be said that it is not an anisotropic high thermal conductive sheet, and it is considered difficult to achieve high thermal conductivity. Prior art document Patent document

Patent document 1: Japanese Patent Publication No. 2019-214663

[The problem the invention is trying to solve]

This technology is proposed in view of this previous actual situation, and provides a heat conductive sheet with high thermal conductivity that can easily perform the quality judgment of the required heat conductive sheet. [Technical means to solve the problem]

The thermal conductive sheet of the present technology is a cured product containing a composition including an adhesive resin, an anisotropic thermal conductive filler, and other thermal conductive fillers other than the anisotropic thermal conductive filler, and meets the following conditions 1 to 3: [Condition 1] The gloss value measured by the light incident from a position 60° relative to the imaginary vertical line on the surface of the thermal conductive sheet is less than 10; [Condition 2] The average particle size of the anisotropic thermal conductive filler is greater than 15 μm and less than 45 μm; [Condition 3] The total content of the anisotropic thermal conductive filler and other thermal conductive fillers in the thermal conductive sheet exceeds 60 volume % and does not reach 75 volume %.

The manufacturing method of the thermal conductive sheet of the present technology includes the following steps: preparing a thermal conductive composition including a curable resin composition, an anisotropic thermal conductive filler, and a thermal conductive filler other than the anisotropic thermal conductive filler; extruding the thermal conductive composition and then curing it to obtain a columnar cured product; and cutting the columnar cured product into a specific thickness along a direction substantially perpendicular to the length direction of the column to obtain a thermal conductive sheet; and the thermal conductive sheet satisfies the above conditions 1 to 3. [Effect of the invention]

This technology can provide a heat conductive sheet with high heat conductivity, which can easily perform the quality judgment of the required heat conductive sheet.

In this specification, the average particle size (D50) of anisotropic thermal conductive fillers and other thermal conductive fillers refers to the particle size at which the cumulative value reaches 50% when the cumulative curve of the particle size value is calculated from the small particle size side of the particle size distribution, when the particle size distribution of the anisotropic thermal conductive filler or other thermal conductive filler is set as 100%. In addition, the particle size distribution (particle size distribution) in this specification is a value calculated based on the volume. As a method for measuring the particle size distribution, for example, a method using a laser diffraction type particle size distribution measuring machine can be cited.

<Thermal Conductive Sheet> Figure 1 is a cross-sectional view showing an example of a thermal conductive sheet 1 of the present technology. The thermal conductive sheet 1 contains a cured product of a composition including an adhesive resin 2, an anisotropic thermal conductive filler 3, and other thermal conductive fillers 4 other than the anisotropic thermal conductive filler 3. In the thermal conductive sheet 1, the anisotropic thermal conductive filler 3 and other thermal conductive fillers 4 are dispersed in the adhesive resin 2, and the anisotropic thermal conductive filler 3 is oriented along the thickness direction B of the thermal conductive sheet 1.

Here, the so-called anisotropic thermally conductive filler 3 is oriented along the thickness direction B of the thermally conductive sheet 1. For example, the ratio of the anisotropic thermally conductive filler 3 whose long axis is oriented along the thickness direction B of the thermally conductive sheet 1 among all the anisotropic thermally conductive fillers 3 in the thermally conductive sheet 1 is 50% or more, or 55% or more, or 60% or more, or 65% or more, or 70% or more, or 80% or more, or 90% or more, or 95% or more, or 99% or more.

Anisotropic thermal conductive filler 3 is a thermal conductive filler having anisotropy in shape. Examples of anisotropic thermal conductive filler 3 include thermal conductive fillers having a long axis, a short axis, and a thickness (e.g., scaly thermal conductive fillers). The so-called scaly thermal conductive filler refers to a thermal conductive filler having a long axis, a short axis, and a thickness, and having a high aspect ratio (long axis/thickness) and isotropic thermal conductivity in the direction of the surface including the long axis. The so-called short axis of the scaly thermal conductive filler refers to a direction that intersects the midpoint of the long axis of the scaly thermal conductive filler on the surface including the long axis of the scaly thermal conductive filler, and is the length of the shortest part of the scaly thermal conductive filler. The thickness of the scaly thermally conductive filler refers to the average value obtained by measuring the thickness of the surface of the scaly thermally conductive filler including the long axis at 10 points. The aspect ratio of the anisotropic thermally conductive filler 3 is not particularly limited and can be appropriately selected according to the purpose. For example, the aspect ratio of the anisotropic thermally conductive filler 3 can be set in the range of 10 to 100. The long axis, short axis and thickness of the anisotropic thermally conductive filler 3 can be measured using, for example, a microscope, a scanning electron microscope (SEM), a particle size distribution meter, etc.

The other thermally conductive filler 4 is a thermally conductive filler other than the anisotropic thermally conductive filler 3, that is, a thermally conductive filler whose shape does not have anisotropy.

FIG2 is a diagram for explaining an example of a method for measuring the gloss value. The inventors of the present application have studied and found that there is the following relationship between the composition of the thermal conductive sheet 1 (especially the orientation of the anisotropic thermal conductive filler 3, the average particle size of the anisotropic thermal conductive filler 3, the total content of the anisotropic thermal conductive filler 3 and other thermal conductive fillers 4, etc.) and the gloss value measured by the light 6 incident on the thermal conductive sheet 1 at a position 60° with respect to the imaginary vertical line 5 of the surface 1A of the thermal conductive sheet 1.

First, due to the influence of the orientation of the anisotropic thermal conductive filler 3 in the thermal conductive sheet 1, the reflection component relative to the incident light increases in the thermal conductive sheet in which the anisotropic thermal conductive filler 3 is not oriented, so there is a tendency for the gloss value to be higher.

Furthermore, as for the influence of the total content of the anisotropic thermal conductive filler 3 and other thermal conductive fillers 4 in the thermal conductive sheet 1 on the gloss value, if the total content of the anisotropic thermal conductive filler 3 and other thermal conductive fillers 4 in the thermal conductive sheet 1 decreases, there is a tendency that the influence of the gloss of the binder resin 2 present on the surface of the thermal conductive sheet 1 becomes greater than the reflection of the particles (anisotropic thermal conductive filler 3 or other thermal conductive fillers 4). For example, when the adhesive resin 2 is a silicone resin, the gloss of the silicone resin overflowing from the heat conductive sheet 1 becomes stronger than the reflection caused by the anisotropic heat conductive filler 3 or other heat conductive fillers 4. It is believed that the reduction in the total content of the anisotropic heat conductive filler 3 and other heat conductive fillers 4 leads to a stronger effect of the silicone resin on the gloss value.

Furthermore, the larger the particle size of the anisotropic thermal conductive filler 3 is, the more the thermal conductivity of the thermal conductive sheet 1 can be expected to increase. However, if the particle size of the anisotropic thermal conductive filler 3 is larger than a certain value, it is difficult to fill the anisotropic thermal conductive filler 3 into the adhesive resin 2 due to the influence of the particle size, and as a result, there is a tendency to be difficult to improve the thermal conductivity. On the other hand, the smaller the particle size of the anisotropic thermal conductive filler 3 is, for example, in order to transfer heat from one end of the thickness direction B of the thermal conductive sheet 1 to the other end, more anisotropic thermal conductive fillers 3 are required, and therefore, more contact points of the anisotropic thermal conductive filler 3 are required. Thus, if the number of contact points of the anisotropic heat conductive filler 3 in the heat conductive sheet 1 increases, the thermal resistance between the contact parts increases, and heat conduction loss is more likely to occur, so it is difficult to improve the thermal conductivity in the thickness direction B of the heat conductive sheet 1. The same is true for the surface direction A of the heat conductive sheet 1.

Therefore, the thermal conductive sheet 1 satisfies the following conditions 1 to 3: [Condition 1] The gloss value measured by the light 6 incident from a position at 60° with respect to the imaginary vertical line 5 with respect to the surface 1A of the thermal conductive sheet 1 is less than 10. [Condition 2] The average particle size of the anisotropic thermal conductive filler 3 is greater than 15 μm and less than 45 μm. [Condition 3] The total content of the anisotropic thermal conductive filler 3 and other thermal conductive fillers 4 in the thermal conductive sheet 1 exceeds 60 volume % and is less than 75 volume %.

Regarding condition 1, the gloss value of the heat conductive sheet 1 measured by the light 6 incident from a position at 60° with respect to the imaginary vertical line 5 of the surface 1A of the heat conductive sheet 1 is less than 10, and may be 8 or less, 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 heat conductive sheet 1 is the same as the method described in the following examples.

If the thermal conductive sheet 1 satisfies condition 1, as described above, there is a tendency for the orientation ratio of the anisotropic thermal conductive filler 3 in the thermal conductive sheet 1 to be higher, and the thermal conductivity in the thickness direction of the thermal conductive sheet 1 becomes good. In addition, if the thermal conductive sheet 1 satisfies condition 1, it is easy to judge whether the manufactured thermal conductive sheet is good or bad, for example, judging whether a thermal conductive sheet containing a thermal conductive filler of a specific particle size in a specific amount has a specific thermal conductivity. In other words, in addition to measuring the thermal conductivity of the thermal conductive sheet 1, the standard of the thermal conductivity of the thermal conductive sheet 1 can also be grasped by measuring the gloss value of the thermal conductive sheet 1. Furthermore, if the thermal conductive sheet 1 satisfies condition 1, when the thermal conductive sheet 1 is used, it is possible to more reliably avoid misidentification of the image when the thermal conductive sheet 1 is picked up by an automatic machine, thereby enabling the thermal conductive sheet 1 to be picked up 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, 20 μm or more, 25 μm or more, 30 μm or more, 35 μm or more, or 40 μm or more. Furthermore, 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 preferably in the range of 20 to 40 μm.

The thermal conductive sheet 1 may contain a single type of anisotropic thermal conductive filler 3, or two or more types of anisotropic thermal conductive fillers 3 having different particle sizes. When the thermal conductive sheet 1 contains two or more types of anisotropic thermal conductive fillers 3 having different particle sizes, the content of the anisotropic thermal conductive filler 3 having a particle size of 20 μm or more and 40 μm or less in the thermal conductive sheet 1 relative to the total content of the anisotropic thermal conductive filler 3 may be 50% by volume or more, 60% by volume or more, 70% by volume or more, 80% by volume or more, 90% by volume or more, or 100% by volume.

From the viewpoint of the formability of the heat conductive sheet 1, the heat conductive sheet 1 preferably includes a single type of anisotropic heat conductive filler 3 as the anisotropic heat conductive filler 3. That is, it is preferred not to use two or more types of anisotropic heat conductive fillers 3 in the heat conductive sheet 1.

Regarding condition 3, from the viewpoint of thermal conductivity or the gloss value of condition 1, the total content of the anisotropic thermal conductive filler 3 and other thermal conductive fillers 4 in the thermal conductive sheet 1 may exceed 60 volume %, and may be 61 volume % or more, 63 volume % or more, 66 volume % or more, or 67 volume % or more. Furthermore, from the viewpoint of the formability of the thermal conductive sheet 1, the total content of the anisotropic thermal conductive filler 3 and other thermal conductive fillers 4 in the thermal conductive sheet 1 may be less than 75 volume %, and may be 74 volume % or less, 70 volume % or less, 69 volume % or less, or 68 volume % or less. Furthermore, the total content of the anisotropic thermally conductive filler 3 and other thermally conductive fillers 4 in the thermally conductive sheet 1 may be in the range of 63 to 67 volume %.

From the viewpoint of the thermal conductivity of the thermal conductive sheet 1 or the gloss value of the above condition 1, the content of the anisotropic thermal conductive filler 3 in the thermal conductive sheet 1 is preferably more than 20 volume %, and may be more than 23 volume %, more than 25 volume %, or more than 26 volume %. Furthermore, from the viewpoint of the formability of the thermal conductive sheet 1, the content of the anisotropic thermal conductive filler 3 in the thermal conductive sheet 1 is preferably less than 35 volume %, and may be less than 30 volume %, and may be less than 28 volume %, and may be less than 27 volume %. Furthermore, the content of the anisotropic thermal conductive filler 3 in the thermal conductive sheet 1 may be in the range of 23 to 27 volume %.

Furthermore, the content of other thermally conductive fillers 4 in the thermally conductive sheet 1 may be set to 10 volume % or more, or 15 volume % or more, or 20 volume % or more, or 25 volume % or more, or 30 volume % or more, or 35 volume % or more. Furthermore, the upper limit of the content of other thermally conductive fillers 4 in the thermally conductive sheet 1 may be set to 50 volume % or less, or 45 volume % or less, or 40 volume % or less. Furthermore, the content of other thermally conductive fillers 4 in the thermally conductive sheet 1 may be in the range of 30-50 volume %, or 35-45 volume %, or 37-42 volume %.

The thermal conductive sheet 1, that is, the cured product of the composition including the binder resin 2, the anisotropic thermal conductive filler 3, and the other thermal conductive filler 4 and satisfying the above conditions 1 to 3, has a higher L* value in the L*a*b* color system on the sheet surface, and has a tendency to have more anisotropic thermal conductive fillers 3 oriented in the thickness direction B, and has better thermal conductivity in the thickness direction B. Therefore, the L* value in the L*a*b* color system on the sheet surface of the thermal conductive sheet 1 is preferably 70 or more, and may be 75 or more, 77 or more, 80 or more, 85 or more, 88 or more, or 89 or more. Furthermore, the upper limit of the L* value in the L*a*b* colorimetric system of the sheet surface 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 a color system described in "JIS Z 8781", for example, which arranges each color in a spherical color space. In the L*a*b color system, the position in the longitudinal (z-axis) direction represents brightness, the position in the peripheral direction represents hue, and the distance from the center axis represents chroma. The position in the longitudinal (z-axis) direction representing brightness is represented by L*. The value of brightness L* is a positive number, and the smaller the number, the lower the brightness, and there is a tendency to darken. Specifically, the value of L* varies between 0, which is equivalent to black, and 100, which is equivalent to white. In the cross-sectional view obtained by horizontally cutting the spherical color space at the position of 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 negative direction of the y-axis is the blue direction. The position in the x-axis direction is represented by a* taking a value of -60 to +60. The position in the y-axis direction is represented by b* taking a value of -60 to +60. Thus, a* and b* are positive and negative numbers representing chromaticity, and the closer to 0, the darker. Hue and chroma are represented by these a* and b* values.

From the perspective of high heat conductivity, the higher the thermal conductivity of the thermal conductive sheet 1, the better. For example, the overall thermal conductivity in the thickness direction B is preferably 8.0 W/m·K or more, and may be 8.1 W/m·K or more, 8.4 W/m·K or more, 8.7 W/m·K or more, or 10.3 W/m·K or more. The thermal conductivity of the thermal conductive sheet 1 can be measured by the method described in the following examples.

The thickness of the thermal conductive sheet 1 is not particularly limited and can be appropriately selected according to the purpose. For example, the thickness of the thermal conductive sheet can be set to be greater than 0.05 mm, or greater than 0.1 mm. In addition, the upper limit of the thickness of the thermal conductive sheet can be set to less than 5 mm, less than 4 mm, or less than 3 mm. From the perspective of the operability of the thermal conductive sheet 1, the thickness of the thermal conductive sheet 1 is preferably set to 0.1 to 4 mm. As the thickness of the thermal conductive sheet 1, for example, the thickness B of the thermal conductive sheet 1 can be measured at any 5 positions and calculated from the arithmetic mean.

Hereinafter, specific examples of components of the heat conductive sheet 1 will be described.

<Binder resin> Binder resin 2 is used to hold anisotropic thermal conductive filler 3 and other thermal conductive fillers 4 in thermal conductive sheet 1. Binder resin 2 is selected based on the mechanical strength, heat resistance, electrical properties, etc. required of thermal conductive sheet 1. Binder resin 2 can be selected from thermoplastic resins, thermoplastic elastomers, and thermosetting resins.

Examples of thermoplastic resins include polyethylene, polypropylene, ethylene-propylene copolymers and other ethylene-α-olefin copolymers, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl alcohol, polyvinyl acetal, polyvinylidene fluoride, polytetrafluoroethylene and other fluorine-based polymers, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polystyrene, polyacrylonitrile, styrene-acrylonitrile Copolymers, acrylonitrile-butadiene-styrene copolymer (ABS) resins, polyphenylene ether copolymer (PPE) resins, modified PPE resins, aliphatic polyamides, aromatic polyamides, polyimides, polyamide imides, polymethacrylic acid, polymethyl methacrylate and other polymethacrylates, polyacrylic acids, polycarbonates, polyphenylene sulfide, polysulfone, polyethersulfone, polyethernitrile, polyetherketone, polyketone, liquid crystal polymers, polysilicone resins, ionomers, etc.

Examples of the thermoplastic elastomer include styrene-butadiene block copolymers or hydrogenates thereof, styrene-isoprene block copolymers or hydrogenates thereof, styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers, polyester-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, and polyamide-based thermoplastic elastomers.

Examples of the thermosetting resin include crosslinked rubber, epoxy resin, phenolic resin, polyimide resin, unsaturated polyester resin, diallyl phthalate resin, etc. Specific examples of the 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 adhesive resin 2, for example, from the viewpoint of the close contact between the heating surface of the heating element (such as electronic parts) and the heat sink surface or from the viewpoint of satisfying the above-mentioned condition 1, polysilicone resin is preferred. As the polysilicone resin, for example, a two-component addition reaction type polysilicone resin including a main agent having polysilicone with alkenyl groups as the main component and containing a curing catalyst, and a curing agent having a hydrosilyl group (Si-H group) can be used. As the polysilicone with alkenyl groups, for example, polyorganosiloxane with vinyl groups can be used. The curing catalyst is a catalyst for promoting the addition reaction between the alkenyl group in the polysilicone with alkenyl groups and the hydrosilyl group in the curing agent with hydrosilyl groups. As the hardening catalyst, a catalyst known as a catalyst used in a hydrosilation reaction can be cited, for example, a platinum-based hardening catalyst such as platinum-based metal elements such as platinum, rhodium, and palladium, or platinum chloride can be used. As a hardener having a hydrosilyl group, for example, a polyorganosiloxane having a hydrosilyl group can be used. The adhesive resin 2 can be used alone or in combination of two or more.

The content of the adhesive resin 2 in the thermal conductive sheet 1 is not particularly limited and can be appropriately selected according to the purpose. For example, the content of the adhesive resin 2 in the thermal conductive sheet 1 can be set to more than 25 volume %, or more than 30 volume %, or more than 32 volume %, or more than 33 volume %. In addition, the upper limit of the content of the adhesive resin 2 in the thermal conductive sheet 1 can be set to less than 60 volume %, or less than 50 volume %, or less than 40 volume %, or less than 37 volume %. In particular, from the viewpoint of reducing the gloss value of the above-mentioned condition 1, the content of the binder resin 2 in the heat conductive sheet 1 is preferably set to more than 25 volume % and less than 40 volume %, and can also be 33 to 37 volume %.

<Anisotropic thermal conductive filler> The material of the anisotropic thermal conductive filler 3 is not particularly limited, and examples thereof include boron nitride (BN), mica, aluminum oxide, aluminum nitride, silicon carbide, silicon dioxide, zinc oxide, molybdenum disulfide, etc. From the perspective of thermal conductivity or the gloss value of the above condition 1, boron nitride is preferred. The anisotropic thermal conductive filler 3 may be used alone or in combination of two or more.

FIG3 schematically shows a three-dimensional view of a scaly boron nitride 3A having a hexagonal crystal shape as an example of anisotropic thermal conductive filler 3. In FIG3, a represents the major axis of scaly boron nitride 3A, b represents the thickness of scaly boron nitride 3A, and c represents the minor axis of scaly boron nitride 3A. As anisotropic thermal conductive filler 3, from the viewpoint of thermal conductivity or gloss value of the above condition 1, it is preferable to use scaly boron nitride 3A having a hexagonal crystal shape as shown in FIG3. In the present technology, by using a scaly thermally conductive filler (e.g., scaly boron nitride 3A) which is cheaper than a spherical thermally conductive filler (e.g., spherical boron nitride) as the anisotropic thermally conductive filler 3, a thermally conductive sheet 1 having both excellent thermal properties (high thermal conductivity) and optical properties (low gloss value) can be obtained at a low cost.

The average particle size of the anisotropic thermally conductive filler 3 can be appropriately selected according to the purpose within the range satisfying the above condition 2.

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 satisfying the above condition 3.

<Other thermally conductive fillers> Other thermally conductive fillers 4 include spherical, powdery, granular, and other thermally conductive fillers. From the perspective of thermal conductivity of the thermally conductive sheet 1, the material of the other thermally conductive filler 4 is preferably a ceramic filler, and specific examples thereof include: alumina (sapphire), aluminum nitride, aluminum hydroxide, zinc oxide, boron nitride, zirconium oxide, silicon carbide, and the like. Other thermally conductive fillers 4 may be used alone or in combination of two or more.

As other thermally conductive fillers 4, especially considering the gloss value of the above-mentioned condition 1, the thermal conductivity of the thermally conductive sheet 1, the specific gravity of the thermally conductive sheet 1, etc., it is preferred to include aluminum oxide, and at least one of aluminum nitride, zinc oxide and aluminum hydroxide. For example, aluminum nitride and aluminum oxide can be used together.

From the perspective of the specific gravity of the heat conductive sheet 1, the average particle size of aluminum nitride can be less than 30 μm, 0.1 to 10 μm, 0.5 to 5 μm, 1 to 3 μm, or 1 to 2 μm. Furthermore, from the perspective of the specific gravity of the heat conductive sheet 1, the average particle size of aluminum oxide can be 0.1 to 10 μm, 0.1 to 8 μm, 0.1 to 7 μm, or 0.1 to 3 μm.

The content of the other thermal conductive filler 4 in the thermal conductive sheet 1 can be appropriately selected according to the purpose within the range satisfying the above condition 3. For example, when aluminum nitride particles and aluminum oxide particles are used as the other thermal conductive filler 4, the content of the aluminum nitride particles in the thermal conductive sheet 1 is preferably set to 10-25 volume % (preferably 17-23 volume %), and the content of the aluminum oxide particles is preferably set to 10-25 volume % (preferably 17-23 volume %).

The preferred form of the thermal conductive sheet 1 is as follows. The thermal conductive sheet 1 is preferably a cured product containing a combination of a silicone resin as a binder resin 2, boron nitride as an anisotropic thermal conductive filler 3, and alumina and aluminum nitride as other thermal conductive fillers 4. In addition, the thermal conductive sheet 1 is preferably a thermal conductive sheet 1 in which the content of boron nitride as an anisotropic thermal conductive filler 3 exceeds 20 volume % and does not reach 35 volume %.

The heat conductive sheet 1 may also contain other components other than the above components within the scope of not impairing the effect of the present technology. Examples of other components include coupling agents, dispersants, hardening accelerators, retarder agents, adhesion agents, plasticizers, flame retardants, antioxidants, stabilizers, colorants, solvents, etc. For example, from the perspective of further improving the dispersibility of the anisotropic heat conductive filler 3 and other heat conductive fillers 4, the heat conductive sheet 1 may use anisotropic heat conductive fillers 3 treated with coupling agents and/or other heat conductive fillers 4 treated with coupling agents.

<Method for manufacturing thermal conductive sheet> The method for manufacturing thermal conductive sheet 1 includes the following steps A, B and C.

<Step A> In step A, the anisotropic thermal conductive filler 3 and the other thermal conductive filler 4 are dispersed in the adhesive resin 2 to prepare a thermal conductive composition comprising the adhesive resin 2, the anisotropic thermal conductive filler 3, and the other thermal conductive filler 4. The thermal conductive composition can be prepared by uniformly mixing the adhesive resin 2, the anisotropic thermal conductive filler 3, the other thermal conductive filler 4, and the other components mentioned above as required by a known method.

<Step B> In step B, the thermal conductive composition prepared in step A is extruded and then hardened to obtain a columnar hardened product (molded block). There is no particular limitation on the extrusion molding method, and it can be appropriately adopted from various known extrusion molding methods according to the viscosity of the thermal conductive composition or the required properties of the thermal conductive sheet 1. In the extrusion molding method, when the thermal conductive composition is extruded from the mold, the binder resin 2 in the thermal conductive composition flows, and the anisotropic thermal conductive filler 3 is oriented along its 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 with a longitudinal size of 0.5 to 15 cm and a transverse size of 0.5 to 15 cm can be used. The length of the rectangular parallelepiped can be determined as needed.

<Step C> In step C, the columnar hardened material obtained in step B is cut into a specific thickness relative to the length direction of the column to obtain a heat conductive sheet 1. The surface (cut surface) of the heat conductive sheet 1 obtained in step C exposes the anisotropic heat conductive filler 3. The cutting method is not particularly limited and can be appropriately selected from known slicing devices (preferably ultrasonic cutting machines) according to the size and mechanical strength of the columnar hardened material. Regarding the cutting direction of the columnar cured product, when the forming method is the extrusion forming method, there are also cases where the anisotropic thermal conductive filler 3 is oriented along the extrusion direction, so it is preferably 60 to 120 degrees relative to the extrusion direction, more preferably 70 to 100 degrees, and further preferably 90 degrees (roughly vertical) direction. In addition to the above content, there is no special restriction on the cutting direction of the columnar cured product, and it can be appropriately selected according to the purpose of use of the thermal conductive sheet 1.

Thus, in the method for manufacturing a heat conductive sheet including step A, step B and step C, a heat conductive sheet 1 satisfying the above conditions 1 to 3 can be obtained.

The manufacturing method of the heat conductive sheet 1 is not limited to the above example. For example, after step C, step D of pressurizing the cut surface may be further included. By further including the pressurizing step D, the surface of the heat conductive sheet 1 obtained in step C can be made smoother, and the adhesion with other components can be further improved. As a pressurizing method, a pressurizing device including a flat plate and a pressure head with a flat surface can be used. In addition, a clamping roller can also be used for pressurization. The pressure during pressurization can be set to 0.1 to 100 MPa, for example. In order to further improve the pressurization effect and shorten the pressurization time, it is better to pressurize at a temperature above the glass transition temperature (Tg) of the adhesive resin 2. For example, the pressurization temperature can be set to 0-180°C, or in the temperature range of room temperature (eg, 25°C) to 100°C, or 30-100°C.

<Electronic device> The heat conductive sheet 1 is disposed, for example, between a heat generating element and a heat sink, thereby making it possible to produce an electronic device (thermal device) having a structure disposed between the heat generating element and releasing the heat generated by the heat generating element to the heat sink. The electronic device has at least a heat generating element, a heat sink, and a heat conductive sheet 1, and may further have other components as needed.

The heat generating element is not particularly limited, and examples thereof include: integrated circuit elements such as CPU (Central Processing Unit), GPU (Graphics Processing Unit), DRAM (Dynamic Random Access Memory), flash memory, and electronic components that generate heat in the circuit, such as transistors and resistors. In addition, the heat generating element also includes components that receive optical signals, such as optical transceivers in communication equipment.

There is no particular limitation on the heat sink, and examples thereof include heat sinks or heat spreaders in combination with integrated circuit components or transistors, optical transceiver housings, etc. Examples of materials for heat sinks or heat spreaders include copper, aluminum, etc. Examples of heat sinks include anything other than heat spreaders or heat sinks that conducts heat generated from a heat source and releases it to the outside, and examples thereof include heat sinks, coolers, wafer holders, printed circuit boards, cooling fans, Peltier elements, heat pipes, vapor chambers, metal covers, housings, etc. A heat pipe is a hollow structure that is, for example, cylindrical, roughly cylindrical, or flattened cylindrical.

FIG4 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 FIG4, a heat conductive sheet 1 is installed in a semiconductor device 50 built into various electronic devices, and is sandwiched between a heat generating body and a heat sink. The semiconductor device 50 shown in FIG4 comprises an electronic component 51, a heat spreader 52, and a heat conductive sheet 1, and the heat conductive sheet 1 is sandwiched between the heat spreader 52 and the electronic component 51. The heat conductive sheet 1 is sandwiched between the heat spreader 52 and the heat sink 53, and together with the heat spreader 52, it constitutes a heat dissipation member for releasing the heat of the electronic component 51. The installation position 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, and can be appropriately selected according to the structure of the electronic machine or semiconductor device. The heat spreader 52 is formed into a square plate, for example, and has a main surface 52a facing the electronic component 51, and a side wall 52b vertically arranged along the outer periphery of the main surface 52a. The heat spreader 52 is provided with the heat conductive sheet 1 on the main surface 52a surrounded by the side wall 52b, and the heat sink 53 is provided on the other surface 52c on the opposite side of the main surface 52a through the heat conductive sheet 1. [Example]

The following describes the embodiments of the present technology. However, the present technology is not limited to the embodiments.

<Example 1> A heat conductive composition is prepared by uniformly mixing 33% by volume of polysilicone resin, 27% by volume of hexagonal scaly boron nitride (D50: 40 μm), 20% by volume of aluminum nitride (D50: 1.2 μm), and 20% by volume of spherical aluminum oxide particles (D50: 2 μm). The heat conductive composition is poured into a mold having a rectangular inner space (opening: 50 mm×50 mm) by extrusion molding, and heated in an oven at 60°C for 4 hours to form a columnar hardened product (molded block). Furthermore, a release polyethylene terephthalate film is previously attached to the inner surface of the mold with the release treated surface as the inner side. The obtained columnar hardened material was cut (sliced) into sheets with a thickness of 2 mm using an ultrasonic cutter in a direction roughly orthogonal to the length direction of the column, thereby obtaining a heat conductive sheet with scaly boron nitride oriented along the thickness direction of the sheet.

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

<Example 3> In Example 3, a heat conductive composition is prepared by uniformly mixing 37 volume % of polysilicone resin, 23 volume % of hexagonal scaly boron nitride (D50 is 30 μm) crystalline form, 20 volume % of aluminum nitride (D50 is 1.2 μm), and 20 volume % of spherical aluminum oxide particles (D50 is 2 μm). A heat conductive sheet is obtained in the same manner as in Example 1 except that the above.

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

<Comparative Example 1> In Comparative Example 1, a heat conductive sheet was obtained by uniformly mixing 40 volume % of polysilicone resin, 20 volume % of hexagonal scaly boron nitride (D50: 40 μm) with a crystal shape of 30 volume % of aluminum nitride (D50: 1.2 μm), and 10 volume % of spherical aluminum oxide particles (D50: 2 μm) to prepare a heat conductive composition.

<Comparative Example 2> In Comparative Example 2, a heat conductive sheet was obtained by uniformly mixing 40 volume % of polysilicone resin, 20 volume % of hexagonal scaly boron nitride (D50: 40 μm) and 20 volume % of aluminum nitride (D50: 1.2 μm) and 20 volume % of spherical aluminum oxide particles (D50: 2 μm) to prepare a heat conductive composition.

<Comparative Example 3> In Comparative Example 3, a heat conductive sheet was obtained by uniformly mixing 40 volume % of polysilicone resin, 20 volume % of hexagonal scaly boron nitride (D50: 40 μm) with a crystal shape of 10 volume % of aluminum nitride (D50: 1.2 μm), and 30 volume % of spherical aluminum oxide particles (D50: 2 μm) to prepare a heat conductive composition.

<Comparative Example 4> In Comparative Example 4, a heat conductive sheet was obtained by uniformly mixing 40 volume % of polysilicone resin, 20 volume % of hexagonal scaly boron nitride (D50: 20 μm) and 20 volume % of spherical alumina particles (D50: 2 μm) to prepare a heat conductive composition.

<Comparative Example 5> In Comparative Example 5, a thermally conductive composition was prepared by uniformly mixing 25 volume % of polysilicone resin, 35 volume % of hexagonal scaly boron nitride (D50: 40 μm) crystalline form, 20 volume % of aluminum nitride (D50: 1.2 μm), and 20 volume % of spherical aluminum oxide particles (D50: 2 μm).

<Comparative Example 6> In Comparative Example 6, a heat conductive composition was prepared by uniformly mixing 33% by volume of polysilicone resin, 27% by volume of hexagonal scaly boron nitride (D50: 40 μm) with a crystal shape of 27% by volume of aluminum nitride (D50: 1.2 μm), and 20% by volume of spherical aluminum oxide particles (D50: 2 μm). The heat conductive composition was formed into a 2 mm thick sheet using a rod coater and heated in an oven at 60°C for 4 hours to obtain a 2 mm thick heat conductive sheet.

<Comparative Example 7> In Comparative Example 7, a heat conductive composition was prepared by uniformly mixing 33 volume % of polysilicone resin, 27 volume % of hexagonal scaly boron nitride (D50: 50 μm) 20 volume % of aluminum nitride (D50: 1.2 μm), and 20 volume % of spherical aluminum oxide particles (D50: 2 μm). A heat conductive sheet was obtained in the same manner as in Example 1 except that the above-mentioned mixture was uniformly mixed.

<Comparative Example 8> In Comparative Example 8, a heat conductive composition was prepared by uniformly mixing 33 volume % of polysilicone resin, 27 volume % of hexagonal scaly boron nitride (D50: 10 μm) 20 volume % of aluminum nitride (D50: 1.2 μm), and 20 volume % of spherical aluminum oxide particles (D50: 2 μm). A heat conductive sheet was obtained in the same manner as in Example 1 except that the above-mentioned mixture was uniformly mixed.

<L* value> Measure the L* value of the surface (cross section) of the heat conductive sheet in the L*a*b colorimetric system. Use a spectrophotometer (product name: CM-700d manufactured by Konica Minolta) to obtain the L* value in accordance with JIS Z 8781. The results are shown in Table 1. In Table 1, "-" indicates that the L* value could not be measured because the heat conductive sheet could not be produced.

<Overall thermal conductivity> Regarding overall thermal conductivity, the thermal resistance of each thermal conductive sheet was measured according to the method of ASTM-D5470. The horizontal axis was set as the thickness of the thermal conductive sheet at the time of measurement (mm), and the vertical axis was set as the thermal resistance of the thermal conductive sheet (℃・cm ² /W). A curve was plotted, and the overall thermal conductivity (W/m・K) of the thermal conductive sheet was calculated from the slope of the curve. Regarding the thermal resistance of the thermal conductive sheet, three types of thermal conductive sheets with different thicknesses were prepared, and the thermal resistance of the thermal conductive sheets of each thickness was measured. The results are shown in Table 1. In Table 1, "-" means that the overall thermal conductivity could not be measured because the thermal conductive sheet could not be produced.

<60° Gloss Value> The gloss value of the surface of the thermal conductive sheet was measured using a micro-tri-gloss (manufactured by BYK Instruments) in accordance with ASTM D523. The results are shown in Table 1. In Table 1, "-" indicates that the gloss value could not be measured because the thermal conductive sheet could not be produced.

[Table 1] Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 Comparison Example 1 Comparison Example 2 Comparison Example 3 Comparison Example 4 Comparison Example 5 Comparative Example 6 Comparison Example 7 Comparative Example 8 Silicone resin [Vol%] 33 33 37 33 40 40 40 40 25 33 33 33 Alumina (D50＝2 μm) [Vol%] 20 20 20 20 10 20 30 20 20 20 20 20 Aluminum nitride (D50＝1.2 μm) [Vol%] 20 20 20 20 30 20 10 20 20 20 20 20 Boron nitride (D50＝50 μm) [Vol%] - - - - - - - - - - 27 - Boron nitride (D50＝40 μm) [Vol%] 27 - - - 20 20 20 - 35 27 - - Boron nitride (D50＝30 μm) [Vol%] - 27 twenty three - - - - - - - - - Boron nitride (D50＝20 μm) [Vol%] - - - 27 - - - 20 - - - - Boron nitride (D50＝10 μm) [Vol%] - - - - - - - - - - - 27 Total amount of filler [Vol%] 67 67 63 67 60 60 60 60 75 67 67 67 L value 89 88 77 80 66 68 69 67 - 88 90 75 Overall thermal conductivity (W/m・K) 10.3 8.7 8.1 8.4 6.5 6.1 5.7 5.1 - 4.3 7.5 7.1 60° gloss value 3.9 5.4 6.2 5.2 12.2 12.5 12.3 12 - 25.8 4.7 4.9 Remarks - - - - - - - - Unable to create Rod coating machine (along the surface direction) - -

It can be seen that the thermally conductive sheets obtained in Examples 1 to 4 contain a cured product of a composition including an adhesive resin, an anisotropic thermally conductive filler, and other thermally conductive fillers, and satisfy the above-mentioned conditions 1 to 3, thereby having a high thermal conductivity.

Furthermore, since the thermally conductive sheets obtained in Examples 1 to 4 satisfy the above-mentioned condition 1, it is possible to easily determine whether the thermally conductive sheets produced are good or bad, for example, whether a thermally conductive sheet containing a thermally conductive filler of a specific particle size in a specific amount has a specific thermal conductivity.

It can be seen that the thermal conductivity of the thermally conductive sheets obtained in Comparative Examples 1 to 4 is poor. This is believed to be because the thermally conductive sheets obtained in Comparative Examples 1 to 4 do not meet the above-mentioned conditions 1 and 3.

Comparative Example 5 cannot be used to produce a thermally conductive sheet due to its high hardness. The reason is believed to be that the total content of the anisotropic thermally conductive filler and other thermally conductive fillers in the thermally conductive composition used in Comparative Example 5 is 75 volume %, which does not meet the above condition 3.

It can be seen that the thermal conductivity of the heat conductive sheet obtained in Comparative Example 6 is poor. It is believed that the reason is that the heat conductive sheet obtained in Comparative Example 6 does not meet the above-mentioned condition 1.

It can be seen that the thermal conductivity of the heat conductive sheets obtained in Comparative Examples 7 and 8 is poor. It is believed that the reason is that the heat conductive sheets obtained in Comparative Examples 7 and 8 do not meet the above-mentioned condition 2.

1: Thermally conductive sheet 1A: Surface 2: Adhesive resin 3: Anisotropic thermally conductive filler 3A: Scaled boron nitride 4: Other thermally conductive fillers 5: Imaginary vertical line 6: Light 50: Semiconductor device 51: Electronic component 52: Heat spreader 52a: Main surface 52b: Side wall 52c: The other side opposite to the main surface 53: Heat sink A: Surface direction of thermally conductive sheet a: Long axis of scaled boron nitride B: Thickness direction of thermally conductive sheet b: Thickness of scaled boron nitride c: Short axis of scaled boron nitride

FIG. 1 is a cross-sectional view showing an example of a heat conductive sheet. FIG. 2 is a view for explaining an example of a method for measuring gloss value. FIG. 3 is a stereoscopic view schematically showing a hexagonal scaly boron nitride crystal as an example of anisotropic heat conductive filler. FIG. 4 is a cross-sectional view showing an example of a semiconductor device using a heat conductive sheet.

1: Heat conduction sheet

2: Adhesive resin

3: Anisotropic thermal conductive filler

4: Other thermally conductive fillers

A: Surface direction of heat conductive sheet

B: Thickness direction of heat conduction sheet

Claims (9)

A thermal conductive sheet, which is a cured product of a composition comprising an adhesive resin, an anisotropic thermal conductive filler, and other thermal conductive fillers other than the anisotropic thermal conductive filler, and satisfies the following conditions 1 to 3: [Condition 1] The gloss value measured by light incident from a position 60° relative to an imaginary vertical line on the surface of the thermal conductive sheet is less than 10; [Condition 2] The average particle size of the anisotropic thermal conductive filler is greater than 15 μm and less than 45 μm; [Condition 3] The total content of the anisotropic thermal conductive filler and the other thermal conductive fillers in the thermal conductive sheet exceeds 60 volume % and does not reach 75 volume %. The thermally conductive sheet of claim 1, wherein the content of the anisotropic thermally conductive filler exceeds 20 volume % and is less than 35 volume %. The heat conductive sheet of claim 1 or 2, wherein the L* value of the surface of the heat conductive sheet in the L*a*b colorimetric system is 70 or more. The thermally conductive sheet of claim 1 or 2 has an overall thermal conductivity of 8 W/m·K or more. The thermally conductive sheet of claim 1 or 2, wherein the anisotropic thermally conductive filler is boron nitride, and the other thermally conductive fillers include aluminum oxide, and at least one of aluminum nitride, zinc oxide, and aluminum hydroxide. A heat conductive sheet as claimed in claim 5, wherein the boron nitride is scaly boron nitride. The thermally conductive sheet of claim 1 or 2, wherein the average particle size of the anisotropic thermally conductive filler is not less than 20 μm and not more than 40 μm. A method for manufacturing a thermal conductive sheet, comprising: Step A, which is to prepare a thermal conductive composition comprising an adhesive resin, an anisotropic thermal conductive filler, and other thermal conductive fillers other than the anisotropic thermal conductive filler; Step B, which is to extrude the thermal conductive composition and then harden it to obtain a columnar hardened product; and Step C, which is to cut the columnar hardened product into a specific thickness along a direction substantially perpendicular to the length direction of the column to obtain a thermal conductive sheet; and The thermal conductive sheet satisfies the following conditions 1 to 3: [Condition 1] The gloss value measured by light incident from a position at 60° to an imaginary vertical line relative to the surface of the thermal conductive sheet is less than 10; [Condition 2] The average particle size of the anisotropic thermal conductive filler is 15 μm or more and 45 μm or less; [Condition 3] The total content of the anisotropic thermal conductive filler and the other thermal conductive fillers in the thermal conductive sheet exceeds 60 volume % and does not reach 75 volume %. An electronic device comprising: a heat generating element, a heat sink, and a heat conductive sheet as claimed in any one of claims 1 to 7 sandwiched between the heat generating element and the heat sink.