Thermal conductive sheet

Abstract

To provide a thermally conductive sheet with high thermal conductivity and appropriate hardness. [Solution] The thermal conductive sheet 1 contains a binder component 11 and a thermal conductive filler 12. The thermal conductive filler 12 includes thermal conductive filler (A) 12a, which is boron nitride with a thickness of 20 μm or less, and other thermal conductive fillers (B) 12b other than thermal conductive filler (A) 12a. The content ratio of thermal conductive filler (A) 12a is 0.01 to 1 mass% based on 100 mass% of the total amount of the thermal conductive sheet 1.

Description

Technical Field

[0001] The present invention relates to a heat conductive sheet.

Background Art

[0002] In recent years, with the development of electronics, many heat-generating components have been used in electronic devices such as power devices. In controlling an electronic circuit, it is important to dissipate heat from these heat-generating components to cool the entire system. A heat conductive sheet (heat dissipation sheet) is installed, for example, between a heat-generating component and a heat dissipation fin or a metal plate, and is brought into close contact with the heat-generating component so as to have no gap by pressure bonding, and exhibits heat conductivity to transfer the heat generated from the heat-generating component to the heat dissipation fin or the like, thereby removing heat from the entire system.

[0003] The above heat conductive sheet is composed of, for example, a heat conductive inorganic filler and a resin. As the inorganic filler, aluminum hydroxide, aluminum oxide (alumina), silicon carbide, boron nitride, aluminum nitride, etc. are used.

[0004] As the above heat conductive sheet, for example, those disclosed in Patent Documents 1 to 5 are known.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0006] In recent years, semiconductors, substrates, and modules used in semiconductors have become smaller and more high-performance, resulting in increased heat generation from electronic components. Therefore, there is a growing demand for thermally conductive sheets with higher thermal conductivity.

[0007] A thermally conductive sheet can be obtained by filling it with a high concentration of thermally conductive filler. However, a drawback of high thermal conductivity is that the thermally conductive sheet becomes rigid when the filling rate of thermally conductive filler is high. When a thermally conductive sheet is rigid, it places a large amount of pressure on the integrated circuit (IC) during mounting, putting a heavy burden on the IC, and also reduces its ability to conform to the substrate.

[0008] Patent documents 1 to 5 disclose formulations with significantly reduced hardness. However, reducing hardness too much presents a problem: the thermal conductive sheet is easily deformed by even small forces. In this case, handling during mounting becomes difficult, and when pressure is applied, the thermal conductive sheet may spread to areas other than the target area. Therefore, there is a need for a thermal conductive sheet with high thermal conductivity and appropriate hardness.

[0009] Therefore, the object of the present invention is to provide a thermally conductive sheet that has high thermal conductivity and appropriate hardness. [Means for solving the problem]

[0010] The present invention relates to a thermally conductive sheet comprising a binder component and a thermally conductive filler. The above thermal conductive filler includes a thermal conductive filler (A) which is boron nitride with a thickness of 20 μm or less, and other thermal conductive fillers (B) other than the above thermal conductive filler (A). The present invention provides a thermal conductive sheet in which the content of the above-mentioned thermal conductive filler (A) is 0.01 to 1% by mass relative to 100% by mass of the total amount of the thermal conductive sheet.

[0011] The thermal conductive sheet of the present invention preferably has an Asker C hardness of 40 to 70.

[0012] The shape of the above-mentioned thermal conductive filler (A) is preferably flaky.

[0013] The shape of the above-mentioned thermal conductive filler (A) is preferably fibrous.

[0014] The above-mentioned thermal conductive filler (B) preferably contains a thermal conductive filler containing at least one of aluminum nitride and alumina as a material.

[0015] The above-mentioned thermal conductive filler (B) preferably contains at least one of spherical and polyhedral thermal conductive fillers.

[0016] The above-mentioned binder component is preferably a silicone resin.

[0017] The thermal conductive sheet of the present invention preferably has a thermal conductivity in the thickness direction of 10.0 W / mK or more when compressed by 10%.

Effect of the Invention

[0018] The thermal conductive sheet of the present invention has a high thermal conductivity and appropriate hardness. Therefore, the thermal conductive sheet of the present invention has high thermal conductivity, excellent followability to the substrate and handling property during mounting, and can suppress the spread to areas other than the target area.

Brief Description of the Drawings

[0019] [Figure 1] It is a partial cross-sectional view showing an embodiment of the thermal conductive sheet of the present invention.

Mode for Carrying Out the Invention

[0020] [Thermal Conductive Sheet] The thermal conductive sheet (heat dissipation sheet) according to an embodiment of the present invention includes at least a binder component and a thermal conductive filler.

[0021] The above-mentioned thermal conductive sheet may be in a form without a base material (base layer), a so-called "base material-less" form, or it may be a thermal conductive sheet provided on at least one side of a base material. Note that the above-mentioned "base material (base layer)" does not include the release film that is peeled off when the thermal conductive sheet is used.

[0022] The thermal conductive sheet may be provided with a release film. The release film may be provided on only one side of the thermal conductive sheet or on both sides. Examples of the release film include a film formed from a low-tack resin or a sheet comprising a release treatment layer provided on the surface of the film. The release film is peeled off and removed when the thermal conductive sheet is used.

[0023] Figure 1 is a schematic cross-sectional view showing one embodiment of the thermal conductive sheet of the present invention. As shown in Figure 1, the thermal conductive sheet 1 includes a binder component 11 which is a matrix component and a thermal conductive filler 12 dispersed in the binder component 11. The thermal conductive filler 12 includes thermal conductive filler (A) 12a which is boron nitride with a thickness of 20 μm or less, and other thermal conductive fillers 12b other than thermal conductive filler (A) 12a. Release films 2 and 3 are provided on both sides of the thermal conductive sheet 1, and the thermal conductive sheet 1 is sandwiched between the two release films 2 and 3.

[0024] <Binder ingredients> The above-mentioned binder component is a component that forms the matrix of the above-mentioned thermally conductive sheet. Examples of the above-mentioned binder component include thermoplastic resins, thermosetting resins, active energy ray curable resins, and other resins (binder resins). Only one type of the above-mentioned binder component may be used, or two or more types may be used.

[0025] Examples of the thermoplastic resins mentioned above include polystyrene resins, vinyl acetate resins, polyester resins, polyolefin resins (e.g., polyethylene resins, polypropylene resin compositions, etc.), polyimide resins, and acrylic resins. Only one type of thermoplastic resin may be used, or two or more types may be used.

[0026] The above-mentioned thermosetting resins include both thermosetting resins and resins obtained by curing the above-mentioned thermosetting resins. Examples of the above-mentioned thermosetting resins include silicone resins, phenolic resins, epoxy resins, urethane resins, urethane urea resins, melamine resins, alkyd resins, polyimide resins, and acrylic resins. Only one type of the above-mentioned thermosetting resin may be used, or two or more types may be used.

[0027] The above-mentioned active energy ray curable resin includes both a resin that can be cured by irradiation with active energy rays (active energy ray curable resin) and a resin obtained by curing the above-mentioned active energy ray curable resin. The above-mentioned active energy ray curable resin is not particularly limited, but for example, a polymer of a polymerizable compound having at least two (meth)acryloyloxy groups in its molecule can be used. The above-mentioned active energy ray curable resin may be used by one type only, or by two or more types.

[0028] Among the binder resins mentioned above, thermosetting resins are preferred. Furthermore, silicone resins are preferred as the binder resin from the viewpoint of excellent thermal conductivity, heat resistance, and insulation properties. As the silicone resin, known or conventional silicone resins used in thermally conductive sheets can be used. As the silicone resin, two-component curing type silicone resins are preferred from the viewpoint of being able to disperse thermally conductive fillers well without using solvents. One type of silicone resin may be used, or two or more types may be used.

[0029] The content of the binder component is preferably 5% by volume or more, more preferably 8% by volume or more, and even more preferably 10% by volume or more, based on 100% by volume of the total amount of the thermal conductive sheet. When the content is 5% by volume or more, the thermal conductive sheet is less likely to become brittle and has excellent moldability. The content is preferably 30% by volume or less, and more preferably 25% by volume or less. When the content is 30% by volume or less, the thermal conductivity of the thermal conductive sheet is better. In this specification, all combinations of the above lower limit and upper limit are included. That is, the content may be, for example, 5 to 30% by volume or 8 to 25% by volume. In particular, it is preferable that the content of the silicone resin be within the above range.

[0030] <Thermal conductive filler> The above-mentioned thermally conductive filler is a filler (particle) that has thermal conductivity and is a component that exhibits thermal conductivity in the above-mentioned thermally conductive sheet. Examples of the above-mentioned thermally conductive filler include metal particles, ceramic fillers, and inorganic fillers such as carbon fillers. Only one type of the above-mentioned thermally conductive filler may be used, or two or more types may be used.

[0031] Examples of metals that make up the above metal particles include gold, silver, copper, aluminum, nickel, zinc, indium, tin, lead, bismuth, and alloys containing two or more of these (such as solder). Only one of the above metals may be used, or two or more may be used.

[0032] Examples of the above-mentioned metal particles include, specifically, silver particles, copper particles, aluminum particles, nickel particles, tin particles, solder particles, and particles in which these particles are coated with a metal. Gold, silver, copper, nickel, and tin are preferred as coating metals.

[0033] Examples of the above ceramic fillers include metal oxides such as alumina (aluminum oxide), titania (titanium oxide), magnesia (magnesium oxide), zirconia (zirconium oxide), and zinc oxide; nitrides such as aluminum nitride, titanium nitride, and boron nitride; metal hydroxides such as aluminum hydroxide; carbides such as silicon carbide; silicon compounds such as glass, silica, silicon carbide, silicon nitride, and silicon; and minerals such as steatite, forsterite, sialon, perlite, mullite, and zeolite.

[0034] Examples of the carbon filler mentioned above include carbon fibers, carbon nanotubes, and carbon material-containing particles such as diamond. The carbon filler may also be coated with a metal. Preferred coating metals include gold, silver, copper, nickel, and tin.

[0035] The shape of the above-mentioned thermally conductive filler is not particularly limited and can be spherical (including perfect spheres and ellipsoids), flake-like (scaly), dendritic, massive, flattened, needle-like, polyhedral, fibrous, or irregular in shape.

[0036] The above-mentioned thermally conductive filler may or may not be surface-treated. Examples of surface treatment agents include silane coupling agents. When the surface is treated with a silane coupling agent, the thermally conductive filler disperses well in the binder component (especially the silicone resin) which is the matrix of the thermally conductive sheet, resulting in superior filling and moldability. One type of silane coupling agent may be used, or two or more types may be used.

[0037] Examples of the silane coupling agents mentioned above include silane coupling agents having functional groups other than alkoxy groups, such as β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-glycidoxypropylmethyldiethoxysilane (functional group-containing silane coupling agents); and silane coupling agents not having functional groups other than alkoxy groups, such as n-octyltriethoxysilane and n-decyltrimethoxysilane (functional group-free silane coupling agents). Among these, functional group-free silane coupling agents are preferred from the viewpoint of good wettability with metal oxides and the expected improvement of bulk strength and flexibility of the thermally conductive sheet, more preferably silane coupling agents in which the terminal other than the alkoxy group is an alkyl group (terminal alkyl group-containing silane coupling agent), and particularly preferably n-octyltriethoxysilane.

[0038] (Thermal conductive filler (A)) The above-mentioned thermal conductive filler includes a thermal conductive filler that is boron nitride with a thickness of 20 μm or less (sometimes referred to as "thermal conductive filler (A)") and other thermal conductive fillers other than thermal conductive filler (A) (sometimes referred to as "thermal conductive filler (B)"). It is presumed that filling the spaces between thermal conductive fillers (B) with thermal conductive filler (A) with a thickness of 20 μm or less increases the number of contact points with thermal conductive filler (B), thereby achieving high thermal conductivity in the thermal conductive sheet while having a moderate hardness because there is no need to incorporate an excessive amount of thermal conductive filler. Thermal conductive fillers (A) and (B) are each particle groups. Thermal conductive fillers (A) and (B) may each be used individually or in combination of two or more types (i.e., two or more particle groups with different median diameters (D50)).

[0039] The thickness of the thermal conductive filler (A) is the length of the shortest line segment in the cross-section in the short-axis direction. For example, if the thermal conductive filler (A) is in the form of flakes, the length perpendicular to the major and minor axes corresponds to the thickness, and if the thermal conductive filler (A) is in the form of fibers, the length perpendicular to the width and length directions corresponds to the thickness. The thickness of the thermal conductive filler (A) is preferably 15 μm or less, more preferably 10 μm or less, even more preferably 7 μm or less, and particularly preferably 5 μm or less. The thickness of the thermal conductive filler (A) is not particularly limited, but for example, it is 0.5 μm or more.

[0040] The ratio of the major axis to the thickness [major axis / thickness] of the thermal conductive filler (A) is preferably 2 or more, more preferably 3 or more, and even more preferably 5 or more. The larger the above ratio, the flatter the thermal conductive filler (A) becomes, allowing for a higher thermal conductivity of the thermal conductive sheet while maintaining a more appropriate hardness. Therefore, there is no particular upper limit to the above ratio.

[0041] The thickness and major axis of the thermally conductive filler (A) can be measured using an optical microscope or an electron microscope.

[0042] The shape of the thermally conductive filler (A) is preferably not one with a small aspect ratio (major axis / minor axis) such as spherical, dendritic, massive, or polyhedral (e.g., 1.3 or less), and examples include flaky, flattened, needle-shaped, fibrous, and irregular shapes. Among these, flaky or fibrous shapes are preferred for the thermally conductive filler (A). Flaky thermally conductive fillers are sufficiently thin, making it easy to fill the spaces between the other thermally conductive fillers and thus easy to achieve high thermal conductivity. Fibrous thermally conductive fillers (A) are flexible, making it easy to fill the spaces between thermally conductive fillers (B) and thus easy to achieve high thermal conductivity.

[0043] When the thermally conductive filler (A) has a particle size (such as flakes), the median diameter (D50) of the thermally conductive filler (A) is preferably 5 to 20 μm, and more preferably 10 to 15 μm. In this specification, unless otherwise specified, "A to B" representing a numerical range means "greater than or equal to A, and less than or equal to B".

[0044] In this specification, the particle size of the thermally conductive filler is measured by laser diffraction and scattering. The median diameter (μm) of the thermally conductive filler can be measured, for example, by the following method. First, the particle size distribution of the particle group is measured using a laser diffraction particle size analyzer to obtain a volume-based cumulative particle size distribution curve. In the obtained cumulative particle size distribution curve, the particle size value at 50% accumulation from the fine particle side is D50. As a laser diffraction particle size analyzer, for example, a particle size distribution analyzer such as the product name "MT3300EXII" (manufactured by Microtrac Co., Ltd.) can be used.

[0045] The content of the thermal conductive filler (A) is 0.01 to 1% by mass, preferably 0.03 to 0.8% by mass, and more preferably 0.07 to 0.5% by mass, based on 100% by mass of the total amount of the thermal conductive sheet. When the content is within the above range, a high thermal conductivity of the thermal conductive sheet can be achieved while ensuring appropriate hardness.

[0046] The content of the thermal conductive filler (A) is preferably 0.01 to 1% by mass, more preferably 0.03 to 0.8% by mass, and even more preferably 0.07 to 0.5% by mass, based on 100% by mass of the total amount of thermal conductive filler in the thermal conductive sheet. When the content is within the above range, it is easier to achieve high thermal conductivity in the thermal conductive sheet while ensuring appropriate hardness.

[0047] As the thermal conductive filler (B), the types and shapes exemplified and described above can be appropriately selected. Among these, the thermal conductive filler (B) preferably includes a thermal conductive filler containing one or more aluminum nitride and alumina as material, from the viewpoint of easily achieving high thermal conductivity of the thermal conductive sheet. Furthermore, the thermal conductive filler (B) preferably includes one or more spherical and polyhedral thermal conductive fillers, from the viewpoint of easily achieving high thermal conductivity of the thermal conductive sheet while ensuring appropriate hardness.

[0048] (Thermal conductive filler (B1)) As the thermal conductive filler (B), it is preferable to include spherical thermal conductive fillers (sometimes referred to as "thermal conductive filler (B1)") having a median diameter of 40 to 140 μm, from the viewpoint of easily achieving particularly high thermal conductivity of the thermal conductive sheet. In particular, if the particle size is 140 μm or less, detachment of particles from the cross-section of the thermal conductive sheet becomes less likely. The thermal conductive filler (B1) is a group of particles. The median diameter of the thermal conductive filler (B1) is preferably 55 to 140 μm, more preferably 70 to 140 μm. Only one type of thermal conductive filler (B1) may be used, or two or more types (i.e., two or more groups of particles with different median diameters) may be used.

[0049] The content of the thermal conductive filler (B1) is preferably 10 to 70% by mass, more preferably 20 to 60% by mass, and even more preferably 30 to 50% by mass, based on 100% by mass of the total amount of the thermal conductive sheet. When the content is within the above range, it is easier to achieve high thermal conductivity in the thermal conductive sheet while ensuring appropriate hardness.

[0050] The content of the thermal conductive filler (B1) is preferably 10 to 70% by mass, more preferably 20 to 60% by mass, and even more preferably 30 to 50% by mass, based on 100% by mass of the total amount of thermal conductive filler in the thermal conductive sheet. When the content is within the above range, it is easier to achieve high thermal conductivity in the thermal conductive sheet while ensuring appropriate hardness.

[0051] (Thermal conductive filler (B2)) As the thermal conductive filler (B), it is preferable to include spherical thermal conductive fillers (sometimes referred to as "thermal conductive filler (B2)") having a median diameter of 1 to 20 μm, from the viewpoint of easily achieving particularly high thermal conductivity of the thermal conductive sheet. The thermal conductive filler (B2) is a group of particles. The median diameter (D50) of the thermal conductive filler (B2) is preferably 1 to 10 μm, more preferably 2 to 8 μm. Only one type of thermal conductive filler (B2) may be used, or two or more types (i.e., two or more groups of particles with different median diameters) may be used.

[0052] The content of the thermal conductive filler (B2) is preferably 10 to 50% by mass, more preferably 15 to 45% by mass, and even more preferably 20 to 40% by mass, based on 100% by mass of the total amount of the thermal conductive sheet. When the content is within the above range, it is easier to achieve high thermal conductivity in the thermal conductive sheet while ensuring appropriate hardness.

[0053] The content of the thermal conductive filler (B2) is preferably 10 to 50% by mass, more preferably 15 to 45% by mass, and even more preferably 20 to 40% by mass, based on 100% by mass of the total amount of thermal conductive filler in the thermal conductive sheet. When the content is within the above range, it is easier to achieve high thermal conductivity in the thermal conductive sheet while ensuring appropriate hardness.

[0054] (Thermal conductive filler (B3)) The thermal conductive filler (B) preferably includes a polyhedral thermal conductive filler (sometimes referred to as "thermal conductive filler (B3)") having a median diameter of 0.1 μm or more and less than 1 μm. Using thermal conductive filler (B3) allows for improved thermal conductivity while maintaining a moderately soft hardness of the thermal conductive sheet. The polyhedral shape of the thermal conductive filler (B) with a particle size within this range increases the contact area between the thermal conductive fillers, which can lead to improved thermal conductivity while maintaining a moderate hardness of the thermal conductive sheet. The median diameter of the thermal conductive filler (B3) is preferably 0.1 to 0.8 μm, more preferably 0.3 to 0.6 μm. If the median diameter is 0.1 μm or more, viscosity increase can be suppressed during kneading of the thermal conductive filler and binder components. If the median diameter is less than 1 μm, it is easier to mix during kneading and the hardness can be kept low. The thermally conductive filler (B3) is a group of particles. Only one type of thermally conductive filler (B3) may be used, or two or more types (i.e., two or more groups of particles with different median diameters) may be used.

[0055] A polyhedral shape refers to a shape formed by combining polygonal faces, for example. The polygonal faces may be flat or not necessarily equiplanar with irregularities. Polyhedral particles may be polyhedral spherical particles or single-crystal particles. A polyhedral shape is different from, for example, spherical (including perfect spheres and ellipsoids), flake-like (scaly), dendritic, massive, flattened, needle-like, fragmented, and amorphous shapes. In particular, fragmented and amorphous shapes differ from polyhedral shapes in that they are uniform in size and shape, while polyhedral shapes are uniform in size and shape. In a group of polyhedral particles with uniform size, the particle size distribution becomes sharp, leading to a high packing efficiency for the entire thermally conductive filler. The sharpness of the particle size distribution of a given group of particles can be determined, for example, by the value of (D90-D10) / D50 in the particle size distribution of that group of particles. The smaller the value, the sharper the particle size distribution of that group of particles can be judged to be. The (D90-D10) / D50 in the particle size distribution of the thermal conductive filler (B3) is preferably 0.1 to 10, and more preferably 0.5 to 5. D10 and D90 can be obtained as the particle diameter values ​​at the cumulative time of 10% and 90% from the fine particle side, respectively, obtained in the measurement method of D50 described above.

[0056] The content of the thermal conductive filler (B3) is preferably 3 to 30% by mass, more preferably 5 to 25% by mass, and even more preferably 7 to 20% by mass, based on 100% by mass of the total amount of the thermal conductive sheet. When the content is within the above range, it is easier to achieve high thermal conductivity of the thermal conductive sheet while ensuring appropriate hardness.

[0057] The content of the thermal conductive filler (B3) is preferably 3 to 30% by mass, more preferably 5 to 25% by mass, and even more preferably 7 to 20% by mass, based on 100% by mass of the total amount of thermal conductive filler in the thermal conductive sheet. When the content is within the above range, it is easier to achieve high thermal conductivity in the thermal conductive sheet while ensuring appropriate hardness.

[0058] As the thermal conductive filler (B) (especially thermal conductive fillers (B1) to (B3)), materials as exemplified and described above can be appropriately selected. When the material of thermal conductive fillers (B1) to (B3) is alumina, a thermal conductive sheet with inexpensive and stable heat dissipation characteristics can be obtained. When one or more of the materials of thermal conductive fillers (B1) to (B3) is aluminum nitride, a thermal conductive sheet with relatively low hardness can be obtained. When the materials of thermal conductive fillers (B2) and (B3) are alumina, and the material of thermal conductive filler (B1) is aluminum nitride, a thermal conductive sheet with a better balance between heat dissipation characteristics and hardness can be obtained.

[0059] The total content ratio (total amount) of thermal conductive fillers (A) and (B1) to (B3) in the thermal conductive sheet is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more, based on 100% by mass of the total amount of thermal conductive fillers contained in the thermal conductive sheet.

[0060] The content ratio (filling rate) of the thermal conductive filler in the thermal conductive sheet is preferably 70 to 95 volume%, and more preferably 75 to 90 volume%, based on 100 volume% of the total amount of the thermal conductive sheet. When the content ratio is 70 volume% or more, the filling rate of the thermal conductive filler in the thermal conductive sheet is high, making it easier to achieve high thermal conductivity. When the content ratio is 95 volume% or less, the thermal conductive sheet is less likely to become brittle, and the moldability when manufacturing the thermal conductive sheet is excellent.

[0061] <Thermal conductive sheet> The above-mentioned thermal conductive sheet may contain a coloring agent. Including a coloring agent can impart opacity to the thermal conductive sheet. The above-mentioned coloring agent can be appropriately selected depending on the purpose, and examples include black coloring agents, cyan coloring agents, magenta coloring agents, yellow coloring agents, etc. For example, as the above-mentioned black coloring agent, black pigments or mixed pigments that have been blackened by subtractive mixing of multiple pigments can be used. Examples of the above-mentioned black pigments include carbon black, Ketjen black, perylene black, titanium black, iron black, and aniline black. The above-mentioned coloring agent may be used by one or two or more types.

[0062] The total amount of the coloring agent in the thermal conductive sheet is, for example, 0.2 to 10% by mass, preferably 0.3 to 8% by mass, based on 100% by mass of the total amount of the thermal conductive sheet.

[0063] The above-mentioned thermal conductive sheet may contain other components in addition to the various components described above. Examples of these other components include thixotropy imparters, dispersants, curing agents, curing accelerators, curing retarders, tackifiers, plasticizers, flame retardants, antioxidants, and stabilizers. Only one of these other components may be used, or two or more may be used.

[0064] The thickness of the above-mentioned thermal conductive sheet is, for example, 10 to 6000 μm, and preferably 200 to 3000 μm.

[0065] The above-mentioned thermal conductive sheet preferably has a thermal conductivity in the thickness direction of 10.0 W / mK or higher when compressed by 10%, more preferably 11.0 W / mK or higher, and even more preferably 11.5 W / mK or higher. When the above-mentioned thermal conductivity is 10.0 W / mK or higher, it exhibits excellent thermal conductivity and heat dissipation in the thickness direction. The specific method for measuring the above-mentioned thermal conductivity is as described in the examples below, for example.

[0066] The above-mentioned thermal conductive sheet preferably has an Asker C hardness of 40 or higher, more preferably 50 or higher, and may also be 55 or higher or 62 or higher. A hardness of 40 or higher provides appropriate hardness and excellent handling properties. From the viewpoint of excellent conformability to the substrate, the above-mentioned thermal conductive sheet preferably has an Asker C hardness of 70 or lower. The above hardness can be measured, for example, by an Asker C hardness tester.

[0067] [Method for manufacturing a thermally conductive sheet] The method for molding the above-mentioned thermal conductive sheet is not particularly limited, and known or conventional molding methods for molded bodies can be used. Among these, molding by roll-to-sheet is preferred from the viewpoint of continuous molding and excellent productivity.

[0068] The above-mentioned thermally conductive sheet can be manufactured, for example, by placing a composition containing the various components described above between the release surfaces of two release films with flat bases or release surfaces, and then molding it by heating or pressurizing.

[0069] The above composition includes, for example, the binder component and the thermally conductive filler. If multiple types of thermally conductive fillers are used, they may be mixed beforehand and then mixed with the binder component, or multiple types of thermally conductive fillers and the binder component may be mixed simultaneously. The above composition is preferably in the form of a paste that does not contain organic solvents.

[0070] The apparatus for producing the above composition sheets is not particularly limited, and known molding equipment such as a roll laminator, roll press, hot press molding machine, or extruder can be used, by placing the material between release films coated with a release agent. [Examples]

[0071] The embodiments of the present invention will be described in more detail below based on the examples, but the present invention is not limited to these examples. Unless otherwise specified, the content of each component listed in the table is expressed in "g".

[0072] Example 1 As thermally conductive fillers, aluminum nitride particles (B1), alumina particles (B2), alumina particles (B3), and boron nitride (A1), along with titanium black as a pigment, were mixed in the masses [g] shown in Table 1. A silane coupling agent (a silane coupling agent having an ethoxy group and an alkyl group) was then added, and the particles were surface-treated with the silane coupling agent using a dry method to prepare the particle composition. A resin paste was prepared by mixing the above particle composition with a thermosetting silicone resin (a two-component addition reaction type silicone resin having a mechanism for crosslinking by hydrosilylation of a polymer having vinyl groups and a polymer having Si-H groups under a platinum catalyst) in the masses shown in Table 1. Subsequently, the above resin paste was placed between the release surfaces of two release films (PET films with a release layer, thickness 50 μm) with flat release surfaces, and a sheet-like resin paste layer was formed using a roll laminator. After standing for 1 hour, the above resin paste layer was placed in a heating furnace and heated at 80°C for 30 minutes, followed by 150°C for 90 minutes to heat-cur and mold a thermally conductive sheet. In this way, a thermally conductive sheet of Example 1 (thickness of the thermally conductive sheet: 1 mm) having a laminated structure of [release film / thermally conductive sheet / release film] was prepared.

[0073] Example 2 and Comparative Examples 1-2 The thermal conductive sheets of Example 2 and Comparative Examples 1-2 were prepared in the same manner as in Example 1, except that the types and amounts of each particle in the thermal conductive sheet were changed as shown in Table 1.

[0074] The thermally conductive fillers shown in the table are as follows: Aluminum nitride particles (B1): median diameter 120 μm, spherical, density 3.30 g / m³ 3 Alumina particles (B2): median diameter 6.8 μm, spherical, density 3.80 g / m³ 3 Alumina particles (B3): median diameter 0.4 μm, polyhedral shape, density 3.97 g / m³ 3 (D90-D10) / D50=2.4 Boron nitride (A1): median diameter 12-13 μm, thickness 5 μm or less, flaky, density 2.27 g / m² 3 Boron nitride (A2): median diameter 25 μm, thickness approximately 25 μm, spherical, density 2.27 g / m³ 3 Boron nitride (A3): Thickness 3-4 μm, width 50 μm or less, fibrous, density 2.27 g / m² 3

[0075] (evaluation) Each thermally conductive sheet obtained in the examples and comparative examples was evaluated as follows. The evaluation results are shown in the table.

[0076] (1) Thickness of the thermally conductive filler For each example, a secondary electron image was obtained at 3000x magnification of the surface of the thermally conductive sheet fabricated using an electron microscope (model number "JSM-7800F", manufactured by JEOL Ltd.). The thickness of the thermally conductive filler (A1) to (A3) was measured at 10 points, and the average value was used as the thickness.

[0077] (2) Median diameter of thermally conductive filler (D50), D10, and D90 The median diameters (D50), D10, and D90 of the thermally conductive filler were measured using a particle size distribution analyzer (product name "MT3300EXII", manufactured by Microtrac Co., Ltd.). When measurement of D50, D10, and D90 of the thermally conductive filler (particles) was difficult, the values ​​listed in the product catalog for the thermally conductive filler (particles) were used as the D50, D10, and D90 values ​​for the thermally conductive filler (particles).

[0078] (3) Thermal conductivity By adjusting the gap of the roll press machine, thermal conductive sheets of three different thicknesses—1.0 mm, 1.5 mm, and 2.0 mm—were fabricated for each example. The release film was then peeled off the thermal conductive sheets, and the thermal resistance of the three thicknesses was measured using a thermal property measuring device (product name "DynTIM," manufactured by Siemens K.K.) after compressing them by 10% in the thickness direction (i.e., to 90% of the original thickness). The thermal conductivity was calculated from the slope of the extrapolation line of the thermal resistance values ​​obtained for each thickness of thermal conductive sheet.

[0079] (4) Asker C hardness The hardness of the thermally conductive sheets fabricated in each example was measured using an Asker C hardness tester.

[0080] [Table 1]

[0081] As can be seen from Table 1, the thermally conductive sheets of the examples were judged to have high thermal conductivity and an Asker C hardness in the range of 40 to 70, indicating appropriate hardness. On the other hand, when the thermally conductive filler (A) was not included (Comparative Example 1) and when boron nitride with a thickness exceeding 20 μm was used (Comparative Example 2), the thermal conductivity was judged to be inferior.

[0082] The following describes variations of the invention according to the present invention. [Note 1] A thermally conductive sheet containing a binder component and a thermally conductive filler. The thermal conductive filler includes a thermal conductive filler (A) which is boron nitride with a thickness of 20 μm or less, and other thermal conductive fillers (B) other than the thermal conductive filler (A). A thermal conductive sheet in which the content ratio of the thermal conductive filler (A) is 0.01 to 1% by mass relative to 100% by mass of the total amount of the thermal conductive sheet. [Note 2] The thermal conductive sheet described in Note 1, with an Asker C hardness of 40-70. [Note 3] The thermal conductive sheet according to Note 1 or 2, wherein the thermal conductive filler (A) is flaky in shape. [Note 4] The thermal conductive sheet described in any one of Notes 1 to 3, wherein the thermal conductive filler (A) is fibrous. [Note 5] The thermal conductive filler (B) is a thermal conductive sheet as described in any one of Notes 1 to 4, comprising a thermal conductive filler containing one or more aluminum nitride and alumina as material. [Note 6] The thermal conductive sheet according to any one of Notes 1 to 5, wherein the thermal conductive filler (B) includes one or more spherical and polyhedral thermal conductive fillers. [Note 7] The thermal conductive sheet according to any one of Notes 1 to 6, wherein the binder component is a silicone resin. [Note 8] A thermally conductive sheet as described in any one of Notes 1 to 7, wherein the thermal conductivity in the thickness direction when compressed by 10% is 10.0 W / mK or higher. [Explanation of Symbols]

[0083] 1. Thermally conductive sheet 2,3 Release film 11 Binder components 12 Thermally conductive fillers 12a Thermally conductive filler (A) 12b Thermally conductive filler (B)

Claims

1. A thermally conductive sheet containing a binder component and a thermally conductive filler, The thermal conductive filler includes a thermal conductive filler (A) which is boron nitride with a thickness of 20 μm or less, and other thermal conductive fillers (B) other than the thermal conductive filler (A). A thermal conductive sheet in which the content ratio of the thermal conductive filler (A) is 0.01 to 1% by mass relative to 100% by mass of the total amount of the thermal conductive sheet.

2. The thermally conductive sheet according to claim 1, wherein the Asker C hardness is 40 to 70.

3. The thermal conductive sheet according to claim 1 or 2, wherein the shape of the thermal conductive filler (A) is flaky.

4. The thermal conductive sheet according to claim 1 or 2, wherein the thermal conductive filler (A) is fibrous.

5. The thermal conductive sheet according to claim 1 or 2, wherein the thermal conductive filler (B) includes a thermal conductive filler containing one or more aluminum nitride and alumina as material.

6. The thermal conductive sheet according to claim 1 or 2, wherein the thermal conductive filler (B) comprises one or more spherical and polyhedral thermal conductive fillers.

7. The thermal conductive sheet according to claim 1 or 2, wherein the binder component is a silicone resin.

8. The thermally conductive sheet according to claim 1 or 2, wherein the thermal conductivity in the thickness direction when compressed by 10% is 10.0 W / mK or more.

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