fins

Abstract

The present application is a heat sink which is a heat sink molded from a thermally conductive resin composition, wherein the thermally conductive resin composition is obtained by mixing an inorganic filler component and a resin component, the inorganic filler component contains a first inorganic filler and a second inorganic filler, the particle size distribution of the inorganic filler component has a first maximum point M1 attributed to the first inorganic filler and a second maximum point M2 attributed to the second inorganic filler, the particle diameter of the first maximum point M1 is 15 μm or more, the particle diameter of the second maximum point M2 is two-thirds or less of the particle diameter of the first maximum point M1, the cumulative amount of the frequency between the peak starting point PS and the peak ending point PE in the peak having the first maximum point M1 is 50% or more, the surface roughness is 1.5 to 3.0 μm, and the thickness is 0.2 mm or less. According to the present application, a thin heat sink having excellent thermal conductivity can be provided.

Description

Technical Field

[0001] This invention relates to heat sinks formed by molding thermally conductive resin compositions. Background Technology

[0002] In power devices, transistors, thyristors, CPUs, and other heat-generating electronic components, effectively dissipating the heat generated during use is a crucial issue. Traditionally, heat dissipation strategies have typically involved (1) making the insulating layer of the printed circuit board (PCB) housing the heat-generating electronic components highly thermally conductive, and (2) mounting the heat-generating electronic components or the PCB housing them onto a heat sink via an electrically insulating thermal interface material. Materials made by filling ceramic powder into silicone resin or epoxy resin are commonly used as the insulating layer and thermal interface material for PCBs.

[0003] In recent years, with the increasing speed and high integration of circuits within heat-generating electronic components and the increasing mounting density of heat-generating electronic components on printed circuit boards, the heat density inside electronic devices has been increasing year by year. Therefore, there is a demand for ceramic powders with higher thermal conductivity than ever before (for example, see Patent Document 1).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 9-202663 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] In recent years, with the miniaturization of heat-generating electronic components, there has been a demand for thin heat sinks. Here, the doctor blade method is known as a method for continuously obtaining thin molded bodies composed of ceramic raw material powder and organic components. The doctor blade method involves spreading a uniform slurry thinly onto a carrier film to obtain a molded body. The doctor blade method is widely used in ceramic substrates for electronic devices, ceramic packaging for ICs, multilayer ceramic packaging, multilayer ceramic circuit boards, ceramic capacitors, etc. From the viewpoint of mass production of thin heat sinks, it is also desirable to use the doctor blade method to produce thin heat sinks. In the doctor blade method, slurry flows out from the gap between the doctor blade and the carrier film to form a sheet-like molded body. Furthermore, by reducing the size between the doctor blade and the carrier film, the molded body can be made thinner. However, when using slurries made from ceramic powder contained in heat sinks of conventional thickness, it is difficult to reduce the size between the doctor blade and the carrier film, thereby producing thin heat sinks while maintaining a high level of thermal conductivity.

[0009] Therefore, the object of the present invention is to provide a thin heat sink with excellent thermal conductivity.

[0010] Methods for solving problems

[0011] In order to achieve the above-mentioned objective, the inventors conducted in-depth research and found that if inorganic fillers with specific particle sizes are used in combination and the inorganic fillers are filled until the surface roughness reaches a specified range, a heat sink with good thermal conductivity of 0.2 mm or less, and further 0.15 mm or less, is obtained.

[0012] This invention is based on the above insights, and its main points are as follows.

[0013] [1] A heat sink is formed by molding a thermally conductive resin composition, wherein the thermally conductive resin composition is formed by mixing an inorganic filler component and a resin component, the inorganic filler component includes a first inorganic filler and a second inorganic filler, the particle size distribution of the inorganic filler component has a first maximum point attributable to the first inorganic filler and a second maximum point attributable to the second inorganic filler, the particle size of the first maximum point is 15 μm or more, the particle size of the second maximum point is less than two-thirds of the particle size of the first maximum point, the cumulative amount of frequency between the peak start point and the peak end point of the peak having the first maximum point is 50% or more, the surface roughness of the heat sink is 1.5 to 3.0 μm, and the thickness of the heat sink is 0.2 mm or less.

[0014] [2] According to the heat sink described in [1] above, the cumulative amount of the frequency of particles with a diameter of 0 to 15 μm in the particle size accumulation of the inorganic filler component is less than 60%.

[0015] [3] The heat sink according to [1] or [2] above further comprises a substrate with a thickness of 0.05 mm or less.

[0016] Invention Effects

[0017] According to the present invention, it is possible to provide a thin heat sink with excellent thermal conductivity. Attached Figure Description

[0018] Figure 1 This is a diagram showing an example of the particle size distribution of inorganic filler components. Detailed Implementation

[0019] The heat sink of the present invention is formed by molding a thermally conductive resin composition, wherein the thermally conductive resin composition is formed by mixing inorganic filler components and resin components.

[0020] [Thermal Conductive Resin Composition]

[0021] The thermally conductive resin composition of the present invention is prepared by mixing inorganic filler components and resin components.

[0022] (Inorganic filler composition)

[0023] The inorganic packing component comprises a first inorganic packing and a second inorganic packing. The particle size distribution of the inorganic packing component has a first maximum attributable to the first inorganic packing and a second maximum attributable to the second inorganic packing. The particle size at the first maximum is 15 μm or larger, and the particle size at the second maximum is less than two-thirds of the particle size at the first maximum. The cumulative frequency between the peak start and peak end of the peak with the first maximum is 50% or larger.

[0024] The particle size distribution of the inorganic filler component in the thermally conductive resin composition can be determined, for example, as follows: The components other than the inorganic filler component in the thermally conductive resin composition are dissolved using solvents such as toluene, xylene, or chlorinated hydrocarbons, thus removing the components other than the inorganic filler component from the thermally conductive composition. Then, the particle size distribution of the remaining inorganic filler component is determined using a Beckman Coulter Inc. laser diffraction scattering particle size distribution measuring apparatus (LS-13 320). Furthermore, in the case of three or more peaks, the peak with the highest frequency of its maxima is designated as the peak attributable to the first inorganic filler, and the peak with the second highest frequency of its maxima is designated as the peak attributable to the second inorganic filler. It should be noted that, in this specification, the unit of frequency in the particle size distribution is volume percentage.

[0025] <First Inorganic Packing Material>

[0026] The first inorganic filler can be any inorganic filler with a thermal conductivity higher than that of the resin component, and there are no particular limitations. Examples of the first inorganic filler include alumina particles, aluminum nitride particles, and boron nitride particles. One of these first inorganic fillers can be used alone, or two or more can be used in combination. Among these, boron nitride particles are preferred as the first inorganic filler. If the first inorganic filler is boron nitride particles, the thermal conductivity of the heat sink can be further improved. From the viewpoint of further improving thermal conductivity, bulk boron nitride particles are more preferred. Bulk boron nitride is formed by the aggregation of hexagonal boron nitride primary particles. While bulk boron nitride particles have the advantage of further improving thermal conductivity, they also have the disadvantage of increasing the viscosity of the thermally conductive resin composition slurry due to primary particle peeling, making it difficult to manufacture thin heat sinks. From this viewpoint, the first inorganic filler is further preferably bulk boron nitride particles formed by the aggregation of hexagonal boron nitride primary particles and having a crushing strength of 6 MPa or higher. By using this substance, when preparing a slurry of a thermally conductive resin composition, it is possible to further suppress the increase in viscosity of the slurry caused by the detachment of a portion of the first inorganic filler from the first inorganic filler. Hereinafter, bulk boron nitride particles with a crushing strength of 6 MPa or higher will be referred to as bulk boron nitride particles, and bulk boron nitride particles with a crushing strength of less than 6 MPa will be referred to as agglomerated boron nitride particles.

[0027] The particle size of the first maximum point attributable to the first inorganic filler is 15 μm or more. If the particle size of the first maximum point attributable to the first inorganic filler is less than 15 μm, the thermally conductive resin composition cannot contain the first inorganic filler in a highly filled manner, resulting in a decrease in the thermal conductivity of the heat sink made using the thermally conductive resin composition. From this viewpoint, the particle size of the first maximum point is preferably 20 μm or more, more preferably 30 μm or more, even more preferably 40 μm or more, and particularly preferably 50 μm or more. Furthermore, the particle size of the first maximum point is preferably 100 μm or less. If the particle size of the first maximum point is 100 μm or less, a thin heat sink can be made using the thermally conductive resin composition. From this viewpoint, the particle size of the first maximum point is more preferably 90 μm or less, and even more preferably 80 μm or less.

[0028] It should be noted that commercially available products can also be used as the first inorganic filler with the aforementioned particle size. Furthermore, when manufacturing bulk boron nitride particles for use as the first inorganic filler, the particle size of the first maximum point can be adjusted, for example, by adjusting the average particle size of B4C, the raw material used as the bulk boron nitride particles. That is, if the average particle size of B4C, the raw material used as the bulk boron nitride particles, is increased, the particle size of the first maximum point becomes larger; if the average particle size of B4C is decreased, the particle size of the first maximum point becomes smaller. Additionally, the phrase "the particle size of the first maximum point is attributed to the first inorganic filler" means that the maximum point of the particle size distribution of the first inorganic filler appears as the first maximum point in the particle size distribution of the inorganic filler component. It should be noted that due to the influence of the particle size distribution of inorganic filler components other than the first inorganic filler, there may be cases where the particle size of the first maximum point differs slightly from the particle size of the maximum point of the particle size distribution of the first inorganic filler.

[0029] As described above, the first inorganic filler is preferably blocky boron nitride particles formed by the aggregation of hexagonal boron nitride primary particles and having a crushing strength of 6 MPa or more. If the crushing strength of the blocky boron nitride particles is less than 6 MPa, when the thermally conductive resin composition is made into a slurry, some of the blocky boron nitride particles will peel off from the blocky boron nitride particles, increasing the viscosity of the thermally conductive resin composition, and sometimes making it impossible to produce thin molded articles by the scraper method. In addition, due to the stress applied to the blocky boron nitride particles during mixing with the resin components and during pressing of the thermally conductive resin composition, the blocky boron nitride particles may sometimes collapse, reducing the thermal conductivity of the heat sink. From this point of view, the crushing strength of the blocky boron nitride particles is preferably 7 MPa or more, more preferably 8 MPa or more, further preferably 9 MPa or more, even more preferably 10 MPa or more, and particularly preferably 11 MPa or more. It should be noted that the upper limit of the crushing strength of the blocky boron nitride particles is not particularly limited, for example, it is 30 MPa or less.

[0030] The crushing strength of blocky boron nitride particles and agglomerated boron nitride particles can be determined according to JIS R1639-5:2007. Specifically, it can be determined as follows: The components other than the inorganic filler in the thermally conductive resin composition are dissolved using solvents such as toluene, xylene, or chlorinated hydrocarbons, thus removing the components other than the inorganic filler from the thermally conductive resin composition. Then, the particle size distribution of the remaining inorganic filler is determined using a laser diffraction scattering particle size distribution measuring device (LS-13 320) manufactured by Beckman Coulter Inc. Next, the inorganic filler is dispersed on the sample stage of a micro-compression tester ("MCT-W500", manufactured by Shimadzu Corporation), and the diameters of the inorganic filler in the X and Y directions are measured. The average value is taken as the particle size of the inorganic filler. Five inorganic filler components with particle sizes within ±5 μm of the first maximum point are selected, and compression tests are performed on each particle. Then, the crushing strength (σ: MPa) is calculated from the dimensionless number (α = 2.48) varying according to the position within the particle, the crushing test force (P: N), and the particle size (d: μm), using σ = α × P / (π × d). 2 The formula is used to calculate the crushing strength of the five inorganic filler components. A Weibull plot is constructed based on JIS R1625:2010 for the crushing strength of the five inorganic filler components. The crushing strength with a cumulative failure rate of 63.2% is taken as the crushing strength of the first inorganic filler. It should be noted that the "63.2% cumulative failure rate" is a known value that satisfies the value of lnln{1 / (1-F(t))}=0 in the Weibull distribution function taught in JIS R1625:2010, as cited in JIS R1639-5:2007, and is a value based on the number of particles.

[0031] The cumulative amount of frequencies between the start and end points of the peak having the first maximum is 50% or more. If the cumulative amount is less than 50%, the viscosity of the thermally conductive resin composition increases due to inorganic fillers other than the first inorganic filler, making it impossible to produce thin molded articles by the doctor blade method. From this point of view, the cumulative amount is preferably 60% or more, more preferably 70% or more. Furthermore, in order to demonstrate the effect of the inorganic filler component containing the second inorganic filler described later, the cumulative amount is preferably 90% or less, more preferably 80% or less. In particular, the combination of the larger, higher-strength first inorganic filler and the second inorganic filler described later can improve manufacturability and enable the production of heat sinks densely packed with inorganic fillers. It should be noted that the cumulative amount of frequencies between the start and end points of the peak having the first maximum is approximately the content (volume %) of the inorganic filler component of the first inorganic filler. Therefore, by analyzing the composition of the inorganic filler component, it is possible to determine the inorganic filler corresponding to the first maximum.

[0032] Reference Figure 1 The cumulative frequency between the peak start point and the peak end point of a peak with the first maximum point is explained. Figure 1 This is a graph showing an example of the particle size distribution of an inorganic filler component. The horizontal axis is logarithmic. The symbol M1 indicates the first maximum, and the symbol M2 indicates the second maximum. Additionally, PS indicates the peak initiation point, and PE indicates the peak termination point. It should be noted that, as... Figure 1 As shown, when the bottoms of adjacent peaks overlap, the location of the trough of the peak becomes the peak start point (PS). Furthermore, the cumulative amount of the sloping portion of the peak having the first maximum point (M1) becomes the cumulative amount of the frequency of the peak having the first maximum point (M1) from the peak start point (PS) to the peak end point (PE). Additionally, when the bottoms of adjacent peaks on the peak end point side overlap, the location of the trough of the peak becomes the peak end point.

[0033] As described above, high-crushing-strength blocky boron nitride particles are preferably used as the first inorganic filler. Therefore, a method for manufacturing these high-crushing-strength blocky boron nitride particles will be described.

[0034] Hexagonal boron nitride particles, formed by the agglomeration of primary particles and having a crushing strength of 6 MPa or higher, can be manufactured by synthesizing boron carbide from boron and acetylene black as raw materials, and then performing a (1) pressure nitriding firing process and a (2) decarburization crystallization process on the obtained boron carbide to produce bulk boron nitride particles. The process is described in detail below.

[0035] (1) Pressure nitriding firing process

[0036] In the pressure nitriding firing process, boron carbide with an average particle size of 6–55 μm and a carbon content of 18–21% is subjected to pressure nitriding firing. This yields boron carbide suitable as a raw material for the blocky boron nitride particles of the present invention.

[0037] (i) Boron carbide raw materials used in the pressure nitriding process

[0038] Since the average particle size of boron carbide used in the pressure nitriding process has a strong influence on the final formed bulk boron nitride particles, it is necessary to select boron carbide with an appropriate particle size. Preferably, boron carbide with an average particle size of 6–55 μm is used as the raw material. Furthermore, it is desirable to have low levels of impurities such as boric acid and free carbon.

[0039] The average particle size of the boron carbide raw material is preferably 6 μm or more, more preferably 7 μm or more, even more preferably 10 μm or more, and preferably 55 μm or less, more preferably 50 μm or less, even more preferably 45 μm or less. Furthermore, the average particle size of the boron carbide raw material is preferably 7 to 50 μm, more preferably 10 to 45 μm. It should be noted that the average particle size of the boron carbide can be measured using a laser diffraction scattering particle size distribution measuring device (LS-13 320) manufactured by Beckman Coulter Inc.

[0040] The boron carbide used in the pressure nitriding process preferably has a carbon content lower than the compositional B4C (21.7%), and preferably has a carbon content of 18-21%. This range of carbon content is chosen because less carbon is produced during the decarburization crystallization process described later, resulting in denser, bulk boron nitride particles; this also aims to reduce the carbon content of the final bulk boron nitride particles. Furthermore, producing stable boron carbide with a carbon content of less than 18% deviates too much from the theoretical composition, making it difficult.

[0041] (ii) Pressurized nitriding firing

[0042] Pressure nitriding is carried out under specific firing temperatures and pressurized atmospheres. The firing temperature in pressure nitriding is preferably 1800–2200°C. The pressure in pressure nitriding is preferably 0.6–1.0 MPa. The atmosphere used in pressure nitriding requires gases that carry out the nitriding reaction, such as nitrogen and ammonia, which can be used alone or in combination of two or more. Nitrogen is preferred due to its nitriding properties and cost considerations. The firing time in pressure nitriding is preferably 6–30 hours.

[0043] (2) Decarbonization crystallization process

[0044] In the decarburization crystallization process, the boron carbonitride obtained in the pressure nitriding process is subjected to the following heat treatment: (a) in an atmosphere above atmospheric pressure, the temperature is raised to (b) a specific temperature until a firing temperature within a specific temperature range is reached (c) and (d) held at the firing temperature for a certain time. This allows the primary particles (which are flake-like hexagonal boron nitride) to agglomerate into blocky boron nitride particles. In particular, if the above heat treatment conditions are within the range described later, a crushing strength of 6 MPa or higher can be achieved.

[0045] In this decarburization crystallization process, as described above, the boron carbonitride obtained from the prepared boron carbide is decarburized and made into scales of a specified size, while being agglomerated to form block boron nitride particles.

[0046] More specifically, in the decarburization crystallization process, 100 parts by mass of boron carbonitride obtained in the pressure nitriding firing process are mixed with 65 to 130 parts by mass of at least one compound selected from boron oxide and boric acid to prepare a mixture. After the mixture is raised to a temperature at which decarburization can begin, it is heated at a rate of 5°C / min or less until it reaches a firing temperature of 1800°C or higher, and then subjected to heat treatment at the firing temperature for more than 0.5 hours and less than 40 hours.

[0047] In the decarburization crystallization process, the pressure condition of "(a) atmosphere at atmospheric pressure or above" is preferably atmospheric pressure or above, more preferably 0.1 MPa or above. Furthermore, there is no particular upper limit to the pressure condition of the atmosphere, but it is preferably 1 MPa or below. The aforementioned "atmosphere" in the decarburization crystallization process is preferably nitrogen.

[0048] The "(b) specific heating temperature" in the decarburization crystallization process can be any of one or more stages. The "temperature at which decarburization can begin" is not particularly limited and can be any temperature normally used, such as around 800–1200°C (preferably around 1000°C). The "heating rate in the first stage" can, for example, be in the range of 5–20°C / min, preferably 8–12°C / min.

[0049] The specific temperature range (the firing temperature after heating) in "heating until reaching (c) the specific temperature range of firing temperature" can be 1800°C or higher, more preferably 2000°C or higher. Furthermore, there is no particular limitation on the upper limit of the holding temperature, but it is preferably 2200°C or lower, more preferably 2100°C or lower. If the holding temperature is too low, below 1800°C, grain growth may not be sufficiently induced, resulting in a decrease in thermal conductivity. On the other hand, if the holding temperature is 1800°C or higher, it facilitates good grain growth and easily improves thermal conductivity.

[0050] Regarding the "holding time" (the firing time after heating) in "(d) holding at the firing temperature for a certain period of time," there is no particular limitation as long as crystallization proceeds sufficiently. In a preferred embodiment, it can be set to a range of more than 0.5 hours and less than 40 hours, more preferably to a range of 1 to 30 hours. Furthermore, the holding time is preferably 1 hour or more, more preferably 3 hours or more, further preferably 5 hours or more, and even more preferably 10 hours or more. Additionally, the upper limit of the holding time is preferably 30 hours or less, more preferably 20 hours or less. When the holding time is 1 hour or more, good grain growth is expected to occur. Furthermore, if the holding time is 30 hours or less, it is expected that excessive grain growth leading to a decrease in particle strength can be reduced. Additionally, it is expected that industrially disadvantageous situations due to long firing times can be reduced.

[0051] Then, through the aforementioned pressure nitriding and calcination process and the aforementioned decarburization and crystallization process, the blocky boron nitride particles of the present invention can be obtained. Furthermore, to break up the weak agglomeration between the blocky boron nitride particles, it is preferable to pulverize or crush the blocky boron nitride particles obtained in the decarburization and crystallization process for further classification. The pulverization and crushing are not particularly limited; commonly used pulverizers and crushers are acceptable. Furthermore, classification can be performed using a conventional sieving method with an average particle size of 20 μm or more. For example, methods such as crushing using a Henschel mixer or mortar and pestle, followed by classification using a vibrating screen, can be employed.

[0052] <Second Inorganic Packing Material>

[0053] The particle size at the second maximum point, attributed to the second inorganic filler, is less than two-thirds of the particle size at the first maximum point. If the particle size at the second maximum point is greater than two-thirds of the particle size at the first maximum point, the thermally conductive resin composition cannot contain the inorganic filler component in a highly filled manner, and sometimes it is impossible to produce a thin heat sink with excellent thermal conductivity. From this point of view, the particle size at the second maximum point is preferably less than 60% of the particle size at the first maximum point, more preferably less than 55% of the particle size at the first maximum point, and even more preferably less than 52% of the particle size at the first maximum point. It should be noted that the lower limit value of the particle size at the second maximum point is, for example, more than 20% of the particle size at the first maximum point, preferably more than 30% or more or more than 40% of the particle size at the first maximum point. In addition, the second maximum point can be measured in the same way as the first maximum point. It should be noted that there can be multiple second maximum points. In addition, the cumulative amount of frequency between the peak start point and the peak end point of the peak with the second maximum point is approximately equal to the content (volume %) of the second inorganic filler in the inorganic component. Therefore, by analyzing the composition of inorganic fillers, it is possible to identify the inorganic filler corresponding to the second maximum point.

[0054] The cumulative frequency between the peak start point and the peak end point of the peak with the second maximum point is less than 50%, less than 45%, less than 40%, or less than 35%. The lower limit can be more than 10%, more than 15%, more than 20%, or more than 25%.

[0055] The second inorganic filler is not particularly limited as long as it is an inorganic filler with a higher thermal conductivity than the resin component. Examples of second inorganic fillers include alumina particles, aluminum nitride particles, and boron nitride particles. These second inorganic fillers can be used alone or in combination of two or more. Among these, boron nitride particles are preferred as the second inorganic filler. If the second inorganic filler is boron nitride particles, the thermal conductivity of the heat sink made using the thermally conductive resin composition can be further improved. From the viewpoint of further improving thermal conductivity, bulk boron nitride particles are more preferred. Bulk boron nitride is formed by the aggregation of hexagonal boron nitride primary particles. Although bulk boron nitride particles have the advantage of further improving thermal conductivity, they also have the disadvantage of being difficult to manufacture due to the peeling of primary particles. From this viewpoint, the second inorganic filler is also more preferably bulk boron nitride particles formed by the aggregation of hexagonal boron nitride primary particles and having a crushing strength of 6 MPa or more. Hereinafter, regarding the second inorganic packing material, blocky boron nitride particles with a crushing strength of 6 MPa or higher will be referred to simply as blocky boron nitride particles, and blocky boron nitride particles with a crushing strength of less than 6 MPa will be referred to as agglomerated boron nitride particles. It should be noted that the blocky boron nitride particles of the second inorganic packing material can be manufactured using the same method as those of the blocky boron nitride particles of the first inorganic packing material. Furthermore, by adjusting the average particle size of B4C used as the raw material for the blocky boron nitride particles, it is possible to make the particle size at the second maximum point attributed to the second inorganic packing material less than two-thirds of the particle size at the first maximum point.

[0056] Regarding the second inorganic filler, the crushing strength of blocky boron nitride particles and agglomerated boron nitride particles can be determined according to JIS R 1639-5:2007. Specifically, it can be determined as follows: The components other than the inorganic filler in the thermally conductive resin composition are dissolved using solvents such as toluene, xylene, or chlorinated hydrocarbons, thus removing the components other than the inorganic filler from the thermally conductive resin composition. Then, the particle size distribution of the remaining inorganic filler is determined using a laser diffraction scattering particle size distribution measuring device (LS-13 320) manufactured by Beckman Coulter Inc. Next, the inorganic filler is dispersed on the sample stage of a micro-compression tester ("MCT-W500", manufactured by Shimadzu Corporation), and the diameters of the inorganic filler components in the X and Y directions are measured. The average value is taken as the particle size of the inorganic filler component. Five inorganic filler components with particle sizes within ±5 μm of the second maximum point are selected, and compression tests are performed on each particle. Furthermore, the crushing strength (σ: MPa) is determined by a dimensionless number (α = 2.48) varying according to the position within the particle, the crushing test force (P: N), and the particle size (d: μm), using the formula σ = α × P / (π × d). 2The formula was used to calculate the crushing strength of the five inorganic filler components according to JIS R1625:2010. The crushing strength with a cumulative failure rate of 63.2% was taken as the crushing strength of the second inorganic filler.

[0057] In the accumulation of particle size in the inorganic filler component, the cumulative amount of the frequency of particle size from 0 to 15 μm is preferably less than 60%. Thus, the content of inorganic filler with a particle size of 15 μm or more in the inorganic filler component is approximately 40% by volume or more, allowing the thermally conductive resin composition to contain the inorganic filler component in a highly filled manner, which further improves the thermal conductivity of the heat sink made using the thermally conductive resin composition. From this viewpoint, in the accumulation of particle size in the inorganic filler component, the cumulative amount of the frequency of particle size from 0 to 15 μm is more preferably less than 50%, more preferably less than 40%, and even more preferably less than 30%.

[0058] (Resin composition)

[0059] Examples of resins used as resin components include epoxy resins, silicone resins (including silicone rubber), acrylic resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, fluoropolymers, polyamides (e.g., polyimide, polyamide-imide, polyether-imide, etc.), polyesters (e.g., polybutylene terephthalate, polyethylene terephthalate, etc.), polyphenylene ether, polyphenylene sulfide, fully aromatic polyesters, polysulfones, liquid crystal polymers, polyethersulfones, polycarbonates, maleimide-modified resins, ABS resins, AAS (acrylonitrile-acrylic rubber-styrene) resins, and AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resins. Among these, silicone resins are preferred from the viewpoints of heat resistance, flexibility, and adhesion to heat sinks, etc. Silicone resins are preferably cured by vulcanization using organic peroxides. From the viewpoint of improving the flexibility of sheet-like molded articles, the viscosity of the thermally conductive resin composition at 25°C is, for example, 100,000 cp or higher.

[0060] The inorganic filler content in the total 100% by volume of the inorganic filler and resin components is preferably 30-85% by volume, more preferably 40-80% by volume. When the inorganic filler content is 30% by volume or more, the thermal conductivity is improved, and sufficient heat dissipation performance is easily obtained. Furthermore, when the inorganic filler content is 85% by volume or less, the likelihood of voids forming during molding can be reduced, and the reduction in insulation and mechanical strength can be minimized. Additionally, the resin content in the 100% by volume of the thermally conductive resin composition is preferably 15-70% by volume, more preferably 20-60% by volume.

[0061] (solvent)

[0062] To adjust the viscosity of the thermally conductive resin composition, the composition may also contain a solvent. The solvent is not particularly limited as long as it can dissolve the resin component and is easily removed from the coated thermally conductive resin composition after application. When the resin component is a silicone resin, examples of solvents include toluene, xylene, and chlorinated hydrocarbons. From the viewpoint of easy removal, toluene is preferred. The solvent content can be appropriately selected according to the target viscosity of the thermally conductive resin composition. For example, the solvent content is 40 to 200 parts by mass relative to 100 parts by mass of the components other than the solvent in the thermally conductive resin composition.

[0063] It should be noted that the thermally conductive resin composition may contain components other than inorganic filler, resin, and solvent. Other components include additives, impurities, etc. The content of other components is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 1 part by mass or less, relative to 100 parts by mass of the total inorganic filler and resin components.

[0064] [Heat sink]

[0065] As described above, the heat sink of the present invention is formed by molding the above-described thermally conductive resin composition. By using the thermally conductive resin composition of the present invention, thin heat sinks can be easily manufactured using a scraper method. The thickness of the heat sink of the present invention is 0.20 mm or less. If the thickness of the heat sink is 0.20 mm or less, the requirement for heat sink thickness accompanying the miniaturization of heat-generating electronic components can be met. From this viewpoint, the thickness of the heat sink is more preferably 0.15 mm or less, more preferably 0.12 mm or less, and even more preferably 0.10 mm or less.

[0066] Furthermore, the surface roughness of the heat sink of the present invention is 1.5 to 3.0 μm. By employing a combination of a first inorganic filler and a second inorganic filler, and by fully filling the inorganic filler components until the surface roughness becomes 1.5 μm or more, the heat sink can be made thinner, and sufficient thermal conductivity can be achieved. This is presumably because, by using a specific combination of inorganic fillers, not only can the filler content be increased, but a filling pattern that facilitates heat transfer can also be achieved. If the surface roughness of the heat sink is less than 1.5 μm, the thermal conductivity sometimes becomes lower. This is believed to be because the proportion of inorganic filler components in the thermally conductive resin composition becomes lower, or the aforementioned specific filling pattern cannot be formed. It should be noted that if the proportion of inorganic filler components in the thermally conductive resin composition is low, the inorganic filler components are embedded in the resin components, and the surface of the heat sink becomes very smooth. On the other hand, if the surface roughness of the heat sink is greater than 3.0 μm, the thermal conductivity sometimes becomes lower. This can be considered as the inorganic filler components not achieving a sufficiently dense filling state, the filling rate not being increased, the aforementioned filling pattern not being achieved, and the thermal conductivity not being improved. The surface roughness of the heat sink is the arithmetic mean roughness Ra, which is measured according to the description in JIS B 0601:2013 "Geometrical Product Specifications (GPS) - Surface texture: Profile method - Terms, definitions and surface texture parameters".

[0067] The heat sink preferably comprises a substrate with a thickness of 0.05 mm or less. This allows the heat sink to be thinner and prevents breakage during heat sink processing. The substrate is not particularly limited as long as it can maintain the thermally conductive resin composition layer, has moderate strength, a thickness of 0.05 mm or less, and is flexible. Examples of substrates include paper, cloth, film, nonwoven fabric, and metal foil. Among these, cloth is preferred from the viewpoint of good adhesion to the thermally conductive resin composition layer and the ability to suppress the substrate's obstruction of thermal conductivity to the thermally conductive resin composition by providing mesh portions. Glass cloth and polyamide-imide fiber cloth are more preferred from the viewpoint of thinning the substrate and maintaining its strength to a certain extent even with increased mesh size, with glass cloth being even more preferred. Furthermore, from the viewpoint of thinning the heat sink, the thickness of the substrate is more preferably 0.03 mm or less. Additionally, from the viewpoint of substrate strength, the thickness of the substrate is preferably 0.005 mm or more. In the case where the substrate is glass cloth, in order to suppress the formation of gaps between the thermally conductive resin composition and the glass cloth, the glass cloth can be subjected to silane coupling treatment.

[0068] Heat sinks can be manufactured using a scraper method. For example, a heat sink can be manufactured as follows: A slurry-like thermally conductive resin composition is prepared by dispersing raw materials other than solvents, such as inorganic filler components and resin components, in a solvent. It should be noted that, hereinafter, the slurry-like thermally conductive resin composition is sometimes simply referred to as "slurry." It should be noted that the crushing strength of the blocky boron nitride particles used as the first inorganic filler is as high as 6 MPa; therefore, when the raw materials other than solvents are dispersed in the solvent, the hexagonal boron nitride primary particles hardly peel off from the blocky boron nitride particles. Thus, when the raw materials other than solvents in the thermally conductive resin composition are dispersed in the solvent, the viscosity increase of the slurry can be suppressed. The viscosity of the slurry can also be reduced by increasing the amount of solvent. However, in this case, when the thermally conductive resin composition is molded into a sheet, the thermally conductive resin composition may sometimes foam, or when the solvent is removed from the molded body in the sheet form, additives such as vulcanizing agents and curing agents in the thermally conductive composition may sometimes become ineffective. Therefore, it is preferable to reduce the viscosity of the slurry without increasing the amount of solvent. Furthermore, the average particle size of the blocky boron nitride particles used as the first inorganic filler is relatively large, approximately 15 μm or more. Therefore, it can suppress the aggregation of the dispersed inorganic filler components, which could cause the slurry to become uneven, after the raw materials other than the solvent in the thermally conductive resin composition are dispersed in the solvent. It should be noted that if the average particle size of the inorganic filler is very small, the dispersed inorganic filler may sometimes aggregate, causing the slurry to become uneven.

[0069] The prepared slurry is fed to a doctor blade device. The doctor blade device causes the slurry to flow out from the gap between the doctor blade and the carrier film, molding the thermally conductive resin composition into a sheet. It should be noted that the thickness of the molded body can be precisely controlled by adjusting the dimensions between the doctor blade and the carrier film and the moving speed of the carrier film. Furthermore, for even more precise control of the slurry pressure and the thickness of the molded body, a doctor blade device with two blades can be used.

[0070] The slurry flowing from the gap between the doctor blade and the carrier film moves together with the carrier film within the doctor blade device, drying and solidifying during movement to form a sheet-like molded body. The resulting sheet-like molded body can be pressurized and heated to solidify it into a heat sink. It should be noted that a release agent can be coated onto the surface of the carrier film to facilitate easy peeling of the heat sink from the carrier film. Examples of release agents include silicone-based release agents, alkyl pendant-based release agents, and condensation wax-based release agents.

[0071] When a heat sink includes a substrate, for example, the heat sink is manufactured as follows: A laminate is obtained by sandwiching the substrate between two sheet-like molded bodies with a carrier film, which are obtained by a scraping method. The layer structure of the laminate at this time is carrier film / thermal conductive resin composition / substrate / thermal conductive resin composition / carrier film. Then, the laminate is pressurized and heated, and the carrier film is peeled off to form a heat sink. It should be noted that, in this case, a release agent may be applied to the surface of the carrier film to facilitate easy peeling of the heat sink from the carrier film.

[0072] Heat sinks can also be manufactured by calendering. However, when the sheet-like thermally conductive resin composition passes through calendering rolls, some of the bulk boron nitride particles may be detached from the bulk boron nitride particles in the thermally conductive resin composition. Therefore, heat sinks are preferably manufactured by a scraper method.

[0073] Example

[0074] The present invention will now be described in detail through embodiments and comparative examples. It should be noted that the present invention is not limited to the following embodiments.

[0075] The thermally conductive resin compositions of the Examples and Comparative Examples were evaluated as follows.

[0076] (Slurry viscosity)

[0077] Regarding the viscosity of the slurry used in the fabrication of the heat sinks in the examples and comparative examples, the viscosity of the slurry after standing for 30 seconds was measured using a Type B viscometer at a rotation speed of 20 rpm.

[0078] (Particle size distribution)

[0079] Toluene was used to dissolve components other than the inorganic filler in the thermally conductive resin composition, thus removing these components from the composition. The particle size distribution of the remaining inorganic filler was measured using a Beckman Coulter Inc. laser diffraction scattering particle size distribution measuring apparatus (LS-13320). The first and second maxima, as well as the cumulative frequency between the peak start and end points of the peak with the first maxima, were then determined based on the obtained particle size distribution.

[0080] (Crushing strength)

[0081] The crushing strength of blocky boron nitride particles and agglomerated boron nitride particles was determined according to JIS R1639-5:2007. Specifically, components other than the inorganic filler component in the thermally conductive resin composition were dissolved using solvents such as toluene, xylene, and chlorinated hydrocarbons to remove these components from the composition. Then, the particle size distribution of the remaining inorganic filler component was measured using a Beckman Coulter Inc. laser diffraction scattering particle size distribution measuring apparatus (LS-13 320). Next, the inorganic filler was dispersed on the sample stage of a micro-compression tester ("MCT-W500", manufactured by Shimadzu Corporation), and the diameters of the inorganic filler component in the X and Y directions were measured. The average value was taken as the particle size of the inorganic filler component. Five inorganic filler components with particle sizes within ±5 μm of the first maximum point were selected, and compression tests were performed on each particle. Furthermore, the crushing strength (σ: MPa) is determined by a dimensionless number (α = 2.48) varying according to the position within the particle, the crushing test force (P: N), and the particle size (d: μm), using the formula σ = α × P / (π × d). 2 The crushing strength of the five inorganic packing components was calculated using the formula. A Weibull plot was constructed based on JIS R1625:2010 for the crushing strength of the five inorganic packing components. The crushing strength with a cumulative failure rate of 63.2% was taken as the crushing strength of the first inorganic packing. The crushing strength of the second inorganic packing was also determined using the same method.

[0082] (Cumulative frequency of particle sizes from 0 to 15 μm)

[0083] Toluene was used to dissolve all components of the thermally conductive resin composition except for the inorganic filler, removing these components from the heat sink. Then, the cumulative particle size of the remaining inorganic filler was measured using a Beckman Coulter Inc. laser diffraction scattering particle size distribution measuring apparatus (LS-13 320). The cumulative frequency of the particle size range of 0–15 μm was then calculated based on the obtained cumulative particle size.

[0084] The heat sinks of the embodiments and comparative examples are evaluated as follows.

[0085] (Thermal resistance)

[0086] The thermal resistance of the heat sink was measured by applying a load of 1 MPa according to ASTM D5470.

[0087] (Relative density)

[0088] The relative density is calculated by dividing the density of the heat sink by the theoretical density using Archimedes' method.

[0089] (Surface roughness Ra)

[0090] The surface roughness of the heat sink is the arithmetic mean roughness Ra, which is measured according to JIS B 0601:2013.

[0091] [Example 1]

[0092] Example 1 is described below, in which bulk boron nitride particles are produced through boron carbide synthesis, pressure nitriding, and decarburization crystallization.

[0093] (Borne carbide synthesis)

[0094] Boron carbide (B4C) was synthesized by mixing 100 parts by mass of boric acid (hereinafter referred to as boric acid) manufactured by Nippon Denko Corporation and 35 parts by mass of acetylene black (HS100) manufactured by Denka Corporation using a Henschel mixer. The mixture was then filled into a graphite crucible and heated at 2200°C for 5 hours under an argon atmosphere in an electric arc furnace. The synthesized boron carbide blocks were pulverized by ball milling for 1 hour and sieved to a particle size of less than 75 μm. The mixture was further washed with nitric acid aqueous solution to remove impurities such as iron, filtered, and dried to produce boron carbide powder with an average particle size of 20 μm. The carbon content of the obtained boron carbide powder was 20.0%.

[0095] (Pressure nitriding process)

[0096] After the synthesized boron carbide was filled into a boron nitride crucible, it was heated in a resistance furnace at 2000°C and 9 atmospheres (0.8 MPa) for 10 hours to obtain boron carbonitride (B4CN4).

[0097] (Decarburization crystallization process)

[0098] 100 parts by mass of synthesized boron carbonitride and 90 parts by mass of boric acid were mixed using a Henschel mixer and then filled into a boron nitride crucible. The mixture was then heated in a resistance furnace under a nitrogen atmosphere at a pressure of 0.2 MPa, with a heating rate of 10 °C / min from room temperature to 1000 °C and a heating rate of 2 °C / min from 1000 °C onwards. The mixture was then calcined at 2020 °C for 10 hours, thereby synthesizing primary particle agglomeration into blocky boron nitride particles. The synthesized blocky boron nitride particles were then crushed using a Henschel mixer for 15 minutes and classified using a sieve, specifically a nylon sieve with a 150 μm aperture. Through crushing and grading of the calcined material, primary particle agglomeration into blocky boron nitride particles 1 was obtained.

[0099] The average particle size (D50) of the obtained bulk boron nitride particles 1, determined by laser scattering, was 40 μm. Furthermore, the crushing strength of the bulk boron nitride particles 1 was 12 MPa.

[0100] (Making a heatsink)

[0101] The following were added to a mixer (manufactured by HEIDON, trade name "Three-One Motor"): relative to the obtained bulk boron nitride particles 1, agglomerated boron nitride particles (manufactured by Denka Corporation, trade name "SGPS", average particle size: 20 μm, crushing strength: 1.5 MPa), flake-like boron nitride particles (manufactured by Denka Corporation, trade name "SP-3-7", average particle size: 3 μm) and liquid silicone resin 1 (methyl vinyl polysiloxane, Dow The total composition of Boron Nitride (manufactured by Toray Corporation, trade name "CF-3110") is as follows: 45% by volume of bulk boron nitride particles, 12% by volume of aggregated boron nitride particles, 3% by volume of flake boron nitride particles, and 40% by volume of silicone resin; 1 part by mass of curing agent (2,5-dimethyl-2,5-bis(tert-butylperoxide)hexane, manufactured by Nouryon Corporation, trade name "Trigonox 101") relative to 100 parts by mass of silicone resin; and 0.5% by mass of silane coupling agent (dimethyldimethoxysilane, manufactured by Dow Toray Corporation, trade name "DOWSIL") relative to 100 parts by mass of the bulk boron nitride particles, aggregated boron nitride particles, and flake boron nitride particles. Z-6329Silane”, viscosity at 25°C: 1 cp); 15 parts by mass of water relative to 100 parts by mass of the silane coupling agent; and 110 parts by mass of toluene relative to 100 parts by mass of the above raw materials, were mixed using a turbine-type stirring blade for 15 hours to prepare a slurry of a thermally conductive resin composition. The viscosity of the slurry was 10000 cp.

[0102] Then, using a doctor blade method, the above slurry is coated onto a 0.05mm thick PET film (carrier film) with a thickness of 0.2mm, and dried at 75°C for 5 minutes to produce a sheet-like molded body with the PET film. The glass cloth (thickness: 0.025mm) is sandwiched between the sheet-like molded body with the PET film, with the coated surface of the thermally conductive resin composition in contact with both sides, to produce a laminate. It should be noted that the layer structure of the laminate is PET film / thermally conductive resin composition / glass cloth / thermally conductive resin composition / PET film. Next, relative to the obtained laminate, it is subjected to a temperature of 150°C and a pressure of 160 kg / cm². 2 Under these conditions, the PET film on both sides is peeled off after 25 minutes of heating and pressing to form a sheet with a thickness of 0.09 mm. Next, it is heated twice for 4 hours under normal pressure and 150°C to produce the heat sink of Example 1.

[0103] [Example 2]

[0104] The amount of toluene in the mixture was changed from 110 parts by mass to 60 parts by mass, and the coating conditions of the doctor blade method were changed to produce a heat sink with a thickness of 0.20 mm. Otherwise, the heat sink of Example 2 was produced in the same manner as in Example 1. It should be noted that the viscosity of the slurry was 7000 cp.

[0105] [Example 3]

[0106] Instead of mixing 45% by volume of blocky boron nitride particles 1 with an average particle size of 40 μm and a crushing strength of 12 MPa, 42% by volume of blocky boron nitride particles 2 with an average particle size of 75 μm and a crushing strength of 12 MPa were mixed; instead of mixing 12% by volume of agglomerated boron nitride particles, 11% by volume of blocky boron nitride particles 3 with an average particle size of 38 μm and a crushing strength of 12 MPa were mixed; and flaky boron nitride particles were not mixed. The amount of silicone resin 1 was changed from 40% by volume to 47% by volume, the amount of toluene was changed from 110 parts by mass to 100 parts by mass, and the coating conditions of the doctor blade method were changed to produce a heat sink with a thickness of 0.10 mm. Except for the above aspects, the heat sink of Example 3 was produced in the same manner as in Example 1. It should be noted that, regarding the blocky boron nitride particles 2 and 3 used in the heat sink of Example 3, the grinding time of the ball mill used to synthesize the boron carbide blocks and the average particle size of the boron carbide powder were changed. Otherwise, they were prepared using the same method as the blocky boron nitride particles 1 used in the heat sink of Example 1. In addition, the viscosity of the slurry was 10000 cp.

[0107] [Example 4]

[0108] By changing the coating conditions of the scraper method, a heat sink with a thickness of 0.20 mm was produced. Otherwise, the heat sink of Example 4 was produced in the same manner as in Example 3.

[0109] [Example 5]

[0110] Instead of bulk boron nitride particles 2, bulk boron nitride particles 4 with an average particle size of 55 μm and a crushing strength of 10 MPa were mixed in, and a heat sink with a thickness of 0.10 mm was prepared by changing the coating conditions of the doctor blade method. Except for the above aspects, the heat sink of Example 5 was prepared in the same manner as in Example 1. It should be noted that, regarding the bulk boron nitride particles 4 used in the heat sink of Example 5, the average particle size of the boron carbide powder was changed based on the grinding time of the ball mill, but otherwise, it was prepared using the same method as the bulk boron nitride particles 1 used in the heat sink of Example 1. Furthermore, the viscosity of the slurry was 9500 cp.

[0111] [Example 6]

[0112] By changing the coating conditions of the scraper method, a heat sink with a thickness of 0.20 mm was produced. Otherwise, the heat sink of Example 6 was produced in the same manner as in Example 5.

[0113] [Comparative Example 1]

[0114] Without mixing blocky boron nitride particles 1 and flake boron nitride particles, the mixing amount of agglomerated boron nitride particles was changed from 12% by volume to 60% by volume, the mixing amount of silane coupling agent was changed from 0.5 parts by mass to 0.2 parts by mass, and the coating conditions of the doctor blade method were changed to produce a heat sink with a thickness of 0.20 mm. Except for the above aspects, the heat sink of Comparative Example 1 was produced in the same manner as in Example 1. It should be noted that the viscosity of the slurry was 12000 cp. Furthermore, due to the high viscosity of the slurry, it was impossible to produce a heat sink with a thickness of less than 0.15 mm.

[0115] [Comparative Example 2]

[0116] A heat sink with a thickness of 0.30 mm was produced by changing the coating conditions of the scraper method. Otherwise, the heat sink of Comparative Example 2 was produced by operating in the same manner as Comparative Example 1.

[0117] [Comparative Example 3]

[0118] The bulk boron nitride particles 3 were replaced with bulk boron nitride particles 1, and the slurry was prepared in the same manner as in Example 5. However, due to the high viscosity of the slurry (16000 cp), it was impossible to produce a heat sink with a thickness of 0.20 mm.

[0119] [Comparative Example 4]

[0120] The amount of bulk boron nitride particles 1 was changed from 45% by volume to 12% by volume, and the amount of agglomerated boron nitride particles was changed from 12% by volume to 45% by volume. Except for the above aspects, the slurry was prepared in the same manner as in Example 1. However, due to the high viscosity of the slurry (18000 cp), it was impossible to produce a heat sink with a thickness of 0.20 mm.

[0121] The evaluation results of the heat sinks of Examples 1-6 and Comparative Examples 1-4 are shown in Table 1.

[0122] [Table 1]

[0123]

[0124] According to the evaluation results of the heat sinks in Examples 1 to 6, if the particle size distribution of the inorganic filler component in the heat sink has a first maximum point attributable to the first inorganic filler and a second maximum point attributable to the second inorganic filler, the particle size of the first maximum point is 15 μm or more, the particle size of the second maximum point is less than two-thirds of the particle size of the first maximum point, the cumulative amount of frequency between the peak start point and the peak end point of the peak with the first maximum point is 50% or more, the surface roughness of the heat sink is 1.5 to 3.0 μm, and the thickness of the heat sink is 0.2 mm or less, then a thin heat sink with excellent thermal conductivity can be obtained.

[0125] The evaluation results of the heat sinks in Comparative Examples 1 and 2 show that the thermal conductivity deteriorates without the second inorganic filler. Furthermore, it is known that without the second inorganic filler, it is impossible to manufacture heat sinks thinner than 0.15 mm.

[0126] Regarding Comparative Example 3, although it was impossible to manufacture a heat sink, based on the formulation of the thermally conductive resin composition, it was considered that the particle size of the second maximum point was greater than two-thirds of the particle size of the first maximum point.

[0127] Regarding Comparative Example 4, although a heat sink could not be made, based on the formulation of the thermally conductive resin composition, it was considered that the cumulative amount of frequency between the peak start point and the peak end point of the peak with the first maximum point was less than 50%.

[0128] [Example 7]

[0129] The silicone resin CF3110 was replaced with an epoxy resin (bisphenol-type epoxy resin manufactured by Mitsubishi Chemical Corporation, model: JER-807), and the curing agent Trigonox 101 (1 part by weight) was replaced with the curing agent MEH-8005 (manufactured by Meiwa Chemical Co., Ltd., 10 parts by weight). 2PHZ-PW (manufactured by Shikoku Chemical Industry Co., Ltd., 1 part by weight) was added as a curing accelerator. Otherwise, the process was the same as in Example 4, and a 0.2 mm heat sink was fabricated. The thermal resistance was measured using the method described above. It should be noted that the surface roughness was 2.6 μm.

[0130] [Comparative Example 5]

[0131] The silicone resin CF3110 was replaced with an epoxy resin (bisphenol-type epoxy resin manufactured by Mitsubishi Chemical Corporation, model: JER-807), and the curing agent Trigonox 101 (1 part by weight) was replaced with the curing agent MEH-8005 (manufactured by Meiwa Chemical Co., Ltd., 10 parts by weight). 2PHZ-PW (manufactured by Shikoku Chemical Industry Co., Ltd., 1 part by weight) was added as a curing accelerator. Otherwise, the procedure was the same as in Comparative Example 1, and a 0.2 mm heat sink was fabricated. The thermal resistance was measured using the method described above. It should be noted that the surface roughness was 3.2 μm.

[0132] When the thermal resistance of Example 7 was compared with that of Comparative Example 5, the thermal resistance of Example 7 was lower, which is a good result. Therefore, the effect obtained by combining specific inorganic fillers can be achieved regardless of the type of resin.

Claims

1. A heat sink, which is a heat sink molded from a thermally conductive resin composition, wherein, The thermally conductive resin composition is prepared by mixing inorganic filler components and resin components. The inorganic packing material consists of a first inorganic packing material and a second inorganic packing material. The first inorganic filler is blocky boron nitride particles formed by the aggregation of hexagonal boron nitride primary particles. The second inorganic filler is blocky boron nitride particles formed by the aggregation of hexagonal boron nitride primary particles. The particle size distribution of the inorganic filler component has a first maximum point attributable to the first inorganic filler and a second maximum point attributable to the second inorganic filler. The particle size at the first maximum point is between 15 μm and 90 μm, and the particle size at the second maximum point is between 20% and two-thirds of the particle size at the first maximum point. The cumulative frequency between the peak initiation point and the peak termination point of the peak with the first maximum point is more than 70%. The surface roughness of the heat sink is 1.5–3.0 μm. The thickness of the heat sink is less than 0.2 mm.

2. The heat sink according to claim 1, wherein, In the particle size accumulation of the inorganic filler component, the cumulative frequency of particle size of 0-15 μm is less than 60%.

3. The heat sink according to claim 1 or 2, further comprising a substrate with a thickness of 0.05 mm or less.

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