thermal grease

Abstract

To provide an inexpensive heat radiation grease having excellent thermal-conductivity and reliability.SOLUTION: A heat radiation grease 2 contains a dispersant and a thermal-conductive filler, the dispersant contains non-silicone-based oil, the thermal-conductive filler contains aspherical aluminum oxide powder, the aluminum oxide powder has a tap density of 0.95 to 1.30 g / cm2, and satisfies D / d=10 to 100 when the average particle diameter is D and the α crystal particle diameter is d, the heat radiation grease further contains a dispersing agent, and the dispersant contains a polar medium.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to thermal grease that is applied between a heat-generating body (such as a semiconductor element) and a heat-dissipating body (such as a heat sink or housing) as a thermally conductive material (TIM: Thermal Interface Material) to transfer heat. In particular, the present invention relates to thermal grease that is used to improve heat dissipation in semiconductor devices such as CPUs and LSIs, power transistors, power modules, batteries, etc., and to improve adhesion with measurement points such as thermistors and thermocouples. [Background technology]

[0002] In semiconductor devices, power supplies, and other devices, the increase in heat generation during use is becoming a problem. To protect integrated circuits and other devices from the heat generated, it is common practice to conduct the heat generated from heat-generating bodies such as semiconductor elements to heat dissipation bodies such as heat sinks and fins, and then release it outside the system. To cope with the increasing amount of heat generated, there is a need to improve the thermal conductivity within the system and further increase the heat dissipation efficiency.

[0003] To improve thermal conductivity within a system, thermal grease with excellent thermal conductivity is placed between the heat generating element and the heat sink. Thermal grease is a liquid (paste-like) heat dissipation material made by highly filling a chemically synthesized oil with a thermally conductive filler (e.g., inorganic powder). Thermal grease is a material made by filling a base oil (e.g., low molecular weight oil) that acts as a binder with a filler, and is also known as an "oil compound." By adjusting the base oil, the type of filler, and the compounding ratio, the thermal conductivity and fluidity of thermal grease can be changed to suit the application.

[0004] For example, Patent Document 1 describes a thermally conductive composition that mainly uses a silicone-based oil as the base oil, which has excellent chemical stability and thermal properties, exhibits little viscosity change due to temperature, and is resistant to deterioration.

[0005] As an example of thermal grease using a non-silicone oil as the base oil, Patent Document 2 describes a highly thermally conductive grease using a synthetic hydrocarbon oil such as an ester oil as the base oil.

[0006] Patent Document 3 describes a thermally conductive grease that uses mineral oil, synthetic hydrocarbon oil, diester, or the like as a base oil and contains, as a filler, metal oxides such as alumina (aluminum oxide) and zinc oxide, and nitrides with higher thermal conductivity such as boron nitride and aluminum nitride. Metal oxides and metal nitrides are commonly used as thermally conductive fillers for thermal grease because of their excellent thermal conductivity and insulating properties.

[0007] Among metal oxides, alumina is widely used as a thermally conductive filler due to its excellent chemical stability, mechanical strength, hardness, etc. For example, Patent Document 4 describes the use of α-alumina as a heat dissipation filler, and Patent Document 5 describes a grease obtained by incorporating aluminum powder and alumina powder of a predetermined particle size into silicone oil. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 5843364 [Patent Document 2] Patent Publication No. 2021-84921 [Patent Document 3] Patent No. 5944306 [Patent Document 4] Japanese Patent Application Laid-Open No. 2008-127257 [Patent Document 5] Japanese Patent Application Laid-Open No. 2005-170971 Summary of the Invention [Problem to be solved by the invention]

[0009] Thermal grease requires a high level of thermally conductive filler to achieve high thermal conductivity. Furthermore, when the thermal grease is sandwiched between a heat generating element and a heat sink, it may be required to be easily thinned to facilitate heat conduction. To achieve this, the thermal grease must be reasonably easy to flow (fluidity).

[0010] Here, Patent Document 4 describes that when α-alumina is used as a heat dissipating filler, the particle shape must be as uniform and as close to spherical as possible, and the particle size distribution must be as narrow as possible (uniform particle size), in terms of fillability into resin. Furthermore, Patent Document 5 describes that the higher the sphericity of the shape of the thermally conductive inorganic powder, the higher the fluidity of the grease.

[0011] Alumina with uniform particle size and spherical alumina are produced by melting high-purity aluminum, then feeding it into an oxygen-containing air stream and burning it at high temperatures. Therefore, it is extremely expensive (several dozen times more expensive) than inexpensive, common alumina used for ceramics, refractories, polishing, etc. Furthermore, when silicone-based oil is used as the base oil, low-molecular-weight siloxanes are generated due to the effects of heat and moisture, and the evaporated low-molecular-weight siloxanes can reattach to surrounding components, causing problems such as poor electrical circuit contacts and clouding of optical components.

[0012] The present invention has been made in view of the above circumstances, and aims to provide a thermal grease that is inexpensive and has excellent thermal conductivity and reliability. [Means for solving the problem]

[0013] The thermally conductive grease of the present invention is a thermally conductive grease containing a dispersion medium and a thermally conductive filler, wherein the dispersion medium contains a non-silicone oil, and the thermally conductive filler contains non-spherical aluminum oxide powder, and the aluminum oxide powder has a tap density of 0.95 to 1.30 g / cm. 2 The powder is characterized by satisfying D / d=10 to 100, where D is the average particle size and d is the α-crystal particle size.

[0014] The thermal grease contains a dispersant, and the dispersion medium contains a polar medium. The aluminum oxide powder has a BET specific surface area of ​​1.1 to 3.5 m 2 / g, the non-silicone oil is a poly-α-olefin oil, and the dispersant is a non-ionic surfactant.

[0015] The thermal grease is characterized in that it contains a polyoxyethylene sorbitan fatty acid ester as a dispersant, and the dispersion medium contains a poly-alpha olefin oil as the non-silicone oil and water as a polar medium.

[0016] The thermal grease is characterized by a thermal conductivity of 1.2 W / m·K or more as measured by the hot disk method in accordance with ISO 22007-2. [Effects of the Invention]

[0017] The thermally conductive grease of the present invention is highly reliable and inexpensive because the dispersion medium contains a non-silicone oil and the thermally conductive filler contains non-spherical aluminum oxide powder. The aluminum oxide powder has a tap density of 0.95 to 1.30 g / cm. 2 When the average particle size is D and the α-crystal particle size is d, the powder satisfies D / d=10 to 100, so the fillers easily come into contact with each other and have excellent thermal conductivity.

[0018] The thermal grease contains a dispersant and a polar medium, allowing for high loading of thermally conductive fillers including non-spherical aluminum oxide powder. The non-silicone oil is a polyalphaolefin oil, making it less expensive. The dispersant is a nonionic surfactant, allowing for higher loading of thermally conductive fillers.

[0019] The thermal grease contains polyoxyethylene sorbitan fatty acid ester as a dispersant, and the dispersion medium contains poly-alpha olefin oil as a non-silicone oil and water as a polar medium, so it has excellent dispersibility for the thermally conductive filler and miscibility with dispersion media of different polarities, allowing for even higher loading of the thermally conductive filler.

[0020] The thermal grease has a thermal conductivity of 1.2 W / m·K or higher when measured using the hot disk method in accordance with ISO 22007-2, making it suitable for a variety of heat dissipation applications. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a schematic cross-sectional view showing an example of use of the thermal grease of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] The thermally conductive grease of the present invention includes a dispersion medium, a thermally conductive filler, and a dispersant. In this specification, "thermal grease" refers to a paste-like composition used to efficiently conduct and release heat generated by a heat-generating element outside the system. In the present invention, a dispersion medium that imparts fluidity to the composition is used as the base of the thermally conductive grease. A thermally conductive filler can be uniformly dispersed in the base to form a paste. If necessary, a dispersant can be used to disperse the thermally conductive filler in the dispersion medium. The thermally conductive filler can act as a thickener. Each component is described below.

[0023] (thermal conductive filler) The thermally conductive filler includes non-spherical aluminum oxide (Al2O3) powder that has not been subjected to a micronization treatment. The shape of the thermally conductive filler is not particularly limited as long as it is non-spherical and can be appropriately selected depending on the purpose. Examples include irregular shapes, flat shapes, fibrous shapes, and confetti shapes. Here, the non-spherical aluminum oxide powder is specifically an aggregate of aluminum oxide particles having α-crystal particles (α-alumina), which are hexagonal plate-shaped aluminum oxide crystal particles, on the surface. The interior of the aluminum oxide particles may be α-alumina, or alumina of a crystal system other than the α-crystal system, or amorphous alumina.

[0024] The thermally conductive filler preferably contains non-spherical aluminum oxide powder as a main component. The thermally conductive filler containing aluminum oxide as a main component means that the thermally conductive filler contains aluminum oxide powder in the largest amount by mass. The content of aluminum oxide powder in the thermally conductive filler is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass.

[0025] The aluminum oxide powder satisfies D / d = 10 to 100, where D is the average particle diameter and d is the α-crystal particle diameter. D / d is, for example, preferably 10 to 95, more preferably 10 to 50, and even more preferably 10 to 20. Furthermore, D / d is, for example, preferably 30 to 100, more preferably 50 to 100, and even more preferably 90 to 100. When D / d is 10 to 100, the surface of the aluminum oxide powder is uneven, allowing adjacent aluminum oxide powder particles to easily come into contact with each other in the thermal grease. This facilitates the formation of numerous contact points between the aluminum oxide powder particles, resulting in excellent thermal conductivity. The average particle diameter D refers to the 50% particle diameter on a volume basis and can be measured using a laser scattering particle size analyzer. The α-crystal particle diameter d can be calculated by image analysis of 20 α-crystal particles selected from SEM photographs of the surface of non-spherical aluminum oxide powder taken with a scanning electron microscope. The α-crystal particles can be identified by their hexagonal plate-like shape.

[0026] The aluminum oxide powder may be entirely α-crystallized, or may be partially α-crystallized. The α-crystallization rate varies depending on the firing conditions and the raw materials used, and from the viewpoint of improving the thermal conductivity of the aluminum oxide particles, the α-crystallization rate is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more. The α-crystallization rate of the aluminum oxide powder can be determined by XRD analysis.

[0027] The average particle diameter D of the aluminum oxide powder is, for example, preferably 10 to 200 μm, more preferably 30 to 150 μm, and even more preferably 30 to 110 μm. From the viewpoints of dispersibility and thin layer formation, the average particle diameter D is preferably 10 to 100 μm, more preferably 20 to 70 μm, even more preferably 30 to 60 μm, and even more preferably 30 to 50 μm. When the average particle diameter D is 10 μm or more, the production cost can be reduced. Furthermore, when the average particle diameter D is 200 μm or less, uniform dispersion is facilitated.

[0028] The α-crystal particle diameter d of the aluminum oxide powder is, for example, preferably 0.1 to 20 μm, more preferably 0.5 to 10 μm, even more preferably 1 to 7 μm, and even more preferably 2 to 6 μm. From the viewpoint of increasing contact between the aluminum oxide powder particles, the aluminum oxide powder preferably has a confetti-like shape, and it is particularly preferable that the α-crystal particles cover the entire particle surface so as to form the protrusions of the confetti-like shape.

[0029] Aluminum oxide powder has a tap density of 0.95 to 1.30 g / cm 2 The tap density is, for example, 0.95 to 1.25 g / cm 2 is preferred, and 0.95 to 1.20 g / cm 2 More preferably, 0.95 to 1.15 g / cm 2 More preferably, the tap density is 0.95 to 1.30 g / cm 2In this case, it is considered that the surface irregularities of adjacent aluminum oxide powder particles are likely to come into contact with each other, resulting in excellent thermal conductivity. The tap density can be measured in accordance with JIS R9301-2-3:1999.

[0030] The BET specific surface area is, for example, 0.5 to 20.0 m 2 The BET specific surface area can be, for example, 0.8 to 4.0 m 2 / g is preferred, and 1.1 to 3.5m 2 / g is more preferable, and 1.1 to 2.0m 2 The BET specific surface area is a value measured by nitrogen gas adsorption method.

[0031] Examples of aluminum oxide powders include standard alumina A-11 (manufactured by Nippon Light Metal Co., Ltd., the same applies hereinafter), standard alumina A-12, standard alumina A-13, standard alumina A-14, standard alumina SA-11, standard alumina SA-12, standard alumina SA-13, and standard alumina SA-14. Examples of aluminum oxide powders include alumina A-21 (manufactured by Sumitomo Chemical Co., Ltd., the same applies hereinafter), alumina A-25, alumina A-26, and alumina A-210. These aluminum oxide powders may be used alone or in combination of two or more.

[0032] The content of the thermally conductive filler in the thermal grease can be, for example, 20 to 80% by mass. The content of the thermally conductive filler is preferably 25 to 70% by mass, and more preferably 35 to 60% by mass. When the content of the thermally conductive filler is 25% by mass or more, thermal conductivity can be effectively improved. Furthermore, when the content of the thermally conductive filler is 70% by mass or less, the dispersibility of the thermally conductive filler can be sufficiently ensured, making it easier to ensure the fluidity of the thermal grease.

[0033] The thermally conductive filler may be a single type of non-spherical aluminum oxide powder, or a combination of two or more types. The thermally conductive filler is not particularly limited as long as it contains the non-spherical aluminum oxide powder, and may further contain other fillers, such as metals, metal oxides, metal nitrides, metal carbides, metal oxynitrides, metal carbonitrides, metal hydroxides, nitrogen compounds, graphite, etc.

[0034] The average particle size of the thermally conductive filler other than aluminum oxide powder is, for example, preferably 10 to 200 μm, more preferably 30 to 150 μm, and even more preferably 50 to 110 μm. When the average particle size is 10 μm or more, production costs can be reduced. When the average particle size is 200 μm or less, uniform dispersion is facilitated. The average particle size here means the 50% particle size on a volume basis, and can be measured using a laser scattering particle size analyzer.

[0035] (dispersion medium) The dispersion medium includes a non-silicone oil. Examples of non-silicone oils include mineral oils such as paraffinic mineral oil and naphthenic mineral oil, synthetic hydrocarbon oils such as poly-α-olefin oil (PAO oil) and alkylbenzene oil, ester oil, ether oil, and fluorine oil. These non-silicone oils may be used alone or in combination of two or more. Among these, synthetic oils are preferred, and at least one oil selected from synthetic hydrocarbon oils, ether oils, and ester oils is particularly preferred.

[0036] The synthetic hydrocarbon oil is preferably PAO oil. PAO oil is a mixture of α-olefins or isomerized α-olefin oligomers or polymers. Specific examples of α-olefins include 1-octene, 1-nonene, 1-decene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, and 1-octadecene.

[0037] Examples of ester oils include aromatic ester oils such as trioctyl trimellitate, tridecyl trimellitate, and tetraoctyl pyromellitate, and diester oils such as butyl sebacate, di-2-ethylhexyl sebacate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate, ditridecyl glutarate, and methyl acetylsinolate.

[0038] Examples of the ether oil include alkyl diphenyl ether oil, alkyl triphenyl ether oil, alkyl tetraphenyl ether oil, and polyphenyl ether oil.

[0039] The content of the dispersion medium in the thermal grease is preferably 10 to 70% by mass, more preferably 15 to 60% by mass, even more preferably 20 to 50% by mass, and even more preferably 20 to 40% by mass. When the content of the dispersion medium is 10% by mass or more, the thermal grease has appropriate fluidity and can be endowed with excellent applicability and adhesion. This makes it easier to apply the thermal grease to the gap between the heat generating element and the heat dissipating element. When the content of the dispersion medium is 70% by mass or less, separation of the dispersion medium and the thermally conductive filler is easily suppressed.

[0040] The kinematic viscosity (40°C) of the non-silicone oil is not particularly limited, but is preferably 50 to 2000 mm 2 / s is preferably 50 to 1000 mm 2 / s is more preferable, and 100 to 600 mm 2 / s is more preferable, and 200 to 600 mm 2 / s is more preferable, and 300 to 500 mm 2 It is particularly preferred that the ratio is / s.

[0041] It is preferable that the thermal grease be substantially free of silicone-based oil. If silicone-based oil is included, low-molecular-weight siloxanes may be generated. If the volatilized low-molecular-weight siloxanes adhere to surrounding components, they may turn into silicon dioxide, which may cause poor contact in electrical circuits. The content of silicone-based oil in the thermal grease is preferably 1% by mass or less, more preferably 0.1% by mass or less, and most preferably 0% by mass.

[0042] It is preferable that the dispersion medium further contains a polar medium. Examples of polar media include protic polar media having a hydroxyl group such as water and alcohols, and aprotic polar media such as ethers, carbonates, acetone, and acetonitrile. Examples of water that can be used include pure water, distilled water, and tap water, and it is preferable to use pure water or distilled water. Examples of alcohols include monohydric alcohols, dihydric alcohols, and trihydric alcohols. Examples of monohydric alcohols include alcohols having 1 to 12 carbon atoms (e.g., propanol, butanol, and hexanol). Examples of dihydric alcohols include ethylene glycol, polyethylene glycol, propylene glycol, and polypropylene glycol. Examples of trihydric alcohols include glycerin. Examples of ethers include tetrahydrofuran. Examples of carbonates include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, and butylene carbonate.

[0043] These polar media may be used alone or in combination of two or more. Water is particularly preferred as the polar medium because it is low cost and is less likely to cause the above-mentioned problems due to re-adhesion after evaporation. The content of water in the polar medium is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and most preferably 100% by mass.

[0044] Furthermore, ethylene glycol can be preferably used as the polar medium. The content of ethylene glycol in the polar medium is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably 100% by mass. When the polar medium contains ethylene glycol, the kinematic viscosity of the thermal grease can be relatively high, and since the boiling point is relatively high and the grease is less likely to volatilize, the problem of redeposition is less likely to occur.

[0045] The content of the polar medium in the dispersion medium is preferably 20 to 90% by mass, more preferably 40 to 80% by mass, and even more preferably 60 to 80% by mass. When the content of the polar medium is 20 to 90% by mass, emulsification with the non-silicone oil is facilitated, and the thermally conductive filler is likely to be well dispersed. As a result, the thermal conductivity effect can be efficiently obtained. In particular, when the dispersion medium consists only of a non-silicone oil and a polar medium and the content of the polar medium is 60 to 80% by mass, the non-silicone oil is easily dispersed as oil droplets in the polar medium as a continuous phase (oil-in-water type), and the dispersibility of the thermally conductive filler is particularly excellent.

[0046] (dispersant) The thermal grease preferably contains a dispersant, which allows the non-polar medium, such as non-silicone oil, to be mixed uniformly with the polar medium, and also allows the thermally conductive filler to be uniformly dispersed in the dispersant.

[0047] Examples of dispersants include soaps, anionic surfactants, cationic surfactants, nonionic surfactants, and polymeric surfactants, and preferably nonionic surfactants. These dispersants may be used alone or in combination of two or more.

[0048] Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylaryl ethers, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene hydrogenated castor oil, etc. In particular, polyoxyethylene sorbitan fatty acid esters are preferred as nonionic surfactants from the viewpoints of the dispersibility of thermally conductive fillers containing non-spherical aluminum oxide powder and the miscibility of dispersion media with significantly different polarities when the dispersion media contain dispersion media with significantly different polarities.

[0049] The number of carbon atoms in the fatty acid of the polyoxyethylene sorbitan fatty acid ester is preferably 10 to 24, and more preferably 12 to 18. Examples of polyoxyethylene sorbitan fatty acid esters include polyoxyethylene sorbitan trioleate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan distearate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan triisostearate, polyoxyethylene sorbitan diisostearate, polyoxyethylene sorbitan monoisostearate, polyoxyethylene sorbitan trilaurate, polyoxyethylene sorbitan dilaurate, and polyoxyethylene sorbitan monolaurate. Preferred polyoxyethylene sorbitan fatty acid esters are polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan distearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan triisostearate, and polyoxyethylene sorbitan diisostearate. Furthermore, the polyoxyethylene sorbitan fatty acid ester is more preferably polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan distearate, or polyoxyethylene sorbitan tristearate. The polyoxyethylene sorbitan fatty acid ester may be used alone or in combination of two or more kinds.

[0050] These nonionic surfactants are commercially available. More specifically, examples of polyoxyethylene sorbitan monolaurate include Rheodol (manufactured by Kao Corporation; the same applies hereinafter) TW-L120, Rheodol TW-L106, and Rheodol Super TW-L120. Examples of polyoxyethylene sorbitan monopalmitate include Rheodol TW-P120. Examples of polyoxyethylene sorbitan monostearate include Rheodol TW-S120, Rheodol TW-S106, and Rheodol Super TW-S120. Examples of polyoxyethylene sorbitan tristearate include Rheodol TW-S320V. Examples of polyoxyethylene sorbitan monooleate include Rheodol TW-O120, Rheodol TW-O106, Rheodol Super TW-O120, and Emazol (manufactured by Kao Corporation; the same applies hereinafter) O-105R. Examples of polyoxyethylene sorbitan trioleates include Rheodol TW-0320, etc. Examples of polyoxyethylene sorbitan tetraoleate include Rheodol 430, Rheodol 440, Rheodol 460, etc.

[0051] The HLB of the nonionic surfactant is preferably 3.0 to 16.0, preferably 5.0 to 15.0, and preferably 8.0 to 13.0.

[0052] The content of the dispersant in the thermal grease is preferably 1 to 20% by mass, and more preferably 3 to 12% by mass. When the content of the dispersant is 1% by mass or more, sufficient dispersibility can be obtained. Furthermore, when the content of the dispersant is 20% by mass or less, it becomes easier to blend a sufficient amount of thermally conductive filler.

[0053] In addition to the above-mentioned components, the thermal grease may contain optional components. Examples of optional components include thickeners such as metal soaps, extreme pressure additives, antioxidants, rust inhibitors, friction modifiers, anticorrosion agents, and solid lubricants. When the thermal grease contains a polar medium such as water in its composition, it preferably contains a rust inhibitor. The content of the optional components in the thermal grease is, for example, 0.1 to 15 mass %, and preferably 0.5 to 5 mass %.

[0054] The thermal conductivity of the thermal grease of the present invention, as measured by the hot disk method in accordance with ISO 22007-2, is preferably 1.2 W / m·K or higher, and more preferably 1.4 W / m·K or higher. The thermal conductivity can be adjusted by the content of the thermally conductive filler. The viscosity of the grease can be, for example, 10 to 1,000 Pa·s. The viscosity is preferably 20 to 500 Pa·s, and particularly preferably 100 to 300 Pa·s. A viscosity of 20 to 500 Pa·s allows for thin layers to be formed, and the grease is less likely to flow out from between the heat generating element and the heat sink. Grease with a viscosity of 20 to 500 Pa·s and a thermal conductivity of 1.2 W / m·K or higher can be used in a wide range of applications, such as thin-layer coatings for semiconductor devices and potting for battery packs. The thermal grease of the present invention can be produced inexpensively, making it particularly suitable for battery applications, where large amounts are likely to be used.

[0055] An example of an application of the thermal grease of the present invention will be described with reference to FIG. 1. FIG. 1 is a schematic cross-sectional view showing an example of the use of the thermal grease when it is applied to an electronic device. As shown in FIG. 1, in the electronic device 1, the thermal grease 2 is sandwiched in the gap between a heat-generating electronic component 4, which is a heat generating body, provided on a circuit board 3, and a heat sink 5, which is a heat dissipating body, and is in close contact with both. There are no particular limitations on the method for sandwiching the thermal grease 2 in the gap, and methods such as injection, dispense application, print application, spray application, roller application, and brush application can be used. [Example]

[0056] Examples are described below, but the present invention is not limited to these examples.

[0057] (Examples 1 to 3, Comparative Examples 1 to 3) The thermal conductivity of each sample was evaluated. As Comparative Example 3, a commercially available silicone-based thermal grease, thermal oil compound G777 manufactured by Shin-Etsu Chemical Co., Ltd., was also evaluated.

[0058] The raw materials used to prepare the thermal grease are listed below. These raw materials were thoroughly mixed and homogenized in a jar using a resin spatula to obtain the thermal grease. (A) Thermally conductive filler (A-1) Standard alumina A-14 (Nippon Light Metal Co., Ltd., α-crystal coated type) (A-2) Standard alumina A-12 (Nippon Light Metal Co., Ltd., α-crystal coated type) (A-3) Standard alumina A-11 (Nippon Light Metal Co., Ltd., α-crystal coated type) (A-4) Fine powder alumina SA-32 (Nippon Light Metal Co., Ltd., fine powder type) (A-5) Alumina AA18 (Sumitomo Chemical Co., Ltd., spherical type) (B) Dispersion medium (B-1) SYNTON PAO40 (manufactured by Chemtura Corporation, polyalphaolefin, kinematic viscosity (40°C) 400 mm 2 / s) (B-2) Distilled water (C) Dispersant (C-1) Rheodor TW-S320V (Kao Corporation, non-ionic surfactant)

[0059] <Thermal conductivity> The thermal conductivity was evaluated by measuring the thermal conductivity using a hot disc method thermophysical property measuring device TPS-500S (Kyoto Electronics Manufacturing Co., Ltd.) The measurement was performed by wrapping several grams of each sample in plastic wrap into a flat plate, folding it, and sandwiching the probe between the samples.

[0060] The composition and thermal conductivity measurement results for each sample are shown in Table 1. In the table below, the numerical values ​​for each of the raw materials A to C represent the mass % of the total composition of the thermal grease.

[0061] [Table 1]

[0062] It has α-crystal grains on the surface and a tap density of 0.95 to 1.30 g / cm 2 The samples (Examples 1 to 3) containing non-spherical standard alumina A-14, 12, and 11, with an average particle size D / α crystal particle size d = 10 to 100, exhibited excellent thermal conductivities of 1.2 W / m·K or more, higher than Comparative Example 1 containing fine alumina SA32 and Comparative Example 2 containing spherical alumina AA18. Furthermore, since Examples 1 to 3 do not use silicone oil as a dispersion medium, there is no risk of low-molecular-weight siloxane volatilization, as in Comparative Example 3, which is based on silicone oil, and it is believed that these samples have better reliability.

[0063] As in Examples 1 to 3, by using a filler having a surface roughness due to the presence of numerous α-crystals on the particle surface, the contact points (contact area) between the fillers are increased, which is thought to result in a higher thermal conductivity than the expensive spherical alumina or fine powder alumina that have been used conventionally. The relationship between the surface roughness of alumina particles and tap density is thought to be such that the tap density increases as the surface roughness decreases, and decreases as the surface roughness increases. Furthermore, the relationship between surface roughness and D / d is thought to be such that the finer the surface roughness, the larger D / d, and the coarser the surface roughness, the smaller D / d.

[0064] By using the composition of the above example, it was possible to obtain a thermal grease with superior thermal conductivity compared to when using a relatively expensive filler such as spherical alumina, even when using a relatively inexpensive thermally conductive filler such as standard alumina A-14. [Industrial Applicability]

[0065] The thermal grease of the present invention has excellent thermal conductivity and reliability, and is inexpensive, making it suitable for a variety of applications, particularly in the field of non-silicone thermal grease, where market growth is expected. [Explanation of symbols]

[0066] 1 Electronic equipment 2 thermal paste 3 Circuit Board 4. Heat-generating electronic components 5 Heatsink

Claims

1. A thermal grease containing a dispersion medium and a thermally conductive filler, the dispersion medium includes a non-silicone oil, and the thermally conductive filler includes non-spherical aluminum oxide powder; The aluminum oxide powder has a tap density of 0.95 to 1.30 g / cm 2 The thermal grease is characterized in that it is a powder that satisfies the relationship D / d=10 to 100, where D is the average particle diameter and d is the α crystal particle diameter.

2. The thermal grease includes a dispersant, The thermal grease of claim 1 , wherein the dispersion medium includes a polar medium.

3. The aluminum oxide powder has a BET specific surface area of ​​1.1 to 3.5 m 2 The thermal grease according to claim 1 or 2, characterized in that the thermal grease has a viscosity of 1 / g.

4. 3. The thermal grease according to claim 1, wherein the non-silicone oil is a poly-alpha olefin oil.

5. The thermal grease according to claim 2, wherein the dispersant is a non-ionic surfactant.

6. The thermal grease contains polyoxyethylene sorbitan fatty acid ester as a dispersant, 2. The thermal grease according to claim 1, wherein the dispersion medium contains poly-alpha olefin oil as the non-silicone oil and water as the polar medium.

7. The thermal grease according to claim 1 or 2, characterized in that the thermal conductivity of the thermal grease measured by the hot disk method in accordance with ISO 22007-2 is 1.2 W / m·K or more.

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