JP7541874B2 - Thermally conductive composition and thermally conductive sheet using same - Google Patents

Description

This technology relates to a thermally conductive composition and a thermally conductive sheet using the same.

In recent years, as the power density of semiconductor devices increases, materials used in the devices are required to have more advanced heat dissipation properties. To achieve such heat dissipation properties, materials called thermal interface materials are used in various forms, such as sheets, gels, and greases, to reduce the thermal resistance of the path through which heat generated by semiconductor elements is released to a heat sink or housing.

Typically, thermal interface materials are composite materials (thermally conductive compositions) in which a thermally conductive filler is dispersed in, for example, epoxy resin or silicone resin. Metal oxides and metal nitrides are often used as thermally conductive fillers. Silicone resin, an example of a resin, is widely used from the standpoint of heat resistance and flexibility.

In recent years, high thermal conductivity is required for thermally conductive sheets due to the high density mounting of semiconductor elements and the increase in heat generation. To address this issue, for example, it is possible to increase the amount of thermally conductive filler added to the thermally conductive composition.

However, increasing the amount of thermally conductive filler added to the thermally conductive composition tends to reduce the flexibility of the resulting thermally conductive sheet. If a thermally conductive sheet with reduced flexibility is sandwiched between a semiconductor element and a heat sink, for example, the stress on the semiconductor element, which has relatively weak strength, is large, and excessive force is applied to the semiconductor element. Furthermore, in the case of a semiconductor element mounted on a substrate, the stress on the substrate also increases, and the stress on the substrate increases, which may cause the substrate to bend. There is also a concern that such substrate bending may cause the semiconductor element mounted on the substrate to peel off.

The thermally conductive sheet is usually sandwiched between the heat-generating component and the heat-dissipating component under a load. However, if the heat-generating component or the heat-dissipating component has concave or convex parts, the surface of the thermally conductive sheet may not adequately contact the concave or convex parts of the heat-generating component or the heat-dissipating component. In this way, if a thermally conductive sheet that does not have good conformability (flexibility) to the components it comes into contact with is used, there is a concern that the thermal conductivity of the thermally conductive sheet may decrease.

International Publication No. 2018/131486

This technology was proposed in light of the current situation, and aims to provide a thermally conductive composition that can form a thermally conductive sheet with good thermal conductivity and flexibility, and a thermally conductive sheet using the same.

After extensive research, the inventors of the present invention have found that the above-mentioned problems can be solved by adding a specific acrylic-silicone copolymer to a thermally conductive composition containing an organopolysiloxane, a thermally conductive filler, and an alkoxysilane compound, and by setting the total content of the alkoxysilane compound and the siloxane-modified acrylic resin relative to the organopolysiloxane to a specific value or more.

The thermally conductive composition according to the present technology contains an organopolysiloxane, a thermally conductive filler, an alkoxysilane compound, and a siloxane-modified acrylic resin, and when the content of the organopolysiloxane is taken as 100 parts by mass, the total content of the alkoxysilane compound and the siloxane-modified acrylic resin is 100 parts by mass or more.

The thermally conductive sheet according to this technology is made from the cured product of the thermally conductive composition.

This technology makes it possible to provide a thermally conductive sheet with good thermal conductivity and flexibility.

FIG. 1 is a cross-sectional view showing an example of a thermally conductive sheet. FIG. 2 is a cross-sectional view showing an example of a semiconductor device.

<Thermal Conductive Composition>
The thermally conductive composition according to the present technology contains an organopolysiloxane, a thermally conductive filler, an alkoxysilane compound, and a siloxane-modified acrylic resin. In addition, when the content of the organopolysiloxane in the thermally conductive composition is 100 parts by mass, the total content of the alkoxysilane compound and the siloxane-modified acrylic resin may be 100 parts by mass or more, 200 parts by mass or more, 300 parts by mass or more, 400 parts by mass or more, 500 parts by mass or more, 600 parts by mass or more, 700 parts by mass or more, or 800 parts by mass or more. In addition, when the content of the organopolysiloxane in the thermally conductive composition is 100 parts by mass, the upper limit of the total content of the alkoxysilane compound and the siloxane-modified acrylic resin is not particularly limited, and can be, for example, 1000 parts by mass or less. Each component will be described in detail below.

<Organopolysiloxane>
The thermally conductive composition according to the present technology contains an organopolysiloxane from the viewpoints of moldability, weather resistance, adhesion and conformity to electronic components, etc. An organopolysiloxane is a polymeric compound in which an organic group is added to a structure having a portion in which a silicon atom is bonded to another silicon atom via oxygen. An organopolysiloxane is usually an organic polymer having a siloxane bond as the main chain. An organopolysiloxane can be cured by applying heat energy, light energy, or the like in the presence of a curing catalyst. Organopolysiloxanes can be classified according to the curing mechanism, and include an addition polymerization curing type (addition reaction type), a condensation polymerization curing type (condensation type), an ultraviolet curing type, and a peroxide crosslinking type. An organopolysiloxane may be used alone or in combination of two or more types.

In particular, when the thermally conductive composition is applied to a thermally conductive sheet sandwiched between a heat generating body and a heat dissipating member, it is preferable to use an addition reaction type silicone resin (addition reaction type liquid silicone resin) as the organopolysiloxane in terms of adhesion between the heat generating surface of the electronic component and the heat sink surface. Examples of the addition reaction type silicone resin include a two-liquid addition reaction type silicone resin that is mainly composed of (i) silicone having an alkenyl group, (ii) a base agent containing a curing catalyst, and (iii) a curing agent having a hydrosilyl group (Si-H group). As the silicone having an alkenyl group (i), for example, an organopolysiloxane having a vinyl group can be used. The (ii) curing catalyst is a catalyst for promoting the addition reaction between the alkenyl group in the silicone having an alkenyl group (i) and the hydrosilyl group in the curing agent having a hydrosilyl group (iii). (ii) The curing catalyst may be any of the well-known catalysts used in hydrosilylation reactions, such as platinum group curing catalysts, such as platinum group metals such as platinum, rhodium, and palladium, and platinum chloride. (iii) The curing agent having a hydrosilyl group may be, for example, an organopolysiloxane having a hydrosilyl group.

The organopolysiloxane component may contain a silicone resin containing Si-OH groups. Examples of silicone resins containing Si-OH groups include organopolysiloxanes consisting of a copolymer having M units (R ₃ SiO _1/2 ) and at least one unit selected from the group consisting of Q units (SiO ₂ ), T units (RSiO _3/2 ) and D units (R ₂ SiO), where R represents a monovalent hydrocarbon group or a hydroxyl group. The silicone resin containing Si-OH groups is preferably an organopolysiloxane (MQ resin) consisting of a copolymer having M units and Q units.

As an addition reaction type silicone resin, which is an example of organopolysiloxane, a desired commercially available product can be used, taking into consideration the hardness of the cured product obtained by curing the thermally conductive composition. Examples include CY52-276, CY52-272, EG-3100, EG-4000, EG-4100, 527 (all manufactured by Dow Corning Toray Co., Ltd.), KE-1800T, KE-1031, KE-1051J (all manufactured by Shin-Etsu Chemical Co., Ltd.), etc.

<Thermal conductive filler>
The thermally conductive filler can be selected from known substances in consideration of the desired thermal conductivity and filling property, and examples thereof include metal hydroxides such as aluminum hydroxide and magnesium hydroxide, metals such as aluminum, copper, and silver, metal oxides such as alumina and magnesium oxide, metal nitrides such as aluminum nitride, boron nitride, and silicon nitride, carbon nanotubes, metal silicon, and fiber fillers (glass fibers, carbon fibers).The thermally conductive filler may be used alone or in combination of two or more types.

For example, from the viewpoint of realizing good flame retardancy, the thermally conductive composition according to the present technology preferably contains an inorganic filler as a thermally conductive filler, more preferably contains a nitrogen compound, and even more preferably contains a nitrogen compound having a thermal conductivity of 60 W/m·K or more. As such nitrogen compounds, aluminum nitride and boron nitride are preferable, and aluminum nitride is more preferable. In addition, the thermally conductive composition according to the present technology may contain at least one of aluminum nitride, metal hydroxide, metal oxide, and carbon fiber as a thermally conductive filler. Examples of the metal hydroxide and metal oxide include aluminum hydroxide, alumina, aluminum nitride, and magnesium oxide. For example, only alumina, only aluminum nitride, or only carbon fiber may be used as the thermally conductive filler. In particular, from the viewpoint of flame retardancy and thermal conductivity, the thermally conductive composition according to the present technology preferably contains at least aluminum nitride as a thermally conductive filler, and more preferably uses a mixture of aluminum nitride, alumina, and magnesium oxide, and this mixture may further contain carbon fiber.

The content of the thermally conductive filler in the thermally conductive composition can be appropriately determined according to the desired thermal conductivity, and the volume content in the thermally conductive composition can be, for example, 80 to 90% by volume. If the content of the thermally conductive filler in the thermally conductive composition is less than 80% by volume, it tends to be difficult to obtain sufficient thermal conductivity. Also, if the content of the thermally conductive filler in the thermally conductive composition exceeds 90% by volume, it tends to be difficult to fill the thermally conductive filler. The content of the thermally conductive filler in the thermally conductive composition can be 83% by volume or more, 84% by volume or more, 85% by volume or more, or 83 to 85% by volume. When two or more types of thermally conductive fillers are used in combination, it is preferable that the total amount of the fillers satisfies the above content range.

In addition, when the thermally conductive filler contains aluminum nitride, the content of aluminum nitride in the thermally conductive filler can be 1 to 100 volume percent.

<Alkoxysilane Compound>
The thermally conductive composition contains an alkoxysilane compound. In the thermally conductive composition, the alkoxysilane compound is hydrolyzed with, for example, the moisture contained in the thermally conductive filler, and bonds to the thermally conductive filler, thereby contributing to the dispersion of the thermally conductive filler. The alkoxysilane compound is a compound having a structure in which one to three of the four bonds of a silicon atom (Si) are bonded to an alkoxy group, and the remaining bond is bonded to an organic substituent.

Examples of the alkoxy group contained in the alkoxysilane compound include a methoxy group, an ethoxy group, a protoxy group, a butoxy group, a pentoxy group, and a hexatoxy group. From the viewpoint of availability, the alkoxysilane compound is preferably an alkoxysilane compound having a methoxy group or an ethoxy group. From the viewpoint of further increasing the affinity with the thermally conductive filler as an inorganic substance, the number of alkoxy groups contained in the alkoxysilane compound is preferably two or more, and more preferably three (trialkoxysilane). A specific example of the alkoxysilane compound is preferably at least one selected from a trimethoxysilane compound and a triethoxysilane compound.

Examples of functional groups contained in the organic substituents of the alkoxysilane compound include acryloyl groups, alkyl groups, carboxyl groups, vinyl groups, methacrylic groups, aromatic groups, amino groups, isocyanate groups, isocyanurate groups, epoxy groups, hydroxyl groups, and mercapto groups. Here, when an addition reaction type organopolysiloxane containing a platinum catalyst is used as the precursor of the above-mentioned addition reaction type silicone resin, it is preferable that the alkoxysilane compound is one that is unlikely to affect the curing reaction of the organopolysiloxane. For example, when an addition reaction type organopolysiloxane containing a platinum catalyst is used as the organopolysiloxane, it is preferable that the organic substituents of the alkoxysilane compound do not contain amino groups, isocyanate groups, isocyanurate groups, hydroxyl groups, or mercapto groups.

From the viewpoint of further increasing the dispersibility of the thermally conductive filler and facilitating higher loading of the thermally conductive filler, an alkylalkoxysilane compound having an alkyl group bonded to a silicon atom, that is, an alkyl group-containing alkoxysilane compound, is preferred. In the alkyl group-containing alkoxysilane compound, the number of carbon atoms of the alkyl group bonded to the silicon atom is preferably 4 or more, may be 6 or more, may be 8 or more, or may be 10 or more. In addition, from the viewpoint of further suppressing the viscosity of the thermally conductive composition, the number of carbon atoms of the alkyl group bonded to the silicon atom in the alkyl group-containing alkoxysilane compound is preferably 16 or less, may be 14 or less, or may be 12 or less. In the alkyl group-containing alkoxysilane compound, the alkyl group bonded to the silicon atom may be linear, branched, or cyclic.

The alkoxysilane compounds may be used alone or in combination of two or more. Specific examples of alkoxysilane compounds include alkyl group-containing alkoxysilane compounds, vinyl group-containing alkoxysilane compounds, acryloyl group-containing alkoxysilane compounds, methacryl group-containing alkoxysilane compounds, aromatic group-containing alkoxysilane compounds, amino group-containing alkoxysilane compounds, isocyanate group-containing alkoxysilane compounds, isocyanurate group-containing alkoxysilane compounds, epoxy group-containing alkoxysilane compounds, and mercapto group-containing alkoxysilane compounds.

Examples of alkyl group-containing alkoxysilane compounds include methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, cyclohexylmethyldimethoxysilane, n-octyltriethoxysilane, n-decyltrimethoxysilane, and hexadecyltrimethoxysilane. Among the alkyl group-containing alkoxysilane compounds, at least one selected from isobutyltrimethoxysilane, isobutyltriethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, cyclohexylmethyldimethoxysilane, n-octyltriethoxysilane, n-decyltrimethoxysilane, and hexadecyltrimethoxysilane is preferred, and at least one of n-decyltrimethoxysilane and hexadecyltrimethoxysilane is more preferred.

Examples of vinyl group-containing alkoxysilane compounds include vinyltrimethoxysilane and vinyltriethoxysilane.

Examples of alkoxysilane compounds containing an acryloyl group include 3-acryloxypropyltrimethoxysilane.

Examples of methacryl group-containing alkoxysilane compounds include 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, and 3-methacryloxypropyltriethoxysilane.

Examples of aromatic group-containing alkoxysilane compounds include phenyltrimethoxysilane and phenyltriethoxysilane.

Examples of amino group-containing alkoxysilane compounds include N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane.

Examples of isocyanate group-containing alkoxysilane compounds include 3-isocyanatepropyltriethoxysilane. Examples of isocyanurate group-containing alkoxysilane compounds include tris-(trimethoxysilylpropyl)isocyanurate.

Examples of epoxy group-containing alkoxysilane compounds include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-glycidoxypropyltriethoxysilane.

Examples of mercapto group-containing alkoxysilane compounds include 3-mercaptopropyltrimethoxysilane.

In particular, the thermally conductive composition according to the present technology preferably contains an alkoxysilane compound having a melting point of -40°C or higher and a boiling point of 100°C or higher. By having the boiling point of the alkoxysilane compound be 100°C or higher, the alkoxysilane compound can be more effectively prevented from vaporizing at room temperature, and as a result, the thermally conductive sheet can be more reliably prevented from becoming too hard due to condensation or the like. In this specification, "room temperature" refers to the range of 15 to 25°C as specified in JIS K 0050:2019 (General Rules for Chemical Analysis Methods). In addition, by having the melting point of the alkoxysilane compound be -40°C or higher, the thermally conductive sheet can be more effectively prevented from becoming hard at room temperature (e.g., 1 to 30°C) or lower, and the flexibility of the sheet can be improved. There is no particular upper limit on the boiling point of the alkoxysilane compound, and the higher the better. Examples of alkoxysilane compounds having a melting point of -40°C or higher and a boiling point of 100°C or higher include decyltrimethoxysilane, hexadecyltrimethoxysilane, n-octadecyltrimethoxysilane, n-dodecyltrimethoxysilane, n-dodecyltriethoxysilane, and hexyltrimethoxysilane. The thermally conductive composition according to the present technology preferably uses a combination of decyltrimethoxysilane and hexadecyltrimethoxysilane.

In the thermally conductive composition, when the content of the organopolysiloxane is 100 parts by mass, the content of the alkoxysilane compound can be, for example, 50 parts by mass or more, 100 parts by mass or more, 200 parts by mass or more, 300 parts by mass or more, 350 parts by mass or more, 400 parts by mass or more, 500 parts by mass or more, or 600 parts by mass or more. In addition, in the thermally conductive composition, when the content of the organopolysiloxane is 100 parts by mass, the upper limit of the content of the alkoxysilane compound can be, for example, 750 parts by mass or less, 700 parts by mass or less, or 650 parts by mass or less.

The content of the alkoxysilane compound in the thermally conductive composition is not particularly limited, and can be, for example, 0.1 to 4.0 parts by mass, or 0.2 to 2.0 parts by mass, per 100 parts by mass of the thermally conductive filler. When two or more types of alkoxysilane compounds are used in combination, it is preferable that the total amount falls within the above content range.

When decyltrimethoxysilane and hexadecyltrimethoxysilane are used in combination as the alkoxysilane compounds, the mass ratio of decyltrimethoxysilane to hexadecyltrimethoxysilane (decyltrimethoxysilane:hexadecyltrimethoxysilane) is preferably in the range of 100:98 to 100:201.

<Siloxane-modified acrylic resin>
The thermally conductive composition according to the present technology contains a siloxane-modified acrylic resin. The siloxane-modified acrylic resin is a copolymer of a (meth)acrylic acid ester having one or more polydimethylsiloxane structures (-(CH ₃ ) ₂ SiO) _n -; n is an integer of 1 or more) and a (meth)acrylic acid alkyl ester. The siloxane-modified acrylic resin is a component for softening a sheet obtained from the thermally conductive composition. The siloxane-modified acrylic resin can further improve the dispersibility of a thermally conductive filler in the thermally conductive composition, as compared with, for example, silicone oil.

Examples of (meth)acrylic acid esters having one or more polydimethylsiloxane structures include dimethicone methacrylate. Examples of (meth)acrylic acid alkyl esters include methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethylhexyl acrylate, tridecyl acrylate, and stearyl acrylate.

Specific examples of siloxane-modified acrylic resins include stearyl-modified acrylate silicone (a copolymer of acrylate, stearyl acrylate, and dimethicone methacrylate), behenyl-modified acrylate silicone (a copolymer of acrylate, behenyl acrylate, and dimethicone methacrylate), and ethylhexyl-modified acrylate silicone (a copolymer of acrylate, ethylhexyl acrylate, and dimethicone methacrylate). The siloxane-modified acrylic resin may have hydrophilic functional groups such as carboxyl groups, epoxy groups, carbonyl groups, hydroxyl groups, and ether groups.

In particular, the thermally conductive composition according to the present technology preferably contains a siloxane-modified acrylic resin having a melting point of 55°C or less, and more preferably contains a siloxane-modified acrylic resin having a melting point in the range of 0 to 45°C. The siloxane-modified acrylic resin has a melting point of 55°C or less, which has the advantage that it exhibits flexibility in the range of practical use and is more easily adhered to semiconductor chips such as ICs, CPUs (Central Processing Units), and APs (Application Processors). The lower limit of the melting point of the siloxane-modified acrylic resin is not particularly limited, but is preferably 25°C or more, for example. When the melting point of the siloxane-modified acrylic resin is 25°C or more, the siloxane-modified acrylic resin becomes solid at room temperature and becomes liquid when heated, so that the adhesion to the heat source can be further improved when the thermally conductive sheet is formed.

Commercially available siloxane-modified acrylic resins include KP-541, KP-543, KP-545, KP-545L, KP-550, KP-561P, KP-562P, KP-574, and KP-578 (all manufactured by Shin-Etsu Silicone Co., Ltd.), and SIMAC (registered trademark) US-350 (manufactured by Toagosei Co., Ltd.). Among these commercially available siloxane-modified acrylic resins, from the viewpoint of a melting point of 55°C or less, KP-561P and KP-562P are preferred, and it is more preferred to include KP-561P. The siloxane-modified acrylic resins may be used alone or in combination of two or more types. In addition, two or more types of siloxane-modified acrylic resins having a melting point of 55°C or less may be used in combination.

In the thermally conductive composition, when the content of the organopolysiloxane is 100 parts by mass, the content of the siloxane-modified acrylic resin can be, for example, 50 parts by mass or more, 100 parts by mass or more, 200 parts by mass or more, 300 parts by mass or more, or 350 parts by mass or more. In addition, in the thermally conductive composition, when the content of the organopolysiloxane is 100 parts by mass, the upper limit of the content of the siloxane-modified acrylic resin can be, for example, 500 parts by mass or less, 450 parts by mass or less, or 400 parts by mass or less.

The lower limit of the content of the siloxane-modified acrylic resin can be, for example, 0.1 parts by mass or more, 0.3 parts by mass or more, or 1 part by mass or more, per 100 parts by mass of the thermally conductive filler. The upper limit of the content of the siloxane-modified acrylic resin can be, for example, 10 parts by mass or less, 7 parts by mass or less, 5 parts by mass or less, 2 parts by mass or less, or 1 part by mass or less, per 100 parts by mass of the thermally conductive filler. When two or more types of siloxane-modified acrylic resins are used in combination, it is preferable that the total amount satisfies the above content range.

<Antioxidants>
The thermally conductive resin composition according to the present technology may further contain an antioxidant in addition to the above-mentioned components in order to further enhance the effect of the present technology. As the antioxidant, for example, a hindered phenol-based antioxidant may be used, or a hindered phenol-based antioxidant and a thiol-based antioxidant may be used in combination. The hindered phenol-based antioxidant, for example, captures radicals (peroxy radicals) and contributes more effectively to suppression of oxidative deterioration of organopolysiloxane (addition reaction type silicone resin). The thiol-based antioxidant, for example, decomposes hydroxide radicals and contributes more effectively to suppression of oxidative deterioration of organopolysiloxane (addition reaction type silicone resin).

<Hindered phenol antioxidant>
Examples of the hindered phenol-based antioxidant include those having a structure represented by the following formula 1 as a hindered phenol skeleton. The hindered phenol-based antioxidant preferably has one or more skeletons represented by the following formula 1, and may have two or more skeletons represented by the following formula 1.

(Equation 1)

In formula 1, it is preferable that R ¹ and R ² represent a t-butyl group and R ³ represent a hydrogen atom (hindered type), that R ¹ represents a methyl group, R ² represents a t-butyl group and R ³ represents a hydrogen atom (semi-hindered type), and that R ¹ represents a hydrogen atom, R ² represents a t-butyl group and R ³ represents a methyl group (less hindered type). From the viewpoint of long-term thermal stability in a high-temperature environment, the semi-hindered type or hindered type is preferable. In addition, it is preferable that the hindered phenol-based antioxidant has three or more skeletons represented by the above-mentioned formula 1 in one molecule, and that the three or more skeletons represented by formula 1 are linked by a hydrocarbon group or a group consisting of a combination of a hydrocarbon group, -O- and -CO-. The hydrocarbon group may be linear, branched or cyclic. The number of carbon atoms of the hydrocarbon group can be, for example, 3 to 8. The molecular weight of the hindered phenol-based antioxidant can be, for example, 300-850, or can be 500-800.

The hindered phenol-based antioxidant may have an ester bond in its structure. Examples of such phenol-based antioxidants include stearyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis[3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate], and 2,2'-dimethyl-2,2'-(2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diyl)dipropane-1,1'-diyl=bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propanoate]. In addition, examples of hindered phenol-based antioxidants that may be used include those that do not have an ester bond in their structure, such as 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane.

Commercially available phenolic antioxidants include Adeka STAB AO-30, Adeka STAB AO-50, Adeka STAB AO-60, Adeka STAB AO-80 (all manufactured by ADEKA CORPORATION), Irganox 1010, Irganox 1035, Irganox 1076, Irganox 1135 (all manufactured by BASF Corporation). The phenolic antioxidants may be used alone or in combination of two or more types.

The lower limit of the content of the phenolic antioxidant can be, for example, 0.1 parts by mass or more, and can also be 0.5 parts by mass or more, per 100 parts by mass of the organopolysiloxane. The upper limit of the content of the phenolic antioxidant can be, for example, 10 parts by mass or less, and can also be 5 parts by mass or less, per 100 parts by mass of the organopolysiloxane. When two or more types of phenolic antioxidants are used in combination, it is preferable that the total amount thereof satisfies the above content range.

<Thiol-based antioxidants>
Examples of the thiol-based antioxidant include a type having a thioether skeleton, a type having a hindered phenol skeleton, etc. Examples of the thiol-based antioxidant include ditridecyl 3,3'-thiobispropionate, pentaerythritol tetrakis[3-(dodecylthio)propionate], and 4,6-bis(octylthiomethyl)-o-cresol.

Commercially available thiol-based antioxidants include Adeka STAB AO-412S, Adeka STAB AO-503, Adeka STAB AO-26 (all manufactured by ADEKA CORPORATION), Sumilizer TP-D (manufactured by Sumitomo Chemical Co., Ltd.), and Irganox 1520L (manufactured by BASF Japan Ltd.). Among these thiol-based antioxidants, tetrakis[3-(dodecylthio)propionic acid]pentaerythritol (commercially available products: Adeka STAB AO-412S, Sumilizer TP-D (manufactured by Sumitomo Chemical Co., Ltd.), and Irganox 1520L) are preferred because they cause less curing inhibition. The thiol-based antioxidants may be used alone or in combination of two or more types.

The content of the thiol-based antioxidant in the thermally conductive composition may be approximately the same as that of the phenol-based antioxidant, or may be greater than that of the phenol-based antioxidant. For example, the lower limit of the content of the thiol-based antioxidant may be, for example, 0.1 parts by mass or more per 100 parts by mass of the organopolysiloxane. The upper limit of the content of the thiol-based antioxidant may be, for example, 20 parts by mass or less, or may be 10 parts by mass or less per 100 parts by mass of the organopolysiloxane. When two or more types of thiol-based antioxidants are used in combination, it is preferable that the total amount satisfies the above content range.

As described above, the thermally conductive composition according to the present technology contains an organopolysiloxane, a thermally conductive filler, an alkoxysilane compound, and a siloxane-modified acrylic resin. By using these components in combination, the synergistic effect can improve the thermal conductivity and flexibility when the thermally conductive composition is made into a thermally conductive sheet. Furthermore, the thermally conductive composition according to the present technology can improve the thermal conductivity and flexibility when made into a sheet even when the thermally conductive composition contains 80 to 90 volume % of a thermally conductive filler.

The thermally conductive composition according to the present technology may further contain other components in addition to the above-mentioned components, as long as the effect of the present technology is not impaired. For example, the thermally conductive composition may further contain a heavy metal deactivator for the purpose of improving the deterioration resistance of the thermally conductive sheet. Examples of heavy metal deactivators include the Adeka STAB ZS series (such as Adeka STAB ZS-90) manufactured by ADEKA Corporation.

The thermally conductive composition according to the present technology can be obtained, for example, by kneading the above-mentioned components using a kneader (such as a planetary kneader, a ball mill, or a Henschel mixer). When using, for example, a two-liquid addition reaction type silicone resin as the organopolysiloxane, the base agent, the curing agent, and the thermally conductive filler are not mixed at once, but the required amount of the thermally conductive filler may be divided into the base agent and the curing agent and mixed, and the component containing the base agent and the component containing the curing agent may be mixed at the time of use.

<Thermal conductive sheet>
FIG. 1 is a cross-sectional view showing an example of a thermally conductive sheet. The thermally conductive sheet 1 is made of a cured product of the thermally conductive composition described above. For example, the thermally conductive sheet 1 is obtained by applying a thermally conductive composition to a desired thickness on a release film 11 formed of, for example, PET (polyethylene terephthalate), PEN (polyethylene naphthalate), polyolefin, polymethylpentene, glassine paper, or the like, and heating the composition to cure the organopolysiloxane, which is a binder resin. The thickness of the thermally conductive sheet 1 (the thickness of the sheet body excluding the release film 11) can be appropriately selected according to the purpose, and can be, for example, 0.05 to 5 mm.

By using the above-mentioned thermally conductive composition, the thermally conductive sheet 1 can have a thermal conductivity of 3.5 W/m·K or more, 4.0 W/m·K or more, 4.5 W/m·K or more, 5.0 W/m·K or more, 6.0 W/m·K or more, 7.0 W/m·K or more, or 7.5 W/m·K or more. The upper limit of the thermal conductivity of the thermally conductive sheet 1 is not particularly limited, but can be, for example, 12.0 W/m·K or less, 11.0 W/m·K or less, or 9.0 W/m·K or less. The method for measuring the thermal conductivity is the same as in the examples described below.

In addition, since the thermal conductive sheet 1 itself is softened by heat, it is possible to increase the degree of adhesion with a heat generating element or a heat sink, thereby lowering the thermal resistance value (contact thermal resistance value). For example, the thermal conductive sheet 1 can have a thermal resistance value of 1.0°C· ^cm2 /W or less, 0.9°C· ^cm2 /W or less, 0.7°C· ^cm2 /W or less, 0.5°C· ^cm2 /W or less, 0.3°C· ^cm2 /W or less, or 0.2°C· ^cm2 /W or less. The lower limit of the thermal resistance value of the thermal conductive sheet 1 is not particularly limited, but can be, for example, 0.01°C· ^cm2 /W or more. The method for measuring the thermal resistance value is the same as that of the examples described later.

Furthermore, the thermal conductive sheet 1 can have a thermal conductivity retention rate, as shown in the following formula 2, of 70% or more, 75% or more, 80% or more, or 90% or more, when aged under conditions of, for example, 200°C and 24 hours.
Equation 2: (Thermal conductivity of the thermal conductive sheet after aging treatment/Thermal conductivity of the thermal conductive sheet before aging treatment)×100

In addition, since the thermally conductive sheet 1 uses the thermally conductive composition described above, it has good flexibility, and for example, the ratio of the compression ratio (amount of change from the initial thickness of the thermally conductive sheet) when pressure is applied at 45°C with a load of 1 kgf/ ^cm2 divided by the initial thickness of the thermally conductive sheet, that is, the compression ratio represented by the following formula 3, can be 60% or more, 70% or more, or even 80% or more. The upper limit of the compression ratio is not particularly limited, but can be, for example, 90% or less.
Equation 3: Compression rate (%)=((initial thickness of thermal conductive sheet−initial compressed thickness of thermal conductive sheet)/initial thickness of thermal conductive sheet)×100

As described above, the thermally conductive sheet 1 is made of the thermally conductive composition described above, and therefore has good thermal conductivity and flexibility due to the synergistic effect of the organopolysiloxane, the thermally conductive filler, the alkoxysilane compound, and the siloxane-modified acrylic resin. In particular, even if the thermally conductive sheet 1 is made of a thermally conductive composition containing 80 to 90 volume % of the thermally conductive filler, it has good thermal conductivity and flexibility. In addition, the thermally conductive sheet 1 has low repulsion against compression, and the sheet itself softens due to heat, so it has good adhesion to, for example, heating elements and heat sinks. In other words, the thermally conductive sheet 1 has high conformability to heating elements and heat sinks.

As described above, the thermally conductive sheet 1 has good thermal conductivity and flexibility, and can be applied to a heat dissipation structure in which the thermally conductive sheet 1 is sandwiched between a heat generating body and a heat dissipation member. Examples of heat generating bodies include integrated circuit elements such as CPUs, GPUs (Graphics Processing Units), DRAMs (Dynamic Random Access Memory), and flash memories, as well as electronic components that generate heat in electrical circuits, such as transistors and resistors. Heat generating bodies also include components that receive optical signals, such as optical transceivers in communication devices. Heat dissipation members can be anything that conducts heat generated from a heat generating body and dissipates it to the outside, and examples of such heat dissipation members include heat sinks and heat spreaders that are used in combination with integrated circuit elements, transistors, optical transceiver housings, and the like. Examples of heat dissipation members include heat sinks, coolers, die pads, printed circuit boards, cooling fans, Peltier elements, heat pipes, metal covers, housings, and the like.

2 is a cross-sectional view showing an example of a semiconductor device. In actual use, for example, the thermally conductive sheet 1 from which the release film 11 has been peeled off can be mounted inside electronic components such as semiconductor devices or various electronic devices. For example, as shown in FIG. 2, the thermally conductive sheet 1 is mounted on a semiconductor device 50 built into various electronic devices and sandwiched between a heat generating body and a heat dissipation member. That is, the electronic device includes a heat generating body, a heat dissipation member, and a thermally conductive sheet 1 disposed between the heat generating body and the heat dissipation member. The semiconductor device 50 shown in FIG. 2 has at least an electronic component 51, a heat spreader 52, and a thermally conductive sheet 1, and the thermally conductive sheet 1 is sandwiched between the heat spreader 52 and the electronic component 51. By using the thermally conductive sheet 1, the semiconductor device 50 has high heat dissipation properties. In addition, the thermally conductive sheet 1 is sandwiched between the heat spreader 52 and the heat sink 53, and together with the heat spreader 52, the thermally conductive sheet 1 constitutes a heat dissipation member that dissipates heat from the electronic component 51. The location where the thermally conductive sheet 1 is mounted is not limited to between the heat spreader 52 and the electronic component 51, or between the heat spreader 52 and the heat sink 53, but can be selected appropriately depending on the configuration of the electronic device or semiconductor device.

This technology can also be applied to articles equipped with the above-mentioned heat dissipation structure. Examples of articles equipped with such heat dissipation structures include personal computers, server equipment, mobile phones, wireless base stations, and ECUs (Electronic Control Units) used to control electrical components such as engines, power transmission systems, steering systems, and air conditioners in transport machines such as automobiles.

Below, an example of the present technology is described. In this example, a thermally conductive composition was obtained from the raw materials shown in Table 1. The dispersibility of this thermally conductive composition was evaluated. In addition, the thermally conductive sheet obtained from the thermally conductive composition was evaluated in each of the ways shown in Table 1. Note that the present technology is not limited to the following examples.

<Preparation of Thermally Conductive Composition>
The raw materials used in this example are as follows:

Silicone resin A (product name: CY52-276A, manufactured by Dow Corning Toray Co., Ltd.)
Silicone resin B (product name: CY52-276B, manufactured by Dow Corning Toray Co., Ltd.)
Graft copolymer consisting of acrylic polymer and dimethylpolysiloxane (product name: KP-561P, melting point 25-35°C, manufactured by Shin-Etsu Silicones)
Graft copolymer consisting of acrylic polymer and dimethylpolysiloxane (product name: KP-578, melting point 55°C or less, manufactured by Shin-Etsu Silicones)
Polyglycerin-modified silicone surfactant with branched silicone chains (product name: KF-6106, manufactured by Shin-Etsu Silicone Co., Ltd.)
Alkyltrialkoxysilane: hexadecyltrimethoxysilane (product name: Dynasylan 9116 (melting point 1°C, boiling point 155°C), manufactured by Evonik Japan)
Alkyltrialkoxysilane: decyltrimethoxysilane (product name: Z-6210 (melting point -37°C, boiling point 115°C), manufactured by Dow Corning Toray Co., Ltd.)
Phenol-based antioxidant (product name: AO-80, manufactured by ADEKA Corporation)
Heavy metal deactivator (ZS-90, manufactured by ADEKA)
A mixture of aluminum nitride, alumina (spherical alumina), and magnesium oxide A mixture of aluminum nitride and alumina (spherical alumina)

<Examples 1 to 5, Comparative Examples 1 and 2>
A mixture of aluminum nitride and alumina, or a mixture of aluminum nitride, alumina and magnesium oxide was used as the thermally conductive filler. In the case of Examples 1 and 3 using a mixture of aluminum nitride and alumina, the mixing amount was about 10640 parts by mass of aluminum nitride and about 1880 parts by mass of alumina per 100 parts by mass of silicone resin, and each type was added to the silicone resin and stirred. In the case of Examples 2, 4 and 5 using a mixture of aluminum nitride, alumina and magnesium oxide, the mixing amount was about 4220 parts by mass of aluminum nitride, about 2800 parts by mass of alumina and about 4980 parts by mass of magnesium oxide per 100 parts by mass of silicone resin, and each type was added to the silicone resin and stirred. In addition, in the case of Comparative Examples 1 and 2 using a mixture of aluminum nitride, alumina and magnesium oxide, the mixing amount was about 8000 parts by mass of aluminum nitride, alumina and magnesium oxide per 100 parts by mass of silicone resin (aluminum nitride: alumina: magnesium oxide = 1.5: 1: 1.78 ratio), and each type was added to the silicone resin and stirred. A planetary stirrer was used for stirring, and the rotation speed was 1200 rpm. Next, the thermally conductive composition was applied to a release film (material: PET, thickness 125 μm) using a bar coater so as to have a thickness of 2 mm or 1.5 mm, and then a cover film (material: PET, thickness 50 μm) coated with a release agent was placed on the film, and the film was heated at 80 ° C for 6 hours to obtain a thermally conductive sheet.

[Dispersibility]
The thermally conductive fillers were added one by one to the thermally conductive composition in which the components other than the thermally conductive filler were mixed, and then stirred. A commercially available planetary centrifugal mixer (planetary centrifugal vacuum mixing and degassing mixer (device name: V-mini 300, manufactured by EME) was used for stirring, and the rotation speed was set to 1200 rpm. The time until the thermally conductive filler was dispersed in the thermally conductive composition was visually evaluated. The results are shown in Table 1.
A: Within 2 minutes B: More than 2 minutes, within 4 minutes C: More than 4 minutes, within 6 minutes D: More than 6 minutes, within 10 minutes E: No mixing even after stirring for more than 10 minutes

[Initial thermal conductivity]
Using a thermal resistance measuring device conforming to ASTM-D5470, the initial thermal conductivity (W/m·K) in the thickness direction of the thermal conductive sheet was measured with a load of 1 kgf/cm ^2. The sheet temperature during the measurement was 45° C. The results are shown in Table 1.

[Compression ratio]
The compression ratio (initial compression ratio) was calculated by cutting the thermally conductive sheets produced in each of the Examples and Comparative Examples to a predetermined size (20 mmφ×2000 μm thickness), setting the average temperature of the thermally conductive sheets to 45° C., applying a load of 1 kgf/ ^cm2 , measuring the thickness after stabilization (initial compression thickness [μm]), and calculating the compression ratio (%) according to the above-mentioned formula 3. The results are shown in Table 1.

[Thermal resistance value]
The thermal resistance value (°C·cm ² /W) of the thermally conductive sheet was measured using a thermal resistance measuring device conforming to ASTM-D5470 with a load of 1 kgf/cm ² applied. For practical purposes, it is preferable that the thermal resistance value is 1.0 (°C·cm ² /W) or less. The results are shown in Table 1.

[Handling (room temperature)]
When the thermally conductive sheet could be easily peeled off from the release film at room temperature (25° C.), the handling was evaluated as “OK”, and when the thermally conductive sheet could not be peeled off, the handling was evaluated as “NG”. The results are shown in Table 1.

[Softening property]
The maximum stress when a thermal conductive sheet of 25.4 mm square and 1.5 mm thick was compressed by 70% at a compression speed of 25.4 mm/min and the residual stress of the sheet when the compressed state was maintained for 10 minutes were observed, and when the maximum stress was 300 psi or less and the residual stress was 50 psi or less, it was evaluated as OK, and when it was otherwise, it was evaluated as NG. The results are shown in Table 1.

[Heat resistance stability]
The thermal conductive sheet was cut to a thickness of 2 mm, 30 mm x 30 mm, and subjected to aging (super accelerated test) at 200 ° C. for 24 hours to evaluate whether the shape of the thermal conductive sheet was maintained and oil bleeding was also minimal (heat resistance stability). When there was no change in shape and oil bleeding was within 1 mm, the heat resistance stability was evaluated as "◯", when the shape was slightly deformed but the oil bleeding was within 1 mm, the heat resistance stability was evaluated as "△", and when the shape was significantly deformed or did not fall under "◯" or "△", the heat resistance stability was evaluated as "×". For practical purposes, it is preferable that the heat resistance stability is evaluated as "◯" or "△". The results are shown in Table 1.

In Examples 1 to 5, a thermally conductive composition was used that contained an organopolysiloxane, a thermally conductive filler, an alkoxysilane compound, and a siloxane-modified acrylic resin, and in which the total content of the alkoxysilane compound and the siloxane-modified acrylic resin was 100 parts by mass or more when the content of the organopolysiloxane was taken as 100 parts by mass, and it was found that a thermally conductive sheet with good initial thermal conductivity and softening properties (flexibility) was obtained.

On the other hand, in Comparative Example 1, a thermally conductive composition that did not contain an alkoxysilane compound was used, and it was found that the dispersibility of the thermally conductive composition was not good, making it difficult to form it into a thermally conductive sheet.

In Comparative Example 2, a thermally conductive composition that did not contain siloxane-modified acrylic resin was used, and it was found that the softening properties were not good.

REFERENCE SIGNS LIST 1 Thermally conductive sheet, 11 Release film, 50 Semiconductor device, 51 Electronic component, 52 Heat spreader, 53 Heat sink

Claims (10)

An organopolysiloxane;
A thermally conductive filler;
an alkoxysilane compound having a melting point of −40° C. or higher and a boiling point of 100° C. or higher ;
A siloxane-modified acrylic resin having a melting point of 55° C. or less and being solid at room temperature ;
the total content of the alkoxysilane compound and the siloxane-modified acrylic resin is 100 parts by mass or more when the content of the organopolysiloxane is 100 parts by mass;
the content of the alkoxysilane compound is 200 parts by mass or more and 650 parts by mass or less, relative to 100 parts by mass of the organopolysiloxane;
The thermally conductive composition has a content of the siloxane-modified acrylic resin of 200 parts by mass or more and 450 parts by mass or less, based on 100 parts by mass of the organopolysiloxane . The thermally conductive composition according to claim 1 , comprising 80 to 90 volume % of said thermally conductive filler. The thermally conductive composition according to claim 1 or 2 , wherein the alkoxysilane compound contains at least one of decyltrimethoxysilane and hexadecyltrimethoxysilane. The thermally conductive composition according to claim 3 , wherein the mass ratio of the decyltrimethoxysilane to the hexadecyltrimethoxysilane (decyltrimethoxysilane:hexadecyltrimethoxysilane) is in the range of 100:98 to 100:201. 5. The thermally conductive composition according to claim 1 , wherein the organopolysiloxane is an addition reaction type organopolysiloxane. The thermally conductive composition according to any one of claims 1 to 5 , wherein the organopolysiloxane is a two-part addition reaction type silicone resin comprising an organopolysiloxane having a vinyl group, a curing agent having a hydrosilyl group, and a curing catalyst. A thermally conductive sheet comprising a cured product of the thermally conductive composition according to any one of claims 1 to 6 . The thermally conductive sheet according to claim 7 , having a thermal conductivity of 6.0 W/m·K or more. 9. The thermally conductive sheet according to claim 7 , which has a compressibility of 60% or more when a pressure of 1 kgf/cm2 is applied at 45°C, as represented by the following formula ³ :
Formula 3: Compressibility (%)=((initial thickness of the thermal conductive sheet−initial compressed thickness of the thermal conductive sheet)/initial thickness of the thermal conductive sheet)×100 A heating element;
A heat dissipation member;
a thermally conductive sheet disposed between the heat generating body and the heat dissipating member;
The thermally conductive sheet of an electronic device is made of a cured product of the thermally conductive composition according to any one of claims 1 to 6 .

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