Thermally conductive sheet and method for producing same

Abstract

A thermally conductive sheet provided with a thermally conductive layer containing a polymer matrix and a thermally conductive filler, and an acrylic adhesive layer provided on the surface of the thermally conductive layer, the acrylic adhesive layer having a reactive double bond.

Description

TECHNICAL FIELD

[0001] The present application relates to a thermally conductive sheet and a manufacturing method thereof. BACKGROUND

[0002] In recent years, with the high-density of the wiring of a multilayer wiring board, the high-density of the wiring of a semiconductor package, the increase in the mounting density of electronic components, the increase in the amount of heat per unit area due to the high integration of semiconductor elements themselves, and the like, it is desired to improve the heat dissipation from a semiconductor package. It is known that a semiconductor package is heat-dissipated by sandwiching a heat-dissipating material between a heat-generating body such as a semiconductor chip and a heat sink called a heat dissipator and making them adhere. The heat-dissipating material used by being disposed between a semiconductor chip and a heat dissipator has widely used a thermally conductive grease in the past.

[0003] A semiconductor package is generally heated to a certain temperature or more at the time of use or the like. Since each member such as a substrate, a semiconductor chip, a heat dissipator, and the like differs in the thermal expansion rate, warping occurs at the time of heating. In recent years, with the large-scale of chips, the expansion of the gap due to warping also becomes large, and the thermally conductive grease cannot follow such warping, and a gap generating adverse conditions occurs, so the use of a thermally conductive sheet instead of a thermally conductive grease has been studied.

[0004] The thermally conductive sheet used in the above use is required to improve the heat dissipation while also improving the followability to warping by improving the softness. However, if the thermally conductive sheet is intended to improve both the heat dissipation and the softness, the adhesion to the surrounding members decreases, so as with the thermally conductive grease, it cannot follow the warping, and there is a concern that it is peeled off from the semiconductor chip or the heat dissipator. Therefore, for example, in Patent Literature 1, an attempt is made to improve the adhesive force by compounding a liquid polybutene, an acrylate-based polymer, an ethylene / α-olefin copolymer, a hot melt agent, or the like in the thermally conductive sheet, and to suppress the peeling from the semiconductor chip or the heat dissipator.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: Japanese Patent No. 7067571 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] A semiconductor package is generally manufactured by a reflow process which generally involves high-temperature heating. Therefore, sometimes the thermally conductive sheet used by being disposed between a semiconductor chip and a heat dissipator is required to maintain the adhesion to the adherend such as a semiconductor chip, a heat dissipator, or the like even after high-temperature heating.

[0010] However, as described in Patent Document 1, if the thermally conductive sheet merely has the adhesive force improved, there is a problem that the adhesive force decreases at the time of high-temperature heating in a reflow process or the like, and peeling from the adherend occurs.

[0011] Therefore, the present application has an object to provide a thermally conductive sheet which can be closely adhered to an adherend and can prevent peeling from the adherend even after high-temperature heating such as reflow.

[0012] Means for solving the problem

[0013] The present inventors and others have conducted intensive studies, and as a result, have found that in a thermally conductive sheet having a thermally conductive layer containing a high-molecular matrix and a thermally conductive filler material, and an acrylic adhesive layer provided on the surface of the thermally conductive layer, the above problem can be solved by having the acrylic adhesive layer contain a reactive double bond, thereby completing the following present application.

[0014] That is, the present application provides the following [1] to

[14] .

[0015] [1] A thermally conductive sheet having a thermally conductive layer containing a high-molecular matrix and a thermally conductive filler material, and an acrylic adhesive layer provided on the surface of the thermally conductive layer, The above acrylic adhesive layer has a reactive double bond.

[0016] [2] The thermally conductive sheet according to the above [1], wherein the intensity ratio A / B of the peak intensity A of C=C stretching vibration to the peak intensity B of C=O stretching vibration in the Raman spectrum of the above acrylic adhesive layer is 0.2 or more.

[0017] [3] The thermally conductive sheet according to the above [1] or [2], wherein the above high-molecular matrix is an organic polysiloxane.

[0018] [4] The thermally conductive sheet according to any one of the above [1] to [3], wherein the above thermally conductive layer contains an anisotropic filler material oriented in the thickness direction of the thermally conductive layer.

[0019] [5] The thermally conductive sheet according to any one of the above [1] to [4], wherein the surface of the above thermally conductive layer is a sliced surface.

[0020] [6] The thermally conductive sheet according to any one of the above [1] to [5], wherein the above acrylic adhesive layer is infiltrated in the above thermally conductive layer.

[0021] [7] A method of manufacturing a thermally conductive sheet, comprising the following steps: a step of obtaining a mixed composition by mixing at least a curable high-molecular composition and a thermally conductive filler material; a step of obtaining a cured product by curing the above mixed composition by heating; and a step of applying an adhesive to the surface of the cured product, The adhesive is an acrylic adhesive having a reactive double bond.

[0022] [8] The method for producing a thermally conductive sheet according to the above [7], wherein the mixed composition is heated to obtain a molded product, and the molded product is sliced to make the cured product into a sheet shape.

[0023] [9] The method for producing a thermally conductive sheet according to the above [7] or [8], wherein, in addition to the cured polymer composition and the thermally conductive filler, a compatibility substance is further mixed to obtain the mixed composition, and at least a part of the compatibility substance is volatilized by the heating.

[0024]

[10] The method for producing a thermally conductive sheet according to any one of the above [7] to [9], wherein the applied adhesive is infiltrated into the cured product.

[0025]

[11] A bonding method comprising: a bonding step of sandwiching and bonding a semiconductor chip and a heat sink with a thermally conductive sheet according to any one of the above [1] to [6]; and a bonding step of bonding the semiconductor chip and the heat sink heated to 200°C or higher after the bonding step.

[0026]

[12] The bonding method according to the above

[11] , wherein, in the bonding step, the semiconductor chip and the heat sink are bonded by pressing them at 50°C or higher and 200°C or lower after sandwiching them with the thermally conductive sheet.

[0027]

[13] The bonding method according to the above

[11] or

[12] , wherein the bonding step is performed in a state without pressing.

[0028]

[14] Use of a thermally conductive sheet in bonding of a semiconductor chip and a heat sink in a reflow process, the thermally conductive sheet comprising a thermally conductive layer containing a polymer matrix and a thermally conductive filler, and an acrylic adhesive layer provided on a surface of the thermally conductive layer, The acrylic adhesive layer has a reactive double bond.

[0029] Effects of the Invention

[0030] According to the present invention, it is possible to provide a thermally conductive sheet that can be bonded to an adherend and that prevents peeling from the adherend even after high-temperature heating such as a reflow process. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a schematic view of a thermal resistance measuring instrument.

[0032] Figure 2FIG. 1 is a schematic diagram showing a method for measuring the shear strength of a chip. DETAILED DESCRIPTION

[0033] Thermally conductive sheet

[0034] The thermally conductive sheet of the present application has a thermally conductive layer containing a high molecular matrix and a thermally conductive filler, and an acrylic adhesive layer provided on the surface of the thermally conductive layer. Hereinafter, the thermally conductive sheet will be described in detail.

[0035] Acrylic adhesive layer

[0036] In the present application, the acrylic adhesive layer has a reactive double bond. The acrylic adhesive layer, by having a reactive double bond, can maintain the state of close contact even when heated to a high temperature in a reflow process or the like in a state of close contact with an adherend such as a heat sink or a semiconductor chip, and can prevent peeling from the adherend. Further, even when used in a high-temperature environment of, for example, about 150°C in actual use, a high close contact property can be maintained.

[0037] Generally, it is known that if an acrylic adhesive is heated to a high temperature, the adhesive force greatly decreases, but in the present application, the acrylic adhesive layer, by having a reactive double bond, can maintain or improve the adhesive force to the adherend, contrary to the properties of conventional general acrylic adhesives. The principle is not clear, but it is presumed that the reactive double bond in the acrylic adhesive layer reacts by heating, for example, binds to the adherend, or crosslinks with each other through the reactive double bond, thereby increasing the mechanical strength of the adhesive layer, and further, depending on the case, reacts with unreacted hydrogen silyl groups or the like in the organopolysiloxane constituting the high molecular matrix, and they act together to increase the close contact property.

[0038] The acrylic adhesive layer is formed of an acrylic adhesive. The acrylic adhesive contains an acrylic polymer as a main agent of the adhesive, and it is preferable that the acrylic polymer has the above-mentioned reactive double bond. The acrylic adhesive layer, by containing the acrylic polymer, can exhibit adhesiveness. Further, it is considered that by the acrylic polymer having the above-mentioned reactive double bond, the mechanical strength of the adhesive layer is greatly increased by crosslinking with each other through the reactive double bond.

[0039] The acrylic adhesive layer of the present application preferably has a strength ratio A / B of a peak intensity A of C=C stretching vibration in Raman spectroscopy to a peak intensity B of C=O stretching vibration of 0.2 or more. Here, the peak intensity A is a peak generated by the reactive double bond (C=C double bond). Further, the peak intensity B is a peak generated by the C=O bond contained in the acrylic polymer. Therefore, the strength ratio A / B of the peak intensity A to the peak intensity B can be said to be an index indicating the proportion of the reactive double bond in the acrylic polymer.

[0040] The acrylic adhesive layer has a strength ratio A / B of 0.2 or greater, and thus has a sufficient amount of reactive double bonds, and can appropriately maintain adhesion to the adherend even when heated to a high temperature in a reflow process or the like in a state of being intimately bonded to the adherend.

[0041] The strength ratio A / B is more preferably 0.3 or greater, further preferably 0.4 or greater, and still further preferably 0.5 or greater. In addition, the strength ratio A / B is not particularly limited, and for example, is 1.0 or less, preferably 0.8 or less, and more preferably 0.7 or less.

[0042] Note that the peak of the C=0 stretching vibration is typically a peak that appears near a wave number of 1720 cm -1 in addition, the peak of the C=C stretching vibration is typically a peak that appears near a wave number of 1636 cm -1 However, these peaks sometimes shift slightly depending on the structure of the acrylic polymer or the like.

[0043] The acrylic polymer used for the acrylic adhesive layer preferably contains an acrylic polymer having a reactive double bond (acrylic polymer containing a reactive double bond). The acrylic polymer containing a reactive double bond preferably has a reactive double bond in a side chain. Note that the reactive double bond is a saturated carbon-carbon double bond that does not form an aromatic ring, and is typically formed by a group having a structure represented by H2C=CH-* or H2C=CCH3-*(the * represents a bonding site), and specifically, a vinyl group, an acryloyl group, a methacryloyl group, or the like can be given as examples.

[0044] In addition, the acrylic polymer containing a reactive double bond can have a functional group such as a hydroxyl group, a carboxyl group, an epoxy group, an amino group, or the like in a side chain in addition to the group having a reactive double bond, and preferably has at least one of a hydroxyl group and a carboxyl group in a side chain, and further preferably has both a hydroxyl group and a carboxyl group.

[0045] The weight average molecular weight of the acrylic polymer containing a reactive double bond is not particularly limited, and for example, is around 100,000 or greater and 1,200,000 or less, and is preferably around 200,000 or greater and 1,000,000 or less. Note that the weight average molecular weight is measured using gel permeation chromatography (GPC) and is calculated as a polystyrene conversion value. Note that by adjusting the molecular weight, the solid content concentration and the viscosity of the adhesive containing an organic solvent described later can be adjusted. Specifically, in a case where it is desired to make the solid content concentration high while adjusting to a low viscosity, it is good to make the molecular weight small. In addition, in a case where it is desired to make the solid content concentration low while adjusting to a high viscosity, it is sufficient to make the molecular weight large.

[0046] The acrylic polymer containing a reactive double bond can be obtained, for example, by reacting an acrylic polymer having a functional group such as a hydroxyl group, a carboxyl group, an epoxy group, an amino group, or the like in a side chain (hereinafter, also referred to as acrylic polymer (X)) with a compound containing a reactive double bond having a reactive group which reacts with the functional group and a reactive double bond (hereinafter, also referred to as compound containing a reactive double bond (Y)).

[0047] As the acrylic polymer (X), it is only necessary to include a structural unit derived from a (meth)acrylate, and typically, a structural unit derived from an alkyl (meth)acrylate is included as a main component. As the acrylic polymer (X), more specifically, a copolymer of an alkyl (meth)acrylate and a monomer containing a functional group, a copolymer of an alkyl (meth)acrylate and a monomer containing a functional group and another monomer other than them, or the like can be mentioned.

[0048] Note that the term (meth)acrylate is used as a term indicating one or both of an acrylate and a methacrylate, and the same applies to other similar terms.

[0049] The alkyl (meth)acrylate is an ester of (meth)acrylic acid and an alkyl alcohol. The alkyl group in the alkyl (meth)acrylate can be linear, can have a branched structure, or can have a cyclic structure.

[0050] As the alkyl (meth)acrylate, a methyl (meth)acrylate, an ethyl (meth)acrylate, a propyl (meth)acrylate, a n-butyl (meth)acrylate, an isobutyl (meth)acrylate, a t-butyl (meth)acrylate, a 2-ethylhexyl (meth)acrylate, a n-octyl (meth)acrylate, an isooctyl (meth)acrylate, an isononyl (meth)acrylate, an isomyristyl (meth)acrylate, a stearyl (meth)acrylate, a cyclohexyl (meth)acrylate, an isobornyl (meth)acrylate, or the like can be mentioned.

[0051] The alkyl (meth)acrylate can be used alone or two or more kinds thereof can be used in combination.

[0052] The alkyl (meth)acrylate is preferably an alkyl (meth)acrylate in which the number of carbon atoms of the alkyl group is 1 to 12, and more preferably an alkyl acrylate in which the number of carbon atoms of the alkyl group is 2 to 8 is included. It is good that a structural unit derived from an alkyl acrylate in which the number of carbon atoms of the alkyl group is 2 to 8 is a main component in the acrylic polymer (X), and in the acrylic polymer (X), it is only necessary to be, for example, 50% by mass or more, and it is preferably 60% by mass or more and 95% by mass or less, and more preferably 70% by mass or more and 90% by mass or less.

[0053] The functional group in the monomer containing a functional group can be exemplified by a carboxyl group, a hydroxyl group, an amino group, an epoxy group, among which a carboxyl group and a hydroxyl group are preferred. As the monomer containing a carboxyl group, (meth)acrylic acid, crotonic acid, and the like can be exemplified, among which (meth)acrylic acid is more preferred.

[0054] Further, as the monomer containing a hydroxyl group, for example, (meth)acrylic acid 2-hydroxyethyl ester, (meth)acrylic acid 2-hydroxypropyl ester, (meth)acrylic acid 3-hydroxypropyl ester, (meth)acrylic acid 2-hydroxybutyl ester, (meth)acrylic acid 4-hydroxybutyl ester, (meth)acrylic acid 5-hydroxypentyl ester, (meth)acrylic acid 6-hydroxyhexyl ester, and the like (meth)acrylic acid esters having a hydroxyl group, allyl alcohol, and the like can be exemplified. Among them, (meth)acrylic acid 2-hydroxyethyl ester and the like (meth)acrylic acid esters having a hydroxyl group are preferred.

[0055] The structural unit derived from the monomer containing a functional group is, for example, about 1 mass% or more and 35 mass% or less, preferably 5 mass% or more and 30 mass% or less, and more preferably 10 mass% or more and 25 mass% or less in the acrylic polymer (X).

[0056] The monomer containing a functional group can be used alone or two or more kinds can be used in combination.

[0057] As the other monomer, a monomer other than the alkyl (meth)acrylate and the above-mentioned monomer containing a functional group can be exemplified, and there is no particular limitation as long as it can be copolymerized with the alkyl (meth)acrylate and the monomer containing a functional group. Specifically, styrene, α-methylstyrene, p-methylstyrene, p-chlorostyrene, divinylbenzene, and the like styrene derivatives, vinyl acetate, vinyl propionate, and the like compounds having a vinyl ester group, N-vinylpyrrolidone, N-vinylmorpholine, (meth)acrylonitrile, N-cyclohexylmaleimide, N-phenylmaleimide, N-laurylmaleimide, N-benzylmaleimide, n-propyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, t-butyl vinyl ether, and the like can be exemplified. The other monomer can be used alone or two or more kinds can be used in combination.

[0058] The compound (Y) containing a reactive double bond is a compound having a reactive group which reacts with the above-mentioned functional group and a reactive double bond. As the reactive group, an isocyanate group, an epoxy group, a carboxyl group, a hydroxyl group, and the like can be exemplified, among which an isocyanate group and an epoxy group are preferred, and an isocyanate group is more preferred.

[0059] Note that the content of the reactive double bond included in the acrylic adhesive layer can be adjusted by the amount of the functional group included in the acrylic polymer (X) and the proportion of the above-mentioned functional group that reacts with the compound (Y) containing a reactive double bond. Furthermore, the amount of the functional group included in the above-mentioned acrylic polymer (X) can be adjusted by the proportion of the functional group-containing monomer used at the time of synthesizing the acrylic polymer (X).

[0060] The acrylic polymer included in the acrylic adhesive layer can be composed of an acrylic polymer containing a reactive double bond, but can also contain an acrylic polymer that does not have a reactive double bond in addition to the acrylic polymer containing a reactive double bond. As the acrylic polymer that does not have a reactive double bond, the above-mentioned acrylic polymer (X) can be exemplified.

[0061] The acrylic adhesive can contain, in addition to the above-mentioned acrylic polymer, components that are generally mixed in adhesives, and can appropriately contain a crosslinking agent, an adhesion improver, a filler, an antioxidant, an ultraviolet inhibitor, a plasticizer, a viscosity modifier, and the like as additives.

[0062] The acrylic adhesive layer can be provided on one surface of the thermally conductive layer, or on both surfaces of the thermally conductive layer. Note that the one surface or both surfaces referred to here are surfaces in the vertical direction along the thickness direction of the thermally conductive layer, and are surfaces also referred to as so-called main surfaces.

[0063] By providing the acrylic adhesive layer on both surfaces of the thermally conductive layer, the adhesion of both surfaces of the thermally conductive sheet to an adherend can be improved. Therefore, in the case where the thermally conductive sheet is used in a semiconductor application, for example, it is possible to adhere to both a semiconductor chip and a heat sink with high adhesion, and furthermore, even when heated at a high temperature in a reflow process or the like in a state where it is adhered to them, it is easy to prevent peeling of the thermally conductive sheet from both the semiconductor chip and the heat sink.

[0064] The amount of the acrylic adhesive layer per surface is, for example, 0.05 mg / cm 2 The above is preferably 0.1 mg / cm 2 The above is more preferably 0.2 mg / cm 2 The above is further preferably 0.3 mg / cm 2 The above, furthermore, is, for example, 1.0 mg / cm 2 The below is preferably 0.75 mg / cm 2 The below is more preferably 0.5 mg / cm 2 The below is further preferably 0.45 mg / cm 2The acrylic adhesive layer is preferably impregnated into the thermally conductive layer. It is preferable that the acrylic adhesive layer be partially impregnated into the thermally conductive layer, but it can be entirely impregnated into the thermally conductive layer as long as the adhesion to the adherend can be exhibited by the acrylic adhesive layer. By being impregnated into the thermally conductive layer, the amount of adhesive present on the surface of the thermally conductive layer can be reduced, and the decrease in thermal conductivity due to the acrylic adhesive layer can be suppressed.

[0065] The acrylic adhesive layer is preferably impregnated into the thermally conductive layer. It is preferable that the acrylic adhesive layer be partially impregnated into the thermally conductive layer, but it can be entirely impregnated into the thermally conductive layer as long as the adhesion to the adherend can be exhibited by the acrylic adhesive layer. By being impregnated into the thermally conductive layer, the amount of adhesive present on the surface of the thermally conductive layer can be reduced, and the decrease in thermal conductivity due to the acrylic adhesive layer can be suppressed.

[0066] Further, the thermally conductive sheet can ensure high adhesion even if the adhesive is impregnated into the thermally conductive layer. The reason is not clear, but it is presumed that the thermally conductive sheet is generally compressed or the like when used, and the adhesive that has been impregnated by this compression is exuded to the surface, thereby improving the adhesion.

[0067] Note that the acrylic adhesive layer is impregnated into the thermally conductive layer by being contained in the bubbles formed by the volatilization of the volatile substance, as described later.

[0068] Further, the acrylic adhesive layer can be formed so as to cover the entirety of each surface of the thermally conductive layer, but it can also be formed so as to cover only a part thereof as long as the adhesion to the adherend can be exhibited.

[0069] Note that the bubbles described above are spaces divided by the high molecular matrix and the thermally conductive filler material in the thermally conductive layer, and are continuous spaces that are the volatilization paths of the volatile substance. By having such continuity, the adhesive can be impregnated into the interior of the thermally conductive layer.

[0070] [Thermally conductive layer]

[0071] The thermally conductive layer of the present application contains a high molecular matrix and a thermally conductive filler material. The high molecular matrix is a matrix formed of an organic high molecule, and is preferably an organic high molecule such as an elastomer or a rubber. It is preferable to use a substance formed by curing a liquid high molecular composition (curable high molecular composition) composed of a main agent and a curing agent or the like. The curable high molecular composition can be composed of, for example, an uncrosslinked rubber and a crosslinking agent, and can contain a monomer, a prepolymer, or the like, and a curing agent or the like. Further, the curing reaction can be a room temperature curing or a heat curing.

[0072] The high molecular matrix is preferably an organic polysiloxane. In the present application, by using an organic polysiloxane, it is possible to make the high molecular matrix after curing soft, and to make the filling property of the thermally conductive filler material good. The organic polysiloxane is preferably silicone rubber. Furthermore, the organic polysiloxane is preferably a curable silicone, and more preferably an addition reaction type silicone.

[0073] In the case of an addition reaction type silicone, the curable high molecular composition is composed of an organic polysiloxane containing an alkenyl group (a main agent) and a hydrogen organic polysiloxane (a curing agent), and the high molecular matrix is a substance obtained by curing them. If an addition reaction type silicone is used, the reactive double bond contained in the acrylic adhesive layer reacts with unreacted hydrogen silyl groups by high temperature heating in a reflow process or the like, and thus it is considered that the adhesion to the adherend is easily improved. In particular, since the organic polysiloxane is a resin also used in the release layer, it has been common sense that the acrylic adhesive does not adhere to silicone. However, unexpectedly, as described above, the acrylic adhesive layer contains a reactive double bond, and if a prescribed heating process is performed, the adhesion is improved.

[0074] As the rubber, various synthetic rubbers can be used in addition to silicone rubber, and in specific examples, for example, acrylic rubber, nitrile rubber, isoprene rubber, urethane rubber, ethylene-propylene rubber, styrene-butadiene rubber, butadiene rubber, fluororubber, butyl rubber, and the like can be given. In the case where these rubbers are used, the synthetic rubber can be crosslinked in the thermally conductive sheet, or can be in an uncrosslinked (i.e., uncured) state. The uncrosslinked rubber is mainly used for flow orientation.

[0075] Furthermore, in the case of being crosslinked (i.e., cured), as described above, the high molecular matrix is a substance obtained by curing a curable high molecular composition composed of an uncrosslinked rubber composed of these synthetic rubbers and a crosslinking agent.

[0076] Furthermore, as the elastomer, a thermoplastic elastomer such as a polyester-based thermoplastic elastomer, a urethane-based thermoplastic elastomer, and the like, a thermosetting elastomer formed by curing a mixed system liquid high molecular composition composed of a main agent and a curing agent can also be used. For example, a urethane-based elastomer formed by curing a high molecular composition containing a high molecule having a hydroxyl group and an isocyanate can be given.

[0077] Further, the polymer composition used for forming the polymer matrix can be composed of only the organic polymer, or can be composed of the organic polymer and a plasticizer. The plasticizer is suitably used in the case of using a synthetic rubber, and by including the plasticizer, it is possible to improve the flexibility of the polymer matrix before crosslinking. For example, in the case where the polymer matrix is an organic polysiloxane, it is preferable to use silicone oil as the plasticizer. That is, the curable polymer composition can be composed of the main agent and the curing agent, or can be composed of the main agent, the curing agent, and the plasticizer.

[0078] The content of the polymer matrix is preferably 15% by volume or more and 50% by volume or less, more preferably 17% by volume or more and 45% by volume or less, and further preferably 20% by volume or more and 40% by volume or less, with respect to the total amount of the thermally conductive sheet, when expressed in terms of the filling rate (volume filling rate) on a volume basis.

[0079] (Thermally conductive filler)

[0080] The thermally conductive filler contained in the thermally conductive layer is preferably dispersed in the polymer matrix and is preferably held in the polymer matrix. As the thermally conductive filler, an anisotropic filler, a non-anisotropic filler, or the like can be given, but it is preferable to use at least an anisotropic filler.

[0081] The anisotropic filler is preferably oriented in the thickness direction of the thermally conductive sheet. By this, the thermally conductive layer is easily improved in thermal conductivity. Note that the anisotropic filler is oriented in the thickness direction even if the long axis direction thereof is not strictly parallel to the thickness direction, and is oriented in the thickness direction even if the long axis direction is inclined with respect to the thickness direction to some extent. Specifically, a substance in which the long axis direction is inclined by less than about 20° is also an anisotropic filler oriented in the thickness direction, and if such an anisotropic filler is the majority (for example, more than 60%, and preferably more than 80%, with respect to the total number of the anisotropic fillers) in the thermally conductive sheet, it is oriented in the thickness direction.

[0082] The content of the thermally conductive filler is preferably 150 parts by mass or more and 3000 parts by mass or less, more preferably 200 parts by mass or more and 1800 parts by mass or less, and further preferably 300 parts by mass or more and 1000 parts by mass or less, with respect to 100 parts by mass of the polymer matrix. By making the content of the thermally conductive filler 150 parts by mass or more, it is possible to impart a certain thermal conductivity to the thermally conductive layer. Further, by being 3000 parts by mass or less, it is possible to appropriately disperse the thermally conductive filler in the polymer matrix. Further, it is also possible to prevent the viscosity of the mixture composition described later from becoming excessively high.

[0083] Further, the volume filling rate of the thermally conductive filler with respect to the total amount of the thermally conductive layer is preferably 30% or more and 85% or less, more preferably 50% or more and 83% or less, and further preferably 60% or more and 80% or less. By making the volume filling rate be the above lower limit value or more, a certain thermal conductivity can be imparted to the thermally conductive layer. Further, by being the upper limit value or less, the manufacture of the thermally conductive layer becomes easy.

[0084] (anisotropic filler)

[0085] The anisotropic filler is a filler having a shape with anisotropy, and is a filler capable of orientation. As the anisotropic filler, a fibrous material, a flaky material, and the like can be given. The anisotropic filler has a high aspect ratio, and specifically, the aspect ratio is more than 2, and the aspect ratio is preferably 5 or more. By making the aspect ratio be more than 2, the anisotropic filler is easily oriented in one direction such as the thickness direction, and the thermal conductivity of the thermally conductive layer in one direction such as the thickness direction is easily improved. Further, the upper limit of the aspect ratio is not particularly limited, but is 100 in practice.

[0086] Note that the aspect ratio is the ratio of the length in the long axis direction of the anisotropic filler to the length in the short axis direction, and in the case of a fibrous material, it refers to the fiber length / diameter of the fiber, and in the case of a flaky material, it refers to the length in the long axis direction / thickness of the flaky material.

[0087] The content of the anisotropic filler in the thermally conductive layer is preferably 10 parts by mass or more and 500 parts by mass or less, more preferably 30 parts by mass or more and 300 parts by mass or less, and further preferably 50 parts by mass or more and 250 parts by mass or less, with respect to 100 parts by mass of the high molecular matrix.

[0088] By making the content of the anisotropic filler be 10 parts by mass or more, the thermal conductivity is easily improved. Further, by being 500 parts by mass or less, the viscosity of the mixture composition described later is easily made appropriate, and the orientation of the anisotropic filler becomes good. Further, the dispersibility of the anisotropic filler in the high molecular matrix also becomes good.

[0089] In the case where the anisotropic filler is a fibrous material, the average fiber length is preferably 10 μm or more and 300 μm or less, more preferably 20 μm or more and 200 μm or less, and further preferably 30 μm or more and 100 μm or less. If the average fiber length is made to be 10 μm or more, in the inside of the thermally conductive layer, the anisotropic fillers appropriately contact each other, the heat transfer path is ensured, and the thermal conductivity of the thermally conductive layer becomes good.

[0090] On the other hand, by making the average fiber length 500 μm or less, the volume of the anisotropic filler material becomes low, and it is possible to highly fill the anisotropic filler material in the adhesive component.

[0091] Further, the average fiber length of the fibrous material is preferably shorter than the thickness of the thermally conductive sheet. By being shorter than the thickness, the fibrous material is prevented from excessively protruding from the surface of the thermally conductive sheet.

[0092] Note that the average fiber length described above can be calculated by observing the anisotropic filler material with a microscope. More specifically, the fiber length of 50 arbitrary anisotropic filler materials is measured using, for example, an electron microscope or an optical microscope, and the average value (arithmetic mean) thereof is set as the average fiber length.

[0093] Further, in the case where the anisotropic filler material is a flaky material, the average particle diameter thereof is preferably 10 μm or more and 300 μm or less, more preferably 15 μm or more and 200 μm or less, and further preferably 20 μm or more and 100 μm or less. By making the average particle diameter 10 μm or more, the anisotropic filler material is easily brought into contact with each other in the thermally conductive layer, the heat transfer path is ensured, and the thermal conductivity of the thermally conductive layer becomes good. On the other hand, if the average particle diameter is made 400 μm or less, the volume of the thermally conductive sheet becomes low, and it is possible to highly fill the anisotropic filler material in the adhesive component.

[0094] Note that the average particle diameter of the flaky filler material is D50, and the length diameter of the flaky filler material can be calculated as the diameter by observing the flaky filler material with a microscope. More specifically, it means that the length diameter of 500 or more arbitrary flaky filler materials is measured using, for example, an electron microscope or an optical microscope, and the particle diameter corresponding to the cumulative frequency of 50% is obtained. Specifically, the flaky filler material can be taken as a sample, and a particle diameter distribution curve in which the horizontal axis is the particle diameter and the vertical axis is the cumulative frequency can be obtained. This particle diameter distribution curve is a number-based particle diameter distribution curve obtained by sequentially cumulating the flaky filler materials from those having a small particle diameter.

[0095] The anisotropic filler material can use a publicly known material having thermal conductivity, and in the case of being oriented by a magnetic field as described later, it is preferable to have good diamagnetism. On the other hand, in the case of being oriented by flow orientation or not being oriented, it can not have diamagnetism.

[0096] As specific examples of the anisotropic filler material, there are carbon-based materials typified by carbon fibers or flaky carbon powders, metal materials typified by metal fibers, metal oxides, boron nitride, metal nitrides, metal carbides, metal hydroxides, poly-p-phenylene benzobisoxazole fibers, and the like. carbon fibers, graphite fibers, aramid fibers, polyethylene fibers, polypropylene fibers, polytetrafluoroethylene fibers, polyimide fibers, polyamide fibers, polybenzazole fibers, etc. Among them, carbon-based materials are preferred because of their small specific gravity and good dispersibility in the adhesive component, and more preferably, graphitized carbon materials having a high thermal conductivity. Graphitized carbon materials have a consistent alignment of graphite planes in a prescribed direction, and thus have a diamagnetic property.

[0097] Further, as the anisotropic filler material, boron nitride is also preferred. The boron nitride is not particularly limited, and is preferably used as a flaky material. The flaky boron nitride can or can not be agglomerated, but is preferably partially or entirely unagglomerated. Note that boron nitride and the like also have a consistent alignment of crystal planes in a prescribed direction, and thus have a diamagnetic property.

[0098] Further, the thermal conductivity of the anisotropic filler material in the direction having anisotropy (i.e., the long axis direction) is not particularly limited, but is generally 30 W / m-K or more, preferably 60 W / m-K or more, more preferably 100 W / m-K or more, and further preferably 200 W / m-K or more. The upper limit of the thermal conductivity of the anisotropic filler material is not particularly limited, and is, for example, 2000 W / m-K or less. The thermal conductivity can be measured by a laser flash method or the like.

[0099] The anisotropic filler material can be used alone or two or more can be used in combination. For example, as the anisotropic filler material, at least two anisotropic filler materials having different average particle diameters or average fiber lengths from each other can be used. It is believed that if anisotropic filler materials of different sizes are used, the smaller anisotropic filler material enters between the relatively larger anisotropic filler materials, and thus the anisotropic filler material can be densely filled in the adhesive component, and the conduction efficiency of heat can be improved.

[0100] Further, among the above, the anisotropic filler material preferably contains a fibrous material. A thermal conductive layer containing a fibrous material has a tendency to have a reduced adhesion due to the formation of unevenness on the surface by slicing and the shedding of the fibrous material, but in the present application, the adhesion can be sufficiently improved by providing the acrylic adhesive layer, and thus the acrylic adhesive layer enters the recesses.

[0101] Further, from the viewpoint of good thermal conductivity, the thermal conductive layer preferably contains a flaky material as the anisotropic filler material in addition to the fibrous material. In this case, the content ratio of the flaky material to the fibrous material (flaky material / fibrous material) is, for example, 0.01 or more and 1 or less, preferably 0.02 or more and 0.5 or less, and more preferably 0.1 or more and 0.3 or less, on a mass basis.

[0102] The carbon fiber used as the anisotropic filler is preferably graphitized carbon fiber. Further, as the flaky carbon powder, flaky graphite powder is preferred. As the anisotropic filler, it is also preferred to use graphitized carbon fiber in combination with flaky graphite powder.

[0103] The crystal planes of the graphite of the graphitized carbon fiber are connected in the fiber axis direction, and the graphitized carbon fiber has high thermal conductivity in the fiber axis direction. Therefore, by aligning the fiber axis direction in a prescribed direction, the thermal conductivity in a specific direction can be increased. Further, the crystal planes of the graphite of the flaky graphite powder are connected in the in-plane direction of the flaky plane, and the flaky graphite powder has high thermal conductivity in the in-plane direction. Therefore, by aligning the flaky plane in a prescribed direction, the thermal conductivity in a specific direction can be increased. The graphitized carbon fiber and the flaky graphite powder preferably have high graphitization degree.

[0104] As the graphitized carbon material such as the above-described graphitized carbon fiber, flaky graphite powder, a substance obtained by graphitizing the following raw material can be used. For example, condensed polycyclic hydrocarbon compounds such as naphthalene, condensed heterocyclic compounds such as PAN (polyacrylonitrile), pitch, and the like can be mentioned, and graphitized mesophase pitch, polyimide, polybenzazole having high graphitization degree are particularly preferred. By using, for example, mesophase pitch, in the following spinning process, the pitch is oriented in the fiber axis direction by its anisotropy, and a graphitized carbon fiber having excellent thermal conductivity in the fiber axis direction can be obtained.

[0105] As for the use form of the mesophase pitch in the graphitized carbon fiber, there is no particular limitation as long as it can be spun, and the mesophase pitch can be used alone or in combination with other raw materials. However, the graphitized carbon fiber in which the mesophase pitch is used alone, that is, the content of the mesophase pitch is 100%, is most preferred in terms of high thermal conductivity, spinnability, and stability of quality.

[0106] The graphitized carbon fiber can use a substance obtained by sequentially performing spinning, infusibilization, and carbonization, and pulverizing or cutting to a prescribed particle diameter, and then graphitizing, or a substance obtained by pulverizing or cutting after carbonization, and then graphitizing. In the case of pulverizing or cutting before graphitization, the surface newly exposed to the surface by pulverization easily undergoes polycondensation reaction and cyclization reaction at the time of graphitization treatment, and thus the graphitization degree can be increased, and a graphitized carbon fiber in which the thermal conductivity is further increased can be obtained. On the other hand, in the case of pulverizing after graphitizing the carbon fiber obtained by spinning, the graphitized carbon fiber is hard and thus is easily pulverized, and by pulverizing for a short time, a carbon fiber powder having a narrow fiber length distribution can be obtained.

[0107] The average fiber length of the graphitized carbon fiber is preferably 10 μm or more and 300 μm or less, more preferably 20 μm or more and 200 μm or less, and further preferably 30 μm or more and 100 μm or less, as described above. In addition, the aspect ratio of the graphitized carbon fiber is preferably 5 or more, as described above. The thermal conductivity of the graphitized carbon fiber is not particularly limited, and the thermal conductivity in the fiber axis direction is preferably 400 W / m-K or more, and more preferably 800 W / m-K or more.

[0108] The thermally conductive layer can or can not expose the anisotropic filler material on the surface of the thermally conductive layer, but is preferably exposed. By exposing the anisotropic filler material, the anisotropic filler material comes into contact with the adherend such as a heat generating body or a heat dissipating body, and thus it is easy to make the thermal resistance low. In addition, if the anisotropic filler material is exposed, the adhesion to the adherend is not easily improved, but even in such a case, in the present application, it is easy to improve the adhesion by providing the acrylic adhesive layer.

[0109] (non-anisotropic filler material)

[0110] The thermally conductive filler material in the present application can also contain a non-anisotropic filler material, and it is preferable to use the above-described anisotropic filler material in combination with the non-anisotropic filler material.

[0111] The non-anisotropic filler material is particularly used in combination with the anisotropic filler material oriented in one direction such as the thickness direction, and thus the gap between the oriented anisotropic filler materials can make the thermal conductivity higher. The non-anisotropic filler material is a filler material whose shape is substantially not anisotropic, and is a filler material that does not orient in a prescribed direction even in an environment in which the anisotropic filler material is oriented in the prescribed direction due to the generation of a magnetic force line or the application of a shear force, or the like.

[0112] The aspect ratio of the non-anisotropic filler material is 2 or less, and is preferably 1.5 or less. Such a non-anisotropic filler material having a low aspect ratio is easily arranged in the gap of the anisotropic filler material when used in combination with the anisotropic filler material, and thus it is easy to make the thermal conductivity high. In addition, by making the aspect ratio 2 or less, the viscosity of the mixed composition described later is prevented from increasing, and high filling is possible.

[0113] Specific examples of the non-anisotropic filler material can be, for example, metals, metal oxides, metal nitrides, metal hydroxides, carbon materials, oxides, nitrides, and carbides other than metals, and the like. In addition, the shape of the non-anisotropic filler material can be, for example, spherical, polyhedral, amorphous powder, and the like.

[0114] Among the non-anisotropic filler materials, as the metal, aluminum, copper, nickel, etc. can be exemplified, as the metal oxide, alumina represented by aluminum trioxide, magnesium oxide, zinc oxide, etc. can be exemplified, as the metal nitride, aluminum nitride, etc. can be exemplified. As the metal hydroxide, aluminum hydroxide can be exemplified. Further, as the carbon material, spheroidal graphite, etc. can be exemplified. As the oxide, nitride, carbide other than the metal, quartz, boron nitride, silicon carbide, etc. can be exemplified.

[0115] Among them, alumina, aluminum are preferable in that the thermal conductivity is high and spheroidal materials are easily obtained.

[0116] The non-anisotropic filler material can use one of the above materials alone, or two or more of them in combination.

[0117] The average particle diameter of the non-anisotropic filler material is, for example, 0.1 μm or more and 200 μm or less, preferably 0.5 μm or more and 100 μm or less, more preferably 1 μm or more and 70 μm or less.

[0118] Further, in the case where the non-anisotropic filler material is used in combination with the anisotropic filler material, the average particle diameter of the non-anisotropic filler material is preferably 0.1 μm or more and 50 μm or less, more preferably 0.5 μm or more and 35 μm or less, further preferably 1 μm or more and 15 μm or less. By making the average particle diameter 50 μm or less, even when used in combination with the anisotropic filler material, the adverse conditions such as disordering of the orientation of the anisotropic filler material do not easily occur. Further, by making the average particle diameter 0.1 μm or more, the specific surface area of the non-anisotropic filler material does not become excessively large, even when a large amount of the non-anisotropic filler material is mixed, the viscosity of the mixed composition does not easily increase, and it is easy to highly fill the non-anisotropic filler material.

[0119] The non-anisotropic filler material can use, for example, at least two non-anisotropic filler materials having mutually different average particle diameters as the non-anisotropic filler material.

[0120] Note that the average particle diameter of the non-anisotropic filler material can be measured by observation with an electron microscope or the like. More specifically, using, for example, an electron microscope, an optical microscope, the particle diameters of 500 or more of the arbitrary non-anisotropic filler material are measured, and D50 is preferably obtained by the same method as the flaky filler material.

[0121] The content of the non-anisotropic filler material is preferably 50 parts by mass or more and 2500 parts by mass or less, more preferably 100 parts by mass or more and 1500 parts by mass or less, and further preferably 200 parts by mass or more and 750 parts by mass or less, relative to 100 parts by mass of the polymer matrix. By being 50 parts by mass or more, the thermal conductivity of the thermal conductive sheet can be made good. On the other hand, by being 1500 parts by mass or less, the non-anisotropic filler material is appropriately dispersed in the adhesive component, and an effect of improving the thermal conductivity corresponding to the content can be obtained. In addition, it is also possible to prevent the viscosity of the mixed composition from excessively rising.

[0122] The content of the non-anisotropic filler material is preferably 50 parts by mass or more and 2500 parts by mass or less, more preferably 100 parts by mass or more and 1500 parts by mass or less, and further preferably 200 parts by mass or more and 750 parts by mass or less, relative to 100 parts by mass of the polymer matrix. By being 50 parts by mass or more, the thermal conductivity of the thermal conductive sheet can be made good. On the other hand, by being 1500 parts by mass or less, the non-anisotropic filler material is appropriately dispersed in the adhesive component, and an effect of improving the thermal conductivity corresponding to the content can be obtained. In addition, it is also possible to prevent the viscosity of the mixed composition from excessively rising.

[0123] In the thermal conductive layer, a component other than the above can be further mixed in the polymer matrix within a range that does not impair the function as a thermal conductive layer. Specifically, at least one or more selected from among a dispersing agent, a flame retardant, an antioxidant, a coloring agent, a settlement preventing agent, and the like can be mentioned. In addition, in the case of crosslinking, curing, or the like of the curable polymer composition as described above, a crosslinking accelerator, a curing accelerator, a curing catalyst, or the like that promotes crosslinking, curing, or the like can be mixed as an additive. In the case where the polymer matrix is an organic polysiloxane, a platinum catalyst can be used as the curing catalyst.

[0124] The surface of the thermal conductive layer is preferably a sliced surface. By being a sliced surface, the anisotropic filler material or the like is easily exposed to the surface of the thermal conductive layer as described above, and the thermal resistance value can be effectively reduced. The thermal conductive sheet can have one surface as a sliced surface, or both surfaces as sliced surfaces, but it is preferable that the surface on which the acrylic adhesive layer is provided be a sliced surface. Note that the sliced surface is a surface formed by cutting with a cutting knife, laser, or the like, as described later.

[0125] The sliced surface is often in a state where the protrusions and the like of the anisotropic filler material are large in concave-convex. However, by filling the concave portions with the acrylic adhesive layer, it is possible to reduce the air layer at the time of use, and it is possible to improve the adhesion while improving the thermal resistance value.

[0126] Further, the surface of the thermally conductive sheet is preferably a ground surface. By making at least one surface of the thermally conductive sheet a ground surface, the thermal resistance value can be more effectively reduced. The thermally conductive sheet can have one surface as a ground surface, or both surfaces as ground surfaces, but it is preferable that the surface on which the acrylic adhesive layer is provided be a ground surface, and it is particularly preferable that the surface on which the acrylic adhesive layer is provided be a cut surface and a ground surface. A ground surface has a relatively high smoothness, and thus the adhesion to the adherend can be easily improved in combination with the acrylic adhesive layer.

[0127] The thickness of the thermally conductive layer is not particularly limited, and is, for example, about 1200 μm or less, but from the viewpoint of being able to be suitably used in semiconductor applications and the viewpoint of preventing the thermal resistance value from increasing, it is preferable that the thickness be thin, and the thickness is preferably 500 μm or less, more preferably 300 μm or less, and further preferably 200 μm or less. Further, the thickness of the thermally conductive layer is not particularly limited, but is, for example, 10 μm or more in practical use, and is preferably 20 μm or more, and more preferably 70 μm or more. Note that the thickness of the thermally conductive layer refers to the initial thickness measured in a state in which no load is applied in the thickness direction.

[0128] (Arithmetic Mean Height (Sa))

[0129] The arithmetic mean height (Sa) of the surface of the thermally conductive sheet on which the acrylic adhesive layer is provided is, for example, 20 μm or less, preferably 12 μm or less, more preferably 6 μm or less, and further preferably 5 μm or less. By making the arithmetic mean height of the surface on which the acrylic adhesive layer is provided low, the thermal resistance value can be more effectively reduced. Further, by the acrylic adhesive layer, the adhesion to the adherend can be more effectively improved. Note that the arithmetic mean height of the surface of the thermally conductive sheet is easily relatively large if the surface is a cut surface as described above, but by performing grinding after cutting, the arithmetic mean height (Sa) can be made low as described above.

[0130] The arithmetic mean height (Sa) of the surface of the thermally conductive sheet on which the acrylic adhesive layer is provided is not particularly limited, and is preferably 0.5 μm or more, more preferably 1 μm or more, and further preferably 2 μm or more. By being 0.5 μm or more, 1 μm or more, or 2 μm or more, the arithmetic mean height (Sa) can be easily obtained by performing grinding even if the surface is a cut surface.

[0131] (E hardness)

[0132] The heat conductive layer of the present application preferably has an E-type hardness (hereinafter, also referred to as "E hardness") of 10 or more and 80 or less, more preferably 20 or more and 70 or less, and further preferably 30 or more and 65 or less, as defined in JIS K6253. If the E hardness is the above lower limit value or more, the mechanical strength of the heat conductive sheet is easily improved. In addition, if the E hardness is the above upper limit value or less, the heat conductive sheet is imparted with a certain softness, and the adhesion to the adherend is also easily improved.

[0133] (Thermal resistance value of the heat conductive sheet)

[0134] The thermal resistance value of the heat conductive sheet of the present application is, for example, 0.5°C-cm 2 or less, preferably 0.25°C-cm 2 or less, more preferably 0.2°C-cm 2 or less, further preferably 0.16°C-cm 2 or less. If the thermal resistance value is the above upper limit value or less, the efficiency of the heat transfer from the heat generating body to the heat radiating body via the heat conductive sheet is improved, and an excellent heat conductivity can be obtained. In the present application, the lower the thermal resistance value is, the better, and it is only necessary to be 0°C-cm 2 or more, but in practice, for example, 0.01°C-cm 2 or more, preferably 0.05°C-cm 2 or more.

[0135] Note that the thermal resistance value is a value measured when a pressure of 20 psi (138 kPa) is applied in the thickness direction, and specifically, it can be obtained by the measurement method described in the examples.

[0136] [Method for producing the heat conductive sheet]

[0137] The heat conductive sheet of the present application can be produced by a method having at least the following steps 1 to 3. However, the heat conductive sheet of the present application can also be produced by a method other than the following production method.

[0138] Step 1: a step of obtaining a mixed composition by mixing at least a curable polymer composition and a heat conductive filler

[0139] Step 2: a step of obtaining a cured product by curing the above mixed composition by heating

[0140] Step 3: a step of applying an adhesive to the surface of the above cured product

[0141] In addition, in the present application, it is preferable to have the following step 4.

[0142] Step 4: a step of allowing the above applied adhesive to penetrate into the above cured product

[0143] (Step 1)

[0144] In Step 1, it is preferable to mix at least the curable high-molecular composition and the thermally conductive filler to obtain a mixed composition, but it is more preferable to further mix a volatile substance in the mixed composition. In addition, other components such as an additive, which is compounded as needed, can also be appropriately added to the mixed composition.

[0145] In Step 1, as long as the above components can be mixed to obtain a mixed composition, the mixing method and the mixing order are not particularly limited, and it is preferable to appropriately mix the curable high-molecular composition, the thermally conductive filler, the volatile substance, which is added as needed, and other components, which are optionally added, in an arbitrary order to obtain a mixed composition.

[0146] The curable high-molecular composition is preferably composed of a main agent and a curing agent (for example, for an addition reaction type silicone, an alkyl group-containing organopolysiloxane and a hydride organopolysiloxane) as described above, and in that case, it is preferable to mix the main agent, the curing agent, the thermally conductive filler, the volatile substance, which is optionally added as needed, and other components in an arbitrary order to obtain a mixed composition.

[0147] Note that the form of the mixed composition can be a single component type or a two component type in which a first agent and a second agent are combined. The two component type is a substance in which the first agent and the second agent are mixed to obtain a mixed composition at the time of use.

[0148] (Volatile substance)

[0149] The volatile substance used in the present application is only a component that volatilizes in Step 2 described later. The volatile substance volatilizes by heating at the time of curing, and thus the content ratio of the thermally conductive filler in the thermally conductive sheet can be made large. In addition, the mixed composition has a reduced viscosity by containing the volatile substance. Therefore, it is easy to make the compounding amount of the thermally conductive filler large, and further, it is easy to orient the anisotropic filler in a prescribed direction by the magnetic field orientation described later or the like.

[0150] Further, by volatilization of the volatile substance, fine bubbles are formed in a large amount in the cured product, and thus the adhesive easily penetrates into the inside of the thermally conductive layer in Step 4 described later.

[0151] In addition, the volatile substance is preferably a compatible substance that is compatible or dissolved in the curable high-molecular composition. If the volatile substance is a compatible substance, the curable high-molecular composition and the volatile substance can be uniformly mixed, and thus it is easy to reduce the viscosity or make the compounding amount of the thermally conductive filler large. Further, it is also possible to make the bubbles that are formed by volatilization of the volatile substance fine and uniform.

[0152] The volatile substance is preferably a substance that is liquid at normal temperature (25°C) and 1 atm.

[0153] As the volatile substance, an alkoxysilane compound, a hydrocarbon-based solvent, an alkoxysiloxane compound, or the like can be given. These compounds are easy to reduce the viscosity of the mixed composition or increase the amount of the thermally conductive filler to be mixed, because they can increase the solubility or compatibility in the curable polymer composition. In addition, the bubbles formed are easy to be fine and uniform by the volatilization of the volatile substance.

[0154] The volatile substance can be used alone or in combination of two or more.

[0155] As the volatile substance, an alkoxysilane compound is preferably used. By using an alkoxysilane compound, the appearance of the thermally conductive sheet obtained by curing becomes good because roughness or the like is not observed on the surface of the thermally conductive sheet.

[0156] The alkoxysilane compound used as the volatile substance is a compound having a structure in which one to three of the four bonds of a silicon atom (Si) are combined with an alkoxy group, and the remaining bonds are combined with an organic substituent. The alkoxysilane compound can improve the compatibility with the curable polymer composition composed of the curable polymer composition and, in particular, the organopolysiloxane, by having an alkoxy group and an organic substituent.

[0157] As the alkoxy group of the alkoxysilane compound, a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentoxy group, and a hexyloxy group, for example, can be given. The alkoxysilane compound can be contained as a dimer in the curable polymer composition.

[0158] Among the alkoxysilane compounds, from the viewpoint of ease of obtaining, an alkoxysilane compound having at least one of a methoxy group and an ethoxy group is preferable. From the viewpoint of the compatibility, solubility, or the like with the curable polymer composition, the number of the alkoxy groups of the alkoxysilane compound is preferably two or three, and more preferably three. The alkoxysilane compound is specifically preferably at least one selected from a trimethoxysilane compound, a triethoxysilane compound, a dimethoxysilane compound, and a diethoxysilane compound.

[0159] As the functional group included in the organic substituent of the alkoxysilane compound, there can be mentioned, for example, acryl group, alkyl group, carboxyl group, vinyl group, methacryl group, aromatic group, amino group, isocyanate group, isocyanurate group, epoxy group, hydroxyl group, and mercapto group. Here, in the case where a platinum catalyst is used as the curing catalyst of the curable high molecular composition constituted by the organopolysiloxane, it is preferable to select an alkoxysilane compound which does not easily cause an influence on the curing reaction of the organopolysiloxane. Specifically, in the case where an addition reaction type organopolysiloxane utilizing a platinum catalyst is used, the organic substituent of the alkoxysilane compound preferably does not include amino group, isocyanate group, isocyanurate group, hydroxyl group, or mercapto group.

[0160] From the viewpoint of the compatibility with the curable high molecular composition constituted by the organopolysiloxane, the alkoxysilane compound preferably includes an alkylalkoxysilane compound having an alkyl group bonded to a silicon atom, that is, an alkoxysilane compound having an alkyl group as the organic substituent. Therefore, a dialkyldialkoxysilane compound, an alkyltrialkoxysilane compound are preferable, with the alkyltrialkoxysilane compound being more preferable.

[0161] The number of carbon atoms of the alkyl group bonded to the silicon atom is, for example, preferably from 1 to 16. Further, in the case of a trialkoxysilane compound such as a trimethoxysilane compound, a triethoxysilane compound, the number of carbon atoms of the above-mentioned alkyl group is preferably 6 or more, further preferably 8 or more, and further, the number of carbon atoms is preferably 12 or less, more preferably 10 or less.

[0162] On the other hand, in the case of a dialkoxysilane compound such as a dimethoxysilane compound, a triethoxysilane compound, the number of carbon atoms of the above-mentioned alkyl group can be 1 or more, and further, the number of carbon atoms is preferably 10 or less, more preferably 6 or less, further preferably 4 or less.

[0163] As the alkoxysilane compound having an alkyl group, there can be mentioned, for example, methyltrimethoxysilane, dimethyldimethoxysilane, diethyldimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, di-n-propyldimethoxysilane, di-n-propyldiethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, methylcyclohexyldimethoxysilane, methylcyclohexyldiethoxysilane, n-octyltrimethoxysilane, n-octyltriethoxysilane, n-decyltrimethoxysilane, n-decyltriethoxysilane, and the like.

[0164] Among the alkyl group-containing alkoxysilane compounds, further more preferably from the viewpoint of compatibility with the organopolysiloxane constituting the curable polymer composition, n-decyltrimethoxysilane, n-octyltriethoxysilane.

[0165] The alkoxysiloxane compound used as the volatile substance has a structure in which two or more siloxane bonds and an alkoxyl group are bonded to at least one silicon atom. The alkoxysiloxane compound has a structure in which an organic substituent is bonded to at least one silicon atom constituting the siloxane bond. The alkoxysiloxane compound, by having an alkoxyl group and an organic substituent, can improve the compatibility with the organopolysiloxane constituting the curable polymer composition.

[0166] As the alkoxyl group and the organic substituent possessed by the alkoxysiloxane compound, the groups exemplified in the above description of the alkoxysilane compound can be given, and from the viewpoint of compatibility with the organopolysiloxane constituting the curable polymer composition, at least an alkyl group is preferable.

[0167] As the alkoxysiloxane compound, for example, methylmethoxysiloxane oligomer, methylphenylmethoxysiloxane oligomer, methylglycidoxy-methoxysiloxane oligomer, methylmercapto-methoxysiloxane oligomer, and methylacryloyl-methoxysiloxane oligomer can be given.

[0168] The alkoxysiloxane compound can be used singly or two or more kinds.

[0169] As the hydrocarbon-based solvent used as the volatile substance, an aromatic hydrocarbon-based solvent can be given. Among these, from the viewpoint of compatibility with the curable polymer composition, an aromatic hydrocarbon-based solvent is preferable. As the aromatic hydrocarbon-based solvent, an aromatic hydrocarbon-based solvent having a carbon number of about 6 to 10 can be given, and for example, toluene, xylene, mesitylene, ethylbenzene, propylbenzene, butylbenzene, t-butylbenzene, and the like can be given, and toluene, xylene, and the like are preferable.

[0170] In the mixed composition, the content of the volatile substance with respect to 100 parts by mass of the curable polymer composition is preferably 6 parts by mass or more and 60 parts by mass or less. If it is 6 parts by mass or more, it is easy to exert the effect of containing the volatile substance, and for example, a moderate amount of fine bubbles can be formed in the polymer matrix. Further, by being 60 parts by mass or less, an effect commensurate with the use amount of the volatile substance can be obtained. From these viewpoints, the above content of the volatile substance is more preferably 8 parts by mass or more and 50 parts by mass or less, and further preferably 10 parts by mass or more and 35 parts by mass or less.

[0171] Note that the volatile substance is preferably volatilized partially or entirely by the heating of Step 2. Thus, the volatile substance can also not be contained in the thermally conductive sheet, or can be contained in the thermally conductive sheet in an amount less than the content in the mixed composition.

[0172] Note that the detailed description of the components other than the volatile substance in the mixed composition (i.e., the curable polymer composition, the thermally conductive filler, other additives, etc.) is as described above. Further, the content of the thermally conductive filler in the mixed composition is also as described above. However, in the above, the content of each component is shown as an amount based on 100 parts by mass of the polymer matrix, but in the mixed composition, it is an amount based on 100 parts by mass of the curable polymer composition.

[0173] (Step 2)

[0174] Step 2 is a step of curing the mixed composition by heating. The temperature at the time of heating the mixed composition is not particularly limited as long as the curable polymer composition can be cured by heating, and is preferably a temperature higher than room temperature (25°C), more preferably a temperature of 50°C or higher, and even more preferably a temperature of 70°C or higher. Further, the heating temperature is not particularly limited, but is a temperature at which the thermally conductive layer and the mixed composition do not deteriorate by heat, for example, 200°C or lower, preferably 180°C or lower, and more preferably 160°C or lower. Further, the heating can be performed in one stage, or can be performed in two or more stages. In the case of being performed in two or more stages, the heating temperature in at least any one of the stages can be within the above range, but the heating temperature in all of the stages is preferably within the above range, and further preferably the heating in at least the first stage is performed at a temperature lower than the boiling point of the volatile compound. Further, the heating time is, for example, 10 minutes or more and 24 hours or less. In the case of being performed in two or more stages, it is preferable that the mixed composition be semi-cured in the first stage (primary curing), and the mixed composition be completely cured by the heating after the second stage (secondary curing). Further, the curing can be complete curing by the primary curing, and the heating after the second stage does not accompany the curing.

[0175] As described later, in the case where the molded body obtained from the mixed composition is sliced to produce a sheet-shaped molded body, it is also preferable that the primary curing be performed by the heating in the first stage before the slicing, and the heating in the second stage (secondary curing) be further performed after the slicing. By heating after the slicing, the volatile substance is easily volatilized by the heating after the second stage.

[0176] In the case where curing is performed in two or more stages, the heating in the first stage (primary curing) is preferably performed at 50°C or higher and 120°C or lower, more preferably at 60°C or higher and 100°C or lower, and even more preferably at 70°C or higher and 90°C or lower. Further, the heating in the second stage or later (secondary curing) is preferably performed at a temperature higher than the temperature of the primary curing, for example, at 100°C or higher and 200°C or lower, more preferably at 120°C or higher and 180°C or lower, and even more preferably at 140°C or higher and 160°C or lower. Note that the heating time in the first stage is preferably 5 minutes or longer and 20 hours or shorter, and more preferably 30 minutes or longer and 12 hours or shorter. Further, the heating time in the second stage or later is, for example, 10 minutes or longer and 15 hours or shorter, and more preferably 1 hour or longer and 10 hours or shorter.

[0177] By performing the heating in the first stage at a low temperature as described above, the volatile compound is less likely to foam to generate large bubbles, and the molded body can be cured with the volatile compound remaining in the molded body.

[0178] Further, if the heating in the second stage is performed at a high temperature after the molded body is sliced, the molded body is cured and thus does not foam to generate large bubbles even at a high temperature, and the space in which the volatile compound exists becomes fine bubbles. The size of the bubbles is, for example, 1 μm or less, and more preferably 0.2 μm or less. Further, the lower limit of the size of the bubbles is not particularly limited, and is, for example, 0.001 μm or more.

[0179] In the process 2, the mixed composition is molded into a prescribed shape such as a block or a sheet, and is heated to be cured. Further, in the process 2, in the case where the mixed composition contains an anisotropic filler material as a thermally conductive filler material, the anisotropic filler material is oriented in one direction and is heated to be cured. The anisotropic filler material can be oriented by a magnetic field orientation method or a flow orientation method, but is preferably oriented by the magnetic field orientation method.

[0180] In the magnetic field orientation method, the mixed composition is injected into the inside of a mold or the like, and is placed in a magnetic field to orient the anisotropic filler material in the direction of the magnetic field. Further, the cured high-molecular composition is cured to obtain an oriented molded body. The curing of the mixed composition is performed by the heating conditions as described above.

[0181] The oriented molded body is preferably a block, but can be a sheet. By being a sheet, the oriented molded body can be coated with an adhesive without being sliced in the process 3. On the other hand, by being a block, the orientation of the anisotropic filler material is improved.

[0182] For the magnetic field orientation method, a release film can be arranged inside the mold at a portion that comes into contact with the mixed composition. The release film uses, for example, a resin film having good release properties, a resin film that has been subjected to release treatment on one side with a release agent, or the like. By using the release film, the oriented molded body is easily released from the mold.

[0183] For the magnetic field orientation, the viscosity of the mixed composition used in the magnetic field orientation method is preferably 10 Pa-s or more and 300 Pa-s or less. By being 10 Pa-s or more, the thermally conductive filler material is less likely to settle. Further, by being 300 Pa-s or less, the flowability becomes good, the anisotropic filler material is appropriately oriented in the magnetic field, and no adverse conditions occur in which orientation takes too much time. Note that the viscosity is the viscosity measured at 25°C at a rotation speed of 10 rpm using a rotational viscometer (Brookfield viscometer DV-E, rotor SC4-14).

[0184] However, in the case of using a thermally conductive filler material that is difficult to settle, or a combination of an additive such as a settlement preventing agent, the viscosity of the mixed composition can be less than 10 Pa-s.

[0185] In the magnetic field orientation method, as a source of magnetic field lines for applying a magnetic force line, a superconducting magnet, a permanent magnet, an electromagnet, or the like can be given, and a superconducting magnet is preferable in terms of being able to generate a high magnetic flux density. The magnetic flux density of the magnetic field generated from these sources of magnetic field lines is preferably 1 to 30 tesla. If the magnetic flux density is 1 tesla or more, the above-described anisotropic filler material composed of a carbon material or the like can be easily oriented. Further, by being 30 tesla or less, practical production can be achieved.

[0186] For the flow orientation method, a shear force is applied to the mixed composition, and a primary sheet in which the anisotropic filler material is oriented in the plane direction is produced. More specifically, for the flow orientation method, first, the mixed composition prepared in Step 1 is elongated flat while being given a shear force, and is molded into a sheet shape (primary sheet). By applying a shear force, the anisotropic filler material can be oriented in the shear direction. As a means of molding the sheet, for example, the mixed composition is coated on a base film by a bar coater, a coater for coating such as a doctor blade, or extrusion molding, discharge from a nozzle, or the like, and then, if necessary, drying is performed, or the mixed composition is semi-cured or fully cured. The thickness of the primary sheet is preferably 50 μm or more and 5000 μm or less or thereabouts. In the primary sheet, the anisotropic filler material is oriented in one direction along the plane direction of the sheet.

[0187] The mixed composition used in the flow orientation method is of a relatively high viscosity so that a shear force is applied when it is elongated into a sheet shape. The viscosity of the mixed composition is specifically preferably 3 Pa-s or more and 500 Pa-s or less.

[0188] The primary sheet can be used as a thermally conductive sheet without forming a block as described below. Alternatively, the primary sheets can be stacked in a manner that the orientation directions are the same, and then cured by heating as needed, and the primary sheets can be adhered to each other by heat pressing or the like to form a stacked block (a block-shaped orientation-molded body).

[0189] Alternatively, in the case of forming a stacked block, vacuum ultraviolet rays can be irradiated to at least one of the surfaces of the primary sheets that are overlaid on each other, and then the primary sheets can be overlaid. If the primary sheets are overlaid via the surfaces irradiated with the vacuum ultraviolet rays, the primary sheets can be firmly adhered to each other. Alternatively, in the case of irradiating vacuum ultraviolet rays, the mixed composition can be completely cured when the primary sheets are produced, and it is not necessary to cure the primary sheets by heating or the like when the primary sheets are overlaid to form a stacked block.

[0190] For the flow orientation method, the curing of the mixed composition is preferably performed by the heating conditions as described above.

[0191] As described above, in the case of forming a block-shaped orientation-molded body, it is preferable to cut the obtained orientation-molded body in a direction perpendicular to the direction in which the orientation-molded body is oriented with respect to the anisotropic filler material, and to produce a sheet-shaped molded body. The cutting is preferably performed by slicing or the like using a cutting knife, a laser, or the like. The sheet-shaped molded body can have a part of the fibrous filler material exposed from the matrix in each surface as a cutting surface by the cutting by slicing or the like. The exposed fibrous filler material is hardly collapsed and oriented in the thickness direction.

[0192] However, in Step 2, the fibrous filler material contained in the orientation-molded body can be cut by the cutting of the orientation-molded body by slicing or the like without impairing the effects of the present application.

[0193] The sheet-shaped molded body obtained by the cutting can be directly coated with an adhesive in Step 3 described below, or can be further subjected to other treatments. For example, each surface as a cutting surface can be polished. Alternatively, as described above, secondary curing can be performed. Note that the secondary curing can be performed after the polishing, or can be performed before the polishing.

[0194] The sheet-shaped molded body is polished, and thus the surface state of the sheet-shaped molded body becomes better, and it is easy to further reduce the thermal resistance value. The sheet-shaped molded body is polished, and thus it is possible to smooth the sheet surface in a state in which a certain amount of fibrous filler material or the like anisotropic filler material is exposed to the surface. Alternatively, it is also possible to make the fibrous filler material be in a collapsed state or the like. Thus, it is easy to adhere the surface of the thermally conductive sheet to another member, and it is easy to make the surface of the sheet be covered with the fibrous filler material over a certain area, and it is easy to reduce the thermal resistance value.

[0195] As for polishing, it is good to polish at least one surface of the obtained sheet-shaped molded body, but it is preferable to polish both surfaces of the sheet-shaped molded body. The polishing of the surface is preferably performed using, for example, a polishing paper, a polishing film, a polishing cloth, a polishing tape, or the like.

[0196] As the properties of the polishing paper, the average particle diameter (D50) of the abrasive grains contained is preferably 0.1 μm or more and 100 μm or less, and more preferably 1 μm or more and 60 μm or less. Furthermore, as the particle size of the abrasive grains of the polishing paper, it is preferably 120 to 20,000, and more preferably 300 to 15,000.

[0197] The polishing method can be a method in which, in addition to continuously abutting the polishing paper in the same linear direction with respect to the surface of the sheet-shaped molded body, the polishing is performed by reciprocating a certain distance, or by rotating in the same direction, or by abutting in various directions.

[0198] Furthermore, as for the degree of polishing, for example, it is performed while observing the surface state, and in the case of reciprocating polishing, it is preferably 1 or more and 300 or less times of reciprocation, and more preferably 2 or more and 200 or less times of reciprocation, and further preferably 3 or more and 50 or less times of reciprocation.

[0199] The polishing of the surface of the sheet-shaped molded body can be performed in two polishing steps. For example, after the first polishing using a polishing paper having a large average particle diameter of abrasive grains, the second polishing using a polishing paper having a small average particle diameter of abrasive grains compared to the first polishing is good.

[0200] (Step 3)

[0201] In Step 3, an adhesive is applied to the surface of the cured product such as the sheet-shaped molded body obtained in Step 2 as described above. In the present application, as the adhesive to be applied, it is good to use an acrylic adhesive having a reactive double bond as described above.

[0202] Furthermore, in the present production method, in Step 4, it is preferable that the adhesive penetrates into the thermally conductive layer, and it is preferable that the adhesive penetrates into the inside of the thermally conductive layer only by applying the adhesive. That is, Steps 3 and 4 are preferably performed by being performed at the same time.

[0203] The adhesive can be diluted by a diluent, and applied to the surface of the sheet-shaped molded body as an adhesive diluent. By diluting the adhesive by the diluent, it is easy to make the adhesive penetrate into the thermally conductive layer. As the diluent, there is no particular limitation as long as it is a liquid at 25°C, 1 atm, has solubility or compatibility with the adhesive, and is a component that volatilizes by drying as described later, and an organic solvent can be preferably used.​​​

[0204] As the organic solvent used, there is no particular limitation, and examples include ketone compounds such as acetone, methyl ethyl ketone, and cyclohexanone; aromatic hydrocarbon compounds such as toluene, xylene, and tetramethylbenzene; cellosolve; methyl cellosolve; butyl cellosolve; carbitol; methyl carbitol; butyl carbitol; propylene glycol monomethyl ether; dipropylene glycol monomethyl ether; dipropylene glycol diethyl ether; tripropylene glycol monomethyl ether; polyethylene glycol monoethyl ether; ester compounds such as ethyl acetate, butyl acetate, butyl lactate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, and propylene glycol monopropyl ether acetate; and aliphatic hydrocarbon compounds such as hexane, octane, and decane.

[0205] Note that, from the viewpoint of allowing the adhesive to be appropriately infiltrated into the thermally conductive layer by the subsequent spraying, it is preferable to include any one of cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, and polyethylene glycol monoethyl ether, which have a volatilization speed that is not too fast, as the organic solvent.

[0206] Further, it is preferable to further include an organic solvent having a lower boiling point than the above-described organic solvents. Specifically, examples include methyl ethyl ketone, methyl isobutyl ketone, hexane, ethyl acetate, butyl acetate, and toluene.

[0207] The dilution concentration of the diluent is not particularly limited, but it is preferable to be adjusted so that the solid content concentration of the adhesive becomes, for example, 5% by mass or more and 50% by mass or less, preferably 8% by mass or more and 35% by mass or less, and further preferably 10% by mass or more and 25% by mass or less. If the solid content concentration is 5% by mass or more, it is possible to prevent excessive heating at the time of drying, and it is possible to allow a prescribed amount of the adhesive to be appropriately infiltrated into the thermally conductive layer together with the organic solvent. Further, by being 50% by mass or less, the prescribed amount is not excessively large, and further, it is possible to adjust the viscosity so as to be easily infiltrated, and thus it is possible to allow the adhesive to be appropriately infiltrated into the thermally conductive layer. Note that the amount of the adhesive infiltrated into the thermally conductive layer can be adjusted by the viscosity, the solid content concentration, the type of solvent, and the like, and for example, in a case where it is desired to increase the amount of the adhesive infiltrated, it is preferable to have a low viscosity and to adjust the solid content concentration to be a high concentration. Further, in a case where it is desired to decrease the amount of the adhesive infiltrated, it is sufficient to have a high viscosity and to make the solid content concentration a low concentration.

[0208] The method of applying the adhesive is not particularly limited, and a publicly known application method is preferably used, and spraying is particularly preferred. By spraying, the amount of the adhesive applied can be controlled to be small, and in addition, the adhesive can be easily caused to penetrate into the thermally conductive layer. In addition, by spraying and controlling the amount of the adhesive applied, a portion having the adhesive layer and a portion not having the adhesive layer can be provided on the surface of the thermally conductive layer. Note that, in the case of spraying, the adhesive containing a fast-drying organic solvent such as ethyl acetate and a slow-drying organic solvent such as polyethylene glycol monoethyl ether, propylene glycol monomethyl ether acetate, or the like is preferably used. More specifically, by containing the slow-drying organic solvent, the organic solvent is not excessively volatilized when the adhesive discharged from the sprayer is applied to the surface of the thermally conductive layer, and thus the adhesive can be easily caused to penetrate into the thermally conductive layer. On the other hand, by containing the fast-drying solvent, the viscosity is preferably adjusted to be suitable for spraying.

[0209] The applied adhesive is then preferably dried so that the diluent is volatilized. The drying temperature is preferably performed at a temperature at which the reaction of the reactive double bond possessed by the adhesive is substantially not performed, for example, at 80°C or lower, preferably at 70°C or lower, and more preferably at 60°C or lower. In addition, the lower limit of the drying temperature is not particularly limited, and can be performed at room temperature or higher, for example, at 20°C or higher, but from the viewpoint of shortening the drying time, the temperature is preferably 30°C or higher, more preferably 40°C or higher, and further preferably 45°C or higher.

[0210] In addition, the drying time is only required to be a time at which the diluent contained in the applied adhesive is substantially completely volatilized, for example, 1 minute or more, preferably 2 minutes or more, and further preferably 3 minutes or more. In addition, the drying time is not particularly limited, but is preferably short from the viewpoint of workability, for example, 24 hours or less, preferably 3 hours or less, and more preferably 1 hour or less.

[0211] [USES OF THE THERMALLY CONDUCTIVE SHEET]

[0212] The thermally conductive sheet is interposed between a heat generating body and a heat radiating body, and conducts and moves the heat generated from the heat generating body to the heat radiating body, and radiates the heat from the heat radiating body. The thermally conductive sheet is used in electronic equipment applications, semiconductor applications, and the like, and is preferably used in semiconductor applications. In semiconductor applications, the thermally conductive sheet can be used in any application, and is preferably referred to as TIM1, and is used in applications in which the thermally conductive sheet is directly applied to a semiconductor chip such as a silicon chip, for example, and is preferably used between a semiconductor chip and a heat sink.

[0213] Of course, it can be referred to as TIM2, and is used in applications in which the thermally conductive sheet is not directly applied to a semiconductor chip, and in this case, the thermally conductive sheet is preferably used between a heat sink and a heat radiating member, a cooling unit such as a heat pipe, or the like.

[0214] Further, the thermally conductive sheet can be used between various electronic components that become heat generating bodies and heat dissipating bodies such as heat sinks, heat radiating members, heat pipes, heat pumps, and metal housings of electronic devices, in addition to the above.

[0215] The thermally conductive sheet is preferably used between two members (adherends) such as heat dissipating bodies and heat generating bodies in a state of being in close contact with and compressed by each member (adherend).

[0216] The thermally conductive sheet is preferably used in a use in which it is heated to a high temperature of, for example, 200°C or higher and 300°C or lower, preferably 220°C or higher and 270°C or lower, in a state of being in close contact with an adherend via an acrylic adhesive layer. The thermally conductive sheet of the present application maintains or, depending on the case, increases the adhesive force to the adherend even when it is heated to a high temperature in a state of being in close contact with the adherend. Therefore, even when it is heated to a high temperature in a state of being in close contact with the adherend as described above, peeling from the adherend can be prevented. Note that, in the above heating, heating is preferably performed in a state of not being pressurized.

[0217] For semiconductor use, the thermally conductive sheet is preferably subjected to a reflow process in a state of being in close contact with an adherend via an acrylic adhesive layer, and is preferably heated in the above temperature range in the reflow process. Note that the thermally conductive sheet is, for example, heated to a high temperature in a state of being in close contact with one or both of a semiconductor chip and a heat sink via an acrylic adhesive layer by a reflow process. In this way, the thermally conductive sheet of the present application can be used in a reflow process for adhering a semiconductor chip and a heat sink.

[0218] Note that, preferably, before the above heating to 200°C or higher, a close contact process of bringing the thermally conductive sheet into a state of being in close contact with an adherend via an acrylic adhesive layer is performed. The close contact process is performed, for example, by pressurizing in a state of sandwiching the thermally conductive sheet between the adherend by heating to a temperature of 50°C or higher and 180°C or lower. The heating temperature is preferably 120°C or higher and 160°C or lower.

[0219] As described above, in the present application, it is also possible to provide an adhering method that sequentially performs a close contact process of sandwiching a thermally conductive sheet between a semiconductor chip and a heat sink and bringing them into close contact, and an adhering process of adhering the semiconductor chip and the heat sink heated to 200°C or higher after the above close contact process.

[0220] In the above close contact process, pressurization is preferably performed after sandwiching the thermally conductive sheet between the semiconductor chip and the heat sink, and is preferably performed at 50°C or higher and 200°C or lower, more preferably at 50°C or higher and 180°C or lower, and further preferably at 120°C or higher and 160°C or lower.

[0221] Further, the heating temperature in the above-mentioned bonding step is preferably 220°C or higher, and is preferably 300°C or lower, more preferably 270°C or lower. The above-mentioned bonding step is preferably performed in a state without pressure.

[0222] Examples

[0223] Hereinafter, the present application will be described in more detail by examples, but the present application is not limited to these examples.

[0224] The measurement method and the evaluation method in this example are described below.

[0225] [A / B ratio]

[0226] To a coating liquid of an adhesive prepared in the same manner as the adhesive used in each of the examples and comparative examples, 1 drop of the liquid was applied to a gold-plated stainless steel plate, and after the application, the plate was sufficiently dried to volatilize the solvent, thereby forming an acrylic adhesive layer on the plate. Note that the drying was performed by leaving the plate to which the adhesive was applied at 80°C for 15 minutes.

[0227] The acrylic adhesive layer formed on the plate was analyzed by Raman analysis, and the A / B value was calculated under the following device and measurement conditions. Note that in each of the examples and comparative examples, the intensity at a wave number of 1636.1 cm -1 was set as "A", and the intensity at a wave number of 1724.4 cm -1 was set as "B".

[0228] (Use device)

[0229] " inVia Qontor ", manufactured by Renishaw

[0230] (Measurement conditions)

[0231] Laser power: 50 cumulative number of times: 1 time

[0232] Laser wavelength: 785 nm grating: 1200 l / mm

[0233] Magnification: 50 times

[0234] Focus: aligned with the surface of the sample on which the acrylic adhesive layer was formed

[0235] [Confirmation of presence or absence of penetration of the acrylic adhesive layer]

[0236] In the diluent of the adhesive used in each of the examples and comparative examples, 0.5 parts by mass of a fluorescent agent ​OB (manufactured by Nippon Chemical Industry Co., Ltd.). Using the thus prepared dilution, a thermally conductive sheet was produced using the same method as in the Examples and Comparative Examples. A cross-section (observation surface) of this thermally conductive sheet, sliced ​​along the thickness direction, was observed using a fluorescence microscope. The presence of adhesive penetration into the thermally conductive layer was confirmed by confirming that the areas where fluorescence due to the fluorescent agent was present were areas where the adhesive had penetrated. The fluorescence microscopy conditions were as follows.

[0237] Fluorescence microscope: OLYMPUS "Polarizing Microscope BX51"

[0238] Light source: OLYMPUS mercury lamp "U-RFL-T"

[0239] Measurement conditions: The observation surface was illuminated with 365nm light through a filter that transmits visible light and absorbs ultraviolet light below 400nm. The focus was adjusted within the 10x field of view of the objective lens. Next, the distribution of the fluorescent agent's luminescence (blue luminescence) was observed using the "Stream Basic" software with an exposure time of 800ms. It should be noted that the exposure time is not limited to 800ms; any condition that allows the distribution of the fluorescent agent's luminescence to be discerned can be used. For example, it can be adjusted based on the width of the field of view or the intensity of the light source.

[0240] [Initial sheet thickness]

[0241] The thickness of the thermally conductive sheet before compression (initial thickness) was measured using a thickness gauge.

[0242] [E hardness]

[0243] The E-type hardness of the thermally conductive sheet was measured based on Japanese Industrial Standards JIS K 6253. Specifically, the E-type hardness of the oriented molded body produced in each example was measured using an E-type hardness meter.

[0244] [Arithmetic mean altitude (Sa)]

[0245] The arithmetic mean height (Sa) of the surface of the thermally conductive sheet was measured using a laser microscope ( Surface properties analysis of a thermally conductive sheet (made by VK-X150) was conducted in accordance with ISO 25178. Specifically, a surface profile of a two-dimensional region with a surface area of ​​1000 μm x 1000 μm was measured using a laser method at a lens magnification of 10x. The average value of three measurements on the same sample was used as the arithmetic mean height (Sa) of the peak points. It should be noted that for thermally conductive sheets with an acrylic adhesive layer, the arithmetic mean height (Sa) of the surface of the thermally conductive sheet with the acrylic adhesive layer was measured.

[0246] [Thermal resistance]

[0247] Thermal resistance values were measured using a thermal resistance measuring instrument as shown below. Figure 1 The thermal resistance measuring instrument as shown below was used to measure the thermal resistance values.

[0248] Specifically, for each sample, a test piece S having a size of 30 mm x 30 mm was prepared for the test. Then, each test piece S was attached to a copper block 22 having a measuring surface of 25.4 mm x 25.4 mm and the side surface of which was covered with a heat insulating material 21, and a load was applied by a load cell 26 at a pressure of 10 psi with a copper block 23 above. Here, the copper block 22 below was in contact with a heater 24. In addition, the copper block 23 above was covered with a heat insulating material 21 and was connected to a heat sink 25 with a fan. Then, the heater 24 was heated to 80°C, and after 10 minutes when the temperature became substantially stable, the temperature (θ j0 ) of the copper block 23 above, the temperature (θ j1 ) of the copper block 22 below, and the amount of heat (Q) of the heater were measured, and the thermal resistance value of each sample was calculated from the following equation (1). Note that the thickness of the thermally conductive sheet at the time of measurement of the thermal resistance value was also measured at the same time.

[0249] Equation (1)

[0250] In equation (1), θ j1 is the temperature of the copper block 22 below, θ j0 is the temperature of the copper block 23 above, and Q is the amount of heat.

[0251] Note that the same measurement was performed by changing the pressure applied by the load cell 26 to 20 psi, 30 psi, and 40 psi, respectively, and the results are shown in Table 2. In addition, for the thermal resistance value at a pressure of 20 psi, the ratio of the thermal resistance value when the thermal resistance value of a blank thermally conductive sheet was taken as a reference (100%) was calculated as the thermal resistance change rate. Note that a thermally conductive sheet having the same configuration except that the acrylic adhesive layer was not provided was taken as a blank.

[0252] [Chip shear strength]

[0253] As Figure 2As shown in the drawing, a nickel-plated copper plate 10 having an outer shape of 50 mm x 50 mm and a thickness of 2 mm was placed on the thermally conductive sheet 11 of 3 mm x 3 mm obtained in each of the examples and comparative examples, and a silicon chip 12 of 3 mm x 3 mm and 600 μm in thickness was further placed on the thermally conductive sheet 11. The resulting laminate was pressed in the thickness direction at a pressure of 1 MPa for 60 seconds in a normal temperature environment, and the thermally conductive sheet 11 was bonded to the nickel-plated copper plate 10 and the silicon chip 12, thereby obtaining a sample 15 for measurement. The sample 15 for measurement was placed on a hot plate adjusted to 250°C with the side of the nickel-plated copper plate 10 as the lower side, and was heated for 3 minutes. Note that the heating at 250°C for 3 minutes is assumed to be a reflow process.

[0254] Then, the chip shear strength was measured at 25°C in an environment using a chip shear tester ("Dage-S4000", manufactured by Dage The height of the tip of the tool 17 was adjusted so that the tip was 300 μm from the surface of the thermally conductive sheet 10. Then, the tool 17 was brought into contact with the silicon chip 12 at a speed of 150 μm / s in the shear direction S, and the load required to break the joint was set as the chip shear strength.

[0255] Further, the chip shear strength was measured at 25°C in an environment for the sample for measurement which was not subjected to heating at 250°C for 3 minutes. Note that the chip shear strength measured at 25°C in an environment for the sample for measurement which was not subjected to heating at 250°C for 3 minutes was set as a blank.

[0256] The measurement of the chip shear strength using the chip shear tester was also performed at 80°C and 150°C in an environment for the sample for measurement which was produced by the same method. The chip shear strengths measured at 25°C, 80°C and 150°C in an environment are shown in Table 2.

[0257] The chip shear strength measured at 25°C, 80°C and 150°C in an environment for the sample for measurement which was subjected to heating at 250°C for 3 minutes (i.e., a reflow process) was expressed as a percentage (%) with respect to the blank, and the rate of change in the chip shear strength was shown in Table 2. Note that the result was good if the rate of change in the chip shear strength was 75% or more.

[0258] As the raw material of the thermally conductive sheet, the following components were used.

[0259] (Polymer composition)

[0260] Cured silicone: an addition reaction type organopolysiloxane composed of an alkenyl group-containing organopolysiloxane as a main agent and a hydride organopolysiloxane as a curing agent (wherein a platinum catalyst is contained in a catalytic amount).

[0261] (Volatile substance)

[0262] n-decyltrimethoxysilane

[0263] (Thermally conductive filler)

[0264] Alumina 1: spherical, average particle diameter (D50) = 3 μm, aspect ratio 1.0

[0265] Alumina 2: polyhedral shape, average particle diameter (D50) = 0.5 μm, aspect ratio 1.0

[0266] Aluminum: spherical, average particle diameter (D50) = 3 μm, aspect ratio 1.0 to 1.5

[0267] Graphitized carbon fiber: average fiber length (arithmetic mean) 85 μm, diameter 10 μm, aspect ratio 8.5, thermal conductivity 900 W / m-K

[0268] Scaly boron nitride: average particle diameter (D50) = 50 μm, aspect ratio 20 to 50, thermal conductivity 200 W / m-K

[0269] Scaly graphite powder: average particle diameter (D50) = 15 μm, aspect ratio 10, thermal conductivity 550 W / m-K

[0270] (Adhesive)

[0271] Adhesive 1: adhesive in which the adhesive main agent is an acrylic polymer in which a structural unit derived from 2-ethylhexyl acrylate is a main component, and a hydroxyl group, a carboxyl group, and a vinyl group are present in a side chain. A / B = 0.588

[0272] Adhesive 2: adhesive in which the adhesive main agent is an acrylic polymer in which a structural unit derived from 2-ethylhexyl acrylate is a main component, and a hydroxyl group, a carboxyl group, and a vinyl group are present in a side chain. A / B = 0.405

[0273] Adhesive 3: adhesive in which the adhesive main agent is an acrylic polymer in which a structural unit derived from 2-ethylhexyl acrylate and butyl acrylate is a main component, and a hydroxyl group and a carboxyl group are present in a side chain but no reactive double bond is present. A / B = 0.138

[0274] Adhesive 4: adhesive in which the adhesive main agent is an acrylic polymer in which a structural unit derived from butyl acrylate is a main component, and a hydroxyl group and a carboxyl group are present in a side chain but no reactive double bond is present. A / B = 0.138

[0275] *Note that the diluent 100 parts by mass of the adhesive diluted with ethyl acetate to a solid content concentration of 33% by mass was further diluted with propylene glycol monomethyl ether acetate 120 parts by mass (solvent) to prepare a coating liquid having a solid content concentration of 15% by mass, which was used in each of the examples and comparative examples.

[0276] [Example 1]

[0277] A mixed composition was obtained by mixing the components according to the formulation 1 of Table 1 using a planetary mixer at 25°C for 50 minutes. Subsequently, the mixed composition was injected into a mold set to a thickness sufficiently larger than that of the thermally conductive sheet, and a magnetic field of 8T was applied in the thickness direction to orient the carbon fibers and flaky graphite in the thickness direction. Then, the curable silicone was once cured by heating at 80°C for 8 hours to obtain a block-shaped oriented molding.

[0278] Next, the block-shaped oriented molding was sliced into a sheet shape having a thickness of about 120 μm by using a shear knife to obtain a sheet-shaped molding in which the carbon fibers were exposed. Then, the sheet-shaped molding was twice cured by heating at 150°C for 6 hours.

[0279] Subsequently, the sheet-shaped molding was reciprocally ground 25 times by a coarse grinding paper A (grit #800) having an average particle diameter (D50) of 20 μm of abrasive grains, and then further reciprocally ground 10 times by a coarse grinding paper B (grit #4000) having an average particle diameter (D50) of 3 μm of abrasive grains.

[0280] On both surfaces of the obtained sheet-shaped molding, the coating liquid of the adhesive 1 was sprayed while adjusting the discharge amount so that the dry basis area of the acrylic adhesive layer became the amount described in Table 1, and then dried at 50°C for 3 minutes to obtain a thermally conductive sheet in which the acrylic adhesive layer was provided on both surfaces of the thermally conductive layer. It was confirmed that fine bubbles were present inside the thermally conductive layer, and the acrylic adhesive penetrated into the fine bubbles near both surfaces. Note that the filling rate of the thermally conductive filler in the thermally conductive layer was 64.0% by volume, and the anisotropic filler was oriented in the thickness direction. In addition, the thickness of the thermally conductive sheet was as described in the table.

[0281] [Examples 2, 3, and 7]

[0282] The conditions for spraying were changed so that the dry basis area of the acrylic adhesive layer became as described in Table 2, and otherwise, the same as in Example 1 was performed.

[0283] [Example 4]

[0284] The kind of the adhesive was changed as in Table 2, and the conditions of spraying were changed so that the dry weight of the acrylic adhesive layer would be as described in Table 2, and otherwise, the same as in Example 1 was carried out.

[0285] [Example 5]

[0286] The block-shaped oriented molded body was sliced into a sheet shape with a thickness of about 80 μm, and otherwise, the same as in Example 1 was carried out.

[0287] [Example 6]

[0288] The components were mixed for 50 minutes at 25°C using a planetary mixer according to the compounding 3 of Table 1 to obtain a mixed composition. The mixed composition was coated on a substrate film made of polyethylene terephthalate (PET) in one direction using a bar coater as a coating applicator at 25°C. The anisotropic filler was oriented in a direction in which the long axis direction was along the coating direction and the short axis direction was in a direction orthogonal to the coating direction. Next, the coated mixed composition was heated at 80°C for 8 hours to cure the liquid composition, thereby obtaining a 1st sheet having a thickness of 2 mm.

[0289] The VUV irradiation device (trade name "VUV-150", manufactured by MINI, Co., Ltd.) was used to irradiate the surface of the 1st sheet with VUV under conditions of a cumulative light quantity of 20 mJ / cm 2 at room temperature (25°C) in the atmosphere. Next, the 1st sheet on which VUV had been irradiated was laminated 100 times, and was pressed by a roll at a pressure of 1.6 kgf / 50 mm in an environment at 25°C, thereby obtaining a laminated block. The laminated block was sliced by a cutting knife in parallel to the laminating direction and perpendicular to a direction along the long axis direction of the flaky filler, thereby obtaining a sheet-shaped molded body having a thickness of 2 mm and a sheet thickness of about 0.30 mm for each unit layer. In the sheet-shaped molded body, the anisotropic filler was oriented in the thickness direction. Then, the sheet-shaped molded body was further heated at 150°C for 6 hours to perform secondary curing.

[0290] Then, the conditions of spraying were changed so that the dry weight of the acrylic adhesive layer would be as described in Table 2, and otherwise, the same as in Example 1 was carried out, thereby obtaining a thermally conductive sheet having an acrylic adhesive layer on both surfaces of the thermally conductive layer. Note that the filling rate of the thermally conductive filler in the thermally conductive layer was 70.2 vol%, and the anisotropic filler was oriented in the thickness direction.

[0291] [Example 8]

[0292] The compounding of the mixed composition was changed to Compounding 2 shown in Table 1, and the conditions of spraying were changed in such a manner that the dry weight of the acrylic adhesive layer became as described in Table 2, and otherwise similarly to Example 1, a thermally conductive sheet having an acrylic adhesive layer on both surfaces of the thermally conductive layer was obtained. No fine bubbles were present inside the thermally conductive layer, and no penetration of the acrylic adhesive into the fine bubbles was confirmed. Note that the filling rate of the thermally conductive filler in the thermally conductive layer was 59.9 vol%, and the anisotropic filler was oriented in the thickness direction.

[0293] [Comparative Examples 1, 2]

[0294] The type of adhesive was changed as in Table 2, and the conditions of spraying were changed in such a manner that the dry weight of the acrylic adhesive layer became as described in Table 2, and otherwise similarly to Example 1.

[0295] [Comparative Example 3]

[0296] The coating liquid of the adhesive was not applied to the sheet-shaped molded body, and otherwise similarly to Example 1.

[0297] [Comparative Example 4]

[0298] The coating liquid of the adhesive was not applied to the sheet-shaped molded body, and otherwise similarly to Example 8.

[0299] [Comparative Example 5]

[0300] The coating liquid of the adhesive was not applied to the sheet-shaped molded body, and otherwise similarly to Example 6.

[0301] [Table 1]

[0302] * The values of each component are mass parts in each compounding.

[0303] * The sheet hardness is a value measured for the cured product obtained from these Compounding 1, 2, 3 in each of the examples and comparative examples.

[0304] [Table 2]

[0305] * In Comparative Example 3, the chip shear strength could not be measured because the thermally conductive sheet could not be tightly adhered to the silicon chip or the nickel-plated copper plate.

[0306] In the above embodiments, by providing the acrylic adhesive layer having a reactive double bond on the surface of the thermally conductive sheet, the chip shear strength is improved, and the adhesion to the adherend is improved. Furthermore, even after heating to a high temperature of about 250°C in a state where the thermally conductive sheet is adhered to the adherend, the high chip shear strength is maintained, and peeling or the like of the adhered thermally conductive sheet can be prevented even after a reflow process or the like. The same results are obtained even when the chip shear strength is measured at 80°C and 150°C in a use environment.

[0307] On the other hand, in Comparative Examples 1 and 2, the chip shear strength is also improved by providing the acrylic adhesive layer on the surface of the thermally conductive sheet. However, since the acrylic adhesive layer does not have a reactive double bond, if heated to a high temperature (250°C) in a state where the thermally conductive sheet is adhered to the adherend, the high chip shear strength cannot be maintained, and peeling or the like is feared to occur through a reflow process or the like. Furthermore, in Comparative Examples 3 to 5, since the acrylic adhesive layer is not provided on the surface of the thermally conductive sheet, the chip shear strength cannot be improved.

Claims

1. A thermally conductive sheet comprising a thermally conductive layer containing a polymer matrix and a thermally conductive filler, and an acrylic adhesive layer provided on a surface of the thermally conductive layer, the acrylic adhesive layer having a reactive double bond.

2. The thermally conductive sheet according to claim 1, wherein an intensity ratio A / B of a peak intensity A of C=C stretching vibration to a peak intensity B of C=0 stretching vibration in a Raman spectrum of the acrylic adhesive layer is 0.2 or more.

3. The thermally conductive sheet according to claim 1 or 2, wherein the polymer matrix is an organopolysiloxane.

4. The thermally conductive sheet according to claim 1 or 2, wherein the thermally conductive layer contains an anisotropic filler oriented in a thickness direction of the thermally conductive layer.

5. The thermally conductive sheet according to claim 1 or 2, wherein the surface of the thermally conductive layer is a sliced surface.

6. The thermally conductive sheet according to any one of claims 1 to 5, wherein the acrylic adhesive layer is infiltrated in the thermally conductive layer.

7. A method for producing a thermally conductive sheet, comprising the steps of: a step of obtaining a mixed composition by mixing at least a curable polymer composition and a thermally conductive filler; a step of obtaining a cured product by curing the mixed composition by heating; and a step of applying an adhesive to a surface of the cured product, the adhesive being an acrylic adhesive having a reactive double bond.

8. The method for producing a thermally conductive sheet according to claim 7, wherein the mixed composition is heated to obtain a molded product, and the molded product is sliced to make the cured product into a sheet shape.

9. The method for producing a thermally conductive sheet according to claim 7 or 8, wherein, in addition to the curable polymer composition and the thermally conductive filler, a compatible substance is further mixed to obtain the mixed composition, and at least a part of the compatible substance is volatilized by the heating.

10. The method for producing a thermally conductive sheet according to claim 7 or 8, wherein the applied adhesive is infiltrated into the cured product.

11. A bonding method comprising the steps of: a bonding step of sandwiching a thermally conductive sheet according to claim 1 or 2 between a semiconductor chip and a heat sink and bonding them; and a bonding step of bonding the semiconductor chip and the heat sink heated to 200°C or higher after the bonding step.

12. The bonding method according to claim 11, wherein, in the bonding step, the semiconductor chip and the heat sink are bonded by pressing them at 50°C or higher and 200°C or lower after sandwiching the thermally conductive sheet between the semiconductor chip and the heat sink.

13. The bonding method according to claim 11 or 12, wherein the bonding step is performed in a state without pressing.

14. Use of a thermally conductive sheet in bonding of a semiconductor chip and a heat sink in a reflow process, the thermally conductive sheet comprising a thermally conductive layer containing a polymer matrix and a thermally conductive filler, and an acrylic adhesive layer provided on a surface of the thermally conductive layer, the acrylic adhesive layer having a reactive double bond. ​ ​ ​

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