Thermally conductive sheet

Abstract

This thermally conductive sheet comprises a thermally conductive layer including a polymer matrix and a thermally conductive filler, and has at least one adhesive surface. The thermally conductive sheet has a volatile component amount of 2-80 mass ppm as measured by thermal desorption GC-MS at 150°C.

Description

Thermally conductive sheet

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

[0002] In recent years, with the increasing density of wiring in multilayer wiring boards, the increasing density of wiring in semiconductor packages, the increased mounting density of electronic components, and the increased heat generation per unit area due to the high integration of semiconductor elements themselves, there has been a demand for improved heat dissipation from semiconductor packages. It is known that semiconductor packages dissipate heat by sandwiching a heat dissipation material between a heat-generating body such as a semiconductor chip and a heat sink, also known as a heat spreader, and bringing them into close contact with each other. Thermally conductive grease has traditionally been widely used as the heat dissipation material disposed between the semiconductor chip and the heat spreader.

[0003] Semiconductor packages are generally heated above a certain temperature during use. Because each component, such as the substrate, semiconductor chip, and heat spreader, has a different thermal expansion coefficient, warping can occur when heated. As chips have become larger in recent years, the gap between the semiconductor chip and the heat spreader has widened due to the warping of the semiconductor chip. Thermally conductive grease cannot accommodate this warping, resulting in gaps and other issues. Therefore, the use of thermally conductive sheets instead of thermally conductive grease is being considered.

[0004] Thermally conductive sheets used in the above applications are required to have improved heat dissipation properties while also improving warpage compliance. This is because poor compliance with surrounding components could result in the sheet being unable to conform to warpage, as with thermally conductive grease, and potentially peeling from the semiconductor chip or heat spreader. Meanwhile, conventional thermally conductive sheets sometimes have an adhesive layer formed on their surface to improve tack, for example. For example, Patent Document 1 discloses a thermally conductive sheet in which an acrylic adhesive liquid is spray-applied and dried in ambient air at room temperature for one minute, forming an adhesive layer on one side.

[0005] Furthermore, in the semiconductor inspection process, which checks the performance of semiconductor packages, there is a demand for inspection technology that improves heat dissipation from semiconductor packages due to the increasing heat generated by semiconductor packages. In the semiconductor inspection process, a test head is pressed against the semiconductor package via a heat dissipation material to check the temperature of the semiconductor chip. Because the heat dissipation material must be reusable, the use of a thermally conductive sheet instead of thermally conductive grease is being considered, but this requires high adhesion to the test head.

[0006] Japanese Patent Application Laid-Open No. 2020-116874

[0007] Semiconductor packages are generally manufactured through a reflow process involving high-temperature heating. Therefore, a thermally conductive sheet placed between a semiconductor chip and a heat spreader is often required to maintain adhesion to an adherend, such as a semiconductor chip or a heat spreader, even after high-temperature heating. A thermally conductive sheet having an adhesive layer formed under the conditions described in Patent Document 1 is thought to have improved initial adhesion to an adherend. However, when used in applications involving high-temperature heating, such as a reflow process, there is a problem in that adhesion between the thermally conductive sheet and the adherend interface decreases during high-temperature heating.

[0008] Furthermore, in the semiconductor testing process, high adhesion to the test head is required, but conventional thermally conductive sheets do not have sufficient adhesion when heated to high temperatures, making it difficult to mount them on the test head.

[0009] Therefore, an object of the present invention is to provide a thermally conductive sheet that can maintain high adhesion before and after high-temperature heating such as in a reflow process.

[0010] The inventors investigated the causes of reduced adhesion in thermally conductive sheets and found that trace amounts of volatile components remaining in the adhesive layer or thermally conductive sheet volatilize during heating processes, such as the reflow process and the mounting process prior to the reflow process, generating bubbles, thereby reducing the adhesion between the thermally conductive sheet and the adherend interface. They also found that a certain amount of volatile components can improve the adhesion of the thermally conductive sheet to the adherend. Based on these findings, they found that the above-mentioned problem can be solved by imparting adhesiveness to at least one surface of the thermally conductive layer constituting the thermally conductive sheet while adjusting the amount of volatile components within a specified range when the thermally conductive sheet is heated at 150°C. Specifically, the present invention provides the following [1] to

[10] .

[0011] [1] A thermally conductive sheet comprising a thermally conductive layer containing a polymer matrix and a thermally conductive filler, at least one surface of which is adhesive, wherein the amount of volatile components in the thermally conductive sheet measured by thermal desorption GC-MS at 150°C is 2 ppm by mass or more and 80 ppm by mass or less. [2] The thermally conductive sheet according to [1], wherein the polymer matrix is ​​organopolysiloxane. [3] The thermally conductive sheet according to [1] or [2], wherein an adhesive layer is provided on at least one surface of the thermally conductive layer. [4] The thermally conductive sheet according to [3], wherein the adhesive layer is formed by spray coating. [5] The thermally conductive sheet according to [3] or [4], wherein the adhesive layer is an acrylic adhesive layer. [6] The thermally conductive sheet according to [5], wherein the acrylic adhesive layer has a reactive double bond. [7] The thermally conductive sheet according to any one of [1] to [6], wherein the adhesiveness disappears when heated at 260°C for 3 minutes. [8] The thermally conductive sheet according to any one of [1] to [7], wherein the amount of volatile components measured by thermal desorption GC-MS at 260°C is 2,500 ppm by mass or less. [9] The thermally conductive sheet according to any one of [1] to [8], wherein the adhesive strength measured by a tack test of at least one surface is 2 N or more.

[10] A thermally conductive sheet comprising a thermally conductive layer containing a polymer matrix and a thermally conductive filler, at least one surface of the thermally conductive layer being adhesive, wherein the amount of volatile components measured by thermal desorption GC-MS at 150°C is 2 ppm by mass or more and 80 ppm by mass or less.

[0012] According to the present invention, it is possible to provide a thermally conductive sheet that can maintain high adhesion before and after high-temperature heating such as a reflow process.

[0013] FIG. 2 is a schematic diagram showing an example of a method for mounting a thermally conductive sheet.

[0014] [Thermal Conductive Sheet] The thermal conductive sheet of the present invention comprises a thermally conductive layer containing a polymer matrix and a thermally conductive filler, and at least one surface of the thermally conductive sheet is adhesive. The thermally conductive sheet will be described in detail below.

[0015] (Amount of Volatile Components) The thermally conductive sheet of the present invention has a volatile component amount measured by thermal desorption GC-MS at 150°C (hereinafter simply referred to as "amount of volatile components at 150°C") of 2 ppm by mass or more and 80 ppm by mass or less. If the amount of volatile components at 150°C is less than 2 ppm by mass, the amount of volatile components contained in the adhesive in the thermally conductive sheet or the thermally conductive sheet itself will be too small, resulting in insufficient flexibility of the adhesive and insufficient ability to conform to gaps with the adherend, which may result in poor initial adhesion before high-temperature heating such as a reflow process. Furthermore, if the amount of volatile components at 150°C exceeds 80 ppm by mass, the thermally conductive sheet will contain excessive volatile components. Therefore, bubbles generated during high-temperature heating may reduce the adhesion of the thermally conductive layer to the adherend. From the above viewpoints, the amount of volatile components at 150°C is preferably 3 ppm by mass or more and 70 ppm by mass or less, and more preferably 4 ppm by mass or more and 60 ppm by mass or less.

[0016] The thermally conductive sheet of the present invention preferably has a volatile component amount measured by thermal desorption GC-MS at 260°C (hereinafter also referred to as "volatile component amount at 260°C") of 2500 ppm by mass or less. As described below, the adhesion of the thermally conductive layer to the adherend may improve after high-temperature heating such as a reflow process. However, by having a volatile component amount of 2500 ppm by mass or less at 260°C, the improvement in adhesion is less likely to be hindered by the volatile components. From this perspective, the volatile component amount at 260°C is more preferably 2300 ppm by mass or less, and even more preferably 1800 ppm by mass or less. Furthermore, the volatile component amount at 260°C is not particularly limited, but from the viewpoint of keeping the volatile component amount at 150°C in the desired range, it is preferably 30 ppm by mass or more, more preferably 50 ppm by mass or more, even more preferably 70 ppm by mass or more, and even more preferably 100 ppm by mass or more. The amount of volatile components at 150°C and 260°C can be adjusted to a desired range by adjusting the drying process described below, the basis weight of the adhesive layer, the type of volatile components, curing conditions, etc. Examples of volatile components include volatile substances such as alkoxysilane compounds described below, and diluents such as organic solvents. Detailed procedures and measurement conditions for thermal desorption GC-MS are as described in the Examples.

[0017] (Adhesiveness) At least one surface of the thermally conductive sheet of the present invention is adhesive. The thermally conductive sheet may be adhesive on only one surface or on both surfaces. Furthermore, as described below, the thermally conductive sheet may have an adhesive layer on at least one surface of the thermally conductive layer, or may contain an adhesive agent in the thermally conductive layer to impart adhesiveness to the surface of the thermally conductive layer, thereby making the surface of the thermally conductive sheet adhesive. The adhesive strength of at least one surface of the thermally conductive sheet, i.e., the thermally conductive layer, is preferably 2N or more, more preferably 2.5N or more, even more preferably 3N or more, and even more preferably 4N or more. Adhesive strength above the above lower limit can be considered to be good adhesiveness. Furthermore, the adhesive strength is not particularly limited, but in practice it is, for example, 10N or less, preferably 9.5N or less, and more preferably 9N or less. The adhesive strength is measured by a tack test, also known as a tack value, the detailed procedure of which is described in the Examples.

[0018] Furthermore, it is preferable that at least one adhesive surface of the thermally conductive sheet loses its adhesiveness when heated at 260°C for 3 minutes. Here, "loss of adhesiveness" means that when the thermally conductive sheet is adhered to an adherend and then heated at 260°C for 3 minutes, at least one surface loses its adhesiveness due to hardening or other factors, resulting in an adhesiveness that makes the thermally conductive sheet inde- pendent from the adherend. The thermally conductive sheet's ability to lose its adhesiveness allows it to adhere to the adherend with high adhesive strength without peeling after high-temperature heating. Whether or not the thermally conductive sheet loses its adhesiveness can be determined, for example, by the following method. That is, after heating the thermally conductive sheet at 260°C for 3 minutes, the thermally conductive sheet is cooled to 23°C, and the tack value is measured at 23°C. If the tack value is 1.5 N or less, it is determined that the adhesiveness has been lost. Furthermore, in the present invention, although not particularly limited, the adhesive layer may be an acrylic adhesive layer having a reactive double bond, as described below, and have the property of losing its adhesiveness when heated at 260°C for 3 minutes. In this case, the reactive double bond reacts with the heat to lose its adhesiveness, but if the adhesive layer is in contact with the adherend at this time, the reaction forms a chemical bond with the adherend, increasing the adhesive strength with the adherend. At the same time, the adhesive layer hardens, increasing its mechanical strength. Therefore, it is believed that peeling from the adherend is less likely to occur when heated at high temperatures, such as during a reflow process.

[0019] (Polymer Matrix) The polymer matrix is ​​a matrix made of an organic polymer, such as an elastomer or rubber, and is preferably formed by curing a liquid polymer composition (curable polymer composition) made of a mixture of a base agent and a curing agent. The curable polymer composition may be made of, for example, uncrosslinked rubber and a crosslinking agent, or may contain a monomer, prepolymer, or the like and a curing agent. The curing reaction may be room temperature curing or heat curing.

[0020] The polymer matrix is ​​preferably an organopolysiloxane. In the present invention, the use of an organopolysiloxane makes the polymer matrix flexible after curing, thereby improving the filling ability of the thermally conductive filler. The organopolysiloxane is preferably silicone rubber. The organopolysiloxane is also preferably a curable silicone, and more preferably an addition reaction silicone. In the case of an addition reaction silicone, the curable polymer composition is composed of an alkenyl group-containing organopolysiloxane (main component) and a hydrogen organopolysiloxane (curing agent), and the polymer matrix may be formed by curing these components. It is believed that the use of an addition reaction silicone makes it easier to improve adhesion to the adherend by high-temperature heating such as in a reflow process.

[0021] In addition to silicone rubber, various synthetic rubbers can be used as rubber. Specific examples include acrylic rubber, nitrile rubber, isoprene rubber, urethane rubber, ethylene propylene rubber, styrene-butadiene rubber, butadiene rubber, fluororubber, and butyl rubber. When using these rubbers, the synthetic rubbers may be crosslinked or left uncrosslinked (i.e., uncured) in the thermally conductive sheet. Uncrosslinked rubbers are primarily used in flow orientation. Furthermore, when crosslinked (i.e., cured), as described above, the polymer matrix may be formed by curing a curable polymer composition comprising an uncrosslinked synthetic rubber and a crosslinking agent. Furthermore, thermoplastic elastomers such as polyester-based thermoplastic elastomers and polyurethane-based thermoplastic elastomers, as well as thermosetting elastomers formed by curing a liquid polymer composition containing a base resin and a curing agent, can also be used. For example, a polyurethane-based elastomer formed by curing a polymer composition containing a hydroxyl-containing polymer and an isocyanate can be used.

[0022] The polymer composition for forming the polymer matrix may consist of an organic polymer alone, or may be a mixture containing an organic polymer plus a plasticizer or polymer dispersant. Plasticizers are preferably used when synthetic rubber is used, and the inclusion of a plasticizer can increase the flexibility of the polymer matrix when not crosslinked. For example, when the polymer matrix is ​​an organopolysiloxane, silicone oil may be used as the plasticizer. Furthermore, examples of polymer dispersants that can be used include alkoxysiloxane compounds, aromatic ring-containing siloxane compounds, and hydroxyl group-containing siloxane compounds, as described below. That is, the curable polymer composition may consist of a base agent and a curing agent, or may contain a plasticizer or polymer dispersant in the base agent and curing agent. Furthermore, curable polymer compositions containing a base agent, a curing agent, and a polymer dispersant are particularly preferred, from the viewpoints of preventing excessive volatile component content and adjusting the viscosity of the composition to a low level, making it easier to load the thermally conductive filler described below.

[0023] The alkoxysiloxane compound used as a polymer dispersant has two or more siloxane bonds (also referred to as a siloxane skeleton) and a structure in which an alkoxy group is bonded to at least one silicon atom. The alkoxysiloxane compound has a structure in which an organic substituent is bonded to at least one of the silicon atoms constituting the siloxane bond. The alkoxysiloxane compound can improve compatibility with the organopolysiloxane constituting the curable polymer composition by containing the alkoxy group and the organic substituent. The number of repeating units n of the siloxane skeleton is preferably 11 or more. The number of repeating units n of the siloxane skeleton (—Si—O—) is preferably 11 or more and 350 or less, more preferably 20 or more and 300 or less, even more preferably 50 or more and 270 or less, and even more preferably 100 or more and 250 or less. When the number of repeating units n of the siloxane skeleton is equal to or greater than the above lower limit, compatibility with the organopolysiloxane forming the matrix is ​​improved, and the amount of volatile components can be further suppressed. Furthermore, when the number of repeating units n of the siloxane skeleton is equal to or less than the upper limit, the viscosity of the composition can be easily adjusted to a low level. Examples of the alkoxy group and organic substituent possessed by the alkoxysiloxane compound include those exemplified in the description of the alkoxysilane compound. From the viewpoint of compatibility with the organopolysiloxane constituting the curable polymer composition, it is preferable that the compound has at least an alkyl group.

[0024] Examples of the alkoxysiloxane compound include methyl methoxy siloxane oligomer, methyl phenyl methoxy siloxane oligomer, methyl epoxy methoxy siloxane oligomer, methyl mercapto methoxy siloxane oligomer, and methyl acryloyl methoxy siloxane oligomer, etc. One or more types of alkoxy siloxane compounds can be used.

[0025] Furthermore, as the polymer dispersant, an aromatic ring-containing siloxane compound having a structure represented by the following formula (1) can also be used. In formula (1), R １are each independently a group represented by A-B or a monovalent hydrocarbon group having 1 to 4 carbon atoms, and １ At least one R １ is a group represented by A-B. A is a divalent organic group bonded to a silicon atom. B has 3 to 6 conjugated aromatic 6-membered rings. Among the atoms constituting A, when the atom bonded to the aromatic 6-membered ring possessed by B is defined as an α-position atom, the atom bonded to the α-position atom is defined as a β-position atom, and the atom bonded to the β-position atom other than the α-position atom is defined as a γ-position atom, any of the α-position atom, β-position atom, and γ-position atom is a heteroatom, and n is an integer of 1 or more. A may also have heteroatoms in portions other than the α-position atom, β-position atom, and γ-position atom. Here, the heteroatom is not particularly limited, and examples thereof include an oxygen atom, a nitrogen atom, a sulfur atom, and a boron atom. Among these, an oxygen atom is preferred from the viewpoint of effectively improving the fluidity of the polysiloxane phosphor.

[0026] The aromatic ring-containing siloxane compound having the structure represented by formula (1) has three to six conjugated aromatic six-membered rings and has a large conjugated moiety in its molecular structure. Therefore, the aromatic ring-containing siloxane compound has high adsorptivity to thermally conductive fillers having π electrons due to π-π interactions, making it easy to disperse the thermally conductive filler.

[0027] A is preferably a divalent organic group having 11 or less carbon atoms, and more preferably a divalent organic group having 10 or less carbon atoms. As such, aromatic ring-containing siloxane compounds in which A has a certain number of carbon atoms or less are preferred because they tend to improve the dispersibility of the thermally conductive filler. In addition, although there is no particular limitation on the lower limit of the number of carbon atoms in A, A is preferably a divalent organic group having 4 or more carbon atoms. In addition, as described above, A has a heteroatom, and therefore has a structural unit having a heteroatom. Examples of the structural unit include ether, ester, amide, urethane, thioether, thioester, etc. Among them, from the viewpoint of improving the dispersibility in the thermally conductive filler and improving the fluidity, ether or ester is preferred, ether is more preferred, and cyclic ether is particularly preferred. Note that a cyclic ether is an ether having a structure in which the carbon of a cyclic hydrocarbon is substituted with oxygen.

[0028] Furthermore, from the viewpoint of improving the dispersibility and fluidity of the thermally conductive filler, it is preferable that A has a cyclic ether structure represented by the following formula (5-1) or an ester skeleton represented by the following formula (5-2). In formula (5-1), *1 and *2 are bonds, and R ４ is a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms, preferably a hydrogen atom. ４ may be the same or different. ３ is a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms, preferably a hydrocarbon group having 1 to 4 carbon atoms, more preferably a hydrocarbon group having 1 to 3 carbon atoms, and even more preferably an ethyl group. ５ is a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms, preferably a hydrogen atom. The oxygen atom in formula (5-1) is the above-mentioned β-position atom or γ-position atom, preferably a β-position atom. In formula (5-2), *3 and *4 are bonds. The oxygen atom having the bond *3 is the above-mentioned α-position atom, β-position atom or γ-position atom. Among the above, it is preferable that A has a skeleton represented by formula (5-1).

[0029] Furthermore, from the viewpoint of improving the dispersibility and fluidity of the thermally conductive filler, A is preferably any of the structures represented by the following formulas (6) to (10), and more preferably any of the structures represented by the following formulas (6) or (7). In formulas (6) to (10), *5 is a bond bonded to the aromatic six-membered ring that B has, and *6 is a bond bonded to the silicon atom of formula (1).

[0030] In formula (1), B has 3 to 6 conjugated aromatic 6-membered rings. Conjugation refers to the fact that unsaturated bonds and single bonds are alternately connected in the molecular structure, resulting in stabilization due to the interaction of p orbitals and delocalization of electrons (presence spread throughout the conjugated system). Note that 3 to 6 conjugated aromatic 6-membered rings are included in the concept of the polycyclic aromatic structure described above. When the number of aromatic 6-membered rings is 6 or less, the fluidity of the aromatic ring-containing siloxane compound is improved, and when the number of aromatic 6-membered rings is 3 or more, the adsorption to the thermally conductive filler is improved, and the dispersibility of the thermally conductive filler is improved. From the viewpoint of improving both the adsorption to the thermally conductive filler and the fluidity in a balanced manner, it is preferable that the number of aromatic 6-membered rings is 4 to 5.

[0031] The conjugated 3 to 6 aromatic 6-membered rings may be a fused ring compound composed of 3 to 6 aromatic 6-membered rings or a non-fused ring compound, but is preferably a fused ring compound. In this way, when B contains a fused ring compound or when B is a fused ring compound, it is preferable from the viewpoint of further improving the adsorption to the thermally conductive filler and enhancing the dispersibility.

[0032] Examples of the fused ring compound include anthracene, anthracene derivatives, phenanthrene, phenanthrene derivatives, triphenylene, triphenylene derivatives, pyrene, pyrene derivatives, tetracene, tetracene derivatives, picene, picene derivatives, perylene, perylene derivatives, pentaphene, pentaphene derivatives, pentacene, pentacene derivatives, hexaphene, and hexaphene derivatives. Among these, pyrene, pyrene derivatives, perylene, and perylene derivatives are preferred. Here, the term "derivative" refers to an anthracene having a substituent. For example, an anthracene derivative refers to an anthracene having a substituent, and the same applies to other derivatives. When the fused ring compound has a substituent, at least one of the hydrogen atoms constituting the fused ring compound is substituted with the substituent. Examples of the substituent include organic groups having 1 to 10 carbon atoms. From the viewpoint of improving the flowability of the aromatic ring-containing siloxane compound of the present invention, it is preferable that the fused ring compound does not have a substituent. Therefore, it is particularly preferable that B is pyrene or perylene. In addition, the fused ring compound may be any compound as long as any of the carbon atoms constituting the fused ring is bonded to the above A.

[0033] In the present invention, B can be any of the above-mentioned compounds without any particular limitation, but the preferred structure of B is shown below. In the above formulas (11) to (14), * represents a bond to A.

[0034] Among the above formulas (11) to (14), the compounds of any of formulas (11) to (13), which are fused ring compounds, are preferred, and among them, pyrene of formula (11) or perylene of formula (12) is more preferred, and pyrene of formula (11) is even more preferred.

[0035] In formula (1), at least one R １ is the group represented by A-B above, and the remaining R １ is a hydrocarbon group having 1 to 4 carbon atoms. １Among these, the number of groups represented by A-B is preferably 1 to 5, more preferably 1 or 2, and the remainder is preferably a monovalent hydrocarbon group having 1 to 4 carbon atoms. When there are multiple groups represented by A-B, the multiple groups represented by A-B may be the same or different. Examples of monovalent hydrocarbon groups having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, and a butyl group, and of these, a methyl group is preferred. When there are multiple monovalent hydrocarbon groups having 1 to 4 carbon atoms, the multiple monovalent hydrocarbon groups having 1 to 4 carbon atoms may be the same or different.

[0036] In formula (1), n ​​represents the number of repeating units of the siloxane skeleton, and n is an integer of 1 or greater. While n is not particularly limited as long as it is an integer of 1 or greater, it is preferably 400 or less, more preferably 300 or less, even more preferably 250 or less, and preferably 10 or more, more preferably 40 or more, and even more preferably 200 or greater. When the number of repeating units n of the siloxane skeleton is equal to or greater than the lower limit, compatibility with the organopolysiloxane that forms the matrix is ​​improved, and the amount of volatile components can be prevented from increasing. Furthermore, when the number of repeating units n of the siloxane skeleton is equal to or less than the upper limit, the viscosity of the composition can be easily adjusted low, resulting in good flowability.

[0037] (Siloxane Compound Having Hydroxyl Group) The polymer dispersant may be a siloxane compound having a hydroxyl group. The siloxane compound having a hydroxyl group has a hydroxyl group at a portion of the terminal of the main chain, at a side chain, or at both. That is, the siloxane compound having a hydroxyl group in the present invention may be a siloxane compound having a hydroxyl group at a portion of the terminal of the main chain or at a side chain, or may be a siloxane compound having hydroxyl groups at both a portion of the terminal of the main chain and at a side chain. The siloxane compound having a hydroxyl group is a hydroxyl-containing siloxane compound other than a siloxane compound having hydroxyl groups at both terminals of the main chain. Here, the term "terminal of the main chain" refers to the end of the longest part of the molecular chain in the molecular structure (the straight-chain part with the largest number of constituent atoms in the molecular structure).

[0038] The hydroxyl group-containing siloxane compound having this specific structure is likely to react or interact with the functional groups on the surface of the thermally conductive filler due to the presence of the hydroxyl group. Furthermore, since the hydroxyl group-containing siloxane compound does not have hydroxyl groups at both ends, it does not react or interact with the thermally conductive filler at both ends. Therefore, it is believed that the dispersibility of the thermally conductive filler in the composition can be improved and the viscosity can be effectively reduced.

[0039] The siloxane compound having a hydroxyl group of the present invention may have only one hydroxyl group, or may have two or more hydroxyl groups. The upper limit of the number of hydroxyl groups is not particularly limited, but is preferably 6 or less, and more preferably 3 or less. Among these, a siloxane compound having two hydroxyl groups is particularly preferred because it has a high viscosity-reducing effect. The number of hydroxyl groups in the siloxane compound having a hydroxyl group of the present invention may be one, and one embodiment includes a siloxane compound having a hydroxyl group only at one end of the main chain.

[0040] The hydroxyl group-containing siloxane compound of the present invention has a siloxane skeleton (—Si—O—), and the number of repeating units n of the siloxane skeleton is preferably 11 or more. The number of repeating units n of the siloxane skeleton is preferably 11 or more and 350 or less, more preferably 20 or more and 300 or less, even more preferably 50 or more and 270 or less, and even more preferably 100 or more and 250 or less. When the number of repeating units n of the siloxane skeleton is equal to or greater than the above-mentioned lower limit, compatibility with the organopolysiloxane that forms the matrix is ​​improved, and an increase in volatile components can be suppressed. Furthermore, when the number of repeating units n of the siloxane skeleton is equal to or less than the above-mentioned upper limit, the viscosity of the composition can be easily adjusted to a low level.

[0041] The polymer dispersant in the present invention is contained in a polymer composition. When the total amount of the polymer composition is taken as 100% by mass, the content of the polymer dispersant in the polymer composition is preferably 1% by mass or more and 50% by mass or less, more preferably 2% by mass or more and 30% by mass or less, and even more preferably 3% by mass or more and 15% by mass or less, from the viewpoint of effectively reducing the viscosity of the composition. Note that the total amount of the polymer composition here refers to the total amount of components forming the polymer matrix. The polymer composition includes not only organic polymers such as organopolysiloxanes, but also additives such as plasticizers and dispersants, but does not include components that volatilize during production or thermally conductive fillers. Therefore, the total amount of the polymer composition can also be said to be the amount obtained by subtracting the amounts of thermally conductive fillers and volatile substances from the total amount of the mixed composition used to form the thermally conductive layer.

[0042] The content of the polymer matrix, expressed as a volume-based filling rate (volume filling rate), is preferably 15% by volume or more and 50% by volume or less, more preferably 17% by volume or more and 46% by volume or less, and even more preferably 20% by volume or more and 42% by volume or less, relative to the total amount of the thermal conductive sheet.

[0043] (Thermal Conductive Filler) The thermal conductive filler contained in the thermal conductive layer is preferably dispersed in a polymer matrix and held in the polymer matrix. Examples of the thermal conductive filler include anisotropic fillers and non-anisotropic fillers, but it is preferable to use at least anisotropic fillers.

[0044] The anisotropic filler is preferably oriented in the thickness direction of the thermally conductive sheet. This makes it easier for the thermally conductive layer to increase its thermal conductivity. When the anisotropic filler is oriented in the thickness direction, its long axis direction does not need to be strictly parallel to the thickness direction; even if the long axis direction is slightly tilted relative to the thickness direction, it is still considered to be oriented in the thickness direction. Specifically, an anisotropic filler whose long axis direction is tilted by less than 20° is also considered to be oriented in the thickness direction, and if such anisotropic fillers constitute the majority of the thermally conductive sheet (for example, more than 60%, preferably more than 80% of the total number of anisotropic fillers), they are considered to be oriented in the thickness direction.

[0045] The content of the thermally conductive filler is preferably 150 parts by mass or more and 3,000 parts by mass or less, more preferably 200 parts by mass or more and 1,800 parts by mass or less, and even more preferably 300 parts by mass or more and 1,000 parts by mass or less, per 100 parts by mass of the polymer matrix. By setting the content of the thermally conductive filler to 150 parts by mass or more, a certain level of thermal conductivity can be imparted to the thermally conductive layer. Furthermore, by setting the content to 3,000 parts by mass or less, the thermally conductive filler can be properly dispersed in the polymer matrix. Furthermore, it is possible to prevent the viscosity of the mixed composition described below from becoming unnecessarily high. Furthermore, the volume filling rate of the thermally conductive filler relative to the total amount of the thermally conductive layer is preferably 40% by volume or more and 85% by volume or less, more preferably 48% by volume or more and 83% by volume or less, and even more preferably 56% by volume or more and 80% by volume or less. By setting the volume filling rate of the thermally conductive filler to be equal to or greater than the above lower limit, a certain level of thermal conductivity can be imparted to the thermally conductive layer. Furthermore, by setting the volume filling rate of the thermally conductive filler to the upper limit or less, the thermally conductive layer can be easily manufactured.

[0046] (Anisotropic Filler) An anisotropic filler is a filler that has an anisotropic shape and can be oriented. Examples of anisotropic fillers include fibrous materials and scaly materials. An anisotropic filler has a high aspect ratio, specifically, an aspect ratio of greater than 2, preferably 5 or greater. By increasing the aspect ratio to greater than 2, the anisotropic filler is more 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 increased. The upper limit of the aspect ratio is not particularly limited, but is practically 100. The aspect ratio is the ratio of the major axis length to the minor axis length of the anisotropic filler. In the case of fibrous materials, it means the fiber length / fiber diameter, and in the case of scaly materials, it means the major axis length / thickness of the scaly material.

[0047] 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 even more preferably 50 parts by mass or more and 250 parts by mass or less, relative to 100 parts by mass of the polymer matrix. By setting the content of the anisotropic filler to 10 parts by mass or more, thermal conductivity is easily improved. Furthermore, by setting the content to 500 parts by mass or less, the viscosity of the mixed composition described below is easily adjusted, resulting in good orientation of the anisotropic filler. Furthermore, the dispersibility of the anisotropic filler in the polymer matrix is ​​also improved.

[0048] When the anisotropic filler is a fibrous material, its 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 even more preferably 30 μm or more and 100 μm or less. When the average fiber length is 10 μm or more, the anisotropic fillers are in proper contact with each other within the thermally conductive layer, ensuring a heat transfer path and improving the thermal conductivity of the thermally conductive layer. On the other hand, when the average fiber length is 500 μm or less, the bulk of the anisotropic filler is reduced, allowing it to be highly packed into the binder component. Furthermore, the average fiber length of the fibrous material is preferably shorter than the thickness of the thermally conductive sheet. Being shorter than the thickness prevents the fibrous material from protruding more than necessary from the surface of the thermally conductive sheet. The above average fiber length can be calculated by observing the anisotropic filler under a microscope. More specifically, the fiber lengths of 50 arbitrary anisotropic fillers can be measured using, for example, an electron microscope or an optical microscope, and the average value (arithmetic mean value) can be used as the average fiber length.

[0049] Furthermore, when the anisotropic filler is a scaly material, its average particle size is preferably 5 μm to 1000 μm, more preferably 8 μm to 750 μm, and even more preferably 10 μm to 500 μm. In particular, when the orientation method described below is a magnetic field orientation method, its average particle size is preferably 5 μm to 300 μm, more preferably 8 μm to 200 μm, and even more preferably 10 μm to 100 μm. By setting the average particle size to 5 μm or more, the anisotropic fillers in the thermally conductive layer are more likely to come into contact with each other, ensuring a heat transfer path and improving the thermal conductivity of the thermally conductive layer. On the other hand, setting the average particle size to 300 μm or less reduces the bulk of the thermally conductive sheet, allowing for a high loading of the anisotropic filler in the binder component. Furthermore, when the orientation method is a flow orientation method, the average particle size of the scaly material is preferably 5 μm to 1000 μm, more preferably 10 μm to 750 μm, and even more preferably 15 μm to 500 μm. By setting the average particle size to 5 μm or more, the anisotropic fillers in the thermally conductive layer are more likely to come into contact with each other, ensuring a heat transfer path and improving the thermal conductivity of the thermally conductive layer. On the other hand, setting the average particle size to 1000 μm or less reduces the bulk of the thermally conductive sheet, allowing the anisotropic filler to be highly loaded into the binder component. The average particle size of the scaly filler is D50, which can be calculated by observing the scaly filler under a microscope and using the long diameter as the diameter. More specifically, this means the particle size corresponding to a cumulative frequency of 50% when the long diameter of at least 500 random scaly fillers is measured using, for example, an electron microscope or optical microscope. Specifically, using a scaly filler as a sample, the particle size distribution curve can be determined by plotting the particle size on the horizontal axis and the cumulative frequency on the vertical axis. The particle size distribution curve is a numerical particle size distribution curve obtained by integrating the particle sizes of the scaly filler starting from the smallest particle size.

[0050] The anisotropic filler may be any known material having thermal conductivity. However, when oriented by magnetic field orientation as described below, it is preferable for the filler to have diamagnetic properties. On the other hand, when oriented by flow orientation or when the anisotropic filler is not oriented, it does not need to have diamagnetic properties. Specific examples of anisotropic fillers include carbon-based materials such as carbon fiber or flake carbon powder, metal materials such as metal fiber and metal oxides, boron nitride, metal nitrides, metal carbides, metal hydroxides, and polyparaphenylene benzoxazole fibers. Among these, carbon-based materials are preferred due to their low specific gravity and good dispersibility in binder components, and graphitized carbon materials with high thermal conductivity are more preferred. Graphitized carbon materials have diamagnetic properties due to the alignment of graphite planes in a specific direction. Boron nitride is also a preferred anisotropic filler. While not particularly limited, boron nitride is preferably used as a flake material. The flake-like boron nitride may be agglomerated or not, but it is preferable that it is not agglomerated in part or in whole. Note that boron nitride also has diamagnetic properties when its crystal planes are aligned in a specific direction.

[0051] Furthermore, the anisotropic filler is not particularly limited, but its thermal conductivity along the anisotropic direction (i.e., the long axis direction) is generally 30 W / m K or more, preferably 60 W / m K or more, more preferably 100 W / m K or more, and even more preferably 200 W / m K or more. The upper limit of the thermal conductivity of the anisotropic filler is not particularly limited, but is, for example, 2000 W / m K or less. The thermal conductivity can be measured by a laser flash method or the like.

[0052] The anisotropic filler may be used alone or in combination of two or more. For example, the anisotropic filler may be an anisotropic filler having at least two different average particle sizes or average fiber lengths. When anisotropic fillers of different sizes are used, the smaller anisotropic fillers are embedded between the relatively larger anisotropic fillers, which is thought to enable the anisotropic fillers to be densely packed in the binder component and to improve heat conduction efficiency.

[0053] Furthermore, among the above, the anisotropic filler preferably includes a fibrous material. As described below, when a thermally conductive layer containing a fibrous material is sliced, the fibrous material falls off, creating unevenness on the surface and reducing adhesion. However, in the present invention, for example, by impregnating the thermally conductive layer with an adhesive or by providing an adhesive layer on at least one surface of the thermally conductive layer, the adhesive or adhesive layer penetrates into the recesses, thereby sufficiently improving adhesion even with a thermally conductive layer containing a fibrous material. Furthermore, from the viewpoint of improving thermal conductivity, the thermally conductive layer preferably contains a scaly material in addition to the fibrous material as an anisotropic filler. In this case, the content ratio of the scaly material to the fibrous material (scaly material / fibrous material) is, for example, 0.01 to 1, preferably 0.02 to 0.5, and more preferably 0.1 to 0.3, by mass.

[0054] The carbon fiber used as the anisotropic filler is preferably graphitized carbon fiber. Furthermore, the scaly carbon powder is preferably scaly graphite powder. It is also preferable to use a combination of graphitized carbon fiber and scaly graphite powder as the anisotropic filler. Graphitized carbon fiber has graphite crystal planes aligned in the fiber axis direction, providing high thermal conductivity in the fiber axis direction. Therefore, by aligning the fiber axis direction in a predetermined direction, thermal conductivity in a specific direction can be increased. Furthermore, scaly graphite powder has graphite crystal planes aligned in the in-plane direction of the scaly surfaces, providing high thermal conductivity in the in-plane direction. Therefore, by aligning the scaly surfaces in a predetermined direction, thermal conductivity in a specific direction can be increased. The graphitized carbon fiber and scaly graphite powder preferably have a high degree of graphitization.

[0055] The graphitized carbon materials, such as the graphitized carbon fiber and flake graphite powder, can be obtained by graphitizing the following raw materials. Examples include condensed polycyclic hydrocarbon compounds such as naphthalene, condensed heterocyclic compounds such as PAN (polyacrylonitrile), and pitch. However, it is particularly preferable to use graphitized mesophase pitch, polyimide, or polybenzazole, which have a high degree of graphitization. For example, by using mesophase pitch, the pitch is anisotropically oriented in the fiber axis direction during the spinning process described below, thereby producing graphitized carbon fibers with excellent thermal conductivity in the fiber axis direction. The use of mesophase pitch in graphitized carbon fibers is not particularly limited as long as it can be spun. Mesophase pitch may be used alone or in combination with other raw materials. However, using mesophase pitch alone, i.e., graphitized carbon fibers with a 100% mesophase pitch content, is most preferable in terms of high thermal conductivity, spinnability, and quality stability.

[0056] The graphitized carbon fiber can be one that has been subjected to spinning, infusibilization, and carbonization in sequence, and then pulverized or cut to a predetermined particle size before graphitization, or one that has been carbonized, pulverized, or cut and then graphitized. When pulverization or cutting is performed before graphitization, condensation polymerization reactions and cyclization reactions are more likely to proceed on the newly exposed surface during the graphitization treatment, thereby increasing the degree of graphitization and enabling the production of graphitized carbon fibers with even improved thermal conductivity. On the other hand, when spun carbon fiber is pulverized after graphitization, the graphitized carbon fiber is stiff and therefore easy to pulverize, and carbon fiber powder with a relatively narrow fiber length distribution can be obtained by pulverization for a short period of time.

[0057] As described above, 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 even more preferably 30 μm or more and 100 μm or less. Furthermore, as described above, the aspect ratio of the graphitized carbon fiber is greater than 2, preferably 5 or more. The thermal conductivity of the graphitized carbon fiber is not particularly limited, but the thermal conductivity in the fiber axis direction is preferably 400 W / m·K or more, more preferably 800 W / m·K or more.

[0058] When the thermally conductive layer contains an anisotropic filler, it may or may not be exposed on the surface of the thermally conductive layer, but it is preferably exposed. When the anisotropic filler is exposed, the anisotropic filler comes into contact with an adherend such as a heat generating body or a heat dissipating body, which makes it easier to reduce the thermal resistance value. Furthermore, when the anisotropic filler is exposed, it is difficult to improve adhesion to the adherend. Even in such cases, in the present invention, it is easy to improve adhesion by providing an adhesive or adhesive layer.

[0059] (Non-anisotropic filler) The thermally conductive filler of the present invention may contain a non-anisotropic filler, and it is preferable to use the above-mentioned anisotropic filler in combination with a non-anisotropic filler. When the non-anisotropic filler is used in combination with an anisotropic filler oriented in one direction, such as the thickness direction, the non-anisotropic filler is interposed in the gaps between the oriented anisotropic fillers, thereby further increasing thermal conductivity. The non-anisotropic filler is a filler that has substantially no anisotropy in shape, and is a filler that does not orient in a predetermined direction even under environments in which the anisotropic filler orients in a predetermined direction, such as under the generation of magnetic field lines or under the action of shear force, as described below.

[0060] The aspect ratio of the non-anisotropic filler is 2 or less, and preferably 1.5 or less. When used in combination with an anisotropic filler, a non-anisotropic filler with such a low aspect ratio is more likely to be arranged in the gaps between the anisotropic filler, making it easier to improve thermal conductivity. Furthermore, by setting the aspect ratio to 2 or less, an increase in the viscosity of the mixed composition described below can be prevented, enabling high filling.

[0061] Specific examples of non-anisotropic fillers include metals, metal oxides, metal nitrides, metal hydroxides, carbon materials, and oxides, nitrides, and carbides other than metals. The shapes of the non-anisotropic fillers include spherical, polyhedral, and irregularly shaped powders. Examples of metals in non-anisotropic fillers include aluminum, copper, and nickel. Examples of metal oxides include aluminum oxide (e.g., alumina), magnesium oxide, and zinc oxide. Examples of metal nitrides include aluminum nitride. Examples of metal hydroxides include aluminum hydroxide. Examples of carbon materials include spherical graphite. Examples of oxides, nitrides, and carbides other than metals include quartz, boron nitride, and silicon carbide. Among these, aluminum oxide and aluminum are preferred because of their high thermal conductivity and the ease of obtaining spherical fillers. The non-anisotropic fillers may be used alone or in combination of two or more of the above.

[0062] The average particle size of the non-anisotropic filler is, for example, 0.1 μm to 200 μm, preferably 0.5 μm to 100 μm, and more preferably 1 μm to 70 μm. Furthermore, when a non-anisotropic filler is used in combination with an anisotropic filler, the average particle size of the non-anisotropic filler is preferably 0.1 μm to 50 μm, more preferably 0.5 μm to 35 μm, and even more preferably 1 μm to 15 μm. By setting the average particle size to 50 μm or less, problems such as disturbance of the orientation of the anisotropic filler are less likely to occur even when used in combination with an anisotropic filler. Furthermore, by setting the average particle size to 0.1 μm or more, the specific surface area of ​​the non-anisotropic filler does not become larger than necessary, and even when a large amount is blended, the viscosity of the mixed composition is less likely to increase, making it easier to highly fill the non-anisotropic filler. For example, at least two non-anisotropic fillers having different average particle sizes may be used as the non-anisotropic filler. The average particle size of the non-anisotropic filler can be measured by observation using an electron microscope, etc. More specifically, for example, the particle sizes of 500 or more particles of any non-anisotropic filler can be measured using an electron microscope or an optical microscope, and D50 can be calculated in the same manner as for the scaly filler.

[0063] The content of the non-anisotropic filler 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 even more 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 setting the content at 50 parts by mass or more, the thermal conductivity of the thermal conductive sheet can be improved. On the other hand, by setting the content at 1500 parts by mass or less, the non-anisotropic filler can be properly dispersed in the binder component, thereby achieving the effect of increasing the thermal conductivity according to the content. In addition, an unnecessary increase in the viscosity of the mixed composition can be prevented.

[0064] The mass ratio of the content of the non-anisotropic filler to the content of the anisotropic filler is not particularly limited, but is preferably from 0.5 to 15, more preferably from 1 to 10, and more preferably from 1.1 to 7. By setting the mass ratio within the above range, the non-anisotropic filler is appropriately filled between the anisotropic fillers, forming efficient heat transfer paths, thereby further improving the thermal conductivity of the thermally conductive sheet.

[0065] In the thermally conductive layer, the polymer matrix may further contain components other than those described above, provided that the functionality of the thermally conductive layer is not impaired. Specific examples include at least one selected from dispersants, flame retardants, antioxidants, colorants, anti-settling agents, etc. Furthermore, when the curable polymer composition is to be crosslinked or cured as described above, additives such as a crosslinking accelerator, curing accelerator, or curing catalyst that accelerates crosslinking or curing may be added. When the polymer matrix is ​​an organopolysiloxane, a platinum catalyst may be used as the curing catalyst.

[0066] The surface of the thermally conductive layer is preferably a sliced ​​surface. By having the surface of the thermally conductive layer as a sliced ​​surface, the anisotropic filler and the like can be easily exposed to the surface of the thermally conductive layer as described above, thereby effectively reducing the thermal resistance value. The thermally conductive sheet may have one or both surfaces as sliced ​​surfaces. However, it is preferable that the adhesive surface, particularly the surface on which the adhesive layer is provided, be a sliced ​​surface. As described below, a sliced ​​surface is a surface formed by cutting with a shearing blade or laser. Sliced ​​surfaces often have large irregularities due to the protrusion or detachment of the anisotropic filler. However, by filling the recesses with an adhesive layer, the air gap can be reduced during use, improving the thermal resistance value while also increasing adhesion.

[0067] It is also preferable that the thermally conductive sheet has a polished surface. By having at least one surface of the thermally conductive sheet be a polished surface, the thermal resistance value can be more effectively reduced. The thermally conductive sheet may have one surface or both surfaces polished, but it is preferable that the adhesive surface, especially the surface on which the adhesive layer is provided, is a polished surface, and it is particularly preferable that the surface is both a sliced ​​surface and a polished surface. The polished surface has relatively high smoothness, and therefore, when an adhesive layer is provided, it is easier to increase adhesion to the adherend.

[0068] The thickness of the thermally conductive layer is not particularly limited, but is, for example, approximately 1200 μm or less. However, from the viewpoint of suitable use in semiconductor applications and preventing high thermal resistance, it is preferable to make it relatively thin, preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. Furthermore, from the viewpoint of easily improving adhesion to the adherend, the thickness of the thermally conductive layer is preferably 50 μm or more, more preferably 80 μm or more, and even more preferably 120 μm or more. The thickness of the thermally conductive layer refers to the initial thickness measured without applying a load in the thickness direction. When used between a semiconductor chip and a heat spreader, the thickness of the thermally conductive layer is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 130 μm or less, and preferably 50 μm or more, more preferably 80 μm or more, and even more preferably 100 μm or more. When the thermally conductive layer is disposed between a test head and a semiconductor package in a semiconductor inspection process, the thickness of the thermally conductive layer is preferably 2000 μm or less, more preferably 1500 μm or less, and even more preferably 1000 μm or less, from the viewpoint of improving heat dissipation. The lower limit of the thickness of the thermally conductive layer is preferably 150 μm or more as a range applicable to semiconductor inspection applications, but is not particularly limited, and may be 200 μm or more, or may be 300 μm or more.

[0069] (Adhesive Layer) The thermally conductive sheet of the present invention preferably includes an adhesive layer on at least one surface of the thermally conductive layer. In this case, the thermally conductive sheet may be provided with adhesive properties on at least one surface of the thermally conductive layer by the adhesive layer. The thermally conductive layer having its surface made adhesive by the adhesive layer may be used as the thermally conductive sheet, or may be disposed on the surface of the thermally conductive sheet, thereby providing adhesive properties to the surface of the thermally conductive sheet as described above. The adhesive layer may be provided on only one surface of the thermally conductive layer, or on both surfaces of the thermally conductive layer. This allows the thermally conductive sheet to be configured with adhesive properties on both surfaces. Examples of adhesive layers that can be used include acrylic adhesive layers, rubber adhesive layers, urethane adhesive layers, and silicone adhesive layers. Among these, acrylic adhesive layers are preferred. The use of an acrylic adhesive layer increases adhesion to adherends such as heat spreaders, heat sinks, and semiconductor chips before and after high-temperature heating, such as during a reflow process.

[0070] The acrylic adhesive layer is formed from an acrylic adhesive. The acrylic adhesive preferably contains an acrylic polymer as a main component of the adhesive. The acrylic adhesive layer can exhibit adhesiveness by containing the acrylic polymer.

[0071] The acrylic adhesive layer may or may not have a reactive double bond, but preferably has a reactive double bond. When the acrylic adhesive layer has a reactive double bond, the reactive double bond reacts with high-temperature heating, thereby eliminating the adhesiveness and improving the adhesive strength to the adherend. Therefore, even when the thermally conductive sheet is adhered to an adherend such as a heat spreader or semiconductor chip and heated to a high temperature in a reflow process, the adherent state can be maintained and peeling from the adherend can be prevented. Furthermore, even when used in a relatively high-temperature environment of, for example, about 150°C in actual use, high adhesion can be maintained. The reactive double bond is an unsaturated carbon-carbon double bond that does not constitute an aromatic ring, and is typically a H ２ C=CH-* or H ２ C=CCH ３It is composed of a group having a structure represented by -* (* represents a bond), and specific examples include a vinyl group, an acryloyl group, and a methacryloyl group. The acrylic polymer having a reactive double bond (reactive double bond-containing acrylic polymer) may have functional groups such as a hydroxyl group, a carboxyl group, an epoxy group, or an amino group in the side chain in addition to the reactive double bond, but it preferably has at least one of a hydroxyl group and a carboxyl group in the side chain, and more preferably has both a hydroxyl group and a carboxyl group. The reactive double bond-containing acrylic polymer 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, or an amino group in the side chain (hereinafter also referred to as acrylic polymer (X)) with a reactive double bond-containing compound having a reactive group that reacts with the functional group and a reactive double bond (hereinafter also referred to as reactive double bond-containing compound (Y)).

[0072] The acrylic polymer (X) may be any polymer containing a structural unit derived from (meth)acrylate, but typically contains a structural unit derived from alkyl(meth)acrylate as the main component. More specifically, the acrylic polymer (X) may be a copolymer of alkyl(meth)acrylate and a functional group-containing monomer, or a copolymer of alkyl(meth)acrylate, a functional group-containing monomer, and a monomer other than these. The term "(meth)acrylate" is used to mean either or both of acrylate and methacrylate, and the same applies to other similar terms.

[0073] Alkyl (meth)acrylates are esters of (meth)acrylic acid and alkyl alcohols. The alkyl group in the alkyl (meth)acrylate may be linear, branched, or cyclic. Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, isomyristyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. One type of alkyl (meth)acrylate may be used alone, or two or more types may be used in combination. The alkyl (meth)acrylate is preferably an alkyl (meth)acrylate in which the alkyl group has 1 to 12 carbon atoms, and more preferably includes an alkyl acrylate in which the alkyl group has 2 to 8 carbon atoms. The structural unit derived from the alkyl acrylate in which the alkyl group has 2 to 8 carbon atoms may be the main component in the acrylic polymer (X), and may account for, for example, 50% by mass or more, 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.

[0074] As described above, examples of the functional group in the functional group-containing monomer include a carboxyl group, a hydroxyl group, an amino group, and an epoxy group. Of these, a carboxyl group and a hydroxyl group are preferred. Examples of monomers containing a carboxyl group include (meth)acrylic acid and crotonic acid. Of these, (meth)acrylic acid is more preferred. Examples of monomers containing a hydroxyl group include (meth)acrylates having a hydroxyl group, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate, and allyl alcohol. Of these, a (meth)acrylate having a hydroxyl group, such as 2-hydroxyethyl (meth)acrylate, is preferred. The content of the structural units derived from the functional group-containing monomer in the acrylic polymer (X) is, for example, about 1% by mass to 35% by mass, preferably 5% by mass to 30% by mass, and more preferably 10% by mass to 25% by mass. The functional group-containing monomers may be used alone or in combination of two or more.

[0075] Examples of other monomers include alkyl (meth)acrylates and monomers other than the functional group-containing monomers described above, and are not particularly limited as long as they are copolymerizable with the alkyl (meth)acrylates and functional group-containing monomers. Specific examples include styrene derivatives such as styrene, α-methylstyrene, p-methylstyrene, p-chlorostyrene, and divinylbenzene; compounds having a vinyl ester group such as vinyl acetate and vinyl propionate; 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, and tert-butyl vinyl ether. One type of other monomer may be used alone, or two or more types may be used in combination.

[0076] The reactive double bond-containing compound (Y) is a compound having a reactive group that reacts with the above-mentioned functional group and a reactive double bond. Examples of the reactive group include an isocyanate group, an epoxy group, a carboxyl group, and a hydroxyl group. Among these, an isocyanate group and an epoxy group are preferred, and an isocyanate group is more preferred. The content of the reactive double bond contained in the acrylic adhesive layer can be adjusted by the amount of functional groups contained in the acrylic polymer (X) and the ratio of the functional groups that react with the reactive double bond-containing compound (Y). The amount of functional groups contained in the acrylic polymer (X) can be adjusted by the ratio of functional group-containing monomers used in synthesizing the acrylic polymer (X).

[0077] The acrylic polymer contained in the acrylic adhesive layer may be an acrylic polymer containing a reactive double bond, or may contain an acrylic polymer without a reactive double bond in addition to the acrylic polymer containing a reactive double bond. The acrylic polymer may also be an acrylic polymer without a reactive double bond. An example of an acrylic polymer without a reactive double bond is the acrylic polymer (X) described above. In addition to the acrylic polymer described above, the acrylic adhesive may contain components that are generally blended into adhesives, and may also contain additives such as a crosslinker, a tackifier, a filler, an antioxidant, an ultraviolet protection agent, a plasticizer, and a viscosity modifier, as appropriate.

[0078] The weight-average molecular weight of the acrylic polymer is not particularly limited, but is, for example, about 100,000 to 1,200,000, and preferably about 200,000 to 1,000,000. The weight-average molecular weight is measured by gel permeation chromatography (GPC) and calculated as a polystyrene equivalent value.

[0079] The adhesive layer may be provided on one surface of the thermally conductive layer or on both surfaces of the thermally conductive layer. Here, "one surface" or "both surfaces" refers to the surface perpendicular to the thickness direction of the thermally conductive layer, also referred to as the "main surface." By providing the adhesive layer on both surfaces of the thermally conductive layer, the adhesion of both surfaces of the thermally conductive sheet to the adherend can be improved. Therefore, when the thermally conductive sheet is used in semiconductor applications, it can adhere to both the semiconductor chip and the heat spreader with relatively high adhesive strength. Furthermore, even when the thermally conductive sheet is heated at high temperatures through a reflow process or the like while in close contact with these, peeling of the thermally conductive sheet from both the semiconductor chip and the heat spreader is easily prevented.

[0080] The weight per unit area of ​​the adhesive layer on each surface is, for example, 0.05 mg / cm ２ or more, preferably 0.1 mg / cm ２ More preferably, 0.15 mg / cm ２ More preferably, 0.3 mg / cm ２ or more, and for example, 1.5 mg / cm ２ or less, preferably 1.3 mg / cm ２ or less, more preferably 1.1 mg / cm ２ More preferably, 0.9 mg / cm ２ The adhesive layer can ensure sufficient adhesive strength to the adherend by setting the basis weight to a certain amount or more. Also, it is easier to keep the amount of volatile components at 150°C above a certain amount. On the other hand, by setting the basis weight to a certain amount or less, it is easier to suppress the amount of volatile components at 150°C below a certain amount. Also, it is possible to prevent the thermal resistance value from decreasing due to the adhesive layer, making it easier to ensure good thermal conductivity.

[0081] The adhesive layer preferably permeates into the thermally conductive layer. Typically, a portion of the adhesive layer permeates into the thermally conductive layer. However, the entire adhesive layer may permeate into the thermally conductive layer as long as the adhesive layer can exert adhesive force on the adherend. By permeating the thermally conductive layer, the amount of adhesive present on the surface of the thermally conductive layer can be reduced, thereby preventing the adhesive layer from reducing thermal conductivity. Furthermore, the thermally conductive sheet can ensure high adhesion even if the adhesive permeates into the thermally conductive layer. While the mechanism behind this is unclear, it is believed that this is because thermally conductive sheets are generally compressed or otherwise pressurized during use, and the permeated adhesive seeps out to the surface due to this pressure, enhancing adhesion.

[0082] The adhesive layer can be impregnated into the thermally conductive layer in an appropriate amount by impregnating bubbles formed by the evaporation of the volatile substance, as described below. The adhesive layer may be formed to cover the entire surface of the thermally conductive layer, or may be formed to cover only a portion of the surface as long as it can exert adhesive force to the adherend.

[0083] Although the above describes an embodiment in which an adhesive layer is provided on at least one surface of the thermally conductive layer, the provision of an adhesive layer is not necessarily required. For example, an adhesive may be incorporated into the thermally conductive layer without providing an adhesive layer, thereby imparting adhesiveness to at least one surface of the thermally conductive layer. In this case, the adhesive may be incorporated into the thermally conductive layer by, for example, blending the adhesive into the mixed composition described below. Examples of adhesives that may be incorporated into the thermally conductive layer include acrylic adhesives, rubber adhesives, urethane adhesives, and silicone adhesives, with acrylic adhesives being preferred. Details of the acrylic adhesive are as described above. The adhesive may be a material that already has adhesiveness when blended into the mixed composition, or a material that does not have adhesiveness when blended into the mixed composition and exhibits adhesiveness in response to external stimuli such as heat, pressure, or light may be used.

[0084] When an adhesive is contained in the thermally conductive layer, the content of the adhesive in the thermally conductive layer may be, for example, 0.1 parts by mass or more and 20 parts by mass or less, preferably 0.3 parts by mass or more and 15 parts by mass or less, and more preferably 0.5 parts by mass or more and 12 parts by mass or less, relative to 100 parts by mass of the polymer matrix.

[0085] (SAT Coverage) The thermally conductive sheet of the present invention preferably has an SAT coverage of 60% or more, more preferably 70% or more, and even more preferably 80% or more when thermocompressed at 150°C for 10 minutes at 30 psi (hereinafter also referred to as "thermocompression SAT coverage"). When the SAT coverage by thermocompression is equal to or greater than the above lower limit, the initial adhesion is good. The upper limit of the SAT coverage by thermocompression is not particularly limited and may be 100%, but in practice it is, for example, 95%, preferably 90%, and more preferably 85%. The SAT coverage by thermocompression can be determined as follows. First, a sample is obtained by sandwiching a thermally conductive sheet between a silicon wafer and a copper plate and thermocompressing the sheet at 150°C for 10 minutes at 30 psi. The obtained sample is then subjected to ultrasonic testing (SAT) to obtain an image of the adhesive interface between the copper plate and the thermally conductive sheet, which is then binarized by a predetermined image processing method. The SAT coverage is then obtained based on the binarized image. The detailed procedure is as described in the Examples. The SAT coverage after high-temperature heating, which will be described later, can also be determined in the same manner, except that the sample is further heated at high temperature at 260°C for 3 minutes after compression bonding.

[0086] The thermally conductive sheet of the present invention preferably has an SAT coverage of 50% or more, more preferably 60% or more, and even more preferably 70% or more after being heated at high temperature for 3 minutes at 260°C under pressure at 150°C for 10 minutes (hereinafter also referred to as "SAT coverage after high-temperature heating"). If the SAT coverage after high-temperature heating is equal to or greater than the lower limit, the gap between the thermally conductive sheet and the adherend is reduced after high-temperature heating such as in a reflow process, resulting in good adhesion to the adherend. The upper limit of the SAT coverage after high-temperature heating is not particularly limited, and as long as it is 100%, practically it is, for example, 95%, preferably 90%, and more preferably 85%.

[0087] (E Hardness) The thermally conductive layer of the present invention preferably has a type E hardness (hereinafter also referred to as "E hardness") as defined in JIS K6253 of 10 or more and 80 or less, more preferably 20 or more and 70 or less, and even more preferably 30 or more and 65 or less. When the E hardness is equal to or greater than the above lower limit, the mechanical strength of the thermally conductive sheet is easily increased. Furthermore, when the E hardness is equal to or less than the above upper limit, the thermally conductive sheet is imparted with a certain degree of flexibility and its adhesion to the adherend is easily improved. When the thermally conductive sheet is used by being disposed between a semiconductor chip and a heat spreader, the E hardness of the thermally conductive layer is preferably equal to or greater than 30 and 50 or less, more preferably 35 or more and 45 or less. When the E hardness is equal to or greater than the above lower limit, the mechanical strength of the thermally conductive sheet is easily increased. Furthermore, when the E hardness is equal to or less than the above upper limit, the thermally conductive sheet is imparted with a certain degree of flexibility and its adhesion to the adherend is easily improved. When the thermally conductive sheet is used by being disposed between a test head and a semiconductor package in a semiconductor inspection process, the E-hardness of the thermally conductive layer is preferably 30 or more and 80 or less, and more preferably 40 or more and 70 or less. When the E-hardness is equal to or greater than the above-mentioned lower limit, the mechanical strength of the thermally conductive sheet is easily increased, and deformation of the sheet can be suppressed even when used under high load. Furthermore, when the E-hardness is equal to or less than the above-mentioned upper limit, a certain degree of flexibility is imparted to the thermally conductive sheet, and adhesion to the adherend is also easily improved.

[0088] [Method for manufacturing a thermally conductive sheet] The thermally conductive sheet of the present invention can be manufactured by a method comprising at least the following steps 1 to 3. However, the thermally conductive sheet of the present invention may also be manufactured by a method other than the following manufacturing method. Step 1: A step of mixing at least a curable polymer composition and a thermally conductive filler to obtain a mixed composition. Step 2: A step of curing the mixed composition by heating to obtain a cured product. Step 3: A step of applying an adhesive to the surface of the cured product.

[0089] (Step 1) In step 1, a mixed composition may be obtained by mixing at least a curable polymer composition and a thermally conductive filler, and it is preferable to further mix a volatile substance into the mixed composition. In addition, other components such as additives may be appropriately added to the mixed composition as needed.

[0090] In step 1, the mixing method and order of the above components are not particularly limited as long as they can be mixed to obtain a mixed composition. The curable polymer composition, the thermally conductive filler, the volatile substance added as needed, and other components added as needed can be mixed in any order to obtain the mixed composition. As described above, the curable polymer composition may be composed of, for example, a base agent and a curing agent (e.g., an alkenyl group-containing organopolysiloxane and a hydrogen organopolysiloxane in the case of an addition reaction type silicone). In such cases, the base agent, the curing agent, the thermally conductive filler, the volatile substance added as needed, and other components can be mixed in any order to obtain the mixed composition. The mixed composition may be in the form of a one-component type or a two-component type consisting of a first component and a second component. A two-component type is a type in which the first component and the second component are mixed together to obtain the mixed composition at the time of use.

[0091] (Volatile Substance) The volatile substance used in the present invention may be any component that volatilizes in step 2, which will be described later. The volatile substance volatilizes when heated during curing, thereby increasing the content of the thermally conductive filler in the thermally conductive sheet. Furthermore, the viscosity of the mixed composition decreases when the volatile substance is contained. This makes it easier to increase the amount of thermally conductive filler incorporated, and furthermore, makes it easier to orient the anisotropic filler in a predetermined direction by magnetic field orientation, which will be described later. Furthermore, the volatilization of the volatile substance forms a large number of fine bubbles in the cured product, which makes it easier for the adhesive to penetrate into the thermally conductive layer in step 3, which will be described later.

[0092] Furthermore, the volatile substance is preferably a compatible substance that is compatible or soluble in the curable polymer composition. If the volatile substance is a compatible substance, the curable polymer composition and the volatile substance can be mixed uniformly, making it easier to reduce viscosity and increase the amount of thermally conductive filler added. Furthermore, the bubbles formed by the evaporation of the volatile substance can be made fine and uniform.

[0093] The volatile substance is preferably a substance that is liquid at room temperature (25°C) and 1 atmosphere. Examples of the volatile substance include alkoxysilane compounds and hydrocarbon solvents. These compounds can increase the solubility or compatibility with the curable polymer composition, making it easier to reduce the viscosity of the mixed composition and increase the amount of thermally conductive filler added. Furthermore, the evaporation of the volatile substance makes it easier to form fine and uniform bubbles. The volatile substance may be used alone or in combination of two or more.

[0094] An alkoxysilane compound is preferably used as the volatile substance. The use of an alkoxysilane compound results in a cured thermally conductive sheet with a good appearance and no surface roughness. The alkoxysilane compound used as the volatile substance is a compound having a structure in which one to three of the four bonds possessed by a silicon atom (Si) are bonded to alkoxy groups, and the remaining bond is bonded to an organic substituent. The alkoxysilane compound possesses an alkoxy group and an organic substituent, thereby enhancing compatibility with curable polymer compositions, particularly curable polymer compositions composed of organopolysiloxanes. Examples of alkoxy groups possessed by alkoxysilane compounds include methoxy, ethoxy, protoxy, butoxy, pentoxy, and hexatoxy groups. The alkoxysilane compound may be contained in the curable polymer composition as a dimer.

[0095] Among alkoxysilane compounds, from the viewpoint of easy availability, alkoxysilane compounds having at least one of a methoxy group and an ethoxy group are preferred. From the viewpoint of compatibility with the curable polymer composition, solubility, etc., the number of alkoxy groups in the alkoxysilane compound is preferably 2 or 3, more preferably 3. Specifically, the alkoxysilane compound is preferably at least one selected from a trimethoxysilane compound, a triethoxysilane compound, a dimethoxysilane compound, and a diethoxysilane compound.

[0096] Examples of functional groups contained in the organic substituents of alkoxysilane compounds include acryloyl groups, alkyl groups, carboxyl groups, vinyl groups, methacrylic groups, aromatic groups, amino groups, isocyanate groups, isocyanurate groups, epoxy groups, hydroxyl groups, and mercapto groups. When a platinum catalyst is used as a curing catalyst for a curable polymer composition composed of an organopolysiloxane, it is preferable to select and use an alkoxysilane compound that is less likely to affect the curing reaction of the organopolysiloxane. Specifically, when an addition reaction-type organopolysiloxane using a platinum catalyst is used, it is preferable that the organic substituents of the alkoxysilane compound do not contain amino groups, isocyanate groups, isocyanurate groups, hydroxyl groups, or mercapto groups.

[0097] From the viewpoint of compatibility with the curable polymer composition composed of organopolysiloxane, the alkoxysilane compound preferably includes an alkylalkoxysilane compound having an alkyl group bonded to a silicon atom, i.e., an alkoxysilane compound having an alkyl group as an organic substituent. Therefore, dialkyldialkoxysilane compounds and alkyltrialkoxysilane compounds are preferred, with alkyltrialkoxysilane compounds being particularly preferred. The number of carbon atoms in the alkyl group bonded to the silicon atom may be, for example, 1 to 16. Furthermore, in trialkoxysilane compounds such as trimethoxysilane compounds and triethoxysilane compounds, the number of carbon atoms in the alkyl group is preferably 6 or more, more preferably 8 or more, and preferably 12 or less, more preferably 10 or less. Meanwhile, in dialkoxysilane compounds such as dimethoxysilane compounds and triethoxysilane compounds, the number of carbon atoms in the alkyl group may be 1 or more, and preferably 10 or less, more preferably 6 or less, and even more preferably 4 or less.

[0098] Examples of alkyl group-containing alkoxysilane compounds include methyltrimethoxysilane, dimethyldimethoxysilane, diethyldimethoxysilane, trimethylmethoxysilane, 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, and n-decyltriethoxysilane. Among the alkyl group-containing alkoxysilane compounds, n-decyltrimethoxysilane and n-octyltriethoxysilane are even more preferred from the viewpoint of compatibility with the organopolysiloxane that constitutes the curable polymer composition.

[0099] Examples of hydrocarbon solvents used as volatile substances include aromatic hydrocarbon solvents. Among these, aromatic hydrocarbon solvents are preferred from the viewpoint of compatibility with the curable polymer composition. Examples of aromatic hydrocarbon solvents include aromatic hydrocarbon solvents having about 6 to 10 carbon atoms, such as toluene, xylene, mesitylene, ethylbenzene, propylbenzene, butylbenzene, and t-butylbenzene, with toluene and xylene being preferred.

[0100] In the mixed composition, the content of the volatile substance per 100 parts by mass of the curable polymer composition is preferably 1 part by mass or more and 60 parts by mass or less. When the content is 1 part by mass or more, the effect of the volatile substance is easily exerted, for example, an appropriate amount of fine bubbles can be formed in the polymer matrix. Furthermore, when the content is 60 parts by mass or less, an effect commensurate with the amount of volatile substance used can be obtained. From these viewpoints, the content of the volatile substance is more preferably 1.5 parts by mass or more and 50 parts by mass or less, and even more preferably 2 parts by mass or more and 35 parts by mass or less. It is preferable that substantially all of the volatile substance volatilizes upon heating in step 2. It is preferable that the volatile substance is not contained in the thermally conductive sheet, but a small amount may be contained in the thermally conductive sheet as long as the amount of volatile components is within the above-mentioned specified range.

[0101] 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. The content of the thermally conductive filler in the mixed composition is also as described above. However, while the content of each component is shown above as an amount based on 100 parts by mass of the polymer matrix, in the mixed composition, the amount is based on 100 parts by mass of the curable polymer composition.

[0102] (Step 2) Step 2 is a step of curing the mixed composition by heating. The temperature at which the mixed composition is heated is not particularly limited as long as the curable polymer composition can be cured by heating. It is sufficient to heat the mixed composition at a temperature higher than room temperature (25°C), but preferably at 50°C or higher, more preferably at 70°C or higher. The heating temperature is also not particularly limited, but may be any temperature that does not cause thermal degradation of the thermally conductive layer or the mixed composition, for example, 200°C or lower, preferably 180°C or lower, more preferably 160°C or lower. The heating may be performed in one stage or in two or more stages. When performing the heating in two or more stages, the heating temperature may be within the above range in at least one stage, but it is preferable that the heating temperature be within the above range in all stages. Furthermore, it is preferable that at least the first heating stage is heated at a temperature lower than the boiling point of the volatile substance. The total heating time is, for example, about 10 minutes to 24 hours. When the curing is carried out in two or more stages, for example, the mixed composition may be partially cured in the first stage (primary curing) and fully cured by heating in the second or subsequent stage (secondary curing). Alternatively, the curing may be such that the mixed composition is fully cured by the primary curing and the heating in the second or subsequent stage does not involve curing.

[0103] As described below, when slicing a molded product obtained from the mixed composition to form a sheet-like molded product, it is also preferable to perform a first-stage heating before slicing to perform primary curing, and then further heating after slicing to perform a second-stage or subsequent heating (secondary curing). By heating after slicing, volatile substances are more likely to volatilize by the second-stage or subsequent heating. When curing in two or more stages, the heating in the first stage (primary curing) may be performed at a temperature of, for example, 50°C to 120°C, preferably 60°C to 100°C, and more preferably 70°C to 90°C. Furthermore, the heating in the second stage or subsequent (secondary curing) may be performed at a temperature higher than that of the primary curing, for example, 100°C to 200°C, preferably 120°C to 180°C, and more preferably 140°C to 160°C. The heating time in the first stage may be, for example, about 5 minutes to 20 hours, and preferably about 30 minutes to 12 hours. The heating time in the second and subsequent stages is, for example, about 10 minutes to 15 hours, preferably about 1 hour to 10 hours. By performing the first heating stage on the molded body obtained from the mixed composition at a relatively low temperature as described above, the volatile substance is less likely to foam and generate large bubbles, and the molded body can be cured so that the volatile substance remains within the molded body. Furthermore, if the molded body is sliced ​​and then heated in the second stage at a relatively high temperature, the molded body will harden, preventing foaming and generating large bubbles even at high temperatures, and the spaces where the volatile substance was present will become fine bubbles. The size of the bubbles is, for example, 1 μm or less, preferably 0.2 μm or less. There is no particular lower limit to the size of the bubbles, but it is, for example, 0.001 μm or more.

[0104] In step 2, the mixed composition may be formed into a predetermined shape such as a block or sheet, and then heated to harden. Furthermore, in step 2, if the mixed composition contains an anisotropic filler as the thermally conductive filler, the anisotropic filler may be oriented in one direction before being hardened by heating. The anisotropic filler can be oriented by a magnetic field orientation method or a flow orientation method, but magnetic field orientation is preferred.

[0105] In the magnetic field orientation method, the mixed composition is injected into a mold or the like and placed in a magnetic field to orient the anisotropic filler along the magnetic field. The curable polymer composition is then cured to obtain an oriented molded body. The mixed composition is preferably cured under the heating conditions described above. The oriented molded body is preferably in the form of a block, but may also be in the form of a sheet. By using a sheet, the oriented molded body may be coated with an adhesive directly in step 3 without slicing. On the other hand, by using a block, the orientation of the anisotropic filler is enhanced.

[0106] In the magnetic field orientation method, a release film may be placed inside the mold in the portion that comes into contact with the mixed composition. For example, a resin film with good releasability or a resin film whose one side has been treated with a release agent or the like is used as the release film. By using the release film, the oriented molded body can be easily released from the mold.

[0107] The viscosity of the mixed composition used in the magnetic field orientation method is preferably 50 Pa·s or more and 1500 Pa·s or less in order to achieve magnetic field orientation. By setting the viscosity at 50 Pa·s or more, the thermally conductive filler is less likely to settle. Furthermore, by setting the viscosity at 1500 Pa·s or less, the fluidity is improved, the anisotropic filler is properly oriented in the magnetic field, and problems such as excessive time required for orientation do not occur. Note that the viscosity is measured using a rotational viscometer (Brookfield viscometer DV-E, spindle SC4-14) at 25°C and a rotation speed of 5 rpm. However, when using a thermally conductive filler that is less likely to settle or when combining with additives such as anti-settling agents, the viscosity of the mixed composition may be less than 50 Pa·s.

[0108] In the magnetic field orientation method, magnetic field line generating sources for applying magnetic field lines include superconducting magnets, permanent magnets, electromagnets, etc., but superconducting magnets are preferred because they can generate a magnetic field with a high magnetic flux density. The magnetic flux density of the magnetic field generated from these magnetic field line generating sources is preferably 1 to 30 Tesla. If the magnetic flux density is 1 Tesla or higher, it becomes possible to easily orient the above-mentioned anisotropic filler made of a carbon material, etc. Furthermore, if the magnetic flux density is 30 Tesla or lower, practical production becomes possible.

[0109] In the flow orientation method, a primary sheet is produced in which the anisotropic filler is oriented in the plane direction by applying a shear force to the mixed composition. More specifically, in the flow orientation method, the mixed composition prepared in step 1 is first flattened and stretched while applying a shear force to form a sheet (primary sheet). By applying a shear force, the anisotropic filler can be oriented in the shear direction. Examples of sheet-forming methods include applying the mixed composition to a substrate film using a coating applicator such as a bar coater or doctor blade, or by extrusion molding or nozzle discharge, and then drying, semi-curing, or fully curing the mixed composition as needed. The thickness of the primary sheet is preferably approximately 50 μm to 5,000 μm. In the primary sheet, the anisotropic filler is oriented in one direction along the plane direction of the sheet. The mixed composition used in the flow orientation method has a relatively high viscosity so that a shear force is applied when stretched into a sheet. Specifically, the viscosity of the mixed composition is preferably 3 Pa·s or more and 500 Pa·s or less.

[0110] The primary sheet may be used as a thermally conductive sheet without being formed into a block, as described below. Alternatively, a laminated block (a block-shaped oriented molded product) may be formed by stacking multiple primary sheets so that they are oriented in the same direction, and then bonding the primary sheets together using a heat press or the like while curing them by heating as needed. To form a laminated block, at least one of the surfaces of the primary sheets to be stacked may be irradiated with vacuum ultraviolet light, and then the primary sheets may be stacked. By stacking the primary sheets via the surface irradiated with vacuum ultraviolet light, the primary sheets can be firmly bonded to each other. When irradiating with vacuum ultraviolet light, the mixed composition may be fully cured when preparing the primary sheet; curing by heating or the like is not necessary when stacking the primary sheets to form the laminated block. Even in the flow orientation method, the mixed composition may be cured under the heating conditions described above.

[0111] As described above, when forming a block-shaped oriented molded body, the obtained oriented molded body may be cut perpendicular to the orientation direction of the anisotropic filler by slicing or the like to form a sheet-shaped molded body. Slicing may be performed, for example, using a shear blade or a laser. When the sheet-shaped molded body is cut by slicing or the like, a portion of the fibrous filler may be exposed from the matrix at each surface, i.e., the cut surface. Most of the exposed fibrous filler will be oriented in the thickness direction without collapsing. However, in step 2, when the oriented molded body is cut by slicing or the like, the fibrous filler contained in the oriented molded body may be cut to a degree that does not impair the effects of the present invention.

[0112] The sheet-like molded body obtained by cutting may be directly coated with an adhesive in step 3 described below, or may be further processed. For example, each surface, i.e., the sliced ​​surface, may be polished. Furthermore, as described above, secondary curing may be performed. The secondary curing may be performed after or before polishing. By polishing the sheet-like molded body, the surface condition of the sheet-like molded body is improved, making it easier to further reduce the thermal resistance value. By polishing the sheet-like molded body, the sheet surface can be made smooth while leaving a certain amount of anisotropic filler, such as a fibrous filler, exposed on the surface. The fibrous filler can also be made to be in a collapsed state. This makes it easier to adhere the surface of the thermally conductive sheet to other components, and also makes it easier to cover the sheet surface with the fibrous filler over a certain area or more, making it easier to reduce the thermal resistance value.

[0113] The polishing may be performed by polishing at least one surface of the obtained sheet-like molded body, but it is preferable to polish both surfaces of the sheet-like molded body. The surface polishing may be performed using, for example, abrasive paper, abrasive film, abrasive cloth, abrasive belt, or the like. The properties of the abrasive paper are preferably those containing abrasive grains with an average particle size (D50) of 0.1 μm or more and 100 μm or less, more preferably 1 μm or more and 60 μm or less. The grain size of the abrasive grains in the abrasive paper is preferably #120 to 20,000, more preferably #300 to 15,000, and more preferably #320 to 4,000.

[0114] The polishing method can be, for example, polishing the surface of the sheet-like molded body by continuously contacting abrasive paper in the same linear direction, or by polishing by reciprocating a certain distance, by polishing by rotating in the same direction, or by polishing by contacting in various directions. The degree of polishing can be determined, for example, while observing the surface condition. For example, in the case of reciprocating polishing, one to 300 reciprocating strokes is preferred, three to 250 strokes is more preferred, and five to 100 strokes is even more preferred. The surface of the sheet-like molded body may be polished in two separate polishing steps. For example, after the first polishing using abrasive paper with a larger average particle size of abrasive grains, the second polishing using abrasive paper with a smaller average particle size of abrasive grains than that used in the first polishing may be performed.

[0115] (Step 3) In step 3, an adhesive is applied to the surface of the cured product such as the sheet-like molded article obtained in step 2 as described above. In this production method, it is preferable to impregnate the thermally conductive layer with the adhesive, but it is also preferable that the adhesive penetrates into the thermally conductive layer simply by applying the adhesive.

[0116] The adhesive may be diluted with a diluent and applied as a diluted adhesive solution to the surface of the sheet-shaped molded body. Diluting the adhesive with a diluent makes it easier for the adhesive to penetrate into the thermal conductive layer. The diluent is not particularly limited as long as it is a liquid at 25°C and 1 atmosphere, has solubility or compatibility with the adhesive, and is a component that volatilizes upon drying as described below, but an organic solvent is preferably used.

[0117] The organic solvent to be used is not particularly limited, but examples thereof include ketone compounds such as acetone, methyl ethyl ketone, and cyclohexanone; aromatic hydrocarbon compounds such as toluene, xylene, and tetramethylbenzene; glycol ether compounds such as 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, and 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. In order to properly penetrate the adhesive into the thermally conductive layer when spray-coating as described below, it is preferable to use an organic solvent that does not volatilize too quickly, such as 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, or polyethylene glycol monoethyl ether. In addition to the organic solvents listed above, it is also preferable to use an organic solvent with a lower boiling point than these. Specific examples include methyl ethyl ketone, methyl isobutyl ketone, hexane, ethyl acetate, butyl acetate, and toluene.

[0118] The dilution concentration with the diluent is not particularly limited, but it is recommended to adjust the solids concentration of the adhesive to, 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 more preferably 10% by mass or more and 25% by mass or less. A solids concentration of 5% by mass or more can prevent excessive heating during drying and allow a predetermined amount of adhesive, together with the organic solvent, to properly penetrate into the thermally conductive layer. Furthermore, by adjusting the solids concentration to 50% by mass or less, the basis weight is not increased more than necessary, and the viscosity can be adjusted to facilitate penetration, allowing the adhesive to properly penetrate into the thermally conductive layer. Furthermore, by keeping the dilution concentration within the above range, it is easy to adjust the amount of volatile components at 150°C and 260°C to a predetermined range. The amount of adhesive that penetrates into the thermally conductive layer can be adjusted by adjusting the viscosity, solids concentration, type of solvent, etc. For example, if a large amount of adhesive is desired to penetrate, it is recommended to adjust the solids concentration to a high concentration with a low viscosity. Also, if you want to reduce the amount of adhesive material that soaks in, you can make the viscosity high and the solid content low.

[0119] The adhesive application method is not particularly limited, and known application methods may be employed, although spray application is preferred. Spray application prevents the basis weight from becoming excessively high and facilitates the adhesive to properly penetrate the thermally conductive layer. Furthermore, spray application and reduced application volume can provide areas with and without an adhesive layer on the thermally conductive layer surface. When spray application is employed, it is preferable to spray an adhesive containing a fast-drying organic solvent such as ethyl acetate and a slow-drying organic solvent such as polyethylene glycol monoethyl ether or propylene glycol monomethyl ether acetate. More specifically, the inclusion of a slow-drying organic solvent prevents excessive evaporation of the organic solvent when the adhesive is applied to the thermally conductive layer surface from the sprayer, thereby facilitating penetration of the adhesive into the thermally conductive layer. On the other hand, the inclusion of a fast-drying solvent preferably adjusts the viscosity to a level suitable for spray application.

[0120] The applied adhesive may then be dried to volatilize the diluent. The drying temperature is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher, from the viewpoint of maintaining the amount of volatile components at 150°C or lower and facilitating good adhesion after high-temperature heating such as a reflow process. The drying temperature is preferably 170°C or lower, more preferably 150°C or lower, and even more preferably 120°C or lower, from the viewpoint of maintaining the amount of volatile components at 150°C or higher and facilitating good initial adhesion. The drying time may be long enough to volatilize substantially all of the diluent contained in the applied adhesive, but is preferably 10 minutes or longer, more preferably 20 minutes or longer, and even more preferably 30 minutes or longer, from the viewpoint of maintaining the amount of volatile components at 150°C or lower and facilitating good adhesion after high-temperature heating such as a reflow process. The drying time is preferably 30 hours or less, more preferably 6 hours or less, and even more preferably 3 hours or less, from the viewpoint of ensuring a certain level of volatile components at 150°C and improving initial adhesion. The drying is preferably carried out under normal pressure, but may also be reduced-pressure drying or vacuum drying, which is carried out under reduced pressure. In reduced-pressure or vacuum drying, the drying temperature can be appropriately lowered or the drying time can be appropriately shortened.

[0121] The above manufacturing method is merely an example, and the thermally conductive sheet does not necessarily have to be manufactured by the above manufacturing method. For example, it may be manufactured by a method omitting step 3 described above. In this case, the thermally conductive sheet does not need to have an adhesive layer, and the adhesive may be contained in the thermally conductive layer. The thermally conductive layer containing the adhesive may be used as the thermally conductive sheet, or may be disposed on the surface of the thermally conductive sheet, thereby imparting adhesiveness to at least one surface of the thermally conductive sheet. In this case, the adhesive may be incorporated into the mixed composition in step 1. The adhesive contained in the thermally conductive layer is as described above, and therefore a detailed description thereof will be omitted. When the adhesive is contained in the thermally conductive layer and step 3 described above is omitted, the adhesive may be appropriately mixed in any order in step 1 together with the curable polymer composition, the thermally conductive filler, the volatile substance added as needed, and other components added as needed. When the PSA is blended into the mixed composition in step 1, the PSA may be diluted with a diluent and blended into the mixed composition as a diluted PSA solution, or may be blended into the mixed composition without dilution with a diluent. The diluent is also as described above, and a detailed description thereof will be omitted. Furthermore, when a diluted PSA solution is blended into the mixed composition, the diluent may volatilize during heating in step 2 described above.

[0122] [Uses of Thermally Conductive Sheets] Thermally conductive sheets are interposed between a heat-generating element and a heat sink, transferring heat generated by the heat-generating element to the heat sink via thermal conduction and dissipating the heat from the heat sink. Thermally conductive sheets are used in electronic devices, semiconductor applications, and the like, and are preferably used in semiconductor applications. In semiconductor applications, thermally conductive sheets may be used in any application, but are preferably used in applications called TIM1, where they are directly applied to semiconductor chips such as silicon dies, for example, between a semiconductor chip and a heat spreader. Of course, thermally conductive sheets may also be used in applications called TIM2, where they are not directly applied to semiconductor chips. In this case, the thermally conductive sheet may be used, for example, between a heat spreader and a cooling unit such as a heat sink or heat pipe. In addition to the above, thermally conductive sheets may also be used between various electronic components that generate heat and heat sinks, heat pipes, heat pumps, metal housings of electronic devices, and other heat sinks. Thermally conductive sheets are also preferably used in semiconductor inspection processes, where semiconductor elements such as semiconductor packages are inspected. In particular, it is preferable to use the thermally conductive sheet between a test head and a semiconductor package in a semiconductor inspection process.The thermally conductive sheet is preferably placed between two members (adherends) such as a heat sink or a heat generating member, and is preferably used in a state of being in close contact with and compressed by the two members (adherends).

[0123] The thermally conductive sheet may be laminated on the adherend at room temperature, but as described below, it may also be mounted on the adherend by being heated to an appropriate temperature and then laminated on the adherend.

[0124] The thermally conductive sheet may also be used as a laminate having a metal foil such as aluminum foil attached to at least one surface. The laminate may be formed by attaching a metal foil to the thermally conductive sheet of the present invention, which has an adhesive surface, obtained by applying an adhesive to one surface of the thermally conductive sheet to form an adhesive layer. Alternatively, the metal foil may be laminated while preparing the thermally conductive sheet of the present invention by applying an adhesive to the surface of the metal foil and then attaching the metal foil to a thermally conductive sheet that is not coated with the adhesive. Furthermore, when a metal foil is laminated on only one surface of the thermally conductive sheet, the other surface of the thermally conductive sheet may or may not be coated with an adhesive. However, from the viewpoint of improving the adhesion of both surfaces of the thermally conductive sheet to the adherend, it is preferable to apply an adhesive to the other surface of the thermally conductive sheet to form an adhesive layer.

[0125] As shown in FIG. 1 , an adhesive 11 for fixing a LID 10 used in a semiconductor package or the like may be applied near the thermally conductive sheet 12 during mounting. In such cases, when mounting the thermally conductive sheet 12 on an adherend 13 such as an IC chip, the structure 1 including the LID 10, adhesive 11, thermally conductive sheet 12, and adherend 13 may be heated. This heating hardens the adhesive of the adhesive 11, allowing the LID 10 to be fixed to a substrate 14 on which an IC chip or the like is mounted via the adhesive 11 before the reflow process. Note that the member for fixing the LID 10 to the substrate is not limited to the adhesive 11 and may be a sealant or the like. For example, when a sealant is used, the sealant may be attached to the substrate 14, and the adhesive of the sealant may be hardened by heating, while the LID 10 is fixed to the substrate via the sealant. This prevents the LID 10 or the like from shifting during the reflow process. During heating, the thermally conductive sheet 12 may be laminated onto the adherend 13 by thermocompression bonding with appropriate pressure. The thermally conductive sheet 12 may be adhered to the adherend 13 via at least one surface of the adhesive thermally conductive layer. The heating temperature during mounting may be lower than the temperature during high-temperature heating described below, for example, about 100 to 200°C, preferably about 120 to 170°C. Because the thermally conductive sheet has a small amount of volatile components at 150°C, it is possible to prevent a decrease in the adhesion of the thermally conductive sheet to the adherend due to heating during mounting.

[0126] Furthermore, the thermally conductive sheet is preferably used in applications where it is heated to high temperatures, for example, between 200°C and 300°C, preferably between 220°C and 270°C, while in close contact with an adherend via at least one surface of the adhesive thermally conductive layer. Even when heated to high temperatures while in close contact with an adherend, the thermally conductive sheet of the present invention prevents a decrease in adhesive strength to the adherend as described above, thereby preventing peeling from the adherend even when heated to high temperatures. For semiconductor applications, the thermally conductive sheet is preferably mounted in close contact with an adherend such as a substrate or silicon wafer. The thermally conductive sheet is preferably subjected to a reflow process while in close contact with the adherend, and is preferably heated within the high temperature range described above during the reflow process. The thermally conductive sheet may be heated during the reflow process while in close contact with one or both of, for example, a semiconductor chip or a heat spreader.

[0127] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0128] The measurement and evaluation methods in the present examples are as follows.

[0129] [Sheet Thickness] The thickness (initial thickness) of the thermally conductive sheet was measured using a thickness gauge.

[0130] [Tack Value] A tack tester TA-500 manufactured by UBM was used, and the thermally conductive sheet was fixed to the stage with double-sided tape. The maximum load measured under the following measurement conditions was taken as the tack value (N). The double-sided tape used was "Nistack NW-K15" double-sided tape manufactured by Nichiban Co., Ltd. (Measurement conditions) Probe diameter: 5 mmφ Pressing load: 20 N Holding time: 10 seconds Pull-up speed: 0.1 mm / s Measurement environment: 23°C, 50% RH

[0131] [Amount of Volatile Components at 150° C.] To identify the amount of residual solvent in the sample, the amount was measured by thermal desorption GC-MS under the following conditions. <Thermal desorption GC-MS measurement conditions> Thermal desorption apparatus: TurboMatrix 350 (PerkinElmer) Sample amount: 5 mg, precision balance Heating: 150°C, 10 min (20 mL / min) Secondary desorption: 350°C Split: inlet 25 mL / min, outlet 25 mL / min, injection volume 2.5% GC-MS apparatus: Agilent 7890B&JMS-Q1500GC (JEOL Ltd.) Column: EQUITY-1 (non-polar) 0.32 mm x 60 m x 0.25 μm GC temperature rise: 40°C (4 min) → 300°C (10 min) (heat rise at a rate of 10°C / min) He flow rate: 1.5 mL / min (split ratio 1:30) Ionization voltage: 70 eV MS measurement range: 29 to 600 amu (scan 500 ms) MS temperature: ion source 230°C, interface 250°C Quantitative analysis was performed using the toluene peak area measured under the same conditions as the sample using a Tenax tube to which 2 μL of a methanol solution with a toluene concentration of 100 ppm had been adsorbed.

[0132] [Amount of Volatile Components at 260°C] To identify the residual solvent in the sample, the amount of volatile components was measured by thermal desorption GC-MS under the following conditions: The amount of volatile components at 260°C was evaluated using the sample after measuring the amount of volatile components at 150°C. <Thermal desorption GC-MS measurement conditions> Thermal desorption apparatus: TurboMatrix 350 (PerkinElmer) Sample amount: 5 mg, precision balance Heating: 260°C, 5 min (20 mL / min) Secondary desorption: 350°C Split: inlet 25 mL / min, outlet 25 mL / min, injection volume 2.5% GC-MS apparatus: Agilent 7890B&JMS-Q1500GC (JEOL Ltd.) Column: EQUITY-1 (non-polar) 0.32 mm x 60 m x 0.25 μm GC temperature rise: 40°C (4 min) → 300°C (10 min) (heat rise at a rate of 10°C / min) He flow rate: 1.5 mL / min (split ratio 1:30) Ionization voltage: 70 eV MS measurement range: 29 to 600 amu (scan 500 ms) MS temperature: ion source 230°C, interface 250°C Quantitative analysis was performed using the toluene peak area measured under the same conditions as the sample using a Tenax tube to which 2 μL of a methanol solution with a toluene concentration of 100 ppm had been adsorbed.

[0133] [SAT Coverage] The SAT coverage by thermocompression bonding was obtained by the following steps 1 to 3. 1. A 30 mm square copper plate and a silicon wafer were prepared, and the thermally conductive sheet obtained in each Example and Comparative Example was sandwiched between the copper plate and the silicon wafer. A weight was placed on the copper plate, and the plate was heated and compressed at 150°C for 10 minutes under a pressure of 30 psi to obtain a SAT sample.

[0134] 2. Using the sample obtained in 1 above, ultrasonic testing (SAT) was performed to obtain an observation image of the thermally conductive sheet. SAT was performed using a high-precision ultrasonic testing device ("C-SAM D9500" manufactured by Nippon Barnes Co., Ltd.). 3. The image obtained in 2 above was binarized using the image processing software ImageJ at a brightness value of 251, and the colored areas in the image were considered to be the bonded areas. The proportion of the bonded areas to the total area was obtained as the SAT coverage rate due to thermocompression bonding. In the ultrasonic testing, the SAT coverage rate at the interface between the copper plate and the thermally conductive sheet was calculated.

[0135] Furthermore, with regard to the SAT coverage after high-temperature heating, the sample obtained in 1 above was further heated at 260°C for 3 minutes, and then the SAT coverage was determined by the methods in 2 and 3, and this was taken as the SAT coverage after high-temperature heating. The heating at 260°C for 3 minutes was carried out in a reflow furnace ("UNI-5016F" manufactured by Antom Co., Ltd.), similar to the reflow process.

[0136] The following components were used as raw materials for the thermally conductive sheet.

[0137] (Base and curing agent) Curable silicone: Addition reaction type organopolysiloxane consisting of alkenyl group-containing organopolysiloxane as the base and hydrogen organopolysiloxane as the curing agent (however, it contains a catalytic amount of platinum catalyst). (Volatile substance) n-decyltrimethoxysilane

[0138] (Thermal conductive filler) Aluminum oxide 1: polyhedral shape, average particle size (D50) = 0.5 μm, aspect ratio 1.0 Aluminum oxide 2: polyhedral shape, average particle size (D50) = 3.0 μm, aspect ratio 1.0 Aluminum: spherical, average particle size (D50) = 3 μm, aspect ratio 1.0 to 1.5 Graphitized carbon fiber: average fiber length (arithmetic mean) 85 μm, diameter 10 μm, aspect ratio 8.5, thermal conductivity 900 W / m·K Flake graphite powder: average particle size (D50) = 15 μm, aspect ratio 10, thermal conductivity 550 W / m·K (Polymer dispersant) Pyrene dispersant: organopolysiloxane containing pyrene shown in the synthesis method described below, number average molecular weight 17,000

[0139] (Synthesis of pyrene dispersant) 98.6 g of an organosiloxane compound (n=210) having a 1,3-diol group, 1.4 g of 1-pyrenecarboxaldehyde, 50 g of toluene as a solvent, and 0.6 g of a catalyst ("Amberlyst 15 dry" manufactured by Organo Corporation) were reacted in a nitrogen atmosphere at 100°C for 24 hours. After the reaction, the catalyst was removed by filtration through a 5.0 μm PTFE filter, and the filtrate was concentrated using a rotary evaporator and a vacuum dryer to obtain pyrene dispersant 1. The reaction formula is shown below. １ The progress of the following reaction was confirmed by H NMR measurement. The NMR measurement was performed using a JEOL "ECX-400" NMR analyzer under the following conditions: deuterated chloroform as the solvent, sample concentration 1 wt %, 25°C, measurement frequency 400 MHz, and 8 accumulations.

[0140] (Adhesive) An adhesive whose main adhesive component is an acrylic polymer whose main component is a structural unit derived from 2-ethylhexyl acrylate and which has hydroxyl groups, carboxyl groups, and vinyl groups in its side chains. *Note that 100 parts by mass of a diluted solution of the adhesive diluted with ethyl acetate to a solids concentration of 33% by mass was further diluted with 150 parts by mass of propylene glycol monomethyl ether acetate (solvent) to prepare a coating solution with a solids concentration of 13.2% by mass, which was used in each of the Examples and Comparative Examples.

[0141] Example 1: The components in accordance with the formulation in Table 1 were mixed using a planetary mixer at 25°C for 50 minutes to obtain a mixed composition. The mixed composition was then poured into a mold set to a thickness sufficiently greater than that of the thermally conductive sheet, and an 8 T magnetic field was applied in the thickness direction to orient the carbon fibers and flake graphite in the thickness direction. The curable silicone was then primarily cured by heating at 80°C for 8 hours to obtain a block-shaped oriented molded body. Next, the block-shaped oriented molded body was sliced ​​into 100 μm-thick sheets using a shearing blade to obtain a sheet-shaped molded body with exposed carbon fibers. The sheet-shaped molded body was then heated at 150°C for 6 hours to undergo secondary curing. The sheet-shaped molded body was then reciprocally polished 75 times with coarse abrasive paper A (grain size #800) having an average abrasive grain size (D50) of 20 μm, and then further reciprocally polished 10 times with coarse abrasive paper B (grain size #4000) having an average abrasive grain size (D50) of 3 μm.

[0142] *The values ​​for each component in Table 1 are in parts by mass. *The sheet hardness is a Type E hardness measured on the cured product obtained from the above formulation in each example and comparative example.

[0143] The adhesive coating solution was sprayed onto both surfaces of the obtained sheet-like molded article, adjusting the discharge amount so that the basis weight after drying would be the amount shown in Table 5, and then drying was performed under the drying conditions shown in Table 5, thereby obtaining a thermally conductive sheet in which an acrylic adhesive layer was provided on both surfaces of the thermally conductive layer (sheet-like molded article).

[0144] Examples 2 and 4 A thermally conductive sheet having an acrylic adhesive layer provided on both surfaces of a thermally conductive layer was obtained in the same manner as in Example 1, except that the basis weight or drying conditions were changed as shown in Table 5.

[0145] Example 3 A thermally conductive sheet having acrylic adhesive layers on both surfaces of a thermally conductive layer was obtained in the same manner as in Example 1, except that the material of the block-shaped oriented molded body was changed to the composition shown in Table 2.

[0146] *The values ​​for each component in Table 2 are in parts by mass. *The sheet hardness is Type E hardness measured on the cured product obtained from the above formulation in Example 3.

[0147] Example 5 A thermally conductive sheet having an acrylic adhesive layer on both surfaces of a thermally conductive layer was obtained in the same manner as in Example 1, except that a block-shaped oriented molded product was sliced ​​into sheets having a thickness of 200 μm.

[0148] [Example 6] A thermally conductive sheet having an acrylic adhesive layer on one surface of a thermally conductive layer was obtained using the same procedure as in Example 1, except that the material of the block-shaped oriented molded body was changed to the formulation in Table 3, the drying conditions were changed as in Table 6, and the adhesive coating solution was spray-coated on only one surface of the obtained sheet-shaped molded body.

[0149] *The values ​​for each component in Table 3 are in parts by mass. *The sheet hardness is Type E hardness measured for the cured product obtained from the above formulation in Example 6.

[0150] Example 7 A thermally conductive sheet having an acrylic adhesive layer on one surface of a thermally conductive layer was obtained in the same manner as in Example 6, except that the block-shaped oriented molded product was sliced ​​into sheets having a thickness of 200 μm.

[0151] [Example 8] A thermally conductive sheet having an acrylic adhesive layer on one surface of a thermally conductive layer was obtained by the same procedure as in Example 6, except that the block-shaped oriented molded body was sliced ​​into sheets with a thickness of 200 μm and the basis weight was changed as shown in Table 6.

[0152] Example 9 A thermally conductive sheet having an acrylic adhesive layer on one surface of a thermally conductive layer was obtained in the same manner as in Example 6, except that the block-shaped oriented molded product was sliced ​​into sheets with a thickness of 400 μm.

[0153] [Example 10] A thermally conductive sheet having adhesive properties on both surfaces of the thermally conductive layer was obtained in the same manner as in Example 1, except that the material of the block-shaped oriented molded body was changed to the formulation shown in Table 4, an adhesive was contained in the thermally conductive layer instead of providing an adhesive layer, and spray coating was not performed. The adhesive used in Example 10 was the same as that used in the other Examples and Comparative Examples, except that it was not diluted with various diluents.

[0154] *The values ​​of each component in Table 4 are in parts by mass. *The sheet hardness is a Type E hardness measured for the thermally conductive sheet obtained in Example 10.

[0155] Comparative Example 1 A thermally conductive sheet having acrylic adhesive layers provided on both surfaces of a thermally conductive layer was obtained in the same manner as in Example 1, except that the drying conditions and basis weight were changed as shown in Table 7.

[0156] Comparative Example 2 A thermally conductive sheet having acrylic adhesive layers provided on both surfaces of a thermally conductive layer was obtained in the same manner as in Example 1, except that the drying conditions were changed as shown in Table 7.

[0157] Comparative Example 3 A thermally conductive sheet having no acrylic adhesive layer on either surface of the thermally conductive layer was obtained in the same manner as in Example 1, except that the adhesive coating solution was not applied to either surface of the sheet-shaped molded body.

[0158]

[0159]

[0160] *In Tables 5 to 7, the "type of sheet" refers to the type of thermally conductive layer with different formulations. Specifically, "Sheet 1" refers to the thermally conductive layer obtained from the formulation in Table 1, "Sheet 2" refers to the thermally conductive layer obtained from the formulation in Table 2, "Sheet 3" refers to the thermally conductive layer obtained from the formulation in Table 3, and "Sheet 4" refers to the thermally conductive layer obtained from the formulation in Table 4.

[0161] As is clear from the above results, the thermally conductive sheets prepared in each example had a certain amount of volatile components at 150°C within a certain range, resulting in a high SAT coverage, an indicator of adhesion, both before and after the reflow process, which involves high-temperature heating. In contrast, the thermally conductive sheet prepared in Comparative Example 1 had an excessive amount of volatile components at 150°C, resulting in a significant decrease in SAT coverage after the reflow process. Furthermore, the thermally conductive sheet prepared in Comparative Example 2 had an excessively low amount of volatile components at 150°C, resulting in a low SAT coverage not only after the reflow process but also before the reflow process. In other words, excellent initial adhesion was not achieved. Furthermore, the thermally conductive sheet prepared in Comparative Example 3 did not have an adhesive coating solution applied, and therefore, like Comparative Example 2, did not achieve excellent initial adhesion.

[0162] REFERENCE SIGNS LIST 1 Construct 10 LID 11 Adhesive 12 Thermally conductive sheet 13 Adherend 14 Substrate

Claims

1. A thermally conductive sheet comprising a thermally conductive layer containing a polymer matrix and a thermally conductive filler, at least one surface of which is adhesive, wherein the amount of volatile components in the thermally conductive sheet measured by thermal desorption GC-MS at 150°C is 2 ppm by mass or more and 80 ppm by mass or less.

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

3. The thermally conductive sheet according to claim 1 or 2, further comprising an adhesive layer on at least one surface of the thermally conductive layer.

4. The thermally conductive sheet according to claim 3, wherein the adhesive layer is formed by spray coating.

5. The thermally conductive sheet according to claim 3, wherein the adhesive layer is an acrylic adhesive layer.

6. The thermally conductive sheet according to claim 5, wherein the acrylic adhesive layer has a reactive double bond.

7. The thermally conductive sheet according to claim 1 or 2, wherein the adhesiveness disappears when heated at 260°C for 3 minutes.

8. The thermally conductive sheet according to claim 1 or 2, wherein the amount of volatile components in the thermally conductive sheet measured by thermal desorption GC-MS at 260° C. is 2,500 ppm by mass or less.

9. The thermally conductive sheet according to claim 1 or 2, wherein the adhesive strength of at least one of the surfaces is 2 N or more as measured by a tack test.

10. A thermally conductive sheet comprising a thermally conductive layer containing a polymer matrix and a thermally conductive filler, at least one surface of the thermally conductive layer being adhesive, wherein the amount of volatile components in the thermally conductive sheet as measured by thermal desorption GC-MS at 150°C is 2 ppm by mass or more and 80 ppm by mass or less.

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