Thermally conductive sheet and method for producing same

Abstract

This thermally conductive sheet (10) contains a polymer matrix (12) and an anisotropic filler (13) oriented in the thickness direction, has a thickness of less than 0.2 mm, and has a porosity of 1.0-15.0% in a cross-section (S2) parallel to the surface and at a depth of 25 [mu] m from the surface. A resin different from the polymer matrix is provided in at least some voids (14) in at least one surface of the thermally conductive sheet. According to the present invention, it is possible to provide a thin thermally conductive sheet having a low thermal resistance value and good adhesion to an adherend.

Description

TECHNICAL FIELD

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

[0002] In recent years, with the high-density of the wiring of a multilayer wiring board, the high-density of the wiring of a semiconductor package, the increase of the mounting density of electronic parts, the increase of the heat generation per unit area due to the high integration of a semiconductor component itself, and the like, it is desired to improve the heat dissipation of a semiconductor package. It is known that a semiconductor package is heat-dissipated by sandwiching a heat dissipation material between a heat generating body such as a semiconductor chip and a heat sink called a heat dissipation sheet and making them adhere to each other. The heat dissipation material used between the semiconductor chip and the heat dissipation sheet has conventionally widely used a thermally conductive grease.

[0003] A semiconductor package is generally heated to a certain temperature or more when used or the like. Since each member such as a substrate, a semiconductor chip, a heat dissipation sheet, and the like has different thermal expansion rates, there is a case where warping occurs when heated. In recent years, with the large-scale of the chip, the expansion of the gap due to the warping also becomes large, and the thermally conductive grease has a defect that "it cannot follow such warping and a gap is generated", so it is being studied to use a thermally conductive sheet instead of the thermally conductive grease.

[0004] For the thermally conductive sheet for the above use, in order to improve the heat dissipation while improving the followability to the warping, it is required to also improve the softness. However, if both the heat dissipation and the softness are to be improved, the adhesiveness of the thermally conductive sheet to the surrounding members decreases, so there is a concern that the thermally conductive sheet, like the thermally conductive grease, cannot follow the warping and is peeled from the semiconductor chip or the heat dissipation sheet.

[0005] Further, a semiconductor package is generally manufactured through a reflow step with high-temperature heating. Therefore, there is a case where it is required that the thermally conductive sheet used between the semiconductor chip and the heat dissipation sheet maintains the adhesiveness to the adherends such as the semiconductor chip, the heat dissipation sheet, and the like even after the high-temperature heating.

[0006] Based on such a background, a thermally conductive sheet having high adhesiveness to the adherends is desired. In Patent Literature 1, an invention relating to a thermally conductive sheet is disclosed, which has a base sheet containing thermally conductive particles and an organic high molecular compound, and an adhesive component locally present on at least one surface of the above base sheet, and it is described that the thermally conductive sheet is easily fixed to a heat generating body or a heat sink. Further, the example of Patent Literature 1 describes that a laminate obtained by laminating a plurality of sheets "a primary sheet containing flaky graphite particles of an anisotropic filler material (a filler material having a certain length-diameter ratio or more)" is sliced to obtain a base sheet of 0.25 mm, an adhesive component is given to the base sheet, and a thermally conductive sheet is produced.

[0007] [Patent Literature]

[0008] [Patent Literature]

[0009] Patent Literature 1: Japanese Patent No. 6852266 SUMMARY

[0010] [Problems to be Solved by the Invention]

[0011] As the invention described in Patent Literature 1, it is known that a thermally conductive sheet is produced by a step of slicing a laminate of a plurality of pieces containing an anisotropic filler material. From the viewpoint of reducing thermal resistance, it is considered that a block-shaped laminate containing an anisotropic filler material is sliced into thin pieces to reduce the thickness of the thermally conductive sheet. However, even if sliced into thin pieces, there are cases where the thermal resistance does not decrease as expected, and improvement is desired.

[0012] Therefore, an object of the present application is to provide a thermally conductive sheet having a small thickness, a low thermal resistance, and good adhesion to an adherend.

[0013] [Technical Means for Solving the Problems]

[0014] The present inventors have made intensive studies in order to solve the above problems. As a result, it has been found that when a block-shaped molded body containing an anisotropic filler material is sliced into thin pieces, a part of the anisotropic filler material falls off, voids are easily formed on the surface of the thermally conductive sheet, and the voids are the cause of deterioration of thermal resistance and adhesion. Furthermore, it has been found that by filling at least a part of the voids with a resin, the thermal resistance can be reduced and the adhesion to an adherend can be improved, and thus the following present application has been completed.

[0015] That is, the present application provides the following [1] to

[14] .

[0016] [1] A thermally conductive sheet containing a polymer matrix and an anisotropic filler material oriented in the thickness direction, and further

[0017] the thickness of the thermally conductive sheet is less than 0.2 mm,

[0018] the void ratio in the cross section of the thermally conductive sheet at a depth position parallel to the surface and 25 μm from the surface is 1.0 to 15.0%,

[0019] a resin different from the polymer matrix is provided in at least a part of the voids on at least one surface of the thermally conductive sheet.

[0020] [2] The thermally conductive sheet according to the above [1], wherein the resin different from the polymer matrix is an acrylic adhesive.

[0021] [3] The thermally conductive sheet according to the above [2], wherein the acrylic adhesive is an acrylic adhesive having a reactive double bond.

[0022] [4] The thermally conductive sheet according to any one of [1] or [2] above, having an acrylic adhesive layer formed of an acrylic adhesive on a surface.

[0023] [5] The thermally conductive sheet according to [4] above, wherein an intensity ratio A / B of a peak intensity A of C=C stretching vibration to a peak intensity B of C=0 stretching vibration in a Raman spectrum of the acrylic adhesive is 0.2 or greater.

[0024] [6] The thermally conductive sheet according to any one of [1] or [2] above, wherein the high molecular matrix is an organopolysiloxane.

[0025] [7] A method of manufacturing a thermally conductive sheet, comprising the steps of:

[0026] mixing at least a curable high molecular composition and an anisotropic filler material to obtain a mixed composition;

[0027] curing the mixed composition by heating to obtain a cured product;

[0028] slicing the cured product to make it into a sheet shape;

[0029] applying an adhesive to a surface of the cured product; and

[0030] allowing the applied adhesive to penetrate into the cured product.

[0031] [8] The method of manufacturing a thermally conductive sheet according to [7] above, wherein, in addition to the curable high molecular composition and the anisotropic filler material, a volatile substance is further mixed to obtain the mixed composition, and at least a portion of the volatile substance is volatilized by the heating.

[0032] [9] A thermally conductive sheet comprising a high molecular matrix, and an anisotropic filler material oriented in a thickness direction,

[0033] a thickness of the thermally conductive sheet is less than 0.2 mm,

[0034] a ratio of an area occupied by the anisotropic filler material in a cross section SI of the thermally conductive sheet parallel to a surface and a central portion in a thickness direction is set as C S1 a ratio of an area occupied by a resin containing the high molecular matrix is set as P S1 and,

[0035] a ratio of an area occupied by the anisotropic filler material in a cross section S2 of the thermally conductive sheet parallel to a surface and a depth position 25 μm away from the surface is set as C S2The ratio of the area occupied by the resin containing the high molecular matrix is set as P S2 In the case of

[0036] The conditions (1) and (2) below are satisfied:

[0037] C S1 > C S2 (1)

[0038] P S1 < P S2 (2).

[0039]

[10] . The thermally conductive sheet according to any one of the above [1] to [2] can be obtained by the following steps:

[0040] a step of slicing a cured product composed of a mixed composition containing a curable high molecular composition and an anisotropic filler material to make it into a sheet shape;

[0041] and a step of allowing an adhesive to permeate into the sheet-shaped cured product.

[0042]

[11] . A joining method which sequentially performs a close contact step and a joining step,

[0043] In the close contact step, the thermally conductive sheet according to any one of the above [1] to

[10] is sandwiched between a semiconductor chip and a heat dissipation sheet and they are brought into close contact;

[0044] In the joining step, the semiconductor chip and the heat dissipation sheet heated to 200°C or higher are joined after the close contact step.

[0045]

[12] . The joining method according to the above

[11] , in the close contact step, after the thermally conductive sheet is sandwiched between a semiconductor chip and a heat dissipation sheet, they are brought into close contact by pressure at 50°C or higher and 200°C or lower.

[0046]

[13] . The joining method according to the above

[11] or

[12] , the joining step is performed in a state without pressure.

[0047]

[14] . Use of a thermally conductive sheet for joining a semiconductor chip and a heat dissipation sheet in a reflow step, the thermally conductive sheet containing a high molecular matrix, and an anisotropic filler material oriented in a thickness direction,

[0048] the thickness of the thermally conductive sheet is less than 0.2 mm,

[0049] the void fraction in a cross section of the thermally conductive sheet at a depth position parallel to the surface and 25 μm from the surface is 1.0 to 15.0%,

[0050] A resin different from the polymer matrix is provided in at least a part of the voids of at least one surface of the thermally conductive sheet.

[0051] Effects of Invention

[0052] According to the present application, a thermally conductive sheet having a small thickness, a low thermal resistance value, and a good adhesion to an adherend can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0053] Fig. 1 is a cross-sectional view schematically showing an embodiment of the thermally conductive sheet of the present application.

[0054] Fig. 2 is a cross-sectional view schematically showing another embodiment of the thermally conductive sheet of the present application.

[0055] Fig. 3 is a schematic view of a thermal resistance measuring machine.

[0056] Fig. 4 is a schematic view showing a method for measuring a chip shear strength. DETAILED DESCRIPTION

[0057] [Thermally conductive sheet]

[0058] The thermally conductive sheet of the present application contains a polymer matrix and an anisotropic filler material oriented in the thickness direction, and has a thickness of less than 0.2 mm. Further, the void fraction in the cross section of the thermally conductive sheet at a depth position parallel to the surface and 25 μm from the surface is 1.0 to 15.0%, and a resin different from the polymer matrix is provided in at least a part of the voids of at least one surface of the thermally conductive sheet.

[0059] The thermally conductive sheet of the present application will be described with reference to the drawings. Further, the present application is not limited by the contents of the drawings.

[0060] A thermally conductive sheet 10 relating to an embodiment of the present application is shown in Fig. 1. The thermally conductive sheet 10 contains a polymer matrix 12 and an anisotropic filler material 13 oriented in the thickness direction of the thermally conductive sheet 10. In the thermally conductive sheet 10, the anisotropic filler material 13 is dispersed in the polymer matrix 12 and oriented in the thickness direction, and thus the thermal conductivity in the thickness direction is increased, and the heat dissipation property is improved.

[0061] Further, in the case where the anisotropic filler material is oriented in the thickness direction, the long axis direction thereof need not be strictly parallel to the thickness direction, and even if the long axis direction is slightly inclined with respect to the thickness direction, it is regarded as an anisotropic filler material oriented in the thickness direction. Specifically, even if the long axis direction is inclined by less than about 20°, it is regarded as an anisotropic filler material oriented in the thickness direction, provided that such an anisotropic filler material is the majority (for example, more than 60%, and preferably more than 80%, of the total amount of anisotropic filler material) in the thermally conductive sheet. Whether or not the anisotropic filler material is oriented can be confirmed, for example, by observing the cross section of the thermally conductive sheet using an electron microscope.

[0062] The thickness of the thermally conductive sheet 10 is less than 0.2 mm. In general, if the thickness of the sheet is this thin, voids are easily generated on the surface along with the detachment of the anisotropic filler material or the like, which can cause an increase in thermal resistance or a decrease in adhesiveness. This problem is particularly significant in the case where the thermally conductive sheet is manufactured via the following slicing step. In the present application, at least a portion of such voids is provided with a resin different from the polymer matrix 10. As shown in FIG. 1, elongated voids 11 and voids 14 are present on the surface of the thermally conductive sheet 10. The voids 14 are a structure in which the hollow portions of the voids are filled with a resin different from the polymer matrix. Thus, the voids 14 do not have hollow portions. On the other hand, the voids 11 are voids formed by hollows. More specifically, the voids 14 are formed by filling the hollow portions of the voids 11 with a resin different from the polymer matrix.

[0063] Further, it can also be a structure in which a resin different from the polymer matrix is provided in only a portion of the hollow portions, and such a structure in which a resin different from the polymer matrix is provided in only a portion of the hollow portions, the above-described structure in which the hollow portions of the voids are filled with a resin different from the polymer matrix, and voids formed by hollows can be mixedly present.

[0064] Further, with respect to the above-described plurality of structures, it is preferable that at least a portion of the structures be either the structure in which a resin different from the polymer matrix is provided in only a portion of the hollow portions or the voids formed by hollows. The reason for this is that by having spaces that are not filled with a resin different from the polymer matrix, the compressibility of the thermally conductive sheet is improved.

[0065] Further, in the present application, the voids on the surface of the thermally conductive sheet 10 mean voids present in a region 25 μm in the thickness direction from the surface 10a of the thermally conductive sheet.

[0066] Further, the above-described voids mean spaces in the thermally conductive layer that are divided by the polymer matrix and continuous to the surface of the above-described thermally conductive layer.

[0067] The voids 11 and 14 are typically voids generated due to cutting and falling of the anisotropic filler at the time of slicing. Therefore, the thermally conductive sheet has voids having a shape equivalent to that of the anisotropic filler incorporated. Here, the equivalent shape specifically means that the minor axis of the anisotropic filler is equivalent to the minor axis of the void. More specifically, the minor axis of the voids 11 and 14 is, for example, 0.1 to 30 μm.

[0068] The ratio of the voids having the resin different from the polymer matrix, with respect to the total voids on one surface of the thermally conductive sheet, is preferably 50% or more, more preferably 80% or more, and further preferably 100% or more.

[0069] Whether or not the surface of the thermally conductive sheet has voids having the resin different from the polymer matrix, or the ratio of such voids, can be confirmed, for example, by observing a cross section of the thermally conductive sheet cut in parallel to the thickness direction using an electron microscope. Alternatively, in the case of a manufacturing method in which an adhesive layer is provided to the thermally conductive sheet and an adhesive constituting the adhesive layer is infiltrated into the voids, the cross section can be observed using a fluorescence microscope by incorporating a fluorescent agent in a raw material for forming the adhesive layer.

[0070] More specifically, the ratio of the voids having the resin different from the polymer matrix is the ratio of the area of the voids having the resin different from the polymer matrix with respect to the total area of the voids on the surface of the thermally conductive sheet in the above cross section observation.

[0071] It is considered that the surface of the conventional thermally conductive sheet has many voids 11, and thus the thermal resistance value is high and the adhesiveness is low. In contrast, it is considered that the thermally conductive sheet of the present application has the resin different from the polymer matrix in at least some of the voids on at least one surface as in the voids 14, and thus the voids generated in the manufacturing process or the like of the surface of the sheet are reduced, and as a result, the thermal resistance value is low and the adhesiveness to the adherend is improved.

[0072] Further, the thermally conductive sheet 10 of Fig. 1 has the voids 11, but can be a thermally conductive sheet having only the voids 14 without the voids 11, and such a thermally conductive sheet has a further reduced thermal resistance value and improved adhesiveness, and thus is preferred.

[0073] The void ratio in the cross section S2 of the thermally conductive sheet at a depth position parallel to the surface and 25 μm from the surface 10a is 1.0 to 15.0%. The void ratio is the ratio of the total area of the voids present in the cross section S2 with respect to the total area of the cross section S2. Here, the total area of the voids is the total area of the voids 11 and 14 present in the cross section S2.

[0074] If the void ratio in the cross section S2 is in the above range, both the reduction of the thermal resistance value and the improvement of the adhesiveness to the adherend are easily achieved.

[0075] The void fraction in the cross section S2 is preferably 1.0 to 10.0%, more preferably 1.0 to 5.0%.

[0076] Further, in the present application, the void fraction in the cross section (cross section parallel to the surface) of the thermally conductive sheet at a depth position of 25 μm from one surface can be within the above range, and preferably the void fraction in the cross section (cross section parallel to the surface) of the thermally conductive sheet at a depth position of 25 μm from the other surface is also within the above range.

[0077] The above void fraction can be adjusted by the content of the anisotropic filler in the thermally conductive sheet, the slicing method at the time of manufacturing the thermally conductive sheet, and the like.

[0078] The void fraction in the cross section S2 can be measured by X-ray CT, and the detailed measurement method is as described in the examples.

[0079] In the present application, a thermally conductive sheet containing a polymer matrix and an anisotropic filler oriented in the thickness direction, and having a thickness of less than 0.2 mm, can be provided, and satisfies the following (1) and (2):

[0080] C S1 >C S2 (1);

[0081] P S1 <P S2 (2).

[0082] In the cross section S1 of the thermally conductive sheet parallel to the surface 10a and in the central portion in the thickness direction, the ratio of the area occupied by the anisotropic filler is set as C S1 , and the ratio of the area occupied by the resin containing the polymer matrix is set as P S1 .

[0083] In the cross section S2 of the thermally conductive sheet parallel to the surface 10a and at a depth position of 25 μm from the surface, the ratio of the area occupied by the anisotropic filler is set as C S2 , and the ratio of the area occupied by the resin containing the polymer matrix is set as P S2 .

[0084] Further, the area of the resin containing the polymer matrix is the total area of the polymer matrix and the resin different from the polymer matrix.

[0085] In the above formula (1), C S1 >C S2 is specified. This specification means that the central portion in the thickness direction of the thermally conductive sheet has more anisotropic filler than the surface side. The reason for this is that the anisotropic filler near the surface is peeled off due to slicing performed at the time of manufacturing the thermally conductive sheet.

[0086] In the above formula (2), P is defined as follows: S1 <P S2 This specification means that the surface side contains more resin than the central portion of the thermally conductive sheet in the thickness direction. This is because the resin fills at least a portion of the detached anisotropic filler material on the surface. Therefore, the thermal resistance of the thermally conductive sheet is reduced, and its adhesion to the bonded object is improved.

[0087] C S1 With C S2 The difference (C) S1 -C S2 The value is preferably 1 or more, more preferably 3 or more, and preferably 30 or less, more preferably 20 or less.

[0088] P S2 With P S1 The difference (P) S2 -P S1 The value is preferably 1 or more, more preferably 3 or more, and preferably 30 or less, more preferably 20 or less.

[0089] In addition, the above C S1 With C S2 The difference (C) S1 -C S2 ) and P S2 With P S1 The difference (P) S2 -P S1 The preferred relationship is (C) S1 -C S2 ) > (P S2 -P S1 The above (C) is considered... S1 -C S2 ) > (P S2 -P S1 (Hereinafter also referred to as the relationship between the difference in anisotropic filler materials and the difference in resin) reflects the existence of voids not filled by resins different from the aforementioned polymer matrix. Furthermore, the above (C) S1 -C S2 ) > (P S2 -P S1 For example, when the value is adjusted to 0.8 to 5.0, the coating amount or coating area of ​​the adhesive layer is preferably in this case. (C) S1 -C S2 ) > (P S2 -P S1The adhesive coating area or the weight per unit area can be adjusted, for example, if the weight per unit area is increased, the difference between the anisotropic filler and the resin can be made close to the difference between the anisotropic filler and the resin, and if the coating area is reduced, the difference between the anisotropic filler and the resin can be increased.

[0090] Further, the above (C S1 - C S2 ) is a value related to the area ratio of the portion where the anisotropic filler is detached, but strictly speaking, is not consistent with the above void ratio. It is considered that the reason is that, for example, the voids generated by slicing of the cured product collapse due to polishing of the surface of the cured product, and the like.

[0091] The thermally conductive sheet 10 preferably has an adhesive layer 16 on one surface 10a and the other surface 10b as shown in FIG. 2. By having the adhesive layer 16, the adhesion to the adherend is improved. Further, as described below, the adhesive layer is preferably an acrylic adhesive layer formed of an acrylic adhesive.

[0092] As described below, in the case where the thermally conductive sheet 10 is manufactured through a step of allowing the adhesive to infiltrate into a sheet prepared by slicing a cured product, a portion of the adhesive forming the adhesive layer 16 infiltrates into the voids generated due to the slicing and the detachment of the anisotropic filler, forming the above voids 14. When the adhesive layer 16 is formed, a portion of the adhesive infiltrates into the voids, and thus the thermal resistance value of the thermally conductive sheet can be reduced.

[0093] Further, the configuration in which the adhesive layer is provided on both surfaces of the thermally conductive sheet is shown in FIG. 2, and the configuration in which the adhesive layer is provided on only one surface of the thermally conductive sheet can also be employed.

[0094] (Resin different from the polymer matrix)

[0095] As described above, the thermally conductive sheet of the present application has a resin different from the polymer matrix in at least a portion of the voids of at least one surface.

[0096] The kind of the resin different from the polymer matrix is not particularly limited, and from the viewpoint of improving the adhesion to the adherend, an adhesive, and more preferably an acrylic adhesive, is preferred.

[0097] The acrylic adhesive preferably has a reactive double bond. By providing the acrylic adhesive on the surface of the thermally conductive sheet with a reactive double bond, even in a state where the thermally conductive sheet is in close contact with an adherend such as a heat dissipation sheet or a semiconductor chip, and is heated to a high temperature in a reflow step or the like, the close contact state can be maintained, and peeling from the adherend can be prevented. Further, even when used in a high temperature environment of, for example, about 150°C, a high adhesion can be maintained.

[0098] Generally, it is known that if an acrylic adhesive is heated at a high temperature, the bonding force is greatly reduced, but the acrylic adhesive, by having a reactive double bond, can maintain or improve the bonding force to the adherend, contrary to the properties of conventional acrylic adhesives. The principle is not certain, but is presumed as follows. That is, the reactive double bond in the acrylic adhesive reacts by heating, for example, to bond to the adherend, or to improve the mechanical strength of the adhesive layer by cross-linking with each other through the reactive double bond, and further, depending on the case, to react with unreacted hydrogen siloxy groups or the like in the organopolysiloxane constituting the polymer matrix, and they act in combination to improve the adhesion.

[0099] The acrylic adhesive is preferably one containing an acrylic polymer as a main agent of the adhesive, and the acrylic polymer has the above-described reactive double bond. The acrylic adhesive can exhibit adhesiveness by containing the acrylic polymer.

[0100] The intensity ratio A / B of the peak intensity A of C=C stretching vibration to the peak intensity B of C=O stretching vibration in the Raman spectrum of the acrylic adhesive is preferably 0.2 or greater. Here, the peak intensity A is a peak produced by the C=C double bond included in the reactive double bond. Further, the peak intensity B is a peak produced by the C=O bond included in the acrylic polymer. Therefore, the intensity ratio A / B of the peak intensity A to the peak intensity B can be said to be an index indicating the ratio of the reactive double bond in the acrylic polymer.

[0101] By making the intensity ratio A / B 0.2 or greater, the acrylic adhesive has a sufficient amount of reactive double bond, and even if heated at a high temperature in the state of being in close contact with the adherend in the reflow step or the like, the adhesion to the adherend can be appropriately maintained.

[0102] The intensity ratio A / B is more preferably 0.3 or greater, and further preferably 0.4 or greater, and further more preferably 0.5 or greater. Further, the intensity ratio A / B is not particularly limited, and for example, is 1.0 or less, preferably 0.8 or less, and more preferably 0.7 or less.

[0103] Further, the peak of C=O stretching vibration is typically a peak appearing near a wave number of 1720 cm -1 Further, the peak of C=C stretching vibration is typically a peak appearing near a wave number of 1636 cm -1 However, these peaks can slightly shift depending on the structure of the acrylic polymer or the like.

[0104] The acrylic polymer used in the acrylic adhesive can contain an acrylic polymer having a reactive double bond (acrylic polymer containing a reactive double bond). The acrylic polymer containing a reactive double bond preferably has a reactive double bond in a side chain. Further, the reactive double bond is a saturated carbon-carbon double bond not constituting an aromatic ring, and is typically constituted by a group represented by a structure represented by H2C=CH- * or H2C=CCH3- * * indicates a bond), and specifically, vinyl group, acryloyl group, methacryloyl group, and the like can be exemplified.

[0105] Further, the acrylic polymer containing a reactive double bond can have a functional group such as a hydroxyl group, a carboxyl group, an epoxy group, an amino group, or the like in a side chain in addition to the group having a reactive double bond, and preferably has at least one of a hydroxyl group and a carboxyl group in a side chain, and further preferably has both of a hydroxyl group and a carboxyl group.

[0106] The weight average molecular weight of the acrylic polymer containing a reactive double bond is not particularly limited, and is, for example, about 100,000 or more and about 1,200,000 or less, and is preferably about 200,000 or more and about 1,000,000 or less. Further, the weight average molecular weight is measured by a gel permeation chromatograph (GPC) and is calculated as a polystyrene conversion value. Further, by adjusting the molecular weight, the solid content concentration and the viscosity of the adhesive containing the following organic solvent can be adjusted. Specifically, in the case where the solid content concentration is to be increased while being adjusted to be low viscosity, the molecular weight can be decreased. Further, in the case where the solid content concentration is to be decreased while being adjusted to be high viscosity, the molecular weight can be increased.

[0107] The acrylic polymer containing a reactive double bond can be obtained, for example, by reacting an acrylic polymer having a functional group in a side chain (hereinafter, also referred to as an acrylic polymer (X)) with a compound containing a reactive double bond (hereinafter, also referred to as a compound containing a reactive double bond (Y)) having a reactive group which reacts with the functional group and a reactive double bond. As the functional group, a hydroxyl group, a carboxyl group, an epoxy group, an amino group, and the like can be exemplified.

[0108] The acrylic polymer (X) can contain a structural unit derived from a (meth)acrylate, and typically contains a structural unit derived from an alkyl (meth)acrylate as a main component. As the acrylic polymer (X), more specifically, a copolymer of an alkyl (meth)acrylate and a monomer containing a functional group; a copolymer of an alkyl (meth)acrylate, a monomer containing a functional group, and another monomer other than them; and the like can be exemplified.

[0109] Further, the (meth)acrylate is used as a term meaning one or both of an acrylate and a methacrylate, and the same applies to other similar terms. ​

[0110] The (meth)acrylic acid alkyl ester is an ester of (meth)acrylic acid and an alkyl alcohol. The alkyl group in the (meth)acrylic acid alkyl ester can be linear, can have a branched structure, or can have a cyclic structure.

[0111] As the (meth)acrylic acid alkyl ester, there can be mentioned methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-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, isobornyl (meth)acrylate, and the like.

[0112] The (meth)acrylic acid alkyl ester can be used singly or in combination of two or more.

[0113] The (meth)acrylic acid alkyl ester is preferably a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 12 carbon atoms, and more preferably an acrylic acid alkyl ester having an alkyl group having 2 to 8 carbon atoms. The structural unit derived from the acrylic acid alkyl ester having an alkyl group having 2 to 8 carbon atoms can be a main component in the acrylic acid polymer (X), and for example, can be 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 in the acrylic acid polymer (X).

[0114] As the functional group in the monomer containing a functional group, there can be mentioned a carboxyl group, a hydroxyl group, an amino group, an epoxy group, and among these, a carboxyl group and a hydroxyl group are preferred. As the monomer containing a carboxyl group, there can be mentioned (meth)acrylic acid, butenyl acid, and among these, (meth)acrylic acid is more preferred.

[0115] Further, as the monomer containing a hydroxyl group, there can be mentioned, for example, (meth)acrylic acid 2-hydroxyethyl ester, (meth)acrylic acid 2-hydroxypropyl ester, (meth)acrylic acid 3-hydroxypropyl ester, (meth)acrylic acid 2-hydroxybutyl ester, (meth)acrylic acid 4-hydroxybutyl ester, (meth)acrylic acid 5-hydroxypentyl ester, (meth)acrylic acid 6-hydroxyhexyl ester, and the like, (meth)acrylic acid esters having a hydroxyl group, allyl alcohol, and the like. Among these, (meth)acrylic acid esters having a hydroxyl group such as (meth)acrylic acid 2-hydroxyethyl ester are preferred.

[0116] The structural unit derived from the monomer containing a functional group is, for example, 1% by mass or more and 35% by mass or less, preferably 5% by mass or more and 30% by mass or less, and more preferably 10% by mass or more and 25% by mass or less in the acrylic acid polymer (X).

[0117] The functional group-containing monomer can be used singly or in combination of two or more.

[0118] As the other monomer, monomers other than the alkyl (meth)acrylate and the above-mentioned functional group-containing monomer can be exemplified, as long as they are copolymerizable with the alkyl (meth)acrylate or the functional group-containing monomer. Specifically, styrene, α-methylstyrene, p-methylstyrene, p-chlorostyrene, divinylbenzene and the like styrene derivatives; vinyl acetate, vinyl propionate and the like compounds having a vinyl ester group; N-vinylpyrrolidone, N-vinylmorpholine, (meth)acrylonitrile, N-cyclohexylmaleimide, N-phenylmaleimide, N-laurylmaleimide, N-benzylmaleimide, n-propyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, t-butyl vinyl ether and the like can be exemplified. The other monomer can be used singly or in combination of two or more.

[0119] The compound (Y) containing a reactive double bond is a compound having a reactive group which reacts with the above-mentioned functional group and a reactive double bond. As the reactive group, isocyanate group, epoxy group, carboxyl group, hydroxyl group and the like can be exemplified, among which, isocyanate group, epoxy group are preferred, and isocyanate group is more preferred.

[0120] The acrylic polymer contained in the acrylic adhesive can be composed of the acrylic polymer containing a reactive double bond, and can contain an acrylic polymer not having a reactive double bond in addition to the acrylic polymer containing a reactive double bond. As the acrylic polymer not having a reactive double bond, the above-mentioned acrylic polymer (X) can be exemplified.

[0121] The acrylic adhesive can contain, in addition to the above-mentioned acrylic polymer, components generally blended in an adhesive, and can suitably contain a crosslinking agent, a tackifier, a filler, an antioxidant, an ultraviolet ray resistant agent, a plasticizer, a viscosity modifier and the like additives.

[0122] (Adhesive layer)

[0123] As described above, the thermally conductive sheet of the present application preferably has an acrylic adhesive layer formed of an acrylic adhesive on a surface. Further, the acrylic adhesive is preferably an acrylic adhesive having a reactive double bond. Thereby, even in a state where the thermally conductive sheet is tightly attached to an adherend such as a heat dissipation sheet or a semiconductor chip, the tightly attached state can be more favorably maintained even when heated to a high temperature in a reflow step or the like, and peeling from the adherend can be prevented.

[0124] The acrylic adhesive layer in the present application can be provided on one surface of the thermally conductive sheet, or on both surfaces. Further, the one surface or both surfaces herein are surfaces in a vertical direction of the thermally conductive sheet in a thickness direction, and are also called main surfaces.

[0125] By providing the acrylic adhesive layer on both surfaces of the thermally conductive sheet, the adhesion of the thermally conductive sheet to the adherend can be improved. Therefore, in the case of use for semiconductor applications, the thermally conductive sheet can be adhered to both the semiconductor chip and the heat sink with relatively high adhesion, and even if it is heated to a high temperature in a state of being adhered to them by a reflow step or the like, peeling of the thermally conductive sheet from either of the semiconductor chip and the heat sink can be easily prevented.

[0126] The unit area weight of each surface of the acrylic adhesive layer is, for example, 0.05 mg / cm 2 The above is preferably 0.1 mg / cm 2 The above is more preferably 0.2 mg / cm 2 The above is further preferably 0.3 mg / cm 2 The above is, for example, 1.0 mg / cm 2 The above is preferably 0.75 mg / cm 2 The above is more preferably 0.5 mg / cm 2 The above is further preferably 0.45 mg / cm 2 The above. By setting the unit area weight to an amount or more, sufficient adhesion of the adhesive layer to the adherend can be ensured. Further, by setting the unit area weight to an amount or less, a decrease in thermal resistance value due to the acrylic adhesive layer can be prevented, and good thermal conductivity can be easily ensured.

[0127] (Polymer matrix)

[0128] The thermally conductive sheet of the present application includes a polymer matrix, and an anisotropic filler material oriented in the thickness direction.

[0129] The polymer matrix is a matrix composed of an organic polymer, and is an organic polymer such as an elastomer or a rubber. A polymer matrix formed by curing a liquid polymer composition (curable polymer composition) composed of a mixed system such as a main agent and a curing agent is preferably used. The curable polymer composition can be composed of an uncrosslinked rubber and a crosslinking agent, and can include a monomer, a prepolymer, and the like, and a curing agent, and the like. Further, the above curing reaction can be room temperature curing, or heat curing.

[0130] The polymer matrix is preferably an organic polysiloxane. In the present application, by using an organic polysiloxane, the cured polymer matrix can be made soft, and the filling property of the thermally conductive filler material can be made good. The organic polysiloxane is preferably a polysiloxane rubber. Further, the organic polysiloxane is preferably a cured-type polysiloxane, and more preferably an addition reaction-type polysiloxane.

[0131] In the case of an addition reaction type polysiloxane, the curable polymer composition is composed of an organopolysiloxane containing an alkenyl group (a main agent) and a hydride organopolysiloxane (a curing agent), and the polymer matrix is one obtained by curing them. It is considered that if an addition reaction type polysiloxane is used, the reactive double bond contained in the acrylic adhesive layer reacts with the unreacted hydrosilyl group due to the high-temperature heating of the reflow step or the like, and thus the adhesion to the adherend is easily improved.

[0132] In addition to polysiloxane rubber, various synthetic rubbers can also be used as the rubber, and as specific examples, for example, acrylic rubber, nitrile rubber, isoprene rubber, urethane rubber, ethylene propylene rubber, styrene-butadiene rubber, butadiene rubber, fluororubber, butyl rubber, and the like can be listed. In the case where these rubbers are used, the synthetic rubber can be crosslinked in the thermally conductive sheet, or can be left in an uncrosslinked (i.e., uncured) state. The uncrosslinked rubber is mainly used in the case of flow orientation.

[0133] In addition, in the case where crosslinking (i.e., curing) is performed, as described above, the polymer matrix can be one obtained by curing a curable polymer composition composed of the uncrosslinked rubber composed of these synthetic rubbers and a crosslinking agent.

[0134] In addition, as the elastomer, a thermoplastic elastomer such as a polyester-based thermoplastic elastomer, a polyurethane-based thermoplastic elastomer, or a thermosetting elastomer obtained by curing a liquid polymer composition of a mixed system composed of a main agent and a curing agent can also be used. For example, a polyurethane-based elastomer obtained by curing a polymer composition containing a polymer having a hydroxyl group and an isocyanate can be exemplified.

[0135] In addition, the polymer composition used to form the polymer matrix can be composed of a single organic polymer component, or can be composed of an organic polymer and a plasticizer. The plasticizer is suitably used in the case where synthetic rubber is used, and by including the plasticizer, the softness of the polymer matrix at the time of uncrosslinking can be improved. For example, in the case where the polymer matrix is an organopolysiloxane, a polysiloxane oil can be used as the plasticizer. That is, the curable polymer composition can be composed of a main agent and a curing agent, or can be composed of a main agent, a curing agent, and a plasticizer.

[0136] The content of the polymer matrix, when expressed as a filling rate (volume filling rate) on a volume basis, is preferably 15 vol% or more and 50 vol% or less, more preferably 17 vol% or more and 45 vol% or less, and further preferably 20 vol% or more and 40 vol% or less, with respect to the total amount of the thermally conductive layer.

[0137] (Anisotropic filling material)

[0138] The thermally conductive sheet of the present application contains an anisotropic filler material oriented in the thickness direction as a thermally conductive filler material. In addition, as described below, the thermally conductive filler material can also include both an anisotropic filler material and a non-anisotropic filler material.

[0139] The thermally conductive filler material can be dispersed in the polymer matrix and held in the polymer matrix.

[0140] The anisotropic filler material is preferably oriented in the thickness direction of the thermally conductive sheet. By this, the thermally conductive layer is easily improved in thermal conductivity. Further, with respect to the anisotropic filler material, in the case of being oriented in the thickness direction, it is not necessary that the long axis direction be strictly parallel to the thickness direction, even if the long axis direction is slightly inclined with respect to the thickness direction, it is also regarded as being oriented in the thickness direction. Specifically, the long axis direction is inclined by less than 20° or so is also regarded as an anisotropic filler material oriented in the thickness direction, as long as such an anisotropic filler material is the majority (for example, more than 60% with respect to the total amount of anisotropic filler material, preferably more than 80%) in the thermally conductive sheet, it is regarded as being oriented in the thickness direction.

[0141] The anisotropic filler material is a filler material having anisotropic shape, and is a filler material capable of being oriented. As the anisotropic filler material, a fibrous material, a flaky material, or the like can be cited. The anisotropic filler material has a high aspect ratio, specifically, the aspect ratio is more than 2, and the aspect ratio is preferably 5 or more. By making the aspect ratio more than 2, the anisotropic filler material is easily oriented in one direction such as the thickness direction, and the thermal conductivity in one direction such as the thickness direction of the thermally conductive sheet is easily improved. Further, there is no particular limitation on the upper limit of the aspect ratio, and from the viewpoint of practicality, it is 100.

[0142] Further, the aspect ratio is the ratio of the length of the long axis direction of the anisotropic filler material to the length of the short axis direction, and in the case of a fibrous material, it means the fiber length / fiber diameter, and in the case of a flaky material, it means the length of the long axis direction / thickness of the flaky material.

[0143] The content of the anisotropic filler material in the thermally conductive sheet is preferably 10 parts by mass or more and 500 parts by mass or less, more preferably 30 parts by mass or more and 300 parts by mass or less, and further preferably 50 parts by mass or more and 250 parts by mass or less, with respect to 100 parts by mass of the polymer matrix.

[0144] By setting the content of the anisotropic filler material to 10 parts by mass or more, the thermal conductivity is easily improved. Further, by setting it to 500 parts by mass or less, the viscosity of the following mixed composition is easily made appropriate, and the orientation of the anisotropic filler material is made good. Further, the dispersibility of the anisotropic filler material in the polymer matrix is also made good.

[0145] In the case where the anisotropic filler material is a fibrous material, the average fiber length thereof is preferably 10 μm or more and 300 μm or less, more preferably 20 μm or more and 200 μm or less, and further preferably 30 μm or more and 100 μm or less. If the average fiber length is set to 10 μm or more, the anisotropic filler material is in appropriate contact with each other inside the thermally conductive layer, a heat transfer path is ensured, and the thermal conductivity of the thermally conductive layer becomes good.

[0146] On the other hand, if the average fiber length is set to 300 μm or less, the volume of the anisotropic filler material becomes small, and the anisotropic filler material can be highly filled in the adhesive component.

[0147] Further, the average fiber length of the fibrous material is preferably shorter than the thickness of the thermally conductive sheet. By making it shorter than the thickness, it is possible to prevent the fibrous material from protruding from the surface of the thermally conductive sheet beyond the necessary degree.

[0148] Further, the average fiber length of the fibrous material is preferably shorter than the thickness of the thermally conductive sheet. By making it shorter than the thickness, it is possible to prevent the fibrous material from protruding from the surface of the thermally conductive sheet beyond the necessary degree.

[0149] Further, in the case where the anisotropic filler material is a flaky material, the average particle diameter thereof is preferably 10 μm or more and 300 μm or less, more preferably 15 μm or more and 200 μm or less, and further preferably 20 μm or more and 100 μm or less. By setting the average particle diameter to 10 μm or more, the anisotropic filler material becomes easily in contact with each other in the thermally conductive layer, a heat transfer path is ensured, and the thermal conductivity of the thermally conductive layer becomes good. On the other hand, if the average particle diameter is set to 300 μm or less, the volume of the thermally conductive sheet becomes small, and the anisotropic filler material can be highly filled in the adhesive component.

[0150] Further, the average particle diameter of the flaky filler material is D50, and the length diameter can be calculated as the diameter by observing the flaky filler material with a microscope. More specifically, it means that the length diameter of 500 or more of the flaky filler material is measured using, for example, an electron microscope or an optical microscope, and the particle diameter at the cumulative frequency of 50% is obtained. Specifically, it can be obtained from a particle diameter distribution curve in which the horizontal axis is set to the particle diameter and the vertical axis is set to the cumulative frequency, using the flaky filler material as a sample. The particle diameter distribution curve is a number-based particle diameter distribution curve obtained by sequentially accumulating the flaky filler material from the one having a smaller particle diameter.

[0151] The anisotropic filler material can be any material having thermal conductivity, and in the case of orientation by magnetic field orientation, can have diamagnetism, as described below. On the other hand, in the case of orientation by flow orientation, or in the case of not orienting the anisotropic filler material, the anisotropic filler material can not have diamagnetism.

[0152] Examples of the anisotropic filler material include carbon-based materials typified by carbon fibers or flaky carbon powder, metal materials or metal oxides typified by metal fibers, boron nitride or metal nitride, metal carbide, metal hydroxide, poly-p-phenylene benzoxazole fibers, and the like. Among these, carbon-based materials are preferred because of their small specific gravity and good dispersibility in the binder component, and more preferably, graphitized carbon materials having high thermal conductivity. Graphitized carbon materials have diamagnetism by aligning the graphite planes in a specific direction.

[0153] Further, boron nitride is also preferred as the anisotropic filler material. The boron nitride is not particularly limited, and is preferably used as a flaky material. The flaky boron nitride can or can not be agglomerated, and is preferably partially or entirely unagglomerated. Further, boron nitride and the like have diamagnetism by aligning the crystal planes in a specific direction.

[0154] Further, the anisotropic filler material is not particularly limited, and the thermal conductivity in the direction having anisotropy (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 material is not particularly limited, and is, for example, 2000 W / m-K or less. The thermal conductivity can be measured by a laser flash method or the like.

[0155] The anisotropic filler material can be used singly or in combination of two or more. For example, as the anisotropic filler material, at least two anisotropic filler materials having different average particle diameters or average fiber lengths from each other can be used. It is considered that if anisotropic filler materials of different sizes are used, the smaller anisotropic filler material enters between the relatively larger anisotropic filler materials, and thus the anisotropic filler material can be densely filled in the binder component, and the conduction efficiency of heat can be improved.

[0156] Further, the anisotropic filler material is preferably a fiber material among the above-described materials. A thermal conductive layer containing a fiber material has a tendency to have reduced adhesiveness due to the fiber material falling off because of slicing and forming unevenness on the surface, but in the present application, by providing the adhesive layer, the adhesive layer enters the recesses, and thus the adhesiveness can be sufficiently improved even for a thermal conductive layer having a fiber material.

[0157] Further, from the viewpoint of imparting good thermal conductivity, the thermally conductive layer preferably contains, in addition to the fibrous material as the anisotropic filler material, a flaky material as the anisotropic filler material. In this case, the content ratio of the flaky material to the fibrous material (flaky material / fibrous material) is, for example, 0.01 or more and 1 or less, preferably 0.02 or more and 0.5 or less, and more preferably 0.1 or more and 0.3 or less, on a mass basis.

[0158] The carbon fiber used as the anisotropic filler material is preferably graphitized carbon fiber. Further, as the flaky carbon powder, flaky graphite powder is preferred. As the anisotropic filler material, it is preferred to use both graphitized carbon fiber and flaky graphite powder.

[0159] The crystal planes of graphite of the graphitized carbon fiber are connected in the fiber axis direction, and it has a high thermal conductivity in the fiber axis direction. Therefore, by making the fiber axis direction coincide with the specific direction, the thermal conductivity in the specific direction can be increased. Further, the crystal planes of graphite of the flaky graphite powder are connected in the in-plane direction of the flaky plane, and it has a high thermal conductivity in the in-plane direction. Therefore, by making the flaky plane coincide with the specific direction, the thermal conductivity in the specific direction can be increased. The graphitized carbon fiber and the flaky graphite powder preferably have a high degree of graphitization.

[0160] As the graphitized carbon material such as the above-mentioned graphitized carbon fiber, flaky graphite powder, etc., graphitized carbon material obtained by graphitizing the following raw material can be used. For example, condensed polycyclic hydrocarbon compounds such as naphthalene, PAN (polyacrylonitrile), condensed heterocyclic compounds such as pitch, etc. can be listed, and in particular, it is preferred to use graphitized mesophase pitch or polybenzazole having a high degree of graphitization. For example, by using mesophase pitch, in the following spinning step, the pitch is oriented in the fiber axis direction by its anisotropy, and graphitized carbon fiber having excellent thermal conductivity in the fiber axis direction can be obtained.

[0161] The use form of the mesophase pitch in the graphitized carbon fiber is not particularly limited as long as it can be spun, and the mesophase pitch can be used alone or in combination with other raw materials. Among them, from the aspects of high thermal conductivity, spinnability, and stability of quality, it is most preferred to use the mesophase pitch alone, i.e., graphitized carbon fiber having a mesophase pitch content of 100%.

[0162] The graphitized carbon fiber can use, for example, a carbon fiber obtained by performing graphitization after pulverization or cutting into a specific particle diameter after performing each of the processes of spinning, infusibilization, and carbonization in this order, or a carbon fiber obtained by performing graphitization after pulverization or cutting after carbonization. In the case where the pulverization or cutting is performed before graphitization, the surface newly exposed to the surface due to the pulverization is subjected to graphitization, and thus the condensation reaction and the cyclization reaction are easily performed, and a graphitized carbon fiber having an increased graphitization degree and further increased thermal conductivity can be obtained. On the other hand, in the case where the graphitized carbon fiber is pulverized after the spun carbon fiber is graphitized, the graphitized carbon fiber is hard, and thus is easily pulverized, and a carbon fiber powder having a relatively narrow fiber length distribution can be obtained by pulverization for a short time.

[0163] 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 further preferably 30 μm or more and 100 μm or less. Further, as described above, the aspect ratio of the graphitized carbon fiber is more than 2, and is preferably 5 or more. The thermal conductivity of the graphitized carbon fiber is not particularly limited, and the thermal conductivity in the fiber axis direction is preferably 400 W / m·K or more, and more preferably 800 W / m·K or more.

[0164] In the case where the thermally conductive sheet contains the anisotropic filler material, the anisotropic filler material can or can not be exposed to the surface of the thermally conductive sheet, and is preferably exposed. By exposing the anisotropic filler material, the anisotropic filler material comes into contact with the adherend such as a heat generating body or a heat radiating body, and it becomes easy to reduce the thermal resistance value. Further, if the anisotropic filler material is exposed, the adhesion to the adherend is not easily improved, but in this case, in the present application, the adhesion is easily improved by providing the adhesive layer.

[0165] (non-anisotropic filler material)

[0166] The thermally conductive sheet of the present application can also contain a non-anisotropic filler material as the thermally conductive filler material, and it is preferable to use the above-described anisotropic filler material in combination with the non-anisotropic filler material.

[0167] The non-anisotropic filler material, in particular, by being used in combination with the anisotropic filler material oriented in one direction such as the thickness direction, can intervene in the gap between the oriented anisotropic filler material, and further improve the thermal conductivity. The non-anisotropic filler material is a filler material having substantially no anisotropy in shape, and is a filler material which does not orient in a specific direction even in an environment in which the anisotropic filler material is oriented in the specific direction due to the generation of the magnetic force line described below or the action of the shear force or the like.

[0168] The aspect ratio of the non-anisotropic filler is 2 or less, and preferably 1.5 or less. In this way, the non-anisotropic filler having a low aspect ratio is easily arranged in the gaps of the anisotropic filler in the case of being used in combination with the anisotropic filler, and it becomes easy to increase the thermal conductivity. Further, by setting the aspect ratio to 2 or less, it is possible to prevent an increase in the viscosity of the mixed composition, and to achieve a high degree of filling.

[0169] As specific examples of the non-anisotropic filler, for example, metals, metal oxides, metal nitrides, metal hydroxides, carbon materials, oxides, nitrides, and carbides other than metals can be given. Further, as the shape of the non-anisotropic filler, a spherical shape, a polyhedral shape, irregularly shaped powder, and the like can be given.

[0170] In the non-anisotropic filler, as the metal, for example, aluminum, copper, nickel, and the like can be given, as the metal oxide, for example, alumina represented by aluminum trioxide, magnesium oxide, zinc oxide, and the like can be given, and as the metal nitride, for example, aluminum nitride can be given. As the metal hydroxide, for example, aluminum hydroxide can be given. Further, as the carbon material, for example, spherical graphite and the like can be given. As the oxides, nitrides, and carbides other than metals, for example, quartz, boron nitride, silicon carbide, and the like can be given.

[0171] Among these, in terms of having a high thermal conductivity and being easily obtained in a spherical shape, alumina or aluminum is preferable.

[0172] The non-anisotropic filler can be used alone using one of the above-described materials, or two or more of the above-described materials can be used in combination.

[0173] The average particle diameter of the non-anisotropic filler is, for example, 0.1 μm or more and 200 μm or less, and is preferably 0.5 μm or more and 100 μm or less, and more preferably 1 μm or more and 70 μm or less.

[0174] Further, in the case of using the non-anisotropic filler in combination with the anisotropic filler, the average particle diameter of the non-anisotropic filler is preferably 0.1 μm or more and 50 μm or less, more preferably 0.5 μm or more and 35 μm or less, and further preferably 1 μm or more and 15 μm or less. By setting the average particle diameter to 50 μm or less, even in the case of being used in combination with the anisotropic filler, defects such as disturbing the orientation of the anisotropic filler are not easily generated. Further, by setting the average particle diameter to 0.1 μm or more, the specific surface area of the non-anisotropic filler does not increase to a necessary degree or more, and even in the case of being mixed in a large amount, the viscosity of the mixed composition does not easily increase, and it is easy to highly fill the non-anisotropic filler.

[0175] The non-anisotropic filler can be used, for example, using at least two kinds of non-anisotropic fillers having mutually different average particle diameters as the non-anisotropic filler.

[0176] Further, the average particle diameter of the non-anisotropic filler can be measured by observation with an electron microscope or the like. More specifically, for example, the particle diameters of 500 or more of the non-anisotropic filler can be measured using an electron microscope or an optical microscope, and D50 can be calculated in the same manner as the flaky filler.

[0177] 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 further preferably 200 parts by mass or more and 750 parts by mass or less, relative to 100 parts by mass of the polymer matrix. By setting it to 50 parts by mass or more, the thermal conductivity of the thermal conductive sheet can be made good. On the other hand, by setting it to 1500 parts by mass or less, the effect of appropriately dispersing the non-anisotropic filler in the adhesive component and improving the thermal conductivity corresponding to the content can be obtained. In addition, it is also possible to prevent the viscosity of the mixed composition from increasing more than necessary.

[0178] The mass ratio of the content of the non-anisotropic filler to the content of the anisotropic filler is not particularly limited, and is preferably 0.5 or more and 15 or less, more preferably 1 or more and 10 or less, and preferably 1.1 or more and 7 or less. By setting the mass ratio to the above range, the non-anisotropic filler is moderately filled between the anisotropic fillers, and an efficient heat transfer path can be formed, so that the thermal conductivity of the thermal conductive sheet can be further improved.

[0179] The content of the thermally conductive filler in the thermal conductive sheet is preferably 150 parts by mass or more and 3000 parts by mass or less, more preferably 200 parts by mass or more and 1800 parts by mass or less, and further preferably 300 parts by mass or more and 1000 parts by mass or less, relative to 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 thermal conductivity can be imparted to the thermal conductive layer. In addition, by setting it to 3000 parts by mass or less, the thermally conductive filler can be appropriately dispersed in the polymer matrix. In addition, it is also possible to prevent the viscosity of the mixed composition described below from increasing more than necessary.

[0180] In addition, the volume filling rate of the thermally conductive filler is preferably 30% by volume or more and 85% by volume or less, more preferably 50% by volume or more and 83% by volume or less, and further preferably 60% by volume or more and 80% by volume or less, relative to the total amount of the thermal conductive sheet. By setting the volume filling rate to the above lower limit value or more, a certain thermal conductivity can be imparted to the thermal conductive layer. In addition, by setting it to the upper limit value or less, the manufacture of the thermal conductive layer becomes easy.

[0181] The thermally conductive sheet can also incorporate components other than those described above, within a range that does not impair the function as a thermally conductive layer. Specifically, at least one or more selected from among, for example, dispersing agents, flame retardants, antioxidants, colorants, and precipitation preventing agents can be cited. Furthermore, in the case of crosslinking, curing, and the like of the curable polymer composition as described above, as an additive, a crosslinking accelerator, a curing accelerator, a curing catalyst, and the like that promote crosslinking and curing can be incorporated. In the case where the polymer matrix is an organopolysiloxane, a platinum catalyst can be used as the curing catalyst.

[0182] The surface of the thermally conductive sheet is preferably a sliced surface. By making the surface a sliced surface, as described above, it is easy to expose the anisotropic filler material and the like to the surface of the thermally conductive layer, and the thermal resistance value can be effectively reduced. The thermally conductive sheet can have one surface that is a sliced surface, or both surfaces can be sliced surfaces, and it is preferable that the surface on which the adhesive layer is provided be a sliced surface. Furthermore, the sliced surface is a surface that is formed by cutting with a shear cutter or laser and the like, as described below.

[0183] The sliced surface is often in a state in which the protrusions or the like of the anisotropic filler material are large, and by filling the recesses with an acrylic adhesive layer, the air layer can be reduced at the time of use, the thermal resistance value can be improved, and the adhesion can be improved.

[0184] Furthermore, the surface of the thermally conductive sheet is preferably a ground surface. By making at least one surface of the thermally conductive sheet a ground surface, the thermal resistance value can be more effectively reduced. The thermally conductive sheet can have one surface that is a ground surface, or both surfaces can be ground surfaces, and it is preferable that the surface on which the adhesive layer is provided be a ground surface, and it is particularly preferable that the surface on which the adhesive layer is provided be a sliced surface and a ground surface. The ground surface has relatively high smoothness, and therefore the adhesion to the adherend can be easily improved when the adhesive layer is provided.

[0185] The thickness of the thermally conductive sheet is less than 0.2 mm. Generally, if the thermally conductive sheet is thinned in this way, in the step of slicing, voids that accompany the falling off of the anisotropic filler material are easily formed, the thermal resistance value becomes high, and the adhesion can be easily reduced, but in the present application, at least a portion of the voids is filled with resin, and therefore the thermal resistance value can be maintained to be low, and the adhesion is improved.

[0186] From the viewpoint of being suitably used for semiconductor applications, and the viewpoint of reducing the thermal resistance value, the thickness of the thermally conductive sheet is preferably 0.18 mm or less, and more preferably 0.15 mm or less. Furthermore, the thickness of the thermally conductive sheet is not particularly limited, and from the viewpoint of practicality, for example, it is 0.01 mm or more, and preferably 0.02 mm or more, and more preferably 0.03 mm or more. Furthermore, the thickness of the thermally conductive sheet is the initial thickness that is measured in a state in which no load is applied in the thickness direction.

[0187] (Arithmetic Mean Height (Sa))

[0188] The arithmetic average height (Sa) of the surface of the thermally conductive sheet is, for example, 20 μm or less, preferably 12 μm or less, more preferably 6 μm or less, and further preferably 5 μm or less. In the case where the thermally conductive sheet has an adhesive layer, the arithmetic average height of the surface of the acrylic adhesive layer is preferably within the above range. By reducing the arithmetic average height of the surface of the thermally conductive sheet on which the acrylic adhesive layer is provided, the thermal resistance value can be more effectively reduced. Furthermore, the thermally conductive sheet can be more effectively brought into close contact with the adherend by the acrylic adhesive layer. Moreover, if the surface of the thermally conductive sheet is, for example, a sliced surface as described above, the arithmetic average height tends to be relatively large, but by polishing after slicing, the arithmetic average height (Sa) can be reduced as described above.

[0189] The arithmetic average height (Sa) of the surface of the thermally conductive sheet is not particularly limited, and is preferably 0.5 μm or more, more preferably 1 μm or more, and further preferably 2 μm or more. By setting the arithmetic average height (Sa) to be equal to or more than these lower limit values, even if the surface is a sliced surface, polishing can be relatively easily performed.

[0190] (E hardness)

[0191] The E hardness (hereinafter, also referred to as "E hardness") of the thermally conductive sheet of the present application, which is defined by JIS K6253, is preferably 10 or more and 80 or less, more preferably 20 or more and 70 or less, and further preferably 30 or more and 65 or less. If the E hardness is equal to or more than the lower limit value described above, the mechanical strength of the thermally conductive sheet can be easily increased. Furthermore, if the E hardness is equal to or less than the upper limit value described above, the thermally conductive sheet is imparted with a certain degree of softness, and the close contact with the adherend can be easily improved.

[0192] (Thermal resistance value of thermally conductive sheet)

[0193] The thermal resistance value of the thermally conductive sheet of the present application is, for example, 0.5°C•cm 2 / W or less, preferably 0.25°C•cm 2 / W or less, more preferably 0.2°C•cm 2 / W or less, and further preferably 0.16°C•cm 2 / W or less.

[0194] If the thermal resistance value is equal to or less than the upper limit value described above, the efficiency of heat transfer from the heat generating body to the heat radiating body via the thermally conductive sheet is improved, and excellent thermal conductivity can be obtained. In the present application, the lower the thermal resistance value, the more preferable it is, and can be 0°C•cm 2 / W or more, for example, 0.01°C•cm 2 / W or more, preferably 0.05°C•cm 2 / W or more.

[0195] Further, the thermal resistance value is a thermal resistance value measured when a pressure of 20 psi is applied in the thickness direction. Furthermore, the thermal resistance value when a pressure of 30 psi or 40 psi is applied in the thickness direction is also preferably within the above range. Specifically, the thermal resistance value can be obtained by the measurement method described in the examples.

[0196] [Method for manufacturing thermally conductive sheet]

[0197] The thermally conductive sheet of the present application can be manufactured by a method comprising at least steps 1 to 5 described below. However, the thermally conductive sheet of the present application can also be manufactured by a method other than the manufacturing method described below.

[0198] Step 1: a step of obtaining a mixed composition by mixing at least a curable polymer composition and an anisotropic filler

[0199] Step 2: a step of obtaining a cured product by curing the mixed composition by heating

[0200] Step 3: a step of slicing the cured product to make it into a sheet shape

[0201] Step 4: a step of applying an adhesive to the surface of the cured product

[0202] Step 5: a step of allowing the applied adhesive to penetrate into the cured product

[0203] (Step 1)

[0204] In step 1, a mixed composition can be obtained by mixing at least a curable polymer composition and an anisotropic filler, and it is preferable to further mix a volatile substance into the mixed composition. Furthermore, a non-anisotropic filler can be mixed into the mixed composition, and other components such as an additive, etc. can be appropriately added as needed.

[0205] In step 1, as long as the components described above can be mixed to obtain a mixed composition, the mixing method or the mixing order is not particularly limited, and the curable polymer composition, the anisotropic filler, the volatile substance added as needed, and the non-anisotropic filler or other components added as needed can be mixed in any order to obtain a mixed composition.

[0206] As described above, the curable polymer composition can be composed of a main agent and a curing agent (for example, in the case of an addition reaction type polysiloxane, an organic polysiloxane containing an alkenyl group and a hydrogenated organic polysiloxane). In this case, the main agent, the curing agent, the anisotropic filler, the volatile substance added as needed, and other components can be mixed in any order to obtain a mixed composition.

[0207] Further, the form of the mixed composition can be either a liquid type or a two-liquid type in which the first agent and the second agent are combined. The two-liquid type is obtained by mixing the first agent and the second agent at the time of use.

[0208] (Volatile substance)

[0209] The volatile substance used in the present application is a component that volatilizes in the following Step 2. The volatile substance volatilizes by heating at the time of curing, whereby the content ratio of the thermally conductive filler in the thermally conductive sheet can be increased. Further, the viscosity is reduced by containing the volatile substance in the mixed composition. Therefore, it is easy to increase the blending amount of the thermally conductive filler, and further, it is easy to orient the anisotropic filler in a specific direction by the following magnetic field orientation or the like.

[0210] Further, by volatilizing the volatile substance, many fine bubbles are formed in the cured product, and therefore, in the following Step 5, the adhesive easily penetrates into the inside of the thermally conductive sheet.

[0211] Further, the volatile substance can be a compatible substance that is compatible with or dissolved in the curable polymer composition. If the volatile substance is a compatible substance, the curable polymer composition and the volatile substance can be uniformly mixed, and therefore, it is easy to reduce the viscosity or increase the blending amount of the thermally conductive filler. Further, the bubbles formed by volatilizing the volatile substance can also become fine and uniform.

[0212] The volatile substance is preferably a substance that is liquid at normal temperature (25°C) and 1 atm.

[0213] As the volatile substance, an alkoxysilane compound, a hydrocarbon-based solvent, an alkoxysiloxane compound, or the like can be exemplified. These compounds can improve the solubility or compatibility with the curable polymer composition, and therefore, it is easy to reduce the viscosity of the mixed composition or increase the blending amount of the thermally conductive filler. Further, it is easy to make the bubbles formed by volatilizing the volatile substance fine and uniform.

[0214] The volatile substance can be used alone or in combination of two or more.

[0215] The volatile substance is preferably an alkoxysilane compound. By using an alkoxysilane compound, roughness or the like is not observed on the surface of the thermally conductive sheet obtained by curing, and the appearance becomes good.

[0216] The alkoxysilane compound used as the volatile substance is a compound having 1 to 3 of the 4 bonds of a silicon atom (Si) bonded to an alkoxy group, and the remaining bonds bonded to an organic substituent group. By having an alkoxy group and an organic substituent group, the alkoxysilane compound improves the compatibility with the curable high molecular composition, particularly the curable high molecular composition composed of an organopolysiloxane.

[0217] As the alkoxy group of the alkoxysilane compound, there can be mentioned, for example, a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentoxy group, and a hexyloxy group. The alkoxysilane compound can be contained in the curable high molecular composition in the form of a dimer.

[0218] Among the alkoxysilane compounds, from the viewpoint of easy availability, an alkoxysilane compound having at least either a methoxy group or an ethoxy group is preferred. From the viewpoint of the compatibility with the curable high molecular composition, solubility, and the like, the number of alkoxy groups of the alkoxysilane compound is preferably 2 or 3, more preferably 3. Specifically, the alkoxysilane compound is preferably at least one selected from the group consisting of a trimethoxysilane compound, a triethoxysilane compound, a dimethoxysilane compound, and a diethoxysilane compound.

[0219] As the functional group included in the organic substituent group of the alkoxysilane compound, there can be mentioned, for example, an acryloyl group, an alkyl group, a carboxyl group, a vinyl group, a methacryloyl group, an aromatic group, an amino group, an isocyanate group, an isocyanurate group, an epoxy group, a hydroxyl group, and a mercapto group. Here, in the case where a platinum catalyst is used as a curing catalyst for the curable high molecular composition composed of an organopolysiloxane, an alkoxysilane compound which does not easily affect the curing reaction of the organopolysiloxane is preferably selected. Specifically, in the case where an addition reaction type organopolysiloxane using a platinum catalyst is used, the organic substituent group of the alkoxysilane compound preferably does not contain an amino group, an isocyanate group, a trimer isocyanate group, a hydroxyl group, or a mercapto group.

[0220] From the viewpoint of the compatibility with the "curable high molecular composition composed of an organopolysiloxane", the alkoxysilane compound is preferably 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 group. Thus, a dialkyldialkoxysilane compound, an alkyltrialkoxysilane compound is preferred, of which an alkyltrialkoxysilane compound is more preferred.

[0221] The number of carbon atoms of the alkyl group bonded to the silicon atom can be, for example, 1 to 16. Further, in the case of a trialkoxysilane compound such as a trimethoxysilane compound and a triethoxysilane compound, the number of carbon atoms of the above alkyl group is preferably 6 or more, further preferably 8 or more, and in addition, the number of carbon atoms is preferably 12 or less, more preferably 10 or less.

[0222] On the other hand, in the dialkoxysilane compound such as the dimethoxysilane compound and the triethoxysilane compound, the number of carbon atoms of the above-mentioned alkyl group can be 1 or more, and the number of carbon atoms is preferably 10 or less, more preferably 6 or less, and further preferably 4 or less.

[0223] As the alkoxysilane compound containing an alkyl group, for example, methyltrimethoxysilane, dimethyldimethoxysilane, diethyldimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, di-n-propyldimethoxysilane, di-n-propyldiethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, methylcyclohexyldimethoxysilane, methylcyclohexyldiethoxysilane, n-octyltrimethoxysilane, n-octyltriethoxysilane, n-decyltrimethoxysilane, n-decyltriethoxysilane, and the like can be exemplified.

[0224] Among the alkoxysilane compounds containing an alkyl group, from the viewpoint of the compatibility with the organopolysiloxane constituting the curable polymer composition, n-decyltrimethoxysilane and n-octyltriethoxysilane are further more preferable.

[0225] The alkoxysiloxane compound used as the volatile substance has a structure having two or more siloxane bonds, and an alkoxy group bonded to at least one silicon atom. The alkoxysiloxane compound has a structure in which an organic substituent is bonded to at least one silicon atom among the silicon atoms constituting the siloxane bond. By having the alkoxysiloxane compound have an alkoxy group and an organic substituent, the compatibility with the organopolysiloxane constituting the curable polymer composition can be improved.

[0226] As the alkoxy group and the organic substituent possessed by the alkoxysiloxane compound, those exemplified in the above-mentioned description of the alkoxysilane compound are exemplified, and from the viewpoint of the compatibility with the organopolysiloxane constituting the curable polymer composition, at least an alkyl group is preferable.

[0227] As the alkoxysiloxane compound, for example, methylmethoxysiloxane oligomer, methylphenylmethoxysiloxane oligomer, methylglycidoxy-methoxysiloxane oligomer, methylmercapto-methoxysiloxane oligomer, and methylmethacryloyl-methoxysiloxane oligomer, and the like can be exemplified.

[0228] The alkoxysiloxane compound can be used singly or two or more kinds.

[0229] As the hydrocarbon-based solvent to be used as the volatile substance, aromatic hydrocarbon-based solvents can be exemplified. Among them, from the viewpoint of compatibility with the curable polymer composition, aromatic hydrocarbon-based solvents are preferred. As the aromatic hydrocarbon-based solvent, aromatic hydrocarbon-based solvents having a carbon number of about 6 to 10 can be exemplified, and toluene, xylene, 1,3,5-trimethylbenzene, ethylbenzene, propylbenzene, butylbenzene, t-butylbenzene, and the like can be exemplified, with toluene, xylene, and the like being preferred.

[0230] In the mixed composition, the content of the volatile substance is preferably 6 parts by mass or more and 60 parts by mass or less with respect to 100 parts by mass of the curable polymer composition. If the content is 6 parts by mass or more, the effect of containing the volatile substance is easily exerted, and for example, a moderate amount of fine bubbles can be formed in the polymer matrix. Further, by setting the content to 60 parts by mass or less, an effect corresponding to the amount of use of the volatile substance can be obtained. From these viewpoints, the above content of the volatile substance is more preferably 8 parts by mass or more and 50 parts by mass or less, and further preferably 10 parts by mass or more and 35 parts by mass or less.

[0231] Further, the volatile substance is preferably volatilized partially or entirely by the heating of Step 2. Therefore, the volatile substance can not be contained in the thermally conductive sheet, or can be contained in the thermally conductive sheet in an amount less than the content in the mixed composition.

[0232] Further, the details of the components other than the volatile substance in the mixed composition (i.e., the curable polymer composition, the anisotropic filler material, the non-anisotropic filler material, other additives, and the like) are as described above. Further, the content of the thermally conductive filler material in the mixed composition is also as described above. However, among the above components, the content of each component is an amount based on 100 parts by mass of the polymer matrix, but in the mixed composition, it is an amount based on 100 parts by mass of the curable polymer composition.

[0233] (Step 2, Step 3)

[0234] 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, and is preferably higher than room temperature (25°C). The heating can be performed at a temperature of preferably 50°C or higher, more preferably 70°C or higher. In addition, the heating temperature is not particularly limited, and can be a temperature at which the mixed composition does not deteriorate by heat, for example, 200°C or lower, preferably 180°C or lower, more preferably 160°C or lower. In addition, the heating can be performed in one stage, or can be performed in two or more stages. In the case where the heating is performed in two or more stages, the heating temperature in at least one of the stages is preferably within the above-mentioned range, and more preferably the heating temperature in all of the stages is within the above-mentioned range. In addition, the heating is preferably performed at a temperature lower than the boiling point of the volatile compound in at least the first stage. In addition, the heating time is, for example, 10 minutes or longer and 24 hours or shorter. In the case where the heating is performed in two or more stages, the mixed composition can be semi-cured in the first stage (primary curing), and the mixed composition can be fully cured by heating in the second stage or later (secondary curing). In addition, the mixed composition can be fully cured by the primary curing, and the heating in the second stage or later does not accompany the curing.

[0235] As described below, in the case where the molded body obtained from the mixed composition is sliced to produce a sheet-shaped molded body, it is preferable that the primary curing be performed by heating in the first stage before the slicing, and the heating in the second stage or later (secondary curing) be further performed after the slicing. By performing the heating after the slicing, the volatile substance is easily volatilized by the heating in the second stage or later.

[0236] In the case where the curing is performed in two or more stages, the heating in the first stage (primary curing) can be performed at, for example, 50°C or higher and 120°C or lower, preferably 60°C or higher and 100°C or lower, more preferably 70°C or higher and 90°C or lower. In addition, the heating in the second stage or later (secondary curing) can be performed at a higher temperature than the primary curing, for example, at 100°C or higher and 200°C or lower, preferably 120°C or higher and 180°C or lower, more preferably 140°C or higher and 160°C or lower. Further, the heating time in the first stage is, for example, 5 minutes or longer and 20 hours or shorter, and is preferably 30 minutes or longer and 12 hours or shorter. In addition, the heating time in the second stage or later is, for example, 10 minutes or longer and 15 hours or shorter, and is preferably 1 hour or longer and 10 hours or shorter.

[0237] In the case where the molded body obtained from the mixed composition is sliced to produce a sheet-shaped molded body, it is preferable that the primary curing be performed by heating in the first stage before the slicing, and the heating in the second stage or later (secondary curing) be further performed after the slicing. By performing the heating after the slicing, the volatile substance is easily volatilized by the heating in the second stage or later.

[0238] Further, if the second stage of heating is performed at a higher temperature after the shaped body is sliced, the shaped body is cured, and thus even at a high temperature, it does not foam to produce large bubbles, and the space in which the volatile compound is present becomes a fine bubble. The above-mentioned bubble is, for example, 1 μm or less, and is preferably 0.2 μm or less. Further, the lower limit of the bubble is not particularly limited, and is, for example, 0.001 μm or more.

[0239] In step 2, the mixed composition can be shaped into a block or the like, and is heated and cured. Further, in step 2, the mixed composition can be oriented in a single direction by the anisotropic filler, and is cured by heating. The anisotropic filler can be oriented by a magnetic field orientation method, a flow orientation method, and is preferably oriented by the magnetic field orientation method.

[0240] In the magnetic field orientation method, the mixed composition can be oriented in the magnetic field by being placed in the magnetic field after being injected into the inside of a mold or the like. Further, an oriented shaped body can be obtained by curing the curable polymer composition. The curing of the mixed composition can be performed by the heating conditions described above.

[0241] By shaping the oriented shaped body into a block, the orientation of the anisotropic filler is improved.

[0242] In the magnetic field orientation method, a release film can be disposed on the portion of the inside of the mold that contacts the mixed composition. The release film can be, for example, a resin film in which the release property is preferably improved, or a resin film in which one surface has been subjected to a release treatment with a release agent or the like. By using the release film, the oriented shaped body is easily released from the mold.

[0243] In order to perform the magnetic field orientation, the viscosity of the mixed composition used in the magnetic field orientation method is preferably 10 Pa s or more and 300 Pa s or less. By setting the viscosity to 10 Pa s or more, the thermally conductive filler does not easily precipitate. Further, by setting the viscosity to 300 Pa s or less, the flowability is improved, the anisotropic filler is appropriately oriented in the magnetic field, and defects in which the orientation takes too much time do not occur. Further, the viscosity is the viscosity measured at 25°C with a rotational viscometer (Brookfield viscometer DV-E, spindle SC4-14) at a rotational speed of 10 rpm.

[0244] However, in the case in which the thermally conductive filler that does not easily precipitate, or an additive such as a precipitation preventing agent is used in combination, the viscosity of the mixed composition can also be set to less than 10 Pa s.

[0245] In the magnetic field orientation method, as a magnetic line of force generating source for applying a magnetic line of force, a superconducting magnet, a permanent magnet, an electromagnet, or the like can be listed, and in terms of generating a magnetic field with a high magnetic flux density, a superconducting magnet is preferable. The magnetic flux density of the magnetic field generated by these magnetic line of force generating sources is preferably 1 to 30 tesla. If the magnetic flux density is set to 1 tesla or more, the above-mentioned anisotropic filler material composed of a carbon material or the like can be easily oriented. Further, by setting it to 30 tesla or less, practical production can be achieved.

[0246] In the flow orientation method, a shear force is applied to the mixed composition, and a primary sheet in which the anisotropic filler material is oriented in the planar direction is produced. More specifically, in the flow orientation method, first, the mixed composition produced in Step 1 is given a shear force while being elongated flatly, and is molded into a sheet shape (a primary sheet). By applying a shear force, the anisotropic filler material can be oriented in the shear direction. As a means for molding the sheet, for example, the mixed composition can be coated on a base film by a coating applicator such as a bar coater or a doctor blade, or extrusion molding or ejection from a nozzle, and thereafter, drying is performed as necessary, or the mixed composition is semi-cured, or it is fully cured. The thickness of the primary sheet is preferably set to about 50 μm or more and 5000 μm or less. In the primary sheet, the anisotropic filler material is oriented in one direction in the planar direction of the sheet.

[0247] The mixed composition used in the flow orientation method has a relatively high viscosity so as to apply a shear force when elongated into a sheet shape. Specifically, the viscosity of the mixed composition is preferably 3 Pa s or more and 500 Pa s or less.

[0248] After a plurality of sheets are overlapped and stacked in the same orientation direction, the primary sheets are bonded to each other by a heating press or the like while being cured as necessary by heating, whereby a stacked block (a block-shaped orientation molded body) can be formed.

[0249] Further, in the case of forming a stacked block, the primary sheets can be overlapped after vacuum ultraviolet rays are irradiated to at least one of the overlapped surfaces of the primary sheets. If the primary sheets are overlapped with the surfaces irradiated with vacuum ultraviolet rays interposed, the primary sheets can be firmly bonded to each other. Further, in the case of irradiating vacuum ultraviolet rays, the mixed composition can be fully cured at the time of producing the primary sheets, and it is not necessary to cure it by heating or the like at the time of overlapping the primary sheets to form a stacked block.

[0250] In the flow orientation method, the curing of the mixed composition can also be performed by the heating conditions as described above.

[0251] Also, the obtained cured product of the mixed composition, i.e., the block-like oriented molded body, can be cut perpendicularly to the direction in which the anisotropic filler material is oriented by slicing to produce a sheet-like molded body. The slicing can be performed using a cutting knife or a laser, for example. By slicing, a portion of the anisotropic filler material is cut, and a void is formed along with the removal of the anisotropic filler material.

[0252] The sheet-like molded body obtained by the cutting can be coated with an adhesive directly using Step 4 described below, or can be further subjected to other treatments. For example, the surfaces as the sliced surfaces can be polished. Also, as described above, secondary curing can be performed. Further, the secondary curing can be performed after the polishing, or can be performed before the polishing.

[0253] By polishing the sheet-like molded body, the surface state of the sheet-like molded body becomes better, and it is easy to further reduce the thermal resistance value. By polishing the sheet-like molded body, the sheet surface can be smoothed in a state in which a certain amount of the fibrous filler material or the like anisotropic filler material is exposed to the surface. Also, the fibrous filler material can be in a state of being poured, or the like. Thus, it is easy to make the surface of the thermally conductive sheet adhere to other members, and it is easy to become a state in which a certain area or more of the sheet surface is covered with the fibrous filler material, and it is easy to reduce the thermal resistance value.

[0254] As for the polishing, at least one surface of the obtained sheet-like molded body can be polished, and preferably both surfaces of the sheet-like molded body are polished. The polishing of the surface can be performed using polishing paper or a polishing film, a polishing cloth, a polishing tape, or the like, for example.

[0255] As for the properties of the polishing paper, the average particle diameter (D50) of the polishing particles contained therein is preferably 0.1 μm or more and 100 μm or less, and more preferably 1 μm or more and 60 μm or less. Also, the particle size of the polishing particles of the polishing paper is preferably #120 to 20,000, more preferably #300 to 15,000, and further preferably #320 to 4,000.

[0256] As for the polishing method, in addition to polishing the surface of the sheet-like molded body by continuously abutting the polishing paper in the same linear direction, a method in which the polishing is performed by reciprocating a certain distance, a method in which the polishing is performed by rotating in the same direction, or a method in which the polishing is performed in various directions can be used.

[0257] Also, as for the degree of polishing, the surface state can be observed while the polishing is performed, and in the case of reciprocating polishing, for example, the reciprocation is preferably performed 1 time or more and 300 times or less, more preferably 2 times or more and 200 times or less, and further preferably 3 times or more and 50 times or less.

[0258] The polishing of the surface of the sheet-shaped molded body can be performed in two polishing steps. For example, the first polishing can be performed using a polishing paper having a larger average particle diameter of polishing particles, and the second polishing can be performed using a polishing paper having a smaller average particle diameter of polishing particles than the first polishing.

[0259] (Steps 4, 5)

[0260] In Step 4, the surface of the cured product such as the sheet-shaped molded body obtained in Steps 2, 3 is coated with an adhesive as described above. In the present application, as the coated adhesive, an acrylic adhesive having a reactive double bond can be used as described above.

[0261] Further, in the present production method, in Step 5, the adhesive is allowed to penetrate into the thermally conductive sheet. In the thermally conductive sheet, voids are formed due to the cutting of the sheet, accompanied by the shedding of the anisotropic filler material, and further, in the case of using a volatile substance, a large number of fine bubbles are formed accompanied by the volatilization of the volatile substance. Step 4 is a step of allowing the adhesive to penetrate into these voids or fine bubbles.

[0262] It is preferable to coat only the adhesive to allow the adhesive to penetrate into the inside of the thermally conductive sheet. That is, Steps 4, 5 are preferably performed simultaneously.

[0263] The adhesive can be diluted with a diluent, and coated on the surface of the sheet-shaped molded body in the form of an adhesive diluent. The adhesive is diluted with a diluent to allow the adhesive to easily penetrate into the thermally conductive layer. The diluent is a component that is a liquid at 25°C, 1 atm, has solubility or compatibility with the adhesive, and is volatilized by drying, and is not particularly limited, and an organic solvent can be preferably used.

[0264] The organic solvent used is not particularly limited, and examples 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.

[0265] Further, from the viewpoint of allowing the adhesive to appropriately penetrate into the thermally conductive layer by performing the following spraying, it is preferable to include, as the organic solvent, any one of cellulose acetate, butyl cellulose acetate, carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, and polyethylene glycol monoethyl ether, which have a volatilization speed that is not too fast.

[0266] Further, it is preferable to include, in addition to the above-mentioned organic solvent, an organic solvent having a lower boiling point than these. Specifically, methyl ethyl ketone, methyl isobutyl ketone, hexane, ethyl acetate, butyl acetate, toluene, and the like can be mentioned.

[0267] The dilution concentration by the diluent is not particularly limited, and can be adjusted so that the solid content concentration of the adhesive is, for example, 5% by mass or more and 50% by mass or less, preferably 8% by mass or more and 35% by mass or less, and further preferably 10% by mass or more and 25% by mass or less. If the solid content concentration is set to 5% by mass or more, excessive heating during drying can be prevented. Further, by setting it to 50% by mass or less, the weight per unit area does not increase more than necessary, and further, the adhesive can be appropriately penetrated into the thermally conductive layer.

[0268] The method of applying the adhesive is not particularly limited, and a publicly known application method can be used, and spraying is preferable. By performing spraying, the weight per unit area does not increase more than necessary, and further, the adhesive can be easily and appropriately penetrated into the thermally conductive layer. Further, by performing spraying and suppressing the application amount, it is possible to provide a portion having the adhesive layer and a portion not having the adhesive layer on the surface of the thermally conductive layer. Further, in the case of performing spraying, it is preferable to spray an adhesive including a fast-drying organic solvent such as ethyl acetate, and a slow-drying organic solvent such as polyethylene glycol monoethyl ether and propylene glycol monomethyl ether acetate. More specifically, by including a slow-drying organic solvent, the organic solvent does not excessively volatilize when the adhesive sprayed from the atomizer is applied to the surface of the thermally conductive layer, and thus the adhesive can be easily penetrated into the thermally conductive layer. On the other hand, it is preferable to adjust the viscosity to be suitable for spraying by including a fast-drying solvent.

[0269] The applied adhesive can be dried to volatilize the diluent. Regarding the drying temperature, in the case where the adhesive has a reactive double bond, it can be performed at a temperature at which the reaction of the reactive double bond does not substantially proceed. From this viewpoint, the drying temperature can be performed at, for example, 80°C or lower, preferably 70°C or lower, and more preferably 60°C or lower. Further, the lower limit of the drying temperature is not particularly limited, and it can be performed at around room temperature, for example, 20°C or higher, and from the viewpoint of shortening the drying time, it is preferable to be 30°C or higher, more preferably 40°C or higher, and further preferably 45°C or higher.

[0270] Further, the drying time is not particularly limited, and from the viewpoint of workability, the shorter the better, and for example, it is preferably 24 hours or less, more preferably 3 hours or less, and even more preferably 1 hour or less.

[0271] As described above, the thermally conductive sheet of the present application is preferably obtained by at least the following steps: slicing a cured product composed of a mixed composition containing a curable high-molecular composition and an anisotropic filler material to make it into a sheet shape; and allowing an adhesive to permeate into the sheet-shaped cured product.

[0272] [Use of the thermally conductive sheet]

[0273] The thermally conductive sheet is interposed between a heat generating body and a heat dissipating body, conducts and transfers heat emitted from the heat generating body to the heat dissipating body, and dissipates heat from the heat dissipating body. The thermally conductive sheet is used for electronic machine applications, semiconductor applications, and the like, and is preferably used for semiconductor applications. In semiconductor applications, the thermally conductive sheet can be used for any application, and is preferably used in applications called TIM1, which are directly applied to semiconductor chips such as silicon dies, for example, and is preferably used between a semiconductor chip and a heat sink.

[0274] Of course, it can also be used for applications called TIM2, which are not directly applied to semiconductor chips, and in this case, the thermally conductive sheet can be used, for example, between a heat sink and a cooling unit such as a heat dissipator or a heat pipe.

[0275] Further, the thermally conductive sheet, in addition to the above-described applications, can also be used between various electronic parts that are heat generating bodies and heat dissipating bodies such as heat sinks, heat dissipators, heat pipes, heat pumps, and metal housings of electronic machines.

[0276] The thermally conductive sheet can be used between two members (adherends) such as a heat dissipating body and a heat generating body, and can be used in a state of being in close contact with each member (adherend) and being compressed.

[0277] The thermally conductive sheet is preferably used in an application in which it is in close contact with an adherend via an acrylic adhesive layer and is heated to a high temperature of, for example, 200°C or higher and 300°C or lower, and preferably around 220°C or higher and 270°C or lower. The thermally conductive sheet of the present application can maintain, or in some cases improve, the adhesion to the adherend even when it is heated to a high temperature in a state of being in close contact with the adherend, and thus can prevent peeling from the adherend even when it is heated to a high temperature in a state of being in close contact with the adherend as described above. Further, it is preferable to heat in a state of not being pressurized during the above-described heating.

[0278] The thermally conductive sheet is preferably supplied to the reflow step in a state of being in close contact with the adherend via the adhesive layer in the semiconductor application, and heating can be performed in the above temperature range in the reflow step. Further, the thermally conductive sheet can be heated by the reflow step in a state of being in close contact with one or both of a semiconductor chip or a heat dissipation sheet via the adhesive layer. Thus, the thermally conductive sheet of the present application can be used to join a semiconductor chip and a heat dissipation sheet in the reflow step.

[0279] Further, it is preferable to perform a close contact step of bringing the thermally conductive sheet into close contact with the adherend via the adhesive layer (preferably, an acrylic adhesive layer) before heating to 200°C or higher. The close contact step is performed, for example, by heating to a temperature of 50°C or higher and 180°C or lower while pressing in a state of sandwiching the above thermally conductive sheet between the adherend. The above temperature is preferably 120°C or higher and 160°C or lower.

[0280] Thus, in the present application, a joining method can also be provided, which sequentially performs the following steps: a close contact step of sandwiching the thermally conductive sheet between a semiconductor chip and a heat dissipation sheet and bringing them into close contact; and a joining step of joining the semiconductor chip and the heat dissipation sheet heated to 200°C or higher after the above close contact step.

[0281] In the above close contact step, it is preferable to perform pressing after sandwiching the thermally conductive sheet between the semiconductor chip and the heat dissipation sheet at a temperature of preferably 50°C or higher and 200°C or lower, more preferably 50°C or higher and 180°C or lower, and further preferably 120°C or higher and 160°C or lower, to bring them into close contact.

[0282] Further, the heating temperature in the above joining step is preferably 220°C or higher, and is preferably 300°C or lower, and more preferably 270°C or lower. The above joining step is preferably performed in a state of not being pressed.

[0283] Example

[0284] Hereinafter, the present application will be described in more detail by way of examples, but the present application is not limited by these examples at all.

[0285] The measurement method and the evaluation method in the present example are shown below.

[0286] [A / B ratio]

[0287] One drop of the coating liquid of the adhesive prepared in the same manner as the adhesive used in each of the examples and comparative examples was applied to a gold-plated stainless steel plate, and the plate was sufficiently dried after the application to volatilize the solvent, to form an acrylic adhesive layer on the plate. Further, the drying was performed by placing the plate on which the adhesive was applied in an environment at 80°C for 15 minutes.

[0288] The acrylic adhesive layer formed on the plate was analyzed by Raman analysis, and the A / B value was calculated using the following device and measurement conditions. Further, in each of the examples and comparative examples, the intensity at a wave number of 1636.1 cm -1 was set as "A", and the intensity at a wave number of 1724.4 cm -1 was set as "B".

[0289] (Device used)

[0290] "inVia Qontor", manufactured by Renishaw Corporation

[0291] (Measurement conditions)

[0292] Laser power: 50 cumulative number of times: 1

[0293] Laser wavelength: 785 nm grating: 1200 l / mm

[0294] Magnification: 50 times

[0295] Focus: aligned with the surface of the sample on which the acrylic adhesive layer was formed

[0296] [Porosity]

[0297] The porosity of the XZ section at a position 25 μm from the surface and the porosity of the XZ section of the central portion in the thickness direction of the thermally conductive sheet (1.18 mm in width, 1.18 mm in length, and thickness as shown in Table 1) of each example and comparative example was measured by an X-ray CT device in the following manner. Further, the XZ section is a section parallel to the surface of the thermally conductive sheet (a section perpendicular to the thickness direction).

[0298] For the sheet-shaped molded body before the adhesive was applied, the images of the XZ section at a position 25 μm from the surface and the XZ section of the central portion in the thickness direction were obtained by X-ray CT, and image analysis was performed, whereby the porosity at each position was calculated. The porosity was calculated as the ratio of the area of the void portion to the area of the entire section. The measurement conditions and the conditions for image analysis are shown below.

[0299] 1) X-ray CT device

[0300] (Device used)

[0301] 3D X-ray microscope ("High Optical Resolution 3D X-ray Microscope nano3DX", manufactured by Rigaku Corporation)

[0302] (Measurement conditions)

[0303] X-ray target: Mo

[0304] Lens: L0540 (0.54 μm / pixel)

[0305] Binning: 2

[0306] Exposure time: 25 seconds

[0307] Number of shots: 1000 shots

[0308] 2) Image analysis

[0309] Using an image processing software ("Avizo 3D Pro 2022.1", manufactured by Thermo Fisher Scientific), the images obtained by the X-ray CT device were analyzed according to the following procedures.

[0310] (i) Image connection: In the case of a sample that spans multiple fields of view, the images were connected.

[0311] (ii) Extraction of sample region: For the images of (i), Interactive Thresholding was used to adjust so as to extract only the sample region.

[0312] (iii) Extraction of void region: For the images of (ii), Interactive Thresholding was used. The threshold was adjusted so as to extract only the void region.

[0313] And, the void fraction was calculated by the following formula.

[0314] Void fraction (%) = (iii) Total area of void region (pixel) / (ii) Total area of sample region (pixel) x 100

[0315] Further, in the image measurement, a cross-sectional image with a pitch of 1.08 μm was obtained from the surface of the sheet in the thickness direction, and the value of the void fraction in the cross-sectional image closest to the position of 25 μm in thickness was calculated.

[0316] [Ratio of anisotropic filler, ratio of resin containing a polymer matrix]

[0317] In the above image analysis (iii), the threshold was adjusted so as to extract only the anisotropic filler or the polymer matrix, and was calculated by the following formula.

[0318] Ratio of anisotropic filler (%) = (iii) Total area of anisotropic filler region (pixel) / (ii) Total area of sample region (pixel) x 100

[0319] Ratio of polymer matrix (%) = (iii) Total area of polymer matrix region (pixel) / (ii) Total area of sample region (pixel) x 100

[0320] [Presence or absence of resin in void]

[0321] The cross sections of the thermally conductive sheets of each of the examples and comparative examples were observed by a scanning electron microscope ("SU3500" manufactured by Hitachi High-Technologies Corporation), whereby it was confirmed whether or not the resin was present inside the voids of the surface of the thermally conductive sheet.

[0322] [Initial sheet thickness]

[0323] The thickness of the thermally conductive sheet before compression (initial thickness) was measured by a thickness gauge.

[0324] [E hardness]

[0325] The E-type hardness of the thermally conductive sheet was measured based on Japanese Industrial Standard JIS K 6253. Specifically, the E-type hardness of the oriented molded body produced in each example was measured using an E-type hardness tester.

[0326] [Thermal resistance value]

[0327] The thermal resistance value was measured using a thermal resistance measuring machine as shown in FIG. 3, by the method shown below.

[0328] Specifically, with respect to each sample, a test piece S of 30 mm x 30 mm in size for this test was produced. Then, each test piece S was attached to a copper block 22 having a measurement surface of 25.4 mm x 25.4 mm and the side surface covered with a heat insulating material 21, and was sandwiched by a copper block 23 above using a load cell 26 to apply a load at a pressure of 10 psi. Here, the copper block 22 below was in contact with a heater 24. In addition, the copper block 23 above was covered with a heat insulating material 21 and was connected to a heat sink 25 with a fan attached. Next, the heater 24 was heated so as to become 80°C, and after 10 minutes when the temperature became substantially stable, the temperature (θ j0 ) of the copper block 23 above, the temperature (θ j1 ) of the copper block 22 below, and the amount of heat generated by the heater (Q) were measured, and the thermal resistance value of each sample was calculated according to the following equation (1). Further, the thickness of the thermally conductive sheet at the time of measurement of the thermal resistance value was also measured.

[0329] Thermal resistance = (θ j1 - θ j0 ) / Q Equation (1)

[0330] In equation (1), θ j1θ is the temperature of the copper block 22 below j0 θ is the temperature of the copper block 23 above Q is the amount of heat generated.

[0331] Further, the pressure acting on the load cell 26 was changed to 20 psi, 30 psi, and 40 psi, respectively, and the same measurement was performed, and the results are shown in Table 2. In addition, for the thermal resistance value at a pressure of 40 psi, the ratio of the thermal resistance value when the thermal resistance value of the heat-conducting sheet of the blank sample was taken as a reference (100%) was calculated as the thermal resistance change rate. Further, a heat-conducting sheet having the same configuration except that the acrylic adhesive layer was not provided was used as a blank sample.

[0332] Regarding the evaluation of the thermal resistance, a case where the change rate of the thermal resistance rate was less than 30% was evaluated as good "A", and a case where the change rate of the thermal resistance rate was 30% or more was evaluated as poor "B".

[0333] [Chip (die) shear strength]

[0334] As shown in FIG. 4, the heat-conducting sheet 10 of 3 mm x 3 mm obtained in each of the examples and comparative examples was placed on a nickel-plated copper plate 18 of 50 mm x 50 mm and 2 mm in thickness, and further a silicon chip 19 of 3 mm x 3 mm and 600 μm in thickness was placed on the heat-conducting sheet 10. The obtained laminate was pressed in the thickness direction at a pressure of 1 MPa for 60 seconds in a normal temperature environment, and the heat-conducting sheet 10 was bonded to the nickel-plated copper plate 18 and the silicon chip 19, and a measurement sample 15 was obtained. The measurement sample 15 was placed on a hot plate adjusted to 250°C with the nickel-plated copper plate side as the lower side, and heated for 3 minutes. Further, heating at 250°C for 3 minutes was assumed to be reflow processing.

[0335] After that, in a 25°C environment, using a chip shear strength tester ("Dage-S4000", manufactured by Nordson Corporation), the height was adjusted so that the front end of the tool 17 was 300 μm in height from the surface of the heat-conducting sheet 10. Next, the tool 17 was brought into abutment with the silicon chip 19 in the shear direction S at a speed of 150 μm / s, and the load required to break the bonded portion was taken as the chip shear strength. Regarding the evaluation of the adhesiveness, a case where the chip shear strength was 0.05 MPa or more was taken as good "A", and a case where the chip shear strength was less than 0.05 MPa was taken as poor "B".

[0336] Regarding the measurement of the chip shear strength using the chip shear strength tester, the measurement samples produced in the same manner were also subjected to the same measurement in a 80°C environment and a 150°C environment.

[0337] Further, the chip shear strength was measured in the same manner at 25°C, 80°C, and 150°C for the sample that was not subjected to heating at 250°C for 3 minutes (without reflow treatment).

[0338] As a raw material of the thermally conductive sheet, the following components were used.

[0339] (Polymer composition)

[0340] Cured silicone: an addition reaction type organopolysiloxane composed of an alkenyl group-containing organopolysiloxane as a main agent and a hydrogenated organopolysiloxane as a curing agent, which contains a catalytic amount of a platinum catalyst.

[0341] (Volatile substance)

[0342] N-decyltrimethoxysilane

[0343] (Thermally conductive filler)

[0344] Alumina 1: spherical, average particle diameter (D50) = 3 μm, aspect ratio 1.0

[0345] Alumina 2: polyhedral shape, average particle diameter (D50) = 0.5 μm, aspect ratio 1.0

[0346] Aluminum: spherical, average particle diameter (D50) = 3 μm, aspect ratio 1.0 to 1.5

[0347] Graphitized carbon fiber 1: average fiber length (arithmetic mean) 82 μm, diameter 10 μm, aspect ratio 8.2, thermal conductivity 900 W / m·K

[0348] Graphitized carbon fiber 2: average fiber length (arithmetic mean) 55 μm, diameter 10 μm, aspect ratio 5.5, thermal conductivity 200 W / m·K

[0349] Flaky graphite powder 1: average particle diameter (D50) = 15 μm, aspect ratio 10, thermal conductivity 550 W / m·K

[0350] Flaky graphite powder 2: average particle diameter (D50) = 300 μm, thermal conductivity 200 W / m·K

[0351] (Adhesive)

[0352] Adhesive 1: an adhesive in which an acrylic polymer having a structural unit derived from 2-ethylhexyl acrylate as a main component, and a hydroxyl group, a carboxyl group, and a vinyl group in a side chain are used as a main adhesive agent. A / B = 0.588

[0353] Adhesive 2: Adhesive in which the main component of the adhesive main agent is an acrylic polymer having a structural unit derived from 2-ethylhexyl acrylate as a main component, and having a hydroxyl group, a carboxyl group, and a vinyl group in the side chain. A / B = 0.405

[0354] Adhesive 3: Adhesive in which the main component of the adhesive main agent is an acrylic polymer having a structural unit derived from 2-ethylhexyl acrylate and butyl acrylate as a main component, and having a hydroxyl group and a carboxyl group but not having a reactive double bond in the side chain. A / B = 0.138

[0355] * Further, a diluent of the adhesive diluted with ethyl acetate to a solid content concentration of 33 mass% was further diluted with 120 mass parts of propylene glycol monomethyl ether acetate (solvent) to prepare a coating liquid having a solid content concentration of 15 mass%, which was used in each of the examples and comparative examples.

[0356] [Example 1]

[0357] A mixed composition was obtained by mixing the components at 25°C for 50 minutes using a planetary mixer in accordance with the formulation 1 of Table 1. Next, the mixed composition was injected into a mold set to be sufficiently larger in thickness than the thermally conductive sheet, a magnetic field of 8 T was applied in the thickness direction, and the carbon fibers and flaky graphite were oriented in the thickness direction, and then the thermosetting silicone was once cured by heating at 80°C for 8 hours, thereby obtaining a block-shaped oriented molded body.

[0358] Next, the block-shaped oriented molded body was sliced into a sheet shape having a thickness of about 120 μm using a shear knife, thereby obtaining a sheet-shaped molded body in which a part of the surface anisotropic filler material was peeled off. Thereafter, the sheet-shaped molded body was twice cured by heating at 150°C for 6 hours.

[0359] Next, the sheet-shaped molded body was ground back and forth 25 times using a coarse grinding paper A (grit #800) having an average particle diameter (D50) of 20 μm, and then further ground back and forth 10 times using a coarse grinding paper B (grit #4000) having an average particle diameter (D50) of 3 μm.

[0360] The sheet-shaped molded body was obtained. The sheet-shaped molded body was adjusted in such a manner that the weight per unit area after drying became the amount described in Table 2, and the coating liquid of the adhesive 1 was sprayed onto both surfaces of the sheet-shaped molded body, and then dried at 50°C for 3 minutes, thereby obtaining a thermally conductive sheet provided with an acrylic adhesive layer on both surfaces. It was confirmed that the thermally conductive layer had fine bubbles therein, and the acrylic adhesive penetrated into the fine bubbles near both surfaces. Further, the anisotropic filler material was oriented in the thickness direction. The results are shown in Table 2.

[0361] [Examples 2 to 6]

[0362] The conditions of the spray were changed in the manner as described in Table 2 in terms of the kind of the adhesive used and the weight per unit area of the dried adhesive, and otherwise, the same as in Example 1 was performed.

[0363] [Example 7]

[0364] The same as in Example 1 was performed except that the block-like oriented molded body was sliced into a sheet shape having a thickness of about 80 μm.

[0365] [Example 8]

[0366] The same as in Example 8 was performed except that the slicing method of the block-like oriented molded body was changed to slicing by ultrasonic waves.

[0367] [Example 9]

[0368] The same as in Example 9 was performed except that the mixed composition was obtained by mixing the components according to Formulation 3 of Table 1 using a planetary mixer for 50 minutes at 25°C.

[0369] [Example 10]

[0370] The same as in Example 1 was performed except that the mixed composition was obtained by mixing the components according to Formulation 4 of Table 1 using a planetary mixer for 50 minutes at 25°C.

[0371] [Comparative Example 1]

[0372] The same as in Example 1 was performed except that the coating liquid of the adhesive was not applied to the sheet-like molded body.

[0373] [Comparative Example 2]

[0374] The same as in Example 1 was performed except that the block-like oriented molded body was sliced into a sheet shape having a thickness of about 300 μm.

[0375] [Comparative Example 3]

[0376] The same as in Example 1 was performed except that the mixed composition was obtained by mixing the components according to Formulation 2 of Table 1 using a planetary mixer for 50 minutes at 25°C, and the coating liquid of the adhesive was not applied to the sheet-like molded body.

[0377] [Comparative Example 4]

[0378] The same as in Example 10 was performed except that the coating liquid of the adhesive was not applied to the sheet-like molded body.

[0379] * The values of the components are mass parts in each formulation.

[0380] * The sheet hardness is a value obtained by measuring the cured product obtained from each of the formulations in each of the examples and comparative examples.

[0381]

[0382]

[0383] The thermally conductive sheet of Examples 1 to 10 contains a polymer matrix and an anisotropic filler material oriented in the thickness direction, the thickness and the void fraction of the cross section at a depth position of 25 μm from the surface are within a specific range, and the voids at at least a part of the surface are provided with a resin different from the polymer matrix. The thermally conductive sheet satisfying these requirements is as described in Table 2, and the thermal resistance value is evaluated to be good. Furthermore, even if the thermally conductive sheet of each example is heated to a high temperature of about 250°C in a state in which the thermally conductive sheet is in close contact with an adherend, a high die shear strength can be maintained, and peeling or the like of the thermally conductive sheet in close contact can be prevented even after a reflow step or the like.

[0384] In contrast, Comparative Examples 1, 3, and 4 are thermally conductive sheets in which the voids present on the surface are not provided with a resin different from the polymer matrix, and as a result, the close contact property is poor.

[0385] Furthermore, the thermally conductive sheet of Comparative Example 2 is thicker than the specified thickness, and as a result, the thermal resistance value is higher and the heat dissipation property is poorer than in the examples.

[0386] Explanation of Reference Numerals

[0387] 10: Thermally conductive sheet

[0388] 11: Void

[0389] 12: Polymer matrix

[0390] 13: Anisotropic filler material

[0391] 14: Void

[0392] 15: Measurement sample

[0393] 16: Adhesive layer

[0394] 17: Tool

[0395] 18: Nickel-plated copper plate

[0396] 19: Silicon chip

[0397] 21: Thermal insulation material

[0398] 22: Lower copper block

[0399] 23: Upper copper block

[0400] 24: heater

[0401] 25: heat sink

[0402] 26: load cell

[0403] S: test piece

Claims

1. A thermally conductive sheet comprising a polymer matrix and an anisotropic filler material oriented along its thickness direction, and The thickness of the thermally conductive sheet is less than 0.2 mm. The porosity of the cross-section of the thermally conductive sheet at a depth of 25 μm parallel to the surface is 1.0–15.0%. At least a portion of the voids on at least one surface of the thermally conductive sheet contain a resin different from the polymer matrix.

2. The thermally conductive sheet as described in claim 1, wherein the resin different from the polymer matrix is ​​an acrylic adhesive.

3. The thermally conductive sheet as described in claim 2, wherein the acrylic adhesive is an acrylic adhesive having reactive double bonds.

4. The thermally conductive sheet as claimed in claim 1 or 2, wherein the thermally conductive sheet has an acrylic adhesive layer formed by an acrylic adhesive on its surface.

5. The thermally conductive sheet as described in claim 4, wherein the intensity ratio A / B of the peak intensity A of the C=C stretching vibration to the peak intensity B of the C=O stretching vibration in the Raman spectrum of the acrylic adhesive is 0.2 or higher.

6. The thermally conductive sheet as described in claim 1 or 2, wherein the polymer matrix is ​​an organopolysiloxane.

7. A method for manufacturing a thermally conductive sheet, comprising the following steps: The step of mixing a curable polymer composition with an anisotropic filler material to obtain a mixed composition; The step of obtaining a cured product by heating the mixed composition; The step of slicing the solidified material to make it into a sheet; The step of applying an adhesive to the surface of the cured material; and The step of allowing the applied adhesive to penetrate into the cured material.

8. The method for manufacturing a thermally conductive sheet as claimed in claim 7, wherein, in addition to the curable polymer composition and the anisotropic filler material, a volatile substance is further mixed to obtain the mixed composition, and at least a portion of the volatile substance is volatilized by heating.

9. A thermally conductive sheet comprising a polymer matrix and an anisotropic filler material oriented along its thickness direction. The thickness of the thermally conductive sheet is less than 0.2 mm. Let C be the ratio of the area occupied by the anisotropic filler material in the cross-section S1 of the thermally conductive sheet, which is parallel to the surface and at the center of the thickness direction. S1 Let P be the ratio of the area occupied by the resin containing the polymer matrix. S1 ,and, Let C be the ratio of the area occupied by the anisotropic filling material in the cross-section S2 at a depth of 25 μm from the surface of the thermally conductive sheet. S2 Let P be the ratio of the area occupied by the resin containing the polymer matrix. S2 In this case, The following conditions (1) and (2) must be met: C S1 >C S2 (1) P S1 <P S2 (2)。 10. The thermally conductive sheet as described in claim 1 or 2, which can be obtained by the following steps: The step of slicing a cured material consisting of a mixture comprising a curable polymer composition and an anisotropic filler to make it into a sheet; And the step of allowing the adhesive to penetrate into the sheet-like cured material.

11. A joining method, wherein a close contact step and a joining step are performed sequentially, In the bonding step, the thermally conductive sheet of claim 10 is sandwiched between the semiconductor chip and the heat sink and bonded tightly together. In the bonding step, after the bonding step, the semiconductor chip heated to above 200°C is bonded to the heat sink.

12. The bonding method of claim 11, wherein in the bonding step, after the thermally conductive sheet is sandwiched between the semiconductor chip and the heat sink, pressure is applied at a temperature above 50°C and below 200°C to bond them tightly.

13. The joining method of claim 11, wherein the joining step is performed under no pressure.

14. Use of a thermally conductive sheet for bonding a semiconductor chip to a heat sink during a reflow step, said thermally conductive sheet comprising a polymer matrix and an anisotropic filler material oriented along its thickness direction. The thickness of the thermally conductive sheet is less than 0.2 mm. The porosity of the cross-section of the thermally conductive sheet at a depth of 25 μm parallel to the surface is 1.0–15.0%. At least a portion of the voids on at least one surface of the thermally conductive sheet contain a resin different from the polymer matrix.

Images