Thermal Conductive Sheet and Method for Manufacturing Thermal Conductive Sheet

Abstract

To provide a heat conductive sheet having good restoring force when compressed and released.SOLUTION: In a heat conductive sheet 1 in which fibrous fillers 3 are dispersed in a binder resin 2, and the fibrous fillers 3 are arranged at an angle of 70 to 90 degrees in a thickness direction B in a cross-sectional view, when the heat conductive sheet 1 is compressed and released under a condition 1 below, the arrangement angle of the fibrous filler 3 after release is within 10 degrees of the angle before compression in a cross-sectional view, and the condition 1: the thickness of the heat conductive sheet 1 is compressed to 40% of the initial thickness at room temperature for 24 hours, and then released.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present technology relates to a heat conduction sheet and a method for manufacturing the heat conduction sheet.

Background Art

[0002] Conventionally, semiconductor elements mounted on various electrical devices such as personal computers and other devices generate heat when driven, and if the generated heat accumulates, it may have an adverse effect on the driving of the semiconductor element and peripheral devices. Therefore, various cooling methods are used.

[0003] As a cooling method for a device having a semiconductor element, there are known a method of attaching a fan to the device to cool the air inside the device casing, a method of attaching a heat sink such as heat dissipation fins or a heat dissipation plate to the semiconductor element, and a method of immersing in a fluorine-based inert liquid. When cooling is performed by attaching a heat sink to a semiconductor element, a heat conduction sheet is provided between the semiconductor element and the heat sink in order to efficiently release the heat of the semiconductor element.

[0004] As an example of a heat conduction sheet, one in which a filler (for example, a heat conductive filler such as carbon fiber) is dispersed and contained in a binder resin is widely used (for example, see Patent Document 1).

[0005] By the way, electronic components such as the CPU (Central Processing Unit) of a personal computer tend to increase the amount of heat dissipation year by year with the increase in their speed and performance. However, the chip size of a processor or the like has become smaller than or equal to the conventional size due to the progress of fine silicon circuit technology, and the heat flow rate per unit area has increased. In order to avoid problems such as those caused by the temperature rise of such electronic components, it is required to dissipate and cool the electronic components more efficiently.

[0006] In order to improve the heat dissipation characteristics of a heat conduction sheet, for example, it is required to reduce the thermal resistance, which is an index indicating the difficulty of heat transfer. In order to reduce the thermal resistance of the heat conduction sheet, for example, it is effective to improve the adhesion of the heat conduction sheet to a heat generating body (for example, an electronic component) or a heat radiator (for example, a heat sink).

[0007] However, the surface of the heat conduction sheet sliced from a heat conduction molded body for forming the heat conduction sheet usually has irregularities, so the adhesion tends to be poor. If the adhesion of the surface of the heat conduction sheet is poor, in the mounting process, the adhesion of the heat conduction sheet to the heat generating body or the heat radiator deteriorates, and it tends to be difficult to sufficiently reduce the thermal resistance of the heat conduction sheet. In particular, when the compressive stress of the heat conduction sheet is low, once the heat conduction sheet is compressed (crushed), the repulsive force is small. Therefore, when the gap between the heat generating body and the heat radiator opens, the heat conduction sheet disposed between the heat generating body and the heat radiator tends to be difficult to follow the gap.

[0008] Methods are known in which the surface of a heat conduction sheet produced by slicing a heat conduction molded body is pressed, or the heat conduction sheet produced by slicing a heat conduction molded body is allowed to stand for a long time to cause the binder component to ooze out onto the surface of the heat conduction sheet, thereby improving the adhesion between the heat conduction sheet and the adherend (see, for example, Patent Documents 2 and 3).

[0009] However, even if the surface of the heat conduction sheet is pressed, the binder component may not ooze out uniformly on the surface of the heat conduction sheet, and there is a possibility that the adhesion may vary depending on the location on the surface of the heat conduction sheet. Also, when the heat conduction sheet is allowed to stand for a long time, the same tendency as when the surface of the heat conduction sheet is pressed occurs. Further, in the conventional technology, when the heat conduction sheet is compressed and released, it has not been examined whether the restoring force of the heat conduction sheet, particularly the restoring force of the fibrous filler, becomes good.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0011] This technology has been proposed in view of such a conventional situation, and provides a heat conduction sheet having good resilience when compressed and released.

Means for Solving the Problems

[0012] As a result of investigations by the inventors of the present case, when compression and release are performed on a heat conduction sheet in which fibrous fillers are dispersed in a binder resin and the fibrous fillers are arranged at an angle of 70 to 90 degrees in the thickness direction in a cross-sectional view, it has been found that deterioration of the thermal resistance can be suppressed because the resilience of the fibrous fillers is good after compression and release.

[0013] This technology is a heat conduction sheet in which fibrous fillers are dispersed in a binder resin and the fibrous fillers are arranged at an angle of 70 to 90 degrees in the thickness direction in a cross-sectional view. When the heat conduction sheet is compressed and released under the following Condition 1, the arrangement angle of the fibrous fillers after release is within a range of 10 degrees or less of the angle before compression in a cross-sectional view. Condition 1: The thickness of the heat conduction sheet is compressed from the initial thickness by 40% at room temperature for 24 hours and then released.

[0014] The manufacturing method of the heat conduction sheet according to this technology includes a step of preparing a heat conduction composition containing a binder resin and fibrous fillers, a step of forming a molded body block from the heat conduction composition, and a step of slicing the molded body block into a sheet shape to obtain a heat conduction sheet, and the heat conduction sheet is the heat conduction sheet described above.

Effects of the Invention

[0015] According to the present technology, it is possible to provide a heat conduction sheet having good resilience when compressed and released.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0017] In the heat conduction sheet according to the present technology, fibrous fillers are dispersed in a binder resin, and the fibrous fillers are arranged at an angle of 70 to 90 degrees in the thickness direction in a cross-sectional view. Further, when the heat conduction sheet according to the present technology is compressed and released under the following Condition 1, the arrangement angle of the fibrous fillers after compression and release is within a range of 10 degrees or less of the angle before compression in a cross-sectional view. Condition 1: The thickness of the heat conduction sheet is compressed from the initial thickness by 40% at room temperature for 24 hours and then released.

[0018] Thus, the thermal conductive sheet according to the present technology has good resilience, particularly the resilience of the fibrous filler, when compressed and released as in Condition 1. That is, even when the thermal conductive sheet according to the present technology is greatly compressed as in Condition 1, it returns greatly. Here, the resilience of the fibrous filler means the degree of deviation of the arrangement angle of the fibrous filler in the cross-sectional view of the thermal conductive sheet before and after compression and release when the thermal conductive sheet is compressed and released under Condition 1 described above. That the resilience of the fibrous filler is good means that when the thermal conductive sheet is compressed and released under Condition 1, the arrangement angle of the fibrous filler after compression and release is within a range of 10 degrees of the angle before compression in the cross-sectional view of the thermal conductive sheet. When the thermal conductive sheet according to the present technology is disposed between a heat generating body (e.g., an IC (Integrated Circuit)) and a heat dissipating body (e.g., a heat sink), even if the gap between the heat generating body and the heat dissipating body opens, the fibrous filler in the thermal conductive sheet can easily and quickly follow the gap. Thereby, deterioration of the thermal resistance of the thermal conductive sheet can be suppressed.

[0019] FIG. 1 is a cross-sectional view showing an example of a thermal conductive sheet. The thermal conductive sheet 1 includes a binder resin 2 and a fibrous filler 3, and the fibrous filler 3 is arranged at an angle of 70 to 90 degrees in the thickness direction B in the cross-sectional view. In other words, in the thermal conductive sheet 1, the long axis of the fibrous filler 3 is arranged in a range of 70 to 90 degrees with respect to the plane direction A of the thermal conductive sheet 1. Further, the thermal conductive sheet 1 may further include another thermal conductive material 4 other than the fibrous filler 3.

[0020] And when the thermal conductive sheet 1 is compressed and released under Condition 1 described above, the arrangement angle of the fibrous filler 3 after compression and release is within a range of 10 degrees of the angle before compression in the cross-sectional view. That is, in the thermal conductive sheet 1, the angle difference of the fibrous filler 3 before and after compression and release is within 10 degrees, and the angle of the fibrous filler 3 after compression and release tends to return to the angle (position) before compression.

[0021] Regarding the details of the above-mentioned Condition 1, for example, a heat conduction sheet 1 (sample) with a thickness of 2 mm and a diameter of 29 mm is compressed from its initial thickness by 40% at room temperature for 24 hours, and 3 minutes after releasing the compression, the arrangement angle of the fibrous filler 3 in the heat conduction sheet 1 is measured. In Condition 1, the point that the size of the heat conduction sheet 1 is 29 mm in diameter and the temperature is room temperature conforms to JIS K6262. Also, in JIS K6262, the time is under a selection system, and the "24 hours" in Condition 1 is one of the times stipulated in the said standard. Regarding the compression according to Condition 1, more specifically, first, the thickness of the heat conduction sheet 1 is measured, and the heat conduction sheet 1 is processed to a diameter of 29 mm. The processed heat conduction sheet 1 (sample) is sandwiched between jigs with SUS304 on the surface and compressed by 40% with respect to the thickness of the sample. During compression, a spacer with a thickness of 60% of the sample thickness is sandwiched between the screw parts and the screw is tightened. After tightening the screw, to confirm whether the sample can be compressed to a predetermined thickness, it is ensured that the spacer does not shift or move. In the case of a sample with adhesiveness on the surface, it may be compressed by sandwiching it between a film to which the adhesive (sample) does not adhere. "Room temperature" refers to the range of 15 to 25 °C stipulated in JIS K 0050:2019 (General Rules for Chemical Analysis Methods).

[0022] In the heat conduction sheet, if the angle difference of the fibrous filler 3 before and after compression release exceeds 10 degrees, when the heat conduction sheet is arranged between a heating element and a heat sink, when the gap between the heating element and the heat sink opens, it becomes difficult to make the heat conduction sheet follow the gap, and as a result, the thermal resistance of the heat conduction sheet tends to deteriorate easily. The heat conduction sheet 1 is preferably such that the angle difference of the fibrous filler 3 before and after compression release is smaller, and it may be within 8 degrees, within 7 degrees, within 6 degrees, within 5.6 degrees, within 5.2 degrees, within 4 degrees, within 3.8 degrees, or within the range of 3.8 to 5.6 degrees.

[0023] Before compressing the heat conduction sheet 1 under the above-described condition 1, the fibrous filler 3 only needs to be arranged at an angle of 70 to 90 degrees in the thickness direction B of the heat conduction sheet 1 in a cross-sectional view of the heat conduction sheet 1, and may be in the range of 80 to 84 degrees, or may be in the range of 81.9 to 83.1 degrees. Also, the fibrous filler 3 after releasing the compression of the heat conduction sheet 1 under the above-described condition 1 is preferably arranged at an angle of 70 to 90 degrees in the thickness direction B of the heat conduction sheet 1 in a cross-sectional view of the heat conduction sheet 1. For example, it may be in the range of 70 to 80 degrees, or may be in the range of 77.0 to 77.9 degrees.

[0024] In the heat conduction sheet 1, not all the fibrous fillers 3 need to be arranged at an angle of 70 to 90 degrees in the thickness direction B in a cross-sectional view. FIGS. 2 and 3 are perspective views for explaining an example of a method for measuring the arrangement angle of the fibrous filler 3 in the heat conduction sheet 1. In FIGS. 2 and 3, arrow A represents the surface direction of the sample (heat conduction sheet 1), and arrow B represents the thickness direction of the sample (heat conduction sheet 1). For example, as shown in FIG. 2, a sample 5 with a thickness of 2 mm and a diameter of 29 mm is prepared from the heat conduction sheet 1, and the central portion in the plan view (upper surface) of the sample 5 is cut in the thickness direction B with a predetermined width. As shown in FIG. 3, on the cut surface 6A of the cut sample 6, within 5 mm from the outer periphery and in the range 6B of the upper and lower 1 / 3, the average value of the angles of any fibrous filler 3 measured at five points may be in the range of 70 to 90 degrees.

[0025] FIG. 4 is a cross-sectional view showing an example of the heat conduction sheet before and after compression. The arrow in FIG. 4 means that the heat conduction sheet 1 (cut sample 6) is compressed under Condition 1. That is, the upper side of the arrow in FIG. 4 is an example of the heat conduction sheet 1 (cut sample 6) before compression under Condition 1, and the lower side of the arrow in FIG. 4 is an example of the heat conduction sheet 1 (cut sample 6) after compression under Condition 1. The range 6B on the cut surface 6A is, compared with the other range (for example, the central part 6Ac of the cut surface 6A of the cut sample 6), for example, in the heat conduction sheet 1 after compression, the fibrous filler 3 is less likely to be dense in the thickness direction B, and the change in the angle of the fibrous filler 3 before and after compression and decompression tends to appear easily. Also, the range 6B on the cut surface 6A is, compared with the other range (for example, the central part 6Ac of the cut surface 6A), when the heat conduction sheet 1 is compressed under the above-described Condition 1, more force is applied and it tends to collapse more easily. Therefore, it is considered that the change in the angle of the fibrous filler 3 before and after compression and decompression tends to appear more significantly.

[0026] Also, the heat conduction sheet 1 according to the present technology has good resilience when compressed and released as in Condition 1. In addition to reducing the angle difference of the fibrous filler 3 before and after compression and decompression, the change in the outer dimension of the heat conduction sheet 1 before and after compression and decompression can also be reduced.

[0027] For example, for the heat conduction sheet 1 with a thickness of 2 mm and a diameter of 29 mm, that is, sample 5, after compressing it at room temperature for 24 hours by 40% and releasing it, the diameter of sample 5 after 3 minutes can be 32.0 mm or less, can also be 31.0 mm or less, can also be 30.0 mm or less, can also be 29.9 mm or less, can also be 29.6 mm or less, can also be 29.5 mm or less, and can also be in the range of 29.5 to 29.9 mm.

[0028] Thus, when the heat conduction sheet 1 is disposed between the heat generating body and the heat radiating body, even if a gap is formed between the heat generating body and the heat radiating body, the outer shape size of the heat conduction sheet 1 and the fibrous filler 3 in the heat conduction sheet 1 can follow the gap. Therefore, the deterioration of the thermal resistance of the heat conduction sheet 1 can be more effectively suppressed. Further, since the heat conduction sheet 1 can reduce the change in the outer shape size before and after release of compression, the heat conduction sheet 1 can be processed according to the shape of the heat generating body (for example, an IC), and the entire surface of the heat generating body can be cooled more efficiently.

[0029] The heat conduction sheet 1 is preferably relatively soft, for example, the hardness in the Shore type OO is preferably 25 to 40. When the hardness of the heat conduction sheet 1 is in such a range, the resilience of the fibrous filler 3 in the heat conduction sheet 1 and the outer shape size of the heat conduction sheet 1 after release of compression become better. Further, the followability of the heat conduction sheet 1 to the adherend becomes better. The hardness of the heat conduction sheet 1 can be measured by the method of the examples described later.

[0030] Here, a rubber sheet can be cited as a heat-conductive sheet having restorability. However, rubber sheets generally have a high hardness (are hard) in Shore type OO, and for example, the load on an IC as a heat-generating body or a heat sink as a heat-radiating body is high. Also, grease (liquid) can be cited as a heat-conductive agent that is softer than a rubber sheet. However, grease has low shape followability and restorability with respect to an IC as a heat-generating body. Here, in a region with a low compression ratio (compression less than 40% of the initial thickness), even a relatively hard heat-conductive sheet can be crushed, and after crushing the heat-conductive sheet, it is possible to restore the angle of the fibrous filler and the outer shape size of the heat-conductive sheet. However, in the case of a hard heat-conductive sheet, when attempting to compress the heat-conductive sheet by 40% with respect to the initial thickness as in Condition 1, breakage (for example, cracks in the heat-conductive sheet) occurs, and it tends to be difficult to restore the angle of the fibrous filler and the outer shape size of the heat-conductive sheet. Also, in the case of a hard heat-conductive sheet, a great deal of force is required to pressurize (compress) the heat-conductive sheet. On the other hand, the heat-conductive sheet 1 according to the present technology can adjust the hardness in Shore type OO to 25 to 40, is softer than a rubber sheet, and has better restorability and shape followability with respect to an adherend than a grease (liquid) sheet. That is, the heat-conductive sheet 1 is soft with a hardness in Shore type OO of 25 to 40, but has good restorability, and even when compressed under Condition 1, the angle of the fibrous filler 3 and the outer shape size of the heat-conductive sheet 1 are easily restored.

[0031] The thickness of the heat-conductive sheet 1 is not particularly limited and can be appropriately selected according to the purpose. For example, the thickness of the heat-conductive sheet 1 can be 0.05 mm or more, and can also be 0.1 mm or more. Also, the upper limit value of the thickness of the heat-conductive sheet 1 can be 5 mm or less, may be 4 mm or less, or may be 3 mm or less. From the viewpoint of handleability, the heat-conductive sheet 1 preferably has a thickness of 0.1 to 4 mm. The thickness of the heat-conductive sheet 1 can be obtained, for example, by measuring the thickness of the heat-conductive sheet 1 at five arbitrary positions and calculating the arithmetic mean value.

[0032] The following describes specific examples of the components of the heat conductive sheet 1. The heat conductive sheet 1 includes, for example, a binder resin 2, a fibrous filler 3, and another heat conductive material 4.

[0033] <Binder resin> The binder resin 2 is for holding the fibrous filler 3 and another heat conductive material 4 within the heat conductive sheet 1. The binder resin 2 is selected according to the properties such as the mechanical strength, heat resistance, and electrical properties required for the heat conductive sheet 1. The binder resin 2 can be selected from thermoplastic resins, thermoplastic elastomers, and thermosetting resins.

[0034] Examples of the thermoplastic resin include ethylene-α-olefin copolymers such as polyethylene, polypropylene, and ethylene-propylene copolymer; polymethylpentene; polyvinyl chloride; polyvinylidene chloride; polyvinyl acetate; ethylene-vinyl acetate copolymer; polyvinyl alcohol; polyvinyl acetal; fluorine-based polymers such as polyvinylidene fluoride and polytetrafluoroethylene; polyethylene terephthalate; polybutylene terephthalate; polyethylene naphthalate; polystyrene; polyacrylonitrile; styrene-acrylonitrile copolymer; acrylonitrile-butadiene-styrene copolymer (ABS) resin; polyphenylene-ether copolymer (PPE) resin; modified PPE resin; aliphatic polyamides; aromatic polyamides; polyimide; polyamideimide; polymethacrylic acid; polymethacrylic acid methyl ester and other polymethacrylic acid esters; polyacrylic acids; polycarbonate; polyphenylene sulfide; polysulfone; polyethersulfone; polyether nitrile; polyether ketone; polyketone; liquid crystal polymer; silicone resin; ionomer, etc.

[0035] Examples of the thermoplastic elastomer include styrene-butadiene block copolymer or its hydrogenated product, styrene-isoprene block copolymer or its hydrogenated product, styrene-based thermoplastic elastomer, olefin-based thermoplastic elastomer, vinyl chloride-based thermoplastic elastomer, polyester-based thermoplastic elastomer, polyurethane-based thermoplastic elastomer, polyamide-based thermoplastic elastomer, and the like.

[0036] Examples of the thermosetting resin include crosslinked rubber, epoxy resin, phenol resin, polyimide resin, unsaturated polyester resin, diallyl phthalate resin, and the like. Specific examples of the crosslinked rubber include natural rubber, acrylic rubber, butadiene rubber, isoprene rubber, styrene-butadiene copolymer rubber, nitrile rubber, hydrogenated nitrile rubber, chloroprene rubber, ethylene-propylene copolymer rubber, chlorinated polyethylene rubber, chlorosulfonated polyethylene rubber, butyl rubber, halogenated butyl rubber, fluororubber, urethane rubber, and silicone rubber.

[0037] As the binder resin 2, for example, considering the adhesion between the heat-generating surface of the electronic component and the heat sink surface, a silicone resin is preferable. As the silicone resin, for example, a two-component addition reaction type silicone resin composed of a main agent containing silicone having an alkenyl group as a main component and containing a curing catalyst, and a curing agent having a hydrosilyl group (Si-H group) can be used. As the silicone having an alkenyl group, for example, a polyorganosiloxane having a vinyl group can be used. The curing catalyst is a catalyst for promoting the addition reaction between the alkenyl group in the silicone having an alkenyl group and the hydrosilyl group in the curing agent having a hydrosilyl group. Examples of the curing catalyst include catalysts well-known as catalysts used in hydrosilylation reactions, and for example, platinum group-based curing catalysts such as platinum group metals alone such as platinum, rhodium, and palladium, and platinum chloride can be used. As the curing agent having a hydrosilyl group, for example, a polyorganosiloxane having a hydrosilyl group can be used. The binder resin 2 may be used alone or in combination of two or more.

[0038] The content of the binder resin 2 in the heat conduction sheet 1 is not particularly limited and can be appropriately selected according to the purpose. For example, from the viewpoint of the flexibility and resilience of the heat conduction sheet 1, the content of the binder resin 2 in the heat conduction sheet 1 can be 20% by volume or more, and may be 25% by volume or more, 30% by volume or more, or 33% by volume or more. Also, from the viewpoint of the thermal conductivity and resilience of the heat conduction sheet 1, the content of the binder resin 2 in the heat conduction sheet 1 can be 70% by volume or less, and may be 60% by volume or less, 50% by volume or less, 41% by volume or less, or 39% by volume or less. Further, from the viewpoint of the resilience of the heat conduction sheet 1, for example, the content of the binder resin 2 in the heat conduction sheet 1 is preferably 20 to 50% by volume, more preferably more than 35% by volume and 41% by volume or less, and even more preferably 39 to 41% by volume.

[0039] <Fibrous filler> The heat conduction sheet 1 contains a fibrous filler 3. The fibrous filler 3 includes those having a major axis and a minor axis, with different lengths of the major axis and the minor axis and an aspect ratio (average major axis length / average minor axis length) exceeding 1. The fibrous filler 3 may be used alone or in combination of two or more. The fibrous filler 3 can be appropriately selected according to the purpose. For example, metal fibers, carbon fibers, etc. can be used, and carbon fibers are preferred.

[0040] As the carbon fibers, for example, pitch-based carbon fibers, PAN-based carbon fibers, carbon fibers obtained by graphitizing PBO fibers, carbon fibers synthesized by an arc discharge method, a laser evaporation method, a CVD method (chemical vapor deposition method), a CCVD method (catalytic chemical vapor deposition method), etc. can be used. Among these, from the viewpoint of thermal conductivity, pitch-based carbon fibers are preferred.

[0041] The average fiber length (average major axis length) of the fibrous filler 3 can be, for example, 50 to 250 μm, and may be 75 to 220 μm. Also, the average fiber diameter (average minor axis length) of the fibrous filler 3 can be appropriately selected according to the purpose, and can be, for example, 4 to 20 μm, and may be 5 to 14 μm. The aspect ratio of the fibrous filler 3 can be appropriately selected according to the purpose. For example, from the viewpoint of thermal conductivity, it can be, for example, 8 or more, and may be 9 to 30. The average major axis length and average minor axis length of the fibrous filler 3 can be measured, for example, with a microscope or a scanning electron microscope (SEM).

[0042] The carbon fiber may have its surface coated with an insulating film according to the purpose. Thus, insulated coated carbon fiber can be used as the carbon fiber. The insulated coated carbon fiber has a carbon fiber and an insulating film on at least a part of the surface of the carbon fiber, and may contain other components as necessary.

[0043] The insulating film is made of a material having electrical insulation properties, and is formed, for example, of silicon oxide or a cured product of a polymerizable material. The polymerizable material is, for example, a radical polymerizable material, and examples thereof include an organic compound having polymerizability and a resin having polymerizability. The radical polymerizable material can be appropriately selected according to the purpose as long as it is a material that undergoes radical polymerization using energy, and examples thereof include a compound having a radical polymerizable double bond. Examples of the radical polymerizable double bond include a vinyl group, an acryloyl group, and a methacryloyl group. From the viewpoint of heat resistance and strength including solvent resistance, the number of radical polymerizable double bonds in the compound having a radical polymerizable double bond is preferably two or more. Examples of the compound having two or more radical polymerizable double bonds include divinylbenzene (DVB) and a compound having two or more (meth)acryloyl groups. The radical polymerizable material may be used alone or in combination of two or more. The molecular weight of the radical polymerizable material can be appropriately selected according to the purpose, and can be, for example, in the range of 50 to 500. When the insulating film is formed of a cured product of a polymerizable material, the content of the structural unit derived from the polymerizable material in the insulating film can be, for example, 50% by mass or more, and can also be 90% by mass or more.

[0044] The average thickness of the insulating film can be appropriately selected according to the purpose, and from the viewpoint of achieving high insulation properties, it can be 50 nm or more, may be 100 nm or more, or may be 200 nm or more. The upper limit value of the average thickness of the insulating film can be, for example, 1000 nm or less, and may be 500 nm or less. The average thickness of the insulating film can be determined, for example, by observation with a transmission electron microscope (TEM).

[0045] Examples of the method for coating carbon fibers with the insulating film include the sol-gel method, the liquid phase deposition method, the polysiloxane method, and the method of forming an insulating film made of a cured product of a polymerizable material on at least a part of the surface of carbon fibers described in JP-A-2018-98515.

[0046] The content of the fibrous filler 3 in the heat conduction sheet 1 can be, for example, 5% by volume or more, 10% by volume or more, 14% by volume or more, 20% by volume or more, or 25% by volume or more from the viewpoint of the thermal conductivity of the heat conduction sheet 1. Also, the content of the fibrous filler 3 in the heat conduction sheet 1 can be, for example, 30% by volume or less, 28% by volume or less, 25% by volume or less, or 23% by volume or less from the viewpoint of the moldability of the heat conduction sheet 1. The content of the fibrous filler 3 in the heat conduction sheet 1 can be, for example, 5 to 50% by volume, and preferably 14 to 25% by volume. When two or more types of fibrous fillers 3 are used in combination, it is preferable that the total amount satisfies the above-described content.

[0047] <Other heat conduction materials> The other heat conduction material 4 is a heat conduction material other than the above-described fibrous filler 3, and examples thereof include inorganic fillers. Examples of the shape of the other heat conduction material 4 include spherical, crushed, ellipsoidal, massive, granular, and flat shapes. From the viewpoint of filling properties, the shape of the other heat conduction material 4 is preferably crushed, spherical, ellipsoidal, etc., and from the viewpoint of the resilience of the heat conduction sheet 1, particularly when compression and release are performed on the heat conduction sheet 1, the crushed shape is preferable for making the resilience of the fibrous filler 3 better after release. Note that the crushed shape refers to, for example, one having a major axis and a minor axis, and the ratio of the length in the major axis direction to the length in the minor axis direction is 10 or less. The other heat conduction material 4 may be used alone or in combination of two or more.

[0048] The other heat conduction material 4 is, for example, an inorganic filler, and specifically, aluminum oxide (alumina, sapphire), aluminum nitride, aluminum hydroxide, aluminum, zinc oxide, etc. can be used. In particular, from the viewpoints of the resilience and thermal conductivity of the heat conduction sheet 1, it is preferable to use at least one of aluminum hydroxide and alumina. Specific examples include a mode of using alumina alone and a mode of using aluminum hydroxide alone.

[0049] The average particle size (D50) of the alumina particles can be, for example, 0.1 to 10 μm, may be 0.1 to 8 μm, may be 0.1 to 7 μm, or may be 0.1 to 2 μm. The average particle size (D50) of the aluminum hydroxide particles can be, for example, 0.1 to 10 μm, may be 0.1 to 8 μm, may be 0.1 to 7 μm, or may be 0.1 to 2 μm.

[0050] The average particle size of the other heat conductive material 4 refers to the particle size when the cumulative value becomes 50% when obtaining the cumulative curve of the particle size values from the small particle size side of the particle size distribution, assuming the entire particle size distribution of the other heat conductive material 4 is 100%. The particle size distribution (particle diameter distribution) is determined based on the volume standard. As a method for measuring the particle size distribution, for example, a method using a laser diffraction type particle size distribution measuring machine can be mentioned.

[0051] The other heat conductive material 4 may be surface-treated. As the surface treatment, for example, treating the other heat conductive material 4 with a coupling agent such as an alkoxysilane compound can be mentioned. The treatment amount of the coupling agent can be, for example, in the range of 0.1 to 1.5 volume% with respect to the total amount of the other heat conductive material 4.

[0052] The alkoxysilane compound is a compound having a structure in which 1 to 3 of the 4 bonds of the silicon atom (Si) are bonded to alkoxy groups and the remaining bonds are bonded to organic substituents. Examples of the alkoxy group of the alkoxysilane compound include a methoxy group, an ethoxy group, and a butoxy group. Specific examples of the alkoxysilane compound include a trimethoxysilane compound and a triethoxysilane compound.

[0053] The content of other heat-conducting materials 4 in the heat-conducting sheet 1 is not particularly limited and can be appropriately selected according to the purpose. When the heat-conducting sheet 1 contains other heat-conducting materials 4, from the viewpoints of the resilience and thermal conductivity of the heat-conducting sheet 1, the content of the heat-conducting materials 4 can be more than 21% by volume, and may be 36% by volume or more, may be 40% by volume or more, and may be 42% by volume or more. Further, from the viewpoint of the resilience of the heat-conducting sheet 1, the content of other heat-conducting materials 4 in the heat-conducting sheet 1 can be 50% by volume or less, may be 45% by volume or less, and may be 40% by volume or less. From the viewpoint of making the resilience of the heat-conducting sheet 1 better, for example, the content of other heat-conducting materials 4 in the heat-conducting sheet 1 is preferably 36 to 45% by volume. When two or more other heat-conducting materials 4 are used in combination, it is preferable that the total amount thereof satisfies the above-mentioned content.

[0054] When the heat-conducting sheet 1 contains the fibrous filler 3 and other heat-conducting materials 4, from the viewpoints of the resilience and thermal conductivity of the heat-conducting sheet 1, the total content of the fibrous filler 3 and other heat-conducting materials 4 in the heat-conducting sheet 1 can be 50% by volume or more, and may be 55% by volume or more, may be 59% by volume or more, and may be 60% by volume or more. Further, from the viewpoint of the resilience of the heat-conducting sheet 1, the total content of the fibrous filler 3 and other heat-conducting materials 4 in the heat-conducting sheet 1 can be less than 77% by volume, and may be 67% by volume or less, may be 65% by volume or less, may be 64% by volume or less, may be 63% by volume or less, may be 62% by volume or less, and may be 61% by volume or less. For example, the total content of the fibrous filler 3 and other heat-conducting materials 4 in the heat-conducting sheet 1 is preferably 59% by volume or more and less than 65% by volume.

[0055] The heat-conducting sheet 1 may further contain other components other than the above-mentioned components as long as the effects of the present technology are not impaired. Examples of other components include dispersants, curing accelerators, retarders, tackifiers, plasticizers, flame retardants, antioxidants, stabilizers, colorants, and the like.

[0056] <Manufacturing method of heat-conducting sheet> The manufacturing method of the heat conduction sheet according to the present technology includes a step of preparing a heat conduction composition containing a binder resin 2 and a fibrous filler 3 (hereinafter also referred to as step A), a step of forming a molded body block from the heat conduction composition (hereinafter also referred to as step B), and a step of slicing the molded body block into a sheet shape to obtain the heat conduction sheet 1 (hereinafter also referred to as step C).

[0057] As described above, in the heat conduction sheet 1 obtained in step C, the fibrous filler 3 is dispersed in the binder resin 2, and the fibrous filler 3 is arranged at an angle of 70 to 90 degrees in the thickness direction B in a cross-sectional view. When the heat conduction sheet 1 is compressed and released under the above-described condition 1, the arrangement angle of the fibrous filler 3 after compression and release is within a range of 10 degrees or less of the angle before compression in a cross-sectional view.

[0058] The heat conduction sheet 1 obtained by this manufacturing method has good restoring force when compressed and released as in condition 1, particularly the restoring force of the fibrous filler 3. Therefore, when the heat conduction sheet 1 is disposed between a heating element and a heat sink, even if a gap is opened between the heating element and the heat sink, the fibrous filler 3 in the heat conduction sheet 1 can easily and quickly follow the gap. Thereby, deterioration of the thermal resistance of the heat conduction sheet 1 can be suppressed.

[0059] [Step A] In step A, a heat conduction composition containing a binder resin 2 and a fibrous filler 3 is prepared. The heat conduction composition may contain the other heat conduction material 4 described above. The heat conduction composition may be uniformly mixed by a known method together with various additives and volatile solvents.

[0060] [Step B] In Project B, a molded body block is formed from the heat-conducting composition. Examples of the method for forming the molded body block include an extrusion molding method and an injection molding method. The extrusion molding method and the injection molding method are not particularly limited, and can be appropriately adopted from various known extrusion molding methods and injection molding methods according to the viscosity of the heat-conducting composition, the characteristics required for the heat-conducting sheet 1, and the like. For example, when extruding the heat-conducting composition from a die in the extrusion molding method, or when press-fitting the heat-conducting composition into a mold in the injection molding method, the binder resin 2 flows, and the long axis of the fibrous filler 3 is oriented along the flow direction.

[0061] The size and shape of the molded body block can be determined according to the size of the required heat-conducting sheet. For example, a rectangular parallelepiped with a vertical cross-sectional size of 0.5 to 15 cm and a horizontal size of 0.5 to 15 cm can be cited. The length of the rectangular parallelepiped can be determined as needed. In the extrusion molding method, it is easy to form a columnar molded body block made of a cured product of the heat-conducting composition and having the long axis of the fibrous filler 3 oriented in the extrusion direction.

[0062] The obtained molded body block is preferably heat-cured. The curing temperature in the heat curing can be appropriately selected according to the purpose. For example, when the binder resin 2 is a silicone resin, it can be in the range of 60°C to 120°C. The curing time in the heat curing can be, for example, in the range of 30 minutes to 10 hours.

[0063] [Process C] In Process C, the formed body block is sliced into a sheet shape to obtain a heat conduction sheet 1 in which the long axis of the fibrous filler 3 is oriented in the thickness direction B. On the surface (sliced surface) of the sheet obtained by slicing, the fibrous filler 3 is exposed. The slicing method is not particularly limited, and it can be appropriately selected from known slicing devices according to the size and mechanical strength of the formed body block. Examples of the slicing device include an ultrasonic cutter and a plane iron (plane). As the slicing direction of the formed body block, when the forming method is an extrusion molding method, since there are cases where the long axis of the fibrous filler 3 is oriented in the extrusion direction, it is preferably 60 to 120 degrees with respect to the extrusion direction, more preferably in the direction of 70 to 100 degrees, and even more preferably in the direction of 90 degrees (perpendicular).

[0064] Thus, in the manufacturing method having Process A, Process B, and Process C, it is a heat conduction sheet 1 in which the fibrous filler 3 is dispersed in the binder resin 2, and the fibrous filler 3 is arranged at an angle of 70 to 90 degrees in the thickness direction B in a cross-sectional view. When compression and release are performed under the above-described Condition 1, a heat conduction sheet 1 can be obtained in which the arrangement angle of the fibrous filler 3 after compression and release is within a range of 10 degrees or less of the angle before compression in a cross-sectional view.

[0065] The manufacturing method of the heat conduction sheet 1 is not limited to the above-described example. For example, after Process C, it may further have a Process D of pressing the sliced surface. In the manufacturing method having such a Process D, the surface of the heat conduction sheet 1 obtained in Process C is further smoothed, and the adhesion with other members can be further improved. As the pressing method, a pair of pressing devices including a flat plate and a pressing head with a flat surface can be used. Also, the surface of the heat conduction sheet 1 may be pressed with pinch rollers.

[0066] The pressure during pressing can be, for example, in the range of 0.1 to 100 MPa, may be in the range of 0.1 to 1 MPa, or may be in the range of 0.1 to 0.5 MPa. The pressing time can be appropriately selected according to the pressure during pressing, the sheet area, etc., and can be, for example, in the range of 10 seconds to 5 minutes, or may be in the range of 30 seconds to 3 minutes.

[0067] As one aspect, pressing may be performed while heating using a press head incorporating a heater. The pressing temperature can be, for example, in the range of 0 to 180 °C, may be in the range of room temperature (e.g., 25 °C) to 100 °C, or may be in the range of 30 to 100 °C. In order to enhance the effect of pressing and shorten the pressing time, pressing may be performed at a temperature equal to or higher than the glass transition temperature (Tg) of the binder resin constituting the molded body sheet.

[0068] <Electronic device> The heat conduction sheet 1 can be, for example, an electronic device (thermal device) having a structure arranged between a heat generating body and a heat radiating body to release the heat generated by the heat generating body to the heat radiating body by being disposed therebetween. The electronic device has at least a heat generating body, a heat radiating body, and the heat conduction sheet 1, and may further have other members as required.

[0069] The heat generating body is not particularly limited, and examples include integrated circuit elements such as CPUs, GPUs (Graphics Processing Units), DRAMs (Dynamic Random Access Memories), flash memories, electronic components that generate heat in electric circuits such as transistors and resistors, etc. The heat generating body also includes components that receive optical signals such as optical transceivers in communication devices.

[0070] The heat dissipater is not particularly limited, and examples thereof include those used in combination with integrated circuit elements, transistors, optical transceiver housings, etc., such as heat sinks and heat spreaders. Examples of the material of the heat sink and the heat spreader include copper, aluminum, etc. As the heat dissipater, in addition to the heat spreader and the heat sink, any object that conducts the heat generated from the heat source and dissipates it to the outside may be used. Examples thereof include radiators, coolers, die pads, printed circuit boards, cooling fans, Peltier elements, heat pipes, vapor chambers, metal covers, housings, etc. The heat pipe is, for example, a hollow structure in a cylindrical shape, a substantially cylindrical shape, or a flat cylindrical shape.

[0071] FIG. 5 is a cross-sectional view showing an example of a semiconductor device to which a heat conduction sheet is applied. For example, as shown in FIG. 5, the heat conduction sheet 1 is mounted on a semiconductor device 50 incorporated in various electronic devices and is sandwiched between a heat generating body and a heat dissipater. The semiconductor device 50 shown in FIG. 5 includes an electronic component 51, a heat spreader 52, and a heat conduction sheet 1, and the heat conduction sheet 1 is sandwiched between the heat spreader 52 and the electronic component 51. When the heat conduction sheet 1 is sandwiched between the heat spreader 52 and the heat sink 53, together with the heat spreader 52, it constitutes a heat dissipating member that dissipates the heat of the electronic component 51. The mounting location of the heat conduction sheet 1 is not limited to between the heat spreader 52 and the electronic component 51 or between the heat spreader 52 and the heat sink 53, and can be appropriately selected according to the configuration of the electronic device or the semiconductor device. The heat spreader 52 is formed, for example, in a square plate shape and has a main surface 52a facing the electronic component 51 and side walls 52b erected along the outer periphery of the main surface 52a. The heat conduction sheet 1 is provided on the main surface 52a surrounded by the side walls 52b of the heat spreader 52, and the heat sink 53 is provided on the other surface 52c opposite to the main surface 52a via the heat conduction sheet 1.

Example

[0072] Hereinafter, examples of the present technology will be described. The present technology is not limited to these examples.

[0073] <Example 1> In Example 1, as shown in Table 1, 45% by volume of alumina particles with an average particle size of 2 μm that were coupling-treated with a silane coupling agent, and 14% by volume of pitch-based carbon fibers with an average fiber length of 200 μm as a fibrous filler were mixed into a two-component addition reaction type liquid silicone resin, and a silicone composition was prepared. The two-component addition reaction type liquid silicone resin used 41% by volume of a material mainly composed of polyorganosiloxane, and was adjusted so that the hardness in Shore type OO of the completed sheet would be 25. The obtained silicone composition was extrusion-molded into a hollow square columnar mold (50 mm × 50 mm) to form a 50 mm□ silicone molded body. The silicone molded body was heated in an oven at 100 °C for 6 hours to obtain a silicone cured product. The silicone cured product was cut with a slicer so that the thickness would be 2.0 mm to obtain a heat conduction sheet.

[0074] <Example 2> In Example 2, as shown in Table 1, 45% by volume of crushed aluminum hydroxide particles with an average particle size of 1.2 μm that were coupling-treated with a silane coupling agent were used instead of 45% by volume of alumina particles with an average particle size of 2 μm that were coupling-treated with a silane coupling agent, and a heat conduction sheet was obtained in the same manner as in Example 1 except that the hardness in Shore type OO of the completed sheet was adjusted to be 30.

[0075] <Example 3> In Example 3, as shown in Table 1, 36% by volume of alumina particles with an average particle size of 4 μm that were coupling-treated with a silane coupling agent and 25% by volume of pitch-based carbon fibers with an average fiber length of 120 μm as a fibrous filler were mixed into a two-component addition reaction type liquid silicone resin to prepare a silicone composition. 39% by volume of a material mainly composed of polyorganosiloxane was used as the two-component addition reaction type liquid silicone resin, and a heat conduction sheet was obtained in the same manner as in Example 1 except that the hardness in Shore type OO of the completed sheet was adjusted to be 40.

[0076] <Comparative Example 1> In Comparative Example 1, as shown in Table 1, 42% by volume of alumina particles with an average particle size of 4 μm that had been subjected to a coupling treatment with a silane coupling agent, 23% by volume of pitch-based carbon fibers with an average fiber length of 150 μm as a fibrous filler, and 35% by volume of a two-component addition reaction type liquid silicone resin mainly composed of polyorganosiloxane were mixed into a silicone composition. A heat conduction sheet was obtained in the same manner as in Example 1, except that the hardness in Shore type OO of the completed sheet was adjusted to 40.

[0077] <Comparative Example 2> In Comparative Example 2, as shown in Table 1, 21% by volume of alumina particles with an average particle size of 4 μm that had been subjected to a coupling treatment with a silane coupling agent, 24% by volume of aluminum nitride particles with an average particle size of 1.3 μm, 22% by volume of pitch-based carbon fibers with an average fiber length of 150 μm as a fibrous filler, and 33% by volume of a two-component addition reaction type liquid silicone resin mainly composed of polyorganosiloxane were mixed into a silicone composition. A heat conduction sheet was obtained in the same manner as in Example 1, except that the hardness in Shore type OO of the completed sheet was adjusted to 50.

[0078] <Comparative Example 3> In Comparative Example 3, as shown in Table 1, 36% by volume of alumina particles with an average particle size of 4 μm that had been subjected to a coupling treatment with a silane coupling agent, 25% by volume of aluminum nitride particles with an average particle size of 1.3 μm, 16% by volume of aluminum powder with an average particle size of 15 μm, and 23% by volume of a two-component addition reaction type liquid silicone resin mainly composed of polyorganosiloxane were mixed into a silicone composition. A heat conduction sheet was obtained in the same manner as in Example 1, except that the hardness in Shore type OO of the completed sheet was adjusted to 40. Thus, in Comparative Example 3, a heat conduction sheet not containing carbon fibers was obtained.

[0079] <Bulk Thermal Conductivity> The bulk thermal conductivity was measured by a method conforming to ASTM-D5470 for the thermal resistance of each thermal conductive sheet. The thickness (mm) of the thermal conductive sheet during measurement was plotted on the horizontal axis, and the thermal resistance (°C·cm 2 / W) of the thermal conductive sheet was plotted on the vertical axis, and the bulk thermal conductivity (W / m·K) of the thermal conductive sheet was calculated from the slope of the plot. The thermal resistance of the thermal conductive sheet was measured for three types of thermal conductive sheets with different thicknesses. The results are shown in Table 1.

[0080] <Preparation of Samples for Evaluation> The thermal conductive sheets obtained in the examples and comparative examples were processed to a diameter of 29 mm to prepare samples for evaluation. Three or more samples were prepared and used for (1) checking the outer dimensions, (2) observing the cross-section before compression, and (3) observing the cross-section after compression release.

[0081] <Outer Dimensions of the Sample after Compression Release> The outer dimensions of the sample after compression release were visually measured for the maximum length and the minimum length using a vernier caliper and taken as the average value. Specifically, a sample with a thickness of 2 mm and a diameter of 29 mm was compressed by 40% of the initial thickness at room temperature for 24 hours, and the outer dimensions of the sample were measured 3 minutes after compression release. The results are shown in Table 1.

[0082] <Inclination of Carbon Fibers before Compression> For the cross-section observation of sample 5 (thermal conductive sheet 1) before compression, as shown in Figure 2, the central part of sample 5 was cut with a razor blade to a width of 5 mm in the thickness direction B to obtain sample 6. Then, as shown in Figure 3, in sample 6, within 5 mm from the outer periphery and in the range 6B of the upper and lower 1 / 3 of the cross-section, the angles of any carbon fibers 3A were measured at 5 points and the average value was obtained. The measurement of the angle of carbon fibers 3A was performed at a magnification of 100 times using a microscope VHX-5000 (manufactured by Keyence Corporation). The measurement of the angles of the 5 points of carbon fibers 3A was carried out after aligning sample 6 so that the angle of carbon fibers 3A changed from 0 degrees to 90 degrees.

[0083] Figure 6 is a digital microscope photograph of the cross-section of the heat conduction sheet before compression. As an example, the method for calculating the angle of the carbon fiber in Sample 6 of Example 3 will be described. For those with an angle exceeding 90 degrees as shown by "[6] 93 degrees" in Figure 6, it was set as 180 degrees - 93 degrees = 87 degrees. The angles of five points of the carbon fiber 3A in Sample 6 of Example 3 before compression were 87 degrees, 79 degrees, 82 degrees, 93 degrees (87 degrees), and 78 degrees, and the average was 82.6 degrees. The results are shown in Table 1.

[0084] <Tilt of carbon fiber after compression release> The cross-section observation of Sample 6 after compression release was carried out simultaneously with the cross-section observation of Sample 6 before compression. Sample 5 shown in Figure 2 was compressed by 40% of the initial thickness at room temperature for 24 hours. Three minutes after compression release, as shown in Figures 2 and 3, the central part of Sample 5 after compression release was cut with a razor blade in the thickness direction B with a width of 5 mm to obtain Sample 6. At the cut surface (surface) of this Sample 6, within 5 mm from the outer periphery and in the range 6B of the upper and lower 1 / 3 of the cross-section, the angles of any five points of the carbon fiber 3A were measured and the average value was obtained.

[0085] Figure 7 is a digital microscope photograph of the cross-section of the heat conduction sheet after compression release. As an example, the method for calculating the angle of the carbon fiber 3A in Sample 6 of Example 3 will be described. As shown in Figure 7, the angles of five points of the carbon fiber 3A in Sample 6 of Example 3 after compression release were 74 degrees, 79 degrees, 70 degrees, 78 degrees, and 84 degrees, and the average was 77.0 degrees. The results are shown in Table 1.

[0086] <Angle difference of carbon fiber before and after compression release> The average difference (degrees) of the angles of five points of the carbon fiber 3A in Sample 6 before and after compression release was obtained. The results are shown in Table 1.

[0087] <Hardness in Shore type OO> The hardness of the heat conduction sheet in Shore type OO was taken as the average value of the measurement results obtained by a measurement method conforming to ASTM-D2240. Five 2-mm-thick heat conduction sheets were stacked to a thickness of 10 mm, and five points were measured on one side and a total of ten points were measured on both sides. The results are shown in Table 1.

[0088]

Table 1

[0089] In the heat conduction sheets obtained in Examples 1 to 3, the fibrous filler 3 was dispersed in the binder resin 2, and the fibrous filler 3 was arranged at an angle of 70 to 90 degrees in the thickness direction B in a cross-sectional view. When compression and release were performed under the above-described Condition 1, it was found that the arrangement angle of the fibrous filler 3 after compression and release was within a range of 10 degrees or less of the angle before compression in a cross-sectional view. That is, it was found that the heat conduction sheets obtained in Examples 1 to 3 had good restoring force, particularly the restoring force of the carbon fiber 3A (fibrous filler 3), when compression and release were performed as in Condition 1. Therefore, when the heat conduction sheets obtained in Examples 1 to 3 were disposed between a heating element and a heat radiating element, even if a gap between the heating element and the heat radiating element opened, the fibrous filler 3 in the heat conduction sheet could easily and quickly follow the gap. Accordingly, it is considered that the heat conduction sheets obtained in Examples 1 to 3 can suppress deterioration of the thermal resistance.

[0090] Further, when the heat conduction sheets obtained in Examples 1 to 3 had a thickness of 2 mm and a diameter of 29 mm, and were compressed at room temperature by 40% for 24 hours, it was found that the diameter after 3 minutes of release was 32.0 mm or less. That is, it was also found that the heat conduction sheets obtained in Examples 1 to 3 had a small change in the outer dimension after compression and release.

[0091] On the other hand, in the heat conduction sheets obtained in Comparative Examples 1 and 2, when compression and release were performed under the above-described Condition 1, it was found that the arrangement angle of the fibrous filler 3 after compression and release was not within a range of 10 degrees or less of the angle before compression in a cross-sectional view. That is, it was found that the heat conduction sheets obtained in Comparative Examples 1 and 2 did not have good restoring force, particularly the restoring force of the carbon fiber 3A (fibrous filler 3), when compression and release were performed as in Condition 1, as compared with the heat conduction sheets of Examples 1 to 3. Further, it was found that the change in the outer dimension of the heat conduction sheets obtained in Comparative Examples 1 to 3 was larger than that of Examples 1 to 3 after compression and release.

Explanation of Reference Numerals

[0092] 1 Thermal conductive sheet, 2 Binder resin, 3 Fibrous filler, 3A Carbon fiber, 4 Other thermal conductive materials, 5 Sample, 6 Cut sample, 6A Cut surface, 6Ac Central part, 50 Semiconductor device, 51 Electronic component, 52 Heat spreader, 52a Main surface, 52b Side wall, 52c Other surface, 53 Heat sink

Claims

1. A heat-conductive sheet in which fibrous fillers are dispersed in a binder resin, further comprising other heat-conductive materials other than the fibrous fillers, and the fibrous fillers are arranged at an angle of 70 to 90 degrees in the thickness direction in a cross-sectional view, wherein the fibrous fillers are carbon fibers, the content of the fibrous fillers is 5% by volume or more, the content of the other heat-conductive materials is more than 21% by volume, the hardness of the heat-conductive sheet in Shore type OO is 25 to 40, when the heat-conductive sheet is compressed and released under the following Condition 1, the arrangement angle of the fibrous fillers after release is within a range of 10 degrees or less of the angle before compression in a cross-sectional view. A heat-conductive sheet. Condition 1: The thickness of the heat-conductive sheet is compressed from the initial thickness by 40% at room temperature for 24 hours and then released.

2. The heat-conductive sheet having a thickness of 2 mm and a diameter of 29 mm is compressed by 40% at room temperature for 24 hours, and the diameter 3 minutes after release is 32.0 mm or less. The heat-conductive sheet according to Claim 1.

3. The heat-conductive sheet according to Claim 1 or 2, wherein the content of the fibrous fillers is 5 to 50% by volume.

4. The heat-conductive sheet according to any one of Claims 1 to 3, wherein the content of the binder resin is 20 to 50% by volume.

5. The heat-conductive sheet according to any one of Claims 1 to 4, wherein the binder resin is a silicone resin.

6. The heat-conductive sheet according to any one of Claims 1 to 5, wherein the fibrous fillers are pitch-based carbon fibers.

7. The total content of the fibrous fillers and the other heat-conductive materials is less than 65% by volume. The heat-conductive sheet according to any one of Claims 1 to 6.

8. The other heat-conductive material is at least one of aluminum hydroxide and alumina. The heat-conductive sheet according to any one of Claims 1 to 7.

9. A step of preparing a heat-conductive composition containing a binder resin and fibrous fillers, a step of forming a molded body block from the heat-conductive composition, and a step of slicing the molded body block into a sheet shape to obtain a heat-conductive sheet, wherein the heat-conductive sheet is the heat-conductive sheet according to any one of Claims 1 to 8. A method for manufacturing a heat-conductive sheet.

10. A heating element, a heat sink, An electronic device comprising the heat-conductive sheet according to any one of Claims 1 to 8 disposed between the heating element and the heat sink.

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