JP2022129325A - Thermally conductive sheet and method for producing thermally conductive sheet - Google Patents

Abstract

A heat conductive sheet having good restoring force when compressed and released is provided.
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 conductive sheet 1 is compressed and released under 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. Condition 1: After compressing the thickness of the heat conductive sheet 1 by 40% from the initial thickness at room temperature for 24 hours, it is released.
[Selection drawing] Fig. 1

Description

The present technology relates to a thermally conductive sheet and a method for manufacturing the thermally conductive sheet.

Conventionally, semiconductor devices installed in various electrical devices such as personal computers and other equipment generate heat when driven, and accumulation of the generated heat can adversely affect the operation of semiconductor devices and peripheral devices. , various cooling methods are used.

Cooling methods for devices with semiconductor elements include attaching a fan to the device to cool the air inside the device housing, attaching heat sinks such as heat sinks and heat sinks to the semiconductor device, and immersing the device in a fluorine-based inert liquid. There are known methods for When a heatsink is attached to a semiconductor element for cooling, a heat-conducting sheet is provided between the semiconductor element and the heatsink in order to efficiently dissipate the heat of the semiconductor element.

As an example of a thermally conductive sheet, a binder resin in which a filler (for example, a thermally conductive filler such as carbon fiber) is dispersed is widely used (see, for example, Patent Document 1).

By the way, electronic parts such as a CPU (Central Processing Unit) of a personal computer tend to increase the amount of heat released year by year as the speed and performance thereof increase. However, the chip size of processors and the like has become smaller than before due to advances in fine silicon circuit technology, and the heat flux per unit area has increased. In order to avoid problems caused by the temperature rise of such electronic parts, it is required to heat and cool the electronic parts more efficiently.

In order to improve the heat dissipation properties of the heat conductive sheet, for example, it is required to lower the thermal resistance, which is an index indicating the difficulty of heat transfer. In order to reduce the thermal resistance of the thermally conductive sheet, it is effective, for example, to improve the adhesion of the thermally conductive sheet to a heating element (eg, electronic component) or radiator (eg, heat sink).

However, the surface of a thermally conductive sheet obtained by slicing a thermally conductive molded body for forming a thermally conductive sheet usually has irregularities, and therefore tends to have poor adhesion. If the adhesion of the surface of the thermally conductive sheet is poor, the adhesiveness of the thermally conductive sheet to the heating element and the heat dissipating body becomes poor in the mounting process, and it tends to be difficult to sufficiently lower the thermal resistance of the thermally conductive sheet. In particular, when the compressive stress of the thermal conductive sheet is low, once the thermal conductive sheet is compressed (crushed), the repulsive force is small. It tends to be difficult for the heat-conducting sheet placed between the heating element and the radiator to follow.

A method of pressing the surface of a thermally conductive sheet prepared by slicing a thermally conductive molded article, or a method of allowing a thermally conductive sheet prepared by slicing a thermally conductive molded article to stand still for a long period of time allows the binder component to be removed from the thermally conductive sheet. There is known a method of improving the adhesion between a thermally conductive sheet and an adherend by exuding it to the surface (see Patent Documents 2 and 3, for example).

However, even if the surface of the thermally conductive sheet is pressed, the binder component may not uniformly ooze out on the surface of the thermally conductive sheet, and there is a risk that the adhesion may vary depending on the location of the surface of the thermally conductive sheet. Also, when the thermally conductive sheet is left standing for a long time, there is a tendency similar to when the surface of the thermally conductive sheet is pressed. Further, in the prior art, no study has been made as to whether or not the restoring force of the thermally conductive sheet, particularly the restoring force of the fibrous filler, is improved when the thermally conductive sheet is compressed and released.

JP 2012-23335 A JP 2015-029076 A JP 2015-029075 A

The present technology has been proposed in view of such conventional circumstances, and provides a thermally conductive sheet having a good restoring force when compression and release are performed on the thermally conductive sheet.

As a result of investigation by the present inventors, the fibrous filler is dispersed in the binder resin, and the fibrous filler is arranged at an angle of 70 to 90 degrees in the thickness direction in a cross-sectional view. In this case, it was found that deterioration of thermal resistance can be suppressed by the good restoring force of the fibrous filler after compression release.

The present technology is a heat conductive 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 compression and release are performed in 1, the arrangement angle of the fibrous filler after release is within 10 degrees of the angle before compression in a cross-sectional view.
Condition 1: The thickness of the heat conductive sheet is compressed to 40% of the initial thickness at room temperature for 24 hours, and then released.

A method for producing a thermally conductive sheet according to the present technology includes steps of preparing a thermally conductive composition containing a binder resin and a fibrous filler, forming a molded block from the thermally conductive composition, and forming a molded block into a sheet. and obtaining a heat conductive sheet by slicing into a shape, and the heat conductive sheet is the heat conductive sheet described above.

According to the present technology, it is possible to provide a thermally conductive sheet having a good restoring force when the thermally conductive sheet is compressed and released.

FIG. 1 is a cross-sectional view showing an example of a heat conductive sheet. FIG. 2 is a perspective view for explaining an example of a method of measuring the placement angle of fibrous fillers in a heat conductive sheet. FIG. 3 is a perspective view for explaining an example of a method for measuring the placement angle of fibrous fillers in a heat conductive sheet. FIG. 4 is a cross-sectional view showing an example of a heat conductive sheet before and after compression. FIG. 5 is a cross-sectional view showing an example of a semiconductor device to which a heat conductive sheet is applied. FIG. 6 is a digital microscope photograph of a cross section of the thermally conductive sheet before compression. FIG. 7 is a digital microscope photograph of a cross section of the thermally conductive sheet after compression release.

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

As described above, the thermally conductive sheet according to the present technology has good restoring force when compression and release are performed as in condition 1, especially the restoring force of the fibrous filler. In other words, even if the heat conductive sheet according to the present technology is greatly crushed as in condition 1, it returns greatly. Here, the restoring force of the fibrous filler is the degree of displacement of the arrangement angle of the fibrous filler in the cross-sectional view of the thermally conductive sheet before and after compression and release when the thermally conductive sheet is compressed and released under the condition 1 described above. means Good restoring force of the fibrous filler means that when the heat conductive sheet is compressed and released under condition 1, the arrangement angle of the fibrous filler after compression release is the same as before compression in the cross-sectional view of the heat conductive sheet. It means to be within 10 degrees of the angle. When the thermally conductive sheet according to the present technology is arranged between a heating element (for example, an IC (Integrated Circuit)) and a radiator (for example, a heat sink), even if a gap is opened between the heating element and the radiator, , the fibrous filler in the heat conductive sheet can easily and quickly follow the gap. Thereby, deterioration of the heat resistance of the heat conductive sheet can be suppressed.

FIG. 1 is a cross-sectional view showing an example of a heat conductive sheet. The heat conductive sheet 1 contains a binder resin 2 and fibrous fillers 3, and the fibrous fillers 3 are arranged at an angle of 70 to 90 degrees in the thickness direction B when viewed in cross section. In other words, in the heat conductive sheet 1 , the long axis of the fibrous filler 3 is arranged within the range of 70 to 90 degrees with respect to the surface direction A of the heat conductive sheet 1 . Moreover, the thermally conductive sheet 1 may further contain a thermally conductive material 4 other than the fibrous filler 3 .

In the heat conductive sheet 1, when compression and release are performed under the condition 1 described above, the arrangement angle of the fibrous filler 3 after compression release is within 10 degrees of the angle before compression in a cross-sectional view. That is, in the heat conductive sheet 1, the angle difference of the fibrous fillers 3 before and after compression release is within 10 degrees, and the angle of the fibrous fillers 3 after compression release tends to return to the angle (position) before compression. .

Regarding the details of condition 1 described above, for example, a heat conductive sheet 1 (sample) having a thickness of 2 mm and a diameter of 29 mm is compressed by 40% from the initial thickness (relative to the initial thickness) at room temperature for 24 hours, and after releasing the compression, 3 Minutes later, the arrangement angle of the fibrous filler 3 in the heat conductive sheet 1 is measured. In condition 1, the size of the thermally conductive sheet 1 is set to 29 mm in diameter and the temperature is set to room temperature in accordance with JIS K6262. Also, in JIS K6262, the time is optional, and condition 1 "24 hours" is one of the times stipulated by the standard. Regarding the compression under condition 1, more specifically, first, the thickness of the heat conductive sheet 1 is measured, and the heat conductive sheet 1 is processed to have a diameter of 29 mm. The processed thermally conductive sheet 1 (sample) is sandwiched between jigs with SUS304 as the surface, and compressed by 40% with respect to the thickness of the sample. When compressing, a spacer having a thickness of 60% of the thickness of the sample is sandwiched between the threads and the screws are tightened. After tightening the screws, check that the spacers do not move to see if the sample has been compressed to the desired thickness. In addition, in the case of a sample having a sticky surface, it may be sandwiched between films to which the sticky substance (sample) does not adhere and then compressed. “Normal temperature” refers to the range of 15 to 25° C. defined in JIS K 0050:2019 (general rules for chemical analysis methods).

In the thermally conductive sheet, if the angle difference between the fibrous fillers 3 before and after compression and release exceeds 10 degrees, when the thermally conductive sheet is placed between the heat generating body and the heat radiating body, the gap between the heat generating body and the heat radiating body becomes large. When the gap opens, it becomes difficult for the thermally conductive sheet to follow the gap, and as a result, the thermal resistance of the thermally conductive sheet tends to deteriorate. In the heat conductive sheet 1, the smaller the angle difference of the fibrous fillers 3 before and after compression release, the better. It may be within 0.6 degrees, may be within 5.2 degrees, may be within 4 degrees, may be within 3.8 degrees, and may be within 3.8 to 5.6 degrees. It can be a range.

If the fibrous filler 3 before compressing the thermally conductive sheet 1 under the condition 1 described above is arranged at an angle of 70 to 90 degrees in the thickness direction B of the thermally conductive sheet 1 in a cross-sectional view of the thermally conductive sheet 1 It may be in the range of 80 to 84 degrees, or it may be in the range of 81.9 to 83.1 degrees. In addition, the fibrous filler 3 after compressing and releasing the heat conductive sheet 1 under the condition 1 described above is also arranged at an angle of 70 to 90 degrees in the thickness direction B of the heat conductive sheet 1 in a cross-sectional view of the heat conductive sheet 1. For example, it may be in the range of 70 to 80 degrees, or it may be in the range of 77.0 to 77.9 degrees.

In the heat conductive 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 when viewed in cross section. 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 conductive sheet 1. FIG. 2 and 3, arrow A indicates the surface direction of the sample (thermal conductive sheet 1), and arrow B indicates the thickness direction of the sample (thermal conductive sheet 1). For example, as shown in FIG. 2, a sample 5 having a thickness of 2 mm and a diameter of 29 mm is prepared from the heat conductive sheet 1, and the central portion of the sample 5 in plan view (upper surface) is cut into a predetermined width in the thickness direction B. , As shown in FIG. 3, on the cut surface 6A of the cut sample 6, the average value of the angles of the arbitrary fibrous filler 3 measured at 5 points in the range 6B of 5 mm inside from the outer periphery and 1/3 of the top and bottom is 70 ~ It may be in the range of 90 degrees.

FIG. 4 is a cross-sectional view showing an example of a heat conductive sheet before and after compression. The arrow in FIG. 4 means that the heat conductive 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 conductive sheet 1 (cut sample 6) before compression under Condition 1, and the lower side of the arrow in FIG. An example of conductive sheet 1 (cut sample 6). In the range 6B on the cut surface 6A, for example, the fibrous filler 3 in the heat conductive sheet 1 after compression is in the thickness direction compared to the other range (for example, the central portion 6Ac of the cut surface 6A of the cut sample 6). It is difficult for B to become dense, and there is a tendency that the change in the angle of the fibrous filler 3 before and after compression release is likely to appear. In addition, when the heat conductive sheet 1 is compressed under the above-described condition 1, the range 6B on the cut surface 6A is subjected to more force than the other range (for example, the central portion 6Ac of the cut surface 6A). Therefore, it is considered that the change in the angle of the fibrous filler 3 before and after the compression release tends to be more pronounced.

In addition, the heat conductive sheet 1 according to the present technology has good restoring force when compression and release are performed as in condition 1, and in addition to reducing the angle difference of the fibrous filler 3 before and after compression release Also, the change in the outer size of the heat conductive sheet 1 before and after the compression release can be reduced.

For example, the heat conductive sheet 1 with a thickness of 2 mm and a diameter of 29 mm, that is, the sample 5, is compressed by 40% at room temperature for 24 hours, and the diameter of the sample 5 after 3 minutes after release is 32.0 mm or less. 0 mm or less, 30.0 mm or less, 29.9 mm or less, 29.6 mm or less, 29.5 mm or less, 29 It can also be in the range of 0.5 to 29.9 mm.

In this way, when the thermally conductive sheet 1 is arranged between the heating element and the radiator, even if the gap between the heating element and the radiator is widened, the external size of the thermally conductive sheet 1 is larger than the gap. and the fibrous filler 3 in the heat conductive sheet 1 can follow. Therefore, deterioration of the thermal resistance of the heat conductive sheet 1 can be suppressed more effectively. In addition, since the heat conductive sheet 1 can reduce the change in the outer size before and after compression release, the heat conductive sheet 1 can be processed according to the shape of the heat generating element (for example, IC) to make the entire surface of the heat generating element more efficient. can be cooled.

The heat conductive sheet 1 is preferably relatively soft, and preferably has a Shore type OO hardness of 25 to 40, for example. When the hardness of the heat conductive sheet 1 is within such a range, the fibrous filler 3 in the heat conductive sheet 1 after compression release and the restoring force of the external size of the heat conductive sheet 1 are improved. In addition, the conformability of the heat conductive sheet 1 to the adherend is improved. The hardness of the heat conductive sheet 1 can be measured by the method of Examples described later.

Here, a rubber sheet is exemplified as a thermally conductive sheet having resilience. However, the rubber sheet generally has a high hardness (hardness) in Shore type OO, and the load on an IC as a heating element and a heat sink as a radiator is high. Grease (liquid) can be used as a heat conductive agent that is softer than the rubber sheet. However, grease has low shape-following property and restoring property to an IC as a heating element. Here, in a region where the compressibility is low (compression of less than 40% with respect to the initial thickness), even a relatively hard heat conductive sheet can be crushed, and after crushing the heat conductive sheet, the angle of the fibrous filler and the heat conduction It is possible to return the outline size of the sheet. However, with a hard thermally conductive sheet, if you try to compress the thermally conductive sheet by 40% with respect to the initial thickness as in condition 1, breakage (for example, cracks in the thermally conductive sheet) will occur, and the angle of the fibrous filler will be Also, it tends to be difficult to restore the external size of the heat conductive sheet. In addition, a hard heat conductive sheet requires a great deal of force to pressurize (compress) the heat conductive sheet. On the other hand, the heat conductive sheet 1 according to the present technology can be adjusted to have a Shore type OO hardness of 25 to 40, is softer than a rubber sheet, and has better restorability and conformability to an adherend than a grease (liquid) sheet. is good. That is, the heat conductive sheet 1 is soft with a hardness of 25 to 40 in Shore type OO, but has good restorability. Easy to return to external size.

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. Moreover, the upper limit of the thickness of the heat conductive sheet 1 may be 5 mm or less, may be 4 mm or less, or may be 3 mm or less. From the standpoint of handleability, the heat conductive sheet 1 preferably has a thickness of 0.1 to 4 mm. The thickness of the thermally conductive sheet 1 can be determined, for example, by measuring the thickness of the thermally conductive sheet 1 at five arbitrary points and calculating the arithmetic average value thereof.

Specific examples of the components of the thermally conductive sheet 1 will be described below. The thermally conductive sheet 1 contains binder resin 2, fibrous filler 3, and other thermally conductive material 4, for example.

<Binder resin>
The binder resin 2 is for holding the fibrous filler 3 and other thermally conductive material 4 within the thermally conductive sheet 1 . The binder resin 2 is selected according to properties such as 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.

Examples of thermoplastic resins include polyethylene, polypropylene, ethylene-α-olefin copolymers such as ethylene-propylene copolymers, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymers, Fluorinated polymers such as polyvinyl alcohol, polyvinyl acetal, polyvinylidene fluoride and polytetrafluoroethylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polystyrene, polyacrylonitrile, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer Polymer (ABS) resin, polyphenylene-ether copolymer (PPE) resin, modified PPE resin, aliphatic polyamides, aromatic polyamides, polyimide, polyamideimide, polymethacrylic acid, polymethacrylic acid such as polymethacrylic acid methyl ester acid esters, polyacrylic acids, polycarbonates, polyphenylene sulfides, polysulfones, polyethersulfones, polyethernitrile, polyetherketones, polyketones, liquid crystal polymers, silicone resins, ionomers and the like.

Thermoplastic elastomers include styrene-butadiene block copolymers or hydrogenated products thereof, styrene-isoprene block copolymers or hydrogenated products thereof, styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers. , polyester-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, polyamide-based thermoplastic elastomers, and the like.

Thermosetting resins include crosslinked rubbers, epoxy resins, phenol resins, polyimide resins, unsaturated polyester resins, diallyl phthalate resins, and the like. Specific examples of 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.

As the binder resin 2, for example, a silicone resin is preferable in consideration of the adhesion between the heat generating surface of the electronic component and the heat sink surface. As the silicone resin, for example, a two-component addition reaction type silicone resin composed of a silicone having an alkenyl group as a main component, a main agent containing a curing catalyst, and a curing agent having a hydrosilyl group (Si—H group). can be used. As the alkenyl group-containing silicone, for example, a vinyl group-containing polyorganosiloxane can be used. The curing catalyst is a catalyst for promoting the addition reaction between the alkenyl group in the alkenyl group-containing silicone and the hydrosilyl group in the hydrosilyl group-containing curing agent. As the curing catalyst, well-known catalysts used for hydrosilylation reaction can be used. For example, platinum group curing catalysts, such as platinum group metals such as platinum, rhodium and palladium, and platinum chloride can be used. As the curing agent having hydrosilyl groups, for example, polyorganosiloxane having hydrosilyl groups can be used. The binder resin 2 may be used individually by 1 type, and may use 2 or more types together.

The content of the binder resin 2 in the heat conductive sheet 1 is not particularly limited, and can be appropriately selected according to the purpose. For example, the content of the binder resin 2 in the thermally conductive sheet 1 can be 20% by volume or more, and may be 25% by volume or more, from the viewpoint of the flexibility and resilience of the thermally conductive sheet 1. It may be 30% by volume or more, or 33% by volume or more. In addition, the content of the binder resin 2 in the heat conductive sheet 1 can be 70% by volume or less, and may be 60% by volume or less, from the viewpoint of the thermal conductivity and resilience of the heat conductive sheet 1. , 50% by volume or less, 41% by volume or less, or 39% by volume or less. In addition, the content of the binder resin 2 in the thermally conductive sheet 1 is preferably 20 to 50% by volume, for example, from the viewpoint of the restoring property of the thermally conductive sheet 1, and more than 35% by volume and 41% by volume or less. more preferably 39 to 41% by volume.

<Fibrous filler>
The heat conductive sheet 1 contains fibrous fillers 3 . The fibrous filler 3 has a major axis and a minor axis, and the major axis and minor axis are different in length, and the aspect ratio (average major axis length/average minor axis length) exceeds 1. including. The fibrous filler 3 may be used singly or in combination of two or more. The fibrous filler 3 can be appropriately selected depending on the intended purpose. For example, metal fiber, carbon fiber, etc. can be used, and carbon fiber is preferable.

Carbon fibers include, for example, pitch-based carbon fiber, PAN-based carbon fiber, carbon fiber obtained by graphitizing PBO fiber, arc discharge method, laser evaporation method, CVD method (chemical vapor deposition method), CCVD method (catalytic chemical vapor deposition method), growth method) or the like can be used. Among these, pitch-based carbon fibers are preferable from the viewpoint of thermal conductivity.

The average fiber length (average long axis length) of the fibrous filler 3 can be, for example, 50 to 250 μm, and may be 75 to 220 μm. 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 depending on the purpose. The average major axis length and average minor axis length of the fibrous filler 3 can be measured with a microscope or scanning electron microscope (SEM), for example.

The surface of the carbon fiber may be covered with an insulating coating depending on the purpose. Thus, insulation-coated carbon fibers can be used as the carbon fibers. The insulation-coated carbon fiber has a carbon fiber and an insulation coating on at least part of the surface of the carbon fiber, and may contain other components as necessary.

The insulating film is made of an electrically insulating material, such as silicon oxide or a cured polymer material. The polymerizable material is, for example, a radical polymerizable material such as a polymerizable organic compound and a polymerizable resin. The radically polymerizable material can be appropriately selected according to the purpose as long as it is a material that undergoes radical polymerization using energy. Examples thereof include compounds having a radically polymerizable double bond. Examples of radically polymerizable double bonds include vinyl groups, acryloyl groups, and methacryloyl groups. The number of radically polymerizable double bonds in the compound having radically polymerizable double bonds is preferably two or more from the viewpoint of strength including heat resistance and solvent resistance. Examples of compounds having two or more radically polymerizable double bonds include divinylbenzene (DVB) and compounds having two or more (meth)acryloyl groups. The radically polymerizable material may be used singly or in combination of two or more. The molecular weight of the radically polymerizable material can be appropriately selected depending on the purpose, and can be in the range of 50-500, for example. When the insulating coating is formed of a cured product of a polymerizable material, the content of structural units derived from the polymerizable material in the insulating coating can be, for example, 50% by mass or more, and can be 90% by mass or more. can also

The average thickness of the insulating film can be appropriately selected depending on the purpose, and from the viewpoint of realizing high insulation, it can be 50 nm or more, may be 100 nm or more, or may be 200 nm or more. . The upper limit of the average thickness of the insulating coating can be, for example, 1000 nm or less, and may be 500 nm or less. The average thickness of the insulating coating can be determined, for example, by observation with a transmission electron microscope (TEM).

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

The content of the fibrous filler 3 in the heat conductive sheet 1 can be, for example, 5% by volume or more, or can be 10% by volume or more, from the viewpoint of the thermal conductivity of the heat conductive sheet 1. % or more, 20 volume % or more, or 25 volume % or more. In addition, the content of the fibrous filler 3 in the heat conductive sheet 1 can be, for example, 30% by volume or less, 28% by volume or less, and 25% by volume from the viewpoint of the moldability of the heat conductive sheet 1. It can be vol % or less, and can also be 23 vol % or less. The content of the fibrous filler 3 in the heat conductive sheet 1 can be, for example, 5 to 50% by volume, preferably 14 to 25% by volume. When two or more kinds of fibrous fillers 3 are used in combination, it is preferable that the total amount thereof satisfies the content described above.

<Other thermal conductive materials>
The other thermally conductive material 4 is a thermally conductive material other than the fibrous filler 3 described above, and includes, for example, an inorganic filler. Other shapes of the heat-conducting material 4 include, for example, a spherical shape, a crushed shape, an ellipsoidal shape, a massive shape, a granular shape, a flat shape, and the like. The shape of the other heat conductive material 4 is preferably a crushed shape, a spherical shape, an ellipsoidal shape, or the like from the viewpoint of filling properties. A crushed shape is preferable from the viewpoint of improving the restoring force of the fibrous filler 3 after release. The term "pulverized" means, for example, one having a long axis and a short axis and a length ratio of 10 or less between the long axis direction and the short axis direction. Other thermally conductive materials 4 may be used singly or in combination of two or more.

The other thermally conductive 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 viewpoint of the restorability and thermal conductivity of the heat conductive sheet 1, it is preferable to use at least one of aluminum hydroxide and alumina. aspects.

The average particle diameter (D50) of the alumina particles may be, for example, 0.1 to 10 μm, may be 0.1 to 8 μm, may be 0.1 to 7 μm, may be 0.1 to It may be 2 μm. The average particle size (D50) of the aluminum hydroxide particles may be, for example, 0.1 to 10 μm, may be 0.1 to 8 μm, may be 0.1 to 7 μm, and may be 0.1 to 8 μm. It may be 1-2 μm.

The average particle size of the other thermally conductive material 4 is obtained by calculating the cumulative curve of the particle size value from the small particle size side of the particle size distribution when the entire particle size distribution of the other thermally conductive material 4 is taken as 100%. means the particle diameter when the cumulative value reaches 50%. The particle size distribution (particle size distribution) is determined by volume. Examples of the method for measuring the particle size distribution include a method using a laser diffraction particle size distribution analyzer.

The other thermally conductive material 4 may be surface-treated. The surface treatment includes, for example, treating the other thermally conductive material 4 with a coupling agent such as an alkoxysilane compound. The processing amount of the coupling agent can be, for example, in the range of 0.1 to 1.5% by volume with respect to the total amount of the other thermally conductive material 4.

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

The content of the other thermally conductive material 4 in the thermally conductive sheet 1 is not particularly limited, and can be appropriately selected according to the purpose. When the thermally conductive sheet 1 contains another thermally conductive material 4, the content of the thermally conductive material 4 can be more than 21% by volume from the viewpoint of the restorability and thermal conductivity of the thermally conductive sheet 1. It may be vol % or more, 40 vol % or more, or 42 vol % or more. In addition, the content of the other thermally conductive material 4 in the thermally conductive sheet 1 can be 50% by volume or less, and may be 45% by volume or less, from the viewpoint of the resilience of the thermally conductive sheet 1. It may be 40% by volume or less. The content of the other thermally conductive material 4 in the thermally conductive sheet 1 is preferably 36 to 45% by volume, for example, from the viewpoint of improving the restorability of the thermally conductive sheet 1 . When using two or more other thermally conductive materials 4 together, it is preferable that the total amount thereof satisfies the content described above.

When the heat conductive sheet 1 contains the fibrous filler 3 and the other heat conductive material 4, the total content of the fibrous filler 3 and the other heat conductive material 4 in the heat conductive sheet 1 is the restoration of the heat conductive sheet 1 From the viewpoint of properties and thermal conductivity, the content may be 50% by volume or more, may be 55% by volume or more, may be 59% by volume or more, or may be 60% by volume or more. In addition, the total content of the fibrous filler 3 and the other thermally conductive material 4 in the thermally conductive sheet 1 can be less than 77% by volume, and 67% by volume from the viewpoint of the resilience of the thermally conductive sheet 1. may be less than or equal to, may be less than or equal to 65% by volume, may be less than or equal to 64% by volume, may be less than or equal to 63% by volume, may be less than or equal to 62% by volume, or may be 61% by volume It may be below. The total content of the fibrous filler 3 and the other thermally conductive material 4 in the thermally conductive sheet 1 is preferably, for example, 59% by volume or more and less than 65% by volume.

The heat conductive sheet 1 may further contain components other than the components described above within a range that does not impair the effects of the present technology. Other components include, for example, dispersants, curing accelerators, retarders, tackifiers, plasticizers, flame retardants, antioxidants, stabilizers, colorants, and the like.

<Method for manufacturing heat conductive sheet>
The method for producing a thermally conductive sheet according to the present technology includes a step of preparing a thermally conductive composition containing a binder resin 2 and a fibrous filler 3 (hereinafter also referred to as step A); and a step of slicing the molded block into sheets to obtain the heat conductive sheet 1 (hereinafter also referred to as step C).

In the heat conductive sheet 1 obtained in step C, as described above, 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. are placed. When the thermal conductive sheet 1 is compressed and released under the condition 1 described above, the arrangement angle of the fibrous filler 3 after compression and release is within 10 degrees of the angle before compression in a cross-sectional view.

The thermally conductive sheet 1 obtained by this production method has good restoring force when compression and release are performed as in condition 1, especially the restoring force of the fibrous filler 3 . Therefore, when the thermally conductive sheet 1 is arranged between the heat generating body and the heat radiating body, even if there is a gap between the heat generating body and the heat radiating body, the fibrous shape of the heat conductive sheet 1 will fill the gap. The filler 3 can be easily and quickly followed. Thereby, deterioration of the thermal resistance of the heat conductive sheet 1 can be suppressed.

[Step A]
In step A, a thermally conductive composition containing binder resin 2 and fibrous filler 3 is prepared. The thermally conductive composition may contain other thermally conductive materials 4 as described above. The thermally conductive composition may be uniformly mixed with various additives and volatile solvents by known methods.

[Step B]
In step B, a molded block is formed from the thermally conductive composition. Examples of methods for forming the molded block include an extrusion molding method and a mold molding method. The extrusion molding method and the mold molding method are not particularly limited, and various known extrusion molding methods and mold molding methods can be selected depending on the viscosity of the heat conductive composition and the properties required for the heat conductive sheet 1. can be adopted as appropriate. For example, in the extrusion molding method, when the thermally conductive composition is extruded from a die, or in the mold molding method, when the thermally conductive composition is pressed into the mold, the binder resin 2 flows, and the fibers are formed along the flow direction. The long axis of the shaped filler 3 is oriented.

The size and shape of the molded block can be determined according to the required size of the heat conductive sheet. For example, a rectangular parallelepiped having a cross-sectional length of 0.5 to 15 cm and a width of 0.5 to 15 cm can be used. The length of the rectangular parallelepiped may be determined as required. In the extrusion molding method, it is easy to form a columnar molding block made of a cured product of the heat conductive composition, in which the long axis of the fibrous filler 3 is oriented in the extrusion direction.

The molded block obtained is preferably heat-cured. The curing temperature in thermosetting can be appropriately selected according to the purpose, and can be in the range of 60.degree. C. to 120.degree. C. when the binder resin 2 is a silicone resin, for example. Curing time in thermal curing can be, for example, in the range of 30 minutes to 10 hours.

[Step C]
In step C, the molded block is sliced into sheets to obtain a thermally conductive sheet 1 in which the long axes of fibrous fillers 3 are oriented in the thickness direction B. The fibrous filler 3 is exposed on the surface (sliced surface) of the sheet obtained by slicing. The slicing method is not particularly limited, and can be appropriately selected from among known slicing devices according to the size and mechanical strength of the compact block. Examples of the slicing device include an ultrasonic cutter and a planer. When the molding method is extrusion molding, the slicing direction of the molded block is 60 to 120 degrees with respect to the extrusion direction because the long axis of the fibrous filler 3 is oriented in the extrusion direction in some cases. preferably 70 to 100 degrees, and even more preferably 90 degrees (perpendicular).

Thus, in the manufacturing method including Step A, Step B, and Step C, the heat conductive sheet 1 in which the fibrous filler 3 is dispersed in the binder resin 2, and the fibrous filler 3 has a thickness in cross section. When arranged at an angle of 70 to 90 degrees in direction B and compressed and released under condition 1 described above, the arrangement angle of the fibrous filler 3 after compression and release is within 10 degrees of the angle before compression in cross-sectional view. It is possible to obtain the heat conductive sheet 1 in the range of

The method for manufacturing the thermally conductive sheet 1 is not limited to the example described above, and for example, after the step C, the step D of pressing the sliced surface may be further included. In the manufacturing method having such a step D, the surface of the thermally conductive sheet 1 obtained in the step C is made smoother, and the adhesion with other members can be further improved. As a method of pressing, a pair of pressing devices comprising a flat plate and a press head having a flat surface can be used. Alternatively, the surface of the heat conductive sheet 1 may be pressed with pinch rolls.

The pressure during pressing may 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, and may be in the range of 30 seconds to 3 minutes. .

As one mode, pressing may be performed while heating using a press head with a built-in heater. The pressing temperature may range, for example, from 0 to 180°C, may range from room temperature (eg, 25°C) to 100°C, or may range from 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 forming the compact sheet.

<Electronic equipment>
The thermally conductive sheet 1 is, for example, an electronic device (thermal device) having a structure arranged between a heat generating body and a radiator so that the heat generated by the heat generating body is released to the heat radiator. can be An electronic device has at least a heating element, a radiator, and a thermally conductive sheet 1, and may further have other members as necessary.

The heat generating element is not particularly limited, and includes, for example, CPU, GPU (Graphics Processing Unit), DRAM (Dynamic Random Access Memory), integrated circuit elements such as flash memory, transistors, resistors, and other electronic components that generate heat in electric circuits. etc. The heating element also includes components for receiving optical signals, such as optical transceivers in communication equipment.

The radiator is not particularly limited, and examples thereof include heat sinks, heat spreaders, and the like, which are used in combination with integrated circuit elements, transistors, optical transceiver housings, and the like. Materials for the heat sink and heat spreader include, for example, copper and aluminum. As the radiator, in addition to the heat spreader and the heat sink, any material can be used as long as it conducts the heat generated from the heat source and dissipates it to the outside. Heat pipes, vapor chambers, metal covers, housings, and the like. A heat pipe is, for example, a cylindrical, substantially cylindrical, or flat cylindrical hollow structure.

FIG. 5 is a cross-sectional view showing an example of a semiconductor device to which a heat conductive sheet is applied. For example, as shown in FIG. 5, the heat conductive sheet 1 is mounted on a semiconductor device 50 built in various electronic devices and sandwiched between a heat generator and a radiator. A semiconductor device 50 shown in FIG. 5 includes an electronic component 51 , a heat spreader 52 , and a heat conductive sheet 1 . By sandwiching the heat conductive sheet 1 between the heat spreader 52 and the heat sink 53 , together with the heat spreader 52 , a heat dissipation member for dissipating the heat of the electronic component 51 is configured. The mounting location of the heat conductive 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, but can be appropriately selected according to the configuration of the electronic device or semiconductor device. The heat spreader 52 is formed, for example, in the shape of a square plate, and has a main surface 52a facing the electronic component 51 and side walls 52b erected along the outer circumference of the main surface 52a. The heat spreader 52 is provided with the heat conductive sheet 1 on the principal surface 52a surrounded by the side walls 52b, and is provided with the heat sink 53 via the heat conductive sheet 1 on the other surface 52c opposite to the principal surface 52a.

Examples of the present technology will be described below. The present technology is not limited to these examples.

<Example 1>
In Example 1, as shown in Table 1, 45% by volume of alumina particles having an average particle diameter of 2 μm and having been subjected to coupling treatment with a silane coupling agent were added to the two-liquid addition reaction type liquid silicone resin at 45% by volume, and as a fibrous filler, 14% by volume of pitch-based carbon fibers having an average fiber length of 200 μm were mixed to prepare a silicone composition. 41% by volume of the two-liquid addition reaction type liquid silicone resin containing polyorganosiloxane as the main component was used, and the completed sheet was adjusted to have a Shore type OO hardness of 25. The resulting silicone composition was extruded into a hollow quadrangular prism-shaped mold (50 mm x 50 mm) to form a 50 mm square silicone molding. The silicone molded product was heated in an oven at 100° C. for 6 hours to obtain a cured silicone product. The cured silicone material was cut with a slicer so as to have a thickness of 2.0 mm to obtain a thermally conductive sheet.

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

<Example 3>
In Example 3, as shown in Table 1, 36% by volume of alumina particles having an average particle diameter of 4 μm, which were subjected to coupling treatment with a silane coupling agent, to a two-liquid addition reaction type liquid silicone resin, and an average A silicone composition was prepared by mixing 25% by volume of pitch-based carbon fiber with a fiber length of 120 μm, and 39% by volume of a two-liquid addition reaction type liquid silicone resin containing polyorganosiloxane as a main component was used. A heat conductive sheet was obtained in the same manner as in Example 1, except that the completed sheet had a hardness of 40 in Shore type OO.

<Comparative Example 1>
In Comparative Example 1, as shown in Table 1, 42% by volume of alumina particles having an average particle size of 4 μm, which were subjected to coupling treatment with a silane coupling agent, to a two-liquid addition reaction type liquid silicone resin, and an average of 4 μm as a fibrous filler. A silicone composition was prepared by mixing 23% by volume of pitch-based carbon fiber with a fiber length of 150 μm, and 35% by volume of a two-liquid addition reaction type liquid silicone resin containing polyorganosiloxane as a main component was used. A heat conductive sheet was obtained in the same manner as in Example 1, except that the completed sheet had a hardness of 40 in Shore type OO.

<Comparative Example 2>
In Comparative Example 2, as shown in Table 1, 21% by volume of alumina particles having an average particle diameter of 4 μm and having an average particle diameter of 1.0 μm, which were subjected to coupling treatment with a silane coupling agent, were added to a two-liquid addition reaction type liquid silicone resin. A silicone composition was prepared by mixing 24% by volume of 3 μm aluminum nitride particles and 22% by volume of pitch-based carbon fiber having an average fiber length of 150 μm as a fibrous filler, and a two-liquid addition reaction type liquid silicone resin. Heat conductive sheet in the same manner as in Example 1, except that 33% by volume of a material containing polyorganosiloxane as a main component was used as the heat conductive sheet, and the hardness of the completed sheet in Shore type OO was adjusted to 50. got

<Comparative Example 3>
In Comparative Example 3, as shown in Table 1, 36% by volume of alumina particles having an average particle diameter of 4 μm and having an average particle diameter of 1.0 μm, which were subjected to coupling treatment with a silane coupling agent, were added to a two-liquid addition reaction type liquid silicone resin. A silicone composition was prepared by mixing 25% by volume of aluminum nitride particles of 3 μm and 16% by volume of aluminum powder with an average particle size of 15 μm, and polyorganosiloxane was used as a two-liquid addition reaction type liquid silicone resin. A heat conductive sheet was obtained in the same manner as in Example 1, except that 23% by volume of the component was used and that the completed sheet had a Shore type OO hardness of 40. Thus, in Comparative Example 3, a heat conductive sheet containing no carbon fiber was obtained.

<Bulk thermal conductivity>
For bulk thermal conductivity, the thermal resistance of each thermal conductive sheet is measured by a method in accordance with ASTM-D5470, the horizontal axis is the thickness (mm) of the thermal conductive sheet at the time of measurement, and the vertical axis is the thermal resistance of the thermal conductive sheet ( °C·cm ² /W) was plotted, 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 thermally conductive sheet was measured by preparing three types of thermally conductive sheets with different thicknesses and measuring the thermally conductive sheets with different thicknesses. Table 1 shows the results.

<Preparation of sample for evaluation>
The heat conductive sheets obtained in Examples and Comparative Examples were processed to have a diameter of 29 mm to prepare samples for evaluation. Three or more samples were prepared and used for (1) checking the external size, (2) observing the cross section before compression, and (3) observing the cross section after releasing the compression.

<External size of sample after compression release>
For the outer size of the sample after compression release, the maximum length and the shortest length were visually measured using a vernier caliper, and the average value was taken. Specifically, a sample having 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 external size of the sample was measured 3 minutes after the compression was released. Table 1 shows the results.

<Inclination of carbon fiber before compression>
For cross-sectional observation of sample 5 (heat conductive sheet 1) before compression, as shown in FIG. Then, as shown in FIG. 3, in the sample 6, the angles of the arbitrary carbon fibers 3A were measured at five points in a range 6B which is 5 mm inside from the outer periphery and which is the upper and lower 1/3 of the cross section, and the average value was obtained. The angle of carbon fiber 3A was measured using a microscope VHX-5000 (manufactured by Keyence Corporation) at a magnification of 100 times. The angles of the carbon fibers 3A at five points were measured so that the angles of the carbon fibers 3A ranged from 0 degrees to 90 degrees after the parallelism of the sample 6 was obtained.

FIG. 6 is a digital microscope photograph of a cross section of the thermally conductive sheet before compression. As an example, a method of calculating the angle of the carbon fibers in Sample 6 of Example 3 will be described. When the angle exceeds 90 degrees, such as "[6] 93 degrees" shown in Fig. 6, 180 degrees - 93 degrees = 87 degrees. The five-point angles of 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. . Table 1 shows the results.

<Inclination of carbon fiber after compression release>
The cross-sectional observation of the sample 6 after compression release was performed at the same time as the cross-sectional observation of the sample 6 before compression. The sample 5 shown in FIG. 2 was compressed to 40% of the initial thickness at room temperature for 24 hours, and three minutes after the compression was released, the central portion of the sample 5 after the compression was released was thickened as shown in FIGS. A sample 6 was obtained by cutting with a razor blade in the width direction B to a width of 5 mm. On the cut surface (surface) of this sample 6, the angles of arbitrary carbon fibers 3A were measured at five points in a range 6B which is 5 mm inside from the outer periphery and which is 1/3 of the top and bottom of the cross section, and the average value was obtained.

FIG. 7 is a digital microscope photograph of a cross section of the thermally conductive sheet after compression release. As an example, a method of calculating the angle of the carbon fibers 3A in Sample 6 of Example 3 will be described. As shown in FIG. 7, the five-point angles of carbon fiber 3A in sample 6 of example 3 after compression release are 74 degrees, 79 degrees, 70 degrees, 78 degrees, and 84 degrees, with an average of 77.0 degrees. It was degrees. Table 1 shows the results.

<Angle difference of carbon fiber before and after compression release>
An average difference (degrees) in the angles of five points of the carbon fibers 3A in the sample 6 before and after the compression release was determined. Table 1 shows the results.

<Hardness in Shore type OO>
The hardness of the shore type OO thermal conductive sheet is measured by a method based on ASTM-D2240, and five 2 mm thick thermal conductive sheets are stacked to make a thickness of 10 mm. Average value. Table 1 shows the results.

In the heat conductive sheets obtained in Examples 1 to 3, 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 when viewed in cross section. It was found that when compression and release were performed under condition 1 described above, the arrangement angle of the fibrous filler 3 after compression and release was within 10 degrees of the angle before compression in a cross-sectional view. That is, the heat conductive sheets obtained in Examples 1 to 3 have good restoring force when compressed and released as in Condition 1, especially the restoring force of carbon fiber 3A (fibrous filler 3). I found out. Therefore, when the thermally conductive sheets obtained in Examples 1 to 3 are arranged between the heating element and the radiator, even if the gap between the heating element and the radiator opens, the gap The fibrous filler 3 in the heat conductive sheet can be easily and quickly followed. As a result, the thermally conductive sheets obtained in Examples 1 to 3 are considered to be able to suppress the deterioration of thermal resistance.

Further, it was found that the heat conductive sheets obtained in Examples 1 to 3 were 2 mm thick and 29 mm in diameter, compressed by 40% at room temperature for 24 hours, and had a diameter of 32.0 mm or less 3 minutes after release. In other words, it was also found that the thermally conductive sheets obtained in Examples 1 to 3 show little change in outer size after compression is released.

On the other hand, in the heat conductive sheets obtained in Comparative Examples 1 and 2, when compression and release were performed under the above-described condition 1, the arrangement angle of the fibrous filler 3 after compression and release was the same as the angle before compression in cross-sectional view. It was found that it was not within the range of 10 degrees. That is, the heat conductive sheets obtained in Comparative Examples 1 and 2 have a higher restoring force when compression and release are performed as in Condition 1, especially the carbon fiber 3A, compared to the heat conductive sheets of Examples 1 to 3. It was found that the restoring force of (fibrous filler 3) was not good. In addition, it was found that the heat conductive sheets obtained in Comparative Examples 1 to 3 showed a greater change in the outer size after the release of compression than in Examples 1 to 3.

1 thermally conductive sheet, 2 binder resin, 3 fibrous filler, 3A carbon fiber, 4 other thermally conductive material, 5 sample, 6 cut sample, 6A cut surface, 6Ac core, 50 semiconductor device, 51 electronic component, 52 Heat spreader, 52a main surface, 52b side wall, 52c other surface, 53 heat sink

Claims (11)

A heat conductive sheet in which a fibrous filler is dispersed in a binder resin, and the fibrous filler is arranged at an angle of 70 to 90 degrees in the thickness direction in a cross-sectional view,
A thermally conductive sheet, wherein when the thermally conductive sheet is compressed and released under condition 1 below, the arrangement angle of the fibrous filler after release is within 10 degrees of the angle before compression in a cross-sectional view.
Condition 1: The thickness of the heat conductive sheet is compressed to 40% of the initial thickness at room temperature for 24 hours, and then released. 2. The heat conductive sheet according to claim 1, wherein the heat conductive sheet having a thickness of 2 mm and a diameter of 29 mm has a diameter of 32.0 mm or less 3 minutes after being compressed by 40% at room temperature for 24 hours. 3. The heat conductive sheet according to claim 1, wherein the content of the fibrous filler is 5-50% by volume. 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. The heat conductive sheet according to any one of claims 1 to 4, which has a hardness of 25 to 40 in Shore type OO. The heat conductive sheet according to any one of claims 1 to 5, wherein the binder resin is a silicone resin. The heat conductive sheet according to any one of claims 1 to 6, wherein the fibrous filler is pitch-based carbon fiber. Further containing other thermally conductive materials other than the fibrous filler,
The thermally conductive sheet according to any one of claims 1 to 7, wherein the total content of the fibrous filler and the other thermally conductive material is less than 65% by volume. Further containing other thermally conductive materials other than the fibrous filler,
The thermally conductive sheet according to any one of claims 1 to 8, wherein the other thermally conductive material is at least one of aluminum hydroxide and alumina. preparing a thermally conductive composition containing a binder resin and a fibrous filler;
forming a molded block from the thermally conductive composition;
and obtaining a heat conductive sheet by slicing the molded block into a sheet,
A method for producing a thermally conductive sheet, wherein the thermally conductive sheet is the thermally conductive sheet according to any one of claims 1 to 9. a heating element;
a radiator;
An electronic device comprising the thermally conductive sheet according to any one of claims 1 to 9 arranged between the heating element and the radiator.

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