WO2023190726A1

WO2023190726A1 - Heat-conducting sheet and production method for heat-conducting sheet

Info

Publication number: WO2023190726A1
Application number: PCT/JP2023/012900
Authority: WO
Inventors: 圭佑武笠; 栄治太田; 真理奈戸端; 大地森; 義知宮崎
Original assignee: デクセリアルズ株式会社
Priority date: 2022-03-30
Filing date: 2023-03-29
Publication date: 2023-10-05

Abstract

Provided is a heat-conducting sheet having a reduced contact thermal resistance.　This heat-conducting sheet 1 comprises a cured product of a heat-conducting composition containing a binder resin 2, a fibrous filler 3, and a heat-conducting filler 4 other than the fibrous filler 3. In the heat-conducting sheet 1, the fibrous filler 3 is aligned in the thickness direction B. The average height Spk of peaks on the heat-conducting sheet 1 as measured using a scanning white-light interference microscope having a 20x objective lens in accordance with ISO 25178 is at most 3 μm. The contact thermal resistances of the heat-conducting sheet 1 as measured in accordance with ASTM-D5470 when applied with pressure at 1.4 kgf/cm2 and 2.1 kgf/cm2 are at most 0.10°C·cm2/W.

Description

Thermal conductive sheet and method for manufacturing the thermally conductive sheet

The present technology relates to a thermally conductive sheet and a method for manufacturing a thermally conductive sheet. This application is based on Japanese Patent Application No. 2022-055354 filed in Japan on March 30, 2022 and Japanese Patent Application No. 2023-052788 filed in Japan on March 29, 2023. These applications are incorporated by reference into this application.

With the further improvement in the performance of electronic devices, the density and packaging of semiconductor elements are increasing. In proportion to this, the heat generation amount and heat generation density from ICs (Integrated Circuits), etc. tend to increase, and heat is more efficiently transferred to heat dissipation members such as heat dissipation fins and heat dissipation plates through thermally conductive sheets. That is required. In addition, electronic devices are rapidly becoming smaller and thinner, and the thickness of the thermally conductive sheet required is also becoming thinner, leading to a demand for lower thermal resistance. Examples of thermally conductive sheets that meet such requirements include thermally conductive sheets using fibrous fillers (eg, carbon fibers) (see, eg, Patent Documents 1 to 5). Carbon fiber, which is an example of a fibrous filler, is an anisotropic filler having a thermal conductivity of about 600 to 1200 W/(m·K) in the fiber direction. It is known that thermal conductivity can be dramatically improved by orienting the fiber direction of carbon fibers in the thickness direction of a thermally conductive sheet, which is the direction of heat transfer.

In order to achieve low thermal resistance using a thermally conductive sheet with oriented carbon fibers, it is also important to consider the contact thermal resistance of the thermally conductive sheet. Contact thermal resistance is thermal resistance that occurs between a thermally conductive sheet and an adherend. However, even if carbon fibers have high thermal conductivity, when viewed from the entire thermally conductive sheet, the contact between the adherend and the carbon fibers is point contact, and even if the carbon fibers sink into the binder resin due to pressure, There is a problem that air gets mixed in between the thermally conductive sheet and the adherend.

Additionally, as the thermally conductive sheet used becomes thinner, the contribution of contact thermal resistance generated between the thermally conductive sheet and the adherend tends to increase. In particular, in a thermally conductive sheet in which fibrous filler such as carbon fiber is oriented in the thickness direction, the contact thermal resistance tends to increase as the thickness decreases.

Patent No. 5752299 Patent No. 4814550 Patent No. 6650175 Patent No. 6671735 International Publication No. 2020/067141

The present technology has been proposed in view of such conventional circumstances, and provides a thermally conductive sheet with reduced contact thermal resistance.

As a result of intensive studies, the inventors of the present application have found that the above-mentioned problem can be solved by setting the average height Spk of the protruding peaks to a predetermined value or less for a thermally conductive sheet in which fibrous filler is oriented in the thickness direction. I found it.

The present technology is a thermally conductive sheet made of a cured product of a thermally conductive composition containing a binder resin, a fibrous filler, and a thermally conductive filler other than the fibrous filler, in which the fibrous filler The average height Spk of the protruding peaks of the thermally conductive sheet is 3 μm, which is oriented in the thickness direction of the conductive sheet and measured according to ISO 25178 using a scanning white interference microscope with a 20x objective lens. The contact thermal resistance when applying a pressure of 1.4 kgf/cm ² and when applying a pressure of 2.1 kgf/cm ² is 0.10° C.cm ² /W or less, measured according to ASTM-D5470.

A method for manufacturing a thermally conductive sheet according to the present technology includes molding a thermally conductive composition containing a binder resin, a fibrous filler, and a thermally conductive filler other than the fibrous filler into a predetermined shape and curing it. A step of obtaining a molded body of the thermally conductive composition by doing so, a step of cutting the molded body into sheet shapes to obtain a molded body sheet, and a process of polishing the molded body sheet with a polishing member to form a thermally conductive sheet. A polishing residue containing a binder resin, a fibrous filler, and other thermally conductive fillers generated by the polishing is left on the surface of the thermally conductive sheet.

The present technology can provide a thermally conductive sheet with reduced contact thermal resistance.

FIG. 1 is a sectional view showing an example of a thermally conductive sheet. FIG. 2 is a cross-sectional view showing an example of the surface of a thermally conductive sheet. FIG. 3 is a perspective view of a brush that is an example of a polishing member. FIG. 4 is a perspective view for explaining an example of a method of polishing the surface of a molded sheet with a brush. FIG. 5 is a perspective view for explaining an example of a method of continuously polishing the surfaces of a plurality of molded body sheets with a brush. FIG. 6 is a cross-sectional view showing an example of a semiconductor device to which a thermally conductive sheet is applied. FIG. 7 shows the results of Examples and Comparative Examples with the horizontal axis representing the arithmetic mean curvature Spc (1/mm) of the peak of the thermally conductive sheet and the vertical axis representing the developed area ratio Sdr (%) of the interface of the thermally conductive sheet. This is a plotted graph.

In this specification, the average particle diameter (D50) refers to the cumulative value when a cumulative curve of particle diameter values is calculated from the small particle diameter side of the particle diameter distribution, assuming that the entire particle diameter distribution is 100%. This refers to the particle diameter when 50%. Note that the particle size distribution (particle size distribution) in this specification is determined on a volume basis. Examples of methods for measuring particle size distribution include a method using a laser diffraction type particle size distribution analyzer.

FIG. 1 is a cross-sectional view showing an example of a thermally conductive sheet 1 according to the present technology. The thermally conductive sheet 1 is made of a cured product of a thermally conductive composition containing a binder resin 2, a fibrous filler 3, and a thermally conductive filler 4 other than the fibrous filler 3. In the thermally conductive sheet 1, a fibrous filler 3 and another thermally conductive filler 4 are dispersed in a binder resin 2, and the fibrous filler 3 is oriented in the thickness direction B of the thermally conductive sheet 1. Here, the fact that the fibrous filler 3 is oriented in the thickness direction B of the thermally conductive sheet 1 means that, for example, among all the fibrous fillers 3 in the thermally conductive sheet 1, the thickness of the thermally conductive sheet 1 The proportion of the fibrous filler 3 whose long axis is oriented in direction B is 50% or more, may be 55% or more, may be 60% or more, may be 65% or more, It may be 70% or more, 80% or more, 90% or more, 95% or more, or 99% or more. When the long axis of the fibrous filler 3 is oriented in the thickness direction B of the thermally conductive sheet 1, for example, the long axis of the fibrous filler 3 is oriented in the direction A of the thermally conductive sheet 1 by 60° to The angle may be in the range of 120 degrees, may be in the range of 70 to 100 degrees, or may be 90 degrees (substantially vertical).

The thermally conductive sheet 1 has an average height Spk of protruding peaks of 3 μm or less, as measured in accordance with ISO 25178 using a scanning white interference microscope with an objective lens set at a magnification of 20 times. The average height Spk of the protruding peaks is influenced by the objective lens magnification of the scanning white interference microscope. Hereinafter, it will also be simply referred to as "average height Spk of the protruding peaks measured according to ISO 25178" or "average height Spk of the protruding peaks". Furthermore, the thermally conductive sheet 1 has a contact thermal resistance of 0.10°C·cm ^{2 /} when a pressure of 1.4 kgf/cm ² is applied and when a pressure of 2.1 kgf/cm ² is applied, which is measured according to ASTM-D5470. W or less. Note that the values measured according to ISO 25178, which will be described later, are also affected by the objective lens magnification of the scanning white interference microscope.

Since the average height Spk of the protruding peaks of the thermally conductive sheet 1 is 3 μm or less, the contact area between the thermally conductive sheet 1 and the adherend increases, and the contact area between the thermally conductive sheet 1 and the adherend increases. Since air is prevented from entering between the two, contact thermal resistance can be reduced. Specifically, the thermally conductive sheet 1 has an average height Spk of the protruding peaks of 3 μm or less, so that the thermally conductive sheet 1 has a pressure of 1.4 kgf/cm ² and 2.1 kgf measured according to ASTM-D5470. /cm ² The contact thermal resistance when pressurized can be 0.10° C.cm ² /W or less. In this manner, since the average height Spk of the protruding peaks is 3 μm or less, the thermally conductive sheet 1 can reduce contact thermal resistance even under low load (low pressurization).

The thermally conductive sheet 1 has an average height Spk of the protruding peaks measured according to ISO 25178 of 3 μm or less, may be 2.5 μm or less, may be 2 μm or less, and may be 1.2 μm or less. 1.1 μm or less, 1.0 μm or less, 0.9 μm or less, 0.8 μm or less, 0.7 μm or less The thickness may be 0.6 μm or less, or 0.5 μm or less. The lower limit of the average height Spk of the protruding peaks of the thermally conductive sheet 1 is not particularly limited, but may be, for example, 0.4 μm or more. The average height Spk of the protruding peaks of the thermally conductive sheet 1 may be in the range of 0.494 to 2.967 μm, may be in the range of 0.494 to 2.342 μm, and may be in the range of 0.494 to 2.342 μm. ~1.212μm, 0.494~1.143μm, 0.494~0.887μm, 0.494~0.566μm It may be a range. It is preferable that the average height Spk of the protruding peaks on at least one surface of the thermally conductive sheet 1 satisfies the above-mentioned range, and the average height Spk of the protruding peaks on both surfaces may satisfy the above-mentioned range. The average height Spk of the protruding peaks of the thermally conductive sheet 1 can be measured by the method described in Examples described below.

The thermally conductive sheet 1 may have an average depth Svk of the protruding valleys of 5.5 μm or less as measured in accordance with ISO 25178 using a scanning white interference microscope with a 20x objective lens; 4. 5 μm or less, 4.0 μm or less, 3.5 μm or less, 3.0 μm or less, 2.5 μm or less, 2. It may be 0 μm or less, 1.5 μm or less, or 1.2 μm or less. The lower limit of the average depth Svk of the protruding valleys of the thermally conductive sheet 1 is not particularly limited, and may be, for example, 1.0 μm or more. Further, the average depth Svk of the protruding valleys of the thermally conductive sheet 1 may be in the range of 1.165 to 5.156 μm, or may be in the range of 1.165 to 4.490 μm, or may be in the range of 1.165 to 4.490 μm. It may be in the range of .165 to 4.291 μm, may be in the range of 1.165 to 3.711 μm, or may be in the range of 1.165 to 3.559 μm. It is preferable that the average depth Svk of the protruding troughs on at least one surface of the thermally conductive sheet 1 satisfies the above-mentioned range, and the average depth Svk of the protruding troughs on both surfaces may satisfy the above-mentioned range. The average depth Svk of the protruding valleys of the thermally conductive sheet 1 can be measured by the method described in Examples described below.

Thermal conductive sheet 1 has an average height Spk (μm) of protruding peaks and an average depth Svk ( The value (Spk/(Spk+Svk)) of the average height Spk (μm) of the protruding peaks relative to the sum of the peaks (Spk/(Spk+Svk)) is preferably 40% or less, may be 30% or less, and may be 25% or less. It may be 22% or less, 20% or less, or 18% or less. The lower limit of (Spk/(Spk+Svk)) of the thermally conductive sheet 1 is not particularly limited, and may be, for example, 10% or more, 15% or more, or 18% or more. It's okay. (Spk/(Spk+Svk)) of the thermally conductive sheet 1 may be in the range of 18.14 to 39.78%, may be in the range of 18.14 to 39.69%, or may be in the range of 18.14 to 39.69%, or It may be in the range of .14 to 29.76%, it may be in the range of 18.14 to 27.58%, it may be in the range of 18.14 to 22.02%, It may range from 18.14% to 19.29%. In the thermally conductive sheet 1, it is preferable that Spk/(Spk+Svk) on at least one surface satisfies the above-mentioned range, and Spk/(Spk+Svk) on one surface and the other surface may satisfy the above-mentioned range.

The thermally conductive sheet 1 preferably has a volume Vmp of the protruding peaks of 0.15 ml/m ² or less, as measured in accordance with ISO 25178 using a scanning white interference microscope with a 20x objective lens; It may be 0.12ml/ ^m2 or less, 0.10ml/ ^m2 or less, 0.08ml/ ^m2 or less, or 0.06ml/ ^m2 or less. Generally, it may be 0.04 ml/m ² or less, or 0.03 ml/m ² or less. The lower limit of the volume Vmp of the protruding peaks of the thermally conductive sheet 1 is not particularly limited, and may be, for example, 0.01 ml/m ² or more, or 0.02 ml/m ² or more. . The thermally conductive sheet 1 may have a volume Vmp of the protruding peaks in the range of 0.025 to 0.137 ml/ ^m2 , or in the range of 0.025 to 0.114 ml/ ^m2 . It may be in the range of 0.025 to 0.058 ml/ ^m2 , it may be in the range of 0.025 to 0.055 ml/ ^m2 , or it may be in the range of 0.025 to 0.040 ml/m2. ² or 0.025 to 0.027 ml/m ² . It is preferable that the volume Vmp of the protruding peaks on at least one surface of the thermally conductive sheet 1 satisfies the above-mentioned range, and the volume Vmp of the protruding peaks on both surfaces may satisfy the above-mentioned range.

It is preferable that the root mean square gradient Sdq of the thermally conductive sheet 1 is equal to or less than a predetermined value, as measured in accordance with ISO 25178 using a scanning white interference microscope with an objective lens set at a magnification of 20 times. The root mean square gradient Sdq of the thermally conductive sheet 1 represents the average size of the local gradient (differential of the shape) of the uneven shape on the surface of the thermally conductive sheet 1. For example, when the surface of the thermally conductive sheet 1 is completely flat, the root mean square gradient Sdq is zero. Moreover, the steeper the surface of the thermally conductive sheet 1 is, the larger the root mean square gradient Sdq becomes. The root mean square gradient Sdq of the thermally conductive sheet 1 is preferably less than 1.1, may be 0.8 or less, may be 0.7 or less, and may be 0.6 or less. It may be 0.5 or less, 0.4 or less, or 0.3 or less. The lower limit of the root mean square gradient Sdq of the thermally conductive sheet 1 is not particularly limited, and may be, for example, 0.1 or more, or 0.2 or more. The root mean square gradient Sdq of the thermally conductive sheet 1 may be, for example, in the range of 0.304 to 0.697, may be in the range of 0.304 to 0.578, or may be in the range of 0.304 to 0.578. 0.565, 0.304 to 0.508, 0.304 to 0.507, or 0.304 to 0. It may be in the range of .0.316. It is preferable that the root mean square gradient Sdq of at least one surface of the thermally conductive sheet 1 satisfies the above range, and the root mean square gradient Sdq of both surfaces may satisfy the above range.

It is preferable that the arithmetic mean curvature Spc of the peak of the thermally conductive sheet 1 is less than or equal to a predetermined value, as measured in accordance with ISO 25178 using a scanning white interference microscope with a 20x objective lens. The arithmetic mean curvature Spc of the peaks of the thermally conductive sheet 1 represents the average of the principal curvatures of the peaks of the surface of the thermally conductive sheet 1. The smaller the arithmetic mean curvature Spc of the peak of the thermally conductive sheet 1, the more rounded the point in the thermally conductive sheet 1 that contacts another object (for example, an adherend) is. On the other hand, the larger the arithmetic mean curvature Spc of the peak of the thermally conductive sheet 1, the sharper the point of contact with another object on the thermally conductive sheet. The arithmetic mean curvature Spc of the peak of the thermally conductive sheet 1 is preferably 2500 (1/mm) or less, may be 2300 (1/mm) or less, and may be 2100 (1/mm) or less. 2000 (1/mm) or less, 1900 (1/mm) or less, 1700 (1/mm) or less, 1500 (1/mm) or less It may be 1300 (1/mm) or less, 1100 (1/mm) or less, or 1000 (1/mm) or less. The lower limit of the arithmetic mean curvature Spc of the peak of the thermally conductive sheet 1 is not particularly limited, and may be, for example, 0 (1/mm) or more, or 500 (1/mm) or more. However, it may be 900 (1/mm) or more. The arithmetic mean curvature Spc of the peak of the thermally conductive sheet 1 may be, for example, in the range of 951 to 2290 (1/mm), or may be in the range of 951 to 2105 (1/mm), It may be in the range of 951 to 1937 (1/mm), it may be in the range of 951 to 1879 (1/mm), it may be in the range of 951 to 1455 (1/mm), or it may be in the range of 951 to 1455 (1/mm). , 951 to 1399 (1/mm). It is preferable that the arithmetic mean curvature Spc of the peaks on at least one surface of the thermally conductive sheet 1 satisfies the above-mentioned range, and the arithmetic mean curvature Spc of the peaks on both surfaces may satisfy the above-mentioned range.

It is preferable that the developed area ratio Sdr of the interface of the thermally conductive sheet 1 is equal to or less than a predetermined value, as measured in accordance with ISO 25178 using a scanning white interference microscope with a 20x objective lens. The developed area ratio Sdr of the interface of the thermally conductive sheet 1 represents how much the developed area (surface area) of the defined region of the thermally conductive sheet 1 increases relative to the area of the defined region. For example, when the surface of the thermally conductive sheet 1 is completely flat, the developed area ratio Sdr of the interface is 0%. The thermally conductive sheet 1 preferably has an interface development area ratio Sdr of 20% or less, which may be 15% or less, 10% or less, or 9% or less, It may be 7% or less, or 4% or less. The lower limit of the developed area ratio Sdr of the interface of the thermally conductive sheet 1 is not particularly limited, and may be, for example, 0% or more, or 2% or more. The developed area ratio Sdr of the interface of the thermally conductive sheet 1 may be, for example, in the range of 3.56 to 15.55%, or may be in the range of 3.56 to 10.44%, It may be in the range of 3.56 to 10.32%, it may be in the range of 3.56 to 9.44%, or it may be in the range of 3.56 to 8.34%. It is preferable that the developed area ratio Sdr of the interface on at least one surface of the thermally conductive sheet 1 satisfies the above range, and the developed area ratio Sdr of the interfaces on both surfaces may satisfy the above range.

Thermal conductive sheet 1 has the arithmetic mean curvature of the peak Spc (1/mm) and the developed area ratio of the interface Sdr (%), which are measured according to ISO 25178 using a scanning white interference microscope with a 20x objective lens. When a graph is created in which the values are plotted with Spc as the horizontal axis and Sdr as the vertical axis, it is preferable that Spc and Sdr satisfy the following formula 1. The thermally conductive sheet 1 can more effectively reduce contact thermal resistance under low load by satisfying Formula 1 in addition to having an average height Spk of the protruding peaks of 3 μm or less.
Formula 1: Y=0.0153X-(15.547±10)
(In

formula

1, 0≦X≦2500 and 0≦Y≦20.)

That is, when the values of the thermally conductive sheet 1 are plotted with the arithmetic mean curvature Spc (1/mm) of the peak on the horizontal axis and the developed area ratio Sdr (%) of the interface on the vertical axis, the plotted values are as follows. Preferably, it exists within a region surrounded by Formula 1A and Formula 1B.
Formula 1A: Y=0.0153X-25.547
Formula 1B: Y=0.0153X-5.547
(In Formula 1A and Formula 1B, 0≦X≦2500 and 0≦Y≦20.)

The thermally conductive sheet 1 has ^a contact thermal resistance of 0.10° C.cm 2 /W or less when 1.4 kgf/cm ² is applied, measured according to ASTM-D5470, and 0.09° C.cm ² /W. It may be below W, it may be below 0.08°C·cm ² /W, it may be below 0.07°C·cm ² /W, it may be below 0.06°C·cm ² /W. It may be. The lower limit of the contact thermal resistance of the thermally conductive sheet 1 when pressurized with 1.4 kgf/cm ² is not particularly limited, and is preferably a lower value, exceeding 0° C.cm ² /W, for example 0 It can be .02°C·cm ² /W or more, or it can be 0.05°C·cm ² /W or more. The thermally conductive sheet 1 may have a contact thermal resistance when pressurized with 1.4 kgf/cm ² in the range of 0.020 to 0.083° C.cm ² /W, and may be in the range of 0.060 to 0.083. It may be in the range of °C·cm ² /W, it may be in the range of 0.060 to 0.082 °C·cm ² /W, it may be in the range of 0.060 to 0.077 °C·cm ² /W It may be in the range of 0.060 to 0.075°C·cm ² /W.

The thermally conductive sheet 1 has ^a contact thermal resistance of 0.10° C.cm 2 /W or less when 2.1 kgf/cm ² is applied, measured according to ASTM-D5470, and 0.08° C.cm ² /W. It may be below W, may be below 0.07°C·cm ² /W, and may be below 0.06°C·cm ² /W. The lower limit of the contact thermal resistance of the thermally conductive sheet 1 when pressurized with 2.1 kgf/cm ² is not particularly limited, and is preferably a lower value, exceeding 0° C.cm ² /W, for example 0 It can be .03°C·cm ² /W or more, or it can be 0.05°C·cm ² /W or more. The thermally conductive sheet 1 may have a contact thermal resistance when pressurized with 2.1 kgf/cm ² in the range of 0.039 to 0.093° C.cm ² /W, or 0.055 to 0.075. It may be in the range of °C·cm ² /W, it may be in the range of 0.055 to 0.073 °C·cm ² /W, it may be in the range of 0.055 to 0.070 °C·cm ² /W It may be in the range of 0.055 to 0.069°C·cm ² /W.

The thermally conductive sheet 1 may have a contact thermal resistance of 0.072°C·cm 2 /W or less when 2.8 kgf/cm ² is applied, measured according to ASTM-D5470, and may have a contact thermal resistance of 0.065°C·cm ² /W or less. It may be less than cm ² /W. The lower limit of the contact thermal resistance of the thermally conductive sheet 1 when pressurized with 2.8 kgf/cm ² is not particularly limited, and is preferably a lower value, exceeding 0° C.cm ² /W, for example 0 It can be .04° C.cm ² /W or more. The thermally conductive sheet 1 may have a contact thermal resistance of 0.052 to 0.072° C.cm 2 /W when pressurized with 2.8 kgf/cm ² , for example, and may have a contact thermal resistance of 0.052 to 0.072° C.cm ² /W. It may be in the range of 0.071°C.cm ² /W, it may be in the range of 0.052 to 0.065°C.cm ² /W, it may be in the range of 0.052 to 0.064°C.cm ² /W. It may be in the range of 0.052 to 0.061°C·cm ² /W, or may be in the range of 0.052 to 0.054°C·cm ² /W.

The thermally conductive sheet 1 may have a contact thermal resistance of 0.086° C.cm ² /W or less when 3.5 kgf/cm ² is applied, measured according to ASTM-D5470, and 0.068° C. cm ² /W or less, or 0.062° C.cm ² /W or less. The lower limit of the contact thermal resistance of the thermally conductive sheet 1 when pressurized with 3.5 kgf/cm ² is not particularly limited, and is preferably a lower value, exceeding 0° C.cm ² /W, for example 0 It can be .02°C·cm ² /W or more, or it can be 0.04°C·cm ² /W or more. The thermally conductive sheet 1 may have a contact thermal resistance of, for example, 0.024 to 0.086° C.cm 2 /W when pressurized with 3.5 kgf/cm ² , or 0.045 to 0.086° C.cm ² /W. It may be in the range of 0.068°C.cm ² /W, it may be in the range of 0.045 to 0.062°C.cm ² /W, it may be in the range of 0.045 to 0.060°C.cm ² /W. It may be within a range of 0.045 to 0.051° C.cm ² /W.

FIG. 2 is a cross-sectional view showing an example of the surface of the thermally conductive sheet 1. As shown in FIG. As shown in FIG. 2, for example, at least one surface of the thermally conductive sheet 1 is a polished surface, and it is preferable that this polished surface has polishing residue 5. The polishing residue 5 is, for example, a lump made of a thermally conductive composition containing a binder resin 2, a fibrous filler 3, and another thermally conductive filler 4. By having the polishing residue 5 on the surface of the thermally conductive sheet 1, the surface of the thermally conductive sheet 1 can be made smoother, and as described above, the average height Spk of the protruding peaks of the thermally conductive sheet 1 can be made smoother. is 3 μm or less, and ^contact thermal resistances of 0.10° C.cm 2 /W or less when pressurized at 1.4 kgf/cm ² and 2.1 kgf/cm ² tend to be obtained.

The thermally conductive sheet 1 having polishing residue 5 means that the polishing residue 5 is present on the surface of the thermally conductive sheet 1 to such an extent that the average height Spk of the protruding peaks of the thermally conductive sheet 1 is 3 μm or less. is preferable, and for example, it may have polishing residue 5 almost uniformly over the entire surface, or it may have polishing residue 5 partially (in the form of islands) on the surface, for example, as shown in FIG. . Whether or not the thermally conductive sheet 1 has polishing residues 5 on the surface can be determined, for example, by pasting an adhesive tape on the surface of the thermally conductive sheet 1 and then peeling off the adhesive tape. You can check whether it is transferred or not.

Regarding the size of the polishing residue 5, as described above, the average height Spk of the protruding peaks of the thermally conductive sheet 1 is 3 μm or less, and when a pressure of 1.4 kgf/cm ² is applied, and when a pressure of 2.1 kgf/cm ² is applied. In order to keep the contact thermal resistance at 0.10° C.cm ² /W or less, it is preferable that the average particle size and maximum particle size of the polishing residue 5 are not too large. For example, the average particle diameter of the polishing residue 5 may be 50 μm or less, 40 μm or less, 35 μm or less, 30 μm or less, or 20 μm or less. The thickness may be 15 μm or less, 10 μm or less, or in the range of 0.5 to 40 μm. Regarding the average particle diameter of the polishing residue 5, in the case of the irregularly shaped polishing residue 5, the length (diameter) of the longest part of the particle is taken into consideration. Further, the maximum particle diameter of the polishing residue 5 may be, for example, 100 μm or less, 90 μm or less, 80 μm or less, 70 μm or less, or 50 μm or less. It may be in the range of ~100 μm.

The thickness of the thermally conductive sheet 1 can be appropriately selected depending on the purpose, and may be, for example, 0.05 mm or more, 0.1 mm or more, or 0.2 mm or more. It may be 0.3 mm or more. Further, the upper limit of the thickness of the thermally conductive sheet 1 can be, for example, 5 mm or less, may be 4 mm or less, may be 3 mm or less, may be 2 mm or less, and may be 1 mm or less. It may be 0.5 mm or less. For example, the thickness of the thermally conductive sheet 1 can be determined by measuring the thickness B of the thermally conductive sheet 1 at five arbitrary locations and calculating the arithmetic mean value thereof.

In the thermally conductive sheet 1, as the thermal resistance of the sheet itself becomes lower, the contribution of the contact thermal resistance to the total thermal resistance generated between the sheet and the adherend tends to increase. As mentioned above, this tendency becomes more pronounced as the sheet becomes thinner. In other words, in the thermally conductive sheet 1, as the thermal conductivity of the sheet itself increases, the proportion of the contact thermal resistance in the total thermal resistance value increases. In this technology, the contact thermal resistance is reduced by setting the average height Spk of the protruding peaks of the thermally conductive sheet 1 to a predetermined value or less for the thermally conductive sheet 1 in which the fibrous filler 3 is oriented in the thickness direction. As a result, the total thermal resistance value can be reduced.

Next, the binder resin 2, fibrous filler 3, and other thermally conductive filler 4, which are examples of the structure of the thermally conductive sheet 1, will be explained.

<Binder resin>
Binder resin 2 is for holding fibrous filler 3 and other thermally conductive filler 4 within thermally conductive sheet 1 . The binder resin 2 is selected depending on the properties required of the thermally conductive sheet 1, such as mechanical strength, heat resistance, and electrical properties. 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, Fluoropolymers 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 polyamide, aromatic polyamide, polyimide, polyamideimide, polymethacrylic acid, polymethacrylic acid methyl ester, etc. Examples include acid esters, polyacrylic acids, polycarbonates, polyphenylene sulfides, polysulfones, polyethersulfones, polyethernitrile, polyetherketones, polyketones, liquid crystal polymers, and ionomers.

Examples of 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, and vinyl chloride-based thermoplastic elastomers. , polyester thermoplastic elastomer, polyurethane thermoplastic elastomer, polyamide thermoplastic elastomer, and the like.

Examples of the thermosetting resin include crosslinked rubber, epoxy resin, phenol resin, polyimide resin, unsaturated polyester resin, diallyl phthalate resin, addition reaction type silicone resin, condensation reaction type silicone resin, 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, Examples include chlorosulfonated polyethylene rubber, butyl rubber, halogenated butyl rubber, fluororubber, urethane rubber, and silicone rubber.

As the binder resin 2, silicone resin is preferable, for example, from the viewpoint of adhesion between the heat generating surface of the heat generating element (for example, an electronic component) and the heat sink surface. The silicone resin is, for example, a two-component addition type, which is mainly composed of silicone (polyorganosiloxane) having an alkenyl group, a main resin containing a curing catalyst, and a curing agent having a hydrosilyl group (Si-H group). Reactive silicone resins can be used. As the silicone having an alkenyl group, a polyorganosiloxane having at least two alkenyl groups in one molecule can be used. As an example, polyorganosiloxanes having vinyl groups can be used. The curing catalyst is a catalyst for promoting an addition reaction between an alkenyl group in the silicone having an alkenyl group and a 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, such as platinum group curing catalysts, such as simple platinum group metals such as platinum, rhodium, and palladium, platinum chloride, and complexes of platinum and organic compounds. etc. can be used. As the curing agent having a hydrosilyl group, for example, a polyorganosiloxane having a hydrosilyl group (organohydrogenpolysiloxane having at least two hydrogen atoms in one molecule directly bonded to a silicon atom) can be used.

For example, when using the above-mentioned two-component addition reaction type silicone resin as the binder resin 2, the ratio of the main component (silicone main component) to the curing agent component, that is, the polyorganosiloxane having a vinyl group and The mixing ratio of the polyorganosiloxane having a hydrosilyl group is not particularly limited, and may be a mixing ratio such that the hydrosilyl group is in the range of 0.3 to 0.9 mol per mol of the vinyl group. The mixing ratio may be in the range of 4 to 0.7 mol.

The content of the binder resin 2 in the thermally conductive sheet 1 is not particularly limited, and can be appropriately selected depending on the purpose. For example, the content of the binder resin 2 in the thermally conductive sheet 1 may be 20 volume% or more, may be 24 volume% or more, may be 28 volume% or more, or may be 30 volume%. The content may be more than 32% by volume, or more than 34% by volume. Further, the upper limit of the content of the binder resin 2 in the thermally conductive sheet 1 can be 60 volume% or less, may be 50 volume% or less, or may be 40 volume% or less, It may be 38 volume% or less, 35 volume% or less, 32 volume% or less, or 30 volume% or less. The content of the binder resin 2 in the thermally conductive sheet 1 may be, for example, in the range of 24 to 35% by volume, or may be in the range of 24 to 32% by volume. The binder resin 2 may be used alone or in combination of two or more. When using two or more types of binder resins 2, it is preferable that the total amount thereof satisfies the above-mentioned content.

<Fibrous filler>
The fibrous filler 3 is not particularly limited as long as it is fibrous and has the necessary thermal conductivity, and examples thereof include carbon fibers, aluminum nitride whiskers, and the like. Below, the case where carbon fiber is used as a fibrous thermally conductive filler will be described in detail as an example. The fibrous filler 3 has a shape that has a long axis and a short axis, the lengths of the long axis and the short axis are different, and the aspect ratio (average long axis length / average short axis length) exceeds 1. including. The fibrous filler 3 may be used alone or in combination of two or more.

Examples of carbon fiber include 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) Carbon fibers synthesized by a method such as a carbon fiber growth method) can be used. Among these, pitch-based carbon fibers are preferred from the viewpoint of thermal conductivity.

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. Further, the average fiber diameter (average minor axis length) of the fibrous filler 3 can be appropriately selected depending on the purpose, and can be, for example, 4 to 20 μm, or may be 5 to 14 μm. The aspect ratio of the fibrous filler 3 can be appropriately selected depending on the purpose. For example, from the viewpoint of thermal conductivity, it can be set to 8 or more, and may be in the range of 9 to 30. The average major axis length and average minor axis length of the fibrous filler 3 can be measured using, for example, a microscope or a scanning electron microscope (SEM).

From the viewpoint of thermal conductivity of the thermally conductive sheet 1, the content of the fibrous filler 3 in the thermally conductive sheet 1 can be, for example, 5% by volume or more, and may be 10% by volume or more. , may be 14 volume% or more, may be 20 volume% or more, may be 22 volume% or more, may be 24 volume% or more, or may be 26 volume% or more. . Further, from the viewpoint of formability of the thermally conductive sheet 1, the content of the fibrous filler 3 in the thermally conductive sheet 1 can be, for example, 30% by volume or less, and even if it is 28% by volume or less. Generally, it may be 26% by volume or less, 20% by volume or less, or 18% by volume or less. The content of the fibrous filler 3 in the thermally conductive sheet 1 may be, for example, in the range of 14 to 28% by volume, or may be in the range of 14 to 26% by volume. When using two or more types of fibrous fillers 3, it is preferable that the total amount thereof satisfies the above-mentioned content.

<Other thermally conductive fillers>
The other thermally conductive filler 4 is a thermally conductive filler other than the fibrous filler 3. Other thermally conductive fillers 4 include, for example, spherical, powdery, granular, scale-like, and other thermally conductive fillers. From the viewpoint of thermal conductivity of the thermally conductive sheet 1, the material of the other thermally conductive filler 4 includes, for example, an inorganic filler, preferably a ceramic filler, and specific examples include aluminum oxide (alumina, sapphire), Examples include aluminum nitride, aluminum, aluminum hydroxide, and boron nitride. The other thermally conductive fillers 4 may be used alone or in combination of two or more. For example, as the other thermally conductive filler 4, two or more types of thermally conductive fillers having different average particle diameters may be used in combination.

In particular, other thermally conductive fillers 4 are selected from aluminum oxide, aluminum nitride, aluminum, and aluminum hydroxide, taking into consideration the thermal conductivity of the thermally conductive sheet 1 and the specific gravity of the thermally conductive sheet 1. It is preferable that at least one kind is selected. For example, as the other thermally conductive filler 4, aluminum oxide and aluminum nitride may be used together, aluminum oxide, aluminum nitride and aluminum may be used together, or aluminum hydroxide may be used alone. good.

The average particle diameter of aluminum nitride may be in the range of 0.1 to 10 μm, for example from the viewpoint of the specific gravity of the thermally conductive sheet 1, may be in the range of 0.5 to 5 μm, and may be in the range of 0.5 to 5 μm. The range may be 3 μm or 0.5 to 2 μm. The average particle diameter of aluminum oxide can be in the range of 0.1 to 10 μm, for example from the viewpoint of the specific gravity of the thermally conductive sheet 1, and may be in the range of 0.1 to 8 μm, and may be in the range of 0.1 to 8 μm. It may be in the range of 7 μm or may be in the range of 0.1 to 3 μm. The average particle diameter of aluminum hydroxide may be in the range of 0.1 to 10 μm, 0.5 to 5 μm, or 0.5 μm in terms of the specific gravity of the thermally conductive sheet 1, for example. 3 μm, or 0.5 to 2 μm. The average particle diameter of aluminum can be less than 15 μm, for example from the viewpoint of the specific gravity of the thermally conductive sheet 1, and may be in the range of 1 to 14 μm.

The content of other thermally conductive fillers 4 in the thermally conductive sheet 1 can be appropriately selected depending on the purpose. The content of the other thermally conductive filler 4 in the thermally conductive sheet 1 may be, for example, 10% by volume or more, may be 15% by volume or more, or may be 20% by volume or more. , may be 25 volume% or more, may be 30 volume% or more, may be 35 volume% or more, may be 39 volume% or more, may be 45 volume% or more. . Further, the upper limit of the content of the other thermally conductive filler 4 in the thermally conductive sheet 1 can be, for example, 55% by volume or less, 50% by volume or less, and 49% by volume or less. The content may be 45% by volume or less, or may be 40% by volume or less. The content of the other thermally conductive filler 4 in the thermally conductive sheet 1 may be in the range of 39 to 50% by volume, or may be in the range of 39 to 49% by volume, for example.

For example, when using aluminum oxide and aluminum nitride together as the other thermally conductive filler 4, the content of aluminum nitride in the thermally conductive sheet 1 is in the range of 15 to 35% by volume, and the content of aluminum oxide is in the range of 15 to 35% by volume. It can range from 5 to 25% by volume. In addition, when using aluminum oxide, aluminum nitride, and aluminum together as other thermally conductive filler 4, for example, the content of aluminum nitride in the thermally conductive sheet 1 should be in the range of 10 to 30% by volume, and aluminum oxide The content of aluminum can be in the range of 1 to 20% by volume, and the content of aluminum can be in the range of 10 to 30% by volume.

<Other ingredients>
The thermally conductive 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 coupling agents, dispersants, curing accelerators, retarders, tackifiers, plasticizers, flame retardants, antioxidants, stabilizers, colorants, and solvents. For example, in order to further improve the dispersibility of the fibrous filler 3 and other thermally conductive fillers 4, the thermally conductive sheet 1 may be treated with a fibrous filler 3 treated with a coupling agent and/or a coupling agent. Other thermally conductive fillers 4 may also be used.

The hardness of such a thermally conductive sheet 1 is preferably, for example, 40 to 95 in terms of Shore OO hardness, from the viewpoint of ease of polishing and conformability to an adherend due to the flexibility of the sheet.

<Method for manufacturing thermally conductive sheet>
Next, a method for manufacturing the thermally conductive sheet 1 will be explained. The method for manufacturing the thermally conductive sheet 1 includes the following steps A, B, and C.

<Process A>
In step A, a thermally conductive composition containing a binder resin 2, a fibrous filler 3, and a thermally conductive filler 4 other than the fibrous filler 3 is molded into a predetermined shape and cured. A molded body of the conductive composition is obtained.

In an example of process A, first, by dispersing the fibrous filler 3 and other thermally conductive filler 4 into the binder resin 2, the binder resin 2, the fibrous filler 3, and the other thermally conductive filler 4 are combined. A thermally conductive composition containing the following is produced. The thermally conductive composition is prepared by uniformly mixing the binder resin 2, the fibrous filler 3, the other thermally conductive filler 4, and other components mentioned above as needed by a known method. Can be prepared.

Subsequently, the prepared thermally conductive composition is extruded and then cured to obtain a columnar cured product (molded body). The extrusion molding method is not particularly limited, and can be appropriately adopted from various known extrusion molding methods depending on the viscosity of the thermally conductive composition, the characteristics required of the thermally conductive sheet 1, and the like. In the extrusion molding method, when extruding the thermally conductive composition from a die, the binder resin 2 in the thermally conductive composition flows, and the fibrous filler 3 is oriented along the flow direction. The size and shape of the columnar cured product can be determined depending on the required size of the thermally conductive sheet 1. For example, a rectangular parallelepiped with a vertical cross section of 0.5 to 15 cm and a horizontal cross section of 0.5 to 15 cm may be mentioned. The length of the rectangular parallelepiped may be determined as necessary.

<Process B>
In step B, the molded body of the thermally conductive composition obtained in step A is cut into sheets to obtain molded sheets. In an example of step B, the columnar cured product obtained in step A is cut into a predetermined thickness in the length direction of the column to obtain a molded sheet. The fibrous filler 3 is exposed on the surface (cut surface) of the molded sheet obtained in step B. The method for cutting the molded body is not particularly limited, and can be appropriately selected from known slicing devices depending on the size and mechanical strength of the molded body. When extrusion molding is used to obtain a molded product, the fibrous filler 3 may be oriented in the extrusion direction, so the cutting direction of the molded product is 60 to 120 degrees to the extrusion direction. The direction is preferably 70 to 100 degrees, and even more preferably 90 degrees (substantially perpendicular). The cutting direction of the molded body is not particularly limited other than the above, and can be appropriately selected depending on the purpose of use of the thermally conductive sheet 1 and the like.

<Process C>
Usually, the molded sheet obtained in step B has irregularities on its surface. For example, as shown in FIG. 2, the molded sheet obtained in step B has a plurality of convex portions 1a on the surface and concave portions adjacent to the convex portions 1a. Therefore, the molded sheet obtained in step B usually has an average height Spk of the protruding peaks measured according to ISO 25178 of more than 3 μm. When using a molded sheet with such irregularities on its surface, air tends to get mixed in between the molded sheet and the adherend, making it difficult to reduce the contact thermal resistance of the molded sheet. .

Therefore, in step C, by polishing the molded sheet obtained in step B, binder resin 2, fibrous filler 3, and other thermally conductive filler 4 are removed from the convex portions 1a on the surface of the molded sheet. As a result, the concave portions on the surface of the formed sheet are covered (in other words, the polishing residue 5 scraped from the convex portions 1a remains in the concave portions), so that the average height Spk of the protruding peaks of the thermally conductive sheet 1 is reduced to 3 μm. The contact area between the thermally conductive sheet 1 and the adherend can be improved, suppressing the mixing of air between the thermally conductive sheet 1 and the adherend, and improving the thermal conductivity. The contact thermal resistance of the sheet 1 can be reduced. In addition to this, by coating the surface of the thermally conductive sheet 1 with the bled binder resin 2, the reduction in the average height Spk of the protruding peaks of the thermally conductive sheet 1 is facilitated, and the thermal conduction The contact area between the thermally conductive sheet 1 and the adherend is further improved, and the mixture of air between the thermally conductive sheet 1 and the adherend is more effectively suppressed, and the contact heat of the thermally conductive sheet 1 is reduced. It is believed that the resistance can be further reduced.

In step C, for example, the molded sheet obtained in step B is polished with a polishing member. Examples of the polishing member include those that can be brought into surface contact with the surface of the molded sheet for polishing. Examples of such abrasive members include sandpaper, wrapping films, brushes, etc., and are appropriately selected depending on durability, accuracy of abrasive grain size, and throughput. A lapping film is a film in which abrasive grains are fixed to a resin film as a base material using an adhesive. By using a polishing member such as a wrapping film that can be polished by bringing it into surface contact with the surface of the molded sheet, the binder resin 2, fibrous filler 3, and others are scraped out from the convex portions 1a on the surface of the molded sheet. The heat conductive filler 4 can more efficiently cover the recesses on the surface of the molded sheet.

As the wrapping film, for example, one using a polyester film as the base material and aluminum oxide with an average particle size of 2 to 40 μm as the abrasive grains can be used. Alternatively, a lapping film with a nominal value of #400 to #6000 can be used as an indicator of the particle size of the abrasive grains. The size and thickness of the wrapping film can be changed as appropriate depending on the size of the molded sheet to be polished. For example, the thickness of the wrapping film can be 0.01 to 0.5 mm.

FIG. 3 is a perspective view of a brush 6, which is an example of a polishing member. The brush 6 has a shape in which bristles 8 are arranged in the length direction of a columnar base material 7, as shown in FIG. 3, for example. The hair material 8 is a bundle of a plurality of hairs, and has a length B, a depth C, and a width A. The material of the brush 6 is not particularly limited, and for example, from the viewpoint of versatility, abrasion resistance, flexibility, bending resilience, etc., nylon can be used.

FIG. 4 is a perspective view for explaining an example of a method of polishing the surface of the molded sheet 9 with the brush 6. When polishing the molded sheet 9 one by one using the brush 6 as the polishing member, use a fixing means such as a suction pad or tape (not shown) to polish the back side of the surface of the molded sheet 9 to be polished or It is preferable to temporarily fasten the end on the side where processing is to be started. As an example of temporary fixing using tape, when polishing with the brush 6 in the direction of D1 in FIG. to move the brush 6. When temporarily fixing the back surface of the molded sheet 9, there is no restriction on the moving direction of the brush 6. The means for moving the brush 6 may be manual or automatic. When polishing the molded sheet 9, move the brush 6 so that the tips of the bristles 8 touch the surface of the molded sheet 9 in the entire direction A, and stroke with the tips of the bristles 8. It is preferable to let

The polishing method is not limited to moving the polishing member in one direction from one end side 9A to the other end side 9B of the surface of the molded sheet 9. For example, polishing the surface of the molded sheet 9 from one end 9A to the other end 9B with a polishing member, and polishing the surface of the molded sheet 9 from the other end 9B to one end 9A with a polishing member. In other words, the polishing member may be reciprocated to polish the surface of the molded sheet 9 from one end side 9A to the other end side 9B. As an example, when the brush 6 is used, it may be polished by reciprocating in the D1 direction and the D2 direction from one end side 9A to the other end side 9B of the surface of the molded sheet 9 in FIG. FIG. 5 is a perspective view for explaining an example of a method of continuously polishing the surfaces of a plurality of molded body sheets with a brush. As shown in FIG. 5, when polishing a plurality of thermally conductive sheets 1 in succession, for example, the polishing member is fixed, a plurality of formed sheets 9 are placed on a conveyor 10, and the conveyor 10 is By moving, a plurality of molded sheets 9 may be polished continuously. The direction of movement of the conveyor 10 may be one direction, D3 direction or D4 direction in FIG. 5, or may be reciprocated in the D3 direction and D4 direction. It is also possible to install and use a plurality of brushes. Furthermore, a rolled brush may be rotated and used.

Regarding the polishing method, only one side of the molded sheet 9 may be polished, or after one side of the molded sheet 9 is polished, the other side may also be polished.

When using a wrapping film as the polishing member, the polishing method is the same as the polishing method for the brush 6 described above, as long as the wrapping film is brought into contact with the surface of the molded sheet 9 and at least one of the molded sheet 9 and the wrapping film is moved. In addition, various modifications can be made in the movement method, movement direction, arrangement, and shape.

The number of times of polishing can be changed as appropriate depending on the polishing method, the type of polishing member, the particle size of the polishing member, etc. It is believed that the greater the number of times of polishing, the easier it is for the concave portions on the surface of the molded sheet 9 to be covered by the binder resin 2, fibrous filler 3, and other thermally conductive filler 4 scraped out from the convex portions 1a on the surface of the molded sheet. Therefore, it is preferable to set the number of times to a certain number or more. The number of times of polishing can be, for example, 1 or more times, 10 times or more, 20 times or more, 30 or more times, 40 times or more, 50 times or more, It may be more than 60 times, it may be more than 70 times, it may be more than 80 times, it may be more than 90 times, it may be more than 100 times, it may be more than 200 times, it may be more than 300 times, it may be more than 400 times. The number of times may be more than 1,000 times, or may be in the range of 100 to 1,000 times, or may be in the range of 100 to 400 times. In this specification, the number of times of polishing is defined as one time of polishing in one direction from one end side 9A to the other end side 9B of the surface of the molded sheet 9 in FIG. 4, for example.

As described above, the thermally conductive sheet 1 obtained in step C has polishing residue 5 generated by polishing the convex portions 1a existing on the surface of the molded sheet with a polishing member. As described above, by having the polishing residue 5 on the surface, the thermally conductive sheet 1 has the above-mentioned physical properties, that is, the average height Spk of the protruding peaks measured according to ISO 25178 is 3 μm or less, and the ASTM-D5470 The contact thermal resistance when pressurized with 1.4 kgf/cm ² and when pressurized with 2.1 kgf/cm ² is 0.10° C.cm ² /W or less, which is measured according to the standard, tends to be easily satisfied.

The size of the polishing residue 5 that the thermally conductive sheet 1 has on the surface can be changed as appropriate depending on the material and particle size of the polishing member used. For example, when a lapping film or brush 6 is used as the polishing member, the maximum size of the polishing residue 5 can be 100 μm or less, and can also be in the range of 0.5 to 100 μm.

The polishing member may have the same roughness in the polishing step (step C). Polishing members having the same roughness in the polishing process mean, for example, polishing members with the same abrasive grain size in step C, rather than using two or more types of polishing members with different abrasive grain sizes together. It means to use. In the method for manufacturing the thermally conductive sheet 1, even when the molded sheet 9 is polished using a polishing member having the same roughness in step C, the protruding peaks of the thermally conductive sheet 1 measured according to ISO 25178 By setting the average height Spk of 3 μm or less, the contact thermal resistance of the thermally conductive sheet 1 can be reduced. In this way, in the method for manufacturing the thermally conductive sheet 1, the average height of the protruding peaks of the thermally conductive sheet 1 can be improved in polishing in step C without using two or more types of polishing members with different abrasive grain sizes. Since the thickness Spk can be reduced to 3 μm or less, the process can be simplified. In addition, in step C of the method for manufacturing the thermally conductive sheet 1, two or more types of polishing members having different abrasive grain sizes may be used together.

According to the method for manufacturing a thermally conductive sheet having such steps A, B, and C, the thermally conductive sheet 1 described above can be obtained.

The method for manufacturing the thermally conductive sheet 1 is not limited to the above-mentioned example, and may further include a pressing step D. Process D may be between process B and process C, or may be after process C. For example, an example of the method for manufacturing the thermally conductive sheet 1 includes, in addition to the above-mentioned steps A to C, a step D of pressing the surface of the molded sheet 9 obtained in step B, and in step C, The thermally conductive sheet 1 may be obtained by polishing the surface of the molded sheet 9 pressed in step D. By further including the pressing step D, the surface of the resulting thermally conductive sheet 1 can be made smoother, and its adhesion to other members can be further improved. As a pressing method, a pair of press devices consisting of a flat plate and a press head with a flat surface can be used. Alternatively, it may be pressed using pinch rolls. The pressure during pressing can be, for example, 0.1 to 100 MPa. In order to further enhance the pressing effect and shorten the pressing time, the pressing is preferably performed at a temperature equal to or higher than the glass transition temperature (Tg) of the binder resin 2. For example, the pressing temperature can be from 0 to 180°C, may be within the temperature range of room temperature (eg, 25°C) to 100°C, or may be from 30 to 100°C.

<Electronic equipment>
The thermally conductive sheet 1 is, for example, placed between a heating element and a heat radiating element to allow the heat generated by the heating element to escape to the heat radiating element. ). The electronic device includes at least a heating element, a heat radiating element, and a thermally conductive sheet 1, and may further include other members as necessary. In this way, electronic devices to which the thermally conductive sheet 1 is applied can achieve high thermal conductivity due to the thermally conductive sheet 1 because the thermally conductive sheet 1 is sandwiched between the heating element and the heat radiating element. , the thermally conductive sheet 1 has excellent adhesion to the heating element, and excessive bleeding of the binder resin 2 from the thermally conductive sheet 1 can be suppressed.

In particular, in electronic devices to which the thermally conductive sheet 1 is applied, since the average height Spk of the protruding peaks of the thermally conductive sheet 1 is 3 μm or less, as described above, the thermally conductive sheet 1 and the adherend are The contact area with a certain heating element or heat radiating element is increased, and air is prevented from entering between the thermally conductive sheet 1 and the adherend, so the contact heat during low load (low pressurization) is reduced. Resistance can be reduced more effectively.

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

The heat sink is not particularly limited, and includes, for example, heat sinks, heat spreaders, and other heat sinks that are used in combination with integrated circuit elements, transistors, optical transceiver casings, and the like. Examples of the material for the heat sink and heat spreader include copper and aluminum. In addition to heat spreaders and heat sinks, the heat dissipation body may be anything that conducts heat generated from a heat source and dissipates it to the outside, such as a heat dissipator, cooler, die pad, printed circuit board, cooling fan, Peltier element, etc. Examples include heat pipes, vapor chambers, metal covers, and casings. A heat pipe is, for example, a cylindrical, substantially cylindrical, or flat cylindrical hollow structure.

FIG. 6 is a cross-sectional view showing an example of a semiconductor device to which a thermally conductive sheet is applied. For example, as shown in FIG. 6, the thermally conductive sheet 1 is mounted on a semiconductor device 50 built into various electronic devices, and is sandwiched between a heat generating body and a heat radiating body. A semiconductor device 50 shown in FIG. 6 includes an electronic component 51, a heat spreader 52, and a thermally conductive sheet 1, and the thermally conductive sheet 1 is sandwiched between the heat spreader 52 and the electronic component 51. The thermally conductive sheet 1 is sandwiched between the heat spreader 52 and the heat sink 53, thereby forming a heat radiating member that radiates heat from the electronic component 51 together with the heat spreader 52. The mounting location of the thermally 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, and can be appropriately selected depending on the configuration of the electronic device or semiconductor device. The heat spreader 52 is formed into a rectangular plate shape, for example, and has a main surface 52a facing the electronic component 51, and a side wall 52b erected along the outer periphery of the main surface 52a. In the heat spreader 52, a thermally conductive sheet 1 is provided on a main surface 52a surrounded by side walls 52b, and a heat sink 53 is provided on the other surface 52c opposite to the main surface 52a via the thermally conductive sheet 1.

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

<Example 1>
32% by volume of silicone resin, 14% by volume of aluminum oxide (average particle diameter: approximately 2 μm), 25% by volume of aluminum nitride (average particle diameter: approximately 1 μm), and 28% by volume of carbon fiber (average fiber length: approximately 150 μm). A thermally conductive composition was prepared by uniformly mixing the above and 1% by volume of a coupling agent. This thermally conductive composition was poured into a mold (opening: 50 mm x 50 mm) having a rectangular parallelepiped internal space by extrusion molding, and heated in an oven at 100°C for 6 hours to form a columnar cured product ( A molded body block) was formed. Note that a polyethylene terephthalate film that had been subjected to a peeling treatment was pasted on the inner surface of the mold so that the peeled surface was on the inside. By cutting (slicing) the obtained columnar cured product into a sheet with a thickness of 0.2 mm using a slicer in a direction substantially perpendicular to the length direction of the column, the carbon fibers are cut into sheets with a thickness of 0.2 mm. A molded sheet oriented in the direction was obtained. Both surfaces of this molded sheet were rubbed 400 times in one direction from one end to the other with a #4000 wrapping film (manufactured by 3M) having a thickness of about 100 μm. A thermally conductive sheet was obtained. Thus, the thermally conductive sheet obtained in Example 1 had a polished surface and had polishing residue on the surface.

<Example 2>
A thermally conductive sheet was obtained by polishing the surface of a molded sheet in the same manner as in Example 1, except that the thickness of the thermally conductive sheet was changed to 0.3 mm. Thus, the thermally conductive sheet obtained in Example 2 had a polished surface and had polishing residue on the surface.

<Example 3>
A thermally conductive sheet was obtained by polishing the surface of a molded sheet in the same manner as in Example 1, except that the thickness of the thermally conductive sheet was changed to 0.5 mm. Thus, the thermally conductive sheet obtained in Example 3 had a polished surface and had polishing residue on the surface.

<Example 4>
24% by volume of silicone resin, 10% by volume of aluminum oxide (average particle diameter: approximately 2 μm), 20% by volume of aluminum nitride (average particle diameter: approximately 1 μm), and 19% by volume of aluminum (average particle diameter: approximately 6 μm). A thermally conductive composition was prepared by uniformly mixing 26% by volume of carbon fibers (average fiber length: about 150 μm) and 1% by volume of a coupling agent. This thermally conductive composition was poured into a mold (opening: 50 mm x 50 mm) having a rectangular parallelepiped internal space by extrusion molding, and heated in an oven at 100°C for 6 hours to form a columnar cured product ( A molded body block) was formed. Note that a polyethylene terephthalate film that had been subjected to a peeling treatment was pasted on the inner surface of the mold so that the peeled surface was on the inside. By cutting (slicing) the obtained columnar cured product into a sheet with a thickness of 0.3 mm using a slicer in a direction substantially perpendicular to the length direction of the column, the carbon fibers are cut into sheets with a thickness of 0.3 mm. A molded sheet oriented in the direction was obtained. Both surfaces of this molded sheet were rubbed 100 times in one direction from one end of the surface to the other end with a #4000 wrapping film (manufactured by 3M) to form a thermally conductive sheet. I got it. Thus, the thermally conductive sheet obtained in Example 4 had a polished surface and had polishing residue on the surface.

<Example 5>
Uniformly mix 35% by volume of silicone resin, 50% by volume of aluminum hydroxide (average particle diameter: approximately 1 μm), 14% by volume of carbon fiber (average fiber length: approximately 150 μm), and 1% by volume of coupling agent. A thermally conductive composition was prepared. This thermally conductive composition was poured into a mold (opening: 50 mm x 50 mm) having a rectangular parallelepiped internal space by extrusion molding, and heated in an oven at 100°C for 6 hours to form a columnar cured product ( A molded body block) was formed. Note that a polyethylene terephthalate film that had been subjected to a peeling treatment was pasted on the inner surface of the mold so that the peeled surface was on the inside. By cutting (slicing) the obtained columnar cured product into a sheet with a thickness of 0.3 mm using a slicer in a direction substantially perpendicular to the length direction of the column, the carbon fibers are cut into sheets with a thickness of 0.3 mm. A molded sheet oriented in the direction was obtained. Both surfaces of this molded sheet were rubbed 400 times with a No. 4000 (#4000) wrapping film (manufactured by 3M Company) to obtain a thermally conductive sheet. Thus, the thermally conductive sheet obtained in Example 5 had a polished surface and had polishing residue on the surface.

<Example 6>
28% by volume of silicone resin, 22% by volume of aluminum oxide (average particle diameter: approximately 2 μm), 23% by volume of aluminum nitride (average particle diameter: approximately 1 μm), and 26% by volume of carbon fiber (average fiber length: approximately 150 μm). A thermally conductive composition was prepared by uniformly mixing the above and 1% by volume of a coupling agent. This thermally conductive composition was poured into a mold (opening: 50 mm x 50 mm) having a rectangular parallelepiped internal space by extrusion molding, and heated in an oven at 100°C for 6 hours to form a columnar cured product ( A molded body block) was formed. Note that a polyethylene terephthalate film that had been subjected to a peeling treatment was pasted on the inner surface of the mold so that the peeled surface was on the inside. By cutting (slicing) the obtained columnar cured product into a 1.0 mm thick sheet with a slicer in a direction substantially perpendicular to the length direction of the column, the carbon fibers are cut into sheets with a thickness of 1.0 mm. A molded sheet oriented in the direction was obtained. Both surfaces of this molded sheet were rubbed 200 times in one direction from one end of the surface to the other with a #4000 wrapping film (manufactured by 3M) having a thickness of about 100 μm. A thermally conductive sheet was obtained. Thus, the thermally conductive sheet obtained in Example 6 had a polished surface and had polishing residue on the surface.

<Example 7>
A thermally conductive sheet was obtained by polishing the surface of the molded sheet in the same manner as in Example 6, except that the thickness of the molded sheet was changed to 2.0 mm. The thermally conductive sheet obtained in Example 7 had a polished surface and had polishing residue on the surface.

<Comparative example 1>
In Comparative Example 1, a molded sheet obtained in the same manner as in Example 2 in which carbon fibers were oriented in the thickness direction of the sheet was pressed. Thus, in Comparative Example 1, the surface of a molded sheet obtained by slicing a columnar cured product into 0.3 mm thick sheets was pressed with a wrapping film without polishing it. Therefore, the molded sheet obtained in Comparative Example 1 did not have any polishing residue on its surface.

<Comparative example 2>
In Comparative Example 2, a composition in which silicone resin, carbon fibers, and other inorganic fillers were mixed was injected into a mold, and a magnetic field was applied in the thickness direction to orient the carbon fibers in the thickness direction. After that, it was cured to form a columnar cured product. By cutting (slicing) the obtained columnar cured product into a sheet with a thickness of 0.3 mm using a slicer in a direction substantially perpendicular to the length direction of the column, the carbon fibers are cut into sheets with a thickness of 0.3 mm. A molded sheet oriented in the direction was obtained. Thus, in Comparative Example 2, after slicing the columnar cured product into 0.3 mm thick slices, the surface of the molded sheet was not polished with a wrapping film. Therefore, the molded sheet obtained in Comparative Example 2 did not have any polishing residue on its surface.

<Comparative example 3>
28% by volume of silicone resin, 22% by volume of aluminum oxide (average particle diameter: approximately 2 μm), 23% by volume of aluminum nitride (average particle diameter: approximately 1 μm), and 26% by volume of carbon fiber (average fiber length: approximately 150 μm). A thermally conductive composition was prepared by uniformly mixing the above and 1% by volume of a coupling agent. This thermally conductive composition was poured into a mold (opening: 50 mm x 50 mm) having a rectangular parallelepiped internal space by extrusion molding, and heated in an oven at 100°C for 6 hours to form a columnar cured product ( A molded body block) was formed. Note that a polyethylene terephthalate film that had been subjected to a peeling treatment was pasted on the inner surface of the mold so that the peeled surface was on the inside. By cutting (slicing) the obtained columnar cured product into a 1.0 mm thick sheet with a slicer in a direction substantially perpendicular to the length direction of the column, the carbon fibers are cut into sheets with a thickness of 1.0 mm. A molded sheet oriented in the direction was obtained. Thus, in Comparative Example 3, after slicing the columnar cured product into 1.0 mm thick slices, the surface of the molded sheet was not polished with a wrapping film. Therefore, the molded sheet obtained in Comparative Example 3 did not have any polishing residue on its surface.

<Comparative example 4>
A molded product sheet was obtained in the same manner as in Comparative Example 3, except that the thickness when cutting (slicing) the columnar cured product into sheet shapes was 2.0 mm. Thus, in Comparative Example 4, after slicing the columnar cured product into 2.0 mm thick slices, the surface of the molded sheet was not polished with a wrapping film. Therefore, the molded sheet obtained in Comparative Example 4 did not have any polishing residue on its surface.

<Surface property parameters of thermally conductive sheet>
The surface property parameters of the thermally conductive sheets obtained in each example and the molded sheets obtained in each comparative example were measured. Specifically, the average height Spk (μm) of the protruding peaks of the thermally conductive sheet (molded body sheet), the average depth Svk (μm) of the protruding valleys, and the volume Vmp (ml/m ² ) of the protruding peaks ), the root mean square gradient Sdq, the arithmetic mean curvature of the peak Spc (1/mm), and the developed area ratio Sdr (%) of the interface were measured. These were measured in accordance with ISO 25178 using a scanning white interference microscope (Nano 3D optical interference measurement system, device name: VS-1800, manufactured by Hitachi High-Tech Corporation, measurement mode: wave mode). The lens magnification was 0.5 times for the lens inside the lens barrel and 20 times for the objective lens, and surface texture parameters were measured in a range of 50 μm in the height direction and 50 μm in the depth direction of the Z axis in an XY region of 562 μm×562 μm. For the volume Vmp of the protruding peak part, a value of 10% of the impossible area ratio was applied. The results are shown in Table 1.

<Contact thermal resistance>
The thermally conductive sheet obtained in each Example and the molded sheet obtained in each Comparative Example were measured in accordance with ASTM-D5470 at a predetermined pressure (1.4 kgf/cm ² pressure, 2 Bulk thermal resistance [℃・cm ² /W] is calculated from ^{the total thermal resistance value [℃・cm 2} ^/ ^W ] of The contact thermal resistance [°C·cm ² /W] was determined by subtracting ² /W]. In the above measurements, what is directly measured is the total thermal resistance value. The formulas used to calculate the contact thermal resistance are shown in the following formulas A and B. The total thermal resistance was measured using a thermal resistance measuring device (manufactured by Dexerials Co., Ltd.) compliant with ASTM-D5470. The pressurization time during the measurement was 250 seconds, and the average value of the measured values from 201 seconds to 250 seconds was taken as the measured value. The measurements were performed on one thermally conductive sheet while sequentially changing the pressure conditions.

Formula A: Contact thermal resistance [℃・cm ² /W] = Total thermal resistance value [℃・cm ² /W] - Bulk thermal resistance [℃・cm ² /W]
Formula B: Bulk thermal resistance [℃・cm ² /W] = Sheet thickness [m] / Bulk thermal conductivity [W/(m・K)] = 10 ^-4 ×℃・m ² /W

The bulk thermal conductivity [W/(m・K)] is determined for the thermally conductive sheet obtained in each example and the molded sheet obtained in each comparative example at a sheet thickness of 0.5 mm and 1.0 mm. , 1.5 mm respectively, and the horizontal axis is the thickness [mm] when compressed by 4 to 12% from the initial thickness of each sheet, and the total when compressed from 4 to 12% from the initial thickness of each sheet. The obtained data was plotted with the thermal resistance value [° C.cm ² /W] as the vertical axis, and the data was calculated from the reciprocal of the slope of the approximate straight line. Here, the total thermal resistance value is the total thermal resistance value of the bulk thermal resistance value and the contact thermal resistance value measured in accordance with ASTM D5470, and the bulk thermal resistance value is the thermal resistance value of the thermal conductive sheet itself. It is a value. Bulk thermal conductivity [W/(m·K)] indicates the thermal conductivity of the thermally conductive sheet itself, without considering contact with a jig during measurement. The results are shown in Table 1.

From the results of Examples 1 to 7, a thermally conductive sheet made of a cured product of a thermally conductive composition containing a binder resin, a fibrous filler, and a thermally conductive filler other than the fibrous filler, The filler is oriented in the thickness direction of the thermally conductive sheet, and the average height Spk of the protruding peaks of the thermally conductive sheet measured according to ISO 25178 is 3 μm or less, as measured according to ASTM-D5470. It was found that the contact thermal resistance when applying a pressure of 1.4 kgf/cm ² and when applying a pressure of 2.1 kgf/cm ² was 0.10° C.cm ² /W or less.

Furthermore, the thermally conductive sheets obtained in Examples 1 to 7 have a contact thermal resistance of 0.072° C.cm ² /W or less when 2.8 kgf/cm ² is applied, as measured in accordance with ASTM-D5470. That's what I found out.

The thermally conductive sheets obtained in Examples 1 to 7 had polished surfaces and had polishing residues on the surfaces. This polishing residue was confirmed to be a lump containing silicone resin, carbon fiber, and other thermally conductive fillers (aluminum oxide, aluminum nitride, aluminum, aluminum hydroxide, etc.) caused by polishing.

FIG. 7 shows the results of Examples and Comparative Examples with the horizontal axis representing the arithmetic mean curvature Spc (1/mm) of the peak of the thermally conductive sheet and the vertical axis representing the developed area ratio Sdr (%) of the interface of the thermally conductive sheet. This is a plotted graph. As shown in FIG. 7, the thermally conductive sheets obtained in Examples 1 to 7 have the arithmetic mean curvature Spc (1/mm) of the peak measured according to ISO 25178 and the developed area ratio Sdr (%) of the interface. It was found that when a graph was created in which the values were plotted with Spc on the horizontal axis and Sdr on the vertical axis, Spc and Sdr satisfied Equation 1 described above.

The molded sheets obtained in Comparative Examples 1 and 2 had an average height Spk of the protruding peaks measured according to ISO 25178 of less than 3 μm, and an average height Spk of 1.4 kgf/cm ² measured according to ASTM-D5470. It was found that the contact thermal resistance under pressure and when 2.1 kgf/cm ² was applied did not satisfy 0.10° C.cm ² /W or less. Furthermore, it was found that the average height Spk of the protruding peaks measured according to ISO 25178 did not satisfy 3 μm or less in the molded sheets obtained in Comparative Examples 3 and 4. This is thought to be because in Comparative Examples 1 to 4, the molded sheet was not polished with a polishing member (wrapping film), so no polishing residue remained on the surface of the molded sheet.

As shown in FIG. 7, the molded sheets obtained in Comparative Examples 1 to 4 have the arithmetic mean curvature of the peak Spc (1/mm) measured according to ISO 25178 and the developed area ratio Sdr (%) of the interface. When a graph is created in which the values are plotted with Spc on the horizontal axis and Sdr on the vertical axis, Spc and Sdr do not satisfy the above formula 1 (in

formula

1, 0≦X≦2500 and 0≦Y ≦20).

1 thermally conductive sheet, 1a convex portion, 2 binder resin, 3 fibrous filler, 4 other thermally conductive filler, 5 polishing residue, 6 brush, 7 base material, 8 bristle material, 9 molded sheet, 10 conveyor, 50 Semiconductor device, 51 Electronic component, 52 Heat spreader, 52a Main surface, 52b Side wall, 52c Other surface, 53 Heat sink

Claims

A thermally conductive sheet made of a cured product of a thermally conductive composition containing a binder resin, a fibrous filler, and a thermally conductive filler other than the fibrous filler,
The fibrous filler is oriented in the thickness direction of the thermally conductive sheet,
The average height Spk of the protruding peaks of the thermally conductive sheet is 3 μm or less, as measured in accordance with ISO 25178 using a scanning white interference microscope with a 20x objective lens;
A thermally conductive sheet having a contact thermal resistance of 0.10° C. cm 2 /W or less when applying a pressure of 1.4 kgf/cm 2 and 2.1 kgf/cm 2 as measured according to ASTM-D5470. .
The thermally conductive sheet according to claim 1, having a contact thermal resistance of 0.072° C.cm 2 /W or less when 2.8 kgf/cm 2 is applied, as measured in accordance with ASTM-D5470.
The arithmetic mean curvature Spc (1/mm) of the peak of the thermally conductive sheet and the developed area ratio Sdr (% ), the thermally conductive sheet according to claim 1 or 2, wherein when a graph is created in which the values are plotted with Spc as the horizontal axis and Sdr as the vertical axis, Spc and Sdr satisfy the following formula 1.
Formula 1: Y=0.0153X-(15.547±10)
(In formula 1, 0≦X≦2500 and 0≦Y≦20.)
The thermally conductive sheet according to claim 1 or 2, wherein the surface is a polished surface.
The thermally conductive sheet according to claim 1 or 2, which has polishing residue on the surface.
The thermally conductive sheet according to claim 5, wherein the polishing residue includes the binder resin, the fibrous filler, and the other thermally conductive filler.
The thermally conductive sheet according to claim 1 or 2, wherein the fibrous filler is carbon fiber.
Molding the thermally conductive composition by molding a thermally conductive composition containing a binder resin, a fibrous filler, and a thermally conductive filler other than the fibrous filler into a predetermined shape and curing it. The process of obtaining a body,
cutting the molded body into sheet shapes to obtain a molded body sheet;
obtaining a thermally conductive sheet by polishing the molded sheet with a polishing member,
A method for producing a thermally conductive sheet, wherein a polishing residue generated by the polishing and containing the binder resin, the fibrous filler, and the other thermally conductive filler remains on the surface of the thermally conductive sheet.
The method for manufacturing a thermally conductive sheet according to claim 8, wherein the polishing member is a wrapping film.
The method for manufacturing a thermally conductive sheet according to claim 8 or 9, wherein the polishing member is a polishing member having the same roughness in the polishing step.
The method for producing a thermally conductive sheet according to claim 8 or 9, wherein the fibrous filler is carbon fiber.
The method for manufacturing a thermally conductive sheet according to claim 8 or 9, wherein the fibrous filler is oriented in the thickness direction of the thermally conductive sheet.
The thermally conductive sheet has an average height Spk of the protruding peaks of 3 μm or less, which is measured in accordance with ISO 25178 using a scanning white interference microscope with an objective lens set at a magnification of 20 times, and which is measured in accordance with ASTM-D5470. The thermally conductive sheet according to claim 8, wherein the thermally conductive sheet has a contact thermal resistance of 0.10° C.cm 2 /W or less when a pressure of 1.4 kgf/cm 2 is applied and when a pressure of 2.1 kgf/cm 2 is applied. manufacturing method.