Heat conductive sheet

Abstract

To provide a heat conductive sheet which suppresses thermal degradation and mechanical damage of an electronic component, and can maintain quality of an electronic component.SOLUTION: A heat conductive sheet is composed of a heat conductive composition. The heat conductive composition contains a heat conductive filler, and an elastomer resin. A volume fraction of the heat conductive filler is 40% or more and 80% or less, on the basis of the volume of the heat conductive sheet. The storage elastic modulus of the sheet of the composition obtained by excluding the heat conductive filler in the heat conductive composition is 1 kPa or more and 15 kPa or less. The torque change amount of the composition obtained by excluding the heat conductive filler in the heat conductive composition is 0.2 dN m or less. The tack force of the heat conductive sheet is 10 N or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Electronic components are often mounted on printed wiring boards to be used as printed circuit boards, which are installed in a wide variety of electronic products, including home appliances such as refrigerators and microwave ovens, personal computers, and even mobile vehicles such as automobiles. In recent years, electronic components have become smaller and more highly integrated, and as a result, the amount of heat generated per unit area by electronic components has increased dramatically. Therefore, there is a demand for efficient heat dissipation of the heat generated by electronic components.

[0003] Patent Document 1 discloses a thermally conductive silicone rubber composition used as a material for thermally conductive sheets. Thermally conductive sheets transfer heat generated by electronic components to heat sinks, housings, and other heat-dissipating materials. Such thermally conductive sheets are typically used by incorporating them between a printed circuit board (PCB) on which electronic components are mounted and a heat-dissipating material positioned opposite the electronic component mounting surface of the PCB. When the thermally conductive sheet is used, it is compressed and embedded between the printed circuit board and the heat-dissipating material. The restoring force of the compressed thermally conductive sheet as it returns to its original state is utilized to adhere the thermally conductive sheet to the electronic components and the heat-dissipating material. This ensures good thermal conductivity at the contact surfaces between the thermally conductive sheet and the electronic components, and between the thermally conductive sheet and the heat-dissipating material. However, if a thermally conductive sheet embedded between the printed circuit board and the heat-dissipating material continuously applies a large restoring force to the electronic components, the electronic components may be damaged. Furthermore, such thermally conductive sheets require a thickness greater than the gap to be filled by the thermally conductive sheet, which increases the weight of the thermally conductive sheet and the printed circuit board incorporating the heat-dissipating mechanism.

[0004] Furthermore, if the thermally conductive sheet described above is installed between a printed circuit board on which multiple electronic components of different heights are mounted and a heat dissipation material, the thermally conductive sheet may exert a large restoring force on the relatively tall electronic components, causing damage, or the printed circuit board may warp and cause damage. On the other hand, the compressibility of the thermally conductive sheet is low for relatively short electronic components, so the adhesion between the thermally conductive sheet and the short electronic components decreases, impairing heat transfer between the thermally conductive sheet and the short electronic components.

[0005] To solve this problem, it is possible to attach multiple thermally conductive sheets of different thicknesses to printed circuit boards that have multiple electronic components of different heights mounted on them. However, this process is extremely inefficient and costly. Furthermore, when electronic components are densely mounted on a printed wiring board, attaching multiple thermally conductive sheets of different thicknesses to correspond to the height of the electronic components is an extremely difficult task.

[0006] For this reason, Patent Document 2 discloses a thermal grease, and Patent Document 3 discloses a thermally conductive paste. However, when incorporating the thermal grease or thermally conductive paste between the printed circuit board and the heat dissipation material, a device for dispensing the thermal grease or thermally conductive paste is required, which increases manufacturing costs. Furthermore, there is a risk of pump-out occurring during use in printed circuit boards with heat dissipation mechanisms incorporating thermal grease. In particular, Patent Document 3 discloses curing the thermally conductive paste placed on the substrate of a semiconductor device, but when this is applied to an actual manufacturing process, an additional curing step is required after applying the thermally conductive paste, which increases the number of manufacturing steps and increases costs. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 11-209618 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-194379 [Patent Document 3] International Publication No. 2018 / 079533 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention provides a thermally conductive sheet that can suppress thermal degradation and mechanical damage of electronic components and maintain the quality of the electronic components. [Means for solving the problem]

[0009] The present invention provides a thermally conductive sheet made from a thermally conductive composition. The thermally conductive composition includes a thermally conductive filler and an elastomer resin. The volume fraction of the thermally conductive filler is 40% or more and 80% or less, based on the volume of the thermally conductive sheet. The storage modulus of the thermally conductive sheet, excluding the thermally conductive filler, is 1 kPa or more and 15 kPa or less. The torque change of the thermally conductive composition, excluding the thermally conductive filler, is 0.2 dN·m or less. The tack strength of the thermally conductive sheet is 10 N or more. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a thermally conductive sheet that can suppress thermal degradation and mechanical damage of electronic components and maintain the quality of the electronic components. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating an example of a printed circuit board having a heat dissipation mechanism incorporating a thermally conductive sheet according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Several embodiments will be described with reference to the drawings. The disclosure is merely an example, and appropriate modifications that can be easily conceived by those skilled in the art while maintaining the gist of the invention are naturally included within the scope of the present invention. Furthermore, the drawings may be schematic in terms of the width, thickness, shape, etc. of each part compared to the actual embodiment for clarity of explanation, but these are merely examples and are not intended to limit the interpretation of the present invention. Furthermore, in this specification and each drawing, components that perform the same or similar functions as those described above with reference to the previous drawings are designated by the same reference numerals, and redundant detailed descriptions may be omitted as appropriate.

[0013] The thermally conductive sheet according to the embodiment will be described below.

[0014] The thermally conductive sheet according to the embodiment is made of a thermally conductive composition. The thermally conductive composition includes a thermally conductive filler and an elastomer resin. The volume fraction of the thermally conductive filler is 40% or more and 80% or less, based on the volume of the thermally conductive sheet. The storage modulus of the thermally conductive composition sheet, excluding the thermally conductive filler, is 1 kPa or more and 15 kPa or less. The torque change of the thermally conductive composition, excluding the thermally conductive filler, is 0.2 dN·m or less. The tack strength of the thermally conductive sheet according to the embodiment is 10 N or more.

[0015] The thermally conductive sheet according to the embodiment is applied to a printed circuit board with a heat dissipation material, which includes a printed circuit board having multiple electronic components of different heights mounted on the printed wiring board, and a heat dissipation material disposed opposite the mounting surface of the electronic components of the printed circuit board. FIG. 1 is a cross-sectional view schematically illustrating an example of a printed circuit board having a heat dissipation mechanism incorporating a thermally conductive sheet according to the embodiment. As shown in FIG. 1, the printed circuit board 1 includes, for example, a printed wiring board 2 and multiple electronic components 3 of different heights mounted on the printed wiring board 2. The multiple electronic components 3 are electrically connected to each other while mounted on the printed wiring board 2. The heat dissipation material 5 is disposed so as to face the mounting surface 1a of the electronic components 3 on the printed circuit board 1. The thermally conductive sheet 4 according to the embodiment is incorporated, for example, between the printed circuit board 1 and the heat dissipation material 5, in close contact with the mounting surface 1a of the printed circuit board 1, the outer peripheral surface of the multiple electronic components 3, and the surface 5a of the heat dissipation material 5 facing the printed circuit board 1, thereby constituting a printed circuit board 6 having a heat dissipation mechanism according to the embodiment. The printed circuit board 6 having such a heat dissipation mechanism can transfer heat h (indicated by the white arrow in the figure) generated in the electronic component 3 to the heat dissipation material 5 via the thermally conductive sheet 4, thereby achieving a high heat dissipation effect for the electronic component 3. Furthermore, the printed circuit board 6 having the heat dissipation mechanism can reduce the load (stress) applied to the electronic component 3 due to the characteristics of the thermally conductive sheet 4 according to the embodiment, which will be described later. As a result, thermal deterioration, thermal damage, mechanical breakage, etc. of the electronic component 3 can be suppressed, thereby maintaining the quality of the electronic component.

[0016] The thermally conductive sheet according to the embodiment is made of a thermally conductive composition, which contains a thermally conductive filler and an elastomer resin.

[0017] The thermally conductive filler preferably has a thermal conductivity of 15 W / (m·K) or higher, more preferably 25 W / (m·K) or higher, which is higher than that of the elastomer resin. The thermally conductive filler is not particularly limited and can be made from one or more materials selected from the group consisting of aluminum oxide (alumina), aluminum nitride, aluminum hydroxide, silicon oxide, silicon nitride, silicon carbide, titanium oxide, glass, zinc oxide, and metals. When made from two or more materials, the combination and ratio of the materials can be selected as desired depending on the purpose.

[0018] The volume fraction of the thermally conductive filler is 40% or more and 80% or less based on the volume of the thermally conductive sheet. Here, the volume fraction of the thermally conductive filler is the ratio of the volume of the thermally conductive filler to the total volume of the thermally conductive sheet. By setting the volume fraction of the thermally conductive filler to 40% or more based on the volume of the thermally conductive sheet, the thermal conductivity of the thermally conductive sheet described below is increased. This allows heat generated in electronic components to be efficiently transferred to the heat dissipation material, thereby suppressing thermal deterioration and thermal damage to the electronic components. Furthermore, by setting the volume fraction of the thermally conductive filler to 80% or less based on the volume of the thermally conductive sheet, the fluidity of the thermally conductive composition raw material is improved in the production of the thermally conductive sheet described below, making it easier to produce the thermally conductive sheet. A preferred volume fraction of the thermally conductive filler is 50% or more and 75% or less based on the volume of the thermally conductive sheet.

[0019] The shape of the thermally conductive filler is not particularly limited, and may be, for example, spherical, scaly, needle-like, or irregular.

[0020] When the thermally conductive filler is spherical, its average particle diameter (D50) is preferably 0.1 μm or more and 300 μm or less, and more preferably 1 μm or more and 100 μm or less. Here, the average particle diameter (D50) is a value determined using the laser diffraction / scattering method as the measurement principle. The average particle diameter (D50) of the thermally conductive filler can be determined, for example, using a laser diffraction particle size distribution analyzer.

[0021] The thermally conductive sheet may further contain an inorganic filler other than the thermally conductive filler. The inorganic filler is not particularly limited, and for example, one or more types of particles selected from the group consisting of aluminum silicate, barium carbonate, barium sulfate, talc, calcium carbonate, clay, diatomaceous earth, etc. can be used. When two or more types of particles are used, the combination and ratio thereof can be selected as desired depending on the purpose.

[0022] The elastomer resin is not particularly limited, and for example, rubber can be used. When two or more types of elastomer resins are used, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0023] The rubber is a raw rubber containing additives as needed, or may be obtained by vulcanizing a raw rubber containing a vulcanizing agent as an additive.

[0024] Known raw rubbers can be used, including, for example, one or a mixture of two or more selected from the group consisting of natural rubber, liquid natural rubber, butadiene rubber, isoprene rubber, butyl rubber, nitrile rubbers such as liquid nitrile rubber and solid nitrile rubber, ethylene propylene rubbers such as liquid ethylene propylene rubber and solid ethylene propylene rubber, acrylic rubber, urethane rubber, silicone rubber, fluororubbers such as liquid fluororubber and solid fluororubber, and chlorosulfonated polyethylene rubber. When a mixture is used, the combination and ratio thereof can be selected as desired depending on the purpose. The raw rubber is preferably urethane rubber or fluororubber.

[0025] Urethane rubber is obtained by polymerizing a polyol, which is a urethane raw material, with an isocyanate compound. When urethane rubber is used as the raw rubber, the ratio of the hydroxyl value to the isocyanate value of the polyol widely varies the properties of the thermally conductive sheet, such as the loss tangent and the storage modulus of the thermally conductive composition excluding the thermally conductive filler. That is, the properties of the thermally conductive sheet can be adjusted by changing the ratio of the hydroxyl value to the isocyanate value of the polyol. Therefore, by using urethane rubber as the raw rubber, the loss tangent of the thermally conductive sheet and the storage modulus of the thermally conductive composition excluding the thermally conductive filler can be easily adjusted to the desired range, i.e., 1 kPa to 15 kPa. The ratio of the hydroxyl value to the isocyanate value of the polyol is preferably 100:60 to 100:70. A more preferred ratio of the hydroxyl value to the isocyanate value of the polyol is 100:62 to 100:68. In addition, urethane rubber is generally known to have excellent tear strength, so by using urethane rubber as the raw rubber, the thermal conductive sheet has excellent tear strength while remaining flexible.

[0026] When fluororubber is used as the raw rubber, a mixture of liquid and solid fluororubber is preferred. By adjusting the ratio of liquid and solid fluororubber in the mixture, the loss tangent of the thermal conductive sheet or the storage modulus of the thermal conductive composition excluding the thermal conductive filler can be easily adjusted to the desired range, i.e., 1 kPa to 15 kPa. The weight ratio of liquid fluororubber to solid fluororubber is preferably 100:13 to 100:20. A more preferred weight ratio is 100:15 to 100:18. Furthermore, liquid fluororubber and solid fluororubber are highly compatible. Therefore, even if the torque change of the thermal conductive composition excluding the thermal conductive filler described below is 0.2 dN·m or less, bleed-out is unlikely to occur. Here, bleed-out refers to the phenomenon in which liquid components ooze out of a thermal conductive sheet or the like over time in a printed circuit board with a heat dissipation mechanism incorporating a thermal conductive sheet. In particular, fluororubber is known to have excellent heat resistance, so by using fluororubber as the raw material, the thermal conductive sheet can be used for a long period of time even in high-temperature environments.

[0027] The additives contained in the raw rubber may be known ones, and for example, one or more selected from the group consisting of vulcanizing agents, catalysts, dispersants, coupling agents, antioxidants, colorants, plasticizers, and flame retardants may be used.

[0028] In the thermally conductive sheet according to the embodiment, the thermally conductive composition excluding the thermally conductive filler (hereinafter sometimes referred to as the "elastomeric resin composition") has a storage modulus of 1 kPa or more and 15 kPa or less. A thermally conductive composition having a storage modulus of 1 kPa or more has a tear strength (described later) of 0.9 kN / m or more, even when the thermally conductive sheet does not have a reinforcing layer or the like, and therefore has excellent handleability, facilitating the incorporation of the thermally conductive sheet between the printed circuit board and the heat dissipation material, thereby improving work efficiency. Furthermore, a thermally conductive composition having a storage modulus of 15 kPa or less has appropriate flexibility, thereby reducing the stress load on electronic components caused by a thermally conductive sheet incorporated between the printed circuit board and the heat dissipation material.

[0029] If the storage modulus of the elastomer resin composition sheet is less than 1 kPa, the Asker C hardness of the thermally conductive sheet described below will be less than 5°, which may result in reduced handleability of the thermally conductive sheet. Furthermore, if the storage modulus of the elastomer resin composition sheet is less than 1 kPa, the compressive stress C immediately after 40% compression described below will be less than 0.2 MPa, which may result in difficulty in handling the thermally conductive sheet when it is incorporated between a printed circuit board and a heat dissipation material. Furthermore, if the storage modulus of the elastomer resin composition sheet is less than 1 kPa, the tear strength of the thermally conductive sheet described below will be less than 0.9 kN / m, which may result in tearing, cracking, or rupture of the thermally conductive sheet when it is incorporated between a printed circuit board and a heat dissipation material.

[0030] If the storage modulus of the elastomer resin composition sheet exceeds 15 kPa, the Asker C hardness of the thermally conductive sheet (described below) will exceed 60°, making it difficult for the sheet to conform to the unevenness of the mounting surface of a printed circuit board (PCB) due to multiple electronic components, potentially reducing the heat transfer efficiency between the electronic components and the thermally conductive sheet. Furthermore, if the storage modulus of the elastomer resin composition sheet exceeds 15 kPa, the compressive stress C immediately after 40% compression (described below) will exceed 3.0 MPa, potentially damaging electronic components in a printed circuit board with a heat dissipation mechanism incorporating the thermally conductive sheet. Furthermore, if the storage modulus of the elastomer resin composition sheet exceeds 15 kPa, the compressive stress D (described below) 10 minutes after 40% compression will exceed 0.5 MPa, potentially damaging electronic components in a printed circuit board with a heat dissipation mechanism.

[0031] In the thermally conductive sheet according to the embodiment, the torque change of the composition excluding the thermally conductive filler in the thermally conductive composition (elastomer resin composition) is 0.2 dN·m or less. The torque change of the elastomer resin composition can be determined, for example, by the following method. When the elastomer resin contained in the thermal conductive composition is rubber, the raw rubber, which optionally contains additives, is subjected to torque measurement using a rubber processability analyzer at a measurement vibration frequency of 0.1 Hz, a measurement vibration angle of 3°, and a measurement temperature of 120°C for 30 minutes. Then, the maximum torque (M H ) and minimum torque (M L ) difference (M H -M L ) to determine the torque change of the elastomer resin composition.

[0032] If the torque change exceeds 0.2 dN·m, a restoring force will remain in the thermal conductive sheet when it is embedded between the printed circuit board and the heat dissipation material, and the compressive stress ratio ([CD] / C) described below will become less than 0.6, which may damage the electronic components.

[0033] In particular, a thermally conductive sheet made of an elastomer resin composition with a storage modulus of 15 kPa or less and a torque change of 0.2 dN·m or less can reduce the restoring force that attempts to return to its original state from a compressed state, even when it is embedded between a printed circuit board and a heat dissipation material. This reduces the stress applied to electronic components when and after the thermally conductive sheet is embedded between the printed circuit board and the heat dissipation material, preventing mechanical damage to the electronic components and maintaining their quality.

[0034] The tack strength of the thermally conductive sheet according to the embodiment is defined as "one of the main properties of an adhesive, the ability to adhere to an adherend in a short time with light force." In other words, tack is a term that means "stickiness." The tack strength of the thermally conductive sheet is 10 N or greater. A thermally conductive sheet with a tack strength of 10 N or greater has excellent adhesion to printed wiring boards, electronic components, and heat dissipation materials. That is, even when the thermally conductive sheet is incorporated between the printed circuit board and the heat dissipation material under low compression, the thermally conductive sheet adheres well to the electronic components and the heat dissipation material, and maintains this adhesion for a long period of time. Therefore, the thermally conductive sheet according to the embodiment can efficiently transfer heat generated by the electronic components to the heat dissipation material, thereby suppressing thermal degradation and thermal damage of the electronic components. Furthermore, when incorporating a thermally conductive sheet with a tack strength of 10 N or greater between the printed circuit board and the heat dissipation material, it is not necessary to excessively compress it to adhere to the electronic components and the heat dissipation material, as is the case with conventional thermally conductive sheets. This reduces the mechanical load (stress) applied to electronic components, preventing damage to the electronic components and maintaining their quality. Furthermore, when incorporating a thermally conductive sheet with a tack strength of 10 N or more between a printed circuit board and a heat dissipation material, excessive compression is not required, allowing for a reduction in its thickness. As a result, the manufacturing cost of the thermally conductive sheet can be reduced, and the weight of the printed circuit board with a heat dissipation mechanism incorporating the thermally conductive sheet can be reduced.

[0035] In some embodiments, the thermally conductive sheet preferably has an Asker C hardness of 5° or more and 60° or less. A thermally conductive sheet with an Asker C hardness of 5° or more and 60° or less has appropriate softness, making it less likely to break and easier to handle when incorporating it between a printed circuit board and a heat dissipation material. Furthermore, a thermally conductive sheet with an Asker C hardness of 5° or more and 60° or less has excellent conformability to irregularities, thereby improving adhesion to electronic components.

[0036] In some embodiments, the compressive stress C of the thermally conductive sheet immediately after 40% compression is preferably 0.2 MPa or more and 3.0 MPa or less. A thermally conductive sheet with a compressive stress C of less than 0.2 MPa easily deforms. This may make it difficult to handle the thermally conductive sheet when incorporating it between a printed circuit board and a heat dissipation material using bare hands, tweezers, an automatic mounting machine, or the like. Furthermore, if the compressive stress C exceeds 3.0 MPa, the electronic component may be damaged due to the large instantaneous stress it receives when incorporating the thermally conductive sheet between the printed circuit board and the heat dissipation material.

[0037] In some embodiments, the compressive stress D of the thermal conductive sheet 10 minutes after being compressed by 40% is preferably 0.5 MPa or less. If the compressive stress D exceeds 0.5 MPa, stress will be applied to the electronic components for a long period of time, which may damage the electronic components.

[0038] In some embodiments, the value ([CD] / C) obtained by dividing the difference between the compressive stress C and the compressive stress D of the thermally conductive sheet by the compressive stress C (hereinafter sometimes referred to as the compressive stress ratio) is preferably 0.6 or more. If the compressive stress ratio ([CD] / C) is less than 0.6, stress will remain in the thermally conductive sheet after it is inserted between the printed circuit board and the heat dissipation material, which may damage the electronic components.

[0039] In such a thermal conductive sheet, by making the compressive stress C immediately after 40% compression 0.2 MPa or more and 3.0 MPa or less, the compressive stress D 10 minutes after 40% compression 0.5 MPa or less, and the compressive stress ratio ([CD] / C) 0.6 or more, it is possible to reduce excessive stress on electronic components and suppress the risk of damage.

[0040] The compressive stress C immediately after 40% compression and the compressive stress D 10 minutes after 40% compression can be measured as follows, for example, using a universal testing machine. In this specification, "40% compression" refers to compressing the sheet so that the thickness is 60% of the thickness before compression. In other words, in this specification, "40% compression" refers to a 40% reduction in the thickness of the sheet due to compression. First, place the thermally conductive sheet under the indenter of the universal testing machine and bring the indenter into contact with the thermally conductive sheet so that almost no pressure is applied. Next, compress the thermally conductive sheet with the indenter. Compress the thermally conductive sheet until its thickness is 60% of its pre-compression thickness, and measure the compressive stress immediately after that to obtain the compressive stress C immediately after compression at 40% compression. Furthermore, after compressing the thermally conductive sheet until its thickness is 60% of its pre-compression thickness, hold the compressed state for 10 minutes, and then measure the compressive stress to obtain the compressive stress D 10 minutes after 40% compression.

[0041] In some embodiments, the tear strength of the thermally conductive sheet is preferably 0.9 kN / m or more. A thermally conductive sheet having a tear strength of 0.9 kN / m or more is easy to handle when being incorporated between a printed circuit board and a heat dissipation material, and high work efficiency can be achieved.

[0042] In some embodiments, the loss tangent of the thermally conductive sheet is preferably 0.7 or greater. When the loss tangent is 0.7 or greater, it is easy to adjust the tack strength of the thermally conductive sheet to 10 N or greater. As described above, a thermally conductive sheet with a tack strength of 10 N or greater has excellent adhesion to printed circuit boards, electronic components, and heat dissipation materials.

[0043] In some embodiments, the thermal conductivity of the thermally conductive sheet is preferably 1.0 W / (m·K) or more, more preferably 2.0 W / (m·K) or more, and even more preferably 3.0 W / (m·K) or more. A thermally conductive sheet with a thermal conductivity of 1.0 W / (m·K) or more can efficiently transfer heat generated by electronic components to a heat dissipation material.

[0044] In some embodiments, the volume resistivity of the thermally conductive sheet is 1.0×10 10 It is preferable that the resistance is Ω·cm or more, and 1.0×10 11 It is more preferable that the resistance is Ω·cm or more, and 1.0×10 12 It is more preferable that the volume resistivity is 1.0×10 Ω·cm or more. 10 If the resistivity is less than Ω·cm, when the voltage applied to a printed circuit board that has a heat dissipation mechanism increases instantaneously, electricity may flow through the thermal conductive sheet, causing a short circuit in the electronic components.

[0045] In some embodiments, the thickness of the thermally conductive sheet is not particularly limited, but is preferably 0.5 mm or more. If the thickness is less than 0.5 mm, there is a risk of the thermally conductive sheet being torn, cracked, or broken when being installed between the printed circuit board and the heat dissipation material. The upper limit of the thickness of the thermally conductive sheet is, for example, 50 mm.

[0046] In some embodiments, the shape of the thermally conductive sheet may be, for example, a ring-shaped, convex, block-shaped, pin-shaped formation, or the like.

[0047] In some embodiments, the thermally conductive sheet may be embossed on one or both sides. When such an embossed thermally conductive sheet is incorporated between a printed circuit board and a heat dissipation material, even if air is trapped between the electronic component and the thermally conductive sheet and / or between the thermally conductive sheet and the heat dissipation material, the air can be quickly released to the outside.

[0048] In some embodiments, the thermally conductive sheet has a tack strength of 10 N or more and is sticky on both sides, so it may be provided with a separator having releasability sandwiched between both sides. By peeling off the separator before interposing such a thermally conductive sheet between the printed circuit board and the heat dissipation material, the thermally conductive sheet can be easily incorporated between them. The separator is not particularly limited, and examples that can be used include releasable separators made of PET, PEN, paper, or the like coated with a release agent such as silicone or a fluorine-based material; separators made of embossed PEN, PET, or the like; and releasable separators such as silicone resin films and fluorine resin films.

[0049] The thermally conductive sheet according to the embodiment described above comprises a thermally conductive composition containing a thermally conductive filler and an elastomer resin, wherein the volume fraction of the thermally conductive filler in the thermally conductive composition is 40% to 80% based on the volume of the thermally conductive sheet, the thermally conductive composition excluding the thermally conductive filler has a storage modulus of 1 kPa to 15 kPa, the thermally conductive composition excluding the thermally conductive filler has a torque change of 0.2 dN·m or less, and the thermally conductive sheet has a tack strength of 10 N or more. When a thermally conductive sheet having such a configuration is incorporated between a printed circuit board (PCB) having multiple electronic components of different heights mounted on the printed wiring board and a heat dissipation material arranged opposite the mounting surface of the electronic components of the printed circuit board, the thermally conductive sheet can be tightly attached to the mounting surface of the printed circuit board, the outer peripheral surface of the multiple electronic components, and the surface of the heat dissipation material facing the printed circuit board without applying excessive compressive force to the thermally conductive sheet. That is, instead of utilizing the restoring force, which is a reaction to the compressive force of the thermally conductive sheet as in the past, by specifying the thermally conductive sheet's tackiness (tackiness of 10 N or more) and storage modulus to be 1 kPa or more and 15 kPa or less, the thermally conductive sheet can be adhered to the mounting surface of the printed circuit board, the outer surfaces of multiple electronic components, and the surface of the heat dissipation material facing the printed circuit board. As a result, heat generated by the electronic components can be efficiently transferred and dissipated to the heat dissipation material via the thermally conductive sheet, thereby suppressing thermal deterioration or damage to the electronic components. At the same time, by specifying the thermally conductive sheet's tackiness (tackiness of 10 N or more) and storage modulus to be 1 kPa or more and 15 kPa or less, the stress applied to the electronic components by the thermally conductive sheet can be alleviated, thereby suppressing damage to the electronic components. Therefore, the quality of multiple electronic components of different heights mounted on a printed wiring board can be maintained.

[0050] The thermally conductive sheet according to the embodiment can be manufactured, for example, by the following method.

[0051] An example of a method for producing a thermally conductive sheet in which the elastomer resin is rubber is described below. First, a thermally conductive filler, raw rubber, and optional additives are mixed, and then kneaded using a vacuum mixer or an open-roll kneader to obtain a thermally conductive composition raw material.

[0052] The amount of the thermally conductive filler may be adjusted so that its volume fraction relative to the total amount of the thermally conductive filler and the elastomer resin is 40% or more and 80% or less based on the volume of the final product, the thermally conductive sheet.

[0053] The thermally conductive composition raw material is then molded into a desired shape to obtain a thermally conductive sheet made of the thermally conductive composition. Both sides of the obtained thermally conductive sheet may be sandwiched between releasable separators.

[0054] The method for molding the thermally conductive composition raw material is not particularly limited, and can be any known method, such as injection molding, compression molding, extrusion molding, etc. When molding the thermally conductive composition raw material, the thermally conductive composition raw material may be cured by heating, etc., as necessary.

[0055] One or both sides of the thermally conductive sheet may be embossed as described above. The method for embossing one or both sides of the thermally conductive sheet is not particularly limited. For example, the embossing may be performed by injection molding or compression molding using an embossed mold. When a separator is used during molding, an embossed separator may be used instead of embossing the thermally conductive sheet.

[0056] As mentioned above, by setting the volume fraction of the thermally conductive filler to 80% or less based on the volume of the thermally conductive sheet, the fluidity of the thermally conductive composition raw material is improved, making it possible to easily produce the thermally conductive sheet.

[0057] The thermally conductive sheet according to the embodiment can be manufactured by the method described above.

[0058] The thermally conductive sheet according to the embodiment can be incorporated between a printed circuit board and a heat dissipation material, for example, by the following method. Here, an example of a method for incorporating a thermally conductive sheet sandwiched between a printed circuit board and a heat dissipation material by peelable separators on both sides will be described.

[0059] First, the separator on one side of the thermally conductive sheet is peeled off. At this time, for example, by using a thermally conductive sheet with an Asker C hardness of 5° or more, tearing and damage during peeling can be prevented. Next, one side of the thermally conductive sheet is placed so that it faces the electronic component mounting surface of the printed circuit board. Since the thermally conductive sheet according to the embodiment has a tack strength of 10 N or more, simply placing the thermally conductive sheet on the electronic component will ensure close contact with the electronic component. If necessary, the separator on the other side of the thermally conductive sheet may be pressed toward the printed circuit board to press the thermally conductive sheet against the electronic component. Next, the separator on the other side of the thermally conductive sheet is peeled off. Next, a heat dissipation material such as a heat sink or a housing is placed on the other side of the thermally conductive sheet. At this time, if necessary, pressure may be applied to the thermally conductive sheet between them from the heat dissipation material side toward the printed circuit board. The heat dissipation material is then fixed to the printed wiring board of the printed circuit board by a known method, such as screwing. This method allows the thermally conductive sheet according to the embodiment to be incorporated between the printed circuit board and the heat dissipation material, thereby obtaining a printed circuit board with a heat dissipation mechanism. [Example]

[0060] The present invention will be described in more detail below by way of examples, but the present invention is not limited to these examples.

[0061] [Example 1] <Production of the first thermally conductive sheet> The thermally conductive fillers used were 160.00 g of spherical alumina (DAM-70, manufactured by Denka Co., Ltd.) with an average particle size (D50) of 74.6 μm, 80.00 g of spherical alumina (DAM-10, manufactured by Denka Co., Ltd.) with an average particle size (D50) of 11.3 μm, and 26.67 g of spherical alumina (CB-P-02, manufactured by Resonac Holdings Inc.) with an average particle size (D50) of 3 μm. The thermally conductive fillers were heated in an oven at 150°C for more than 48 hours and then air-cooled to reduce the temperature of the thermally conductive fillers to below 30°C.

[0062] The air-cooled thermally conductive filler was mixed with 50.00 g of a urethane raw material polyol (Kuraray Polyol P-2050, manufactured by Kuraray Co., Ltd.), 6.79 g of an isocyanate compound (Duranate® TSA-100, manufactured by Asahi Kasei Corporation), and 0.01 g of a catalyst dibutyltin(IV) bisdodecanoate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and then kneaded at room temperature for 5 minutes at 1500 rpm using a planetary vacuum mixer to obtain a thermally conductive composition raw material. The total weight of the mixed thermally conductive composition raw material was 323.47 g. The amounts of the urethane raw materials polyol and isocyanate compound used were adjusted so that the ratio of the hydroxyl value of the polyol to the isocyanate value was 100:60 to 100:70. In the thermally conductive composition raw material of Example 1, the ratio of the hydroxyl value of the polyol to the isocyanate value was 100:66.

[0063] Next, the required amount of thermally conductive composition raw material was measured and filled into a mold with a chamber dimension of 150 mm square and 1 mm deep. Next, using a vacuum press, the filled thermally conductive composition raw material was compression molded for 30 minutes under conditions of a molding temperature of 120°C, a molding pressure of 5 MPa, and a vacuum degree of 100 kPa, to obtain a first thermally conductive sheet of Example 1. <Measurement of the volume fraction of thermally conductive filler> The volume fraction of the thermally conductive filler was examined for the first thermally conductive sheet of Example 1. Here, the volume fraction of the thermally conductive filler can be calculated by the following formula (1).

[0064] Volume fraction of thermally conductive filler (%) = [(weight of thermally conductive filler) / (specific gravity of thermally conductive filler)] / [(total weight of thermally conductive sheet) / (specific gravity of thermally conductive sheet)]...(1)

[0065] <Production of the second thermal conductive sheet> The second thermal conductive sheet of Example 1 was obtained in the same manner as in the production of the first thermal conductive sheet, except that the thermal conductive composition raw material was filled into a mold with a container dimension of 28 mm in diameter and 12 mm in depth.

[0066] <Production of the third thermal conductive sheet> The third thermal conductive sheet of Example 1 was obtained in the same manner as in the production of the first thermal conductive sheet, except that the thermal conductive composition raw material was filled into a mold with a container dimension of 150 mm square and 2 mm deep.

[0067] <Production of a sheet of a thermally conductive composition excluding the thermally conductive filler (hereinafter referred to as an elastomer resin composition)> The urethane raw material polyol (Kuraray Polyol P-2050), an isocyanate compound (Duranate (registered trademark) TSA-100), and the catalyst dibutyltin(IV) bisdodecanoate were mixed, and then kneaded at room temperature for 5 minutes at 1500 rpm using a planetary vacuum mixer to obtain a kneaded mixture. The weights of the mixed urethane raw material and catalyst were the same as those used in the production of the thermal conductive sheet. The total weight of the kneaded mixture was 56.80 g.

[0068] The kneaded mixture was then filled into a mold having a container portion of 150 mm square and 2 mm deep. The kneaded mixture was then compression molded using a vacuum press at a molding temperature of 120°C, a molding pressure of 5 MPa, and a vacuum degree of 100 kPa for 30 minutes to obtain a sheet of the elastomer resin composition of Example 1. In addition, 5 mL of the kneaded product was measured, and the torque of the measured kneaded product was measured using a rubber processability analyzer (Premier RPA, manufactured by Alpha Technologies Japan LLC) at a measurement vibration frequency of 0.1 Hz, a measurement vibration angle of 3°, and a measurement temperature of 120°C for 30 minutes. The maximum torque M H and the minimum value M L Difference (M H -M L ) was obtained, the torque change amount (M H -M L ) was calculated. The torque change amount M H -M L The measurement results are shown in Table 3 below.

[0069] [Example 2] <Production of the first thermally conductive sheet> As thermally conductive fillers, spherical alumina (DAM-70, manufactured by Denka Co., Ltd.) with an average particle size (D50) of 74.6 μm, spherical alumina (DAM-10, manufactured by Denka Co., Ltd.) with an average particle size (D50) of 11.3 μm, and spherical alumina (CB-P-02, manufactured by Resonac Holdings Inc.) with an average particle size (D50) of 3 μm were prepared. The weights of the thermally conductive fillers were the same as those used in Example 1. The thermally conductive fillers were placed in an oven at 150°C for 48 hours or more and then air-cooled to reduce the temperature of the thermally conductive fillers to 30°C or less.

[0070] The air-cooled thermally conductive filler was mixed with 85.00 g of liquid fluororubber (Dai-el G-101, manufactured by Daikin Industries, Ltd.) and 14.00 g of solid fluororubber (Dai-el G-501N, manufactured by Daikin Industries, Ltd.), which were raw rubber materials, and then kneaded using an open roll at room temperature for 15 minutes to obtain a thermally conductive composition raw material. The total weight of the thermally conductive composition raw material was 365.67 g.

[0071] The thermally conductive composition raw material was then filled into a mold having a container portion of 150 mm square and 1 mm deep. The filled thermally conductive composition raw material was then compression molded using a vacuum press at a molding temperature of 120°C, a molding pressure of 5 MPa, and a vacuum of 100 kPa for 30 minutes to obtain a first thermally conductive sheet of Example 2. <Measurement of the volume fraction of thermally conductive filler> The volume fraction of the thermally conductive filler in the first thermally conductive sheet of Example 2 was determined based on formula (1) of Example 1.

[0072] <Production of the second thermal conductive sheet> The second thermally conductive sheet of Example 2 was obtained in the same manner as in the production of the first thermally conductive sheet, except that the thermally conductive composition raw material was filled into a mold with a container portion having a diameter of 28 mm and a depth of 12 mm.

[0073] <Production of the third thermal conductive sheet> The third thermal conductive sheet of Example 2 was obtained in the same manner as in the production of the first thermal conductive sheet, except that the thermal conductive composition raw material was filled into a mold with a container portion measuring 150 mm square and 2 mm deep.

[0074] <Production of Elastomer Resin Composition Sheet> The raw rubbers, liquid fluororubber (Dai-el G-101) and solid fluororubber (Dai-el G-501N), were mixed and then kneaded for 15 minutes at room temperature using an open roll to obtain a kneaded mixture. The weights of the mixed liquid fluororubber and solid fluororubber were the same as the amounts used to manufacture the thermal conductive sheet. The total weight of the kneaded mixture was 99.00 g.

[0075] The kneaded mixture was then filled into a mold having a storage area of ​​150 mm square and 2 mm deep. The kneaded mixture was then compression molded using a vacuum press at a molding temperature of 120°C, a molding pressure of 5 MPa, and a vacuum degree of 100 kPa for 30 minutes to obtain a sheet of the elastomer resin composition of Example 2. In addition, 5 mL of the kneaded product was measured, and the torque of the measured kneaded product was measured using a rubber processability analyzer (Premier RPA, manufactured by Alpha Technologies Japan LLC) at a measurement vibration frequency of 0.1 Hz, a measurement vibration angle of 3°, and a measurement temperature of 120°C for 30 minutes. The maximum torque M H and the minimum value M L Difference (M H -M L ) was obtained, the torque change amount (M H -M L The torque change amount M of the elastomer resin composition of Example 2 was calculated. H -M L The measurement results are shown in Table 3 below.

[0076] Table 1 below shows the compositions, kneading conditions, compression molding conditions, and volume fractions of the thermally conductive fillers of the first to third thermally conductive sheets of Examples 1 and 2. Table 2 below shows the compositions, kneading conditions, and compression molding conditions of the elastomer resin compositions of Examples 1 and 2.

[0077] [Table 1]

[0078] [Table 2]

[0079] [Physical property testing of thermal conductive sheets] <Storage modulus> The storage modulus of the sheets of the elastomer resin compositions of Examples 1 and 2 was measured by the following method.

[0080] A sheet of the elastomer resin composition (150 mm square, 2 mm thick) was punched out into a circle with a diameter of 20 mm. The storage modulus of the punched out sheet of the elastomer resin composition was measured in shear mode using a rheometer (ARES-G2 rheometer) under conditions of a frequency of 1 Hz, a strain rate of 0.1%, an initial compression load of 10 g, and a measurement temperature of 25°C. The measurement results of the storage modulus are shown in Table 3 below.

[0081] <Tack strength> The tackiness of the first thermally conductive sheets of Examples 1 and 2 was measured by the following method.

[0082] A tack tester (Tackiness Checker (registered trademark) HTC-1, manufactured by Toyo Seiki) was placed on top of the thermally conductive sheet. The contact of the tack tester was pressed against the thermally conductive sheet with a pressure of 10 N for 3 seconds. An aluminum flat-surface indenter (dimensions: 15 mm × 10 mm) was used as the contact. After pressing the contact to the thermally conductive sheet, the contact was peeled off from the thermally conductive sheet, and the force acting on the load cell of the tack tester at the time of peeling was measured as the tack force. The measurement was performed at a temperature of 25°C. The tack force measurement results are shown in Table 3 below.

[0083] <Asker C hardness> The Asker C hardness of the second thermally conductive sheets of Examples 1 and 2 was measured. An Asker Rubber Hardness Tester Type C (manufactured by Kobunshi Keiki Co., Ltd.) was used for the measurement. The measurement load was 9.8 N, and the Asker C hardness was measured 15 seconds after the start of the measurement. The measurement was carried out at a temperature of 25°C. The measurement results of the Asker C hardness are shown in Table 3 below.

[0084] <Compressive stress> For the third thermal conductive sheets of Examples 1 and 2, the compressive stress C immediately after compression at 40% compression, the compressive stress D 10 minutes after 40% compression, and the compressive stress ratio ([CD] / C) were measured using the following methods.

[0085] The thermally conductive sheet was punched out into a 28 mm diameter circle. The punched thermally conductive sheet was then placed under the indenter of a Tensilon universal material testing machine (RTG-1250, manufactured by A&D Co., Ltd.) and brought into contact with the thermally conductive sheet so that almost no pressure was applied. The thermally conductive sheet was then compressed with the indenter at a compression rate of 0.5 mm / min. The thermally conductive sheet was compressed until its thickness was 60% of its original thickness. The compressive stress immediately after compression was measured to determine the compressive stress C immediately after 40% compression. After compressing the thermally conductive sheet until its thickness was 60% of its original thickness, the compressed state was maintained for 10 minutes. The compressive stress D was then measured and determined 10 minutes after 40% compression. The compressive stress C and compressive stress D measurements were performed at 25°C. The compressive stress ratio ([C-D] / C) was calculated using the obtained compressive stresses C and D. The measurement results of the compressive stress are shown in Table 3 below.

[0086] <Tear strength> The tear strength of the third thermal conductive sheets of Examples 1 and 2 was measured by the following method.

[0087] The thermally conductive sheet was punched out into an angle shape without any notches. The tear strength of the punched out thermally conductive sheet was then measured in accordance with JIS K6252-1. A Tensilon universal material testing machine (RTG-1250) was used for the measurement. The measurement was carried out at a temperature of 25°C. The tear strength measurement results are shown in Table 3.

[0088] <Loss tangent> The loss tangents of the first thermally conductive sheets of Examples 1 and 2 were measured by the following method.

[0089] The thermally conductive sheet was punched out into a circle with a diameter of 20 mm. The loss tangent of the punched thermally conductive sheet was measured in shear mode using a rheometer (ARES-G2 rheometer, manufactured by TA instruments) under the conditions of a frequency of 1 Hz, a strain of 0.1%, an initial compressive load of 10 g, and a measurement temperature of 25°C. The measurement results of the loss tangent are shown in Table 3.

[0090] <Thermal conductivity> The thermal conductivity of the third thermal conductive sheets of Examples 1 and 2 was measured by the following method.

[0091] The thermal conductive sheet was punched out into a circle with a diameter of 12.8 mm. Using a thermal property measuring device (T3Ster DynTIM Tester, manufactured by Menter Graphics), the thermal resistance of the punched out thermal conductive sheet was measured when it was compressed by 40%, and the thermal resistance value at 40% compression was obtained. Using the obtained thermal resistance value at 40% compression, the thermal conductivity of the thermal conductive sheet was calculated according to the following formula (2). The thermal conductivity measurement results are shown in Table 3.

[0092] λ=L / (S·R)…(2) λ: Thermal conductivity of the thermal conductive sheet [W / (m K)] S: Cross-sectional area of ​​the thermal conductive sheet [m2] L: Thickness of the thermal conductive sheet [m] R: Thermal resistance at 40% compression [K / W]

[0093] <Volume resistivity> The volume resistivities of the first thermally conductive sheets of Examples 1 and 2 were measured by the following method.

[0094] The thermally conductive sheet was cut into a square measuring 100 mm on each side using a cutter. The volume resistivity of the cut thermally conductive sheet was measured in accordance with JIS K6911. A resistivity meter (Hiresta UP MCP-HT450, manufactured by Mitsubishi Chemical Corporation) was used for the measurement. The measurement was carried out at a temperature of 25°C. The results of the volume resistivity measurement are shown in Table 3.

[0095] [Table 3]

[0096] Tables 1 to 3 show that the thermally conductive sheets of Examples 1 and 2 are made of a thermally conductive composition, which contains a thermally conductive filler and an elastomer resin, with the volume fraction of the thermally conductive filler being 40% to 80% based on the volume of the thermally conductive sheet. Furthermore, the thermally conductive sheets of Examples 1 and 2 have a storage modulus of 1 kPa to 15 kPa, indicating that they have appropriate flexibility. The thermally conductive sheets of Examples 1 and 2 have a torque change of 0.2 dN·m or less, indicating that the risk of damage to electronic components can be reduced during and after assembly between a printed circuit board and a heat dissipation material. Furthermore, the thermally conductive sheets of Examples 1 and 2 have a tack strength of 10 N or more, indicating that when assembled between a printed circuit board and a heat dissipation material, they have high adhesion to the electronic components and the heat dissipation material even when a low compressive force is applied to the thermally conductive sheet.

[0097] As can be seen from Tables 1 to 3, the thermally conductive sheets of Examples 1 and 2 have an Asker C hardness of 5° or more and 60° or less. These results show that the thermally conductive sheets of Examples 1 and 2 have appropriate softness and excellent conformability to irregularities, making them easy to handle when incorporated between a printed circuit board and a heat dissipation material.

[0098] As can be seen from Tables 1 to 3, the thermally conductive sheets according to Examples 1 and 2 have a compressive stress C of 0.2 MPa or more and 3.0 MPa or less immediately after compression at 40% compression. These results show that the thermally conductive sheets according to Examples 1 and 2 are less likely to deform excessively, making them easier to handle when incorporated between a printed circuit board and a heat dissipation material. It is also clear that the thermally conductive sheets according to Examples 1 and 2 can reduce the instantaneous stress experienced by electronic components when incorporated between a printed circuit board and a heat dissipation material. In other words, it can be seen that the thermally conductive sheets according to Examples 1 and 2 can reduce the risk of damage to electronic components.

[0099] As can be seen from Tables 1 to 3, the thermally conductive sheets according to Examples 1 and 2 have a compressive stress D of 0.5 MPa or less 10 minutes after being compressed by 40%. This result shows that when the thermally conductive sheets according to Examples 1 and 2 are incorporated between a printed circuit board and a heat dissipation material, the long-term stress applied to electronic components can be reduced. In other words, it can be seen that the thermally conductive sheets according to Examples 1 and 2 can reduce the risk of damage to electronic components.

[0100] As can be seen from Tables 1 to 3, the compressive stress ratio ([CD] / C) is 0.6 or more in the thermally conductive sheets of Examples 1 and 2. These results show that the thermally conductive sheets of Examples 1 and 2 can reduce residual stress in the thermally conductive sheet after it is incorporated between a printed circuit board and a heat dissipation material. In other words, it can be seen that the thermally conductive sheets of Examples 1 and 2 can reduce the risk of damage to electronic components.

[0101] As can be seen from Tables 1 to 3, the thermally conductive sheets of Examples 1 and 2 have a tear strength of 0.9 kN / m or more. These results show that the thermally conductive sheets of Examples 1 and 2 are less susceptible to tearing, ripping, and breaking. In other words, the thermally conductive sheets of Examples 1 and 2 are easy to handle when they are incorporated between a printed circuit board and a heat dissipation material.

[0102] As can be seen from Tables 1 to 3, the thermal conductive sheets of Examples 1 and 2 have a loss tangent of 0.7 or more. This allows the tack strength of the thermal conductive sheet to be 10 N or more, as described above, and it is therefore clear that the thermal conductive sheets of Examples 1 and 2 have excellent adhesion to the electronic components and the heat dissipation material when incorporated between a printed circuit board and a heat dissipation material.

[0103] As can be seen from Tables 1 to 3, the thermal conduction sheets of Examples 1 and 2 have a thermal conductivity of 1.0 W / (m K) or more. These results demonstrate that the thermal conduction sheets of Examples 1 and 2 can efficiently transfer heat generated by electronic components to heat dissipation materials.

[0104] As can be seen from Tables 1 to 3, the thermal conductive sheets according to Examples 1 and 2 have a volume resistivity of 1.0 × 10 10 From these results, it can be seen that the thermal conductive sheets of Examples 1 and 2 can prevent current from flowing through the thermal conductive sheet and causing a short circuit in electronic components when the voltage applied to the printed circuit board increases instantaneously after being incorporated between the printed circuit board and the heat dissipation material.

[0105] Within the scope of the concept of the present invention, a person skilled in the art may conceive of various modifications, and these modifications are also understood to fall within the scope of the present invention. For example, even if a person skilled in the art appropriately adds or deletes components or modifies the design of each of the above-described embodiments, or adds or omits steps or modifies conditions, these modifications are also included within the scope of the present invention as long as they maintain the gist of the present invention.

[0106] Furthermore, with regard to other effects brought about by the aspects described in each of the above-mentioned embodiments, those that are clear from the description in this specification or that can be appropriately thought of by a person skilled in the art are naturally understood to be brought about by the present invention.

Claims

1. A thermally conductive sheet made of a thermally conductive composition, the thermally conductive composition includes a thermally conductive filler and an elastomer resin; the volume fraction of the thermally conductive filler is 40% or more and 80% or less based on the volume of the thermally conductive sheet; the storage modulus of a sheet of the thermally conductive composition excluding the thermally conductive filler is 1 kPa or more and 15 kPa or less; a torque change of the thermal conductive composition excluding the thermal conductive filler is 0.2 dN m or less; A thermally conductive sheet having a tack strength of 10 N or more.

2. 2. The thermally conductive sheet according to claim 1, having an Asker C hardness of 5° or more and 60° or less.

3. When the compressive stress immediately after compression at 40% compression is C, the compressive stress 10 minutes after compression is D, and the difference between the compressive stress C and the compressive stress D divided by the compressive stress C is [C-D] / C, The C is 0.2 MPa or more and 3.0 MPa or less, The D is 0.5 MPa or less, The thermal conductive sheet according to claim 1, wherein the [C−D] / C is 0.6 or more.

4. The thermal conductive sheet according to claim 1, having a tear strength of 0.9 kN / m or more.

5. The thermal conductive sheet according to claim 1 , having a loss tangent of 0.7 or more.

6. The thermal conductivity is 1.0 W / (m·K) or more, and the volume resistivity is 1.0×10 １０ The thermal conductive sheet according to claim 1 , having a resistivity of Ω·cm or more.

7. The present invention is applied to a printed circuit board with a heat dissipation material, which includes a printed circuit board on which a plurality of electronic components having different heights are mounted, and a heat dissipation material arranged opposite to the mounting surface of the electronic components of the printed circuit board, 2. The thermal conductive sheet according to claim 1, which is embedded between the printed circuit board and the heat dissipation material in close contact with the mounting surface of the printed circuit board, the outer peripheral surfaces of the plurality of electronic components, and the opposing surface of the heat dissipation material.

Images