Thermally conductive sheet

Abstract

A thermally conductive sheet that contains a resin and a thermally conductive filler, wherein the ratio R40 / R20 of the thermal resistance value R20 per 1 mm as measured while applying a fastening torque of 20 cN∙m and the thermal resistance value R40 per 1 mm as measured while applying a fastening torque of 40 cN∙m is 0.62 or less.

Description

Thermally conductive sheet

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

[0002] As heat-generating electronic components, such as central processing units (CPUs) in personal computers, become smaller and more powerful, the amount of heat generated per unit area by these electronic components has become extremely large. This amount of heat can reach approximately 20 times that of an iron. To prevent these heat-generating electronic components from breaking down over the long term, they must be cooled. Metal heat sinks and housings are used for cooling. However, when a heat-generating electronic component is directly in contact with a heat sink or similar object, microscopic air may exist at the interface, hindering heat conduction. Therefore, to efficiently transfer heat, a thermally conductive material may be placed between the heat-generating electronic component and the heat sink or similar object.

[0003] Thermally conductive materials include thermally conductive spacers, thermally conductive sheets, and thermally conductive greases, which are made by filling thermosetting resins with thermally conductive fillers. Thermally conductive spacers are thick, highly flexible sheets that can conform to the uneven shapes of mating materials. Thermally conductive sheets are relatively thin sheets that are easy to handle and can improve the thermal conductivity between heat-generating electronic components and heat sinks while ensuring insulation. Thermally conductive grease is made by filling a fluid resin with a thermally conductive filler, which allows for a high degree of freedom in application shape and can reduce thermal resistance by applying it thinly.

[0004] For example, a known thermally conductive sheet has a structure in which silicone composition layers containing a thermally conductive filler are laminated on both sides of a reinforcing layer (see, for example, Patent Document 1).

[0005] Japanese Patent Application Laid-Open No. 2022-126642

[0006] With the recent rapid trend toward miniaturization, high integration, and high output of electronic components, the operating temperatures of heat-generating electronic components have risen, and higher voltages are being applied between the heat-generating electronic components and heat sinks. This has led to demand for further improvements in thermal conductivity and insulation, especially for thinly molded thermally conductive sheets.

[0007] Furthermore, gaps between heat-generating electronic components and thermally conductive sheets, or between heat sinks and thermally conductive sheets, reduce thermal conductivity. Therefore, thermally conductive sheets are sometimes fastened to heat-generating electronic components to ensure close contact between the heat-generating electronic components and heat sinks. However, fastening a thermally conductive sheet with high torque can cause fastening components to sink into the thermally conductive sheet at the fastened portion or cause the heat-generating electronic component to lift off the thermally conductive sheet at a distance from the fastened portion, resulting in reduced thermal resistance and insulation. Alternatively, fastening a thermally conductive sheet with high torque can cause localized stress concentrations, resulting in marks or tears on the thermally conductive sheet, potentially shortening its product lifespan.

[0008] Therefore, there is a need for a thermally conductive sheet that, when tightened to a heat-generating electronic component with a torque applied to achieve a predetermined thermal resistance, can achieve high heat dissipation even with a low torque, thereby reducing the risk of marks or tears at the tightened portion and providing a long product life.

[0009] The present invention has been made in view of the above problems, and has an object to provide a thermally conductive sheet having an excellent product life.

[0010] That is, the first embodiment of the present invention is as follows. [1] A thermally conductive sheet comprising a resin and a thermally conductive filler, wherein the ratio R40 / R20 of the thermal resistance value per mm R20 measured by applying a tightening torque of 20 cN·m to the thermal resistance value R40 measured by applying a tightening torque of 40 cN·m is 0.62 or less. [2] The thermally conductive sheet according to [1], wherein the thermal resistance value R20 is 0.50°C / W·mm or less. [3] The thermally conductive sheet according to [1] or [2], wherein the thermal resistance value R40 is 0.30°C / W·mm or less. [4] The thermally conductive sheet according to any one of [1] to [3], comprising a reinforcing material and resin layers laminated on the front and back surfaces of the reinforcing material, wherein the resin layers contain the resin and the thermally conductive filler. [5] The thermally conductive sheet according to any one of [1] to [4], wherein the thermally conductive filler comprises agglomerated particles of boron nitride having a crushing strength of 3.0 MPa or less. [6] The thermally conductive sheet according to any one of [1] to [5], wherein the ratio R60 / R40 of the thermal resistance value R40 to the thermal resistance value R60 per mm measured by applying a tightening torque of 60 cN m is 0.65 or more. [7] The thermally conductive sheet according to any one of [1] to [6], wherein the thermal resistance value R60 per mm measured by applying a tightening torque of 60 cN m is 0.25°C / W mm or less.

[0011] A second embodiment of the present invention is as follows: [1] A thermally conductive sheet comprising a resin and a thermally conductive filler, wherein, when the thermal resistance per mm measured when a tightening torque of 20 cN·m is R20, the thermal resistance per mm measured when a tightening torque of 40 cN·m is R40, and the thermal resistance per mm measured when a tightening torque of 60 cN·m is R60, the ratio of the ratio R60 / R40 to the ratio R40 / R20 ((R60 / R40) / (R40 / R20)) is 1.20 or greater. [2] The thermally conductive sheet according to [1], wherein the difference between the ratio R60 / R40 and the ratio R40 / R20 {(R60 / R40) - (R40 / R20)} is 0.06 or greater. [3] The thermally conductive sheet according to [1] or [2], comprising a reinforcing material and resin layers laminated on the front and back surfaces of the reinforcing material, the resin layers containing the resin and the thermally conductive filler. [4] The thermally conductive sheet according to any one of [1] to [3], wherein the thermally conductive filler contains agglomerated boron nitride particles having a crushing strength of 3.0 MPa or less.

[0012] According to the present invention, it is possible to provide a thermally conductive sheet having an excellent product life.

[0013] 1 is a schematic cross-sectional view showing an example of the thermal conductive sheet according to the first embodiment and the second embodiment; FIG. 2 is a schematic cross-sectional view showing an example of a body using the thermal conductive sheet according to the first embodiment and the second embodiment; FIG. 3 is a graph showing the change in thermal resistance value with respect to the tightening torque in Example 1 and Comparative Example 1.

[0014] The following describes in detail an embodiment of the present invention, but the present invention is not limited to this and various modifications are possible without departing from the spirit of the present invention. In the drawings, the same elements are designated by the same reference numerals, and redundant explanations will be omitted. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0015] 1. First Embodiment 1.1. Thermally Conductive Sheet The thermally conductive sheet of the first embodiment includes a resin and a thermally conductive filler, and has a ratio R40 / R20 of 0.62 or less between the thermal resistance value R20 per mm measured when a tightening torque of 20 cN m is applied and the thermal resistance value R40 per mm measured when a tightening torque of 40 cN m is applied.

[0016] A schematic cross-sectional view showing an example of the thermally conductive sheet of the first embodiment is shown in Fig. 1. As shown in Fig. 1, the thermally conductive sheet 1 of the first embodiment is not particularly limited as long as it is a sheet containing a resin and a thermally conductive filler, but may have a resin layer 10 containing a resin and a thermally conductive filler, or may further have a reinforcing material 20, with the resin layer 10 laminated on the front and back surfaces of the reinforcing material 20.

[0017] FIG. 2 shows a cross-sectional view of a thermally conductive sheet in use. As shown in FIG. 2, the thermally conductive sheet 1 is positioned between a heat-generating electronic component 2 and a heat sink 3. If there is a gap between the heat-generating electronic component 2 and the thermally conductive sheet 1, or between the heat sink 3 and the thermally conductive sheet 1, the thermal resistance at these interfaces increases, reducing overall thermal conductivity. Therefore, in order to ensure close contact between the heat-generating electronic component 2 and the heat sink 3, the thermally conductive sheet 1 is sometimes fastened to the heat-generating electronic component 2 or the heat sink 3 using fastening screws 4 or the like. However, if the thermally conductive sheet is fastened with a high torque, the fastening parts may sink into the thermally conductive sheet at the fastened portion, or the heat-generating electronic component may lift off the thermally conductive sheet at a location away from the fastened portion. Furthermore, if the thermally conductive sheet is fastened with a high torque, it cannot withstand localized stress concentrations, causing deterioration such as marks or tears in the thermally conductive sheet 1 at the fastened portion, shortening the product life.

[0018] In the first embodiment, the "tightening torque" refers to the rotational moment (cN·m) required when tightening the fastening screw.

[0019] As such, even when using the same thermally conductive sheet, the thermal conductivity exhibited varies depending on the tightening torque, so in order to achieve a predetermined thermal conductivity, the thermally conductive sheet must be fixed with a tightening torque of a certain level or more. However, if the tightening torque is too high, the thermally conductive sheet may be torn or damaged, or the insulating properties may be reduced at such damaged locations, thereby shortening the product life of the thermally conductive sheet.

[0020] In contrast, in the first embodiment, the ratio R40 / R20 between the thermal resistance value R20 per mm measured when a tightening torque of 20 cN·m is applied and the thermal resistance value R40 per mm measured when a tightening torque of 40 cN·m is applied is reduced, thereby specifying that thermal conductivity can be exhibited even at low tightening torques. This makes it difficult for the product life of the thermal conductive sheet to be impaired even when tightened with a predetermined tightening torque to exhibit the desired thermal conductivity. The configuration of the thermal conductive sheet is described in detail below.

[0021] 1.1.1 Thermal Resistance Values ​​for Tightening Torque The ratio R40 / R20 of the thermal resistance value per mm R20 measured when a tightening torque of 20 cN m is applied to the thermal resistance value per mm R40 measured when a tightening torque of 40 cN m is 0.62 or less, and preferably 0 to 0.60 or less, 0.10 to 0.58, 0.20 to 0.56, or 0.30 to 0.54. When the ratio R40 / R20 is 0.62 or less, a predetermined thermal conductivity can be exhibited even when tightened with a low tightening torque, which in turn tends to further improve the product life.

[0022] Furthermore, the ratio R60 / R40 of the thermal resistance value R40 to the thermal resistance value R60 per mm measured when a tightening torque of 60 cN·m is preferably 0.65 or greater, 0.70 to 1.00, 0.75 to 0.96, 0.80 to 0.94, or 0.85 to 0.92. A ratio R60 / R40 of 0.65 or greater indicates that the upper limit at which thermal conductivity does not increase easily even with increasing tightening torque is being approached. This eliminates the need to tighten with an unnecessarily high tightening torque in order to improve thermal conductivity, which in turn tends to improve product life.

[0023] Furthermore, the ratio R60 / R20 of the thermal resistance value R20 to the thermal resistance value R60 is preferably 0.36 to 0.54, 0.38 to 0.52, 0.40 to 0.50, or 0.42 to 0.48. When the ratio R60 / R20 is within the above range, thermal conductivity tends to be further improved depending on the tightening torque.

[0024] The thermal resistance value R20 is preferably 0.50°C / W mm or less, 0 to 0.46°C / W mm, 0.10 to 0.42°C / W mm, or 0.20 to 0.40°C / W mm. By having a thermal resistance value R20 of 0.50°C / W mm or less, a predetermined thermal conductivity can be exhibited even when fastened with a low fastening torque, which in turn tends to further improve the product life.

[0025] The thermal resistance value R40 is preferably 0.30°C / W mm or less, 0 to 0.28°C / W mm, 0.05 to 0.26°C / W mm, 0.10 to 0.24°C / W mm, or 0.15 to 0.22°C / W mm. By having a thermal resistance value R40 of 0.30°C / W mm or less, a predetermined thermal conductivity can be exhibited even when fastened with a relatively low fastening torque, which in turn tends to further improve the product life.

[0026] The thermal resistance value R60 is preferably 0.25°C / W mm or less, 0.05 to 0.23°C / W mm, 0.10 to 0.21°C / W mm, or 0.15 to 0.19°C / W mm. When the thermal resistance value R60 is 0.25°C / W mm or less, if the tightening torque is increased, a correspondingly high thermal conductivity tends to be exhibited.

[0027] In the first embodiment, the ratio of R60 / R40 to R40 ((R60 / R40) / (R40 / R20)) is preferably 1.10 or greater, 1.15 to 2.50, 1.20 to 2.25, 1.25 to 2.00, 1.30 to 1.95, 1.35 to 1.90, or 1.40 to 1.85. A ratio ((R60 / R40) / (R40 / R20)) of 1.10 or greater indicates that the rate of decrease in thermal resistance when the tightening torque is changed from 20 cN·m to 40 cN·m is greater than the rate of decrease in thermal resistance when the tightening torque is changed from 40 cN·m to 60 cN·m. This indicates that a predetermined thermal conductivity can be exhibited even when tightened with a relatively low tightening torque, which in turn tends to improve product life.

[0028] The difference between the ratio (R60 / R40) and the ratio (R40 / R20) {(R60 / R40) - (R40 / R20)} is preferably 0.06 or greater, 0.08 to 0.80, 0.10 to 0.75, 0.12 to 0.70, 0.14 to 0.65, 0.18 to 0.60, or 0.22 to 0.5. When the difference {(R60 / R40) - (R40 / R20)} is 0.06 or greater, the rate of decrease in thermal resistance when the tightening torque is changed from 20 cN m to 40 cN m is greater than the rate of decrease in thermal resistance when the tightening torque is changed from 40 cN m to 60 cN m, and the specified thermal conductivity can be exhibited even when tightened with a relatively low tightening torque, which in turn tends to improve the product life.

[0029] The thermal resistance values ​​R20, R40, and R60 are not particularly limited, and can be measured, for example, by the method described in the Examples. The thermal resistance values ​​R20, R40, and R60 can be adjusted by the crushing strength and particle size of the thermally conductive filler used, and the amount and viscosity of the silicone oil used, which will be described later.

[0030] 1.1.2 Resin Layer The resin layer contains a resin and a thermally conductive filler, and may contain silicone oil or a surfactant, as necessary. When the thermally conductive sheet of the first embodiment further includes a reinforcing material 20, the resin layer 10 may be disposed on one surface of the reinforcing material 20, or on both surfaces thereof, as shown in FIG. 1.

[0031] The thickness of the resin layer is preferably 50 to 200 μm, 75 to 150 μm, or 100 to 125 μm. The thinner the resin layer, the more improved the thermal conductivity, and the thicker the resin layer, the more improved the insulation. Furthermore, the presence of a reinforcing material allows the mechanical strength of the thermally conductive sheet to be maintained, allowing the thickness of the resin layer to be made thinner. Note that the thickness of the resin layer refers to the thickness of each resin layer when a reinforcing material is used and the resin layer is present on both sides of the reinforcing material, as described below.

[0032] 1.1.2.1 Resin The resin is not particularly limited, but examples thereof include silicone resin, silicone rubber, epoxy resin, acrylic resin, phenolic resin, melamine resin, unsaturated polyester, fluororesin, polyimide resin, polyamideimide resin, polyetherimide resin, polyester resin, polyphenylene ether resin, etc. These resins may be used alone or in combination of two or more.

[0033] Among these, silicone resins and silicone rubbers are preferred. These silicone resins and silicone rubbers may be peroxide-curable, condensation-curable, addition-curable, or ultraviolet-curable, or may be those cured by these curing reactions. By using such resins, the mechanical strength and flexibility of the thermally conductive sheet are further improved, and the handling properties are further improved, and the thermal conductivity and insulating properties tend to be further improved.

[0034] The resin content is preferably 25 to 55 volume %, 30 to 50 volume %, or 35 to 45 volume % relative to the total volume of the thermally conductive sheet minus the volume of the reinforcing material, i.e., 100 volume % of the resin layer. By having the resin content within the above range, thermal conductivity and insulation properties tend to be further improved.

[0035] 1.1.2.2. Thermally conductive filler The thermally conductive filler is not particularly limited, but examples thereof include boron nitride, aluminum nitride, aluminum oxide, silicon nitride, silicon oxide, zinc oxide, silica, aluminum hydroxide, magnesium oxide, and carbon.

[0036] Among these, boron nitride or aluminum oxide is preferred, boron nitride is more preferred, and hexagonal boron nitride is more preferred. By using such a thermally conductive filler, thermal conductivity and insulating properties tend to be further improved.

[0037] The thermally conductive filler may be secondary particles formed by agglomeration of primary particles (hereinafter also referred to as "aggregated particles"). For example, by using a thermally conductive filler having anisotropy in thermal conductivity as agglomerated particles, the thermal conductivity due to contact between the thermally conductive fillers is improved and it becomes easier to form a thermal conduction path in any direction, which tends to further improve the thermal conductivity.

[0038] When agglomerated particles are used, the crushing strength is preferably 6.0 MPa or less, 0.1 to 5.0 MPa or less, 0.5 to 4.0 MPa or less, or 1.0 to 3.0 MPa or less. A crushing strength of 6.0 MPa or less tends to further decrease R40 / R20 and further improve R40 / R20. Furthermore, the agglomerated particles are appropriately loosened depending on the tightening torque, forming an appropriate heat conduction path. Therefore, high thermal conductivity can be achieved even with a low tightening torque. Furthermore, a crushing strength of 0.1 MPa or more tends to prevent unintended destruction of the agglomerated particles during the molding process of the thermally conductive sheet.

[0039] The thermally conductive filler preferably contains agglomerated particles of boron nitride having a crushing strength of 3.0 MPa or less as agglomerated particles. By using such agglomerated particles of boron nitride having a low crushing strength, a predetermined thermal conductivity can be exhibited even when fastened with a low fastening torque, which tends to further improve the product life.

[0040] The average particle size of the thermally conductive filler is preferably 70 to 170 μm, 80 to 160 μm, 90 to 150 μm, 100 to 140 μm, or 110 to 130 μm. By having the average particle size of the thermally conductive filler within the above range, the dispersibility and filling ability of the thermally conductive filler in the thermally conductive sheet tend to be further improved. Furthermore, the specified thermal conductivity can be exhibited even when fastened with a low fastening torque, which in turn tends to further improve the product life.

[0041] In the first embodiment, the average particle size refers to the median diameter D50. In addition, when the thermally conductive filler is in the form of agglomerated particles, the average particle size refers to the particle size of the agglomerated particles (secondary particles).

[0042] The total content of the thermally conductive filler is preferably 35 to 75 vol%, 40 to 70 vol%, 45 to 65 vol%, or 50 to 60 vol%, relative to the total volume of the thermally conductive sheet minus the volume of the reinforcing material, i.e., 100 vol% of the resin layer. By having the total content of the thermally conductive filler within the above range, thermal conductivity and insulation tend to be further improved. While a high loading of the thermally conductive filler is preferable from the perspective of improving thermal conductivity, the higher the total content of the thermally conductive filler, the higher the porosity and the lower the insulation tends to be. Therefore, the present invention, which can reduce porosity and improve insulation, is useful.

[0043] 1.1.2.3. Silicone Oil The thermally conductive sheet of the first embodiment, particularly the resin layer, may further contain silicone oil. Examples of silicone oils include, but are not limited to, peroxide-curable, condensation-curable, addition-curable, and ultraviolet-curable non-reactive compounds without curable functional groups. Examples of such silicone oils include, but are not limited to, dimethylpolysiloxane and diphenylpolysiloxane.

[0044] The viscosity of the silicone oil at 23°C is preferably 5.0 x 10 ３ mm ２ / s or more, and 1.0 × 10 ４ ~2.5 x 10 ７ mm ２ / s, and 5.0 × 10 ４ ~2.0 x 10 ７ mm ２ / s, and 1.0 × 10 ５ ~1.5 x 10 ７ mm ２ / s, and 5.0 × 10 ５ ~1.0 x 10 ７ mm ２ / s. The viscosity of the silicone oil at 23°C is 5.0 x 10 ３ mm ２ / s or more, the R40 / R20 tends to decrease further and the R40 / R20 tends to improve further. Furthermore, when the viscosity of the silicone oil at 23°C is within the above range, a predetermined thermal conductivity can be achieved even when tightened with a low tightening torque, and there is no need to tighten with an unnecessarily high tightening torque in order to improve thermal conductivity, which in turn tends to improve the product life.

[0045] The silicone oil may be used alone or in combination of two or more types having different structures, viscosities, etc.

[0046] The content of the silicone oil is preferably 0.5 to 5.0 volume %, 0.5 to 2.5 volume %, or 0.5 to 1.5 volume % relative to the total volume of the thermally conductive sheet minus the volume of the reinforcing material, i.e., 100 volume % of the resin layer. By having the content of the silicone oil within the above range, thermal conductivity and insulating properties tend to be further improved.

[0047] 1.1.2.4. Surfactant The surfactant is not particularly limited, but for example, a polymer having a silicone (meth)acrylic monomer unit γ is preferred, and a copolymer having a (meth)acrylic monomer unit α having an anionic group, a (meth)acrylic monomer unit β having a cationic group, and a silicone (meth)acrylic monomer unit γ is more preferred. The use of such a surfactant tends to improve the dispersibility of the thermally conductive filler component and further reduce thermal resistance.

[0048] The content of the surfactant is 1.0 to 8.0 volume %, 2.0 to 6.0 volume %, 3.0 to 6.0 volume %, or 4.0 to 5.0 volume % relative to the total volume of the thermally conductive sheet minus the volume of the reinforcing material, i.e., 100 volume % of the resin layer. By having the content of the surfactant within the above range, the dispersibility of the thermally conductive filler component tends to be improved, and the thermal resistance tends to be further reduced.

[0049] The surfactant will be described in more detail below. In the first embodiment, a "monomer" refers to a monomer having a polymerizable unsaturated bond before polymerization, and a "monomer unit" refers to a repeating unit that constitutes a part of the surfactant after polymerization and is derived from a specific monomer. Furthermore, (meth)acrylic includes acrylic and methacrylic, and (meth)acrylic monomers include (meth)acrylate and (meth)acrylamide. Furthermore, hereinafter, "(meth)acrylic monomer unit α" and the like will also be simply referred to as "unit α" and the like.

[0050] The (meth)acrylic monomer unit α is a repeating unit having an anionic group. The anionic group is not particularly limited, but examples thereof include a carboxy group, a phosphate group, a phenolic hydroxy group, and a sulfonic acid group. Among these, one or more groups selected from the group consisting of a carboxy group, a phosphate group, and a phenolic hydroxy group are preferred. The presence of such a group tends to further improve the dispersibility of the filler component.

[0051] Such a (meth)acrylic monomer is not particularly limited, but examples thereof include acrylic acid, methacrylic acid, acid phosphooxypropyl methacrylate, acid phosphooxypolyoxyethylene glycol monomethacrylate, acid phosphooxypolyoxypropylene glycol monomethacrylate, phosphoric acid-modified epoxy acrylate, 2-acryloyloxyethyl acid phosphate, 2-methacryloyloxyethyl acid phosphate, 4-hydroxyphenyl acrylate, 4-hydroxyphenyl methacrylate, 2-methacryloyloxyethyl succinic acid, and 2-acrylamido-2-methylpropanesulfonic acid.

[0052] The (meth)acrylic monomer unit β is a repeating unit having a cationic group. The cationic group is not particularly limited, but is preferably, for example, one or more selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, and a quaternary ammonium salt. Among these, a tertiary amino group is more preferred. The presence of such a group tends to further improve the dispersibility of the filler component.

[0053] Such (meth)acrylic monomers are not particularly limited, and examples thereof include 1-aminoethyl acrylate, 1-aminopropyl acrylate, 1-aminoethyl methacrylate, 1-aminopropyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, t-butylaminoethyl (meth)acrylate, dimethylaminoethyl methacrylate quaternary salt, 1,2,2,6,6-pentamethyl-4-piperidyl acrylate, 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate, 2,2,6,6-tetramethyl-4-piperidyl methacrylate, and dimethylaminoethyl acrylate benzyl chloride quaternary salt.

[0054] The (meth)acrylic monomer unit γ is a silicone (meth)acrylic monomer unit, which is a (meth)acrylic monomer that does not contain a cationic group or an anionic group in the molecule but has a silicone group.

[0055] The (meth)acrylic monomer unit γ preferably has a skeleton that has high affinity or compatibility with other matrix components. The (meth)acrylic monomer unit γ has a silicone skeleton such as dimethylsiloxane, methylphenylsiloxane, or diphenylsiloxane. By having such a skeleton, compatibility with other matrix components is improved, and the dispersibility of the filler component in the thermal grease tends to be improved.

[0056] Such a (meth)acrylic monomer is not particularly limited, but examples thereof include (meth)acrylic monomers having a siloxane skeleton, such as α-butyl-ω-(3-methacryloxypropyl)polydimethylsiloxane, etc. The unit γ may be used alone or in combination of two or more.

[0057] 1.1.3. Reinforcing Material The presence of a reinforcing material in a thermally conductive sheet tends to further improve the mechanical strength of the thermally conductive sheet and improve its handling. The position of the reinforcing material 20 is not particularly limited, but it is preferably located, for example, at the center of the thermally conductive sheet in the thickness direction. In other words, it is preferable that the reinforcing material 20 is not present on either surface of the cross section in the thickness direction. This allows resin layers to be disposed on the front and back surfaces of the thermally conductive sheet, and the resin layers come into contact with the heat-generating electronic component and the heat sink, which tends to further improve thermal conductivity and insulation.

[0058] The reinforcing material is not particularly limited, but examples thereof include glass cloth; organic fiber cloth such as cotton, hemp, aramid fiber, cellulose fiber, nylon fiber, and polyolefin fiber; inorganic fiber cloth such as stainless steel, copper, and aluminum; nonwoven fabric; resin film; and metal foil such as copper foil, nickel foil, and aluminum foil. Among these, glass cloth is preferred. The use of such a reinforcing material tends to further improve insulation and thermal conductivity.

[0059] The thickness of the reinforcing material is preferably 10 to 150 μm, 20 to 100 μm, or 30 to 75 μm. When the thickness of the reinforcing material is within the above range, the thermal conductive sheet can be configured to be thin while maintaining mechanical strength, which tends to further improve thermal conductivity.

[0060] 1.1.4. Thickness The thickness of the thermally conductive sheet of the first embodiment is preferably 100 to 800 μm, 125 to 600 μm, or 150 to 400 μm. The thinner the thermally conductive sheet, the better the thermal conductivity, and the thicker the thermally conductive sheet, the better the insulation. Furthermore, the presence of a reinforcing material allows the thermally conductive sheet to maintain its mechanical strength, allowing the thickness of the thermally conductive sheet to be made thinner.

[0061] 1.1.5 Durometer A Hardness The Durometer A hardness of the thermally conductive sheet of the first embodiment is preferably 65 to 90, 70 to 88, 75 to 86, or 80 to 84. When the Durometer A hardness is within the above range, the thermally conductive sheet is less susceptible to damage, and the product life tends to be further improved.

[0062] 1.1.6. Thermal Conductivity The thermal conductivity of the thermally conductive sheet of the first embodiment is preferably 5.0 to 15.0 W / mK, more preferably 6.0 to 15.0 W / mK, and even more preferably 7.0 to 15.0 W / mK.

[0063] 1.2. First Embodiment: Manufacturing Method of Thermally Conductive Sheet The manufacturing method of the thermally conductive sheet of the first embodiment is not particularly limited, but may, for example, include a resin layer forming step of forming a resin layer from a resin composition containing a resin and a thermally conductive filler, and when the thermally conductive sheet has a reinforcing material, may include a pressurizing step of forming two resin layers in the resin layer forming step, sandwiching the reinforcing material between the two obtained resin layers, and applying heat and pressure to form the thermally conductive sheet.

[0064] 1.2.1 Resin Layer Forming Step The resin layer forming step is a step of forming a resin layer using a resin composition containing a resin and a thermally conductive filler. The resin composition contains a resin and a thermally conductive filler, and may also contain a solvent such as toluene, a dispersant for the thermally conductive filler, and the like, as necessary.

[0065] The method for forming the resin layer is not particularly limited, but for example, a method in which a resin composition is applied to a release film such as a PET film and dried at room temperature or under heat can be mentioned.

[0066] The coating method is not particularly limited, and known coating methods such as a doctor blade method, a comma coater method, a screen printing method, a roll coater method, etc. Among these, the doctor blade method and the comma coater method are preferred from the viewpoint of thickness accuracy of the resin layer.

[0067] 1.2.2. Pressurization Process The pressurization process is a process in which a reinforcing material is sandwiched between two resin layers obtained in the resin layer molding process, and heated and pressurized to form a thermally conductive sheet having resin layers on both sides of the reinforcing material. During this process, at least a portion of the resin component of the resin layer melts or deforms and penetrates into the fibers of the reinforcing material. Note that a thermally conductive sheet having a resin layer on one side of the reinforcing material may be formed by pressing and heating one resin layer against one side of the reinforcing material.

[0068] The heating and pressurizing conditions are not particularly limited. For example, the heating temperature is preferably 100 to 200°C, and 125 to 175°C. The pressing pressure is preferably 5 to 15 MPa, and 7.5 to 12.5 MPa. The heating and pressurizing time is preferably 30 to 90 minutes, and 45 to 75 minutes.

[0069] 2. Second Embodiment Next, a thermally conductive sheet and a manufacturing method thereof according to a second embodiment will be described. Note that configurations similar to those in the first embodiment will be described accordingly and overlapping descriptions will be omitted.

[0070] 2.1 Thermally conductive sheet The thermally conductive sheet of the second embodiment includes a resin and a thermally conductive filler, and when the thermal resistance per mm measured when a tightening torque of 20 cN m is R20, the thermal resistance per mm measured when a tightening torque of 40 cN m is R40, and the thermal resistance per mm measured when a tightening torque of 60 cN m is R60, the ratio of the ratio R60 / R40 to the ratio R40 / R20 ((R60 / R40) / (R40 / R20)) is 1.20 or greater.

[0071] The thermally conductive sheet of the second embodiment can also be configured as shown in Fig. 1. The thermally conductive sheet of the second embodiment can also be used as shown in Fig. 2.

[0072] In contrast, in the second embodiment, the ratio of R60 / R40 to R40 ((R60 / R40) / (R40 / R20)) is increased to ensure that thermal conductivity can be achieved even with a low tightening torque. This makes it difficult for the product life of the thermally conductive sheet to be impaired, even when tightened with a specified tightening torque to achieve a specified thermal conductivity. The configuration of the thermally conductive sheet is described in detail below.

[0073] 2.1.1 Thermal Resistance Values ​​for Fastening Torque In the second embodiment, the thermal resistance value per mm measured when a fastening torque of 20 cN m is applied is R20, the thermal resistance value per mm measured when a fastening torque of 40 cN m is R40, and the thermal resistance value per mm measured when a fastening torque of 60 cN m is R60.

[0074] The ratio of R60 / R40 to R40 ((R60 / R40) / (R40 / R20)) is preferably 1.20 or more, 1.20 to 2.25, 1.25 to 2.00, 1.30 to 1.95, 1.35 to 1.90, or 1.40 to 1.85. When the ratio R40 / R20 / (R60 / R40) is 1.20 or more, the rate of decrease in thermal resistance when the tightening torque is changed from 20 cN·m to 40 cN·m is greater than the rate of decrease in thermal resistance when the tightening torque is changed from 40 cN·m to 60 cN·m, and the specified thermal conductivity can be exhibited even when tightened with a relatively low tightening torque, which in turn tends to improve the product life.

[0075] The difference between the ratio R60 / R40 and the ratio R40 / R20 {(R60 / R40) - (R40 / R20)} is preferably 0.06 or greater, 0.08 to 0.80, 0.10 to 0.75, 0.12 to 0.70, 0.14 to 0.65, 0.18 to 0.60, or 0.22 to 0.5. When the difference {(R60 / R40) - (R40 / R20)} is 0.06 or greater, the rate of decrease in thermal resistance when the tightening torque is changed from 20 cN m to 40 cN m is greater than the rate of decrease in thermal resistance when the tightening torque is changed from 40 cN m to 60 cN m, and the specified thermal conductivity can be exhibited even when tightened with a relatively low tightening torque, which tends to further improve the product life.

[0076] The ratio R40 / R20 of the thermal resistance value R20 to the thermal resistance value R40 is preferably 0.62 or less, 0 to 0.60 or less, 0.10 to 0.58, 0.20 to 0.56, or 0.30 to 0.54. When the ratio R40 / R20 is 0.62 or less, a predetermined thermal conductivity can be exhibited even when fastened with a low fastening torque, which tends to further improve the product life.

[0077] The ratio R60 / R40 of the thermal resistance value R40 to the thermal resistance value R60 is preferably 0.65 or more, 0.70 to 1.00, 0.75 to 0.96, 0.80 to 0.94, or 0.85 to 0.92. A ratio R60 / R40 of 0.65 or more indicates that the upper limit at which thermal conductivity does not increase easily even with increased tightening torque is being approached. This eliminates the need to tighten with an unnecessarily high tightening torque in order to improve thermal conductivity, which in turn tends to further improve product life.

[0078] The ratio R60 / R20 of the thermal resistance value R20 to the thermal resistance value R60 is preferably 0.36 to 0.54, 0.38 to 0.52, 0.40 to 0.50, or 0.42 to 0.48. When the ratio R60 / R20 is within the above range, the thermal conductivity tends to be further improved depending on the tightening torque.

[0079] The thermal resistance value R20 is preferably 0.50°C / W mm or less, 0 to 0.46°C / W mm, 0.10 to 0.42°C / W mm, or 0.20 to 0.40°C / W mm. By having a thermal resistance value R20 of 0.50°C / W mm or less, a predetermined thermal conductivity can be exhibited even when fastened with a low fastening torque, which in turn tends to further improve the product life.

[0080] The thermal resistance value R40 is preferably 0.30°C / W mm or less, 0 to 0.28°C / W mm, 0.05 to 0.26°C / W mm, 0.10 to 0.24°C / W mm, or 0.15 to 0.22°C / W mm. By having a thermal resistance value R40 of 0.30°C / W mm or less, a predetermined thermal conductivity can be exhibited even when fastened with a relatively low fastening torque, which in turn tends to further improve the product life.

[0081] The thermal resistance value R60 is preferably 0.25°C / W mm or less, 0.05 to 0.23°C / W mm, 0.10 to 0.21°C / W mm, or 0.15 to 0.19°C / W mm. When the thermal resistance value R60 is 0.25°C / W mm or less, if the tightening torque is increased, a correspondingly high thermal conductivity tends to be exhibited.

[0082] The thermal resistance values ​​R20, R40, and R60 are not particularly limited, and can be measured, for example, by the method described in the Examples. The thermal resistance values ​​R20, R40, and R60 can be adjusted by the crushing strength and particle size of the thermally conductive filler used, and the amount and viscosity of the silicone oil used, which will be described later.

[0083] 2.1.2 Others In the second embodiment, the resin layer, reinforcing material, thickness, durometer A hardness, thermal conductivity, and manufacturing method of the thermal conductive sheet may be similar to those described and exemplified in the first embodiment. Therefore, description of these will be omitted in the second embodiment.

[0084] The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited to the following examples. Unless otherwise specified, all operations were carried out at 23°C and 50% humidity.

[0085] Example 1 Boron nitride agglomerated particles (low-strength BN, crushing strength: 2 MPa, average particle size D50: 120 μm), silicone resin (peroxide-curable silicone, trade name "CF3110" manufactured by Toray Dow Corning Silicone Co., Ltd.), surfactant, toluene, curing agent (2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, trade name "Trigonox 101" manufactured by Kayaku Nouryon Co., Ltd.), and silicone oil KF-96H-1 million CS, manufactured by Shin-Etsu Chemical Co., Ltd., viscosity 1 million mm ２ The resulting resin composition was applied to a PET film by a doctor blade method, and the film was left to stand at room temperature for 1 hour to volatilize the toluene, thereby forming a resin layer having a thickness of 150 μm.

[0086] The surfactant used above was prepared by the following method: First, 100 parts by mass of a (meth)acrylic monomer consisting of 48.4 mol % acrylic acid (manufactured by Toagosei Co., Ltd.), 1.6 mol % 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate (manufactured by ADEKA Corporation, "ADK STAB LA-82"), and 50.0 mol % α-butyl-ω-(3-methacryloxypropyl)polydimethylsiloxane (weight average molecular weight 5,000, manufactured by JNC Corporation, "Silaplane FM-0721") was added to an autoclave equipped with a stirrer. Next, 0.05 parts by mass of azobisisobutyronitrile (manufactured by Tokyo Chemical Industry Co., Ltd.) as an initiator relative to 100 parts by mass of the total of the (meth)acrylic monomers, and 1,000 parts by mass of a mixed solution of toluene (special reagent grade) and 2-propanol (special reagent grade) in a volume ratio of 7:3 were added as a solvent, and the autoclave was purged with nitrogen. The autoclave was then heated in an oil bath at 65°C for 20 hours to carry out radical polymerization. After completion of polymerization, the mixture was degassed under reduced pressure at 120°C for 1 hour to obtain a surfactant copolymer.

[0087] A glass cloth reinforcing material (trade name "H25" manufactured by Unitika Ltd.) was sandwiched between the two resin layers, and heated and pressurized at 150°C, 10 MPa, and 1 hour to form a thermally conductive sheet with a resin layer on both sides of the reinforcing material. The thickness of the resulting thermally conductive sheet was 300 μm.

[0088] The components used and the contents of boron nitride agglomerated particles 1 and 2, boron nitride flake particles, silicone resin, and silicone oil in the thermally conductive sheet obtained by the above procedure are shown in Table 1. The contents are shown as the volume obtained by subtracting the volume of the reinforcing material from the total volume of the thermally conductive sheet, i.e., as a percentage relative to 100% by volume of the resin layer.

[0089] The crushing strength of the agglomerated boron nitride particles was measured in accordance with JIS R1639-5:2007. Specifically, the boron nitride particles were dispersed on the sample stage of a microcompression tester ("MCT-211" manufactured by Shimadzu Corporation), and 20 agglomerated boron nitride particles were selected from the boron nitride particles. A compression test was performed on each particle. The crushing strength (σ: MPa) was calculated using the equation σ = α × P / (π × d2) from the dimensionless number (α = 2.48), which varies depending on the position within the particle, the crushing test force (P: N), and the particle size (d: μm). In accordance with JIS R1625:2010, a Weibull plot of the crushing strengths of 20 inorganic filler components was performed, and the crushing strength at which the cumulative failure rate reached 63.2% was defined as the crushing strength of the boron nitride particles.

[0090] A thermally conductive sheet was placed between the TO-3 model heater and the copper plate. The thermally conductive sheet was then fastened using screws with a nominal diameter of M3 mm at tightening torques of 20 cN m, 40 cN m, and 60 cN m. The contact area between one TO-3 model heater and the heat dissipation sheet was approximately 6 cm. ２ Thereafter, a power supply device (manufactured by Kikusui Electronics Co., Ltd., model number: PMC35-3) was used to apply 15 W of power to the TO-3 model heater. Then, 10 minutes after the application of 15 W of power, the temperature (T1) of the TO-3 model heater and the temperature (T2) of the copper plate were measured, and the thermal resistance was calculated using the following formula: Thermal resistance (°C / W) = (T1 - T2) / 15

[0091] The thermal resistance per unit thickness (°C / W mm) was calculated by dividing the obtained thermal resistance by the thickness of the sheet. Table 1 shows the rounded values ​​of R20, R40, and R60.

[0092] The durometer A hardness of the thermally conductive sheet was measured according to a method in accordance with JIS K 6253. Specifically, the heat dissipation sheet material was cut into a size of 25 mm x 25 mm and stacked to a height of 12 mm or more, and the hardness was measured using a durometer type A (manufactured by Mitutoyo Corporation).

[0093] (Example 2) Silicone oil (KF-96H-1,000,000 CS, manufactured by Shin-Etsu Chemical Co., Ltd., viscosity 1,000,000 mm ２ / s), silicone oil (KF-96H-100,000 CS, manufactured by Shin-Etsu Chemical Co., Ltd., viscosity 100,000 mm ２ A thermally conductive sheet of Example 2 was produced in the same manner as in Example 1, except that the thermally conductive sheet of Example 2 was used.

[0094] (Example 3) Silicone oil (KF-96H-1,000,000 CS, manufactured by Shin-Etsu Chemical Co., Ltd., viscosity 1,000,000 mm ２ The thermally conductive sheet of Example 3 was produced in the same manner as in Example 1, except that the amount of the silicone resin (peroxide-curable silicone, manufactured by Dow Corning Toray Silicones Co., Ltd. under the trade name "CF3110") used was 33.7 vol%.

[0095] Comparative Example 1 A thermally conductive sheet of Comparative Example 1 was produced by the same procedure as in Example 1, except that boron nitride agglomerated particles (high-strength BN, crushing strength: 8 MPa, average particle size D50: 80 μm) were used instead of the boron nitride agglomerated particles (low-strength BN, crushing strength: 2 MPa, average particle size D50: 120 μm).

[0096] Comparative Example 2 A thermally conductive sheet of Comparative Example 2 was produced in the same manner as in Comparative Example 1, except that silicone oil and surfactant were not used and the amount of silicone resin used was as shown in Table 1.

[0097] Comparative Example 3 A thermally conductive sheet of Comparative Example 3 was produced in the same manner as in Example 1, except that silicone oil was not used and the amount of silicone resin used was as shown in Table 1.

[0098] (Comparative Example 4) Silicone oil (KF-96H-1,000,000 CS, manufactured by Shin-Etsu Chemical Co., Ltd., viscosity 1,000,000 mm ２ / s), silicone oil (KF-96-1000CS, manufactured by Shin-Etsu Chemical Co., Ltd., viscosity 1,000 mm ２ A thermally conductive sheet of Comparative Example 4 was produced in the same manner as in Example 1, except that the thermally conductive sheet of Comparative Example 4 was used.

[0099] (Evaluation) (Product Life) A thermally conductive sheet was sandwiched between the TO-220 package and the heat sink, and torque was applied so that the thermal resistance of the thermally conductive sheet was 0.27°C / W mm, as measured by the thermal resistance measurement method described in the examples (thermal resistance measurement using a TO-3 heater), and the product was left for 1 hour. The thermally conductive sheet was then removed and left for another 1 hour, after which it was checked whether or not any traces of the fastening member had sunk into the periphery of the fastening portion of the thermally conductive sheet. A: No traces remained, and there was no problem with the product life even with continued use. B: Slight traces remained, but there was no problem with the product life even with continued use. C: Clear traces remained, and there were concerns about the product life with continued use.

[0100]

[0101] 3 is a graph showing the change in thermal resistance value with respect to the tightening torque for Example 1 and Comparative Example 1. As shown in Fig. 3, it can be seen that in the example, high thermal resistance can be achieved with a low tightening torque, without applying a physical load to the thermal conductive sheet by tightening.

[0102] INDUSTRIAL APPLICABILITY The present invention has industrial applicability as a thermally conductive sheet having excellent thermal conductivity and electrical insulation properties.

[0103] REFERENCE SIGNS LIST 1...thermal conductive sheet, 2...heat-generating electronic component, 3...heat sink, 4...fastening screw, 10...resin layer, 20...reinforcing material

Claims

1. A thermally conductive sheet comprising a resin and a thermally conductive filler, in which the ratio R40 / R20 of the thermal resistance value per mm measured when a tightening torque of 20 cN·m is applied to the thermal resistance value per mm measured when a tightening torque of 40 cN·m is applied is 0.62 or less.

2. The thermal conductive sheet according to claim 1, wherein the thermal resistance value R20 is 0.50°C / W·mm or less.

3. The thermal conductive sheet according to claim 1, wherein the thermal resistance value R40 is 0.30°C / W·mm or less.

4. The thermally conductive sheet according to claim 1, comprising a reinforcing material and resin layers laminated on the front and back surfaces of the reinforcing material, the resin layers containing the resin and the thermally conductive filler.

5. The thermally conductive sheet according to claim 1, wherein the thermally conductive filler comprises agglomerated particles of boron nitride having a crushing strength of 3.0 MPa or less.

6. The thermal conductive sheet according to claim 1, wherein the ratio R60 / R40 of the thermal resistance value R40 to the thermal resistance value R60 per mm measured by applying a tightening torque of 60 cN·m is 0.65 or more.

7. The thermally conductive sheet according to claim 1, wherein the thermal resistance value R60 per mm measured by applying a tightening torque of 60 cN·m is 0.25°C / W·mm or less.

8. A thermally conductive sheet comprising a resin and a thermally conductive filler, wherein the thermal resistance per mm measured when a tightening torque of 20 cN·m is R20, the thermal resistance per mm measured when a tightening torque of 40 cN·m is R40, and the thermal resistance per mm measured when a tightening torque of 60 cN·m is R60, the ratio of the ratio R60 / R40 to the ratio R40 / R20 ((R60 / R40) / (R40 / R20)) is 1.20 or greater.

9. The thermally conductive sheet according to claim 8, wherein the difference between the ratio R60 / R40 and the ratio R40 / R20 {(R60 / R40) - (R40 / R20)} is 0.06 or more.

10. The thermally conductive sheet according to claim 8, comprising a reinforcing material and resin layers laminated on the front and back surfaces of the reinforcing material, the resin layers containing the resin and the thermally conductive filler.

11. The thermally conductive sheet according to claim 8, wherein the thermally conductive filler comprises agglomerated boron nitride particles having a crushing strength of 3.0 MPa or less.

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