Thermally conductive sheet and method for manufacturing same

Abstract

A thermally conductive sheet 11a, 11b contains a non-curable liquid matrix resin (A) and thermally conductive particles (B), wherein: the component (A) is at least one substance selected from the group consisting of an ethylene-α-olefin copolymer (A1) having a kinematic viscosity of 50-10,000 mm2 / s at 40ºC and a mixed oil (A) of polydecene-1 and an ethylene-α-olefin copolymer, the mixed oil having a kinematic viscosity of 50-10,000 mm2 / s at 40ºC; 400-2800 parts by mass of the thermally conductive particles of the component (B) are contained with respect to 100 parts by mass of the component (A); and the thermally conductive sheet 11a, 11b is in a non-cured state. As a result, the present invention provides: a thermally conductive sheet capable of increasing pot life (usage period) in a raw material stage, reducing manufacturing cost by eliminating the need for a heating and curing step, and reducing hardness; and a method for manufacturing the thermally conductive sheet.

Description

Thermally conductive sheet and manufacturing method thereof

[0001] The present invention relates to a thermally conductive sheet suitable for being interposed between a heat-generating portion of an electric or electronic component or the like and a heat sink, and a method for producing the same.

[0002] Recent advances in the performance of semiconductors such as CPUs have resulted in enormous increases in heat generation. Heat sinks are therefore attached to heat-generating electronic components, and thermally conductive silicone greases are used to improve adhesion between heat sinks and heat sinks. However, over long-term use, thermally conductive silicone greases can leak out of the heat sink due to the thermal shock of semiconductor elements, creating voids in the heat sink, resulting in the so-called pumping-out phenomenon. Patent Document 1 proposes a thermally conductive resin containing an α-olefin copolymer with a crystallinity of 10 or less and at least two α-olefins containing 2 to 12 carbon atoms as its main components, and a surface-modified thermally conductive filler. Patent Document 2 proposes a flame-retardant silicone rubber composition containing liquid ethylene-propylene copolymer rubber, an organic peroxide crosslinking agent, and a metal oxide filler. In Patent Document 3, the present inventors have proposed a silicone gel composition and silicone gel sheet that contain an organopolysiloxane capable of undergoing addition reaction curing, an unsaturated hydrocarbon compound having one alkenyl group per molecule, and an addition reaction curing catalyst, and that exhibits little oil bleeding.

[0003] JP 2004-143195 A JP 2010-077220 A Japanese Patent No. 7041793 A

[0004] However, the thermally conductive compositions of the prior art have problems such as a short pot life (usage period) in the raw material stage, high manufacturing costs due to the heat curing step, and high hardness upon curing.

[0005] In order to solve the above-mentioned conventional problems, the present invention provides a thermally conductive sheet and a manufacturing method thereof that has a long pot life (usage period) at the raw material stage, does not require a heat curing process, reduces manufacturing costs, and has low hardness.

[0006] One embodiment of the present invention is a thermally conductive sheet comprising a non-curable liquid matrix resin (A) and thermally conductive particles (B), wherein the component (A) has a kinematic viscosity at 40°C of 50 to 10,000 mm 2 ethylene / α-olefin copolymer (A1) having a kinematic viscosity at 40°C of 50 to 10,000 mm 2 and (A2) a mixed oil of polydecene-1 and an ethylene-α-olefin copolymer, wherein the amount of the thermally conductive particles of the component (B) is 400 to 2,800 parts by mass per 100 parts by mass of the component (A), and the thermally conductive sheet is in an uncured state.

[0007] One embodiment of the method of the present invention is the method for producing the thermally conductive sheet, wherein the non-curable liquid matrix resin (A) has a kinematic viscosity at 40°C of 50 to 10,000 mm 2 ethylene / α-olefin copolymer (A1) having a kinematic viscosity at 40°C of 50 to 10,000 mm 2 and (A2) a mixed oil of polydecene-1 and an ethylene-α-olefin copolymer, and 400 to 2,800 parts by mass of thermally conductive particles (B) per 100 parts by mass of the component (A), followed by molding the mixture into a sheet without a heat curing step.

[0008] The thermally conductive sheet of the present invention is a thermally conductive sheet containing a non-curable liquid matrix resin (A) and thermally conductive particles (B), and the component (A) has a kinematic viscosity at 40°C of 50 to 10,000 mm 2 ethylene / α-olefin copolymer (A1) having a kinematic viscosity at 40°C of 50 to 10,000 mm 2The thermally conductive particles of component (B) are present in an amount of 400 to 2,800 parts by mass per 100 parts by mass of component (A), and the thermally conductive particles are at least one selected from the group consisting of a mixture of polydecene-1 and an ethylene-α-olefin copolymer (A2) at a ratio of 1 / s to 400 parts by mass per 100 parts by mass of component (A). Because the thermally conductive particles are in an uncured state, they have a long pot life (usage period) at the raw material stage, do not require a heat curing step, thereby reducing production costs and hardness. The present invention also provides a thermally conductive sheet and a method for producing the same. The present invention also provides a non-silicone thermally conductive sheet that has good thermal conductivity and a SHORE 00 hardness.

[0009] 1A-B are explanatory diagrams showing a method for measuring the thermal conductivity of a sample in one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a method for using a thermally conductive sheet in one embodiment of the present invention. FIG. 3 is a scanning electron microscope (SEM) photograph (magnification: 5000x) of amorphous alumina (D50 (median diameter) 0.3 μm) used in one embodiment of the present invention. FIG. 4 is a scanning electron microscope (SEM) photograph (magnification: 2000x) of amorphous alumina (D50 (median diameter) 2.2 μm) used in one embodiment of the present invention. FIG. 5 is a scanning electron microscope (SEM) photograph (magnification: 100x) of spherical alumina (D50 (median diameter) 75 μm) used in one embodiment of the present invention. FIG. 6 is a scanning electron microscope (SEM) photograph (magnification: 2000x) of rounded aluminum nitride (D50 (median diameter) 20 μm) used in one embodiment of the present invention. FIG. 7 is a scanning electron microscope (SEM) photograph (magnification: 2000 times) of amorphous aluminum nitride (D50 (median diameter) 20 μm) used in one embodiment of the present invention.

[0010] The present invention provides a thermally conductive sheet comprising a non-curable liquid matrix resin (A) and thermally conductive particles (B). The components (A) and (B) are uniformly mixed to form a compound composition, which is then molded into a sheet. The component (A) has a kinematic viscosity of 50 to 10,000 mm at 40°C. 2 ethylene / α-olefin copolymer (A1) having a kinematic viscosity at 40°C of 50 to 10,000 mm 2The thermally conductive particles of component (B) are at least one selected from the group consisting of a mixed oil (A2) of polydecene-1 and an ethylene-α-olefin copolymer (A1 / s), and the thermally conductive particles of component (B) are contained in an amount of 400 to 2,800 parts by mass per 100 parts by mass of component (A), and are in an uncured state. Being in an uncured state results in a thermally conductive sheet with a long pot life (usage period) in the raw material stage and little risk of changes in hardness, etc., after the product is manufactured. The present invention preferably does not contain a silicone polymer. This eliminates problems caused by the generation of low-molecular-weight siloxanes.

[0011] The components (A1) and (A2) each have a kinematic viscosity at 40°C of 60 to 8,000 mm 2 / s is preferred, and more preferably 70 to 6,000 mm 2 / s, and more preferably 80 to 5,000 mm 2 / s. The ethylene-α-olefin copolymer (A1) is preferably an ethylene-polypropylene copolymer. The copolymerization ratio of ethylene to polypropylene is preferably 90:10 to 10:90 by mass, more preferably 80:20 to 20:80. Furthermore, the mixed oil of polydecene-1 and ethylene-α-olefin copolymer (A2) is preferably a mixture ratio of polydecene-1 to ethylene-α-olefin of 90:10 to 10:90 by mass, more preferably 80:20 to 20:80. Polydecene-1 is a polymer (hydrogenated polydecene) represented by the following (Chemical Formula 1): Here, n is 3 to 500.

[0012] The amount of the thermally conductive particles of the component (B) is 400 to 2800 parts by mass, preferably 600 to 2600 parts by mass, and more preferably 800 to 2400 parts by mass, per 100 parts by mass of the component (A), thereby increasing the thermal conductivity.

[0013] Thermally conductive particles (also referred to as thermally conductive fillers) are particulate materials that are macroscopically powder-like and are mixed with the component (A) to form a composition. Thermally conductive particles refer to particles with excellent thermal conductivity and a higher thermal conductivity than the component (A). Thermally conductive particles include electrically conductive particles and electrically insulating particles, either of which is acceptable. Electrically conductive particles include carbon powders such as carbon black or metal powders. Metal powders with a surface resistance of 1 Ω / □ or less are preferred. Specifically, powders made of metals such as gold, silver, platinum, copper, nickel, iron, palladium, cobalt, chromium, and aluminum, or alloys such as stainless steel, or metal powders whose surfaces are coated with precious metals such as gold and silver to reduce electrical resistance are preferred. The electrically insulating particles are preferably inorganic particles such as alumina (aluminum oxide), zinc oxide, magnesium oxide, aluminum nitride, boron nitride, aluminum hydroxide, and silica other than hydrophilic fumed silica. These inorganic particles may be added alone or in combination. Among these, alumina (aluminum oxide) is preferred because it is inexpensive. When using alumina, α-alumina with a purity of 99.5% by weight or more is preferred. The thermally conductive particles can be in a variety of shapes, including spherical, flaky, polyhedral, and crushed. The specific surface area of ​​the thermally conductive particles should be 0.06 to 10 m. 2 / g is preferred.

[0014] The thermally conductive particles preferably have a particle diameter (D50 (median diameter)) of 0.1 μm or more and 150 μm or less. The thermally conductive particles may be blended singly or in combination. When multiple types are combined, two to six types are preferred. For example, small particles may have a particle diameter (D50 (median diameter)) of 0.1 μm or more and less than 5 μm, medium particles may have a particle diameter (D50 (median diameter)) of 5 μm or more and less than 50 μm, and large particles may have a particle diameter (D50 (median diameter)) of 50 μm or more and 150 μm or less. When multiple types are combined, the medium and / or small particles are packed between the large particles, allowing for a nearly close-packed state and improving thermal conductivity. Furthermore, the composition has low plasticity and is a thermally conductive composition with good moldability. The particle diameter is the D50 (median diameter) of the cumulative particle size distribution on a volume basis, as measured by laser diffraction light scattering. An example of such a measuring device is the laser diffraction / scattering particle distribution measuring device LA-950S2 manufactured by Horiba Ltd.

[0015] The thermally conductive sheet preferably has a thickness of 0.1 mm to 10 mm, more preferably 0.2 to 9 mm, and even more preferably 0.3 to 8 mm. This thickness makes the sheet suitable as a thermally conductive material (TIM) to be interposed between a heat-generating part of an electric or electronic component and a heat sink.

[0016] At least a portion of the thermally conductive particles may be surface-treated in advance with a coupling agent. a Si(OR') 4-a(R is an unsubstituted or substituted hydrocarbon group having 1 to 20 carbon atoms, R' is an alkyl group having 1 to 4 carbon atoms, and a is 0 or 1), or a partial hydrolyzate thereof. Examples of alkoxysilane compounds (hereinafter simply referred to as "silanes") having the above chemical formula include methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, pentyltrimethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, decyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, octadecyltrimethoxysilane, and octadecyltriethoxysilane. The above silane compounds can be used alone or in combination. In particular, if the fine thermally conductive particles having a particle diameter D=50 of less than 5 μm are surface-treated with a coupling agent in advance, they will have better mixability when compounded, improving workability.

[0017] The thermally conductive sheet of the present invention further contains RaSi(OR') as component (C). 4-a (wherein R is an unsubstituted or substituted hydrocarbon group having 8 to 12 carbon atoms, R' is an alkyl group having 1 to 4 carbon atoms, and a is 0 or 1) is preferably contained in an amount of 0.1 to 2.2 parts by mass, and more preferably 0.2 to 2.1 parts by mass, per 100 parts by mass of component (A). Component (C) is not an essential component, but adding component (C) improves mixability when compounded, improving workability.

[0018] The thermal conductivity of the thermally conductive sheet is preferably 1.0 W / m K or more and 20.0 W / m K or less, more preferably 2.0 to 20 W / m K, and even more preferably 3.0 to 20 W / m K. Such a thermally conductive sheet is suitable as a TIM (Thermal Interface Material).

[0019] The SHORE OO hardness of the thermally conductive sheet is preferably 5 or more and 80 or less, more preferably 7 or more and 70 or less, and even more preferably 10 or more and 60 or less. With this hardness, when used as a thermally conductive material (TIM) interposed between a heat-generating part of an electric / electronic component and a heat-dissipating body, the sheet can conform to unevenness in the heat-generating part of the electric / electronic component and / or the heat-dissipating body, facilitating smooth heat transfer. Furthermore, the sheet has good workability. The lower the SHORE OO hardness value, the softer the sheet. The SHORE OO hardness is measured by the method specified in ASTM D2240.

[0020] The method for producing a thermally conductive sheet of the present invention includes the following steps: (1) Compounding step: A non-curable liquid matrix resin (A) having a kinematic viscosity of 50 to 10,000 mm at 40°C is used. 2 ethylene / α-olefin copolymer (A1) having a kinematic viscosity at 40°C of 50 to 10,000 mm 2 A compound is prepared by uniformly mixing 400 to 2,800 parts by mass of thermally conductive particles (B) per 100 parts by mass of component (A) with at least one selected from the group consisting of a mixed oil (A2) of polydecene-1 and ethylene-α-olefin copolymer (single-layer / s). This compound is preferably vacuum degassed. Vacuum degassing involves reducing the pressure of the compound to -0.08 to -0.1 Pa and leaving it for approximately 5 to 10 minutes to degas. (2) Sheet Forming Process: The compound is formed into a sheet without a heat curing process. Sheet formation can be achieved by sandwiching the compound between polyethylene terephthalate (PET) films and rolling it under pressure, or by press rolling, but roll rolling, which allows for continuous sheet formation, is preferred.

[0021] The thermally conductive sheet of the present invention may contain other components as needed. For example, heat resistance improvers such as red iron oxide, titanium oxide, and cerium oxide, flame retardants, and flame retardant assistants may be added. Organic or inorganic particle pigments may also be added for the purpose of coloring and toning.

[0022] The following description will be made with reference to the drawings. In the following drawings, the same reference numerals indicate the same components. FIG. 2 is a schematic cross-sectional view of a heat dissipation structure 10 incorporating a thermally conductive sheet according to one embodiment of the present invention. The thermally conductive sheet 11b dissipates heat generated by an electronic component 13, such as a semiconductor device. The thermally conductive sheet 11b is fixed to a main surface 12a of the heat spreader 12 facing the electronic component 13, and is sandwiched between the electronic component 13 and the heat spreader 2. The thermally conductive sheet 11a is sandwiched between the heat spreader 12 and a heat sink 15. The thermally conductive sheets 11a and 11b, together with the heat spreader 2, constitute a heat dissipation member that dissipates heat from the electronic component 13. The heat spreader 12 is formed, for example, in the shape of a rectangular plate and has a main surface 12a facing the electronic component 13 and a sidewall 12b extending along the outer periphery of the main surface 12a. The heat spreader 2 has a thermally conductive sheet 11b on a main surface 12a surrounded by side walls 12b, and a heat sink 15 on another surface 12c opposite to the main surface 12a, with the thermally conductive sheet 11a interposed therebetween. The electronic component 13 is, for example, a semiconductor element such as a BGA, and is mounted on a wiring board 14.

[0023] The following examples are provided for illustrative purposes only. The present invention is not limited to these examples. Various parameters were measured using the following methods. <Thermal Conductivity> The thermal conductivity of the thermally conductive sheet was measured using a hot disk (in accordance with ISO 22007-2:2008). As shown in FIG. 1A, this thermal conductivity measuring device 1 sandwiches a polyimide film sensor 2 between two samples 3a and 3b. A constant power is applied to the sensor 2 to generate a constant amount of heat, and the thermal characteristics are analyzed based on the temperature rise of the sensor 2. The sensor 2 has a 7 mm diameter tip 4 and, as shown in FIG. 1B, has a double spiral electrode structure with an applied current electrode 5 and a resistance electrode (temperature measurement electrode) 6 located at the bottom. The thermal conductivity is calculated using the following formula (Equation 1): <Hardness> The SHORE 00 hardness specified in ASTM D2240 was measured. The measuring device used was a GS-754G product manufactured by Teclock Corporation. <Kinematic Viscosity> The kinematic viscosity, including the catalog values ​​in the examples, was measured at 40°C using an Ubbelohde viscometer.

[0024] (Examples 1 to 4, Comparative Examples 1 to 3) 1. Matrix resin (Component A) (1) Kinematic viscosity at 40°C of 200 mm 2 / s non-hardening ethylene-propylene copolymer liquid oil (2) kinematic viscosity at 40 ° C. is 100 mm 2 A liquid mixture of non-curing polydecene-1 and ethylene-propylene copolymer with a viscosity of 1000 psi / s. The mixture contains 65% polydecene-1 and 35% ethylene-propylene copolymer. (3) The kinematic viscosity at 40°C is 37,500 mm 2 2. Thermally conductive particles: (1) Irregularly crushed alumina shown in Figure 3, D50 = 0.3 μm, pre-treated with octyltrimethoxysilane. (2) Irregularly crushed alumina shown in Figure 4, D50 = 2.2 μm, pre-treated with decyltrimethoxysilane. (3) Spherical alumina shown in Figure 5, D50 = 75 μm. (4) Rounded aluminum nitride (AlN) shown in Figure 6, D50 = 20 μm. (5) Irregularly crushed aluminum nitride (AlN) shown in Figure 7, D50 = 15 μm. 3. Silane coupling agent (component C): Decyltrimethoxysilane was used. 4. Mixing process: The silane coupling agent and thermally conductive inorganic particles were added to the matrix component and mixed and stirred using a planetary mixer to form a compound. Next, the compound was depressurized to -0.08 to -0.1 Pa and left for 5 to 10 minutes to degas. 5. Sheet molding process: The compound was sandwiched between polyethylene terephthalate (PET) films and rolled. The resulting sheet was 2 mm thick, 200 mm wide, and 300 m long. The mixing process was evaluated to determine whether mixing was easy, and the sheet molding process was evaluated to determine whether sheet molding was easy. This evaluation is important because problems in the mixing and sheet molding processes will prevent practical production. The above conditions and results are summarized in Table 1 below.

[0025]

[0026] The above results revealed the following: (1) In Examples 1 to 4, the thermal conductive sheets had good moldability, a good SHORE 00 hardness, and good thermal conductivity, making them suitable as thermally conductive materials (TIMs) to be interposed between heat-generating parts of electrical and electronic components and heat sinks. Furthermore, it was confirmed that the thermal conductive sheets had a long pot life (usage period) at the raw material stage, no heat curing process was required, low manufacturing costs, and low hardness. (2) In contrast, in Comparative Example 1, the viscosity of the ethylene-propylene copolymer was too high, and the oil and thermally conductive particles (filler) did not mix, and mixing was not possible. In Comparative Example 2, the amount of thermally conductive particles (filler) was too high, and the oil and thermally conductive particles (filler) did not mix, and mixing was not possible. In Comparative Example 3, the amount of thermally conductive particles (filler) was too low, and the mixture became liquid, making it impossible to form into a sheet.

[0027] The thermally conductive silicone sheet of the present invention is suitable as a thermally conductive material (TIM: Thermal Interface Material) to be interposed between a heat-generating portion of an electric or electronic component or the like and a heat sink.

[0028] REFERENCE SIGNS LIST 1 Thermal conductivity measuring device 2 Sensor 3a, 3b Sample 4 Sensor tip 5 Electrode for applied current 6 Electrode for resistance value (electrode for temperature measurement) 10 Heat dissipation structure 11a, 11b Thermally conductive sheet 12 Heat spreader 13 Electronic component 14 Wiring board 15 Heat sink

Claims

1. A thermally conductive sheet comprising a non-curable liquid matrix resin (A) and thermally conductive particles (B), wherein the (A) component has a kinematic viscosity at 40°C of 50 to 10,000 mm 2 ethylene / α-olefin copolymer (A1) having a kinematic viscosity at 40°C of 50 to 10,000 mm 2 and (A2) a mixed oil of polydecene-1 and an ethylene-α-olefin copolymer, wherein the amount of the thermally conductive particles of the component (B) is 400 to 2800 parts by mass per 100 parts by mass of the component (A), and the thermally conductive sheet is in an uncured state.

2. The thermally conductive sheet according to claim 1, wherein the thermally conductive particles have a particle diameter (D50 (median diameter)) of 0.1 μm or more and 150 μm or less.

3. The thermally conductive sheet according to claim 1 or 2, wherein the thermally conductive particles are of one type or a combination of multiple types.

4. The thermally conductive sheet according to any one of claims 1 to 3, wherein the thermally conductive sheet has a thickness of 0.1 mm or more and 10 mm or less.

5. At least a portion of the thermally conductive particles are RaSi(OR') 4-a (wherein R is an unsubstituted or substituted hydrocarbon group having 8 to 12 carbon atoms, R' is an alkyl group having 1 to 4 carbon atoms, and a is 0 or 1).

6. The thermally conductive sheet further contains RaSi(OR') as component (C). 4-a (wherein R is an unsubstituted or substituted hydrocarbon group having 8 to 12 carbon atoms, R' is an alkyl group having 1 to 4 carbon atoms, and a is 0 or 1) is contained in an amount of 0.1 to 2.2 parts by mass per 100 parts by mass of component (A).

7. The thermally conductive sheet according to any one of claims 1 to 6, wherein the thermal conductivity of the thermally conductive sheet is 1.0 W / m·K or more and 20.0 W / m·K or less.

8. The thermally conductive sheet according to any one of claims 1 to 7, wherein the thermally conductive sheet has a SHORE OO hardness of 5 or more and 80 or less.

9. The method for producing a thermally conductive sheet according to any one of claims 1 to 8, wherein the non-curable liquid matrix resin (A) has a kinematic viscosity of 50 to 10,000 mm at 40°C. 2 ethylene / α-olefin copolymer (A1) having a kinematic viscosity at 40°C of 50 to 10,000 mm 2 and (A2) a mixed oil of polydecene-1 and an ethylene-α-olefin copolymer, and 400 to 2,800 parts by mass of thermally conductive particles (B) per 100 parts by mass of the component (A), and then molding the mixture into a sheet without a heat curing step.

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