Heat dissipation device and electronic apparatus

Abstract

The purpose of this invention is to provide a heat dissipation device capable of effectively holding a firm contact state after heat is applied. The present invention is a heat dissipation device comprising the following elements in the stated order in firm contact with each other: a heat-generating body; a heat-conductive sheet which has an A-surface having a surface roughness Sa of 3.00 μm or less, and which contains resin and a heat-conductive filler; and a heat dissipation body which is provided with a B-surface facing the A-surface, the surface roughness Sa of the B-surface being 0.40 μm or less.

Description

Heat dissipation device and electronic device

[0001] The present invention relates to a heat dissipation device and an electronic device.

[0002] In recent years, electronic elements such as transistors such as insulated gate bipolar transistors (IGBTs) and field effect transistors (FETs) included in semiconductor packages, power modules, integrated circuits (ICs, LSIs), plasma display panels (PDPs), and the like that constitute electronic devices, and diodes such as light-emitting diodes (LEDs), have been generating more heat as their performance has improved.

[0003] In order to prevent malfunctions of electronic devices caused by temperature rises in these electronic elements, it is necessary, for example, to improve the heat dissipation properties of the electronic elements and effectively dissipate the heat generated by the electronic elements to the outside.

[0004] Here, a method for improving heat dissipation from an electronic element generally involves attaching a heat dissipator such as a metal heat spreader or heat sink to a heat generating element such as an electronic element or a power module including the electronic element, thereby promoting heat dissipation. When using a heat dissipator, a sheet-like member having thermal conductivity (thermal conduction sheet) is used to efficiently transfer heat from the heat generating element to the heat dissipator, and the heat generating element and the heat dissipator are closely attached via the thermal conduction sheet to form a heat dissipation device, thereby promoting heat dissipation (for example, Patent Document 1, etc.).

[0005] International Publication No. 2018 / 003356

[0006] In order to more efficiently transfer heat from the heat generating body to the heat sink via the heat conductive sheet in the heat dissipation device, it is desirable to maintain a tight contact state between the heat sink and the heat conductive sheet.

[0007] However, in conventional heat dissipation devices, there is room for improvement in terms of maintaining a tight contact state between the heat dissipation body and the thermally conductive sheet (hereinafter, sometimes simply referred to as a "tight contact state") when heat is applied.

[0008] Therefore, an object of the present invention is to provide a heat dissipation device that can effectively maintain a tight contact state after heat is applied, and to provide an electronic device equipped with the heat dissipation device.

[0009] The present inventors have conducted extensive research with the aim of solving the above-mentioned problems, and have newly discovered that the above-mentioned problems can be solved by a heat dissipation device that includes a heating element, a thermally conductive sheet having an A-side with a predetermined surface roughness Sa and containing a predetermined component, and a heat dissipation element having a B-side opposite to the A-side, the B-side having a surface roughness Sa of a predetermined value or less, and that these elements are closely attached to each other in this order, thereby completing the present invention.

[0010] That is, the present invention aims to advantageously solve the above-mentioned problems. [1] The present invention provides a heat dissipation device comprising a heat generating element, a thermally conductive sheet having an A-side surface with a surface roughness Sa of 3.00 μm or less and containing a resin and a thermally conductive filler, and a heat dissipation element having a B-side surface opposite to the A-side surface with a surface roughness Sa of 0.40 μm or less, and the heat dissipation element being closely attached to the A-side surface. With such a heat dissipation element, the close contact state can be effectively maintained after heat is applied. In this specification, the surface roughness Sa of the A-side of the thermally conductive sheet and the surface roughness Sa of the B-side of the heat dissipation element can be measured by the methods described in the examples.

[0011] [2] In the heat dissipation device of the above [1], it is preferable that the material of the side B of the heat dissipation body is metal. If the material of the side B of the heat dissipation body is metal, the heat dissipation performance of the heat dissipation device can be improved.

[0012] [3] In the heat dissipation device according to the above [1] or [2], the tack strength of the thermally conductive sheet is 10.0 N / cm ２ 150.0N / cm or more ２ It is preferable that the tack strength of the thermally conductive sheet is equal to or greater than the above lower limit. If the tack strength of the thermally conductive sheet is equal to or greater than the above lower limit, the adhesion between the heat generating element and the heat dissipating element and the thermally conductive sheet can be improved. On the other hand, if the tack strength of the thermally conductive sheet is equal to or less than the above upper limit, the productivity of the heat dissipating device can be improved. In this specification, the "tack strength of the thermally conductive sheet" can be measured by the method described in the examples of this specification.

[0013] Another object of the present invention is to advantageously solve the above problems, and [4] the present invention is an electronic device equipped with the heat dissipation device according to any one of [1] to [3] above. Such an electronic device has excellent performance.

[0014] According to the present invention, it is possible to provide a heat dissipation device that can effectively maintain a tight contact state after heat is applied, and also to provide an electronic device that includes the heat dissipation device.

[0015] 1A and 1B are schematic diagrams illustrating a process for manufacturing a heat dissipation device according to an embodiment of the present invention;

[0016] Hereinafter, embodiments of the present invention will be described in detail.

[0017] (Heat Dissipation Device) The heat dissipation device of the present invention comprises a heat generating element, a heat conductive sheet having an A-side surface with a surface roughness Sa of 3.00 μm or less and containing a resin and a heat conductive filler, and a heat dissipation element having a B-side surface opposite to the A-side surface with a surface roughness Sa of 0.40 μm or less, and these are bonded together in this order. The heat dissipation device described above can effectively maintain a tight contact state after heat is applied. This is presumably because the heat conductive sheet penetrates into the minute gaps on the heat dissipation element surface, reducing minute voids at the interface, thereby increasing the contact area and improving adhesion strength, while also suppressing delamination originating from the voids. Furthermore, since the heat dissipation device of the present invention can effectively maintain a tight contact state after heat is applied, the thermal resistance between the heat generating element and the heat dissipation element is effectively reduced, resulting in excellent heat dissipation properties as a heat dissipation device. In other words, the heat dissipation device of the present invention can efficiently dissipate heat generated from a heat-generating body, such as an electronic element itself or a power module including an electronic element, to the outside, and as a result, can effectively prevent functional failure caused by heat from the heat-generating body in various devices, such as electronic devices, equipped with the heat dissipation device of the present invention.In addition, since the heat dissipation device of the present invention can maintain a good adhesion state after heat is applied, the adhesive strength (tackiness) of the thermally conductive sheet can be effectively reduced.For example, if the thermally conductive sheet is mistakenly attached to the heat sink and heat-generating body during the process of manufacturing the heat dissipation device, the thermally conductive sheet can be easily peeled off and reattached, thereby improving the productivity of the heat dissipation device.

[0018] In addition to the above-mentioned heating element, heat sink, and thermally conductive sheet, the heat dissipation device of the present invention may further include any other components, such as a fixing member (e.g., a sealant) that fixes the heating element and the heat sink.

[0019] <Heater> The heater is one of the components constituting the heat dissipation device of the present invention, and is a type of adherend to which the thermally conductive sheet is adhered in the heat dissipation device of the present invention. Here, the heater has an adherend surface that faces the heat dissipation body described below. Generally, most of the heat generated by the heater is transferred from the adherend surface to the heat dissipation body via the thermally conductive sheet and dissipated.

[0020] The heat generating element is not particularly limited as long as it generates heat in various devices such as electronic devices. Examples of the heat generating element include semiconductor elements such as transistors, diodes, thyristors, organic electroluminescence (EL), and inorganic electroluminescence (EL); semiconductor-related components such as integrated circuits (IC, LSI) including memories and central processing units (CPUs) equipped with the semiconductor elements, IC chips, semiconductor packages, semiconductor sealing cases, semiconductor die bonding, power modules, power transistors, and power transistor cases; and wiring boards such as rigid wiring boards, flexible wiring boards, ceramic wiring boards, build-up wiring boards, and multilayer substrates (wiring boards also include printed wiring boards). Examples of the transistor include field effect transistors (FETs), metal oxide semiconductor field effect transistors (MOSFETs), and insulated gate bipolar transistors (IGBTs). Examples of the diode include light emitting diodes (LEDs) and photodiodes.

[0021] <Heat Dissipator> The heat dissipator is one of the components constituting the heat dissipation device of the present invention and is a type of adherend to which the thermally conductive sheet is bonded. Here, the heat dissipator has an adherend surface that faces the above-mentioned heat generating element. Generally, most of the heat generated by the heat generating element is transferred from the thermally conductive sheet via the adherend surface to the heat dissipator and dissipated.

[0022] The heat sink has a side B that faces side A of a thermally conductive sheet (described later). The surface roughness Sa of the side B of the heat sink is 0.40 μm or less. The use of such a heat sink in a heat dissipation device can improve adhesion to the thermally conductive sheet after heat is applied.

[0023] Examples of heat dissipators include heat sinks having shaped parts such as plates and fins; blocks connected to heat pipes; blocks having an internal structure for circulating cooling liquid using a pump; Peltier elements; heat sinks equipped with Peltier elements; blocks equipped with Peltier elements; and heat spreaders.

[0024] The material of the B-side of the heat sink is preferably metal. If the B-side of the heat sink is made of metal, the heat dissipation performance of the heat dissipation device can be improved. For example, the heat sink, the block, or the like made of metal can be used as the heat sink. Examples of metals include, but are not limited to, aluminum and copper. Copper is preferred from the viewpoints of adhesion to the thermally conductive sheet after heat is applied, heat dissipation, and small thermal deformation such as thermal expansion. Furthermore, for example, a heat sink, a block, or the like plated with a metal can also be used as the heat sink. Examples of metals used for plating include nickel, gold, silver, tin, copper, and palladium. Among these, Ni plating is preferred from the viewpoints of adhesion to the thermally conductive sheet after heat is applied, corrosion resistance, and heat resistance. Metal-plated heat sinks, blocks, or the like (e.g., nickel-plated copper) can also be used as heat sinks.

[0025] The surface roughness Sa of the heat sink's side B must be 0.40 μm or less, preferably 0.30 μm or less, and more preferably 0.25 μm or less. If the surface roughness Sa of the heat sink's side B is equal to or less than the above upper limit, adhesion to the thermally conductive sheet after heat is applied can be improved. The surface roughness Sa of the heat sink's side B is, for example, 0.01 μm or more, and may be 0.05 μm or more.

[0026] <Thermal Conductive Sheet> The thermal conductive sheet has an A-side having a surface roughness Sa of 3.00 μm or less. The thermal conductive sheet also contains a resin and a thermally conductive filler. Use of such a thermal conductive sheet in a heat dissipation device can improve adhesion to a heat sink after heat is applied.

[0027] [Resin] The resin is not particularly limited, and any known resin that can be used to form a thermally conductive sheet can be used. Specifically, the resin can be a thermoplastic resin or a thermosetting resin. A thermoplastic resin and a thermosetting resin may be used in combination. In this specification, rubber and elastomer are included in the term "resin."

[0028] Examples of thermoplastic resins include acrylic resins such as poly(2-ethylhexyl acrylate), a copolymer of acrylic acid and 2-ethylhexyl acrylate, polymethacrylic acid or its ester, and polyacrylic acid or its ester; acrylic rubber; silicone resin; fluororesin; polyethylene; polypropylene; ethylene-propylene copolymer; polymethylpentene; polyvinyl chloride; polyvinylidene chloride; polyvinyl acetate; ethylene-vinyl acetate copolymer; polyvinyl alcohol; polyvinyl formal; polyacetal; polyvinyl butyral; polyethylene terephthalate; polybutylene terephthalate; polyethylene naphthalate; polystyrene; poly Examples of the polymerizable compound include acrylonitrile, styrene-acrylonitrile copolymer, acrylonitrile-butadiene copolymer (nitrile rubber), acrylonitrile-butadiene-styrene copolymer (ABS resin), styrene-butadiene block copolymer or hydrogenated product thereof, styrene-isoprene block copolymer or hydrogenated product thereof, polyphenylene ether, modified polyphenylene ether, aliphatic polyamides, aromatic polyamides, polyamideimide, polycarbonate, polyphenylene sulfide, polysulfone, polyethersulfone, polyethernitrile, polyetherketone, polyketone, thermoplastic polyurethane, liquid crystal polymer, ionomer, and the like. These may be used alone or in combination of two or more. Among these, fluororesin, acrylic resin, acrylic rubber, and nitrile rubber are preferred, and fluororesin is more preferred.

[0029] Examples of the fluororesin include elastomers obtained by polymerizing fluorine-containing monomers, such as vinylidene fluoride fluororesin, tetrafluoroethylene-propylene fluororesin, and tetrafluoroethylene-perfluorovinyl ether fluororesin. More specific examples include polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, polychlorotrifluoroethylene, ethylene-chlorofluoroethylene copolymer, tetrafluoroethylene-perfluorodioxole copolymer, polyvinyl fluoride, tetrafluoroethylene-propylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, acrylic-modified polytetrafluoroethylene, ester-modified polytetrafluoroethylene, epoxy-modified polytetrafluoroethylene, and silane-modified polytetrafluoroethylene. In addition to the above, examples of fluororesins include vinylidene fluoride / hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropentene-tetrafluoroethylene terpolymer, perfluoropropene oxide polymer, tetrafluoroethylene-propylene-vinylidene fluoride copolymer, etc. These may be used alone or in combination of two or more.

[0030] Thermoplastic resins that are solid at room temperature and atmospheric pressure and thermoplastic resins that are liquid at room temperature and atmospheric pressure can be used independently or in combination. When a thermoplastic resin that is solid at room temperature and atmospheric pressure and a thermoplastic resin that is liquid at room temperature and atmospheric pressure are used in combination, the solid thermoplastic resin component and the liquid thermoplastic resin component can coexist within the thermal conductive sheet under room temperature and atmospheric pressure conditions. This improves the balance between the hardness, strength, and flexibility of the thermal conductive sheet, thereby improving the productivity of the heat dissipation device. Furthermore, in the high-temperature environment during use (heat dissipation) of the heat dissipation device, the solid thermoplastic resin plasticizes at room temperature and atmospheric pressure, thereby improving the adhesion between the heat generating element and the heat dissipation element and the thermal conductive sheet. As a result, the thermal resistance between the heat generating element and the heat dissipation element is further reduced efficiently, and the heat dissipation performance of the heat dissipation device can be more effectively improved. Note that in this specification, "room temperature" refers to 23°C, and "atmospheric pressure" refers to 1 atm (absolute pressure).

[0031] Examples of thermosetting resins include natural rubber, butadiene rubber, isoprene rubber, hydrogenated nitrile rubber, chloroprene rubber, ethylene propylene rubber, chlorinated polyethylene, chlorosulfonated polyethylene, butyl rubber, halogenated butyl rubber, polyisobutylene rubber, epoxy resin, polyimide resin, bismaleimide resin, benzocyclobutene resin, phenolic resin, unsaturated polyester, diallyl phthalate resin, polyimide silicone resin, thermosetting polyurethane, thermosetting polyphenylene ether, thermosetting modified polyphenylene ether, etc. These may be used alone or in combination of two or more.

[0032] The resin content in the thermal conductive sheet is not particularly limited, but is preferably 30% by mass or more, more preferably 35% by mass or more, even more preferably 40% by mass or more, and preferably 85% by mass or less, more preferably 75% by mass or less, and even more preferably 65% ​​by mass or less. If the resin content in the thermal conductive sheet is above the above-mentioned lower limit, the flexibility of the thermal conductive sheet can be improved and the adhesion to the heat sink can be improved. On the other hand, if the resin content in the thermal conductive sheet is below the above-mentioned upper limit, heat can be transferred well in the thickness direction of the thermal conductive sheet.

[0033] Furthermore, when the resin contains a thermoplastic resin that is solid at room temperature and normal pressure and a thermoplastic resin that is liquid at room temperature and normal pressure (hereinafter sometimes referred to as "liquid resin"), the proportion of the liquid resin in the entire resin is not particularly limited, but is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, even more preferably 60% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, and even more preferably 80% by mass or less. If the proportion of the liquid resin in the entire resin is within the above range, the balance between hardness and flexibility of the thermal conductive sheet can be improved under room temperature and normal pressure environments, thereby further improving the productivity of the heat dissipation device. Furthermore, in the high-temperature environment during use (heat dissipation) of the heat dissipation device, the adhesion between the heat generating element and the heat dissipation element and the thermal conductive sheet can be further improved, more efficiently reducing the thermal resistance between the heat generating element and the heat dissipation element, and more effectively improving the heat dissipation performance of the heat dissipation device.

[0034] [Thermal Conductive Filler] The thermal conductive filler is not particularly limited as long as it can impart thermal conductivity to the thermal conductive sheet. As such a thermal conductive filler, a particulate carbon material having high thermal conductivity can be suitably used. Note that the thermal conductive filler may be used alone or in combination of two or more types.

[0035] The particulate carbon material is not particularly limited, and examples thereof include graphite such as artificial graphite, flake graphite, exfoliated graphite, natural graphite, acid-treated graphite, expandable graphite, and expanded graphite; carbon black; etc. These may be used alone or in combination of two or more.

[0036] Among the above, it is preferable to use expanded graphite as the particulate carbon material. The use of expanded graphite increases the thermal conductivity in the thickness direction of the thermal conductive sheet, allowing for even better heat transfer in the thickness direction of the thermal conductive sheet. Here, expanded graphite can be obtained by, for example, chemically treating graphite such as flake graphite with sulfuric acid or the like to obtain expandable graphite, which is then heat-treated to expand the graphite, and then micronizing the expanded graphite. Examples of expanded graphite include EC1500, EC1000, EC500, EC300, EC100, and EC50 (all trade names) manufactured by Ito Graphite Industries Co., Ltd.

[0037] The thermally conductive filler preferably has a volume average particle diameter of 40 μm or more, more preferably 45 μm or more, and preferably 180 μm or less, more preferably 160 μm or less, even more preferably 140 μm or less, and even more preferably 100 μm or less. It is presumed that if the volume average particle diameter of the thermally conductive filler is above the above lower limit, a good heat transfer path of the thermally conductive filler can be formed in the thermally conductive sheet, and the thermal conductivity of the thermally conductive sheet in the thickness direction is increased. As a result, good heat transfer can be achieved in the thickness direction of the thermally conductive sheet. On the other hand, if the volume average particle diameter of the thermally conductive filler is below the above upper limit, adhesion to the heat sink can be improved. In this specification, "volume average particle diameter" can be measured in accordance with JIS Z8825 and refers to the particle diameter at which the cumulative volume calculated from the smallest diameter side becomes 50% in the particle size distribution (volume basis) measured by laser diffraction.

[0038] Furthermore, the aspect ratio (major axis / minor axis) of the thermally conductive filler is preferably greater than 1 and less than 10, more preferably greater than 1 and less than 5. It is presumed that when the aspect ratio of the thermally conductive filler is greater than 1 and less than 10, the thermally conductive filler is more likely to be well oriented in the thickness direction in the thermally conductive sheet, thereby increasing the thermal conductivity of the thermally conductive sheet in the thickness direction. As a result, the thermally conductive sheet can be more effectively transferred heat in the thickness direction. In this specification, the "aspect ratio" can be determined by observing the thermally conductive filler with a scanning electron microscope (SEM), measuring the maximum diameter (major axis) and the particle diameter (minor axis) in the direction perpendicular to the maximum diameter for 50 randomly selected thermally conductive fillers, and calculating the average value of the ratio of the major axis to the minor axis (major axis / minor axis). In the above, for example, when the thermally conductive filler is in the form of flakes such as expanded graphite, the "major axis" refers to the length in the direction of the major axis of the main surface of the flake shape, and the "minor axis" refers to the length in the direction perpendicular to the major axis of the main surface.

[0039] The content of the thermally conductive filler in the thermally conductive sheet is not particularly limited, but is preferably 15% by mass or more, more preferably 25% by mass or more, even more preferably 35% by mass or more, and preferably 70% by mass or less, more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less. If the content of the thermally conductive filler in the thermally conductive sheet is equal to or less than the above upper limit, heat can be transferred well in the thickness direction of the thermally conductive sheet. On the other hand, if the content of the thermally conductive filler in the thermally conductive sheet is equal to or greater than the above lower limit, the flexibility of the thermally conductive sheet can be improved, and adhesion to the heat sink can be improved.

[0040] In the thermally conductive sheet, the volume fraction of the thermally conductive filler relative to the resin (thermally conductive filler / resin x 100 [vol%]) is preferably 20 vol% or more, more preferably 30 vol% or more, even more preferably 40 vol% or more, and preferably 70 vol% or less, more preferably 60 vol% or less, and even more preferably 50 vol% or less. If the volume fraction of the thermally conductive filler relative to the resin is above the above lower limit, heat can be transferred more effectively in the thickness direction of the thermally conductive sheet. On the other hand, if the volume fraction of the thermally conductive filler relative to the resin is below the above upper limit, the flexibility of the thermally conductive sheet can be improved, and adhesion to the heat sink can be improved.

[0041] [Properties of the Thermal Conductive Sheet] The surface roughness Sa of side A of the thermal conductive sheet must be 3.00 μm or less, preferably 2.50 μm or less, more preferably 2.10 μm or less, even more preferably 1.50 μm or less, and even more preferably 1.00 μm or less. If the surface roughness Sa of side A of the thermal conductive sheet is below the above upper limit, adhesion to the heat sink after heat is applied can be improved. The surface roughness Sa of side A of the thermal conductive sheet is, for example, 0.10 μm or more, and may be 0.50 μm or more.

[0042] The surface roughness Sa of the surface opposite to surface A of the thermal conductive sheet, i.e., the surface facing the heating element (hereinafter sometimes referred to as "surface C"), is preferably 3.00 μm or less, more preferably 2.50 μm or less, even more preferably 2.10 μm or less, even more preferably 1.50 μm or less, and even more preferably 1.00 μm or less. If the surface roughness Sa of surface C of the thermal conductive sheet is below the above upper limit, adhesion to the heating element can be improved. The surface roughness Sa of surface C of the thermal conductive sheet is, for example, 0.10 μm or more, and may be 0.50 μm or more.

[0043] The tack strength of the thermal conductive sheet is 10.0 N / cm ２ Preferably, it is 15.0 N / cm or more. ２ More preferably, it is 150.0 N / cm or more. ２Preferably, it is 120.0 N / cm or less. ２ More preferably, it is 100.0 N / cm or less. ２ More preferably, it is 60.0 N / cm or less. ２ It is even more preferable that the value is 50.0 N / cm or less. ２ It is even more preferable that the strength is 30.0 N / cm or less. ２ It is even more preferable that the tack strength of the thermally conductive sheet is equal to or greater than the above lower limit. If the tack strength of the thermally conductive sheet is equal to or greater than the above upper limit, the adhesion between the heat generating element and the heat dissipating element and the thermally conductive sheet can be improved. On the other hand, if the tack strength of the thermally conductive sheet is equal to or less than the above upper limit, the productivity of the heat dissipating device can be improved.

[0044] [Method for Producing a Thermally Conductive Sheet] The thermally conductive sheet can be produced, for example, by pressing a composition containing the above-described resin and thermally conductive filler to form a sheet. Here, the thermally conductive sheet may be, for example, (A) a single sheet-like molded body obtained by pressing the above-described pressurized composition, or (B) a pre-thermally conductive sheet obtained by pressing a plurality of pre-thermally conductive sheets, and then slicing the pre-thermally conductive sheets in the stacking direction. Among the above, the thermally conductive sheet (B) is preferred from the viewpoint of achieving high thermal conductivity in the thickness direction. Below, an example of a method for producing the thermally conductive sheet (B) is described, but the thermally conductive sheet used in the heat dissipation device of the present invention is not limited to this method.

[0045] First, for example, the components such as the resin and thermally conductive filler described above are mixed under any conditions using a known mixing device such as a kneader, roll, Henschel mixer, or Hobart mixer to prepare a composition for a thermally conductive sheet.

[0046] The resulting composition for a thermally conductive sheet is then formed into a sheet using a known forming method such as press forming, rolling, or extrusion to form a pre-thermal conductive sheet. In the pre-thermal conductive sheet thus formed, the thermally conductive filler particles are presumably aligned primarily in the in-plane direction, resulting in improved thermal conductivity in the in-plane direction of the pre-thermal conductive sheet.

[0047] Next, a plurality of the obtained pre-heat conductive sheets are stacked in the thickness direction by any method, or the pre-heat conductive sheets are folded or rolled to obtain a laminate. Here, it is presumed that in the obtained laminate, the heat conductive filler particles are mainly aligned in a direction approximately perpendicular to the stacking direction.

[0048] The resulting laminate is sliced ​​at an angle of 45° or less relative to the stacking direction to obtain a thermally conductive sheet composed of slices of the laminate. The method for slicing the laminate is not particularly limited, and examples include the multi-blade method, laser processing, water jet processing, and knife processing. Among these, the knife processing method is preferred because it facilitates uniform thickness of the thermally conductive sheet. The cutting tool used to slice the laminate is not particularly limited, and a slicing member (e.g., a planer or slicer with a sharp blade) having a smooth plate surface with slits and a blade protruding from the slits can be used. It is believed that the thermally conductive filler particles are aligned in the thickness direction within the thermally conductive sheet obtained in this manner. Therefore, it is believed that the thermally conductive sheet obtained by the above method has high thermal conductivity in the thickness direction.

[0049] From the viewpoint of easily slicing the laminate, it is preferable to slice the laminate while applying pressure in a direction perpendicular to the stacking direction, and it is more preferable to slice the laminate while applying a pressure of 0.1 MPa or more and 0.5 MPa or less in the direction perpendicular to the stacking direction.

[0050] <Method for Manufacturing Heat Dissipation Device> The heat dissipation device of the present invention is not particularly limited as long as it is formed by closely adhering the above-described heat generating element, thermally conductive sheet, and heat dissipation element in this order, and can be manufactured by a conventionally known method. For example, a heat dissipation device can be obtained by stacking the heat generating element, thermally conductive sheet, and heat dissipation element in this order and applying pressure at a predetermined surface pressure. Optionally, the heat generating element and heat dissipation element may be fixed using a fixing member (e.g., a sealant). Here, the surface pressure during pressure application is preferably 0.05 MPa or more, more preferably 0.1 MPa or more, preferably 1.5 MPa or more, and more preferably 1.0 MPa or less. The temperature during pressure application is preferably 100°C or more, more preferably 130°C or more, and preferably 200°C or less, and more preferably 170°C or less.

[0051] (Electronic Device) The electronic device of the present invention includes the heat dissipation device of the present invention described above. Such an electronic device has excellent performance because it includes the heat dissipation device of the present invention that can effectively maintain a tight contact state after heat is applied.

[0052] The heat dissipation device of the present invention can be used, for example, in an electronic device having an electronic element therein as an electronic component including the electronic element. Here, the heat dissipation device of the present invention may be completely incorporated inside the electronic device, or may be provided partially or entirely outside the electronic device.

[0053] Specific examples of electronic devices include servers, server personal computers, desktop personal computers, notebook computers, electronic dictionaries, PDAs, mobile phones, and portable music players.

[0054] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified. In the examples and comparative examples, the surface roughness Sa of side A of the thermal conductive sheet, the surface roughness Sa of side B of the heat sink, the tack strength of the thermal conductive sheet, and the adhesion rate and adhesion between the thermal conductive sheet and the heat sink were measured or evaluated using the following methods.

[0055] <Surface roughness Sa of side A of the thermal conductive sheet> The surface roughness Sa (arithmetic mean height) of one side (side A) of the thermal conductive sheet was measured using a three-dimensional shape measuring instrument (manufactured by Keyence Corporation, product name "One Shot 3D Measurement Macroscope"). Specifically, first, a thermal conductive sheet cut into an arbitrary square of approximately 5 cm square was prepared as a sample. Next, to suppress waviness of the sample, the sample was placed on an adsorption plate connected to a vacuum pump, and the three-dimensional shape of both the front and back main surfaces of the sample was measured using a high-magnification camera (40x). The three-dimensional shape measurement results were then further subjected to L-filter processing (2.5 mm) using software to remove waviness components, and the surface roughness Sa (μm) of the area excluding the edge of the measured area (an area approximately 0.5 mm around) was automatically calculated, and this was taken as the surface roughness Sa of side A of the thermal conductive sheet.

[0056] <Surface roughness Sa of side B of heat sink> The surface roughness Sa (arithmetic mean height) of one side (side B) of the heat sink was measured using a laser microscope (Keyence Corporation, shape analysis laser microscope, VK-X250). Specifically, the surface of the heat sink was measured at 50x magnification, and the surface roughness Sa (μm) for the entire measured area was automatically calculated, and this was taken as the surface roughness Sa of side B of the heat sink.

[0057] <Tackiness of Thermally Conductive Sheet> The tackiness of the thermally conductive sheets obtained in the examples and comparative examples was measured using a probe tack tester (manufactured by Rhesca, product name "TAC1000"). Specifically, first, a thermally conductive sheet punched to a diameter of 4 mm was attached with double-sided tape to a flat probe with a diameter of 5 mm. In this state, the probe was pressed against a heating element (manufactured by Electronics and Materials Corporation, model number: 4" Si bare wafer, length 30 mm x width 30 mm x thickness 0.52 mm) for 10 seconds under conditions of a temperature of 23°C and a pressure of 0.30 MPa. The force required to separate the probe pressed against the heating element was then measured, and this force was expressed as the tackiness (N / cm) of the thermally conductive sheet. ２ )

[0058] Adhesion Ratio Between Thermally Conductive Sheet and Heat Dissipator: The adhesion ratio between the thermally conductive sheet and the heat dissipator (hereinafter, sometimes simply referred to as "adhesion ratio") was calculated using the heat dissipation devices obtained in the examples and comparative examples. Specifically, the heat dissipation devices before heating were first measured using an ultrasonic imaging device FineSAT (FS100III) (manufactured by Hitachi Power Solutions, probe frequency: 25 MHz) to obtain images. In the obtained images, the adhesion portion where the thermally conductive sheet was in close contact with the heat dissipator and the peeled portion where the thermally conductive sheet was peeled from the heat dissipator were identified. The ratio of the area of ​​the adhesion portion to the total area of ​​the adhesion portion and the peeled portion (area of ​​the adhesion portion / total area of ​​the adhesion portion and the peeled portion × 100 [%]) was calculated, and the resulting ratio was defined as the initial adhesion ratio (%). Next, the heat dissipation devices were heated in an oven at 150°C without load for 1 hour. After heating, the heat dissipation devices were cooled to room temperature, and the post-heating adhesion ratio (%) was calculated in the same manner as the initial adhesion ratio. Then, the difference between the initial adhesion rate and the adhesion rate after heating (initial adhesion rate - adhesion rate after heating) was calculated.

[0059] <Adhesion> The difference between the initial adhesion rate and the adhesion rate after heating was used to evaluate the adhesion according to the following criteria. The smaller the difference, the more effectively the adhesion state is maintained after heat is applied. A: The difference between the initial adhesion rate and the adhesion rate after heating is less than 10%. B: The difference between the initial adhesion rate and the adhesion rate after heating is 10% or more and less than 20%. C: The difference between the initial adhesion rate and the adhesion rate after heating is 20% or more and less than 50%. D: The difference between the initial adhesion rate and the adhesion rate after heating is 50% or more.

[0060] Example 1 Preparation of Composition 70 parts of a thermoplastic fluororubber that is liquid at room temperature and normal pressure (manufactured by Daikin Industries, Ltd., trade name "Dai-el G-101"), 30 parts of a thermoplastic fluororubber that is solid at room temperature and normal pressure (manufactured by 3M Japan Limited, trade name "Dyneon FC2211"), and 90 parts of expanded graphite as a particulate carbon material (manufactured by Ito Graphite Industries Co., Ltd., trade name "EC300", volume average particle size: 50 μm) were mixed and stirred for 20 minutes at a temperature of 150° C. using a pressure kneader (manufactured by Nippon Spindle). The resulting mixture was then placed in a crusher (manufactured by Osaka Chemical Co., Ltd., trade name "Wonder Crush Mill D3V-10") and crushed for 10 seconds to obtain a composition.

[0061] <Preparation of Pre-heat Conductive Sheet> Next, 50 g of the obtained composition was sandwiched between sandblasted PET films (protective films) having a thickness of 50 μm, and roll-molded (primary pressing) under conditions of a roll gap of 550 μm, a roll temperature of 50° C., a roll linear pressure of 50 kg / cm, and a roll speed of 1 m / min, to obtain a pre-heat conductive sheet having a thickness of 0.5 mm.

[0062] <Preparation of Laminate> Next, the obtained pre-thermal conductive sheet was cut into a size of 50 mm length × 50 mm width × 0.5 mm thickness, and 110 sheets were stacked in the thickness direction of the pre-thermal conductive sheet. Further, the pre-thermal conductive sheet was pressed (secondary pressing) in the stacking direction at a temperature of 25°C and a pressure of 1.0 MPa for 60 minutes to obtain a laminate with a height of approximately 50 mm.

[0063] <Preparation of Thermally Conductive Sheet> The laminated side of the secondary-pressurized laminate was then pressed with a pressure of 0.3 MPa, and sliced ​​at a 45-degree angle to the lamination direction using a woodworking slicer (Marunaka Iron Works Co., Ltd., product name "Super Mecha S Super Finishing Planer") to obtain a thermally conductive sheet measuring 50 mm long x 50 mm wide x 0.1 mm thick. The surface roughness Sa and tack strength of side A of the obtained thermally conductive sheet were measured. The results are shown in Table 1.

[0064] <Manufacture of heat dissipation device> A Si wafer (manufactured by Electronics and Materials Corporation, model number: 4" Si bare wafer, length 30 mm x width 30 mm x thickness 0.52 mm) was prepared as a heating element. A copper plate (length 30 mm x width 30 mm x thickness 1 mm) with a nickel-plated surface was prepared as a heat dissipation element. The surface roughness Sa of side B of the heat dissipation element was 0.25 μm.

[0065] First, the thermally conductive sheet obtained above was cut into a 15 mm x 15 mm size to prepare a thermally conductive sheet for a heat dissipation device. Next, a sealant (Dow Chemical, model number: DOWSIL® SE4450) was applied to the periphery of the heat sink's side B using a dispenser. Next, as shown in FIG. 1 , the cut thermally conductive sheet 30 was placed on the heat sink 40 so that the side opposite side A (side C) was in contact with the heat sink 40. Furthermore, the heat sink 50 was placed on the thermally conductive sheet 30 so that side B of the heat sink 50 was in contact with side A of the heat sink 30 (so that the sealant 60 was on the heat sink 40 side). At this time, the approximate center of the heat sink 40, the approximate center of the heat sink 40, and the approximate center of the heat sink 50 were aligned. As shown in FIG. 2 , the resulting laminate of the heating element 40, thermally conductive sheet 30, and heat sink 50 was placed in a pressure tool 70 and secured with screws 80, adjusting the torque so that the surface pressure was 0.3 MPa. The laminate secured with the pressure tool and screws was then heated in an oven at 150°C for 1 hour. After heating, it was cooled to room temperature, and the pressure tool and screws were removed. This resulted in a heat sink device in which the heating element, thermally conductive sheet, and heat sink were closely attached in this order. The adhesion rate between the thermally conductive sheet and heat sink was measured for the resulting heat sink device, and the adhesion was evaluated. The results are shown in Table 1.

[0066] (Example 2) In the preparation of the thermally conductive sheet, the surface (side A) of the sliced ​​thermally conductive sheet was roughened with sandpaper having a grit of #100, and the same procedures, measurements, and evaluations were carried out as in Example 1. The results are shown in Table 1.

[0067] (Example 3) In the preparation of the thermally conductive sheet, the surface (side A) of the sliced ​​thermally conductive sheet was roughened with sandpaper having a grit of #80, and the same procedures, measurements, and evaluations were carried out as in Example 1. The results are shown in Table 1.

[0068] (Example 4) In preparing the composition, various operations, measurements and evaluations were carried out in the same manner as in Example 1, except that 70 parts of a thermoplastic acrylic resin (manufactured by Toagosei Co., Ltd., trade name "UH2190") that is liquid at room temperature and normal pressure and 30 parts of a thermoplastic acrylic rubber (ZEON HyTemp H570) that is solid at room temperature and normal pressure were used instead of 70 parts of a thermoplastic fluororubber that is liquid at room temperature and normal pressure and 30 parts of a thermoplastic fluororubber that is solid at room temperature and normal pressure. The results are shown in Table 1.

[0069] (Example 5) In preparing the composition, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that 70 parts of the fluororubber that is liquid at room temperature and normal pressure and 30 parts of the fluororubber that is solid at room temperature and normal pressure were replaced with 100 parts of thermoplastic nitrile rubber (NBR) that is liquid at room temperature and normal pressure (manufactured by Nippon Zeon Co., Ltd., product name "Nipol (registered trademark) 1312"). The results are shown in Table 1.

[0070] Example 6 In preparing the composition, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that 70 parts of the fluororubber that is liquid at room temperature and normal pressure and 30 parts of the fluororubber that is solid at room temperature and normal pressure were replaced with 40 parts of a thermoplastic fluororubber that is liquid at room temperature and normal pressure (manufactured by Daikin Industries, Ltd., product name "Dai-el G-101"), 20 parts of a thermoplastic fluororubber that is solid at room temperature and normal pressure (manufactured by 3M Japan Ltd., product name "Dyneon FC2211"), and 40 parts of a thermoplastic acrylic resin that is liquid at room temperature and normal pressure (manufactured by Toa Gosei Co., Ltd., product name "UH2190"). The results are shown in Table 1.

[0071] (Example 7) Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that the nickel-plated copper plate used as the heat sink was changed to an unplated copper plate (30 mm long x 30 mm wide x 1 mm thick). The results are shown in Table 1.

[0072] (Example 8) Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that the nickel-plated copper plate used as the heat sink was replaced with an unplated aluminum plate (30 mm length × 30 mm width × 1 mm thickness). The results are shown in Table 1.

[0073] Comparative Example 1 Various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that the heat sink used was a nickel-plated copper plate that had been chemically polished (edged) on side B. The results are shown in Table 1.

[0074] (Comparative Example 2) In the preparation of the thermally conductive sheet, the surface (side A) of the sliced ​​thermally conductive sheet was roughened with sandpaper having a grit of #60, and the same procedures, measurements, and evaluations were carried out as in Example 1. The results are shown in Table 1.

[0075]

[0076] As is clear from Table 1, the heat dissipation device of the example can effectively maintain a tight contact state after heat is applied.

[0077] According to the present invention, it is possible to provide a heat dissipation device that can effectively maintain a tight contact state after heat is applied, and also to provide an electronic device that includes the heat dissipation device.

[0078] 30 Thermally conductive sheet 40 Heat generating element 50 Heat dissipation element 60 Sealant 70 Pressurizing jig 80 Screw

Claims

1. A heat dissipation device comprising: a heat generating element; a heat conductive sheet having an A-side surface with a surface roughness Sa of 3.00 μm or less and containing resin and a heat conductive filler; and a heat dissipation element having a B-side surface opposite to the A-side surface and having a surface roughness Sa of 0.40 μm or less, the A-side surface being closely attached to the B-side surface in this order.

2. The heat dissipation device according to claim 1, wherein the material of said side B of said heat sink is metal.

3. The tack strength of the thermal conductive sheet is 10.0 N / cm ２ 150.0N / cm or more ２ 2. The heat dissipation device of claim 1, wherein:

4. An electronic device comprising the heat dissipation device according to any one of claims 1 to 3.

Images