Method for producing thermally conductive sheet

Abstract

The present application relates to a method for producing a thermally conductive sheet. The subject of the present invention is to provide a method for producing a thermally conductive sheet that allows the uncured components of the binder resin to efficiently seep out to the surface of a molded body sheet, thereby improving the adhesion. As a method for solving the subject of the present invention, a method for producing a thermally conductive sheet is provided, which includes the following steps: a step of forming a thermally conductive molded body by molding a thermally conductive resin composition containing a thermally conductive filler in a binder resin into a predetermined shape and curing it, a step of cutting the thermally conductive molded body into sheets to form a molded body sheet, and a step of pressing the molded body sheet under a reduced pressure environment to cover the surface of the molded body sheet with the uncured components of the binder resin that seep out from the sheet body of the molded body sheet.

Description

Technical Field

[0001] The present invention relates to a method for producing a thermally conductive sheet to be attached to electronic components and the like to improve the heat dissipation thereof. Background Art

[0002] In the past, semiconductor elements installed in various electrical devices such as personal computers and other devices generate heat during operation. If the generated heat is accumulated, it will have an adverse effect on the operation of the semiconductor element and peripheral devices, so various cooling methods have been used. As cooling methods for electronic components such as semiconductor elements, there are known methods: installing a fan in the device to cool the air in the device housing; installing a heat sink such as a heat sink or a heat sink plate in the semiconductor element to be cooled, etc.

[0003] When a heat sink is installed in a semiconductor element for cooling, a thermally conductive sheet is provided between the semiconductor element and the heat sink in order to efficiently release the heat of the semiconductor element. As a thermally conductive sheet, a thermally conductive sheet containing fillers such as thermally conductive fillers such as carbon fibers dispersed in a silicone resin is widely used (see Patent Document 1). These thermally conductive fillers have thermal anisotropy. For example, it is known that when carbon fibers are used as thermally conductive fillers, the thermal conductivity is about 600W / m·K to 1200W / m·K in the fiber direction. When boron nitride is used, the thermal conductivity is about 110W / m·K in the surface direction and about 2W / m·K in the direction perpendicular to the surface direction, which is anisotropic.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2012-023335

[0007] Patent Document 2: Japanese Patent Application Publication No. 2015-029076

[0008] Patent Document 3: Japanese Patent Application Publication No. 2015-029075 Summary of the invention

[0009] Problems to be solved by the invention

[0010] Here, the heat dissipation of electronic components such as the CPU of a personal computer tends to increase year by year as it becomes faster and more powerful. However, on the contrary, the chip size of processors and the like has become the same size or smaller than before due to the advancement of micro-silicon circuit technology, and the heat flow rate per unit area has increased. Therefore, in order to avoid adverse conditions caused by this temperature rise, it is required to dissipate heat and cool electronic components such as the CPU more efficiently.

[0011] In order to improve the heat dissipation characteristics of the thermally conductive sheet, it is required to reduce the thermal impedance, which is an indicator of the difficulty of heat conduction. In order to reduce the thermal impedance, it is effective to improve the adhesion with the electronic components as the heat generating body, the heat sink and other heat dissipating bodies, and to reduce the thermal impedance by making the thermally conductive sheet thinner.

[0012] When a thermally conductive molded body is sliced ​​into thin sheets to form a thermally conductive sheet, the surface of the sheet after cutting has unevenness and lacks adhesion. If there is a lack of adhesion, the sheet may fall off the component due to poor adhesion during the mounting process. In addition, there is a problem that air is contained due to poor adhesion with electronic components as heat generating bodies and heat sinks and other heat dissipating bodies, and thermal impedance cannot be sufficiently reduced.

[0013] To address this problem, a technique has been proposed in which the surface of a thermally conductive sheet produced by cutting a thermally conductive molded body is pressed or allowed to stand for a long time to allow uncured components of the binder resin to seep out to the surface, thereby improving the adhesion between the thermally conductive sheet and the electronic component (see Patent Documents 2 and 3).

[0014] However, compared with a thick thermally conductive sheet, the uncured component of the adhesive resin in a thin thermally conductive sheet is small, and even if pressed, it will not fully seep out to the sheet surface. The adhesive does not seep out evenly to the sheet surface, and the adhesion varies depending on the position on the surface of the thermally conductive sheet, which leads to a problem of increased thermal impedance.

[0015] In addition, if the thermally conductive sheet after being sliced ​​is a soft sheet containing a large amount of uncured components, there is a problem that it will stretch and cannot maintain its shape if it is pressed between the electronic component and the heat dissipation member for a long time. On the other hand, if it is a hard thermally conductive sheet, the uncured components of the binder resin are small, and it is not easy to seep out even if pressed, and it cannot reach the surface of the cover sheet to improve the adhesion. This problem is the same even when the thermally conductive sheet is left stationary, and there is a problem that the adhesion becomes insufficient.

[0016] Therefore, an object of the present invention is to provide a method for producing a thermally conductive sheet in which uncured components of a binder resin are efficiently exuded onto the surface of a molded sheet to improve adhesion.

[0017] Methods for solving problems

[0018] In order to solve the above-mentioned problems, the method for manufacturing a thermally conductive sheet according to the present invention includes the following steps: a step of forming a thermally conductive molded body by molding a thermally conductive resin composition containing a thermally conductive filler in a binder resin into a predetermined shape and curing the shape, a step of cutting the thermally conductive molded body into sheets to form a molded body sheet, and a step of pressing the molded body sheet under a reduced pressure environment to cover the surface of the molded body sheet with the uncured components of the binder resin that have seeped out from the sheet body of the molded body sheet.

[0019] Effects of the Invention

[0020] According to the present invention, the thermally conductive sheet can efficiently ooze out the uncured component of the binder resin carried by the sheet body to cover the sheet surface by pressing the molded sheet under a reduced pressure environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a cross-sectional view showing a thermally conductive sheet to which the present invention is applied.

[0022] Figure 2 It is a perspective view showing an example of the process of cutting a thermally conductive formed body.

[0023] Figure 3 This is a cross-sectional view showing a step of pressing a molded body sheet to which a release film is attached under a reduced pressure environment.

[0024] Figure 4 is a cross-sectional view showing an example of a semiconductor device.

[0025] Explanation of symbols

[0026] 1 thermally conductive sheet 1, 2 sheet main body, 3 release film, 5 resin coating layer, 6 thermally conductive molded body, 7 molded body sheet. DETAILED DESCRIPTION

[0027] Hereinafter, the manufacturing method of the thermally conductive sheet to which the present invention is applied will be described in detail with reference to the accompanying drawings. In addition, the present invention is not limited to the following embodiments, and various changes can be made without departing from the main purpose of the present invention. In addition, the accompanying drawings are schematic diagrams, and the ratios of various dimensions are sometimes different from the actual ratios. The specific dimensions should be determined with reference to the following description. In addition, of course, the drawings also contain parts with different dimensional relationships and ratios.

[0028] The method for producing a thermally conductive sheet to which the present invention is applied comprises the following steps: a step of forming a thermally conductive molded body by molding a thermally conductive resin composition containing a thermally conductive filler in a binder resin into a predetermined shape and curing the composition (step A); a step of cutting the thermally conductive molded body into sheets to form a molded body sheet (step B); and a step of pressing the molded body sheet under a reduced pressure environment to coat the surface of the molded body sheet with uncured components of the binder resin that have oozed out from the sheet body of the molded body sheet (step C).

[0029] The thermally conductive sheet manufactured through the above process carries uncured components of the adhesive resin that do not contribute to the reaction in the sheet body of the molded sheet. By pressing the above molded sheet under a reduced pressure environment, the uncured components of the adhesive resin carried by the sheet body can be efficiently seeped out and covered with the sheet surface.

[0030] Thus, according to the present invention, from a sheet body that is thinly cut and does not contain a large amount of uncured components of adhesive resin, the uncured components can be exuded over the entire surface of the sheet surface for coating. In addition, from a sheet body that is cured with an adhesive resin, is relatively hard and has excellent shape retention but does not contain a large amount of uncured components of adhesive resin, the uncured components can be exuded over the entire surface of the sheet surface for coating.

[0031] Therefore, according to the thermally conductive sheet manufactured by the present invention, regardless of the unevenness of the sheet surface, the close adhesion with electronic components and heat dissipation components can be improved, and the thermal impedance can be reduced. In addition, according to the thermally conductive sheet manufactured by the present invention, it is not necessary to apply an adhesive for making it close to electronic components and heat dissipation components on the sheet surface, and the thermal impedance of the sheet does not increase. Furthermore, for the thermally conductive sheet containing a thermally conductive filler in the binder resin, not only can the thermal impedance from the low load area be reduced, but also the viscosity (adhesion force) is excellent, and the mounting performance and thermal characteristics can also be improved.

[0032] [Composition of thermally conductive sheet]

[0033] Figure 1 A thermally conductive sheet 1 to which the present invention is applied is shown. The thermally conductive sheet 1 has a sheet body 2 formed by curing a binder resin containing at least a polymer matrix component and a thermally conductive filler. Both surfaces of the sheet body 2 are coated with uncured components of the binder resin that have seeped out of the sheet body 2, thereby forming a resin coating layer 5. Furthermore, the thermally conductive sheet 1 has release films 3 attached to both surfaces of the sheet body 2, and the uncured components of the binder resin constituting the resin coating layer 5 are retained between the release films 3 and the sheet body 2.

[0034] The two surfaces of the sheet body 2 of the thermally conductive sheet 1 have adhesiveness due to the formation of the resin coating layer 5, and can be attached to a predetermined position by peeling off the release film 3 during use. Moreover, even if the surface of the sheet body 2 has irregularities, the resin coating layer 5 can improve the adhesion with electronic components and heat dissipation members.

[0035] [Polymer matrix component]

[0036] The polymer matrix component constituting the sheet body 2 is a polymer component serving as a base material of the thermally conductive sheet 1. The type thereof is not particularly limited, and a known polymer matrix component can be appropriately selected. For example, a thermosetting polymer can be cited as one of the polymer matrix components.

[0037] As the above-mentioned thermosetting polymer, for example, crosslinked rubber, epoxy resin, polyimide resin, bismaleimide resin, benzocyclobutene resin, phenolic resin, unsaturated polyester, diallyl phthalate resin, silicone resin, polyurethane, polyimide silicone, thermosetting polyphenylene ether, thermosetting modified polyphenylene ether, etc. can be mentioned. These can be used alone or in combination of two or more.

[0038] In addition, examples of the crosslinked rubber include natural rubber, butadiene rubber, isoprene rubber, nitrile rubber, hydrogenated nitrile rubber, chloroprene rubber, ethylene-propylene rubber, chlorinated polyethylene, chlorosulfonated polyethylene, butyl rubber, halogenated butyl rubber, fluororubber, urethane rubber, acrylic rubber, polyisobutylene rubber, silicone rubber, etc. These may be used alone or in combination of two or more.

[0039] Among these thermosetting polymers, silicone resins are preferably used because of their excellent molding processability and weather resistance, and their adhesion and conformability to electronic components. The silicone resin is not particularly limited, and the type of silicone resin can be appropriately selected according to the purpose.

[0040] From the viewpoint of obtaining the above-mentioned molding processability, weather resistance, adhesion, etc., the above-mentioned silicone resin is preferably a silicone resin composed of a main agent of liquid silicone gel and a curing agent. Examples of such silicone resins include addition reaction type liquid silicone resins and heat-curable kneaded silicone resins that use peroxide for vulcanization. Among them, as a heat dissipation component of an electronic device, since the heat-generating surface of the electronic component and the heat sink surface are required to have good adhesion, an addition reaction type liquid silicone resin is particularly preferred.

[0041] As the addition reaction type liquid silicone resin, it is preferable to use a two-component addition reaction type silicone resin having a polyorganosiloxane having a vinyl group as a main agent and a polyorganosiloxane having a Si—H group as a curing agent.

[0042] Here, the liquid silicone component includes a silicone liquid A component as a main agent and a silicone liquid B component including a curing agent, and the mixing ratio of the silicone liquid A component to the silicone liquid B component is preferably a silicone liquid A component containing a larger amount of the silicone liquid B component than that of the silicone liquid B component. Thus, the thermally conductive sheet 1 can impart flexibility to the sheet body 2, and the uncured components of the binder resin (polymer matrix component) can be exuded onto the surfaces 2a and 2b of the sheet body 2 by the pressing process, thereby forming a resin coating layer 5.

[0043] The content of the polymer matrix component in the thermally conductive sheet of the present invention is not particularly limited and can be appropriately selected according to the purpose. From the perspective of ensuring the molding processability and adhesion of the sheet, it is preferably about 15% to 50% by volume, and more preferably 20% to 45% by volume.

[0044] [Thermal conductive filler]

[0045] The thermally conductive filler included in the thermally conductive sheet 1 is a component for improving the thermal conductivity of the sheet. The type of thermally conductive filler is not particularly limited as long as it is a material with high thermal conductivity, and examples thereof include fibrous thermally conductive fillers such as carbon fibers, metals such as silver, copper, and aluminum, and ceramics such as aluminum oxide, aluminum nitride, silicon carbide, and graphite. Among these fibrous thermally conductive fillers, carbon fibers are preferably used in order to obtain higher thermal conductivity.

[0046] In addition, the thermally conductive filler may be used alone or in combination of two or more. Furthermore, when two or more thermally conductive fillers are used, they may all be fibrous thermally conductive fillers or a fibrous thermally conductive filler may be used in combination with a thermally conductive filler of another shape.

[0047] There is no particular restriction on the type of the above-mentioned carbon fiber, and it can be appropriately selected according to the purpose. For example, pitch-based carbon fiber, PAN-based carbon fiber, carbon fiber obtained by graphitizing PBO fiber, carbon fiber synthesized by arc discharge method, laser evaporation method, CVD method (chemical vapor growth method), CCVD method (catalyst chemical vapor growth method) etc. can be used. Among them, from the aspect of obtaining high thermal conductivity, carbon fiber obtained by graphitizing PBO fiber and pitch-based carbon fiber are more preferred.

[0048] In addition, the carbon fiber may be used after a part or all of it has been subjected to surface treatment as required. Examples of the surface treatment include oxidation treatment, nitridation treatment, nitration, sulfonation, or treatment in which metals, metal compounds, organic compounds, etc. are attached or bonded to the functional groups introduced to the surface by these treatments or to the surface of the carbon fiber. Examples of the functional groups include hydroxyl, carboxyl, carbonyl, nitro, amino, etc.

[0049] Furthermore, the average fiber length (average major axis length) of the above-mentioned carbon fibers can be appropriately selected without particular limitation. From the perspective of ensuring high thermal conductivity, the average fiber length is preferably in the range of 50 μm to 300 μm, more preferably in the range of 75 μm to 275 μm, and particularly preferably in the range of 90 μm to 250 μm.

[0050] Furthermore, the average fiber diameter (average minor axis length) of the carbon fibers can be appropriately selected without particular limitation, but is preferably in the range of 4 μm to 20 μm, more preferably in the range of 5 μm to 14 μm, from the viewpoint of surely obtaining high thermal conductivity.

[0051] The aspect ratio (average major axis length / average minor axis length) of the carbon fibers is preferably 8 or more, and more preferably 9 to 30, from the perspective of reliably obtaining high thermal conductivity. If the aspect ratio is less than 8, the fiber length (major axis length) of the carbon fibers is short, so there is a concern that thermal conductivity may be reduced. On the other hand, if the aspect ratio exceeds 30, dispersibility in the thermally conductive sheet is reduced, so there is a concern that sufficient thermal conductivity may not be obtained.

[0052] Here, the average major axis length and the average minor axis length of the carbon fibers can be measured, for example, using a microscope, a scanning electron microscope (SEM), or the like, and the average value can be calculated from a plurality of samples.

[0053] The content of the fibrous thermally conductive filler in the thermally conductive sheet 1 is not particularly limited and can be appropriately selected according to the purpose, but is preferably 4% to 40% by volume, and more preferably 5% to 35% by volume. If the content is less than 4% by volume, it may be difficult to obtain a sufficiently low thermal impedance, and if it exceeds 40% by volume, it may affect the moldability of the thermally conductive sheet 1 and the orientation of the fibrous thermally conductive filler. In addition, the content of the thermally conductive filler including the fibrous thermally conductive filler in the thermally conductive sheet 1 is preferably 15% to 75% by volume.

[0054] [Inorganic fillers]

[0055] The thermally conductive sheet 1 may further contain an inorganic filler as a thermally conductive filler. By containing an inorganic filler, the thermal conductivity of the thermally conductive sheet 1 can be further improved, and the strength of the sheet can be improved. As the above-mentioned inorganic filler, there is no particular limitation on the shape, material, average particle size, etc., and it can be appropriately selected according to the purpose. As the above-mentioned shape, for example, spherical, elliptical, blocky, granular, flat, needle-shaped, etc. can be cited. Among them, from the perspective of filling, spherical and elliptical shapes are preferred, and spherical shapes are particularly preferred.

[0056] As the material of the above-mentioned inorganic filler, for example, aluminum nitride (aluminum nitride: AlN), silicon dioxide, aluminum oxide (Aluminum oxide), boron nitride, titanium dioxide, glass, zinc oxide, silicon carbide, silicon (silicon), silicon oxide, metal particles, etc. can be mentioned. They can be used alone or in combination of two or more. Among them, aluminum oxide, boron nitride, aluminum nitride, zinc oxide, and silicon dioxide are preferred. From the aspect of thermal conductivity, aluminum oxide and aluminum nitride are particularly preferred.

[0057] The inorganic filler may be a surface-treated inorganic filler. If the inorganic filler is treated with a coupling agent as the surface treatment, the dispersibility of the inorganic filler is improved, and the flexibility of the thermally conductive sheet is improved.

[0058] The average particle size of the inorganic filler can be appropriately selected according to the type of inorganic material, etc. When the inorganic filler is alumina, the average particle size is preferably 1 μm to 10 μm, more preferably 1 μm to 5 μm, and particularly preferably 4 μm to 5 μm. If the average particle size is less than 1 μm, the viscosity may increase and the mixing may become difficult. On the other hand, if the average particle size exceeds 10 μm, the thermal impedance of the thermally conductive sheet 1 may increase.

[0059] Furthermore, when the inorganic filler is aluminum nitride, the average particle size is preferably 0.3 μm to 6.0 μm, more preferably 0.3 μm to 2.0 μm, and particularly preferably 0.5 μm to 1.5 μm. If the average particle size is less than 0.3 μm, the viscosity may increase and mixing may become difficult. If it exceeds 6.0 μm, the thermal impedance of the thermally conductive sheet 1 may increase.

[0060] The average particle size of the inorganic filler can be measured, for example, using a particle size distribution meter or a scanning electron microscope (SEM).

[0061] [Other ingredients]

[0062] The thermally conductive sheet 1 may contain other components as appropriate according to the purpose in addition to the above-mentioned polymer matrix component and thermally conductive filler. Examples of other components include magnetic metal powder, thixotropy imparting agent, dispersant, curing accelerator, retarder, micro thickener, plasticizer, flame retardant, antioxidant, stabilizer, colorant, etc. In addition, electromagnetic wave absorption performance can be imparted to the thermally conductive sheet 1 by adjusting the content of the magnetic metal powder.

[0063] [Process for producing thermally conductive sheet]

[0064] [Process A]

[0065] Next, the manufacturing process of the thermally conductive sheet 1 is described. As described above, the manufacturing process of the thermally conductive sheet 1 to which the present invention is applied includes step A, that is, the step of molding a thermally conductive resin composition containing a thermally conductive filler in a binder resin into a predetermined shape and curing it to form a thermally conductive molded body.

[0066] In step A, the polymer matrix component, the thermally conductive filler, and other components as appropriate are mixed to prepare a thermally conductive resin composition. The steps of mixing and preparing the components are not particularly limited, and for example, a thermally conductive filler, an appropriate inorganic filler, a magnetic metal powder, and other components are added to the polymer matrix component and mixed to prepare the thermally conductive resin composition.

[0067] Next, a fibrous thermally conductive filler such as carbon fiber is oriented in one direction. The method for orienting the filler is not particularly limited as long as it is a method that can orient it in one direction. For example, by extruding or pressing the thermally conductive resin composition into a hollow mold under high shear force, the fibrous thermally conductive filler can be oriented in one direction relatively easily, so that the orientation of the fibrous thermally conductive filler is the same (within ±10°).

[0068] As the method of extruding or pressing the thermally conductive resin composition into a hollow mold under high shear force, specifically, an extrusion molding method or a mold molding method can be cited. When the thermally conductive resin composition is extruded from the die head in the extrusion molding method, or when the thermally conductive resin composition is pressed into the mold in the mold molding method, the thermally conductive resin composition flows, and the fibrous thermally conductive filler is oriented along the flow direction. At this time, if a slit is installed at the front end of the die head, it is easier to orient the fibrous thermally conductive filler.

[0069] The thermally conductive resin composition extruded or pressed into a hollow mold is molded into a block shape corresponding to the shape and size of the mold, and the polymer matrix component is cured while maintaining the orientation of the fibrous thermally conductive filler, thereby forming a thermally conductive molded body. The so-called thermally conductive molded body refers to a sheet-cutting base material (molded body) that is a raw material of the thermally conductive sheet 1 obtained by cutting into a predetermined size.

[0070] The size and shape of the hollow mold and the thermally conductive molded body can be determined according to the required size and shape of the thermally conductive sheet 1, and can be, for example, a rectangular parallelepiped having a longitudinal dimension of 0.5 cm to 15 cm and a lateral dimension of 0.5 cm to 15 cm. The length of the rectangular parallelepiped can be determined as required.

[0071] The method and conditions for curing the polymer matrix component can be changed according to the type of the polymer matrix component. For example, when the polymer matrix component is a thermosetting resin, the curing temperature during heat curing can be adjusted. Furthermore, when the thermosetting resin contains a main component of liquid silicone gel and a curing agent, it is preferably cured at a curing temperature of 80°C to 120°C. In addition, there is no particular limitation on the curing time during heat curing, and it can be set to 1 hour to 10 hours.

[0072] Here, in step A, not all of the polymer matrix component is cured, but uncured components are supported. The uncured components seep out to the surface of the sheet in the step of pressing the molded sheet under reduced pressure described below, and form a resin coating layer having adhesiveness.

[0073] [Process B]

[0074] The manufacturing process of the thermally conductive sheet 1 to which the present invention is applied is as follows: Figure 2 As shown in the figure, step B is included, that is, the step of cutting the thermally conductive molded body 6 into sheets to form molded body sheets 7. In step B, the thermally conductive resin molded body 6 is cut into sheets at an angle of 0° to 90° with respect to the long axis direction of the oriented fibrous thermally conductive filler.

[0075] The thermally conductive molded body 6 is cut using a cutting device. The cutting device is not particularly limited as long as it can cut the thermally conductive molded body 6, and a known cutting device can be used as appropriate. For example, an ultrasonic cutter, a planer, etc. can be used.

[0076] The thickness of the molded body sheet 7 is the thickness of the sheet body of the thermally conductive sheet 1 , and can be appropriately set according to the application of the thermally conductive sheet 1 , and is, for example, 0.2 mm to 1.0 mm.

[0077] In the step B, the plurality of molded body pieces 7 may be cut into smaller pieces by providing cuts to the molded body pieces 7 cut out from the thermally conductive molded body 6 .

[0078] [Process C]

[0079] The manufacturing process of the thermally conductive sheet 1 to which the present invention is applied includes step C of pressing the molded sheet 7 under a reduced pressure environment to coat the surface of the molded sheet 7 with the uncured component of the binder resin that has seeped out from the sheet body of the molded sheet 7 .

[0080] The so-called reduced pressure environment refers to a vacuum pressure that is lower than the normal pressure (atmospheric pressure) environment without any reduced pressure treatment. It is set to a vacuum pressure that can make the uncured components of the binder resin seep out on the entire surface of the sheet. It can be appropriately set according to the thickness of the molded body sheet, the proportion of the silicone A liquid component as the main agent of the liquid silicone component constituting the binder resin and the silicone B liquid component containing the curing agent, etc. For example, as a reduced pressure environment, the so-called gauge pressure that sets the atmospheric pressure to zero can be set to -0.2kPa. If the vacuum pressure x (kPa) in the pressing process is too low, the uncured components of the binder resin will volatilize and damage the viscosity of the sheet surface. If it is too high, the seepage of the uncured components cannot be promoted. For example, it can be appropriately set to the range of -5.0kPa≤x≤-0.1kPa.

[0081] The pressing may be performed, for example, using a pair of pressing devices formed of a flat plate and a flat-surface pressing head. Alternatively, the pressing may be performed using nip rollers.

[0082] There is no particular restriction on the pressure during the above-mentioned pressing, and it can be appropriately selected according to the purpose. If it is too low, the thermal impedance tends to remain unchanged compared to when no pressing is performed. If it is too high, the sheet tends to stretch. Therefore, it is preferably set to a pressure range of 0.1MPa to 100MPa, and more preferably set to a pressure range of 0.5MPa to 95MPa.

[0083] Here, as described above, in the thermally conductive molded body, not all of the polymer matrix components are cured, but the molded body sheet carries uncured components of the binder resin (polymer matrix component) in the sheet body, and a part of the uncured components is efficiently exuded to the sheet surface by the pressing process under a reduced pressure environment. Thus, a thermally conductive sheet 1 having a resin coating layer formed on the sheet surface can be formed. The thermally conductive sheet 1 has adhesiveness due to the resin coating layer 5 formed on the sheet surface.

[0084] Furthermore, by undergoing the pressing step, the surface of the molded body sheet is smoothed, thereby enhancing the adhesion of the thermally conductive sheet 1 and reducing the interface contact resistance under light load.

[0085] Thus, according to the present invention, from a sheet body that is thinly cut and does not contain a large amount of uncured components of adhesive resin, the uncured components can be exuded over the entire surface of the sheet surface for coating. In addition, from a sheet body that is cured with adhesive resin, is relatively hard and has excellent shape retention but does not contain a large amount of uncured components of adhesive resin, the uncured components can be exuded over the entire surface of the sheet surface for coating.

[0086] Therefore, according to the thermally conductive sheet manufactured by the present invention, regardless of the unevenness of the sheet surface, the close adhesion with electronic components and heat dissipation components can be improved, and the thermal impedance can be reduced. In addition, according to the thermally conductive sheet manufactured by the present invention, it is not necessary to apply an adhesive to the sheet surface for making it close to electronic components and heat dissipation components, and the thermal impedance of the sheet does not increase. Furthermore, for the thermally conductive sheet containing a thermally conductive filler in the binder resin, not only can the thermal impedance from the low load area be reduced, but also the viscosity (adhesion force) is excellent, and the mounting performance and thermal characteristics can be improved.

[0087] [Release film]

[0088] In addition, in the above step C, if Figure 3 As shown in FIG. 1 , it is preferred to press the molded body sheet 7 with a release film 3 attached to at least one side, preferably both sides. As the release film 3, for example, a PET film is used. In addition, as for the release film 3, a release treatment may also be applied to the surface of the molded body sheet 7 that is attached thereto.

[0089] By attaching the release film 3 to the surface of the sheet body of the molded sheet 7, the uncured components that seep out to the sheet surface during the pressing process under reduced pressure are retained on the sheet surface by the tension acting between the release film 3, and the resin coating layer 5 that uniformly covers the entire surface of the sheet with a uniform thickness can be formed. As a result, the thermal conductive sheet 1 can eliminate the variation in adhesion and reduce the thermal impedance.

[0090] The thermally conductive sheet 1 is formed by going through the above steps. When the thermally conductive sheet 1 is actually used, the release film 3 is peeled off to expose the adhesive resin coating layer 5, and the thermally conductive sheet 1 is provided for mounting on electronic components or the like.

[0091] [Example of use]

[0092] In actual use, the release film 3 of the thermally conductive sheet 1 is peeled off and the thermally conductive sheet 1 is mounted inside electronic components such as semiconductor devices or various electronic devices.

[0093] The thermally conductive sheet 1 is, for example, Figure 4 As shown, the semiconductor device 50 is mounted in various electronic devices and is sandwiched between a heat source and a heat dissipation member. Figure 4 The semiconductor device 50 shown has at least an electronic component 51, a heat spreader 52, and a thermally conductive sheet 1, and the thermally conductive sheet 1 is sandwiched between the heat spreader 52 and the electronic component 51. By using the thermally conductive sheet 1, the semiconductor device 50 has high heat dissipation properties, and also has an excellent electromagnetic wave suppression effect depending on the content of the magnetic metal powder in the binder resin.

[0094] The electronic component 51 is not particularly limited and can be appropriately selected according to the purpose. For example, various semiconductor components such as CPU, MPU, graphics processing element, image sensor, antenna element, battery, etc. can be cited. The heat spreader 52 is not particularly limited as long as it is a component that dissipates the heat generated by the electronic component 51, and can be appropriately selected according to the purpose. The thermal conductive sheet 1 is clamped between the thermal spreader 52 and the electronic component 51. In addition, the thermal conductive sheet 1 is clamped between the thermal spreader 52 and the heat sink 53, thereby constituting a heat dissipation component that dissipates the heat of the electronic component 51 together with the thermal spreader 52.

[0095] The installation position of the heat conducting sheet 1 is not limited to between the heat spreader 52 and the electronic component 51, or between the heat spreader 52 and the heat sink 53, and can be appropriately selected according to the configuration of the electronic device or semiconductor device. In addition, as a heat dissipation component, in addition to the heat spreader 52 and the heat sink 53, any heat dissipation component that conducts the heat generated from the heat source to the outside can be used, for example, a heat sink, a cooler, a chip holder, a printed circuit board, a cooling fan, a Peltier element, a heat pipe, a metal cover, a housing, etc.

[0096] Example

[0097] In the examples and comparative examples, the composition ratio of the binder component to the curing agent component of the thermally conductive resin composition was changed to form samples of thermally conductive sheets, and the adhesiveness and thermal resistance value of each sample were measured.

[0098] [Measurement of Adhesiveness]

[0099] The adhesiveness (gf) of the sheet surface of each sample before and immediately after pressing was measured using an adhesive tester (TACKINESS TESTER MODEL TACII, Lishico). The adhesiveness was measured three times at five points in the four corners and the center of the rectangular sample and the average value of the measured values. The measurement conditions were as follows.

[0100] Immersion speed: 30mm / min

[0101] Test speed: 120mm / min

[0102] Initial load (Pre speed): 196g

[0103] Press time: 5 sec

[0104] Stretching distance: 5mm

[0105] Die head:

[0106] [Measurement of thermal impedance value]

[0107] According to the method of ASTM-D5470, under a load of 1.0kgf / cm 2 The thermal impedance value (K·cm) of each sample was measured under 2 / W).

[0108] [Example 1]

[0109] As shown in Table 1, 42% by volume of alumina particles having an average particle size of 4 μm coupled with a silane coupling agent and 23% by volume of pitch-based carbon fibers having an average fiber length of 150 μm as a fibrous filler were mixed in a two-component addition reaction type liquid silicone to prepare a silicone composition (thermal conductive resin composition). The two-component addition reaction type liquid silicone resin used a silicone resin having an organopolysiloxane as a main component, and was formulated in such a manner that the ratio of silicone agent A to agent B was 57:43.

[0110] The obtained silicone composition was extruded in a hollow quadrangular prism-shaped mold (50mm×50mm) to form a 50mm square silicone molded body. The silicone molded body was heated in an oven at 100°C for 6 hours to prepare a silicone cured product (thermally conductive molded body). The silicone cured product was cut using a slicer to a thickness of 0.5mm to obtain a molded body sheet. The obtained molded body sheet was clamped with a peeling-treated PET film, and then vacuum pressed under a reduced pressure environment of -2.0kPa at a pressure of 2MPa, a temperature of 100°C, and a pressing time of 3 minutes to obtain a sample of a thermally conductive sheet. The adhesiveness of the sample was 20gf before pressing and 178gf after pressing. The thermal impedance value is 0.3K·cm 2 / W.

[0111] [Example 2]

[0112] As shown in Table 1, in a two-component addition reaction type liquid silicone, 20 volume % of alumina particles having an average particle size of 4 μm and 24 volume % of aluminum nitride particles coupled with a silane coupling agent and 23 volume % of pitch-based carbon fibers having an average fiber length of 150 μm as a fibrous filler were mixed to prepare a silicone composition (thermal conductive resin composition). The two-component addition reaction type liquid silicone resin used a silicone resin having an organopolysiloxane as a main component, and was formulated in such a manner that the mixing ratio of silicone agent A to agent B was 50:50.

[0113] The obtained silicone composition was extruded in a hollow quadrangular prism-shaped mold (50mm×50mm) to form a 50mm square silicone molded body. The silicone molded body was heated in an oven at 100°C for 6 hours to prepare a silicone cured product (thermally conductive molded body). The silicone cured product was cut using a slicer to a thickness of 0.5mm to obtain a molded body sheet. The obtained molded body sheet was clamped with a peeling-treated PET film and vacuum pressed under a reduced pressure environment of -2.0kPa at a pressure of 2MPa, a temperature of 100°C, and a pressing time of 3 minutes to obtain a sample of a thermally conductive sheet. The adhesiveness of the sample was 19gf before pressing and 124gf after pressing. The thermal impedance value was 0.25K·cm 2 / W.

[0114] [Example 3]

[0115] As shown in Table 1, the same silicone composition (thermally conductive resin composition) as in Example 2 was extruded in a hollow quadrangular prism-shaped mold (50 mm × 50 mm) to form a 50 mm square silicone molded body. The silicone molded body was heated in an oven at 100°C for 6 hours to prepare a silicone cured product (thermally conductive molded body). The silicone cured product was cut using a slicer to a thickness of 1.0 mm to obtain a molded body sheet. The obtained molded body sheet was clamped with a release-treated PET film and vacuum pressed under a reduced pressure environment of -2.0 kPa at a pressure of 2 MPa, a temperature of 100°C, and a pressing time of 3 minutes to obtain a sample of a thermally conductive sheet. The adhesiveness of the sample was 18 gf before pressing and 152 gf after pressing. The thermal impedance value was 0.40 K·cm 2 / W.

[0116] [Comparative Example 1]

[0117] As shown in Table 1, the same silicone composition (thermally conductive resin composition) as in Example 1 was extruded in a hollow quadrangular prism-shaped mold (50 mm × 50 mm) to form a 50 mm square silicone molded body. The silicone molded body was heated in an oven at 100°C for 6 hours to prepare a silicone cured product (thermally conductive molded body). The silicone cured product was cut using a slicer to a thickness of 0.5 mm to obtain a molded body sheet. The obtained molded body sheet was clamped with a release-treated PET film and then pressed under atmospheric pressure at a pressure of 2 MPa, a temperature of 100°C, and a pressing time of 3 minutes to obtain a sample of a thermally conductive sheet. The adhesiveness of the sample was 12 gf before pressing and 38 gf after pressing. The thermal impedance value was 0.40 K·cm 2 / W.

[0118] [Comparative Example 2]

[0119] As shown in Table 1, the same silicone composition (thermally conductive resin composition) as in Example 2 was extruded in a hollow quadrangular prism-shaped mold (50 mm × 50 mm) to form a 50 mm square silicone molded body. The silicone molded body was heated in an oven at 100°C for 6 hours to prepare a silicone cured product (thermally conductive molded body). The silicone cured product was cut using a slicer to a thickness of 0.5 mm to obtain a molded body sheet. The obtained molded body sheet was clamped with a release-treated PET film and then pressed under atmospheric pressure at a pressure of 2 MPa, a temperature of 100°C, and a pressing time of 3 minutes to obtain a sample of a thermally conductive sheet. The adhesiveness of the sample was 14 gf before pressing and 19 gf after pressing. The thermal impedance value was 0.35 K·cm 2 / W.

[0120] [Comparative Example 3]

[0121] As shown in Table 1, the same silicone composition (thermally conductive resin composition) as in Example 2 was extruded in a hollow quadrangular prism-shaped mold (50 mm × 50 mm) to form a 50 mm square silicone molded body. The silicone molded body was heated in an oven at 100°C for 6 hours to prepare a silicone cured product (thermally conductive molded body). The silicone cured product was cut using a slicer to a thickness of 1.0 mm to obtain a molded body sheet. The obtained molded body sheet was clamped with a release-treated PET film and then pressed under atmospheric pressure at a pressure of 2 MPa, a temperature of 100°C, and a pressing time of 3 minutes to obtain a sample of a thermally conductive sheet. The adhesiveness of the sample was 13 gf before pressing and 15 gf after pressing. The thermal impedance value was 0.48 K·cm 2 / W.

[0122] [Table 1]

[0123]

[0124] When the molded sheets were sandwiched between release-treated PET films and then vacuum pressed as in Examples 1 to 3, the adhesiveness increased and the uncured components of the binder resin efficiently oozed out onto the surface of the molded sheets.

[0125] If Example 1 is compared with Comparative Example 1, it can be seen that even when the sheet thickness is as thin as 0.5 mm, the amount of uncured components carried in the sheet body is small, and the uncured components are not easy to seep out under normal pressure, the uncured components can be promoted to seep out under a reduced pressure environment, the adhesiveness is also high, and the entire surface of the sheet is sticky.

[0126] In addition, in Examples 2 and 3 and Comparative Examples 2 and 3, the ratio of silicone agent A to agent B is 50:50, so that the uncured components carried in the sheet body are small, and the hardness is also increased, which is a condition where it is difficult for the uncured components to seep out. However, the seepage of the uncured components can be promoted under a reduced pressure environment. In addition, in Example 2, even under the condition of a sheet thickness of 0.5 mm, which is further difficult for the uncured components to seep out, stickiness is exhibited on the surface due to the seepage of the uncured components.

Claims

1. A method for manufacturing a thermally conductive sheet, comprising the following steps: A step of forming a thermally conductive molded body by molding a thermally conductive resin composition containing a thermally conductive filler in a binder resin into a predetermined shape and curing the composition. a step of cutting the thermally conductive molded body into sheets to form a molded body sheet, and The step of pressing the molded sheet under a reduced pressure environment to cover the surface of the molded sheet with uncured components of the binder resin that have oozed out from the sheet body of the molded sheet. 2 . The method for producing a thermally conductive sheet according to claim 1 , wherein the vacuum pressure x under the reduced pressure environment is in the range of -5.0 kPa ≤ x ≤ -0.1 kPa when the atmospheric pressure is set to zero. 3 . The method for producing a thermally conductive sheet according to claim 1 , wherein the forming sheet is pressed with a release film attached to at least one surface of the formed sheet. 4 . The method for producing a thermally conductive sheet according to claim 1 , wherein the thickness of the molded sheet is 0.2 mm to 1.0 mm. 5 . The method for producing a thermally conductive sheet according to claim 1 , wherein the binder resin is a liquid silicone component, and the thermally conductive filler is carbon fiber. 6 . The method for producing a thermally conductive sheet according to claim 5 , wherein the liquid silicone component comprises a silicone liquid A component as a main agent and a silicone liquid B component containing a curing agent, and the amount of the silicone liquid A component contained is greater than the amount of the silicone liquid B component.

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