Heat-conducting electroconductive adhesive layer

Abstract

Provided is a heat-conducting electroconductive adhesive layer that exhibits excellent heat conductivity, electroconductivity, adhesion to an adherend, and electromagnetic wave-shielding performance.　A heat-conducting electroconductive adhesive layer 1 contains a binder component 11 and a carbon fiber 12a. The binder component 11 contains a thermosetting-type resin. The carbon fiber 12a has metal supported on the surface thereof. The ratio of the diameter of the carbon fiber 12a to the thickness T of the heat-conducting electroconductive adhesive layer 1 is 0.2-0.5.

Description

Thermally conductive adhesive layer

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

[0002] Conductive adhesives are often used in printed wiring boards, such as conductive adhesive sheets (conductive bonding films) that are used to electrically connect an electromagnetic wave shielding film placed on a printed wiring board to an external ground or reinforcing member for grounding the circuit.

[0003] Known conductive adhesive sheets for use in printed wiring boards include, for example, a conductive layer containing at least a thermosetting resin and dendritic conductive microparticles, the thickness of which satisfies specific conditions, the average particle diameter D50 of the dendritic conductive microparticles being 3 μm or more and 50 μm or less, and the dendritic conductive microparticles being contained in the conductive layer in an amount of 50 wt % or more and 90 wt % or less (see Patent Document 1).

[0004] The printed wiring board is used with electronic components mounted thereon. If the electronic components are exposed to a high-temperature environment for a long period of time, they will no longer be able to perform their intended functions and their lifespan will be shortened. For this reason, a highly heat-dissipating bonding material may be used in the conductive adhesive sheet applied to the printed wiring board in order to efficiently dissipate the heat generated by the semiconductor element.

[0005] Furthermore, the conductive adhesive sheet may also be required to have excellent adhesion when attached to an adherend. For example, Patent Document 2 discloses an electromagnetic wave suppressing heat conductive sheet that contains a binder resin and a fibrous heat conductive filler, with carbon fiber used as the heat conductive filler. The electromagnetic wave suppressing heat conductive sheet is described as having high adhesion to heat sources and heat dissipation members, and excellent thermal conductivity and electromagnetic wave suppression effects.

[0006] International Publication No. 2012 / 164925 Japanese Patent Application Laid-Open No. 2018-129443

[0007] In recent years, electronic components have become smaller and more functional, and the amount of heat generated by semiconductor elements has been increasing. This has led to a demand for thermally conductive sheets with higher thermal conductivity.

[0008] As in Patent Document 2, the thermal conductivity tends to increase by using a carbon material as a thermally conductive filler and increasing the amount of carbon material filled in. However, this method results in a decrease in adhesion to the adherend, electrical conductivity in the thickness direction, and shielding performance.

[0009] Therefore, an object of the present invention is to provide a thermally conductive, electrically conductive adhesive layer that is excellent in thermal conductivity, electrical conductivity, adhesion to an adherend, and electromagnetic wave shielding performance.

[0010] The present invention provides a thermally conductive adhesive layer containing a binder component and carbon fibers, wherein the binder component includes a thermosetting resin, a metal is carried on the surface of the carbon fibers, the ratio of the diameter of the carbon fibers to the thickness of the thermally conductive adhesive layer is 0.2 to 0.5, and the thermally conductive adhesive layer has a thickness of 25 to 100 μm.

[0011] The aspect ratio (diameter / major axis) of the carbon fiber is preferably 0.03 to 1.

[0012] The content of the carbon fiber is preferably 40 to 70 mass % relative to 100 mass % of the total amount of the thermally conductive adhesive layer.

[0013] The amount of the metal supported is preferably 5 to 35 parts by mass per 100 parts by mass of the carbon fiber.

[0014] The diameter of the carbon fiber is preferably 5 to 30 μm.

[0015] The thermally conductive adhesive layer preferably further contains conductive particles.

[0016] The median diameter of the conductive particles is preferably smaller than the diameter of the carbon fibers.

[0017] The thermally conductive adhesive layer of the present invention is excellent in thermal conductivity, electrical conductivity, adhesion to an adherend, and electromagnetic wave shielding performance. Therefore, for example, when the thermally conductive adhesive layer is used to bond a ground circuit to a ground-side reinforcing member, a printed wiring board can be obtained that is excellent in shielding performance and thermal conductivity in the thickness direction, and that combines electrical conductivity and high heat dissipation.

[0018] 1 is a partial cross-sectional view showing an embodiment of the thermally conductive adhesive layer of the present invention, and FIG. 2 is a partial cross-sectional view showing an embodiment of a printed wiring board with a reinforcing member to which the thermally conductive adhesive layer of the present disclosure is applied.

[0019] [Thermal Conductive Adhesive Layer] The thermally conductive adhesive layer of the present invention contains at least a binder component and carbon fiber. The thermally conductive adhesive layer may also contain conductive particles other than carbon fiber. The binder component, carbon fiber, and conductive particles may each be used alone or in combination of two or more.

[0020] The thermally conductive adhesive layer is an adhesive layer in which the resin portion constituted by the binder component can exhibit adhesiveness. The thermally conductive adhesive layer may have isotropic conductivity or anisotropic conductivity.

[0021] 1 shows one embodiment of the thermally conductive adhesive layer of the present invention. The thermally conductive adhesive layer 1 is in the form of a layer (sheet) and contains a binder component 11 and a filler 12. The filler 12 contains carbon fibers 12a and conductive particles 12b. Release sheets 13a and 13b are provided on both sides of the thermally conductive adhesive layer 1, and the thermally conductive adhesive layer 1 is sandwiched between the two release sheets 13a and 13b.

[0022] (Binder Component) The binder component includes at least a thermosetting resin. Examples of the thermosetting resin include both a resin having thermosetting properties (thermosetting resin) and a resin obtained by curing the thermosetting resin. After the thermally conductive adhesive layer is placed on an adherend such as a printed wiring board or a shielded printed wiring board with electromagnetic wave shielding measures, the thermosetting resin can be cured by applying pressure and heat, thereby improving the adhesion of the attachment portion. For example, when the binder component is a thermosetting resin, the binder component after thermocompression bonding becomes a thermosetting resin obtained by curing the thermosetting resin.

[0023] While adhesive layers using thermoplastic resins can exhibit pressure-sensitive adhesion to adherends, the adhesion tends to be poor when a large amount of filler is included. In contrast, the thermally conductive adhesive layer contains a thermosetting resin, and can exhibit excellent adhesion to adherends by curing as described above, even when a large amount of filler is included.

[0024] Examples of the thermosetting resin include silicone resin, phenolic resin, epoxy resin, urethane resin, urethane urea resin, melamine resin, alkyd resin, polyamide resin, polyimide resin, and acrylic resin.

[0025] The thermosetting resin preferably contains an epoxy resin, from the viewpoint of dispersing the carbon fibers well. Furthermore, the thermosetting resin preferably contains a thermosetting resin having a functional group reactive with an epoxy group, from the viewpoint of obtaining excellent reflow resistance, and more preferably an epoxy-modified thermosetting resin or a carboxy-modified thermosetting resin. Examples of such thermosetting resins include epoxy-modified polyester resins, epoxy-modified polyamide resins, epoxy-modified acrylic resins, epoxy-modified urethane urea resins, carboxy-modified polyester resins, carboxy-modified polyamide resins, carboxy-modified acrylic resins, and carboxy-modified urethane urea resins. Among these, carboxy-modified polyester resins, carboxy-modified polyamide resins, and carboxy-modified urethane urea resins are preferred.

[0026] The carboxyl group-modified thermosetting resin preferably has an acid value of 2 to 100 mgKOH / g, more preferably 2 to 50 mgKOH / g, and even more preferably 3 to 30 mgKOH / g. When the acid value is 2 mgKOH / g or more, the resin is sufficiently cured with the epoxy resin, resulting in superior heat resistance of the thermally conductive adhesive layer. When the acid value is 100 mgKOH / g or less, the resin is sufficiently cured with the epoxy resin, resulting in superior adhesion of the thermally conductive adhesive layer to the adherend.

[0027] The epoxy resin is a compound having two or more epoxy groups per molecule. Examples of the epoxy resin include bisphenol-type epoxy resins such as bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, and bisphenol S-type epoxy resins; spirocyclic epoxy resins; naphthalene-type epoxy resins; biphenyl-type epoxy resins; terpene-type epoxy resins; glycidyl ether-type epoxy resins such as tris(glycidyloxyphenyl)methane and tetrakis(glycidyloxyphenyl)ethane; glycidylamine-type epoxy resins such as tetraglycidyldiaminodiphenylmethane; tetrabromobisphenol A-type epoxy resins; novolac-type epoxy resins such as cresol novolac-type epoxy resins, phenol novolac-type epoxy resins, α-naphthol novolac-type epoxy resins, and brominated phenol novolac-type epoxy resins; and rubber-modified epoxy resins.

[0028] The epoxy equivalent of the epoxy resin is preferably 90 to 300 g / eq. When the epoxy equivalent is within this range, the thermally conductive, electrically conductive adhesive layer has better adhesion to the adherend.

[0029] When two or more of the above epoxy resins are used, it is preferable to use a combination of an epoxy resin having an epoxy equivalent of 90 to 300 g / eq and an epoxy resin having an epoxy equivalent of 800 to 10,000 g / eq. In this case, the epoxy resin having an epoxy equivalent of 90 to 300 g / eq and the epoxy resin having an epoxy equivalent of 800 to 10,000 g / eq may have the same or different structural units.

[0030] An epoxy resin having an epoxy equivalent of 90 to 300 g / eq is preferred because the resin has superior heat resistance. The lower limit of the epoxy equivalent is more preferably 150 g / eq, and even more preferably 170 g / eq. The upper limit of the epoxy equivalent is more preferably 250 g / eq, and even more preferably 230 g / eq. Furthermore, it is preferable to use an epoxy resin having an epoxy equivalent of 90 to 300 g / eq that is solid at room temperature.

[0031] Among the epoxy resins having an epoxy equivalent of 90 to 300 g / eq, novolac epoxy resins are preferred. Despite their high resin density, novolac epoxy resins have good miscibility with other epoxy resins and small differences in reactivity between epoxy groups, making it possible to achieve a uniformly high crosslink density throughout the entire coating film.

[0032] Examples of the novolac epoxy resin include cresol novolac epoxy resin, phenol novolac epoxy resin, α-naphthol novolac epoxy resin, and brominated phenol novolac epoxy resin.

[0033] Commercially available epoxy resins that can be used as the epoxy resin having an epoxy equivalent of 90 to 300 g / eq include EPICLONN N-660, N-665, N-670, N-673, N-680, N-695, N-655-EXP-S, N-662-EXP-S, N-665-EXP, N-665-EXP-S, N-672-EXP, N-670-EXP-S, N-685-EXP, N-673-80M, N-680-75M, N-690-75M, N-740, and N-77 Examples of suitable ethylene glycol ether copolymers include N-0, N-775, N-740-80M, N-770-70M, N-865, and N-865-80M (trade names, manufactured by DIC Corporation), jER152, 154, and 157S70 (trade names, manufactured by Mitsubishi Chemical Corporation), and YDPN-638, YDCN-700, YDCN-700-2, YDCN-700-3, YDCN-700-5, YDCN-700-7, YDCN-700-10, YDCN-704, and YDCN-700-A (trade names, manufactured by Nippon Steel Chemical & Material Co., Ltd.).

[0034] Furthermore, when a novolac-type epoxy resin is used as the epoxy resin having an epoxy equivalent of 90 to 300 g / eq, it is preferable to use an epoxy resin other than a novolac-type epoxy resin that is solid at room temperature as the epoxy resin having an epoxy equivalent of 800 to 10,000 g / eq, from the viewpoint of providing better adhesion of the thermally conductive adhesive layer to the substrate.

[0035] The epoxy resin having an epoxy equivalent of 800 to 10,000 g / eq is preferred in that it provides superior adhesion of the thermally conductive adhesive layer to the adherend. The lower limit of the epoxy equivalent is more preferably 1,000 g / eq, and even more preferably 1,500 g / eq. The upper limit of the epoxy equivalent is more preferably 5,000 g / eq, and even more preferably 3,000 g / eq. Furthermore, it is preferable to use an epoxy resin having an epoxy equivalent of 800 to 10,000 g / eq that is solid at room temperature. Being solid at room temperature means that the resin does not have fluidity in a solvent-free state at 25°C.

[0036] Commercially available epoxy resins that can be used as the epoxy resin having an epoxy equivalent of 800 to 10,000 g / eq include EPICLON 4050, 7050, HM-091, and HM-101 (trade names, manufactured by DIC Corporation), jER1003F, 1004, 1004AF, 1004FS, 1005F, 1006FS, 1007, 1007FS, 1009, 1009F, 1010, 1055, 1256, 4250, 4275, 4004P, 4005P, 4007P, and 4010P (trade names, manufactured by Mitsubishi Chemical Corporation), and the like.

[0037] When the thermosetting resin having a functional group reactive with an epoxy group is used in combination with an epoxy-based resin, the content of the epoxy-based resin is preferably 1 to 300 parts by mass, more preferably 3 to 100 parts by mass, and even more preferably 5 to 50 parts by mass, per 100 parts by mass of the thermosetting resin having a functional group reactive with an epoxy group. When the content is within the above range, the degree of crosslinking with the thermosetting resin having a functional group reactive with an epoxy group becomes more appropriate, resulting in better flexibility of the thermally conductive adhesive layer and better adhesion to the adherend. In particular, when the epoxy-based resin is used in an amount of 1 part by mass or more per 100 parts by mass of the thermosetting resin having a functional group reactive with an epoxy group, better heat resistance and adhesion to the adherend are achieved, and when the content is 300 parts by mass or less, better adhesion to metal materials is achieved.

[0038] The content of the binder component is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, relative to the total amount (100% by mass) of the thermally conductive adhesive layer. When the content is 5% by mass or more, the thermally conductive adhesive layer is less likely to become brittle, and the thermally conductive adhesive layer has excellent film-forming properties. The content is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. In particular, it is preferable that the content of the thermosetting resin (particularly the total of the epoxy resin and the thermosetting resin having a functional group reactive with an epoxy group) be within the above range.

[0039] The content of the thermosetting resin in the binder component is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on 100% by mass of the total amount of the binder component. In particular, it is preferable that the content of the thermosetting resin (particularly the total of the epoxy resin and the thermosetting resin having a functional group reactive with an epoxy group) be within the above range.

[0040] (Carbon Fiber) The carbon fiber is a fibrous carbon material, and fibrous graphite is preferred. Because the carbon fiber is fibrous, many of the carbon fibers tend to be oriented in the planar direction while overlapping in the thickness direction within the thermally conductive conductive adhesive layer. Therefore, the thermally conductive conductive adhesive layer containing the carbon fiber has excellent thermal conductivity in both the planar direction and the thickness direction. Furthermore, carbon fiber has a low specific gravity, allowing the thermally conductive conductive adhesive layer to be lightweight even when highly filled.

[0041] The carbon fiber has a metal carried on its surface. By using such carbon fiber, the thermally conductive adhesive layer has excellent thermal conductivity, electrical conductivity, and electromagnetic wave shielding performance.

[0042] The carbon fiber having a metal supported on its surface may be a commercially available product, or may be prepared by plating a carbon fiber having no metal supported thereon with a known or commonly used metal plating method.

[0043] As the metal, known or commonly used metals having electrical conductivity can be used, such as gold, silver, copper, nickel, zinc, indium, tin, lead, bismuth, and alloys containing two or more of these. Among these, silver is preferred from the viewpoint of superior electrical conductivity and electromagnetic wave shielding performance. Only one of the above metals may be used, or two or more may be used.

[0044] The amount of the metal supported on the carbon fiber is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, per 100 parts by mass of unsupported carbon fiber. A supported amount of 5 parts by mass or more provides excellent electrical conductivity and electromagnetic wave shielding performance. From the viewpoint of providing excellent adhesion to the adherend, the supported amount is preferably 35 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less.

[0045] The diameter (thickness) of the carbon fiber is preferably 5 to 30 μm, more preferably 10 to 25 μm. When the diameter is 5 μm or more, the thermal conductivity and electrical conductivity in the thickness direction are superior. When the diameter is 30 μm or less, the adhesion to the adherend is superior.

[0046] The major axis (length) of the carbon fiber is preferably 5 to 500 μm, more preferably 10 to 300 μm. When the major axis is 5 μm or more, the thermal conductivity and electrical conductivity in the planar direction are superior. When the major axis is 500 μm or less, the dispersibility of the carbon fiber in the binder component is superior.

[0047] The aspect ratio [diameter / major axis] of the carbon fiber is preferably 0.03 to 1, more preferably 0.035 to 1. When the aspect ratio is within the above range, electrical conductivity and electromagnetic wave shielding performance are improved. In this specification, the diameter, major axis, and aspect ratio of the carbon fiber refer to the values ​​in the compressed state when the carbon fiber is compressed in the thermally conductive adhesive layer. Carbon fibers satisfying the above diameter and / or aspect ratio may be carbon fibers whose diameter and / or aspect ratio fall within the above ranges, or carbon fibers compressed so that the diameter and / or aspect ratio fall within the above ranges by compressing the thermally conductive adhesive layer containing the carbon fiber.

[0048] The carbon fiber content (total content of carbon fiber and supported metal) is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 55% by mass or more, relative to 100% by mass of the total amount of the thermally conductive adhesive layer. When the content is 40% by mass or more, the electrical conductivity and electromagnetic wave shielding performance are improved. The content is preferably 70% by mass or less, more preferably 65% ​​by mass or less. When the content is 70% by mass or less, the thermally conductive adhesive layer is less likely to become brittle, and the thermally conductive adhesive layer has excellent film-forming properties.

[0049] The carbon fiber content (total content of carbon fiber and supported metal) is preferably 70 mass% or more, more preferably 80 mass% or more, even more preferably 90 mass% or more, and particularly preferably 93 mass% or more, relative to 100 mass% of the total amount of filler contained in the thermally conductive adhesive layer.

[0050] (Conductive Particles) As described above, the thermally conductive adhesive layer may contain conductive particles other than the carbon fiber. When the conductive particles are contained, the thermally conductive adhesive layer has better thermal conductivity, electrical conductivity, and electromagnetic wave shielding performance. In addition, the carbon fiber is more easily dispersed in the binder component.

[0051] The median diameter of the conductive particles is preferably smaller than the diameter of the carbon fiber, more preferably 1 to 30 μm, even more preferably 2 to 20 μm, and particularly preferably 4 to 15 μm. When the median diameter is 1 μm or more, the thermal conductivity, electrical conductivity, and electromagnetic wave shielding effect are improved. When the median diameter is 30 μm or less, the adhesion to the adherend is improved. In this specification, the median diameter (D50) of the conductive particles is the number-based average primary particle diameter measured by a laser diffraction / scattering method. In this specification, the median diameter of the conductive particles refers to the median diameter in the compressed state when the conductive particles are compressed in the thermally conductive adhesive layer.

[0052] Examples of the conductive particles include metal particles, metal-coated resin particles, and metal fibers.

[0053] Examples of the metal constituting the coating portion of the metal particles and the metal-coated resin particles include gold, silver, copper, nickel, zinc, indium, tin, lead, bismuth, and alloys containing two or more of these metals. Only one of the above metals may be used, or two or more of them may be used.

[0054] Specific examples of the metal particles include copper particles, silver particles, nickel particles, silver-coated copper particles, indium particles, tin particles, lead particles, gold-coated copper particles, silver-coated nickel particles, gold-coated nickel particles, indium-coated copper particles, tin-coated copper particles, lead-coated copper particles, bismuth-coated copper particles, indium-coated nickel particles, tin-coated nickel particles, bismuth-coated nickel particles, and silver-coated alloy particles. Examples of the silver-coated alloy particles include silver-coated copper alloy particles in which copper-containing alloy particles (e.g., copper alloy particles composed of an alloy of copper, nickel, and zinc) are coated with silver. The metal particles can be produced by electrolysis, atomization, reduction, or the like.

[0055] Among the conductive particles, metal particles are preferred, and silver particles, silver-coated copper particles, and silver-coated copper alloy particles are preferred. Silver-coated copper particles and silver-coated copper alloy particles are particularly preferred from the viewpoints of excellent thermal conductivity and electrical conductivity, suppressing oxidation and aggregation of the conductive particles, and reducing the cost of the conductive particles.

[0056] Examples of the shape of the conductive particles include spherical (e.g., spherical, elliptical), flake (e.g., scale-like, flat), dendritic, fibrous, amorphous (e.g., polyhedral), block, spike, etc. Among these, spherical shapes are preferred from the viewpoint of superior thermal conductivity and electrical conductivity.

[0057] The content of the conductive particles in the thermally conductive adhesive layer is preferably 1 to 15 mass %, more preferably 1.5 to 10 mass %, and even more preferably 2 to 8 mass %, relative to 100 mass % of the total amount of the thermally conductive adhesive layer. A content of 1 mass % or more improves the thermal conductivity and electrical conductivity in the thickness direction. A content of 15 mass % or less improves adhesion to the adherend. Furthermore, the content of the conductive particles is preferably 1 to 15 mass parts, more preferably 3 to 10 mass parts, relative to 100 mass parts of the total amount of the carbon fiber (the total amount of carbon fiber and supported metal).

[0058] The thermally conductive adhesive layer may contain urethane resin particles for the purpose of modifying the binder component, such as improving conductivity, electromagnetic wave shielding performance, and adhesion to the adherend. The average particle size of the urethane resin particles is preferably 4 to 13 μm, more preferably 5 to 7 μm. The average particle size indicates the median system (D50) and can be measured using a particle size distribution measuring device that applies the laser Doppler method. The urethane resin particles also preferably have a Type A durometer hardness of 55 to 90, as measured in accordance with JIS K6253. The urethane resin particles may be used alone or in combination of two or more types.

[0059] The thermally conductive adhesive layer may contain other components in addition to the above-mentioned components, as long as the intended effects of the present invention are not impaired. Examples of the other components include components contained in known or commonly used adhesives. Examples of the other components include curing accelerators, plasticizers, flame retardants, antifoaming agents, viscosity modifiers, antioxidants, diluents, anti-settling agents, fillers, colorants, leveling agents, coupling agents, UV absorbers, tackifying resins, and anti-blocking agents. One or more of the other components may be used.

[0060] (Thermal Conductive Adhesive Layer) The thickness of the thermally conductive adhesive layer is 25 to 100 μm, more preferably 30 to 80 μm, and even more preferably 35 to 60 μm. A thickness of 25 μm or more improves embedding in openings in printed wiring boards, facilitating contact with ground circuits and enabling better grounding. A thickness of 100 μm or less improves thermal conductivity in the thickness direction. Note that, when fillers protrude from the surface of the thermally conductive adhesive layer, the thickness of the thermally conductive adhesive layer refers to the thickness in the region where the fillers do not protrude (e.g., thickness T shown in FIG. 1 ). Furthermore, when the binder components (adhesive components) constituting the thermally conductive adhesive layer flow due to heating or the like and infiltrate openings formed in the adherend, the thickness of the thermally conductive adhesive layer refers to the thickness of the thermally conductive adhesive layer in the region that does not infiltrate the openings.

[0061] The ratio of the diameter of the carbon fiber to the thickness of the thermally conductive adhesive layer [diameter of carbon fiber / thickness of thermally conductive adhesive layer] is 0.2 to 0.5, preferably 0.25 to 0.47, and more preferably 0.3 to 0.45. By having this ratio within the above range, high thermal conductivity can be achieved.

[0062] The resistance value (initial resistance value) of the thermally conductive conductive adhesive layer determined by the conductivity test described below is not particularly limited, but is preferably less than 1.0Ω, more preferably 0.7Ω or less, and even more preferably 0.5Ω or less. When the initial resistance value is less than 1.0Ω, electrical conduction between adherends via the thermally conductive conductive adhesive layer is good. [Conductivity Test] The thermally conductive conductive adhesive layer is bonded to a SUS plate (thickness: 200 μm) by heating and pressing at a temperature of 120°C and a pressure of 0.5 MPa for 5 seconds, and the surface on the thermally conductive conductive adhesive layer side is bonded to a printed wiring board for evaluation. The board is then evacuated for 60 seconds using a press, and then heated and pressed for 30 minutes at a temperature of 170°C and a pressure of 3.0 MPa to prepare a substrate for evaluation. The printed wiring board used consisted of a base member made of a 12.5 μm thick polyimide film, on which two copper foil patterns (thickness: 18 μm, line width: 3 mm) simulating ground circuits were formed, and on top of that, a coverlay made of an insulating adhesive (thickness: 13 μm) and a 25 μm thick polyimide film was formed. A circular opening with a diameter of 1 mm was formed in the coverlay to simulate a ground connection. For the evaluation board, the electrical resistance between the copper foil patterns and the SUS plate was measured with an ohmmeter to obtain the resistance value.

[0063] The thermal conductivity of the thermally conductive adhesive layer in the planar direction is preferably 7 W / mK or more, more preferably 7.5 W / mK or more, and even more preferably 8 W / mK or more. When the thermal conductivity in the thickness direction is 7 W / mK or more, heat dissipation from the adherend via the thermally conductive adhesive layer is good.

[0064] The thermal conductivity of the thermally conductive adhesive layer in the thickness direction is preferably 5 W / mK or more, more preferably 5.5 W / mK or more, and even more preferably 6 W / mK or more. When the thermal conductivity in the thickness direction is 5 W / mK or more, heat dissipation from the adherend via the thermally conductive adhesive layer is good.

[0065] The adhesion strength (peel force) of the thermally conductive adhesive layer to the gold-plated surface of the gold-plated copper foil laminate film, as determined by a peel test at room temperature under conditions of a tensile speed of 50 mm / min and a peel angle of 90°, is not particularly limited, but is preferably 5.5 N / cm or more, more preferably 6 N / cm or more, and even more preferably 6.5 N / cm or more. An adhesion strength of 5.5 N / cm or more provides superior adhesion of the thermally conductive adhesive layer to the adherend. The gold-plated copper foil laminate film may be reinforced with a plastic film or the like to prevent tearing during the peel test. Specific methods for the peel test are described, for example, in the Examples below.

[0066] The adhesion strength (peel force) of the thermally conductive adhesive layer to a polyimide film, as determined by a peel test at room temperature under conditions of a tensile speed of 50 mm / min and a peel angle of 90°, is not particularly limited, but is preferably 5.5 N / cm or more, more preferably 6 N / cm or more, and even more preferably 6.5 N / cm or more. When the adhesion strength is 5.5 N / cm or more, the thermally conductive adhesive layer has better adhesion to the adherend. The polyimide film may be reinforced with a plastic film or the like to prevent tearing during the peel test. Specific methods for the peel test are described, for example, in the Examples below.

[0067] The thermally conductive adhesive layer preferably has an electric field shielding effect of 30 dB or more per 1 GHz, more preferably 40 dB or more, and even more preferably 50 dB or more. The electric field shielding effect can be measured by the KEC method. Specific methods are described, for example, in the Examples below.

[0068] The thermally conductive adhesive layer is preferably used for printed wiring boards, and particularly preferably for flexible printed wiring boards (FPCs). The thermally conductive adhesive layer is economical, yet provides excellent connection stability between conductive adherends, maintaining connection stability even when exposed to high temperatures. Therefore, the thermally conductive adhesive layer can be preferably used as an electromagnetic wave shielding film or conductive bonding film for printed wiring boards (particularly for FPCs). The conductive bonding film is intended to attach a conductive (metal) reinforcing plate to a printed wiring board, and can also be used as a ground connection lead-out film intended to release electromagnetic waves that have entered or are generated within the printed wiring board to the outside.

[0069] The thermally conductive adhesive layer may have a release sheet (separate film) laminated on at least one surface. That is, the thermally conductive adhesive layer may be provided as a laminate including a release sheet and the thermally conductive adhesive layer formed on the release surface of the release sheet. The release sheet is peeled off when the adhesive layer is used.

[0070] The thermally conductive adhesive layer can be produced by a known or commonly used production method, for example, by applying a composition for forming the thermally conductive adhesive layer onto a temporary substrate or substrate such as a release sheet, and then removing the solvent and / or partially curing the layer as necessary.

[0071] The composition may contain, for example, a solvent in addition to the above-mentioned components. Examples of the solvent include toluene, acetone, methyl ethyl ketone, methanol, ethanol, propanol, and dimethylformamide. The solid content of the composition may be appropriately determined depending on the thickness of the thermally conductive adhesive layer to be formed.

[0072] The composition may be applied using a known coating method, such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a lip coater, a dip roll coater, a bar coater, a knife coater, a spray coater, a comma coater, a direct coater, or a slot die coater.

[0073] [Printed wiring board with reinforcing member] An example in which the above-mentioned thermally conductive adhesive layer is applied to a printed wiring board with a reinforcing member is shown in Figure 2. As shown in Figure 2, a printed wiring board X with a reinforcing member, which is one embodiment of a printed wiring board with a reinforcing member, includes a printed wiring board 3, a thermally conductive adhesive layer 1' provided on the printed wiring board 3, and a conductive reinforcing member 2 provided on the thermally conductive adhesive layer 1'.

[0074] The printed wiring board 3 has a base member 31, a circuit pattern 32 partially provided on the surface of the base member 31, an insulating protective layer 33 that covers and insulates the circuit pattern 32, and an adhesive 34 that covers the circuit pattern 32 and bonds the circuit pattern 32 and the base member 31 to the insulating protective layer 33. The circuit pattern 32 includes a plurality of signal circuits 32a and ground circuits 32b. The adhesive 34 and the insulating protective layer 33 on the ground circuits 32b have openings (through holes) 3a that penetrate the adhesive 34 and the insulating protective layer 33 in the thickness direction.

[0075] The thermally conductive adhesive layer 1' is adhered to the surface of the insulating protective layer 33 of the printed wiring board 3 so as to cover and seal the opening 3a, and the binder component (adhesive component) 11' fills the opening 3a. The thermally conductive adhesive layer 1' is formed from carbon fibers 12a, conductive particles 12b, and the binder component (adhesive component) 11'. The thermally conductive adhesive layer 1' has a thick film portion where the resin layer is relatively thick and a thin film portion where the resin layer is relatively thin. The thick film portion coincides with the portion filling the opening 3a, and the thin film portion coincides with the portion located between the insulating protective layer 33 and the reinforcing member 2. The carbon filler 12a in the thick film portion is located between the reinforcing member 2 and the ground circuit 32b, preferably in contact with and electrically conductive between the reinforcing member 2 and the ground circuit 32b. The carbon filler 12a in the thin film portion is located between the reinforcing member 2 and the insulating protective layer 33, preferably in contact with the reinforcing member 2 and the insulating protective layer 33. With this structure, the ground member 32b and the reinforcing member 2 are electrically connected via the carbon filler 12a, the reinforcing member 2 functions as an external connection conductive layer, and the surface of the reinforcing member 2 is electrically connected to an external ground member.

[0076] The thermally conductive conductive adhesive layer 1' can be obtained, for example, by laminating the thermally conductive conductive adhesive layer 1 before it has flowed or hardened to form the thermally conductive conductive adhesive layer 1' to the surface of the reinforcing member 2 as needed, and then laminating it on the insulating protective layer 33 of the printed wiring board 3, and then heating it to flow or harden the binder component 11 and thermocompressing it, thereby adhering the binder component (adhesive component) 11 to the insulating protective layer 33, and flowing the binder component 11 so that the binder component 11, carbon filler 12a, and conductive particles 12b fill the openings 3a, and hardening the binder component 11 to form the binder component 11'.

[0077] An electronic component 4 is connected to a mounting portion provided on the surface of the printed wiring board 3 opposite the reinforcing member 2. The reinforcing member 2 is disposed opposite the mounting portion to which the electronic component 4 is connected. In this way, the reinforcing member 2 reinforces the mounting portion of the electronic component 4. The conductive reinforcing member 2 is electrically connected to the ground circuit 32b on the printed wiring board 3 via the thermally conductive adhesive layer 1'. As a result, the reinforcing member 2 is maintained at the same potential as the ground circuit 32b, thereby shielding the mounting portion of the electronic component 4 from external noise such as electromagnetic waves.

[0078] Below, one embodiment of the thermally conductive, electrically conductive adhesive layer of the present invention will be described in more detail based on examples, but the thermally conductive, electrically conductive adhesive layer of the present invention is not limited to only these examples.

[0079] Example 1 A binder component was prepared by mixing 92 parts by mass of a carboxyl-modified polyester resin (number average molecular weight: 15,000, Tg: 15°C) with 12 mg KOH / g oxidation and 8 parts by mass of a cresol novolac epoxy resin (epoxy equivalent: 220 g / eq, Tg: 90°C) (40% by mass). The graphite powder and silver-coated copper particles shown in Table 1 were then mixed with the binder component in the ratios shown in Table 1 to prepare a resin paste. The resin paste was then placed between the release-treated surfaces of two release sheets and laminated using a roll laminator to prepare a laminate of [release sheet / resin paste layer / release sheet]. The laminate was then heated at 170°C and pressed at a pressure of 3 MPa for 30 minutes to press the resin paste layer, producing the thermally conductive adhesive layer of Example 1 as a laminate of [release sheet / thermally conductive adhesive layer / release sheet].

[0080] Examples 2 to 5 The thermally conductive adhesive layers of each example were prepared in the same manner as in Example 1, except that the thicknesses of the thermally conductive adhesive layer before and after pressing were changed as shown in Table 1.

[0081] Comparative Example 1 A thermally conductive adhesive layer of Comparative Example 1 was prepared in the same manner as in Example 1, except that the graphite powder shown in Table 1 was used as the graphite powder and the filling amount was changed as shown in Table 1.

[0082] Comparative Examples 2 and 3 A thermally conductive adhesive layer of each example was prepared in the same manner as in Example 1, except that graphite powder was not used and the loading amount was changed as shown in Table 1.

[0083] Comparative Examples 4 to 6 The thermally conductive adhesive layers of each example were prepared in the same manner as in Example 1, except that the thicknesses of the thermally conductive adhesive layer before and after pressing were changed as shown in Table 1.

[0084] (Evaluation) The thermally conductive adhesive layers obtained in the examples and comparative examples were evaluated as follows. The evaluation results are shown in Table 1.

[0085] (1) Conductivity Test The thermally conductive adhesive layer was attached to a reinforcing member made of a SUS plate (thickness: 200 μm) by heating and pressing for 5 seconds at a temperature of 120 ° C. and a pressure of 0.5 MPa. The release sheet on the thermally conductive adhesive layer was peeled off, and the surface on the thermally conductive adhesive layer side was attached to a printed wiring board for evaluation. After vacuuming for 60 seconds using a press, the board was heated and pressed for 30 minutes at a temperature of 170 ° C. and a pressure of 3.0 MPa to prepare an evaluation board. The printed wiring board had two copper foil patterns (thickness: 18 μm, line width: 3 mm) extending parallel to each other at a distance on a base member made of a 12.5 μm thick polyimide film, and an insulating protective layer (thickness: 25 μm) made of an insulating adhesive (thickness: 13 μm) and polyimide covering the copper foil patterns. The insulating protective layer had cylindrical openings (diameter: 1 mm) exposing each copper foil pattern. When the thermally conductive adhesive layer and the printed wiring board were superimposed, the opening was completely covered with the thermally conductive adhesive layer. The electrical resistance between the copper foil pattern of the obtained evaluation board and the SUS plate was measured using a resistance meter, and this was taken as the resistance between the printed wiring board and the SUS plate.

[0086] (2) Adhesion Strength (PI) One release sheet was peeled from the thermally conductive conductive adhesive layer, and the exposed surface was placed on a metal reinforcing plate (thickness: 200 μm) made of SUS304H. The metal reinforcing plate was then heated and pressed using a press at a temperature of 120°C for 5 seconds at a pressure of 0.5 MPa to form a thermocompression bond. The other release sheet was then peeled off to form a metal reinforcing plate with a thermally conductive conductive adhesive layer. Next, a copper foil laminated film base substrate having a polyimide base substrate and copper foil formed on the surface of the base substrate was bonded to the metal reinforcing plate with the thermally conductive sheet under the same conditions as the thermocompression bonding described above. The polyimide film with a thermally conductive adhesive layer was then further bonded using a press at a temperature of 170°C for 30 minutes at a pressure of 3 MPa. Next, the polyimide film with the thermally conductive adhesive layer was fixed to a measurement table with a double-sided adhesive sheet, and the polyimide film was peeled from the thermally conductive sheet at room temperature using a tensile tester (product name "AGS-50NX", manufactured by Shimadzu Corporation) at a tensile speed of 50 mm / min and a peel angle of 90°, and the maximum peel strength at break was measured.

[0087] (3) Adhesion Strength (Au) One release sheet was peeled from the thermally conductive adhesive layer, and the exposed surface was placed on a metal reinforcing plate (thickness: 200 μm) made of SUS304H. The metal reinforcing plate was heated and pressed using a press at a temperature of 120°C for 5 seconds at a pressure of 0.5 MPa, and then the other release sheet was peeled off to produce a metal reinforcing plate with a thermally conductive adhesive layer. Next, a gold-plated layer of a copper foil laminate film having a polyimide base substrate, copper foil formed on the surface of the base substrate, and a gold-plated layer formed on the surface of the copper foil was bonded to the metal reinforcing plate with the thermally conductive adhesive layer under the same conditions as the thermocompression bonding described above, and then further bonded using a press at a temperature of 170°C for 30 minutes at a pressure of 3 MPa to produce a gold-plated laminate film with a thermally conductive adhesive layer. Next, the gold-plated laminate film with the thermally conductive sheet was fixed to a measurement table with a double-sided adhesive sheet, and the gold-plated laminate film was peeled from the thermally conductive adhesive layer at room temperature using a tensile tester (product name "AGS-50NX", manufactured by Shimadzu Corporation) at a tensile speed of 50 mm / min and a peel angle of 90°, and the maximum peel strength at break was measured.

[0088] (4) Thermal Conductivity The thermal diffusivity of the thermally conductive adhesive layer was measured by the laser flash method using a thermal property measuring device (product name "Thermowave Analyzer TA35", manufactured by Bethel Co., Ltd.). The specific heat of the thermally conductive adhesive layer was measured by the DSC method using a differential scanning calorimeter (product name "DSC8500", manufactured by Hitachi High-Tech Science Corporation) at 25°C. The specific gravity of the thermally conductive adhesive layer was measured by the underwater displacement method using an electronic hydrometer (product name "EW-300SG", manufactured by Alpha Mirage Co., Ltd.). The thermal conductivity in the planar direction and thickness direction was then calculated using the thermal diffusivity, specific heat, and specific gravity obtained above.

[0089] (5) Shielding performance One release sheet was peeled off from the thermally conductive adhesive layer, and both sides of the thermally conductive adhesive layer were sandwiched between release films, and the layer was heat-cured by applying heat and pressure using a press under conditions of a temperature of 170°C, a time of 30 minutes, and a pressure of 3 MPa. After removing the release film, the layer was cut into 15 cm squares to obtain a cured product of the thermally conductive adhesive layer. The electric field shielding effect per 1 GHz of the obtained cured product was measured using the KEC method.

[0090] (6) Thickness of Thermally Conductive Adhesive Layer The thickness of the thermally conductive adhesive layer obtained in the examples and comparative examples was measured using a Digimatic micrometer (trade name "PMU-150-50MX", manufactured by Mitutoyo Corporation).

[0091]

[0092] The thermally conductive adhesive layers of the Examples were evaluated in their cured state as having excellent thermal conductivity, electrical conductivity, adhesion to the adherend, and electromagnetic wave shielding performance. On the other hand, when flake-shaped graphite powder was used instead of fibrous graphite powder (Comparative Example 1), adhesion to the adherend was evaluated as poor. Furthermore, when no graphite powder was used and the amount of silver-coated copper particles was increased to the same loading amount as in Example 1 (Comparative Example 2), thermal conductivity was evaluated as poor. When the amount of silver-coated copper particles was further increased from that in Comparative Example 1 to increase the loading amount (Comparative Example 3), thermal conductivity improved, but the adhesion strength was 0 N / cm, meaning no adhesion to the copper foil laminate film, and adhesion to the adherend was evaluated as poor. Furthermore, when the [diameter of graphite powder / thickness of thermally conductive adhesive layer] ratio was less than 0.2 (Comparative Example 4), thermal conductivity in the thickness direction was evaluated as poor. When the ratio of [diameter of graphite powder / thickness of thermally conductive adhesive layer] exceeded 0.5 (Comparative Examples 5 and 6), the electrical conductivity, adhesion to the adherend, and electromagnetic wave shielding performance were evaluated as being poor.

[0093] X: Printed wiring board with reinforcing member 1, 1': Thermally conductive, electrically conductive adhesive layer 11, 11': Binder component (adhesive component) 12: Filler 12a: Carbon filler 12b: Conductive particles 13a, 13b: Release sheet 2: Reinforcing member 3: Printed wiring board 31: Base member 32: Circuit pattern 32a: Signal circuit 32b: Ground circuit 33: Insulating protective layer 34: Adhesive 4: Electronic component

Claims

1. A thermally conductive adhesive layer containing a binder component and carbon fiber, wherein the binder component includes a thermosetting resin, a metal is carried on the surface of the carbon fiber, the ratio of the diameter of the carbon fiber to the thickness of the thermally conductive adhesive layer is 0.2 to 0.5, and the thickness is 25 to 100 μm.

2. The thermally conductive adhesive layer according to claim 1, wherein the aspect ratio [diameter / major axis] of the carbon fiber is 0.03 to 1.

3. A thermally conductive, electrically conductive adhesive layer according to claim 1 or 2, wherein the carbon fiber content is 40 to 70 mass % relative to 100 mass % of the total amount of the thermally conductive, electrically conductive adhesive layer.

4. A thermally conductive adhesive layer according to claim 1 or 2, wherein the amount of the metal carried is 5 to 35 parts by mass per 100 parts by mass of the carbon fiber.

5. The thermally conductive adhesive layer according to claim 1 or 2, wherein the carbon fibers have a diameter of 5 to 30 μm.

6. The thermally conductive adhesive layer according to claim 1 or 2, further comprising conductive particles.

7. The thermally conductive adhesive layer according to claim 6, wherein the median diameter of the conductive particles is smaller than the diameter of the carbon fibers.

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