Conductive adhesive film, conductive adhesive film production method, connection structure, and connection structure production method

Abstract

The present invention provides a conductive adhesive film with which positional deviation hardly occurs during mounting under room temperature conditions.　A conductive adhesive film 1 contains conductive particles, a film-forming component, a liquid epoxy resin, and an epoxy resin curing catalyst. The viscosity of the liquid epoxy resin is 5,000 mPa∙s or less at 25°C. The conductive adhesive film 1 has an arithmetic average height Sa of 1.50 μm or less as measured in accordance with ISO 25178, and has a developed interfacial area ratio Sdr of 2.50% or less.

Description

Conductive adhesive film, method for producing conductive adhesive film, connection structure and method for producing connection structure

[0001] The present technology relates to, for example, a conductive adhesive film for mounting surface mount components, a method for producing the conductive adhesive film, a connection structure connected using the conductive adhesive film, and a method for producing the connection structure. This application claims priority based on Japanese Patent Application No. 2025-52448 filed in Japan on March 26, 2025 and Japanese Patent Application No. 2026-33107 filed in Japan on March 3, 2026, and these applications are incorporated into the present application by reference.

[0002] For example, mounting of surface mount devices (SMDs) on rigid substrates or flexible substrates is generally performed by printing or temporarily attaching solder paste or a film onto the substrate, mounting the surface mount device thereon, and performing mounting in a reflow process.

[0003] For connection materials that connect a substrate and a surface mount device, the tack property of the connection material is an important factor, for example, from the viewpoint of the adhesion of the connection material itself to the substrate before the reflow process and the adhesion to the mounted surface mount device.

[0004] Regarding conductive adhesives, Patent Document 1 describes that controlling the monomer content in an anisotropic conductive film can adjust the adhesiveness between glass and the anisotropic conductive film, thereby improving processability during temporary pressure bonding. Specifically, the anisotropic conductive film described in Patent Document 1 is composed of two layers: a conductive adhesive layer and an insulating adhesive layer. By making the content of reactive monomers in the conductive adhesive layer higher than the content of reactive monomers in the insulating adhesive layer, the adhesive force at the interface between glass and the conductive adhesive layer is increased, which facilitates removal of the release film after temporary pressure bonding of glass and the anisotropic conductive film.

[0005] Furthermore, regarding insulating adhesives, for example, those described in Patent Document 2 as insulating materials used to bond semiconductor chips and wafers can be cited. The insulating material described in Patent Document 2 is also described as being used as a two-layer film in combination with an anisotropic conductive film.

[0006] Japanese Patent Publication No. 2013-110110 Japanese Patent Publication No. 2013-140756

[0007] For example, if a conductive adhesive film containing solder particles is temporarily attached to a substrate and then misaligned, there is a risk that the terminals of the substrate will not be properly soldered together. Therefore, preventing such misalignment of the conductive adhesive film is extremely important. According to the inventors' research, a conductive adhesive film that is less prone to misalignment during assembly, such as pick-and-place, at room temperature is desirable. In particular, a single-layer conductive adhesive film that is less prone to misalignment during assembly at room temperature is considered desirable. However, Patent Documents 1 and 2 neither describe nor suggest this point, nor do they consider it.

[0008] This technology was proposed in light of the conventional situation described above, and provides a conductive adhesive film that is less prone to misalignment during mounting under room temperature conditions.

[0009] The conductive adhesive film according to this technology contains conductive particles, a film-forming component, a liquid epoxy resin, and an epoxy resin curing catalyst, wherein the viscosity of the liquid epoxy resin is 5,000 mPa·s or less at 25°C, the arithmetic mean height Sa measured according to ISO 25178 is 1.50 μm or less, and the interface development area ratio Sdr is 2.50% or less.

[0010] The method for manufacturing a conductive adhesive film according to this technology comprises a mixing step of mixing a resin composition containing conductive particles, a film-forming component, a liquid epoxy resin, and an epoxy resin curing catalyst; a coating step of applying the resin composition onto a release film; a drying step of drying the resin composition applied onto the release film; and a planarization step of obtaining a conductive adhesive film by applying linear pressure to the dried resin composition to flatten it. The viscosity of the liquid epoxy resin is 5,000 mPa·s or less at 25°C, and the conductive adhesive film has an arithmetic mean height Sa measured according to ISO 25178 of 1.50 μm or less, and an interface development area ratio Sdr of 2.50% or less.

[0011] The connection structure related to this technology involves bonding surface mount components to a wiring board or bonding wiring boards to each other via the conductive adhesive film described above.

[0012] The manufacturing method of the connection structure related to this technology involves joining surface mount components to a wiring board or joining wiring boards to each other via the conductive adhesive film described above.

[0013] This technology makes it possible to provide a conductive adhesive film that is less prone to misalignment during mounting under room temperature conditions.

[0014] Figure 1 illustrates an example of a method for measuring the gloss value using light rays incident from a position 60° from a virtual perpendicular to the surface of a conductive adhesive film. Figure 2 is a schematic cross-sectional view showing a conductive adhesive film placed on the terminal row of a wiring board. Figure 3 is a schematic cross-sectional view showing the terminal row of the wiring board and the terminal row of a surface mount component aligned. Figure 4 is a schematic cross-sectional view showing the wiring board and surface mount component heated in a reflow oven.

[0015] <Conductive Adhesive Film> The conductive adhesive film according to this embodiment contains conductive particles, a film-forming component, a liquid epoxy resin, and an epoxy resin curing catalyst, wherein the viscosity of the liquid epoxy resin is 5,000 mPa·s or less at 25°C, the arithmetic mean height Sa measured according to ISO 25178 is 1.50 μm or less, and the interface development area ratio Sdr is 2.50% or less.

[0016] According to the inventors' research, in order to further improve the workability of conductive adhesive films in mounting, it is considered important to improve the tack strength of the conductive adhesive film and to improve the smoothness of the surface of the conductive adhesive film. By improving the smoothness of the surface of the conductive adhesive film, the adhesion between the conductive adhesive film and the adherend is improved, and for example, air entrapment at the interface between the conductive adhesive film and the adherend can be prevented. The inventors' research found that the smoothness of the surface of the conductive adhesive film can be quantified by indicators (surface roughness parameters) such as the arithmetic mean height Sa and the interface development area ratio Sdr.

[0017] Therefore, the conductive adhesive film according to this embodiment has an arithmetic mean height Sa of 1.50 μm or less, measured according to ISO 25178, and an interface development area ratio Sdr of 2.50% or less, in other words, it has good surface smoothness. Furthermore, the conductive adhesive film according to this embodiment can have good tack strength by containing a liquid epoxy resin with a viscosity of 5,000 mPa·s or less at 25°C. Thus, because the conductive adhesive film according to this embodiment has good surface smoothness and good tack strength, even as a single layer, it can be made less prone to misalignment during mounting under room temperature conditions.

[0018] The conductive adhesive film has an arithmetic mean height Sa, measured according to ISO 25178 using, for example, a scanning white-light interference microscope with a 20x objective lens, that is less than or equal to a predetermined value. The arithmetic mean height Sa represents the average of the absolute differences in height between each point relative to the average plane of the surface. The conductive adhesive film has an arithmetic mean height Sa of 1.50 μm or less, preferably 1.40 μm or less, but may also be 1.30 μm or less, 1.20 μm or less, 1.10 μm or less, 1.00 μm or less, 0.90 μm or less, 0.80 μm or less, 0.70 μm or less, 0.60 μm or less, 0.50 μm or less, 0.40 μm or less, 0.30 μm or less, 0.21 μm or less, 0.20 μm or less, 0.17 μm or less, 0.14 μm or less, 0.10 μm or less, or 0.08 μm or less. The lower limit of the arithmetic mean height Sa of the conductive adhesive film is not particularly limited and may be, for example, 0 μm or more, 0.01 μm or more, or 0.02 μm or more. The conductive adhesive film may have an arithmetic mean height Sa of at least one surface that satisfies the above range, or the arithmetic mean height Sa of both surfaces may satisfy the above range. The arithmetic mean height Sa of the conductive adhesive film can be measured by the method described in the examples below.

[0019] It is preferable that the conductive adhesive film has an interface development area ratio Sdr of less than or equal to a predetermined value, which is measured according to ISO 25178 using, for example, a scanning white-light interference microscope with a 20x objective lens. The interface development area ratio Sdr of a conductive adhesive film represents how much the development area (surface area) of the defined region of the conductive adhesive film increases relative to the area of ​​the defined region. For example, if the surface of the conductive adhesive film is perfectly flat, the interface development area ratio Sdr will be 0%.

[0020] The conductive adhesive film has an interface development area ratio Sdr of 2.50% or less, preferably 2.39% or less, but may also be 2.20% or less, 2.10% or less, 2.00% or less, 1.90% or less, 1.80% or less, 1.70% or less, 1.60% or less, 1.50% or less, 1.40% or less, 1.30% or less, 1.20% or less, 1.10% or less, and 1.00%. It may be less than or equal to 0.90%, less than or equal to 0.80%, less than or equal to 0.70%, less than or equal to 0.60%, less than or equal to 0.50%, less than or equal to 0.48%, less than or equal to 0.40%, less than or equal to 0.30%, less than or equal to 0.20%, less than or equal to 0.10%, less than or equal to 0.07%, less than or equal to 0.05%, less than or equal to 0.04%, less than or equal to 0.03%, or less than or equal to 0.02%. The lower limit of the developed area ratio Sdr of the interface of the conductive adhesive film is not particularly limited and may be, for example, 0% or more, or 0.01% or more. The developed area ratio Sdr of the interface of at least one surface of the conductive adhesive film satisfies the range described above, and the developed area ratio Sdr of the interfaces on both sides may satisfy the range described above. The developed area ratio Sdr of the interface of the conductive adhesive film can be measured by the method described in the examples described later.

[0021] Figure 1 illustrates an example of a method for measuring the gloss value of a conductive adhesive film using light rays incident from a position 60° from a virtual perpendicular to the surface of the conductive adhesive film. Preferably, the conductive adhesive film 1 has a gloss value of 30% or more, measured using light rays 3 incident from positions 20°, 60°, and 85°, respectively, from a virtual perpendicular 2 to the surface 1A. The gloss value of the conductive adhesive film 1 can be measured by the method described in the examples below.

[0022] The inventors of this case have found that when the surface smoothness of the conductive adhesive film 1, which contains conductive particles (e.g., solder particles), a film-forming component, a liquid epoxy resin, and an epoxy resin curing catalyst, is good, the conductive adhesive film 1 tends to exhibit more gloss. Furthermore, when the gloss value of the conductive adhesive film 1 measured with light rays 3 incident from positions of 20°, 60°, and 85°, respectively, from a virtual perpendicular 2 to the surface 1A, is 30% or more, the arithmetic mean height Sa measured according to ISO 25178 tends to be 1.50 μm or less, and the interface development area ratio Sdr tends to be 2.50% or less.

[0023] Therefore, when the conductive adhesive film satisfies the above-mentioned range of gloss values, it becomes easy to perform a simple determination of the quality of the manufactured conductive adhesive film, for example, whether the surface smoothness of the manufactured conductive adhesive film is good. In other words, instead of measuring the arithmetic mean height Sa of the conductive adhesive film and the interface area ratio Sdr, the surface smoothness of the conductive adhesive film can also be determined by measuring the gloss value of the conductive adhesive film. Note that the gloss value of conductive adhesive film 1 tends to vary depending on the type of conductive particles.

[0024] The conductive adhesive film 1 may have a gloss value of 30% or more, 31% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 85% or more, 90% or more, 94% or more, or 100% or more, measured with a light ray 3 incident from a position 20° from a virtual perpendicular 2 to the surface 1A. The conductive adhesive film 1 may have a gloss value of 110% or less, 109% or less, 98% or less, 97% or less, 96% or less, 95% or less, 94% or less, 90% or less, or 88% or less, measured with a light ray 3 incident from a position 20° from a virtual perpendicular 2 to the surface 1A.

[0025] The conductive adhesive film 1 may have a gloss value of 46% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, or 100% or more, measured with a light ray 3 incident from a position 60° from a virtual perpendicular 2 to the surface 1A. The conductive adhesive film 1 may have a gloss value of 110% or less, 106% or less, 101% or less, 100% or less, 99% or less, 98% or less, or 90% or less.

[0026] The conductive adhesive film 1 may have a gloss value of 44% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, or 100% or more, measured with a light ray 3 incident from a position 85° from a virtual perpendicular 2 to the surface 1A. The conductive adhesive film 1 may have a gloss value of 100% or less, 99% or less, 98% or less, 97% or less, 94% or less, 92% or less, 90% or less, or 80% or less.

[0027] The conductive adhesive film 1 may be a single layer or may consist of two or more different layers laminated together. As described above, the conductive adhesive film 1 has good surface smoothness and good tack strength, so whether it is a single layer or consists of two or more different layers laminated together, it is possible to make it difficult for misalignment to occur during mounting under room temperature conditions.

[0028] The thickness of the conductive adhesive film 1 can be, for example, 1 to 100 μm, or 10 to 50 μm. The thickness of the conductive adhesive film 1 can be measured using a known micrometer or digital thickness gauge (for example, Mitutoyo MDE-25M, minimum display 0.0001 mm) that can measure 1 μm or less, preferably 0.1 μm or less. The thickness of the conductive adhesive film 1 can be determined by measuring at 10 or more locations and averaging the results. Note that if the thickness of the conductive adhesive film 1 is smaller than the particle diameter of the conductive particles, a contact-type thickness gauge is not suitable, and it is preferable to use a laser displacement meter (for example, Keyence SI-T series spectral interference displacement type).

[0029] Next, an example of the composition of the conductive adhesive film 1 will be described. In the following, as an example, the conductive adhesive film 1 will be described, which consists of an anionic polymerization type resin composition containing a film-forming component, a liquid epoxy resin, an epoxy resin curing catalyst, solder particles as conductive particles, and a flux component.

[0030] [Film-forming component] The film-forming component is, for example, a resin having a weight-average molecular weight (Mw) of 6,000 or more. From the viewpoint of film-forming properties and solder particle fluidity, it is preferable to use a mixture of two or more oligomers and / or polymers with different weight-average molecular weights as the film-forming component. For example, polymers and oligomers with different weight-average molecular weights can be used in combination. When two or more polymers and / or oligomers are used as the film-forming component, the arithmetic mean of the weight-average molecular weights of the film-forming component can be, for example, 10,000 or more and 20,000 or less. By having an arithmetic mean of the weight-average molecular weights of the film-forming component of 10,000 or more, for example, the handling properties of the conductive adhesive film 1 can be improved. Furthermore, by having an arithmetic mean of the weight-average molecular weights of the film-forming component of 20,000 or less, for example, the handling properties of the conductive adhesive film 1 and solder fluidity can be improved, and solder scattering can be suppressed more effectively.

[0031] Here, the arithmetic mean of the weight-average molecular weight of the film-forming components refers to the value expressed in the following formula 1, for example, when the film-forming components consist of two resin components (for example, a first film-forming component and a second film-forming component).

[0032] Equation 1: ((Mw1 × X1) / (X1 + X2)) + ((Mw2 × X2) / (X1 + X2)) (In Equation 1, Mw1 is the weight-average molecular weight of the first film-forming component, Mw2 is the weight-average molecular weight of the second film-forming component, X1 is the amount of the first film-forming component blended, and X2 is the amount of the second film-forming component blended.)

[0033] Examples of film-forming components include phenoxy resin, epoxy resin oligomer, polyester resin, polyurethane resin, polyester urethane resin, acrylic resin, polyimide resin, and butyral resin. The film-forming component may be used alone or in combination of two or more types. From the viewpoint of film formation state and connection reliability, it is preferable to use phenoxy resin (polymer) and epoxy resin oligomer. For example, a phenoxy resin having a fluorene skeleton and a biphenyl skeleton can be used in combination with an epoxy resin oligomer having a bisphenol A skeleton, a hydrogenated bisphenol A skeleton, and a fluorene skeleton.

[0034] The upper limit of the weight-average molecular weight of the phenoxy resin can be, for example, 100,000 or less, 60,000 or less, or 50,000 or less. The lower limit of the weight-average molecular weight of the phenoxy resin can be, for example, 10,000 or more, 25,000 or more, or 35,000 or more.

[0035] The upper limit of the weight-average molecular weight of the epoxy resin oligomer can be, for example, 20,000 or less, 14,000 or less, or 8,000 or less. The lower limit of the weight-average molecular weight of the epoxy resin oligomer can be, for example, 2,000 or more, 5,000 or more, or 6,000 or more.

[0036] The content of the film-forming component is not particularly limited, but for example, it can be 40% to 60% by mass relative to the total resin content, 40% to 55% by mass, or 41% to 48% by mass. In this specification, "total resin content" refers to the total mass of the film-forming component, liquid epoxy resin, flux component, and epoxy resin curing catalyst. The film-forming component may be used alone or in combination of two or more types. When two or more film-forming components are used in combination, it is preferable that the total amount of the film-forming components satisfies the above range.

[0037] [Liquid epoxy resin] The liquid epoxy resin is not particularly limited as long as it is liquid at room temperature and has a viscosity of 5,000 mPa·s or less at 25°C (hereinafter also referred to as "specific liquid epoxy resin"). Monofunctional epoxy resins may be used, difunctional epoxy resins may be used, polyfunctional epoxy resins may be used, monofunctional epoxy resins and difunctional epoxy resins may be used in combination, monofunctional epoxy resins and polyfunctional epoxy resins may be used in combination, or di-monofunctional epoxy resins and polyfunctional epoxy resins may be used in combination.

[0038] The viscosity of a particular liquid epoxy resin may be 4,500 mPa·s or less, 4,000 mPa·s or less, 3,500 mPa·s or less, 3,000 mPa·s or less, 2,500 mPa·s or less, 2,000 mPa·s or less, 1,500 mPa·s or less, 1,000 mPa·s or less, 500 mPa·s or less, 300 mPa·s or less, 250 mPa·s or less, 200 mPa·s or less, 100 mPa·s or less, or 50 mPa·s or less at 25°C. Furthermore, the viscosity of a particular liquid epoxy resin may be, for example, 5 mPa·s or more at 25°C, 10 mPa·s or more, or 17 mPa·s or more. The viscosity of a specific liquid epoxy resin can be measured by the method described in the examples below.

[0039] The epoxy equivalent of a particular liquid epoxy resin can be, for example, 400 g / eq or less, 350 g / eq or less, 300 g / eq or less, 250 g / eq or less, 240 g / eq or less, 210 g / eq or less, 185 g / eq or less, 175 g / eq or less, 170 g / eq or less, or 150 g / eq or less. In addition, the epoxy equivalent of a particular liquid epoxy resin can be, for example, 50 g / eq or more, 75 g / eq or more, 85 g / eq or more, 95 g / eq or more, 105 g / eq or more, or 117 g / eq or more.

[0040] [Monofunctional Epoxy Resins] Monofunctional epoxy resins are not particularly limited as long as they are liquid at room temperature and are monofunctional epoxy resins. Room temperature refers to the range of 15 to 25°C as defined in JIS K 0050:2019 (General Rules for Chemical Analysis Methods). Examples of monofunctional epoxy resins include p-tert-butylphenylglycidyl ether, 2-phenylphenol glycidyl ether, 2-ethylhexylglycidyl ether, phenyl glycidyl ether, ethylene oxide-modified phenyl glycidyl ether, glycidyl ether of long-chain alcohols, glycidyl ether of ethylene oxide-modified long-chain alcohols, N-glycidylphthalimide, and epoxy acrylates having a bisphenol A skeleton. Specific examples of monofunctional epoxy resins include the trade names "Denacol EX-146" and "Denacol EX-142-IM" manufactured by Nagase ChemteX Corporation. Monofunctional epoxy resins may be used individually or in combination of two or more types.

[0041] [Bifunctional Liquid Epoxy Resin] A bifunctional liquid epoxy resin is not particularly limited as long as it is liquid at room temperature and is bifunctional. Examples of bifunctional liquid epoxy resins include bisphenol F type epoxy resin, hydrogenated bisphenol A type epoxy resin, dicyclopentadiene dimethanol type epoxy resin, resorcinol diglycidyl ether, etc. Specific examples of bifunctional liquid epoxy resins include the trade names "YL983U" and "YX8000" from Mitsubishi Chemical Corporation, "Adeka Resin EP4088" from Adeka Corporation, and "Denacol EX-201" from Nagase ChemteX Corporation. A bifunctional epoxy resin may be used alone or in combination of two or more types.

[0042] [Polyfunctional Liquid Epoxy Resin] A polyfunctional liquid epoxy resin is not particularly limited as long as it is a polyfunctional epoxy resin that is liquid at room temperature. Examples of polyfunctional liquid epoxy resins that can be used include trimethylolpropane polyglycidyl ether and N'-tetraglycidyl-m-xylenediamine. Specific examples of polyfunctional liquid epoxy resins include "Denacol EX-321L" manufactured by Nagase ChemteX Corporation and "TETRAD-X" manufactured by Mitsubishi Gas Chemical Company. A single polyfunctional epoxy resin may be used, or two or more may be used in combination.

[0043] The content of the specific liquid epoxy resin may be, for example, 3% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, 32% by mass or more, 34% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, or 50% by mass or more based on the total resin content. Further, the content of the specific liquid epoxy resin may be, for example, 55% by mass or less, 54% by mass or less, 53% by mass or less, 52% by mass or less, 51% by mass or less, 50% by mass or less, 49% by mass or less, 48% by mass or less, 45% by mass or less, or 40% by mass or less based on the total resin content. When two or more specific liquid epoxy resins are used in combination, the total amount of the specific liquid epoxy resins preferably satisfies the above range.

[0044] [Epoxy resin curing catalyst] For the epoxy resin curing catalyst, for example, a thermosetting agent (epoxy resin curing agent) that initiates curing by heat can be used. From the viewpoint of long-term stability of molecular structure and control of reactivity, the epoxy resin curing catalyst is preferably in powder form at ordinary temperature. Examples of the epoxy resin curing catalyst include anionic curing agents such as amines and imidazoles, and cationic curing agents such as sulfonium salts. Further, the epoxy resin curing catalyst may be microencapsulated, for example, so that resistance to the solvent used when forming a film can be obtained. Examples of the anionic curing agent include imidazole-based epoxy resin curing agents such as "2P4MHZ-PW" (2-phenyl-4-methyl-5-hydroxymethylimidazole) manufactured by Shikoku Kasei Co., Ltd. The epoxy resin curing catalyst may be used alone, or two or more thereof may be used in combination.

[0045] The content of the epoxy resin curing catalyst can be, for example, 0.1 to 20 parts by mass, 1 to 20 parts by mass, or 7 to 16 parts by mass, when the total resin content is 100 parts by mass. When two or more epoxy resin curing catalysts are used in combination, it is preferable that the total amount of epoxy resin curing catalysts satisfies the above range.

[0046] [Conductive Particles] Conductive particles are not particularly limited, and for example, solder particles can be used. In the following description, solder particles will be described as an example of conductive particles. Solder particles can be appropriately selected from, for example, the Sn-Pb system, Pb-Sn-Sb system, Sn-Sb system, Sn-Pb-Bi system, Bi-Sn system, Sn-Cu system, Sn-Pb-Cu system, Sn-In system, Sn-Ag system, Sn-Pb-Ag system, Pb-Ag system, etc., as specified in JIS Z 3282-1999, depending on the electrode material and connection conditions. Among these, it is preferable that the solder particles be one or more selected from the group consisting of Sn-Bi-Cu alloy, Sn-Bi-Ag alloy, Sn-Bi alloy, Sn-Pb-Bi alloy, and Sn-In alloy. Specific examples of solder particles include Sn40Bi0.1Cu, Sn30Bi0.5Cu, Sn30Bi, Sn40Bi, Sn50Bi, Sn58Bi, Sn43Pb14Bi, and Sn20In. This allows for excellent connection reliability.

[0047] The lower limit of the melting point of the solder particles is, for example, preferably 110°C or higher, more preferably 120°C or higher, and even more preferably 130°C or higher. The upper limit of the melting point of the solder particles may be, for example, 250°C or lower, preferably 200°C or lower, more preferably 180°C or lower, and even more preferably 160°C or lower. Furthermore, the flux component may be directly bonded to the surface of the solder particles for the purpose of activating the surface. Activating the surface of the solder particles can promote metallic bonding with the electrode portion.

[0048] Preferably, the average particle diameter of the solder particles is, for example, 0.5 times or less of the minimum value of the inter-terminal distance (inter-space distance) in the terminal row of a surface-mounted component and the terminal row of a wiring board, more preferably 0.3 times or less, and still more preferably 0.2 times or less. With such a relationship between the inter-space distance and the average particle diameter of the solder particles, for example, the terminal row of a surface-mounted component and the terminal row of a wiring board can be bonded more reliably using a reflow furnace. If the average particle diameter of the solder particles is, for example, larger than 0.5 times the minimum value of the inter-terminal distance in the terminal row of a surface-mounted component and the terminal row of a wiring board, there is a risk that the possibility of short circuit occurrence will increase.

[0049] The lower limit of the average particle diameter of the solder particles is, for example, preferably 0.5 µm or more, more preferably 3 µm or more, and still more preferably 5 µm or more. Further, the upper limit of the average particle diameter of the solder particles may be, for example, 50 µm or less, or 30 µm or less, preferably 25 µm or less, and more preferably 20 µm or less. Thereby, a more favorable solder bonding state can be obtained, and high reliability can be achieved.

[0050] The average particle diameter refers to the average value of the major axis diameters of particles measured in observation images obtained using an optical microscope, a metal microscope, an electron microscope such as SEM (Scanning Electron Microscope), or the like, with, for example, N=20 or more, preferably N=50 or more, more preferably N=200 or more. When the particles are spherical, it is the average value of the diameters of the particles. The average particle diameter may also be a measured value calculated from an observation image using known image analysis software (e.g., "WinROOF" by Mitani Corporation, "Azo-kun (Registered Trademark)" by Asahi Kasei Engineering Corporation), or a measured value (N=1000 or more) measured using an image-type particle size distribution analyzer (for example, FPIA-3000 manufactured by Malvern Panalytical). The average particle diameter obtained from an observation image or an image-type particle size distribution analyzer can be the average value of the maximum lengths of the particles. When producing the conductive adhesive film 1, manufacturer values such as the particle diameter (D50) at which the cumulative frequency in the particle size distribution obtained by the laser diffraction / scattering method is 50%, or the arithmetic mean diameter (preferably on a volume basis) may be simply used.

[0051] The solder particles are preferably dispersed in the binder, and may be arranged randomly or according to a certain rule. Furthermore, the solder particles may be aggregates formed by the aggregation of multiple particles.

[0052] The solder particle content in the conductive adhesive film 1 can be appropriately determined based on the pitch of the terminal rows of the surface mount components and the wiring board. For example, it is preferable that the content be 10 to 60 volume percent for a pitch of 0.1 to 0.4 mm of the terminal rows of the surface mount components and the wiring board. For example, it is preferable that the content be 20 to 58 volume percent when the pitch is 0.4 mm, 20 to 58 volume percent when the pitch is 0.35 mm, 20 to 48 volume percent when the pitch is 0.2 mm, 15 to 48 volume percent when the pitch is 0.15 mm, and 10 to 38 volume percent when the pitch is 0.1 mm. If the solder particle content is too low, it may be difficult to obtain good conductivity, heat dissipation, and adhesion. If the solder particle content is too high, anisotropy may be easily impaired, and it may be difficult to obtain good conductivity reliability.

[0053] Conductive particles may be used individually or in combination of two or more types. When two or more types of conductive particles are used in combination, it is preferable that the total amount of conductive particles satisfies the above range.

[0054] [Flux Components] Flux components are compounds used, for example, to remove foreign matter or oxide films from the electrode surface, prevent oxidation of the electrode surface, or reduce the surface tension of molten solder. Examples of flux components include carboxylic acids such as levulinic acid, maleic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, and sebacic acid. Among these, glutaric acid is preferred from the viewpoint of being excellent at removing oxide films. Flux components may be used alone or in combination of two or more.

[0055] The flux component content can be, for example, 0.1 to 20 parts by mass, or 6 to 13 parts by mass, when the total resin content is 100 parts by mass. When two or more flux components are used in combination, it is preferable that the total amount of flux components satisfies the above range.

[0056] [Spacer particles] The conductive adhesive film 1 may further contain spacer particles. The spacer particles control the spacing between the electrodes of the surface-mount components to be connected and the electrodes of the wiring board during the manufacturing of the connection structure described later, thereby improving connection reliability. In particular, when a heating and pressing tool is used during the manufacturing of the connection structure described later, the spacing between electrodes can be kept more constant even when the pressure during pressing is high.

[0057] From the viewpoint of improving conductivity reliability, the particle diameter of the spacer particles is preferably, for example, 10 μm or more at the lower limit, more preferably 20 μm or more, and 100 μm or less at the upper limit, and more preferably 80 μm or less. The particle diameter of the spacer particles can be measured in the same way as the average particle diameter of the solder particles described above.

[0058] Examples of spacer particles include resin particles, inorganic particles, and organic-inorganic hybrid particles. Furthermore, spacer particles may be made of a single material or have a core-shell structure. From the viewpoint of ensuring greater uniformity of the inter-electrode distance, it is preferable that the spacer particles be inorganic particles that are not compressed by pressure.

[0059] The shape of the spacer particles is not particularly limited from the viewpoint of providing them with the function of a spacer, such as spherical, flake-shaped, or flaky, but a spherical shape is preferred.

[0060] The content of spacer particles in the conductive adhesive film 1 can be appropriately determined according to the distance between the terminals of the surface mount component and the wiring board, the particle size of the spacer particles, and the amount of solder particles blended. The lower limit of the spacer particle content in the conductive adhesive film 1 is preferably 1 part by mass or more, and more preferably 4 parts by mass or more, per 100 parts by mass of resin. The upper limit of the spacer particle content in the conductive adhesive film 1 is preferably 15 parts by mass or less, and more preferably 10 parts by mass or less, per 100 parts by mass of resin.

[0061] [Additives] In addition to the components described above, the conductive adhesive film 1 may contain various additives that are conventionally used as adhesives, to the extent that they do not impair the effects of this technology. The particle size of the additives is not particularly limited, for example, as long as it does not hinder inter-electrode bonding, but it is preferable that it is smaller than the average particle size of the solder particles.

[0062] Furthermore, the conductive adhesive film 1 may further contain a liquid epoxy resin other than the specified liquid epoxy resin, i.e., a liquid epoxy resin having a viscosity of more than 5,000 mPa·s at 25°C (hereinafter also referred to as "other liquid epoxy resin"), to the extent that it does not impair the effects of this technology. When the conductive adhesive film 1 further contains other liquid epoxy resin, the content of the other liquid epoxy resin is preferably 10% by mass or less, may be 8% by mass or less, may be 6% by mass or less, may be 4% by mass or less, may be 3% by mass or less, may be 2% by mass or less, may be 1% by mass or less, or may be 0% by mass, based on the total resin content.

[0063] <Method for Manufacturing Conductive Adhesive Film> Next, an example of a method for manufacturing the conductive adhesive film 1 will be described. The method for manufacturing the conductive adhesive film 1 includes, for example, a mixing step of mixing a resin composition containing conductive particles, a film-forming component, a specific liquid epoxy resin, and an epoxy resin curing catalyst; a coating step of applying the resin composition onto a release film; a drying step of drying the resin composition applied onto the release film; and a planarization step of applying linear pressure to the dried resin composition to flatten it and obtain the conductive adhesive film 1 described above.

[0064] In the mixing step, for example, conductive particles, a film-forming component, a liquid epoxy resin, an epoxy resin curing catalyst, and a flux component are mixed in a solvent to obtain a resin composition. In the mixing step, high shear may be applied while the solvent is still present in order to further improve the dispersibility of the conductive particles, and for example, a known batch-type planetary agitator can be used.

[0065] In the coating step, for example, the resin composition obtained in the mixing step is applied to a release film to a predetermined thickness. An example of a coating method is the use of a bar coater. In the coating step, the resin composition may be applied multiple times to achieve a predetermined thickness in the resin composition layer. Alternatively, after applying the resin composition to the release film, it may be applied to achieve the predetermined thickness by pressing.

[0066] In the drying process, the resin composition applied in the coating process is dried. The drying method is not particularly limited as long as it can volatilize the solvent in the resin composition; for example, a dryer such as an oven can be used. The amount of residual solvent in the resin composition layer after the drying process is preferably 2% or less, more preferably 1% or less.

[0067] In the planarization step, the resin composition (resin composition layer) obtained in the drying step is planarized by applying linear pressure. The planarization method is not particularly limited, as long as the arithmetic mean height Sa of the conductive adhesive film 1 obtained after the planarization step is 1.50 μm or less and the interface development area ratio Sdr is 2.50% or less. For example, a method can be used in which the surface of the resin composition is planarized by applying linear pressure to the resin composition obtained in the drying step using a laminator. If the linear pressure is too strong, it is undesirable from the viewpoint of controlling the film thickness, and if the linear pressure is too weak, it is undesirable from the viewpoint of controlling the surface state. As for the planarization conditions, for example, a roll laminator can be used, the temperature during pressurization can be 25°C to 80°C, the supply speed of the conductive adhesive film 1 to the laminator can be 0.5 to 5.0 m / min, and the linear pressure can be 0.1 to 1.0 MPa.

[0068] <Method for Manufacturing a Connecting Structure> The method for manufacturing a connecting structure according to this embodiment involves joining surface mount components to a wiring board or joining wiring boards to each other via a conductive adhesive film 1, for example, a conductive adhesive film 1 containing conductive particles, a film-forming component, a liquid epoxy resin, and an epoxy resin curing catalyst, wherein the viscosity of the liquid epoxy resin is 5,000 mPa·s or less at 25°C. Joining refers to connecting two materials or components.

[0069] Surface mount components are not particularly limited, and examples include those comprising a first and second set of terminals arranged in parallel, or a first and second set of terminals arranged in parallel, and a third and fourth set of terminals arranged parallel to and perpendicular to the first and second sets of terminals. A set of terminals refers to a set of terminals (electrodes) arranged in a predetermined direction at predetermined intervals (pitch). The predetermined direction in which the terminals are arranged is called the row direction of the terminal set, and the direction perpendicular to the row direction is called the width direction of the terminal set.

[0070] Specific examples of surface mount components are not limited to LGA type semiconductor chips, connectors, IC (Integrated Circuit) and LSI (Large Scale Integration) packages, LEDs (Light Emitting Diodes), and switches. For example, a connector can be an SMT (Surface Mount type) type, which has a first terminal row in which multiple pins (lead frames) extending outward on one of the short sides are arranged in the longitudinal direction, and a second terminal row in which multiple pins (lead frames) extending outward on the other of the short sides are arranged in the longitudinal direction. Also, for example, IC packages can be surface mount type leaded packages such as SOP (Small Outline Package) and SOJ (Small Outline J-leaded), which have terminal rows on two opposing sides of a rectangle, and QFP (Quad Flat Package) and QFN (Quad Flat No-leaded package), which have terminal rows on all four sides of a rectangle.

[0071] The wiring board is not particularly limited as long as it has wiring on it. For example, any board that can be broadly defined as a so-called printed wiring board (PWB) with electrodes on which surface-mount components can be mounted is acceptable, and it may be a rigid board or a flexible printed circuit board (FPC). Examples of substrates based on material type include glass substrates, ceramic substrates, and plastic substrates.

[0072] The upper limit of the pitch of the terminal rows of surface-mount components and wiring boards is preferably 2 mm or less, more preferably 1 mm or less, and even more preferably 0.5 mm or less, and the lower limit of the pitch of the terminal rows is preferably 0.06 mm or more, more preferably 0.08 mm or more, and even more preferably 0.1 mm or more.

[0073] The following describes the steps of the process: Step A, which involves placing a conductive adhesive film on the terminal rows of the wiring board; Step B, which involves fixing surface-mount components onto the conductive adhesive film; and Step C, which involves joining the terminal rows of the wiring board and the terminal rows of the surface-mount components using a reflow oven, with reference to Figures 2 to 4.

[0074] [Step A] Figure 2 is a schematic cross-sectional view showing a conductive adhesive film provided on the terminal row of a wiring board. As shown in Figure 2, in Step A, for example, a conductive adhesive film 21 containing solder particles 20 as conductive particles is provided on the terminal row 11 of the wiring board 10. The conductive adhesive film 21 is the same as the conductive adhesive film 1 described above, and its preferred range is also the same.

[0075] Step A may be a temporary bonding step in which the conductive adhesive film 21 is bonded to the terminal row 11 of the wiring board 10 at low temperature and low pressure, or it may be a lamination step in which the conductive adhesive film 21 is laminated to the terminal row 11 of the wiring board 10. In Step A, by using a conductive adhesive film 21 that has good surface smoothness and good tack strength, it is possible to reduce the occurrence of misalignment during mounting under room temperature conditions, for example, misalignment of the conductive adhesive film 21 bonded to the terminal row 11 of the wiring board 10.

[0076] [Step B] Figure 3 is a schematic cross-sectional view showing the state in which the terminal row of the wiring board and the terminal row of the surface mount component are aligned. As shown in Figure 3, in Step B, for example, the terminal row 11 of the wiring board 10 and the terminal row 31 of the surface mount component 30 are aligned, and the surface mount component 30 is fixed onto the conductive adhesive film 21.

[0077] In step B, for example, a tool is used to align the terminal row 11 with the terminal row 31 of the surface mount component 30. Preferably, the tool includes a suction mechanism for picking up the surface mount component. Alternatively, in step B, a preliminary crimping may be performed by pressing the surface mount component 30 from the side using the tool.

[0078] [Process C] Figure 4 is a schematic cross-sectional view showing the state in which the wiring board and surface mount components have been heated in a reflow oven. As shown in Figure 4, in process C, for example, a reflow oven set to a temperature above the melting point of the solder particles 20 is used to join the terminal row 11 of the wiring board 10 and the terminal row 31 of the surface mount component 30 with solder 41. This allows the solder particles 20 in the conductive adhesive film 21 to aggregate against the terminal row 11 of the wiring board 10 and the terminal row 31 of the surface mount component 30.

[0079] Examples of reflow ovens include atmospheric pressure reflow, vacuum reflow, atmospheric pressure oven, and autoclave (pressure oven). Among these, it is preferable to use a vacuum reflow oven or autoclave, which can eliminate air bubbles contained in the joint. Reflow ovens heat-bond components without mechanical pressure, meaning that surface-mount components 30 can be bonded to the wiring board 10 without any load, thus suppressing damage to the wiring board 10 and the surface-mount components 30. Here, "no load" refers to a state without mechanical pressure.

[0080] The lower limit of the peak temperature (maximum temperature achievable) in the reflow oven is above the temperature at which the solder particles 20 melt and above the temperature at which the conductive adhesive film 21 begins to harden. Preferably, it is 140°C or higher, but may also be 160°C or higher, 180°C or higher, or 200°C or higher. The upper limit of the peak temperature in the reflow oven is 300°C or lower, more preferably 290°C or lower, but may also be 280°C or lower, or 270°C or lower. This solders the terminal row 11 of the wiring board 10 and the terminal row 31 of the surface mount component 30 together. The areas other than the solder joints of the terminals are bonded by the hardened product 40 of the thermosetting binder. Here, soldering refers to connecting the terminals (electrodes) of opposing electronic components by melting solder.

[0081] According to the manufacturing method of the connecting structure of this embodiment, by using a conductive adhesive film 21 that has good surface smoothness and good tack strength, it is possible to reduce the occurrence of positional displacement during mounting under room temperature conditions.

[0082] In the above-described method for manufacturing the connection structure, step C involves joining the terminal row of the wiring board and the terminal row of the surface mount component using a reflow oven. However, the method is not limited to this, and for example, joining may be performed using a heating and pressing tool, provided that it does not hinder the aggregation of solder particles onto the terminals.

[0083] Alternatively, a conductive adhesive film 21 may be used to bond multiple terminal rows 11 of the wiring board 10 to multiple terminal rows 31 of the surface mount component 30. In the case of a wiring board 10 having multiple terminal rows 11, a conductive adhesive film 21 may be provided for each terminal row 11. This allows, for example, the movement of solder particles 20 between terminal rows 11 due to the self-alignment effect during heating to be restricted, and the solder particles 20 within a predetermined conductive adhesive film 21 to aggregate only in relation to a predetermined terminal row 11.

[0084] <Connection Structure> The connection structure according to this embodiment is obtained, for example, by the method for manufacturing the connection structure described above, and the surface mount component 30 is joined to the wiring board 10 via the conductive adhesive film 21 described above. A connection structure refers to a structure in which two materials or components are electrically connected.

[0085] The following describes some embodiments of this technology. However, this technology is not limited to these embodiments.

[0086] [Preparation of conductive adhesive film] The following materials were prepared.

[0087] <Film-forming components> Fluorene-type phenoxy resin (solid type), Mw: 44,000 Cyclic aliphatic solid epoxy resin oligomer, Mw: 6,500

[0088] <Liquid Epoxy Resins> YL983U (Mitsubishi Chemical Corporation): Bisphenol F type epoxy resin (liquid type), epoxy equivalent 170 g / eq, viscosity: 4,500 mPa·s (25℃) YL980 (Mitsubishi Chemical Corporation): Bisphenol A type epoxy resin, epoxy equivalent 185 g / eq, viscosity: 15,000 mPa·s (25℃) EXA-4850-150 (DIC Corporation): Liquid epoxy resin, epoxy equivalent 450 g / eq, viscosity: 15,000 mPa·s Denacol EX-201 (Nagase ChemteX Corporation): Resorcinol diglycidyl ether, epoxy equivalent 117 g / eq, viscosity: 250 mPa·s (25℃) Denacol EX-146P (manufactured by Nagase ChemteX): p-tert-butylphenylglycidyl ether, epoxy equivalent 210 g / eq, viscosity: 17 mPa·s (25°C) Denacol EX-142-IM (manufactured by Nagase ChemteX): 2-phenylphenol glycidyl ether, epoxy equivalent 240 g / eq, viscosity: 290 mPa·s (25°C) EA-1010LC (manufactured by Shin Nakamura Chemical Industry Co., Ltd.): Bisphenol A type monofunctional high molecular weight epoxy resin, epoxy equivalent 400 g / eq, viscosity: 10,000 mPa·s (25°C)

[0089] <Epoxy resin curing catalyst> 2P4MHZ-PW (manufactured by Shikoku Chemicals Co., Ltd.): 2-phenyl-4-methyl-5-hydroxymethylimidazole

[0090] <Flax component> Glutaric acid (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0091] <Conductive Particles> Solder particles with an average particle diameter of 20 μm (Sn40Bi0.1Cu)

[0092] <Spacer Particles> Spherical monodisperse silica particles (average particle diameter 20 μm) Spherical monodisperse silica particles (average particle diameter 30 μm)

[0093] <Examples 1-13, Comparative Examples 2-4> Each component except the solder particles was mixed in a planetary stirring device to obtain the composition (parts by mass) shown in Table 1. Solder particles were then added to this mixture and mixed again in the planetary stirring device to prepare a varnish. This varnish was applied to a base film (release film with a thickness of 50 μm) using a bar coater to obtain the film thickness (μm) shown in Table 1. It was dried at 50°C for 5 minutes and at 80°C for 5 minutes to obtain a film-like composition (conductive adhesive film: 360 mm long, 320 mm wide). This dried film-like composition was covered with a cover film (release film with a thickness of 25 μm), and the surface was smoothed by applying a linear pressure of 0.2 MPa, a supply rate of the film-like composition to the laminator of 1.0 m / min, and a temperature of 60°C during pressurization. The properties were then evaluated.

[0094] <Comparative Example 1> The characteristics of the film-like composition were evaluated in the same manner as in Examples 1 to 13 and Comparative Examples 2 to 4, except that the surface of the film-like composition after drying was not smoothed.

[0095] [Tack] Using a 5.1 mm diameter probe, a film-like composition was pressed with a load of 200 gf at 2 mm / second and peeled off at 10 mm / second. The tack force (gf) of the surface of the film-like composition was determined using a tackiness tester (Malcolm). The results are shown in Table 1.

[0096] [Surface Properties Parameters (Sa, Sdr)] The surface properties parameters (Sa, Sdr) of the film-like compositions were measured. Specifically, except for Comparative Example 1, the surface roughness Sa (μm) and the interface area ratio Sdr (%) were measured on the surface of the film-like composition that had undergone planarization treatment. In Comparative Example 1, the surface roughness Sa (μm) and the interface area ratio Sdr (%) were measured on one surface of the film-like composition. These surface properties parameters were measured using a nano 3D optical interferometry system (device name: VS-1800, manufactured by Hitachi High-Tech Corporation) in accordance with ISO 25178. The lens magnification was 20x, and the surface properties parameters were measured in a range of 50 μm in the height direction and 50 μm in the depth direction of the Z axis for an XY region of 562 μm × 562 μm. The results are shown in Table 1. A smaller value for surface roughness Sa indicates that the surface of the film-like composition is smoother. Furthermore, the interface development area ratio Sdr represents the extent to which the surface area has increased compared to a perfectly smooth surface; the closer the value is to 0, the flatter the interface of the film-like composition.

[0097] [Gloss Value] The gloss value of the surface of the film-like composition was measured using Microtrigloss (manufactured by BYK Instruments) in accordance with the ASTM D523 method. The results are shown in Table 1. The gloss value evaluates the gloss of the surface of the film-like composition. In Table 1, the results in the 20° column are the gloss values ​​measured with light rays incident from a position 20° from the imaginary perpendicular to the surface of the film-like composition, the results in the 60° column are the gloss values ​​measured with light rays incident from a position 60° from the imaginary perpendicular to the surface of the film-like composition, and the results in the 85° column are the gloss values ​​measured with light rays incident from a position 85° from the imaginary perpendicular to the surface of the film-like composition.

[0098] [Temporary Fixation to FR-4 Substrate] A film-like composition cut to a width of 2 mm and a length of 10 mm was placed on the gold-plated copper wiring of an FR-4 substrate with gold-plated copper wiring, and then pressed onto the sheet using a cotton swab on a 40°C hot plate. After cooling to room temperature (25°C), the edge of the sheet was grasped with tweezers and force was applied in the shear direction. When force was applied in the shear direction, if the entire sheet did not move on the substrate and no displacement occurred (OK), it was marked as "OK", and if displacement occurred (NG), it was marked as "NG". The results are shown in Table 1.

[0099]

[0100] The conductive adhesive films obtained in Examples 1 to 13 had an arithmetic mean height Sa of 1.50 μm or less, measured according to ISO 25178, and an interface development area ratio Sdr of 2.50% or less, indicating good surface smoothness. Furthermore, the conductive adhesive films obtained in Examples 1 to 13 were able to exhibit a tack force of 100 gf or more, indicating good surface tack strength. Thus, because the conductive adhesive films obtained in Examples 1 to 13 have good surface smoothness and good tack strength, no misalignment occurred when bonded to an FR-4 substrate under room temperature conditions, and they could be temporarily fixed to the FR-4 substrate. In other words, the conductive adhesive films obtained in Examples 1 to 13, even as single layers, were found to be less prone to misalignment during mounting under room temperature conditions.

[0101] It was found that the conductive adhesive films obtained in Comparative Examples 1 to 4 experienced misalignment when bonded to the FR-4 substrate under room temperature conditions, and therefore could not be temporarily fixed to the FR-4 substrate.

[0102] One possible reason for the results in Comparative Example 1 is that, in Comparative Example 1, the surface of the film-like composition was not smoothed, so the condition that the arithmetic mean height Sa measured according to ISO 25178 must be 1.50 μm or less was not met, the condition that the interface development area ratio Sdr must be 2.50% or less was not met, and the surface tack force was not good.

[0103] One possible reason for the results in Comparative Example 2 is that, in Comparative Example 2, a film-like composition that did not contain a liquid epoxy resin with a viscosity of 5,000 mPa·s or less at 25°C was used. As a result, the tack force was less likely to be generated due to the small number of epoxy functional groups present on the surface of the film-like composition.

[0104] One possible reason for the results in Comparative Example 3 is that, in Comparative Example 3, a film-like composition that did not contain a liquid epoxy resin with a viscosity of 5,000 mPa·s or less at 25°C was used. As a result, the condition that the interface development area ratio Sdr measured according to ISO 25178 be 2.50% or less was not met, and it is thought that the tack force was not easily generated due to the small number of epoxy functional groups present on the surface of the film-like composition.

[0105] One possible reason for the results in Comparative Example 4 is that, in Comparative Example 4, a film-like composition that did not contain a liquid epoxy resin with a viscosity of 5,000 mPa·s or less at 25°C was used. As a result, the tack force was less likely to be generated due to the small number of epoxy functional groups present on the surface of the film-like composition.

[0106] Furthermore, it was found that the conductive adhesive films obtained in Examples 1 to 13 and Comparative Examples 2 to 4 had a gloss value of 30% or more, measured with light rays incident from positions of 20°, 60°, and 85°, respectively, from a virtual perpendicular to the surface. On the other hand, it was found that the conductive adhesive film obtained in Comparative Example 1 did not meet the requirement of a gloss value of 30% or more, measured with light rays incident from positions of 20°, 60°, and 85°, respectively, from a virtual perpendicular to the surface. From these results, it is considered that when the surface smoothness of the conductive adhesive film is good, the conductive adhesive film tends to exhibit more gloss. It was also found that when the gloss value of the conductive adhesive film measured with light rays incident from positions of 20°, 60°, and 85°, respectively, from a virtual perpendicular to the surface, is 30% or more, it tends to satisfy the requirements of an arithmetic mean height Sa measured according to ISO 25178 being 1.50 μm or less and an interface development area ratio Sdr being 2.50% or less.

[0107] Furthermore, it was found that the surface condition of the conductive adhesive film differed significantly depending on whether or not the surface of the conductive adhesive film was smoothed. Specifically, it was found that when the surface was smoothed (Examples 1-13, Comparative Examples 2-4), Sa and Sdr tended to be smaller and the gloss value tended to be larger compared to when the surface was not smoothed (Comparative Examples).

[0108] 1 Conductive adhesive film, 1A Surface, 2 Imaginary perpendicular to the surface of the conductive adhesive film, 3 Light ray, 10 Wiring board, 11 Terminal row, 20 Solder particles, 21 Conductive adhesive film, 30 Surface mount component, 31 Terminal row, 40 Cured product of thermosetting binder, 41 Solder

Claims

1. A conductive adhesive film comprising conductive particles, a film-forming component, a liquid epoxy resin, and an epoxy resin curing catalyst, wherein the viscosity of the liquid epoxy resin is 5,000 mPa·s or less at 25°C, the arithmetic mean height Sa measured according to ISO 25178 is 1.50 μm or less, and the interface development area ratio Sdr is 2.50% or less.

2. The conductive adhesive film according to claim 1, wherein the conductive particles are solder particles.

3. The conductive adhesive film according to claim 1, wherein the epoxy resin curing catalyst is in powder form at room temperature.

4. The conductive adhesive film according to claim 1, further containing a flux component.

5. The conductive adhesive film according to claim 1, wherein the gloss value measured with light rays incident from positions of 20°, 60°, and 85°, respectively, from a virtual perpendicular to the film surface is 30% or more.

6. A method for manufacturing a connection structure, comprising joining a surface mount component to a wiring board or joining wiring boards to each other via a conductive adhesive film as described in claim 1.

7. A method for manufacturing a connection structure according to claim 6, comprising joining the surface mount components to the wiring board or joining wiring boards to each other using a reflow oven.

8. A connection structure comprising a surface mount component being joined to a wiring board or wiring boards being joined to each other via the conductive adhesive film described in claim 1.

9. A method for producing a conductive adhesive film, comprising: a mixing step of mixing a resin composition containing conductive particles, a film-forming component, a liquid epoxy resin, and an epoxy resin curing catalyst; a coating step of applying the resin composition onto a release film; a drying step of drying the resin composition applied onto the release film; and a planarization step of obtaining a conductive adhesive film by applying linear pressure to the dried resin composition to flatten it, wherein the viscosity of the liquid epoxy resin is 5,000 mPa·s or less at 25°C, and the conductive adhesive film has an arithmetic mean height Sa measured according to ISO 25178 of 1.50 μm or less, and an interface development area ratio Sdr of 2.50% or less.

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