Conductive paste and electronic component

Abstract

Provided is a conductive paste that makes it possible to suppress cracking at an external electrode even when a thermal fatigue–resistant solder is used.　A conductive paste according to the present invention includes (A) metal particles and (B) a thermosetting resin. When the surface of a cured product obtained by thermally curing the conductive paste for 30 minutes at 180°C is observed using a scanning electron microscope, the area percentage of metal as given by expression (1) is at least 50%. The flexural modulus of a cured product obtained by thermally curing the conductive paste for 30 minutes at 180°C is no more than 6.0 GPa. (1) Area percentage (%) of metal=(area occupied by metal÷measurement area)×100.

Description

Conductive paste and electronic components

[0001] The present invention relates to a conductive paste and an electronic component having an electrode formed using the conductive paste.

[0002] Various conductive pastes have been proposed for forming external electrodes in electronic components such as multilayer ceramic capacitors (MLCCs) and multilayer inductors. Conductive pastes for forming external electrodes are required to be safe and highly reliable, and also flexible enough to withstand bending of the substrate (Patent Document 1).

[0003] Furthermore, with the increasing use of electronics in automobiles, demand for in-vehicle laminated electronic components is also expanding. For example, when MLCCs are used as in-vehicle laminated electronic components, they must be more reliable than consumer devices, such as being resistant to thermal shock, in order to withstand use in harsh temperature environments.

[0004] In recent years, solders (thermal fatigue-resistant solders) that are superior in thermal fatigue resistance to ordinary solders have been studied (Patent Documents 2 and 3). Thermal fatigue-resistant solders suppress cracks caused by thermal fatigue that occur in conventional solders. Thermal fatigue-resistant solders are being studied particularly in product fields that require high reliability, such as automotive components.

[0005] JP 2011-233452 A International Publication No. 2017 / 018167 JP 2021-45792 A

[0006] When thermal fatigue-resistant solder is used, the improved thermal fatigue resistance of the solder results in stress being applied to the ceramic body and external electrodes.The inventors have discovered that when thermal fatigue-resistant solder is used, if a conventional conductive paste is used, cracks will occur in the external electrodes.

[0007] An object of the present invention is to provide a conductive paste that can suppress the occurrence of cracks in external electrodes even when thermal fatigue-resistant solder is used. More specifically, an object of the present invention is to provide a conductive paste that can suppress the occurrence of cracks in external electrodes even when thermal fatigue-resistant solder is used, by maintaining adhesion between the surface of the cured conductive paste and the plating layer and ensuring the flexibility of the cured conductive paste.

[0008] To achieve the above object, the conductive paste of the present disclosure includes (A) metal particles and (B) a thermosetting resin, and when the conductive paste is heat-cured under heating conditions at 180°C for 30 minutes and the surface of the cured product is observed using a scanning electron microscope, the area ratio of the metal represented by the following formula (1) is 50% or more, and when the conductive paste is heat-cured under heating conditions at 180°C for 30 minutes, the flexural modulus of the cured product is 6.0 GPa or less: Metal Area Ratio (%) = (Area Occupied by Metal ÷ Measured Area) × 100 (1)

[0009] The conductive paste of the present disclosure can suppress the occurrence of cracks in the external electrodes even when a thermal fatigue resistant solder is used.

[0010] The external electrodes are formed by curing a conductive paste, the conductive paste containing (A) metal particles and (B) a thermosetting resin, and when the conductive paste is heat-cured under heating conditions at 180°C for 30 minutes and the surface of the cured product is observed using a scanning electron microscope, the area ratio of the metal (A) represented by the following formula (1) is 50% or more, and the flexural modulus of the cured product when the conductive paste is heat-cured under heating conditions at 180°C for 30 minutes is 6.0 GPa or less: Metal Area Ratio (%) = (Area Occupied by Metal ÷ Measured Area) × 100 (1)

[0011] According to the present invention, it is possible to provide a conductive paste that can suppress the occurrence of cracks in external electrodes even when thermal fatigue resistant solder is used.

[0012] 1 is a schematic diagram showing the structure of a multilayer ceramic capacitor, and FIG. 2 is a scanning electron microscope image of the surface of a cured product obtained by thermally curing the conductive paste of Example 3.

[0013] An embodiment of the present invention (hereinafter referred to as the present embodiment) will be described below. The present embodiment relates to a conductive paste and an electronic component including an electrode formed using the conductive paste. Note that the present invention is not limited to the present embodiment. Also, the drawings are schematic, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings indicate the same components.

[0014] [Definitions] In this specification, ○ to △ (for example, ○ parts by mass to △ parts by mass) means ○ or more and △ or less (○ parts by mass or more and △ parts by mass or less). In addition, in this specification, the terms "comprise" or "comprises" mean that the specified component is included, but do not exclude the presence of other components.

[0015] [Conductive Paste] The conductive paste of this embodiment is a conductive paste containing (A) metal particles and (B) a thermosetting resin. When the conductive paste is heat-cured at 180°C for 30 minutes and the surface of the cured product is observed using a scanning electron microscope, the area ratio of the metal represented by the following formula (1) is 50% or more, and when the conductive paste is heat-cured at 180°C for 30 minutes, the flexural modulus of the cured product is 6.0 GPa or less. The values ​​of the metal area ratio and flexural modulus can be adjusted by appropriately selecting and using each component contained in the conductive paste, particularly the (A) metal particles and (B) thermosetting resin. Metal Area Ratio (%) = (Area Occupied by Metal ÷ Measured Area) × 100 (1)

[0016] [Area Ratio] When the surface of the conductive paste of this embodiment is thermally cured under heating conditions at 180°C for 30 minutes and the cured product is observed using a scanning electron microscope, the metal area ratio, expressed by the following formula (1), is 50% or more, preferably 55% or more, and more preferably 60% or more: Metal area ratio (%) = (area occupied by metal ÷ measured area) × 100 (1) A metal area ratio of 50% or more maintains adhesion between the surface of the cured conductive paste and the plating layer, and also ensures flexibility of the cured conductive paste.

[0017] The metal area ratio on the cured surface can be measured using the following method. Using a field emission scanning electron microscope (model "MERLIN" manufactured by Carl Zeiss Co., Ltd.), observation is performed perpendicular to the cured surface of the conductive paste under conditions of an acceleration voltage of 2.0 kV, an observation magnification of 1,000x, a probe current of 300 pA, and a working distance of 3.0 mm. An EsB (Energy Selective BSE: in-lens high-angle backscattered electron detector, grid voltage 500 V) image is acquired. By using the EsB detector, high-density metals appear bright (white) and low-density resins appear dark (black). The acquired image (JPEG format, 3,072 x 2,304 pixels) is loaded into image processing software (WinROOF2018 ver. 4.5.5 manufactured by Mitani Shoji Co., Ltd.). To remove noise, the software's median filter function (filter size 3 x 3) was used. Next, the automatic binarization function was used to determine a threshold using the Valley method, and the image was binarized into white (metal) and black (resin) areas. The bright areas of the binarized image were extracted to determine the area ratio of the white (metal) areas, which was used as the area ratio of metal on the surface of the cured conductive paste.

[0018] [Flexural Modulus] The conductive paste of this embodiment has a flexural modulus of 6.0 GPa or less, preferably 5.5 GPa or less, more preferably 5.0 GPa or less, and particularly preferably 4.8 GPa or less, when thermally cured under heating conditions at 180° C. for 30 minutes. By ensuring that the flexural modulus is within this range, stress applied to the ceramic body and the external electrodes can be alleviated, and the occurrence of cracks in the external electrodes can be suppressed.

[0019] The flexural modulus can be measured by the following method. The conductive paste was applied to a substrate such as a Teflon (registered trademark) plate, dried at 120°C for 60 minutes, and then cured in the atmosphere at 180°C for 30 minutes using a blower dryer. The paste was then peeled off from the substrate to prepare three test pieces measuring 40 x 10 x 0.1 mm. Using an autograph manufactured by Shimadzu Corporation, a two-point support, one-point load bending test was performed at a displacement rate of 1 mm / min, and the flexural modulus was calculated from the stress-strain curve. A flexural modulus of 6.0 GPa or less ensures flexibility of the cured conductive paste.

[0020] <(A) Metal Particles> The metal particles are a component for imparting conductivity to the conductive paste. One type of metal particle may be used, or two or more types may be used in combination.

[0021] Examples of metals constituting the metal particles include silver (Ag), copper (Cu), nickel (Ni), palladium (Pd), gold (Au), and platinum (Pt). Since excellent conductivity can be obtained relatively easily, metal particles containing silver are preferred, metal particles containing 90 parts by mass or more of silver are more preferred, and metal particles made of silver are particularly preferred. Note that metal particles made of silver mean that no metal other than silver is intentionally used as the metal particles, and do not exclude the inevitable inclusion of metals other than silver. Note that the metal constituting the metal particles may be an alloy of Ag, Cu, Ni, Pd, Au, and Pt. The metal particles may also be silver-coated metal particles. Silver-coated metal particles are metal particles in which the surface of metal particles other than silver is coated with silver.

[0022] The shape of the metal particles is not particularly limited and may be any shape, such as spherical, flake-like, scale-like, or needle-like. The average particle diameter of the metal particles is preferably 0.5 to 30 μm, as this ensures a good surface condition after printing or coating and can impart excellent conductivity to the formed electrode layer. When the metal particles are (A1) flaky metal particles, the average particle diameter is 0.5 to 30 μm, preferably 1 to 15 μm, more preferably 2 to 12 μm, and particularly preferably 2.5 to 10 μm. When the metal particles are (A2) spherical metal particles, the average particle diameter is 0.2 to 20 μm, preferably 0.5 to 15 μm, more preferably 1 to 12 μm, and particularly preferably 2 to 10 μm. Here, the "average particle diameter" of the metal particles refers to the volume-based median diameter (D50) obtained by a laser diffraction / scattering particle size distribution measurement method.

[0023] The BET specific surface area of ​​the metal particles is not particularly limited, but is preferably 0.1 m ２ / g to 3.0m ２ / g, preferably 0.1m ２ / g to 2.0m ２ / g is more preferable. If the BET specific surface area of ​​the metal particles is too large, the viscosity increases when the particles are made into a paste, and handling becomes difficult. If the BET value (specific surface area) of the metal particles is too small, the conductivity decreases. The BET specific surface area can be measured by the BET method.

[0024] The metal particles have a tap density of 2.0 g / cm ３ or more, preferably 3.0 g / cm ３ More preferably, 3.5 g / cm ３ The upper limit of the tap density of the metal particles is not particularly limited, but in the case of silver particles, it is 8 g / cm ３ Preferably 7 g / cm or less ３ or less, more preferably 6.5 g / cm ３The tap density can be measured as follows. A predetermined weight of metal particles is placed in a predetermined measuring cylinder, and the volume of the metal particles is measured after tapping a predetermined number of times with a tapping device, thereby determining the tap density. A 10 ml measuring cylinder can be used as the predetermined measuring cylinder. The predetermined weight of the metal particles can be 10 g. The tapping conditions can be a height of 20 mm, a tapping speed of 100 taps / minute, and 400 taps. For example, a KRS-406 manufactured by Kuramochi Scientific Instruments Manufacturing Co., Ltd. can be used as the tap density measuring device.

[0025] The (A) metal particles may include surface-treated metal particles. The inclusion of surface-treated metal particles can improve the dispersibility of the metal particles. The surface treatment of the metal particles can be carried out using a liquid fatty acid, a solid fatty acid, or an aliphatic amine. Examples of liquid fatty acids include saturated fatty acids such as butyric acid, valeric acid, caproic acid, heptanoic acid, caprylic acid, and pelargonic acid, and unsaturated fatty acids such as myristoleic acid, palmitoleic acid, ricinoleic acid, oleic acid, linoleic acid, and linolenic acid. These fatty acids may be used alone or in combination of two or more. Examples of solid fatty acids include saturated fatty acids having 10 or more carbon atoms such as capric acid, palmitic acid, and stearic acid, and unsaturated fatty acids such as crotonic acid and sorbic acid. Examples of the aliphatic amine include isobutylamine, octylamine, decylamine, dodecylamine, hexadecylamine, octadecylamine, oleylamine, 2-ethylhexyloxypropylamine, and 3-lauryloxypropylamine.

[0026] The content of metal particles in the conductive paste of this embodiment (when two or more types of metal particles are used, the total amount of these metal particles) is not particularly limited, but is preferably 70 parts by mass or more, more preferably 75 parts by mass or more, and particularly preferably 77 parts by mass or more, per 100 parts by mass of non-volatile components in the conductive paste. When the content of metal particles is within this range, adhesion between the surface of the cured product obtained from the conductive paste and the plating layer can be maintained, and flexibility of the cured product of the conductive paste can be ensured. The upper limit of the content of metal particles is also not particularly limited, but is preferably 97 parts by mass or less, more preferably 95 parts by mass or less, and even more preferably 90 parts by mass or less, per 100 parts by mass of non-volatile components in the conductive paste.

[0027] ((A1) Flake-shaped Metal Particles) From the viewpoint of increasing the area of ​​the metal particles present on the surface when the conductive paste of this embodiment is cured, it is preferable that the (A) metal particles include (A1) flaky metal particles. In this specification, the term "flaky" refers to particles having an aspect ratio (average particle diameter / average thickness), which is the ratio of the average particle diameter to the thickness, of 2 or more, and includes particles having shapes such as flakes, plates, and flats. The average thickness of the metal particles refers to a value measured by observation with a scanning electron microscope (SEM).

[0028] The use of flake metal particles is thought to facilitate leafing, a phenomenon in which flake metal particles appear on the surface of the cured conductive paste, and also improve adhesion between the nickel plating of the plating layer and the cured conductive paste. Leafing is the phenomenon in which flake metal particles in an organic vehicle appear on the surface of the cured conductive paste.

[0029] From the viewpoint of improving leafing properties, the aspect ratio of the flaky metal particles is preferably 5 or more, more preferably 10 or more, and even more preferably 20 or more. The upper limit of the aspect ratio of the flaky metal particles is not particularly limited, but is, for example, 1000 or less, preferably 500 or less, and more preferably 300 or less.

[0030] The flaky metal particles preferably contain silver, and are preferably flaky silver particles or flaky alloy particles containing silver. The flaky silver particles can be produced, for example, by pulverizing spherical or granular silver powder obtained by liquid-phase reduction or atomization using a ball mill, stamp mill, or the like, and then grinding and flattening the particles using mechanical stress. Alternatively, flaky silver particles can be produced directly by wet reduction. The metal particles are not limited to those prepared by methods known to those skilled in the art, and commercially available particles can also be used.

[0031] The (A) metal particles may be a combination of (A1) flaky metal particles and (A2) spherical metal particles. From the viewpoint of improving leafing properties, the content of (A1) flaky metal particles in the (A) metal particles is preferably greater than the content of (A2) spherical metal particles. When (A1) flaky metal particles and (A2) spherical metal particles are used in combination, the ratio of the two is, from the viewpoint of improving leafing properties, preferably 60 parts by mass or more, more preferably 75 parts by mass or more, and particularly preferably 90 parts by mass or more, per 100 parts by mass of the (A) metal particles.

[0032] <(B) Thermosetting Resin> The thermosetting resin functions as a binder in the conductive paste. One type of thermosetting resin may be used, or two or more types may be used in combination.

[0033] The thermosetting resin is not particularly limited, but examples thereof include amino resins such as urea resin, melamine resin, and guanamine resin; epoxy resins such as bisphenol A type epoxy resin, biphenyl type epoxy resin such as diglycidyl biphenyl, novolac type epoxy resin, tetrabromobisphenol A type epoxy resin, and tris(hydroxylphenyl)methane type epoxy resin; oxetane resin; phenolic resins such as resole type phenolic resin, alkyl resole type phenolic resin, novolac type phenolic resin, alkyl novolac type phenolic resin, and aralkyl novolac type phenolic resin; silicone-modified resins such as silicone epoxy and silicone polyester; bismaleimide and polyimide resins.

[0034] The content of the thermosetting resin in the conductive paste of this embodiment (when two or more thermosetting resins are used, the total amount of these thermosetting resins) is not particularly limited, but is preferably 3 mass% or more, more preferably 5 mass% or more, and particularly preferably 8 mass% or more, relative to 100 mass% of the metal particles, from the viewpoint of maintaining the metal area ratio and bending modulus within a predetermined range. When the content of the thermosetting resin is within this range, adhesion between the surface of the cured product obtained from the conductive paste and the plating layer can be maintained, and flexibility of the cured product of the conductive paste can be ensured. The upper limit of the content of the thermosetting resin is also not particularly limited, but is preferably 30 mass% or less, more preferably 25 mass% or less, relative to the total mass of the conductive paste, from the viewpoint of maintaining the metal area ratio and bending modulus within a predetermined range.

[0035] (B1) Epoxy Resin) The thermosetting resin (B) preferably contains an epoxy resin (B1). From the viewpoint of imparting flexibility to the conductive paste when cured, it is preferable to use an epoxy resin with a high epoxy equivalent, for example, an epoxy resin with an epoxy equivalent of 1000 g / eq or more, preferably 1200 g / eq or more, more preferably 1500 g / eq or more, and particularly preferably 2000 g / eq or more, as the epoxy resin (B1). In this specification, the term "epoxy equivalent" refers to the value obtained by dividing the molecular weight of the epoxy resin by the number of epoxy groups in the molecule. Using an epoxy resin with a high epoxy equivalent provides a more flexible skeleton than an epoxy resin with a low epoxy equivalent. This reduces stress applied to the ceramic body and external electrodes when thermal shock is applied, thereby making it possible to suppress the occurrence of cracks in the external electrodes. The upper limit of the epoxy equivalent is not particularly limited, but can be set to 5000 g / eq or less.

[0036] From the viewpoint of maintaining the flexural modulus within a predetermined range, the content of the (B1) epoxy resin is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and particularly preferably 5 parts by mass or more, per 100 parts by mass of the (A) metal particles. The upper limit of the content of the (B1) epoxy resin is not particularly limited, but from the viewpoint of maintaining the metal area ratio within a predetermined range, it is 30 parts by mass or less, 25 parts by mass or less, or 20 parts by mass or less, per 100 parts by mass of the (A) metal particles.

[0037] As the (B1) epoxy resin, two or more epoxy resins with different epoxy equivalents may be used in combination. By using multiple epoxy resins with different epoxy equivalents, when the conductive paste is cured, it is possible to adjust the flexibility of the cured product, mechanical properties such as adhesive strength, etc. For example, it is recommended to combine an epoxy resin with a low epoxy equivalent of 100 to 1000 g / eq with an epoxy resin with a high epoxy equivalent of 1000 g / eq or more, preferably 2000 g / eq or more.

[0038] From the viewpoint of improving flexibility and adhesive strength when the conductive paste is cured, the content of the epoxy resin having an epoxy equivalent of 1000 g / eq or more is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, and particularly preferably 40 parts by mass or more, relative to 100 parts by mass of the thermosetting resin (B). The upper limit is not particularly limited, but is, for example, 90 parts by mass or less.

[0039] As the (B) thermosetting resin, a (B2) phenolic resin can be used in combination with the (B1) epoxy resin. The (B2) phenolic resin is a general term for thermosetting resins that can be crosslinked into a network via the phenolic hydroxyl groups present in the compound, and includes prepolymer compounds prior to crosslinking. The (B2) phenolic resin is an epoxy resin curing agent that reacts with the epoxy groups of the epoxy resin and contributes to imparting wettability to the solder. Examples of the (B2) phenolic resin include phenol novolac resin and its alkylated or allylated products, cresol novolac resin, phenol aralkyl (including phenylene or biphenylene skeleton) resin, naphthol aralkyl resin, triphenolmethane resin, and dicyclopentadiene-type phenolic resin.

[0040] In the conductive paste of the present invention, when component (B) contains epoxy resin (B1), the curing mechanism of the epoxy resin may be a self-curing resin, or a curing agent or curing catalyst such as amines, imidazoles, acid anhydrides, or onium salts, or an amino resin or phenol resin may function as a curing agent for the epoxy resin.

[0041] <(C) Flexible Component> From the viewpoint of improving the properties of the conductive paste, it is preferable to use a (C) flexible component. The flexible component is a component that can improve workability, such as coatability, and impart flexibility to the conductive paste when cured. One type of flexible component may be used, or two or more types may be used in combination. Note that the (C) flexible component in the present invention is a component other than the (B) thermosetting resin that improves flexibility and paste coatability.

[0042] The flexible component is not particularly limited, but examples thereof include (C1) thermoplastic resin and (C2) rubber particles.

[0043] (C1) Thermoplastic Resin The thermoplastic resin is not particularly limited, but examples thereof include novolac type phenolic resin, phenoxy resin, butyral resin, cellulose resin, acrylic resin, methacrylic resin, polyester resin, polyurethane resin, polyamide resin, thermoplastic xylene resin, hydroxystyrene polymer, cellulose derivative, etc. One type of thermoplastic resin may be used, or two or more types may be used in combination.

[0044] The thermoplastic resin preferably contains a butyral resin. From the viewpoint of workability, if the proportion of (A) metal particles, particularly (A1) flaky metal particles, in the conductive paste is increased, the thixotropic index value (TI value) of the conductive paste increases, the dipping property deteriorates, and the coating shape deteriorates. By using a butyral resin, particularly in combination with (C2) rubber particles, the TI value of the conductive paste can be reduced, the sharpness during dipping can be suppressed, and the coating shape can be improved.

[0045] (C2) Rubber Particles: It is preferable that the conductive paste contains rubber particles in order to impart flexibility to the cured product when cured and to alleviate stress applied to the external electrodes. Examples of rubber particles include, but are not limited to, silicone rubber particles and fluororubber particles. One type of rubber particle may be used, or two or more types may be used in combination.

[0046] Examples of silicone rubber particles include particles formed by three-dimensionally crosslinking linear organopolysiloxanes and powdered silicone rubber particles. Furthermore, particles having a structure in which the surfaces of these particles are coated with silicone resin may also be used. Examples of commercially available silicone rubber particles include Trefil E-500, Trefil E-600, Trefil E-601, and Trefil E-850 (all manufactured by Dow Corning Toray Silicone Co., Ltd.), and KMP-600, KMP-601, KMP-602, KMP-605, and KMP-605M (all manufactured by Shin-Etsu Chemical Co., Ltd.).

[0047] Examples of fluororubber particles include particles of a binary copolymer of vinylidene fluoride and hexafluoropropylene, a binary copolymer of vinylidene fluoride and pentafluoropropylene, a binary copolymer of vinylidene fluoride and chlorotrifluoroethylene, a terpolymer of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene, a terpolymer of vinylidene fluoride, pentafluoropropylene, and tetrafluoroethylene, and a terpolymer of vinylidene fluoride, perfluoromethyl vinyl ether, and tetrafluoroethylene.

[0048] The rubber particles are preferably spherical in shape. The average particle size of the rubber particles is preferably 0.01 to 30 μm, more preferably 0.05 to 20 μm, or 0.5 to 10 μm, because a good flexural modulus can be obtained. In this specification, the average particle size of the rubber particles is a value determined by image analysis after observation with a scanning electron microscope (SEM).

[0049] From the viewpoint of workability such as coatability and flexibility when cured, the content of the (C) flexible component is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and particularly preferably 5 parts by mass or more, relative to 100 parts by mass of the (A) metal particles. The upper limit of the content of the (C) flexible component is not particularly limited, but is preferably 20 parts by mass or less, 15 parts by mass or less, or 12 parts by mass or less, relative to 100 parts by mass of the (A) metal particles.

[0050] When a butyral resin is used, the content is 0.05 to 5 parts by mass, preferably 0.2 to 2 parts by mass, more preferably 0.3 to 3 parts by mass, and particularly preferably 0.5 to 1.5 parts by mass, per 100 parts by mass of the (A) metal particles. When (C2) rubber particles are used, the content is 2 to 15 parts by mass, preferably 3 to 13 parts by mass, more preferably 4 to 12 parts by mass, and particularly preferably 5 to 10 parts by mass, per 100 parts by mass of the (A) metal particles, because the rubber component is exposed on the surface of the cured product and the metal area ratio on the surface of the cured product is reduced.

[0051] <Other Components> The conductive paste of this embodiment may contain a curing accelerator, a coupling agent, an antifoaming agent, and a solvent in addition to the components (A) to (C).

[0052] (Curing Accelerator) The curing accelerator has the property of accelerating the curing of the thermosetting resin (B). The curing accelerator is not particularly limited, and examples thereof include imidazole compounds such as 2-methylimidazole, 2-ethyl-4-methylimidazole (2E4MZ), 2-phenyl-4-methylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole (2P4MHZ-PW), 2-phenyl-4,5-dihydroxymethylimidazole (2PHZ-PW), 2-phenylimidazole, and 1-benzyl-2-methylimidazole.

[0053] (Coupling Agent) A coupling agent is blended to enhance the heat resistance and adhesive strength of the conductive paste. The coupling agent is not particularly limited, but examples include various silane coupling agents such as epoxy-based, amino-based, vinyl-based, methacrylic-based, acrylic-based, and mercapto-based silane coupling agents. Among these, epoxy-based silane coupling agents having an epoxy group and methacrylic-based silane coupling agents having a methacryl group are preferred. Examples of silane coupling agents include 3-glycidoxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and 3-methacryloxypropyltrimethoxysilane.

[0054] (Antifoaming agent) The antifoaming agent is not particularly limited, but examples thereof include acrylic, silicone, and fluorosilicone antifoaming agents. The antifoaming agent is added to prevent the generation of bubbles in the conductive paste. The antifoaming agent is not particularly limited, but examples thereof include acrylic, silicone, and fluorosilicone antifoaming agents.

[0055] (Solvent) The viscosity of the conductive paste of this embodiment can be adjusted by blending a solvent. Examples of the solvent include, but are not limited to, alcohols such as butyl carbitol, benzyl alcohol, and 2-phenoxyethanol; aromatic hydrocarbons such as toluene, xylene, mesitylene, and tetralin; ethers such as tetrahydrofuran; ketones such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone; lactones such as 2-pyrrolidone and 1-methyl-2-pyrrolidone; ether alcohols such as ethyl glycol monophenyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether (butyl carbitol), and corresponding propylene glycol derivatives; esters such as corresponding acetates (e.g., butyl carbitol acetate); and diesters such as methyl esters and ethyl esters of dicarboxylic acids such as malonic acid and succinic acid.

[0056] The conductive paste can be prepared by uniformly mixing the ingredients using a mixing means such as a mixing machine, a propeller mixer, a kneader, a roll, a pot mill, etc. The temperature at which the conductive paste is prepared is not particularly limited, but it can be prepared at, for example, 10 to 40°C.

[0057] [Viscosity of Conductive Paste] The viscosity of the conductive paste of this embodiment is not particularly limited and may be adjusted appropriately depending on the application. The viscosity of the conductive paste is usually 10 to 300 Pa·s, and preferably 20 to 100 Pa·s. By adjusting the viscosity of the conductive paste within this range, the coating properties and handling properties of the conductive paste are improved.

[0058] [TI Value of Conductive Paste] The thixotropic index value (TI (Thixotropic Index) value) of the conductive paste of this embodiment is 3.0 or less, preferably 2.5 or less, more preferably 2.0 or less, and particularly preferably 1.8 or less. In this specification, the TI value is the ratio of the viscosity at 10 rpm to that at 100 rpm measured at 25°C using an HB-type viscometer (Brookfield, DV-II, SC4-14 spindle), and is calculated as viscosity at 10 rpm / 100 rpm. The TI value measures the dependency of viscosity on shear rate (rotation speed of the viscometer) and is an index representing thixotropy. A Newtonian fluid such as water, whose viscosity does not change even when the shear rate changes, has a TI value of 1. A TI value smaller than 1 indicates that a smaller shear force results in a smaller viscosity than a larger shear force, and a TI value larger than 1 indicates that a smaller shear force results in a larger viscosity than a larger shear force. The larger the TI value, the more thixotropic the paste is. A TI value of 3 or less improves the workability when applying the conductive paste. Specifically, the conductive paste has good dipping properties and a good application shape.

[0059] [Application of External Electrodes] The application of the conductive paste of this embodiment is not particularly limited, but it is preferably used to form external electrodes of electronic components. Since the conductive paste of this embodiment can suppress the occurrence of cracks in the external electrodes even when a thermal fatigue-resistant solder is used, it is preferable that the external electrodes are connected to wiring electrodes of a circuit board of the electronic component by a solder layer.

[0060] In this specification, thermal fatigue resistant solder means solder that has a shear strength of 20 N or more after being repeatedly exposed to 1500 cycles of holding at −55°C and +125°C for 30 minutes each. The shear strength can be measured by the following method.

[0061] A chip resistor component measuring 3.2 x 1.6 x 0.6 mm was soldered to a soldering pattern (1.6 x 1.2 mm) in a 6-layer FR-4 glass epoxy board measuring 150 mm x 140 mm and 1.6 mm thick. Soldering was performed by printing solder paste on the electrode portion using a 150 μm thick metal mask, followed by heating in a reflow furnace set to a peak temperature of 245°C. The printed circuit board on which the chip resistor component was mounted was then placed in a heat cycle chamber set to hold temperatures of -55°C and +125°C for 30 minutes each, and the mounted board was exposed to a heat cycle environment of 1,500 cycles, resulting in a test sample.

[0062] The chip resistor components of the test samples are peeled off at a shear rate of 5 mm / min using a shear strength tester, and the peel strength (N: Newton) at that time is measured. The number of test samples is 15 to 20 for each test sample, and the average value of the peel strength is taken as the shear strength.

[0063] Commercially available thermal fatigue-resistant solders are not particularly limited, but examples include M794 (manufactured by Senju Metal Industry Co., Ltd., Sn-3.4Ag-0.7Cu-Bi-Sb-Ni-x), M758 (manufactured by Senju Metal Industry Co., Ltd., Sn-3.0Ag-0.8Cu-Bi-Ni), and PS48BR-600-LSP (manufactured by Harima Chemicals Co., Ltd., Sn-3.2Ag-0.5Cu-4.0Bi-3.5Sb-Ni-Co).

[0064] [Electronic Component] The electronic component of this embodiment includes an electrode formed by curing the conductive paste of this embodiment. In particular, it is preferable that the electronic component includes an electrode formed by curing the conductive paste of this embodiment as an external electrode. The electronic component of this embodiment is preferably a multilayer ceramic electronic component. Examples of multilayer ceramic electronic components on which external electrodes are formed include capacitors, capacitor arrays, thermistors, varistors, inductors, and LC, CR, LR, and LCR composite components.

[0065] (Multilayer Ceramic Electronic Component) The multilayer ceramic electronic component of this embodiment will be described using a multilayer ceramic capacitor 1 shown in Fig. 1 as an example. The multilayer ceramic capacitor 1 has a structure in which an external electrode layer 4 is provided on the internal electrode extraction surface of a ceramic composite (element body) in which ceramic dielectrics 2 and internal electrode layers 3 are alternately laminated. Typically, the external electrode has a structure in which a plating layer 5 is applied on the external electrode layer 4. The plating layer 5 typically comprises a nickel plating layer and a tin plating layer.

[0066] When mounting the multilayer ceramic capacitor on the circuit board 7, the external electrodes of the multilayer ceramic capacitor are connected to the wiring electrodes 8 of the circuit board by soldering. Due to this structure, when an external force is applied to the circuit board 7 on which the multilayer ceramic capacitor 1 is mounted or when the circuit board is bent, stress is transmitted to the multilayer ceramic capacitor 1 via the solder layer 6. This stress may cause separation between the external electrode layer 4 and the ceramic composite, or may cause cracks in the ceramic composite. By forming external electrodes that are excellent at mitigating stress using the conductive paste of this embodiment, it is possible to suppress the occurrence of cracks in the external electrodes, even when thermal fatigue-resistant solder is used.

[0067] The multilayer ceramic capacitor 1 of this embodiment is a multilayer ceramic electronic component that includes external electrode layers 4 formed by curing a conductive paste, the conductive paste including (A) metal particles and (B) a thermosetting resin, and when the surface of the conductive paste is heat-cured under heating conditions at 180°C for 30 minutes and the cured product is observed using a scanning electron microscope, the metal area ratio represented by the following formula (1) is 50% or more, and the flexural modulus of the cured product when the conductive paste is heat-cured under heating conditions at 180°C for 30 minutes is 6.0 GPa or less: Metal Area Ratio (%) = (Area Occupied by Metal ÷ Measured Area) × 100 (1)

[0068] The multilayer ceramic capacitor 1 also includes a circuit board 7 on which wiring electrodes 8 are formed, and the external electrode layers 4 are connected to the wiring electrodes 8 by solder layers 6, and the solder layers are formed from a thermal fatigue-resistant solder having a shear strength of 20 N or more after being repeatedly exposed to 1,500 cycles of temperatures of −55°C and +125°C for 30 minutes each.

[0069] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following examples, parts and % represent parts by mass and % by mass unless otherwise specified.

[0070] [Preparation of Conductive Paste] Conductive pastes of Examples and Comparative Examples were prepared by blending the components in Table 1. In Tables 1 and 2, the amount of each component is expressed in parts by mass (unit: g). The components used in the Examples and Comparative Examples are as follows. When preparing the conductive paste, the amount of solvent was adjusted so that the viscosity of the paste was in the range of 32 to 38 Pa·s. The viscosity was measured at room temperature (25°C) at 10 rpm and 100 rpm using an HB-type viscometer (Brookfield, DV2, SC4-14 spindle), and the TI value was calculated from the ratio of the viscosity at 10 rpm to the viscosity at 100 rpm.

[0071] (A) Metal Particles (Component (A)) (A1-1) Flake-shaped Silver Particles 1 (manufactured by Namics Corporation, D50: 3.6 μm, BET specific surface area: 1.0 m) ２ / g, tap density 4.8 g / cm ３ (A1-2) Flake-shaped silver particles 2 (manufactured by Namics Corporation, D50: 7.3 μm, BET specific surface area: 1.0 m ２ / g, tap density 4.6 g / cm ３ (A2) Spherical silver particles (manufactured by Namics Corporation, D50: 2.6 μm, BET specific surface area: 0.4 m ２ / g, tap density 3.4 g / cm ３ )

[0072] (B) Thermosetting Resin (Component (B)) (B1-1) Bisphenol A type epoxy resin (product number: DER 664U, manufactured by Blue Cube Japan, epoxy equivalent: 875 to 955, solid state, softening point: 100 to 110°C, melt viscosity 4,000 to 8,000 mPa·s @ 150°C) (B1-2) Bisphenol A type epoxy resin (product number: JER1009, manufactured by Mitsubishi Chemical Corporation, epoxy equivalent: 2400 to 3300, solid state) (B2) Novolac type phenolic resin (product number: PSM 4324, manufactured by Gun-ei Chemical Industry Co., Ltd.)

[0073] (C) Flexible component (Component (C)) (C1) Butyral resin (thermoplastic resin, product number: BX3Z, manufactured by Sekisui Chemical Co., Ltd.) (C2) Silicone rubber particles (product number: KMP-605M, manufactured by Shin-Etsu Silicones Co., Ltd., spherical, average particle diameter: 2 μm, surface coated with silicone resin)

[0074] Curing accelerator (2-phenyl-4-methyl-5-hydroxymethylimidazole, product number: Curazol 2P4MHZ-PW, manufactured by Shikoku Chemical Industry Co., Ltd.) Silane coupling agent (epoxy silane coupling agent, product number: KBM403, 3-glycidoxypropyltrimethoxysilane) Solvent (product number: Hisolve EPH, 2-phenoxyethanol, manufactured by Toho Chemical Industry Co., Ltd.)

[0075] [Measurement of the area ratio of silver on the surface of the cured conductive paste] The conductive pastes of the examples and comparative examples were applied to an alumina substrate so that the thickness of the cured product after curing was approximately 30 μm, dried in a fan dryer at 120 ° C for 60 minutes, and then cured at 180 ° C for 30 minutes to obtain a cured product. Using a field emission scanning electron microscope (model "MERLIN" manufactured by Carl Zeiss Co., Ltd.), observation was performed from a direction perpendicular to the cured surface of the conductive paste under conditions of an acceleration voltage of 2.0 kV, an observation magnification of 1,000x, a probe current of 300 pA, and a working distance of 3.0 mm. By observing the surface of the cured conductive paste, an EsB (Energy selective BSE: in-lens high-angle backscattered electron detector, grid voltage 500 V) image was obtained. Using the EsB detector, high-density silver appeared bright (white) and low-density resin appeared dark (black). FIG. 2 shows an image of the surface of a cured product prepared under the above conditions using the conductive paste of Example 3.

[0076] The image (JPEG format, 3,072 x 2,304 pixels) obtained when observing the surface of the cured conductive paste using this field emission scanning electron microscope was loaded into image processing software (WinROOF2018 ver. 4.5.5, manufactured by Mitani Shoji Co., Ltd.). The median (filter size 3 x 3), a filter function of the software, was used to remove noise. Next, using the automatic binarization function, a threshold was determined by the Valley method, and the image was binarized into white (silver) and black (resin) areas. The area ratio of the white (silver) area was calculated by extracting bright areas from the binarized image, and this was used as the area ratio of silver on the surface of the cured conductive paste. The area ratio of silver was calculated by photographing three randomly selected locations on each cured product, and the average value of the binarized white areas was used as the area ratio of silver in the examples and comparative examples. Silver area ratio (%) = (area occupied by silver ÷ measured area) × 100 (1)

[0077] The silver area ratio (%) was evaluated as follows: ◯: 60% or more △: 50 to 59% ×: Less than 49%

[0078] [Flexural Modulus] The conductive pastes of the Examples and Comparative Examples were applied to a substrate, dried at 120°C for 60 minutes, and then cured in the atmosphere at 180°C for 30 minutes using a blower dryer. After that, the pastes were peeled off from the substrate to prepare three 40 x 10 x 0.1 mm test pieces (cured products). Using an autograph manufactured by Shimadzu Corporation, a two-point support, one-point load bending test was performed at a displacement rate of 1 mm / min, and the flexural modulus was calculated from the stress-strain curve. Three test pieces were used for each example and comparative example, and the average value was used as the flexural modulus. Test pieces with a flexural modulus of 6.0 GPa or more were evaluated as "x."

[0079] [Continuity of nickel plating] A conductive paste having the composition shown in Table 1 was dip-coated onto the internal electrode contact surface of the ceramic composite of a multilayer ceramic capacitor so that the thickness after curing would be approximately 30 to 40 μm, and after drying at 120° C. for 60 minutes, it was cured in an air drier at 180° C. for 30 minutes to form an external electrode. Subsequently, nickel plating was performed in a Watts bath, and then tin plating was performed by electrolytic plating.

[0080] Scanning electron microscope (SEM) photographs of the cross section near the external electrodes formed using the conductive paste were checked, and the continuity of the nickel plating was evaluated as follows: ∘: A continuous nickel plating film was formed on the surface of the external electrode Δ: The nickel plating was locally interrupted ×: The nickel plating was discontinuous

[0081] [Reliability Evaluation] External electrodes were formed using a conductive paste having the composition shown in Table 1 in the same manner as in the nickel plating continuity test. Nickel plating was then performed in a Watts bath, followed by tin plating by electrolytic plating. Next, soldering was performed using thermal fatigue-resistant solder (product number: M794, manufactured by Senju Metal Industry Co., Ltd., Sn-3.4Ag-0.7Cu-Bi-Sb-Ni-x) to obtain a chip multilayer capacitor.

[0082] The produced multilayer ceramic capacitors were subjected to a moisture absorption reflow test. In the moisture absorption reflow test, the capacitors were left in an environment of 85°C and 85% RH for 168 hours, and then reflow was performed at a peak temperature of 240°C. The results were evaluated by checking scanning electron microscope (SEM) photographs of the cross section near the external electrodes formed using the conductive paste, and the results were rated as follows: ◯: No cracks occurred in the external electrodes, and no peeling occurred between the external electrodes and the nickel plating. △: No cracks occurred in the external electrodes, but partial peeling occurred between the external electrodes and the nickel plating. ×: Cracks occurred in the external electrodes.

[0083]

[0084]

[0085] [Results] As can be seen from Tables 1 and 2, by using a conductive paste with a metal area ratio of 50% or more and a flexural modulus of 6.0 GPa or less, cracking in the external electrodes was suppressed, even when thermal fatigue-resistant solder was used. Specifically, when the conductive pastes of Examples 1 to 8 were used, no cracks occurred in the external electrodes. Furthermore, when the conductive pastes of Examples 1 to 8 were used, the nickel plating did not become discontinuous at the interface with the external electrodes. Furthermore, when the conductive pastes of Examples 6 to 8 were used, no cracks occurred in the external electrodes, no peeling occurred between the external electrodes and the nickel plating, and a continuous nickel plating film was formed on the surface of the external electrodes. The coated shape of the external electrodes was also confirmed. The surfaces of the conductive pastes of Examples 1 to 8 were flat, and the coated shape was good in all cases. On the other hand, the conductive paste of Comparative Example 1 had a high TI value and exhibited defects such as sharp edges in the coated shape.

[0086] In Comparative Example 1, in which the flexural modulus was 6.0 GPa or more, cracks occurred in the external electrodes. In Comparative Example 2, in which the metal area ratio was less than 49%, cracks occurred in the external electrodes and the nickel plating became discontinuous.

[0087] From the above results, it was found that by increasing the proportion of flaky silver particles, the area of ​​silver present on the surface of the cured conductive paste could be increased, thereby improving adhesion to the nickel plating. By improving adhesion between the cured conductive paste and the nickel plating, it was possible to suppress the occurrence of cracks in the external electrodes, even when using thermal fatigue-resistant solder.

[0088] In addition, by using "epoxy resin with an epoxy equivalent of 2000 g / eq or more" and "silicone rubber particles," it was possible to alleviate the stress applied to the ceramic body and external electrodes when thermal shock was applied, and to suppress the occurrence of cracks in the external electrodes. Furthermore, by using butyral resin or a specific epoxy resin, it was possible to reduce the TI value of the conductive paste and improve the coating shape, even when the proportion of flaky silver particles was increased.

[0089] Although the present invention has been described above with reference to the embodiments and examples, the present invention is not limited to the above-described embodiments and examples. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

[0090] The patents, patent applications, and publications cited herein are incorporated by reference into this specification in their entirety as if the contents were specifically set forth herein.

[0091] <Appendix> Some or all of the above embodiments and examples may be described as, but are not limited to, the following appendixes. <Conductive Paste> (Appendix 1) A conductive paste comprising (A) metal particles and (B) a thermosetting resin, wherein, when the conductive paste is heat-cured under heating conditions at 180°C for 30 minutes and the surface of the cured product is observed using a scanning electron microscope, the area ratio of the metal represented by the following formula (1) is 50% or more, and when the conductive paste is heat-cured under heating conditions at 180°C for 30 minutes and the cured product has a flexural modulus of 6.0 GPa or less. Metal Area Ratio (%) = (Area Occupied by Metal ÷ Measured Area) × 100 (1) (Appendix 2) The conductive paste according to Appendix 1, wherein the (A) metal particles include (A1) flaky metal particles. (Appendix 3) The conductive paste according to Appendix 2, wherein the (A1) flaky metal particles have an aspect ratio (average particle diameter / average thickness) of 5 or more. (Appendix 4) The conductive paste according to Appendices 2 or 3, wherein the content of the (A1) flaky metal particles is 60 parts by mass or more relative to 100 parts by mass of the (A) metal particles. (Appendix 5) The conductive paste according to any one of Appendices 1 to 4, wherein the (B) thermosetting resin contains a (B1) epoxy resin, and the (B1) epoxy resin contains an epoxy resin having an epoxy equivalent of 1000 g / eq or more. (Appendix 6) The conductive paste according to Appendices 5, wherein the content of the (B1) epoxy resin is 2 to 30 parts by mass relative to 100 parts by mass of the (A) metal particles. (Appendix 7) The conductive paste according to any one of Appendices 1 to 6, wherein the conductive paste contains a (C) flexible component, and the (C) flexible component contains a (C1) thermoplastic resin. (Appendix 8) The conductive paste according to Appendices 7, wherein the (C1) thermoplastic resin contains a butyral resin. (Appendix 9) The conductive paste according to Appendix 8, wherein the content of the (C1) thermoplastic resin is 0.05 to 5 parts by mass relative to 100 parts by mass of the (A) metal particles. (Appendix 10) The conductive paste according to Appendix 8 or 9, wherein the (C) flexible component includes (C2) rubber particles. (Appendix 11) The conductive paste according to Appendix 10, wherein the content of the (C2) rubber particles is 2 to 15 parts by mass relative to 100 parts by mass of the (A) metal particles.(Appendix 12) The conductive paste according to any one of Appendices 1 to 11, having a thixotropic index value, which is the viscosity at 10 rpm / the viscosity at 100 rpm, measured at 25°C using an E-type viscometer, of 3.0 or less. (Appendix 13) The conductive paste according to any one of Appendices 1 to 12, used to form an external electrode of an electronic component. (Appendix 14) The conductive paste according to Appendices 13, wherein the external electrode is connected to a wiring electrode of a circuit board of the electronic component by a solder layer. (Appendix 15) The conductive paste according to any one of Appendices 1 to 14, wherein the solder layer is formed of solder having a shear strength of 20 N or more after being repeatedly exposed to 1,500 cycles under conditions of holding at −55°C and +125°C for 30 minutes each. <Electrode, Electronic Component> (Appendix 16) An electrode obtained by curing the conductive paste according to any one of Appendices 1 to 15. (Appendix 17) An electronic component, comprising the electrode according to Appendices 16 as an external electrode. (Appendix 18) The electronic component according to Appendix 17, which is a multilayer ceramic electronic component. (Appendix 19) An electronic component, comprising external electrodes formed by curing a conductive paste, the conductive paste containing (A) metal particles and (B) a thermosetting resin, the conductive paste being heat-cured under heating conditions at 180°C for 30 minutes, and when the surface of the cured product is observed using a scanning electron microscope, the area ratio of the (A) metal represented by the following formula (1) is 50% or more, and the cured product when the conductive paste is heat-cured under heating conditions at 180°C for 30 minutes has a flexural modulus of 6.0 GPa or less. Metal area ratio (%) = (area occupied by metal ÷ measured area) × 100 (1) (Appendix 20) An electronic component according to Appendix 19, comprising: a circuit board on which wiring electrodes are formed; the external electrodes are connected to the wiring electrodes by solder layers; and the solder layers are formed of solder having a shear strength of 20 N or more after being repeatedly exposed to 1,500 cycles of holding at −55°C and +125°C for 30 minutes each.

[0092] The conductive paste of the present invention is capable of suppressing the occurrence of cracks in external electrodes even when thermal fatigue-resistant solder is used, and is particularly useful for use as external electrodes in multilayer ceramic electronic components.

[0093] REFERENCE SIGNS LIST 1 Multilayer ceramic capacitor (electronic component) 2 Ceramic dielectric 3 Internal electrode layer 4 External electrode layer 5 Plating layer 6 Solder layer 7 Circuit board 8 Wiring electrode

Claims

1. A conductive paste comprising (A) metal particles and (B) a thermosetting resin, wherein when the conductive paste is heat-cured under heating conditions at 180°C for 30 minutes and the surface of the cured product is observed using a scanning electron microscope, the area ratio of the metal represented by the following formula (1) is 50% or more, and when the conductive paste is heat-cured under heating conditions at 180°C for 30 minutes, the flexural modulus of the cured product is 6.0 GPa or less. Metal Area Ratio (%) = (Area occupied by metal ÷ Measured area) × 100 (1) 2. The conductive paste according to claim 1, wherein the (A) metal particles include (A1) flaky metal particles.

3. The conductive paste according to claim 2, wherein the aspect ratio (average particle diameter / average thickness) of the flaky metal particles (A1) is 5 or more.

4. The conductive paste according to claim 2 or 3, wherein the content of the (A1) flaky metal particles is 60 parts by mass or more per 100 parts by mass of the (A) metal particles.

5. The conductive paste according to any one of claims 1 to 4, wherein the (B) thermosetting resin comprises (B1) an epoxy resin, and the (B1) epoxy resin comprises an epoxy resin having an epoxy equivalent of 1000 g / eq or more.

6. The conductive paste according to claim 5, wherein the content of the epoxy resin (B1) is 2 to 30 parts by mass per 100 parts by mass of the metal particles (A).

7. A conductive paste according to any one of claims 1 to 6, comprising a flexible component (C), wherein the flexible component (C) comprises a thermoplastic resin (C1).

8. The conductive paste according to claim 7, wherein the thermoplastic resin (C1) includes a butyral resin.

9. The conductive paste according to claim 8, wherein the content of the thermoplastic resin (C1) is 0.05 to 5 parts by mass per 100 parts by mass of the metal particles (A).

10. The conductive paste according to claim 8 or 9, wherein the flexible component (C) contains rubber particles (C2).

11. The conductive paste according to claim 10, wherein the content of the (C2) rubber particles is 2 to 15 parts by mass per 100 parts by mass of the (A) metal particles.

12. A conductive paste according to any one of claims 1 to 11, which has a thixotropic index value, which is the ratio of viscosity at 10 rpm to viscosity at 100 rpm, measured at 25°C using an E-type viscometer, of 3.0 or less.

13. The conductive paste according to any one of claims 1 to 12, which is used to form external electrodes of electronic components.

14. The conductive paste according to claim 13, wherein the external electrodes are connected to wiring electrodes on a circuit board of the electronic component by a solder layer.

15. A conductive paste according to any one of claims 1 to 14, wherein the solder layer is formed from a solder having a shear strength of 20 N or more after 1,500 cycles of repeatedly holding the solder at -55°C and +125°C for 30 minutes each.

16. An electrode obtained by curing the conductive paste according to any one of claims 1 to 15.

17. An electronic component comprising the electrode according to claim 16 as an external electrode.

18. The electronic component according to claim 17, which is a multilayer ceramic electronic component.

19. An electronic component comprising external electrodes formed by curing a conductive paste, the conductive paste containing (A) metal particles and (B) a thermosetting resin, wherein the conductive paste is heat-cured at 180°C for 30 minutes, and when the surface of the cured product is observed using a scanning electron microscope, the area ratio of the metal (A) represented by the following formula (1) is 50% or more, and the flexural modulus of the cured product when the conductive paste is heat-cured at 180°C for 30 minutes is 6.0 GPa or less. Metal Area Ratio (%) = (Area occupied by metal ÷ Measured area) × 100 (1) 20. An electronic component according to claim 19, comprising a circuit board on which wiring electrodes are formed, the external electrodes being connected to the wiring electrodes by solder layers, and the solder layers being formed from solder with a shear strength of 20 N or more after 1,500 cycles of repeatedly holding the temperature at -55°C and +125°C for 30 minutes each.

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