Conductive paste and multilayer ceramic electronic component comprising external electrode formed using same

Abstract

The prevent invention is a conductive paste comprising (A) conductive particles, (B) a thermosetting resin, and (C) rubber particles. The rubber particles (C) include a carbon-carbon bond in the main chain skeleton thereof. Rubber particles having an average particle size less of than 1 μm are included. The present invention makes it possible to provide a conductive paste having improved adhesion to a copper base material.

Description

Conductive paste and multilayer ceramic electronic component having external electrodes formed using the same

[0001] The present invention relates to a conductive paste and a multilayer ceramic electronic component having external electrodes formed using the same.

[0002] Chip-type multilayer ceramic electronic components, each consisting of a large number of laminated dielectric layers and electrodes, are widely used in electronic circuits in small devices such as mobile phones and tablet computers, where cost reduction and miniaturization are strongly desired. A conventional multilayer ceramic electronic component will be described using the multilayer ceramic capacitor shown in FIG. 1 as an example. Multilayer ceramic capacitors are miniaturized by providing external electrode layers instead of leads on a structure consisting of a large number of laminated dielectric layers and internal electrodes, significantly contributing to the miniaturization and weight reduction of electronic devices. Multilayer ceramic capacitor 1 has a structure in which ceramic dielectric layers 2 and internal electrode layers 3 are alternately laminated, and an external electrode layer 4 is provided on the internal electrode contact surface of the ceramic composite. Typically, the external electrode has a structure in which a plating layer 5 is applied to the external electrode layer 4. The plating layer 5 typically consists of a nickel plating layer and a tin plating layer. When mounting a multilayer ceramic capacitor on a circuit board 7, the external electrodes of the multilayer ceramic capacitor are connected to the wiring electrodes of the circuit board via solder layers 6.

[0003] Causes of failure in electronic circuits using multilayer ceramic capacitors include physical factors such as external force applied to a circuit board on which the multilayer ceramic capacitor is mounted or deflection of the circuit board. Such external force is transmitted as stress to the laminate composite via the solder layer and external electrode, which can cause separation between the external electrode and the ceramic composite or cracks in the ceramic composite. Providing an electrode layer as a buffer material on the external electrode layer 4 has been proposed as a means of improving the reliability of electronic circuits against external physical force (Patent Document 1). In this technique, a multi-layer external electrode is formed, with a copper substrate as the first conductor layer 11 as the external electrode connected to the internal electrode of the multilayer capacitor, and a resin-containing conductive paste as a buffer material laminated on top of the first conductor layer 12.

[0004] JP 2011-233452 A

[0005] Conductive pastes for forming external electrodes of electronic components are required to be safe and highly reliable, and therefore must be flexible enough to withstand bending of the substrate. To achieve this, a method such as that described in Patent Document 1 has been used. However, the method described in Patent Document 1 requires adhesion between layers because multiple layers are provided as external electrodes. When the conductive paste described in Patent Document 1 is used as a second conductor layer constituting one of the external electrode layers, there is room for improvement in adhesion to the copper underlayer, which is the first conductor layer. Therefore, an object of the present invention is to provide a conductive paste with improved adhesion to the copper underlayer.

[0006] The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention. That is, the present invention includes the following inventions, but is not limited to the following.

[0007] 1. A conductive paste comprising: (A) conductive particles; (B) a thermosetting resin; and (C) rubber particles, wherein the (C) rubber particles have a main chain skeleton containing a carbon-carbon bond and an average particle diameter of less than 1 μm.

[0008] 2. The conductive paste according to item 1 above, wherein the (C) rubber particles contain at least one rubber selected from the group consisting of diene-based rubber, (meth)acrylate-based rubber, urethane-based rubber, isoprene-based rubber, fluorine-based rubber, and chloroprene-based rubber.

[0009] 3. The conductive paste according to item 1 or 2 above, wherein the (C) rubber particles include core-shell type rubber particles.

[0010] 4. The conductive paste according to the above item 3, wherein the core of the core-shell rubber particle is a rubber particle whose main chain skeleton contains a carbon-carbon bond.

[0011] 5. The conductive paste according to item 3 or 4 above, wherein the shell portion of the core-shell rubber particles is a shell portion containing a polymer having a content of a structural unit having an epoxy group of 10 parts by mass or more.

[0012] 6. The conductive paste according to any one of items 1 to 5 above, wherein the amount of the (C) rubber particles is in the range of 0.1 to 10 parts by mass per 100 parts by mass of the (A) component.

[0013] 7. The conductive paste according to any one of items 1 to 6 above, wherein the thermosetting resin (B) contains an epoxy resin and has an epoxy equivalent of 2000 g / eq or less relative to the total mass of the thermosetting resin.

[0014] 8. The conductive paste according to any one of items 1 to 7 above, wherein (A) contains spherical silver particles and flaky silver particles.

[0015] 9. The conductive paste according to any one of items 1 to 8 above, wherein the content of the component (B) is 3 to 25 parts by mass per 100 parts by mass of the component (A).

[0016] 10. The conductive paste according to any one of items 1 to 9, wherein the conductive paste has a flexural modulus of 3 GPa to 15 GPa when dried at 120°C for 60 minutes and then cured in an air dryer at 180°C for 30 minutes.

[0017] 11. After drying at 120°C for 60 minutes, the adhesive strength to the copper substrate was 1.0 kN / cm when cured in an air dryer at 180°C for 30 minutes. ２ 10. The conductive paste according to any one of items 1 to 9 above.

[0018] 12. The conductive paste according to any one of items 1 to 11, having a thixotropic index value, which is the ratio of viscosity at a rotation speed of 10 rpm to viscosity at a rotation speed of 100 rpm, measured at 25°C with an HB type viscometer, of 7 or less.

[0019] 13. The conductive paste according to any one of items 1 to 12 above, for forming a second conductor layer of an external electrode having a first conductor layer connected to an internal electrode and a second conductor layer laminated on the first conductor layer.

[0020] 14. A multilayer ceramic electronic component having external electrodes formed using the conductive paste according to the preceding paragraph 13.

[0021] The conductive paste of the present invention can be used as the second conductor layer of an external electrode, which has improved adhesion to a copper underlayer, thereby providing a safe and highly reliable conductive paste for external electrodes and a multilayer ceramic electronic component.

[0022] FIG. 1 is a schematic diagram showing the structure of a ceramic capacitor having an external electrode made up of multiple conductor layers, in which a second conductor layer containing resin is stacked on top of a first conductor layer connected to an internal electrode.

[0023] Hereinafter, an embodiment of the present invention will be described in detail. In the present invention, the term "first conductor layer" refers to a conductor layer that constitutes an external electrode and is directly connected to an internal electrode. The term "second conductor layer" refers to a conductor layer that constitutes an external electrode and is stacked on the first conductor layer.

[0024] The conductive paste for external electrodes of the present invention comprises (A) conductive particles, (B) a thermosetting resin, and (C) rubber particles, the rubber particles of component (C) having a main chain skeleton containing carbon-carbon bonds and an average particle size of less than 1 μm. Components (A) to (C) are described in detail below.

[0025] (A) Conductive Particles The conductive particles are components for imparting conductivity to the external electrodes, and metal particles are used. Examples of the metal particles include Ag, Cu, Ni, Pd, Au, and Pt metal particles. Ag metal particles are preferred because they can relatively easily provide excellent conductivity.

[0026] The conductive particles are preferably metal particles having a melting point of 700°C or higher. The melting point of the conductive particles is more preferably 800°C or higher. The upper limit of the melting point is not particularly limited, but is usually 1800°C or lower, preferably 1600°C or lower. The conductive particles can be used alone or in combination of two or more types.

[0027] Examples of conductive particles include alloys of Ag, Cu, Ni, Pd, Au, and Pt, and among these, metal particles having a melting point of 700° C. or higher are preferred. Ag alloy particles are preferred because excellent conductivity can be obtained relatively easily.

[0028] Examples of alloy particles include metal particles of an alloy composed of two or more elements selected from the group consisting of Ag, Cu, Ni, Pd, Au, and Pt. Examples of binary Ag alloys include AgCu alloys, AgAu alloys, AgPd alloys, and AgNi alloys. Examples of ternary Ag alloys include AgPdCu alloys and AgCuNi alloys.

[0029] Furthermore, examples of alloy particles include metal particles of an alloy composed of one or more elements selected from Ag, Cu, Ni, Pd, Au, and Pt and one or more other elements, and among these, metal particles having a melting point of 700° C. or higher as an alloy are preferred. Examples of other elements include Zn, Al, and Sn, and in the case of a binary alloy of Sn and Ag, an AgSn alloy can be used in which the mass ratio of Sn to Ag is higher than 25.5:74.5.

[0030] Furthermore, as the conductive particles, multilayer particles can be used, in which the surfaces of metal particles are coated with other metal atoms or metal compounds. By disposing expensive metals such as Ag, Pd, Au, and Pt on the surfaces of relatively inexpensive metal particles such as Cu, the overall cost of the conductive particles can be reduced while utilizing the physical properties of these metals, such as high conductivity, migration resistance, and corrosion resistance. Multilayer particles can be manufactured using known manufacturing methods tailored to the particle shape. For example, core-shell particles can be prepared in which the outer layer has a certain thickness ratio relative to the entire particle, for example, by precipitating a metal on the surface of an inner layer metal particle through a metal precipitation reaction caused by a reduction reaction of a compound containing the metal on the outer layer. Alternatively, particles can be prepared in which a thin coating film is formed on the surface of the inner layer metal particle by immersing the inner layer metal particle in a solution of a metal compound and then drying the resulting particles.

[0031] The thickness and mass ratio of the outer layer and inner layer portions of multilayer particles are not particularly limited. From the viewpoint of placing greater importance on the properties of the metal on the outer layer side, a larger thickness and mass ratio of the outer layer are preferred, while from the viewpoint of cost, a smaller thickness and mass ratio of the outer layer are preferred. The thickness of the outer layer portion is preferably 1 to 100 nm or less and can be controlled by the manufacturing method. Furthermore, it is not necessary for the outer layer portion to cover the entire surface of the metal on the inner layer side; particularly in coated particles, a structure in which the metal of the outer layer coats a portion of the metal particle on the inner layer side may be used. In the case of coated particles, the mass ratio of the outer layer portion is preferably 0.01 to 1.0 parts by mass per 100 parts by mass of the conductive particles. In the case of core-shell particles, it is preferably 5 to 40 parts by mass per 100 parts by mass of the conductive particles.

[0032] Furthermore, as the conductive particles, it is possible to use low-melting-point metal particles of Sn, In, and Bi, whose melting points are 200° C. or more and less than 700° C. The low-melting-point metal particles are preferably non-Pb.

[0033] Furthermore, as the low-melting-point metal particles, metal particles of an alloy of Sn, In, and Bi, having a melting point of 200°C or more and less than 700°C, can also be used. Sn alloys are preferred because they can relatively easily provide excellent conductivity. Examples of alloy particles include metal particles of an alloy composed of two or more elements selected from the group consisting of Sn, In, and Bi, and examples of binary alloys include SnIn alloys.

[0034] The conductive particles may be of any shape, such as spherical, flake-like, scale-like, or needle-like. The average particle diameter of these particles is preferably 0.015 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 conductive particles are spherical, the average particle diameter is more preferably in the range of 0.2 to 5 μm. When the metal particles are flaky, the average particle diameter is more preferably in the range of 5 to 30 μm. In this specification, the average particle diameter refers to the particle diameter in the case of spherical particles, the diameter of the longest part in the case of flaky particles, the major axis of the particle flakes in the case of scale-like particles, and the average length in the case of needle-like particles. Here, the average particle diameter of metal particles is a value determined by image analysis after observation with a scanning electron microscope (SEM).

[0035] The conductive particles preferably comprise a combination of spherical silver particles (A1) and flake-shaped silver particles (A2). The mass ratio of the silver particles (A1) to (A2) is preferably 5:95 to 95:5. By setting the ratio of spherical silver powder to flaky silver powder within the above range, the specific resistance can be reduced, and the thixotropic index (TI) value can be reduced, resulting in improved coating shape and plating properties. A ratio of 20:80 to 85:15 is more preferred, and a ratio of 40:60 to 80:20 is even more preferred. The metal particles used in the present invention may be commercially available or may be prepared by methods known to those skilled in the art.

[0036] (B) Thermosetting Resin The thermosetting resin functions as a binder. The thermosetting resin is not particularly limited as long as it undergoes a polymerization reaction and hardens when heated, and examples thereof include amino resins such as epoxy resins, urea resins, melamine resins, and guanamine resins; oxetane resins; phenolic resins such as resols, alkyl resols, novolacs, alkyl novolacs, and aralkyl novolacs; phenoxy resins; silicone-modified organic resins such as silicone epoxy and silicone polyester; bismaleimides; and polyimide resins. For example, BT resin can also be used. These resins may be used alone or in combination of two or more.

[0037] The use of a thermosetting resin that is liquid at room temperature is preferred because it allows for a reduction in the amount of organic solvent used as a diluent. Examples of such liquid thermosetting resins include liquid epoxy resins and liquid phenolic resins. Furthermore, resins that are compatible with these liquid resins and exhibit solid or ultra-high viscosity at room temperature may be added to the mixture within the range in which the mixture exhibits fluidity. Examples of such resins include epoxy resins such as high-molecular-weight bisphenol A epoxy resins, diglycidyl biphenyl, novolac epoxy resins, and tetrabromobisphenol A epoxy resins; resol phenolic resins, novolac phenolic resins, and aralkyl novolac phenolic resins.

[0038] From the viewpoints of dimensional stability, insulating properties, and chemical resistance, it is preferable to use an epoxy resin as the thermosetting resin. Epoxy resin is a general term for thermosetting resins that can be cured by forming a crosslinked network with epoxy groups present in the compound, and includes prepolymer compounds before crosslinking network formation. The type of epoxy resin is not particularly limited as long as it has two or more epoxy groups. From the viewpoints of curing speed and reliability, compounds having 2 to 6 epoxy groups are more preferable, and bifunctional epoxy resins having two epoxy groups are even more preferable.

[0039] When the (B) thermosetting resin contains an epoxy resin, it is preferable to use the epoxy resin so that the epoxy equivalent relative to the total mass of the thermosetting resin is 2000 g / eq or less. Here, "epoxy equivalent" refers to the value obtained by dividing the molecular weight of the resin by the number of epoxy groups in the molecule. The epoxy equivalent value "relative to the total mass of the thermosetting resin" is the value obtained by multiplying the epoxy equivalent of the epoxy resin itself by the mass fraction of the epoxy resin contained in the (B) thermosetting resin. By keeping the epoxy equivalent within this range, it is possible to keep the specific resistance low and improve adhesive strength. The epoxy equivalent range is preferably 50 to 2000 g / eq, more preferably 70 to 1000 g / eq, and even more preferably 80 to 700 g / eq.

[0040] Examples of epoxy resins include bisphenol A type epoxy resins having an average molecular weight of about 400 or less; branched polyfunctional bisphenol A type epoxy resins such as p-glycidyloxyphenyldimethyltrisbisphenol A diglycidyl ether; bisphenol F type epoxy resins; phenol novolac type epoxy resins having an average molecular weight of about 570 or less; and alicyclic epoxy resins such as vinyl(3,4-cyclohexene) dioxide, (3,4-epoxycyclohexyl)methyl 3,4-epoxycyclohexylcarboxylate, bis(3,4-epoxy-6-methylcyclohexylmethyl adipate), and 2-(3,4-epoxycyclohexyl)5,1-spiro(3,4-epoxycyclohexyl)-m-dioxane. Resins include biphenyl-type epoxy resins such as 3,3',5,5'-tetramethyl-4,4'-diglycidyloxybiphenyl; glycidyl ester-type epoxy resins such as diglycidyl hexahydrophthalate, diglycidyl 3-methylhexahydrophthalate, and diglycidyl hexahydroterephthalate; glycidyl amine-type epoxy resins such as diglycidyl aniline, diglycidyl toluidine, triglycidyl-p-aminophenol, tetraglycidyl-m-xylylenediamine, and tetraglycidyl bis(aminomethyl)cyclohexane; and hydantoin-type epoxy resins such as 1,3-diglycidyl-5-methyl-5-ethylhydantoin; and naphthalene ring-containing epoxy resins. Other examples include epoxy resins having a silicone skeleton such as 1,3-bis(3-glycidoxypropyl)-1,1,3,3-tetramethyldisiloxane; diepoxide compounds such as (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, and cyclohexanedimethanol diglycidyl ether; and triepoxide compounds such as trimethylolpropane triglycidyl ether and glycerin triglycidyl ether.In addition, solid epoxy resins such as bisphenol A epoxy resins, bisphenol F epoxy resins, bisphenol S epoxy resins, naphthalene epoxy resins, phenol novolac epoxy resins, phenol aralkyl epoxy resins, cresol novolac epoxy resins, biphenyl epoxy resins, biphenyl novolac epoxy resins, biphenyl aralkyl epoxy resins, triphenylmethane epoxy resins, and dicyclopentadiene epoxy resins may be used in combination in an amount such that the entire composition (B) is liquid. Bisphenol A epoxy resins and bisphenol F epoxy resins are more preferred examples of the epoxy resins.

[0041] As the (B) thermosetting resin, a phenolic resin can be used in combination with an epoxy resin. Phenolic resin is a general term for thermosetting resins that can be crosslinked into a network via phenolic hydroxyl groups present in the compound, and includes prepolymer compounds prior to crosslinking. Phenolic resins are epoxy resin curing agents that react with the epoxy groups of epoxy resins and contribute to imparting wettability to solder. Examples of phenolic resins include phenol novolac resins and their alkylated or allylated products, cresol novolac resins, phenol aralkyl (including phenylene and biphenylene skeleton) resins, naphthol aralkyl resins, triphenolmethane resins, and dicyclopentadiene-type phenolic resins. Among these, cresol novolac resins and phenol aralkyl resins are preferred because they can enhance solder wettability.

[0042] As the (B) thermosetting resin, a phenoxy resin may be used in combination with an epoxy resin. The phenoxy resin refers to a polyhydroxy polyether synthesized by a direct reaction between a dihydric phenol compound and epichlorohydrin, or by an addition polymerization reaction between a diglycidyl ether of a dihydric phenol compound and a dihydric phenol compound. As the phenoxy resin, a bisphenol A-type phenoxy resin can be used, and is available as a commercially available product (e.g., bisphenol A-type phenoxy resin 4250 (manufactured by Mitsubishi Chemical), bisphenol A-type phenoxy resin Fx316 (manufactured by Nippon Steel & Sumitomo Metal), bisphenol A-type phenoxy resin YP50 (manufactured by Nippon Steel & Sumitomo Metal), etc.).

[0043] In the conductive paste for external electrodes of the present invention, when component (B) contains an epoxy resin, 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.

[0044] In particular, epoxy resins that are cured by a phenolic resin are preferred. The phenolic resin may be a phenolic resin initial condensate that is commonly used as a curing agent for epoxy resins, and may be a resol type or a novolac type. However, in order to obtain excellent heat cycle resistance, it is preferred that 50 mass % or more of the phenolic resin be an alkyl resol type, alkyl novolac type, or aralkyl novolac type phenolic resin, a xylene resin, or an allyl phenol resin. The general formula:

[0045]

[0046] Also preferred are aralkyl novolac phenolic resins, which are phenol-p-xylylene glycol dimethyl ether polycondensates represented by the formula: (wherein n is 0 to 300). Furthermore, in the case of alkyl resole phenolic resins, it is preferable that the average molecular weight is 2,000 or more in order to obtain excellent printability. In these alkyl resole or alkyl novolac phenolic resins, the alkyl group may have 1 to 18 carbon atoms, and preferred are those having 2 to 10 carbon atoms, such as ethyl, propyl, butyl, pentyl, hexyl, octyl, nonyl, and decyl.

[0047] Among these, a combination of an epoxy resin with an aralkyl novolac phenolic resin, a resole phenolic resin, a xylene resin, or an allyl phenolic resin is preferred because it provides excellent adhesion and heat resistance. When a combination of an epoxy resin with an aralkyl novolac phenolic resin, a resole phenolic resin, a xylene resin, or an allyl phenolic resin is used, the mass ratio of the epoxy resin to the phenolic resin is preferably in the range of 5:1 to 1:5, and more preferably 4:1 to 1:2. Polyimide resins and the like are also effective from the viewpoint of heat resistance.

[0048] The content of the (B) thermosetting resin in the conductive paste of the present invention is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and particularly preferably 5 parts by mass or more, per 100 parts by mass of the (A) conductive particles. Furthermore, the content is preferably 25 parts by mass or less, more preferably 20 parts by mass or less, and particularly preferably 15 parts by mass or less, per 100 parts by mass of the (A) conductive particles. By setting the content of the (B) thermosetting resin within this range, sufficient adhesion to the copper undercoat and solder layer can be achieved without impairing the conductivity originally required of the conductive paste.

[0049] (C) Rubber Particles The conductive paste of the present invention contains rubber particles whose main chain skeleton contains carbon-carbon bonds and whose average particle size is 1 μm or less. The rubber particles are a component that contributes to stress relaxation of external electrodes. Furthermore, the conductive paste of the present invention can improve adhesion to a copper substrate by containing rubber particles whose main chain skeleton contains carbon-carbon bonds and whose average particle size is 1 μm or less. While the reason for this improved adhesion is unclear, it is presumed that the inclusion of rubber particles whose average particle size is 1 μm or less allows the rubber particles to be uniformly dispersed in the conductive paste, thereby enhancing adhesion to the copper substrate. Furthermore, it is presumed that the inclusion of carbon-carbon bonds in the main chain skeleton of the (C) rubber particles can also improve physical properties such as toughness. However, the present invention is not bound by these presumptions. The (C) rubber particles may contain rubbers other than those satisfying the above requirements as long as the effects of the present invention are not impaired. However, it is preferable that the conductive paste be composed solely of rubbers satisfying the above requirements.

[0050] The phrase "the main chain skeleton contains a carbon-carbon bond" means that when the molecules constituting the rubber particles are viewed as a chain skeleton, the chain skeleton contains a carbon-carbon bond. From the perspective of improving adhesion to copper substrates and toughness of coating films, it is preferable that 50% or more of the atoms constituting the chain skeleton are carbon atoms. Therefore, as long as the molecular chain is formed by linking carbon atoms and preferably has a high proportion of carbon atoms, the molecular skeleton may contain a functional group containing a heteroatom, such as urethane rubber or acrylic rubber. Furthermore, as long as the chain skeleton is based on a rubber having a carbon-carbon bond, a rubber at least partially halogenated may also be used. It has been discovered that the conductive paste of the present invention contains rubber particles having an average particle size of 1 μm or less and having a carbon-carbon bond in the main chain, thereby improving not only adhesion to copper substrates but also toughness of coating films compared to, for example, a conductive paste containing silicone rubber particles whose chain skeleton is mainly composed of silicon and oxygen bonds.

[0051] The rubber particles may be any organic compound whose main chain skeleton contains a carbon-carbon bond, such as hydrocarbon-derived rubbers like natural rubber, or rubbers whose skeleton contains a functional group containing a heteroatom, such as acrylic rubber and urethane rubber. It is preferable to use at least one rubber selected from the group consisting of diene-based rubbers, (meth)acrylate-based rubbers, urethane-based rubbers, isoprene-based rubbers, fluorine-based rubbers, and chloroprene-based rubbers. These may be used alone or in combination of two or more.

[0052] Examples of diene rubbers include hydrocarbon-derived rubbers such as butadiene rubber, styrene-butadiene rubber, and ethylene-propylene-diene terpolymer rubber, as well as copolymers of dienes and heteroatom-containing compounds such as nitrile rubber. Hydrogenated diene rubbers in which at least a portion of the diene is hydrogenated can also be used. Among diene rubbers, butadiene rubber using 1,3-butadiene and / or butadiene-styrene rubber, which is a copolymer of 1,3-butadiene and styrene, are preferred, with butadiene rubber being more preferred, from the viewpoint of suppressing an increase in viscosity of the conductive paste.

[0053] Examples of the (meth)acrylate rubber include a copolymer of a (meth)acrylic acid ester and 2-chloroethyl vinyl ether, and a copolymer of a (meth)acrylic acid ester and acrylonitrile.

[0054] Examples of urethane rubbers include polyether urethane rubbers obtained by reacting polyether polyols such as polyethylene glycol, polytetramethylene glycol, and ethylene oxide adducts of bisphenol A with polyisocyanates, and polyester urethane rubbers obtained by reacting polyester polyols, which are reaction products of diols and dibasic acids, with polyisocyanates.

[0055] Examples of isoprene-based rubbers include natural rubber, polyisoprene rubber, and butyl rubber (a copolymer of isobutylene and isoprene).

[0056] Examples of the fluororubber include at least partially fluorinated hydrocarbon rubbers, as well as binary copolymers of vinylidene fluoride and hexafluoropropylene, binary copolymers of vinylidene fluoride and pentafluoropropylene, binary copolymers of vinylidene fluoride and chlorotrifluoroethylene, terpolymers of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene, terpolymers of vinylidene fluoride, pentafluoropropylene, and tetrafluoroethylene, and terpolymers of vinylidene fluoride, perfluoromethyl vinyl ether, and tetrafluoroethylene.

[0057] In addition to these rubbers, rubbers derived from hydrocarbons mainly composed of polyolefins, such as ethylene-propylene rubber, styrene rubber, etc., can also be used as the rubber particles. These rubber particles may also be subjected to a crosslinking treatment.

[0058] The average particle diameter of the rubber particles is preferably 1 μm or less, since this allows for both adhesive strength and coating film toughness. From the viewpoint of improving dispersibility in the conductive paste and coating film toughness, the average particle diameter of the rubber particles is more preferably 500 nm or less, even more preferably 400 nm or less, and particularly preferably 300 nm or less. The lower limit of the average particle diameter is not particularly limited, but is 20 nm or more. In this specification, the average particle diameter of the rubber particles is the average primary particle diameter, and is a value obtained by image analysis after observation with a scanning electron microscope (SEM). The shape of the rubber particles can be spherical, plate-like, flake-like, rod-like, or other non-spherical shapes, but spherical shapes are preferred. Spherical rubber particles can improve dispersibility when used in a conductive paste and the flexibility of the coating film. In the present invention, "spherical" is not limited to a perfect sphere, but also includes shapes that are close to a sphere, such as an ellipsoid, and spheres with uneven surfaces. On the other hand, shapes such as plate-like, flake-like, and rod-like do not qualify as spherical. The shape of the rubber particles can be confirmed by observing them with a scanning electron microscope (SEM).

[0059] Rubber particles having a core-shell particle structure can be used. For example, by placing a highly dispersible rubber on the surface (shell) of a core particle with good physical properties such as toughness, modified rubber particles can be obtained that possess both properties, making it possible to design rubber particles that are more suitable for conductive pastes. The core-shell particle structure may be a simple two-layer structure, or may be a laminate of three or more layers.

[0060] When the rubber particles are core-shell type rubber particles, the type of rubber particles selected for each layer, the thickness ratio of each layer, the mass ratio, etc. are not particularly limited and any type and range can be designed, but it is preferable that the core part of the rubber particle is a rubber particle whose main chain skeleton contains a carbon-carbon bond. It is preferable to use a shell part that exhibits different properties from the core part.

[0061] When the (C) rubber particles are core-shell type rubber particles, the core portion corresponds to the rubber particles having the aforementioned main chain skeleton containing carbon-carbon bonds and an average particle size of 1 μm or less. By using the aforementioned rubber particles as the core portion, toughness can be imparted to the coating film and adhesion to the substrate can be improved. Furthermore, by using the aforementioned rubber particles as the core portion, the toughness of the coating film can be improved compared to conductive pastes containing silicone rubber particles.

[0062] When the (C) rubber particles are core-shell rubber particles, the shell portion may be formed of a polymer copolymerizable with the core portion. In this case, the structure has a core portion present inside and at least one shell portion covering a part of its surface. If the average particle size of the core portion is 1 μm or less, the average particle size of the rubber particles including the shell portion may be larger than 1 μm, but it is preferable that the average particle size of the rubber particles including the shell portion is 1 μm or less.

[0063] When the rubber particles are core-shell rubber particles, the shell portion preferably contains a polymer having an epoxy group-containing structural unit content of 10 parts by mass or more. Note that "a polymer having an epoxy group-containing structural unit content of 10 parts by mass or more" refers to a polymer in which the proportion of structural units derived from epoxy group-containing monomers in all structural units of the polymer is 10 parts by mass or more (i.e., a polymer in which the proportion of epoxy group-containing monomers is 10 parts by mass or more when the total mass of the raw material monomers is 100 parts by mass). Note that the content of epoxy group-containing structural units in the polymer is preferably 20 parts by mass or more, more preferably 25 parts by mass or more, and even more preferably 30 parts by mass or more. Note that the shell portion may consist solely of a polymer having an epoxy group-containing structural unit content of 10 parts by mass or more, or may contain such a polymer and other polymers.

[0064] The conductive paste contains core-shell rubber particles having a shell containing a polymer with an epoxy group-containing structural unit content of 10 parts by mass or more, thereby improving the toughness and adhesion of the coating film. While the reason for the improved toughness and adhesion is unclear, it is presumed that the affinity at the interface between the epoxy resin and the shell is enhanced when the polymer contained in the shell contains a certain amount of epoxy groups or more. However, the present invention is not bound by this presumption.

[0065] Examples of the monomer having an epoxy group include ether compounds such as allyl glycidyl ether, and ester compounds (particularly epoxy group-containing (meth)acrylic acid esters) such as glycidyl (meth)acrylate and glycidyl alkyl (meth)acrylate. These may be used alone or in combination of two or more.

[0066] From the viewpoint of keeping the viscosity of the conductive paste low and imparting toughness, the mass ratio of the core portion to the shell portion, expressed as core portion / shell portion (mass ratio of the monomers forming each polymer), is preferably in the range of 50 / 50 to 99 / 1, more preferably 60 / 40 to 95 / 5, and even more preferably 70 / 30 to 95 / 5.

[0067] The content of the (C) rubber particles in the conductive paste of the present invention is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, even more preferably 1.0 parts by mass or more, and particularly preferably 2.0 parts by mass or more, per 100 parts by mass of the (A) conductive particles. Furthermore, the content is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and particularly preferably 5 parts by mass or less, per 100 parts by mass of the (A) conductive particles. By setting the content within the above range, not only can the resistivity be reduced, but also adhesion can be improved, and the flexibility and toughness of the cured coating film can be improved. Furthermore, in the conductive paste for external electrodes of the present invention, from the viewpoint of providing sufficient conductivity, the content of the (C) rubber particles is preferably designed as a ratio of the total amount of the (C) rubber particles and the (B) thermosetting resin to the (A) conductive particles. Specifically, in terms of reducing the flexural modulus of the external electrode, the total amount of the (B) and (C) components is preferably 10 to 45 parts by mass per 100 parts by mass of the (A) conductive particles. It is more preferably 15 to 35 parts by mass, and even more preferably 25 to 35 parts by mass. By setting the mass ratio of (A) to (B) + (C) within the above range, not only can the resistivity be suppressed, but also flexibility and toughness can be imparted, and the TI can be reduced, thereby improving the coating shape and plating ease, which is preferable.

[0068] The mass ratio ((B):(C)) of the thermosetting resin (B) to the rubber particles (C) is preferably 90:10 to 45:55, and more preferably 85:15 to 70:30.

[0069] In addition to components (A) to (C), the conductive paste of the present invention may contain imidazoles such as 2-phenyl-4-methyl-5-hydroxymethylimidazole, curing catalysts such as dicyandiamide, coupling agents, thixotropic agents, and dispersants, as long as the effects of the present invention are not impaired. A thermoplastic resin may also be used in combination with the thermosetting resin. Examples of preferred thermoplastic resins include polysulfone, polyethersulfone, and maleimide resins.

[0070] From the viewpoint of ease of handling and application, the conductive paste of the present invention preferably has a viscosity measured with an HB-type viscometer at 25°C and 10 rpm of 60 Pa s or less, more preferably 40 Pa s or less, and even more preferably 20 Pa s or less. As long as a paste having a uniform composition can be obtained and has fluidity, there is no lower limit to the viscosity, but a viscosity of 5 Pa s or more is preferred.

[0071] Furthermore, the conductive paste of the present invention can be blended with an organic solvent to adjust the viscosity. Examples of organic solvents include 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 ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, and their corresponding propylene glycol derivatives; esters such as their corresponding acetate esters; and diesters such as the methyl esters and ethyl esters of dicarboxylic acids such as malonic acid and succinic acid. The amount of organic solvent used can be selected arbitrarily depending on the method of printing or applying the paste. For example, in the case of screen printing, an amount is preferably used such that the apparent viscosity of the paste at room temperature is 10 to 500 Pa·s, and more preferably 15 to 300 Pa·s.

[0072] The paste of the present invention can further contain known additives as needed. For example, dispersing agents such as aluminum chelate compounds such as diisopropoxy(ethylacetoacetato)aluminum; titanate esters such as isopropyltriisostearoyltitanate; aliphatic polycarboxylic acid esters; unsaturated fatty acid amine salts; surfactants such as sorbitan monooleate; or polymeric compounds such as polyesteramine salts and polyamides can be added. In addition, inorganic and organic pigments, silane coupling agents, leveling agents, thixotropic agents, antifoaming agents, etc. can also be added. Furthermore, a liquid rubber may be used in combination with the component (C).

[0073] The fluidity of the conductive paste can be evaluated by the thixotropic index (TI). From this viewpoint, the thixotropic index, which is the ratio of the viscosity at a rotation speed of 10 rpm to the viscosity at a rotation speed of 100 rpm measured at 25°C with an HB type viscometer, is preferably 7 or less, more preferably 5 or less, and even more preferably 3 or less. The lower limit of TI is not particularly limited, but is 1 or more. By keeping TI within the above range, the coating shape and plating property can be improved. The TI of the conductive paste can be calculated by the following formula: TI=η １ / η １０ (In the formula, η １ is the viscosity measured using a rotational viscometer at a temperature of 25°C and a rotation speed of 10 rpm, and η １０ is η except that the rotation speed is 100 rpm. １ (The viscosity is measured under the same conditions as in Example 1.) When TI is within the above range, the conductive paste can be smoothly discharged from the application means. Furthermore, in the manufacturing process of a multilayer ceramic capacitor, it takes a certain amount of time from applying the conductive paste to the multilayer ceramic chip until it is hardened by a process such as baking, and since the external electrodes are not applied in a flat shape, if the conductive paste has high fluidity, it may naturally spread to some extent between application and the baking process. However, when TI is within the above range, manufacturing can be performed while maintaining the original dimensions.

[0074] According to the above definition of TI, when the TI of a conductive paste is 1 or less, the viscosity of the conductive paste under a relatively high shear stress is the same as or higher than the viscosity of the conductive paste under a relatively low shear stress. However, since the viscosity of a conductive paste varies depending on the measurement conditions, the behavior of the conductive paste under actual compression molding conditions may not match the behavior predicted from the TI defined above.

[0075] The conductive paste of the present invention 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 preparation temperature is not particularly limited, but the paste can be prepared at, for example, 10 to 40°C.

[0076] The conductive paste of the present invention can be used to form a second conductor layer of an external electrode of a multilayer ceramic electronic component, which has a first conductor layer connected to an internal electrode layer and a second conductor layer laminated on the first conductor layer. By using the conductive paste of the present invention as the second conductor layer, an external electrode composed of multiple layers can be formed. The formation method is not particularly limited, and known methods can be used. For example, the paste of the present invention can be printed or applied onto the first conductor layer of the external electrode of a multilayer ceramic electronic component, optionally dried, and then heated and cured to form the second conductor layer.

[0077] The first conductor layer connected to the internal electrode layer may be formed, for example, by applying an electrode paste containing, for example, silver as a main component and glass frit to the internal electrode contact surface of the multilayer ceramic composite, optionally drying the paste, and then firing the paste. Methods for printing, applying, drying, and firing the electrode paste may be any method known to those skilled in the art.

[0078] The coating thickness in the printing / coating step is usually 10 to 200 μm, preferably 20 to 100 μm. The drying step is mainly carried out when an organic solvent is used, and can be carried out at room temperature or by heating (for example, heating at 80 to 160°C). The curing step can usually be carried out at 150 to 250°C. The curing temperature is preferably 150°C or higher, more preferably 180°C or higher. Furthermore, in order to eliminate the adverse effects of heat on the (C) rubber particles, the curing temperature is preferably 250°C or lower, more preferably 220°C or lower.

[0079] The curing time can be changed by changing the curing temperature, etc., but from the viewpoint of workability, 1 to 60 minutes is preferable. For example, when the resin in the paste is an epoxy resin using a phenolic resin as a curing agent, curing is carried out at 150 to 250°C for 10 to 60 minutes, and the second conductor layer constituting the external electrode can be formed.

[0080] The conductive paste of the present invention has flexibility when cured and has excellent stress relaxation capability against physical external forces applied to multilayer ceramic electronic components. The flexibility is evaluated based on the flexural modulus, and the conductive paste of the present invention preferably has a flexural modulus of 3 GPa to 15 GPa, more preferably 4 GPa to 12 GPa, and even more preferably 5 GPa to 10 GPa when dried at 120°C for 60 minutes and then cured in an air dryer at 180°C for 30 minutes.

[0081] A multilayer ceramic electronic component having external electrodes each having a first conductor layer and a second conductor layer formed using the paste of the present invention can suppress a decrease in capacitance after a bending test to 10% or less. The bending test is performed, for example, by supporting the substrate at two points of 90 mm and applying pressure to the center at a displacement rate of 1 mm / sec, thereby bending the substrate by 10 mm.

[0082] The conductive paste of the present invention also exhibits high adhesion to the first conductor layer that constitutes the external electrode and is in contact with the first conductor layer. The metal typically used for the first conductor layer is copper, and the conductive paste of the present invention has an adhesive strength to a copper substrate of 1.0 kN / cm when dried at 120°C for 60 minutes and then cured in an air drier at 180°C for 30 minutes. ２It is preferable that the strength is 1.5 kN / cm or more. ２ More preferably, it is 2.0 kN / cm or more. ２ More preferably, it is 3.0 kN / cm or more. ２ The adhesive strength is measured based on the test method in the examples described below, and when a force that releases adhesion is applied, it is preferable that the adhesive layer breaks down inside (cohesive failure) rather than at the bonding interface with the adhesive layer (interfacial failure).

[0083] The external electrodes thus formed may be plated with nickel, tin, or the like, if necessary, to further increase the adhesive strength when soldered onto a circuit board or the like.

[0084] Examples of multilayer ceramic electronic components having external electrodes formed using the conductive paste of the present invention include capacitors, capacitor arrays, thermistors, varistors, inductors, and LC, CR, LR and LCR composite components.

[0085] 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.

[0086] [Preparation of Conductive Paste] Conductive pastes of Examples and Comparative Examples were prepared by blending the components in Table 1 (numbers in the table are parts by mass unless otherwise specified).

[0087] Conductive particles (component (A)) In the examples and comparative examples, the following were used as component (A): (A1) Flake silver powder (AGC B4, manufactured by Fukuda Metal Foil and Powder Co., Ltd.) average particle size 7.0 μm (A2) Spherical silver powder (HP 15, manufactured by Mitsui Mining and Smelting Co., Ltd.) average particle size 2.0 μm

[0088] Thermosetting Resin (Component (B)) In the Examples and Comparative Examples, the compounds used as component (B) are as follows: (B1) Epoxy resin (ADEKA RESIN EP4901E; epoxy equivalent 170 g / eq) liquid bisphenol F type epoxy resin (B2) Phenolic resin (Gunei Chemical Industry Co., Ltd. PSM4324; epoxy equivalent 105 g / eq) novolac type phenolic resin

[0089] Rubber Component (Component (C)) In the Examples and Comparative Examples, the compounds used as component (C) are as follows: (C1) Butadiene rubber particles (core-shell particles having a core containing butadiene rubber and a shell formed of a polymer of glycidyl methacrylate (10 parts by mass) and methyl methacrylate (90 parts by mass), with an average primary particle size of 100 to 200 nm). These core-shell rubber particles were used after being dispersed in a bisphenol A epoxy resin. (C2) Butadiene rubber particles (core-shell particles having a core containing butadiene rubber and a shell formed of a polymer of glycidyl methacrylate and methyl methacrylate, with an average primary particle size of 100 to 200 nm). These core-shell rubber particles were used after being dispersed in a bisphenol F epoxy resin. (C3) Acrylic rubber particles (core-shell particles having a core containing butyl acrylate and a shell which is a copolymer of methyl methacrylate and styrene, and an average primary particle size of 100 to 200 nm) (C'4) Liquid rubber (CTBN1300 manufactured by Hycar) (C'5) Silicone rubber particles, average particle size 3.0 μm (KMP-605M manufactured by Shin-Etsu Chemical Co., Ltd.) (C'6) Silicone rubber particles (core-shell particles having a core containing silicone rubber and a shell which is a polymer of glycidyl methacrylate and methyl methacrylate, and an average primary particle size of 100 to 200 nm). Note that these core-shell type rubber particles were dispersed in bisphenol F type epoxy resin and used.

[0090] In addition to the above three components, the following optional components were used: Curing catalyst: 2P 4MHZ PW manufactured by Shikoku Chemical Industry Co., Ltd., EH-3842 manufactured by ADEKA Corporation Solvent: Ethylene glycol monophenyl ether (Hisolve EPH manufactured by Toho Chemical Industry Co., Ltd.), Diethylene glycol monoethyl ether (EC manufactured by Taishin Chemical Co., Ltd.)

[0091] In the examples and comparative examples, the properties of the conductive paste were measured as follows.

[0092] (Viscosity) The viscosity of the evaluation sample immediately after preparation was measured using an HB type viscometer (manufactured by Brookfield) (SC4-14 spindle) at a temperature of 25° C. and 10 rpm.

[0093] (Thixotropic Index Value TI) The ratio of viscosity at a rotation speed of 10 rpm to viscosity at a rotation speed of 100 rpm measured at 25° C. using an HB type viscometer was calculated.

[0094] (Specific Resistivity Value) For the conductive pastes of the Examples and Comparative Examples, a zigzag pattern of 71 mm in length, 1 mm in width, and 20 μm in thickness was printed on an alumina substrate of 20 mm in width, 20 mm in length, and 1 mm in thickness using a 250-mesh stainless steel screen. The pattern was dried at 120°C for 60 minutes and then cured in air at 180°C for 30 minutes to form an external electrode. The thickness of the zigzag pattern was determined by averaging the values ​​at six points intersecting the pattern using a Tokyo Seimitsu surface roughness and shape measuring instrument (product name: Surfcom 1400). After curing, the specific resistance was measured using an LCR meter using a four-terminal method.

[0095] (Adhesion strength) 1: Preparation of substrate Copper was printed as an underlayer on an alumina substrate measuring 20 mm in width, 20 mm in length, and 1 mm in thickness using a 250-mesh stainless steel screen so that the printed layer would be 20 mm in width, 20 mm in length, and approximately 20 μm thick after firing. After drying at 150° C. for 10 minutes, the printed layer was fired at 900° C. for 60 minutes in a nitrogen atmosphere to form a fired copper underlayer on the alumina substrate.

[0096] 2: Measurement of Adhesion Strength For the conductive pastes of the Examples and Comparative Examples, a pattern was printed on the alumina substrate on which the fired copper underlayer was formed using a 250-mesh stainless steel screen, with a 5x5 pattern of 1.5 mm width, 1.5 mm length, and a thickness of approximately 25 μm after curing. Ten 3216-size alumina chips were randomly placed on the pattern. After drying at 120°C for 60 minutes, the chips were cured in air at 180°C for 30 minutes to form test pieces. After curing, the bond strength (shear strength) between the alumina chips and the fired copper underlayer was measured using an Aiko Engineering benchtop strength tester (model number: 1605VC) at a displacement rate of 12 mm / min. The adhesive strength was 3.0 kN / cm. ２ or more, 3.0 kN / cm ２Less than 1.0 kN / cm ２ or more, 1.0 kN / cm ２ The failure mode was evaluated by visual inspection of the adhesive surface when the alumina chip was peeled off, to determine whether cohesive failure or interfacial failure had occurred.

[0097] (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. Three test pieces measuring 40 x 10 x 0.13 mm were then peeled off from the substrate to prepare three test pieces. A two-point support, one-point load bending test was performed using a Shimadzu autograph at a displacement rate of 1 mm / min, and the flexural modulus was calculated from the stress-strain curve.

[0098] (Toughness) Whether toughness was imparted was judged by whether three of the test pieces broke after one minute had passed at a displacement rate of 1 mm / min after exceeding the strain point (yield point) at which the maximum stress was calculated from the stress-strain curve (S-S curve) calculated by measuring the flexural modulus. If none of the three test pieces broke after one minute had passed at a displacement rate of 1 mm / min after exceeding the yield point, it was rated as "no break." If one or two of the three test pieces did not break after one minute had passed at a displacement rate of 1 mm / min after exceeding the yield point, it was rated as "partial break." If all three test pieces broke before exceeding the yield point, it was rated as "fracture." Evaluation was made on a three-point scale: break, partial break, or no break.

[0099]

[0100] Table 1 shows that the conductive paste of the present invention, due to the inclusion of specific rubber particles, has a good flexural modulus, high toughness, and conductivity required for an external electrode, while also having high adhesion to copper. Furthermore, Comparative Example 1, which used only liquid rubber as component (C'4), had low adhesion strength to copper and a high resistance value, resulting in problems with its effectiveness as a conductive paste. Furthermore, Comparative Examples 3 and 4, which used silicone rubber particles not primarily composed of carbon as component (C'5), did not have sufficient adhesive strength. It was also clear that the cured products of these comparative examples, including those without rubber particles, lacked toughness and could not serve the purpose of being used as the second conductor layer of an external electrode (Comparative Examples 1 to 4).

[0101] The conductive paste of the present invention has conductivity comparable to that of conventional conductive pastes, has properties that provide flexibility and toughness to external electrodes, and is a material that has high adhesion to copper, making it suitable for use in electronic components such as external electrodes of multilayer ceramic capacitors.

[0102] REFERENCE SIGNS LIST 1 Multilayer ceramic capacitor 2 Ceramic dielectric 3 Internal electrode layer 4 External electrode layer 5 Plated layer 6 Soldering layer 7 Substrate 11 First conductor layer connected to internal electrode 12 Second conductor layer containing resin

Claims

1. A conductive paste comprising: (A) conductive particles; (B) a thermosetting resin; and (C) rubber particles, the rubber particles having a main chain skeleton containing carbon-carbon bonds and an average particle diameter of less than 1 μm.

2. The conductive paste according to claim 1, wherein the (C) rubber particles contain at least one type selected from the group consisting of diene-based rubber, (meth)acrylate-based rubber, urethane-based rubber, isoprene-based rubber, fluorine-based rubber, and chloroprene-based rubber.

3. The conductive paste according to claim 1 or 2, wherein the (C) rubber particles include core-shell type rubber particles.

4. The conductive paste according to claim 3, wherein the core of the core-shell type rubber particle is a rubber particle whose main chain skeleton contains a carbon-carbon bond.

5. The conductive paste according to claim 3 or 4, wherein the shell portion of the core-shell type rubber particles is a shell portion containing a polymer having a content of a structural unit having an epoxy group of 10 parts by mass or more.

6. The conductive paste according to any one of claims 1 to 5, wherein the amount of the rubber particles (C) is in the range of 0.1 to 10 parts by mass per 100 parts by mass of the component (A).

7. The conductive paste according to any one of claims 1 to 6, wherein the thermosetting resin (B) contains an epoxy resin and has an epoxy equivalent relative to the total mass of the thermosetting resin of 2000 g / eq or less.

8. The conductive paste according to any one of claims 1 to 7, wherein (A) contains spherical silver particles and flaky silver particles.

9. The conductive paste according to any one of claims 1 to 8, wherein the content of said component (B) is 3 to 25 parts by mass per 100 parts by mass of said component (A).

10. A conductive paste according to any one of claims 1 to 9, which has a flexural modulus of 3 GPa to 15 GPa when dried at 120°C for 60 minutes and then cured in an air blower at 180°C for 30 minutes.

11. After drying at 120°C for 60 minutes, the adhesive strength to the copper substrate is 1.0 kN / cm when cured in an air drier at 180°C for 30 minutes. ２ The conductive paste according to any one of claims 1 to 9.

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 a rotation speed of 10 rpm to viscosity at a rotation speed of 100 rpm, measured at 25°C using an HB type viscometer, of 7 or less.

13. A conductive paste according to any one of claims 1 to 12 for forming a second conductor layer of an external electrode having a first conductor layer connected to an internal electrode and a second conductor layer laminated on the first conductor layer.

14. A multilayer ceramic electronic component having external electrodes formed using the conductive paste according to claim 13.

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