JP2022133621A - Conductive paste and use thereof - Google Patents

Abstract

To provide a technique capable of improving the adhesiveness of a conductive film including a high heat resistant resin.SOLUTION: A technique provides a conductive paste including conductive particles, a resin component and an organic solvent. The conductive paste includes: a thermosetting polyimide resin used as the resin component; and a thermoplastic polyimide resin having 300°C or more of a thermal decomposition temperature (Td5) decreasing a weight of 5% and 30,000 or more of a weight average molecular weight. When setting the total amount of the thermoplastic polyimide resin and the thermosetting polyimide resin to 100 mass%, the thermosetting polyimide resin is included at a ratio of 5 mass% or more and 50 mass% or less.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a conductive paste and its use. More particularly, it relates to a conductive paste containing a thermoplastic polyimide resin and a thermosetting polyimide resin, and use of the paste.

Along with the miniaturization and high performance of electronic devices, there is a demand for miniaturization and high performance of ceramic electronic components mounted in electronic devices. In particular, in-vehicle electronic components are required to have both high heat resistance and high reliability in addition to miniaturization due to the increasing connectivity of vehicles.

A ceramic electronic component generally includes a component body and external electrodes formed on a pair of opposing end surfaces of the component body, and is mounted on a substrate by soldering the external electrodes to the substrate. Here, it is known that in vehicle-mounted electronic devices and the like, substrates on which ceramic electronic components are mounted may warp due to rapid temperature changes. At this time, since the coefficient of thermal expansion differs between the ceramic electronic component and the substrate, there is concern that the ceramic electronic component mounted on the base material will be subjected to thermal shock, and the brittle ceramic electronic component will be damaged due to cracks or the like. be. Therefore, a conductive film (resin electrode layer) containing a resin component is interposed between the external electrodes of the ceramic electronic component, and the thermal shock applied to the ceramic electronic component is mitigated by the resin electrode layer.

By the way, in order to form a conductive film containing a resin component as described above, for example, a conductive paste containing conductive particles, a resin component, and an organic solvent is used. The conductive film is typically produced by applying such a conductive paste onto a substrate to form a coating film of the conductive paste, and subjecting the substrate and the coating film to heat treatment. . As shown in Patent Documents 1 and 2, conventional conductive pastes of this type use thermosetting resins such as epoxy resins and urethane resins as resin components. However, these epoxy resins and urethane resins have a heat resistance temperature of about 150° C. when used continuously at high temperatures, and there is a problem that the resin component deteriorates when exposed to a temperature environment higher than this.

Moreover, in recent years, from the viewpoint of miniaturization and high performance of electronic devices, the spread of SiC semiconductors and GaN semiconductors has begun. Such semiconductors are expected to be used at high temperatures (for example, 180° C. or higher and 300° C. or lower). Therefore, a conductive paste containing a resin component as described above is also required to have high heat resistance so as to withstand use under such temperature conditions. Super engineering plastics (super engineering plastics) typified by, for example, polyimide resins, polytetrafluoroethylene and PEEK (polyetheretherketone) resins are known as resin components having high heat resistance. Among such super engineering plastics, research and development are vigorously carried out on the use of polyimide resins, which have particularly high heat resistance.

Japanese Patent No. 5854248 Japanese Patent No. 6767309

However, a conductive film produced using a conductive paste containing a resin component with high heat resistance as described above has a problem of insufficient adhesiveness to a substrate. Therefore, there is a demand for a technique for improving the adhesiveness of a conductive film containing a heat-resistant resin.

The present invention has been made in view of the above points, and an object of the present invention is to provide a technique for improving the adhesiveness of a conductive film containing a highly heat-resistant resin.

The present inventors have investigated a conductive paste containing a polyimide resin as a highly heat-resistant resin. Polyimide resins include thermoplastic polyimide resins and thermosetting polyimide resins, and as a result of intensive studies by the present inventors, the thermoplastic polyimide resin and the thermosetting polyimide resin are mixed in a specific range by mass ratio. The inventors have found that the adhesiveness of the conductive film can be improved by blending them so as to obtain a conductive paste, and have completed the present invention.

According to the technique disclosed here, a conductive paste containing conductive particles, a resin component, and an organic solvent is provided. This conductive paste has a thermosetting polyimide resin as the resin component, a thermal decomposition temperature (Td ₅ ) at which the weight is reduced by 5% is 300 ° C. or higher, and a weight average molecular weight is 30,000 or higher. a thermoplastic polyimide resin; Here, when the total of the thermoplastic polyimide resin and the thermosetting polyimide resin is 100% by mass, the thermosetting polyimide resin is contained at a rate of 5% by mass or more and 50% by mass or less.

According to this configuration, the conductive paste has high heat resistance (for example, about 180° C. or higher and 300° C. or lower) by containing the polyimide resin. In addition, by containing both a thermoplastic polyimide resin and a thermosetting polyimide resin as resin components and by adjusting the mass ratio of these resins within a specific range, the adhesiveness of the conductive film can be improved. In addition, the conductive paste having the above structure has rheological properties suitable for producing a coating film in a good state (for example, in a state in which the occurrence of peaks and the like is sufficiently suppressed).

A preferred embodiment of the conductive paste disclosed herein further contains a silicone resin as the resin component. With such a configuration, the adhesiveness of the conductive film can be further improved.

In another preferred embodiment, the resin component is contained at a ratio of 5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the conductive particles. According to such a configuration, the above effects can be realized more preferably.

By using the conductive paste disclosed herein, a heat-resistant conductive film with improved adhesiveness can be formed as described above. Such characteristics can be used to form a resin electrode layer included in an external electrode of a ceramic electronic component used in an environment where vibration occurs at high temperature, or a conductive resin for bonding, for example. can be demonstrated. In a preferred embodiment, the conductive paste disclosed herein is used in an environment of 180°C or higher and 300°C or lower. In another preferred aspect, the conductive paste disclosed herein is used to form resin electrode layers of external electrodes of ceramic electronic components.

From another point of view, the ceramic electronic component disclosed herein comprises a component body including a ceramic body and internal electrodes arranged in the ceramic body, and external electrodes provided on the surface of the component body. . At least a part of the external electrode includes a conductive film (typically a dry film) formed from the conductive paste. As a result, even in a high-temperature environment, it is possible to realize a highly reliable ceramic electronic component that is less likely to be peeled off or damaged by external vibrations.

FIG. 1 is a cross-sectional view schematically showing a laminated ceramic capacitor according to one embodiment.

Preferred embodiments of the present invention are described below. Matters other than those specifically mentioned in the present specification (for example, the configuration of the conductive paste) and necessary for the implementation of the present invention (for example, the method for preparing the conductive paste and the configuration of the ceramic electronic component) etc.) can be grasped as a design matter by a person skilled in the art based on the prior art in the field. The present invention can be implemented based on the contents disclosed in this specification and common general technical knowledge in the field.

In the following description, the conductive paste is applied to the base material, and the unfired unfired paste is heat-treated (dried) at a temperature below the thermal decomposition temperature of the resin component contained in the conductive paste (for example, at 300 ° C. or lower). A film-like body (dry film) is called a “conductive film”. In this specification, the term "conductive film" includes the meanings of "resin electrode film", "conductive resin for bonding", and the like. In addition, the term "weight average molecular weight" as used herein means a weight-based average molecular weight converted using a standard polystyrene calibration curve measured by gel chromatography (Gel Permeation Chromatography: GPC), or a nominal value of a manufacturer, etc. Say. In this specification, the notation of "A to B" indicating a numerical range means "A or more and B or less", and includes those exceeding A and below B.

<Conductive paste>
The conductive paste disclosed herein (hereinafter sometimes simply referred to as "paste") can form a conductive film containing conductive particles by drying. The conductive paste disclosed here contains conductive particles (A), a resin component (B), and an organic solvent (C). In this specification, the term "paste" includes compositions, inks, slurries, suspensions, and the like. Each component will be described in order below.

(A) Conductive Particles Conductive particles are typically prepared in powder form. The conductive particles are components that impart electrical conductivity to the conductive film obtained after drying. Conductive particles are typically metallic. As for the constituent material, one or two or more kinds can be appropriately selected from constituent materials of various metallic conductive particles that are generally used in this type of conductive paste, depending on the application and the like. Specific examples of the metals include aluminum (Al), nickel (Ni), copper (Cu), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), osmium (Os), Examples include simple metals such as iridium (Ir), platinum (Pt), and gold (Au), and alloys containing these metals. Examples of the alloy include silver-palladium (Ag-Pd) alloy, silver-platinum (Ag-Pt) alloy, silver-copper (Ag-Cu) alloy, copper-nickel (Cu-Ni) alloy, copper-manganese (Cu--Mn) alloy, copper--tin (Cu--Sn) alloy, copper--zinc (Cu--Zn) alloy, copper--aluminum (Cu--Al) alloy and the like.

Although it is not particularly limited, it is required to have high electrical conductivity without firing in applications such as forming resin electrode films of laminated ceramic electronic components, conductive resins for bonding, and the like. Examples of such highly conductive metal species include nickel, platinum, palladium, silver and copper.

From the viewpoints of handleability, cost, and electrical conductivity, the conductive particles are preferably composed of silver (Ag) particles. Here, the "silver particles" are not particularly limited in composition as long as they contain silver as a main component, and silver particles having desired conductivity and other physical properties can be used. Examples thereof include particles composed of silver (Ag) alone, particles composed of an alloy containing silver, and silver-coated particles having a coat layer containing silver on the surface of core particles. The silver-coated particles include core-shell particles having, on their surfaces, particles composed of silver alone or an alloy containing silver. Here, the "main component" means the largest component among the components that constitute the silver particles. Silver particles may contain unavoidable impurities, but the higher the purity (content), the higher the electrical conductivity, so it is preferable to use high-purity particles. The silver particles preferably have a purity of 95% or higher, more preferably 97% or higher, and particularly preferably 99% or higher. According to the technology disclosed herein, for example, it is possible to form a suitable conductive film by using silver particles with a purity of about 99.5% or more (for example, about 99.8% or more). be. From this point of view, in the technology disclosed herein, it is possible to form a suitable conductive film even by using silver particles with a purity of 99.99% or less (99.9% or less), for example. be.

The properties of the particles constituting the conductive particles, such as the size and shape of the particles, are within the minimum dimensions of the cross section of the desired conductive film (typically, the thickness and / or width of the conductive film). It is not particularly limited. The average particle size of the conductive particles (in the volume-based particle size distribution determined by a laser diffraction particle size distribution measuring device, the particle size corresponding to the cumulative 50% from the small particle size side; the same shall apply hereinafter) is approximately several tens of nm to It is preferably several tens of μm, for example, 0.1 μm to 10 μm.

Although not particularly limited, the average aspect ratio of the conductive particles may be about 1-100. The average aspect ratio is obtained by observing the conductive particles with an SEM, randomly selecting a plurality of (eg, 10 to 300) particles from the obtained observation image, and determining the aspect ratio based on the major axis and minor axis of each particle. It can be obtained by calculating (the ratio of the major axis and the minor axis) and obtaining the arithmetic mean value.

The shape of the conductive particles can be, for example, spherical or non-spherical. The non-spherical shape may be, for example, plate-like, scale-like, flake-like, irregular shape, and the like. From the viewpoint that the packing density of the conductive particles can be easily increased, the spherical conductive particles preferably have an aspect ratio of 1.2 or less, preferably 1.15 or less, for example 1.1 or less. can be done. Further, from the viewpoint that the contact area of the conductive particles can be easily increased, the non-spherical conductive particles have an aspect ratio of, for example, more than 1.2, preferably 1.3 or more, 1.5 or more, for example 1 .7 or more, more preferably 2 or more. From the viewpoint of synergizing the above effects, the conductive particles may be a mixture of spherical particles and non-spherical particles.

The content of the conductive particles is not particularly limited, but when the entire conductive paste is 100% by mass, it is generally 30% by mass or more, typically 40% to 95% by mass, for example 50% to 85% by mass. should be By satisfying the above range, a conductive film having high electrical conductivity and high density can be suitably realized. In addition, it is possible to improve the handleability of the paste and the workability during film formation.

(B) Resin component The resin component contains a polyimide resin. A polyimide resin is a polymer containing an imide bond in a repeating unit. A macromolecule is a molecule with a high molecular weight (e.g., weight average molecular weight of 1000 or more) and a unit (repeating unit have a structure composed of many (for example, 5 or more) repetitions of A polyimide resin typically includes a repeating unit structure represented by the following formula (1). Here, R and R' in the formula are independently any organic functional groups or oxygen atoms. The optional organic functional group is not particularly limited. The optional organic functional group may be, for example, free of Si. The conductive paste disclosed herein may not contain polyimide silicone resin as a resin component.

Polyimide resins are typically crystalline or non-crystalline polymers in which repeating units containing imide bonds constitute the main chain. From the viewpoint of forming an electrode with higher adhesion, it may be a crystalline polymer. Moreover, from the viewpoint of providing higher heat resistance, it may be a non-crystalline polymer. Furthermore, the polyimide resin, in a homopolymer state, preferably has a heat resistance temperature of 250° C. or higher, for example, a glass transition point of 200° C. or higher, preferably 210° C. or higher, more preferably 220° C. or higher. could be. In the polyimide resin, the ratio of the number of moles of repeating units containing an imide bond to the number of moles of all repeating units is usually 50% or more (for example, 50% to 95%), preferably 65% or more, more preferably is 75% or more, for example 85% or more. For example, all repeating units may be composed of units containing aliphatic or cycloaliphatic.

In the polyimide resin, the kind of repeating unit of imide bond is not particularly limited. Units containing an imide bond include, but are not limited to, s-ODPA, i-ODPA, a-ODPA, 2,2′-BAPB, 4,4′-BAPB, 1,5- NBOA, 2,3-NBOA, 3,3′-ODA, 4,4′-ODA, PMDA, BPDA, BPADA, BTDA, BAFL, 2,2-TFMB, 1,3,3-APB, 1,3, Examples include 4-APB and DDS. Any one of these may be used alone, or any combination of two or more thereof may be used.

The conductive paste disclosed here contains a thermoplastic polyimide resin (B1) and a thermosetting polyimide resin (B2) as resin components. The thermoplastic polyimide resin (B1) is a thermoplastic polyimide resin having a thermal decomposition temperature (Td ₅ ) at which the weight is reduced by 5% is 300° C. or higher. The thermal decomposition temperature (Td ₅ ) is, for example, 350° C. or higher, preferably 370° C. or higher, 400° C. or higher, or 430° C. or higher. From the viewpoint of the heat resistance of the conductive paste and the conductive film, the higher the thermal decomposition temperature (Td ₅ ), the better. Although the upper limit is not particularly limited, it can be, for example, 600° C. or lower, 550° C. or lower, or 500° C. or lower. The thermal decomposition temperature (Td ₅ ) can be determined, for example, by differential thermal analysis (DTA). By using a thermoplastic polyimide resin (B1) having a thermal decomposition temperature (Td ₅ ) of 300° C. or higher as the resin component (B) contained in the conductive film, the operating temperature is 180° C. or higher (about 200° C. or higher, and , about 350° C. or less, or about 300° C. or less).

Further, the thermoplastic polyimide resin (B1) has a weight average molecular weight of 30,000 or more. The weight average molecular weight of the thermoplastic polyimide resin (B1) can be one factor for adjusting the viscosity of the conductive paste, for example. From the viewpoint of producing a good conductive film, the weight average molecular weight of the thermoplastic polyimide resin (B1) is, for example, preferably 31,000 or more, preferably 32,000 or more, and may be 33,000 or more. . Although the upper limit is not particularly limited, it may be, for example, 1 million or less, 500,000 or less, such as 300,000 or less, 200,000 or less, or 100,000 or less.

The thermoplastic polyimide resin (B1) is typically a polyimide resin obtained by reacting a tetracarboxylic dianhydride and a diisocyanate in a reaction solution. Since the thermoplastic polyimide resin (B1) is soluble in organic solvents (eg, various organic solvents described in (C) organic solvent below), it can be handled relatively easily. By including the thermoplastic polyimide resin (B1), the formability of the coating film can be improved. The thermoplastic polyimide resin (B1) contained in the conductive paste may be one type or two or more types.

The type of thermosetting polyimide resin (B2) is not particularly limited, and various thermosetting polyimide resins can be used. The thermal decomposition temperature (Td ₅ ) (typically, the value measured after curing) is preferably as high as possible from the viewpoint of the heat resistance of the conductive paste and conductive film. For example, the Td of the thermoplastic polyimide resin (B1) ₅ may be the same as the preferred range. The weight average molecular weight of the thermosetting polyimide resin (B2) is not particularly limited, but is typically smaller than the weight average molecular weight of the thermoplastic polyimide resin (B1). The weight average molecular weight of the thermosetting polyimide resin (B2) may be, for example, 300 or more, 500 or more, or 700 or more. Although the upper limit is not particularly limited, it may be, for example, 5000 or less, may be 3000 or less, may be 2000 or less, or may be 1500 or less.

The thermosetting polyimide resin (B2) is typically obtained by first obtaining a polyamic acid using an acid anhydride and a diamine as starting materials, and then heating the polyamic acid to cause a dehydration condensation reaction. Polyimide resin. By containing the thermosetting polyimide resin (B2), adhesion can be improved.

In the conductive paste disclosed here, the mass ratio of the thermoplastic polyimide resin (B1) and the thermosetting polyimide resin (B2) is adjusted. In this conductive paste, when the total (B1 + B2) of the thermoplastic polyimide resin (B1) and the thermosetting polyimide resin (B2) is 100% by mass, the thermosetting polyimide resin (B2) is 5% by mass. It is contained at a ratio of 50% by mass or less. Adhesiveness can be improved by containing 5% by mass or more of the thermosetting polyimide resin (B2). Further, by setting the mass ratio of the thermosetting polyimide resin (B2) to 50% by mass or less, it is possible to realize preferable rheological properties for the conductive paste. The mass ratio of the thermosetting polyimide resin (B2) may be, for example, 7% by mass or more, may be 9% by mass or more, may be 15% by mass or more, may be 20% by mass or more, Alternatively, it may be 25% by mass or more. The mass proportion may be 45 mass % or less, may be 40 mass % or less, may be 35 mass % or less, or may be 30 mass % or less. From the viewpoint of realizing the effect of the technique disclosed here, it is particularly preferable to set the above mass ratio to 7% by mass or more and 30% by mass or less.

Although the mechanism by which the effects of the technology disclosed herein are realized is not particularly limited, the present inventors' views are as follows. The thermoplastic polyimide resin (B1) can reduce the viscosity ratio of the conductive paste and improve the formability of the coating film. However, since the thermoplastic polyimide resin (B1) does not react with the substrate, the adhesion may be low. On the other hand, since the thermosetting polyimide resin (B2) has high reactivity, it can react with the substrate. Therefore, containing the thermosetting polyimide resin (B2) can contribute to improving the adhesiveness of the conductive film. However, the inclusion of the thermosetting polyimide resin (B2) may prevent the conductive paste from achieving suitable rheological properties (e.g., viscosity) for forming a coating film in good condition. According to the technology disclosed here, by blending the thermoplastic polyimide resin (B1) and the thermosetting polyimide resin (B2) in a well-balanced manner, while realizing the rheological properties preferable for the conductive paste, the conductive film Adhesion can be improved.

The conductive paste disclosed here may contain at least a thermoplastic polyimide resin (B1) and a thermosetting polyimide resin (B2) as the resin component (B). Other polyimide resins (B3) different from these may be included as the polyimide resin as long as the effects of the technology disclosed herein can be obtained. The type of polyimide resin (B3) is not particularly limited, and may be a thermoplastic polyimide resin or a thermosetting polyimide resin. The preferred range of Td ₅ of the polyimide resin (B3) is the same as the preferred range of Td ₅ of the polyimide resin (B1). The weight average molecular weight of the polyimide resin (B3) does not necessarily have to satisfy the above range. For example, a polyimide resin whose weight average molecular weight does not satisfy the above range may be used as the polyimide resin (B3).

When the conductive paste contains the polyimide resin (B3), from the viewpoint of realizing the effect of the technology disclosed herein, the total amount of the polyimide resin contained in the resin component (B) (i.e., B1 + B2 + B3) is 100 mass. %, the content of the polyimide resin (B3) is preferably 20% by mass or less, more preferably 10% by mass or less, still more preferably 5% by mass or less, and 0% by mass. The closer, the better.

The polyimide resin contained in the resin component (B) is selected from, for example, polyimide materials manufactured by JFE Chemical Co., Ltd., Kyocera Chemical Co., Ltd., Subic Co., Ltd., and PI Technical Research Institute, according to the desired application. It is possible to appropriately select and obtain one that satisfies the characteristics.

The conductive paste disclosed herein may further contain a silicone resin (B4) as an optional resin component. As the silicone resin (B4), among macromolecular organic compounds having a main skeleton formed by a siloxane bond (Si—O—Si) composed of silicon (Si) and oxygen (O), a macromolecular organic compound containing a branched chain is used. can be used. That is, among siloxane compounds called silicone oil, silicone rubber, and silicone resin, it may be silicone rubber and/or silicone resin, excluding linear silicone oil. Silicone rubber is an elastomer having a low degree of branching (degree of cross-linking) and having rubber elasticity at room temperature (for example, 25°C). Silicone resins have a high degree of branching (crosslinking) and a developed three-dimensional polymer structure. Among silicone rubber and silicone resin, it is more preferable to use silicone resin as the silicone resin (B4). The silicone resin (B4) may be solid or liquid at room temperature (eg, 25°C).

Examples of the silicone resin forming the main skeleton include polysiloxanes containing siloxane units represented by the general formula: HO[—Si(R) ₂ O—] _n H, R is hydrogen or any functional group; It may be a polyalkylsiloxane in which R is any alkyl group, or a polymer obtained by polymerizing siloxane units with a different silicon-containing monomer. Specific examples of the silicone resin (B4) include polydialkylsiloxanes such as polydimethylsiloxane, polydiethylsiloxane and polymethylethylsiloxane, polyalkylarylsiloxanes, poly(dimethylsiloxane-methylsiloxane), and the like. A particularly suitable polymer constituting the main skeleton can be, for example, polydimethylsiloxane. In addition, as the silicone resin (B4), a linear modified resin obtained by introducing other substituents such as a polyether group, an epoxy group, an amine group, a carboxyl group, an alkyl group, and a hydroxyl group into the side chain, terminal, or both of the main skeleton. It may be silicone.

Silicone resins are known to include addition-curable silicone resins and dehydration-condensation-curable silicone resins. Among these, in the case of a dehydration-condensation-curing silicone resin, there is a risk that water will be formed as a reaction byproduct and adversely affect the electrode film. Therefore, the silicone resin (B4) is more preferably an addition-curable silicone resin, although it is not necessarily limited to this.

Such a silicone resin can be obtained by appropriately selecting, for example, silicone resins or silicone rubbers manufactured by Shin-Etsu Chemical Co., Ltd. and Asahi Kasei Wacker Silicone Co., Ltd., which satisfy the above characteristics according to the desired application.

When the resin component (B) contains the silicone resin (B4), although not particularly limited, the mass ratio is, for example, 0.5 mass when the total of the resin component (B) is 100 mass%. %, may be 3% by mass or more, may be 5% by mass or more, may be 10% by mass or more, or may be 20% by mass or more. However, if the mass ratio of the silicone resin (B4) is too large, the adhesiveness of the conductive film tends to decrease and the rheological properties tend to deteriorate. Therefore, it is preferable to change the above mass ratio as appropriate. The mass ratio may be, for example, 70% by mass or less, or may be 65% by mass or less. From the viewpoint of better obtaining the effect of improving the adhesiveness of the conductive film and from the viewpoint of realizing rheological properties suitable for producing a coating film in good condition, the content is preferably 50% by mass or less, more preferably 50% by mass or less. It is 30% by mass or less, more preferably 20% by mass or less.

In addition, the larger the ratio of the (B) resin component to 100 parts by mass of the (A) conductive particles, the more external vibrations and thermal shocks applied to the conductive film can be buffered and reduced, which is preferable. . The ratio of the resin component is preferably 4 parts by mass or more, preferably 5 parts by mass or more, more preferably 8 parts by mass or more, or, for example, 10 parts by mass or more. However, if the ratio of the resin component is excessive, the resin component present between the conductive particles may become resistance, which is not preferable. The proportion of the resin component is, for example, preferably 30 parts by mass or less, preferably 25 parts by mass or less, and may be, for example, 22 parts by mass or less, or 20 parts by mass or less.

In addition, the conductive paste disclosed herein may contain other resin components as long as the above characteristics are not impaired. Examples of such resin components include one or two of various known resin components such as rubber-based resins, polyester-based resins, epoxy-based resins, urethane-based resins, polyether-based resins, polyamide-based resins, and fluorine-based resins. It can be more than However, among known resin components, acrylonitrile-butadiene rubber (NBR)-based resins and acrylic-based resins are not included because they do not have the effect of improving the adhesion resistance of polyimide resins, unlike the silicone resins described above. may From the viewpoint of differentiation from the conventional conductive resin paste, for example, the composition may not contain epoxy-based resin or urethane-based resin. When the conductive paste contains resin components other than the polyimide resin and the silicone resin, the total proportion of these other resin components is preferably 10% by mass or less (preferably 5% or less). .

(C) Organic Solvent As the organic solvent, any solvent capable of suitably dissolving the resin component can be used without particular limitation. From the viewpoint of workability during film formation, storage stability, etc., the main component of the organic solvent is a high-boiling organic solvent having a boiling point of about 200 ° C. or higher, for example, 200 to 300 ° C. (a component that accounts for 50% by volume or more.) should be Preferred examples of organic solvents include alcohol solvents having —OH groups such as terpineol, texanol, dihydroterpineol and benzyl alcohol; glycol solvents such as ethylene glycol and diethylene glycol; diethylene glycol monoethyl ether, butyl carbitol ( Glycol ether solvent such as diethylene glycol monobutyl ether), triethylene glycol dimethyl ether; isobornyl acetate, ethyl diglycol acetate, butyl glycol acetate, butyl diglycol acetate, butyl cellosolve acetate, butyl carbitol acetate (diethylene glycol monobutyl ether acetate) , γ-butyrolactone, methyl benzoate, etc., ester-based solvents having an ester bond group (R-C(=O)-OR'); ) and other aprotic polar solvents, mineral spirits, and the like. Among them, organic solvents such as NMP and γ-butyrolactone can be preferably used from the viewpoint of suitably dissolving the resin component. One of these may be used alone, or two or more may be appropriately mixed and used.

The content of the organic solvent (C) is not particularly limited. It is good that it is about mass %. By satisfying the above range, it is possible to impart appropriate fluidity to the paste and improve workability during film formation. Also, the self-leveling property of the paste can be enhanced to realize a conductive film with a smoother surface.

(D) Other components The paste disclosed herein may be composed only of the components (A) to (C) above, and in addition to the components (A) to (C) above, if necessary may contain various additional ingredients. As the additive component, as long as it does not significantly impair the effects of the technology disclosed herein, any known component that can be used in general conductive pastes can be appropriately used.

The additive components are roughly classified into inorganic additives (D1) and organic additives (D2). Examples of the inorganic additive (D1) include sintering aids, inorganic fillers, glass frit, and the like. The inorganic additive (D1) has an average particle size of about 10 nm to 10 μm, and from the viewpoint of keeping the arithmetic mean roughness Ra of the conductive film small, it is preferably 0.3 μm or less, for example. Examples of organic additives (D2) include leveling agents, antifoaming agents, thickeners, plasticizers, pH adjusters, stabilizers, antioxidants, preservatives, colorants (pigments, dyes, etc.), and the like. is mentioned. The organic additive (D2) may or may not have an acid value. The content of the additive component is not particularly limited, but when the entire conductive paste is 100% by mass, it may be approximately 20% by mass or less, typically 10% by mass or less, for example 5% by mass or less. .

Such a paste can be prepared by weighing the above-mentioned materials so as to have a predetermined content ratio (mass ratio) and stirring and mixing them homogeneously. Stirring and mixing of the materials can be performed using various conventionally known stirring and mixing devices such as roll mills, magnetic stirrers, planetary mixers and dispersers. Also, the paste can be applied to the substrate by, for example, a dipping method, a dispenser feeding method, a printing method such as screen printing, gravure printing, offset printing and inkjet printing, or a spray coating method. A dipping method, for example, is suitable for forming resin electrode layers of external electrodes of multilayer ceramic electronic components. In addition, for example, the dispenser supply method is suitable for bonding applications when mounting a multilayer ceramic electronic component on a substrate.

<Performance of paste>
(1) Heat resistance The conductive paste disclosed herein has improved heat resistance. The heat resistance of the conductive paste can be evaluated based on the results obtained by measuring the weight loss rate (%) of the sample using, for example, a commercially available thermogravimetry device. For example, TG-DTA/H manufactured by Rigaku Co., Ltd. can be used as the thermogravimetry device, although it is not particularly limited. Moreover, as the sample, a dry film of a conductive paste can be used. This dry film can be prepared, for example, as described in the Examples below. For example, the heat resistance of the conductive paste can be evaluated by measuring the weight loss rate (%) when a dried film of about 15 mg is held at 300° C. for 2 hours. It can be judged that the smaller the weight loss rate measured in this way (that is, the closer it is to 0%), the higher the heat resistance. For example, the weight reduction rate is preferably less than 40% (typically 0% or more), more preferably less than 30%.

(2) Rheological Properties The conductive paste disclosed herein has rheological properties suitable for forming a conductive film. As an index showing the rheological properties of the conductive paste disclosed herein, for example, the viscosity of the conductive paste is exemplified. As an example of a specific method for measuring the viscosity, a method using a rotational viscometer (Brookfield viscometer) can be mentioned as described in the examples below. In an environment of 25 ° C., the viscosity V1 (Pa s) of the conductive paste measured at a rotation speed of 1 rpm using a rotational viscometer, and the viscosity V2 (Pa s) of the conductive paste measured at a rotation speed of 100 rpm ) is preferably 26 or less, more preferably 18 or less, and even more preferably 9 or less. The conductive paste disclosed herein is prepared to achieve such rheological properties, and having such rheological properties improves workability during film formation. A conductive paste having rheological properties as described above is particularly suitable for forming a conductive film by a dipping method. When a conductive film is formed by a dipping method, if the rheological properties of the paste are not suitable, a flat conductive film may not be formed due to, for example, formation of bumps.

(3) Adhesiveness The conductive paste disclosed herein has improved adhesiveness between a conductive film formed using the conductive paste and a substrate (for example, a metal plate). The adhesiveness of the conductive film is evaluated by performing a tensile shear test according to JIS K6850: 1999 (testing method for tensile shear adhesive strength of rigid adherends), for example, as described in the examples below. be able to. The adhesive strength (shear strength) measured by the above test is preferably 4 N/mm ² or more, more preferably 5 N/mm ² or more, and even more preferably 6 N/mm ² or more. The adhesive strength (shear strength) is, for example, 15 N/mm ² or less. The conductive paste disclosed herein is prepared to achieve such adhesive strength and achieves suitable adhesion to the substrate.

<Application of paste>
According to the conductive paste disclosed herein, a conductive film having excellent heat resistance and adhesiveness can be formed on any base material. This conductive film is cured by drying to form a conductive film in an unfired state. Therefore, the conductive paste disclosed herein can be preferably used as a conductive paste or the like for forming a resin electrode layer or the like of a ceramic electronic component that is vulnerable to temperature changes such as firing. In addition, it can also be used to form a bonding conductive resin for adhesion instead of solder when mounting ceramic electronic components on a board.

In this specification, the term "ceramic electronic component" is a general term for electronic components having an amorphous ceramic substrate (glass-ceramic substrate) or a crystalline (that is, non-glass) ceramic substrate. . For example, chip inductors with ceramic substrates, high frequency filters, ceramic capacitors, low temperature co-fired ceramic substrates (LTCC substrates), high temperature co-fired ceramic substrates Ceramics Substrate: HTCC substrate) and the like are typical examples included in the term “ceramic electronic component” as used herein.

FIG. 1 is a cross-sectional view schematically showing the configuration of a multilayer ceramic capacitor (MLCC) as a ceramic electronic component 1. As shown in FIG. The ceramic electronic component 1 typically includes a component body 10 and external electrodes 30 formed on a pair of opposing end faces of the component body 10 .

In the component body 10 , a plurality of internal electrodes 20 are laminated with dielectric layers 12 interposed therebetween. Each dielectric layer 12 is composed of, for example, a laminated sintered body of ceramic green sheets containing a ceramic dielectric. In an actual MLCC, the bonding boundaries between the dielectric layers 12 are integrated to such an extent that they are not visible. Here, a part of the internal electrode 20 is exposed at the end faces (left and right ends in FIG. 1) of the component body 10 .

The external electrodes 30 are arranged on the outer surface of the component body 10 . The external electrodes 30 are connected to the wirings 3 of the substrate 2 via the soldering layers 4 . The external electrodes 30 are formed on each of a pair of opposing end faces (left and right ends in FIG. 1) of the component body 10 . The external electrode 30 has a first metal electrode layer 32 , a conductive film (resin electrode layer) 34 , a second metal electrode layer 36 and a third metal electrode layer 38 .

The first metal electrode layer 32 mainly contains copper (Cu), which is a base metal, and is physically and electrically connected to the internal electrodes 20 . The first metal electrode layer 32 is formed continuously on the pair of left and right end faces of the component body 10 and the outer surfaces of the four side faces connected thereto. The first metal electrode layer 32 is formed by applying a conductive paste containing Cu powder to the pair of end faces of the component body 10 and the outer surfaces of the four side faces connected thereto, followed by baking. The thickness of the first metal electrode layer 32 is, for example, 10 μm to 30 μm.

The conductive film 34 is a layer formed by drying and curing the conductive paste disclosed herein. The conductive film 34 is formed by applying the conductive paste disclosed here to the outer surfaces of the pair of end faces of the component body 10 and the four side faces connected thereto, leaving the peripheral edge of the first metal electrode layer 32. formed by drying. Here, the drying temperature may vary depending on the imide resin and silicone resin used, but is approximately 180° C. or higher and 300° C. or lower. The thickness of the conductive film 34 is, for example, 20 μm to 100 μm. This allows the conductive paste disclosed herein to be cured to form the conductive film 34 as part of the external electrode 30 .

The second metal electrode layer 36 contains Ni or a Ni alloy as its main component. The second metal electrode layer 36 is formed, for example, by Ni-plating the surface of the first conductive film 34 . The thickness of the second metal electrode layer 36 is, for example, 1 μm to 5 μm. The third metal electrode layer 38 contains Sn or Sn alloy as a main component. The third metal electrode layer 38 is formed by plating the surface of the second metal electrode layer 36 with Sn or Sn alloy. The thickness of the third metal electrode layer 38 is, for example, 1 μm to 5 μm.

As described above, the ceramic electronic component 1 can be manufactured. Here, the external electrodes 30 are electrically connected to the internal electrodes 20 exposed on both end surfaces of the component body 10 . As a result, the current sent from the outside to the internal electrode 20 through one of the external electrodes 30 can be stored in the MLCC and insulated without being sent to the other external electrode 30 as it is. Also, when a current is passed through the external load, the charges stored in the MLCC are sequentially sent to the external circuit through the external electrodes 30 . At this time, the presence of the MLCC makes it possible to stably supply charges to the external circuit even when the power supply voltage is unstable. Such an MLCC includes a conductive film 34 having excellent heat resistance and adhesiveness in the external electrode 30 . As a result, even if the electronic device on which the MLCC is mounted is exposed to a high-temperature environment such as a continuously running vehicle, and the substrate on which the MLCC is mounted is bent, the conductive film 34 will remain in the second state. It adheres to the metal electrode layer 36 with good adhesion, buffers such bending, and can stably maintain electrical connection with the component body 10 . Thereby, the ceramic electronic component 1 having high reliability even in a high temperature environment is provided. This conductive paste can also be used as a bonding paste when mounting the ceramic electronic component 1 (multilayer ceramic component, MLCC) on the substrate 2 .

Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

[Conductive paste]
Conductive pastes of Examples 1 to 18 were prepared by mixing conductive particles, a resin component, and an organic solvent according to the formulation shown in Table 1. As the conductive particles, flaky Ag powder (with a tap density of 3.1 g/cm ³ ) having an average particle size of 4.7 µm was commonly used in all the examples. As an organic solvent, γ-butyrolactone was commonly used. The amount of the organic solvent used in each example was adjusted according to the viscosity of the conductive paste. In addition, although not specifically shown, even if the types of conductive particles and organic solvent are changed, there is no significant difference in the tendencies of the conductivity, rheological properties, and adhesive properties of the conductive paste described later. is confirmed.

As resin components, the following four types of polyimide resins and a silicone resin were prepared. Note that Td ₅ of "polyimide resin 3" and "polyimide resin 4" is Td ₅ of the resin after curing.
"Polyimide resin 1": thermoplastic polyimide resin (Td ₅ : 460°C, Mw: 33,000)
"Polyimide resin 2": thermoplastic polyimide resin (Td ₅ : 450°C, Mw: 63,000)
"Polyimide resin 3": thermosetting polyimide resin (Td ₅ : 440°C, Mw: 950)
“Polyimide resin 4”: thermosetting polyimide resin (Td ₅ : 400° C., Mw: 1100)
"Silicone resin": addition curing silicone resin (Mw: 2500)

The "mass ratio ^*1 (mass%)" in Table 1 is the mass ratio of the thermosetting polyimide resin when the total of the thermoplastic polyimide resin and the thermosetting polyimide resin is 100% by mass. “Mass ratio ^*2 (% by mass)” is the mass ratio of the silicone resin contained in all the resin components. "Mass ratio ^*3 (parts by mass)" is the mass ratio of the resin component to 100 parts by mass of the conductive particles.

<Evaluation of adhesiveness>
The prepared conductive paste of each example was applied to the tips of two copper plates (2 cm×5 cm, without surface treatment) in an area of 2 cm×1 cm and a thickness of about 50 μm. The copper plate coated with the conductive paste was first dried at 130° C. for 15 minutes, then at 180° C. for 30 minutes, and further dried at 280° C. for 45 minutes to cure the conductive paste. Thus, a conductive film having a predetermined size was formed on the copper plate. Next, an epoxy adhesive is applied to the conductive film portions of the two copper plates on which the conductive films are formed, and the copper plate portions are oriented so that they are arranged on opposite sides of each other, and the conductive films are superimposed on each other. glued together. Thus, a test piece for evaluation of substrate adhesiveness of the conductive film of each example was prepared.

The copper plate portions at both ends of the test piece for evaluation are fixed to the upper and lower chucks of a tensile tester (manufactured by Shimadzu Corporation, universal testing machine Autograph), respectively, and JIS K6850: 1999 (tensile shear adhesion of rigid adherends strength test method). In the tensile shear test, a tensile load (shear force) perpendicular to the adhesive surface of the test piece for evaluation is applied at a predetermined load rate, and from the tensile shear load (breaking force) when the test piece for evaluation breaks, the adhesion Strength (shear strength) was measured.

Based on the above results, the adhesiveness was evaluated using the following indices. The results are shown in the "Adhesion" column of Table 1.
"A": Adhesive strength was 6 N/mm ² or more.
"◯": The adhesive strength was 5 N/mm ² or more and less than 6 N/mm ² .
"Δ": The adhesive strength was 4 N/mm ² or more and less than 5 N/mm ² .
"x": Adhesive strength was less than 4 N/ ^mm2 .
The adhesive strength of the epoxy adhesive used to prepare the test piece for evaluation was 15 N/mm ² or more in a tensile shear test by itself, and the epoxy adhesive part peeled off or broke before the conductive film. no. In Table 1, "◎" is "Excellent", "○" is "Good", "△" is "Acceptable", and "×" is "Poor". is shown. The same applies to other evaluation items.

<Evaluation of rheological properties>
The rheological properties of the conductive paste of each example were evaluated. Specifically, using a Brookfield viscometer (manufactured by Brookfield, DV-III ULTRA spindle SC4-14), for each conductive paste, a rotor is rotated in the conductive paste in an environment of 25 ° C. The viscosity V1 (mPa.s) when rotated at a rotation speed of 1 rpm and the viscosity V2 (mPa.s) when rotated at a rotation speed of 100 rpm were measured, and the ratio (V1/V2) was calculated.

Based on the above results, rheological properties were evaluated using the following indices. The results are shown in the "Rheology" column of Table 1.
"A": The ratio (V1/V2) was 1 or more and 9 or less.
"Good": The ratio (V1/V2) was greater than 9 and 18 or less.
"Δ": The ratio (V1/V2) was greater than 18 and 26 or less.
"x": the ratio (V1/V2) was greater than 26;

<Evaluation of conductivity>
Using the conductive paste of each example, a square pattern of 2 cm × 2 cm with a thickness of about 20 μm is applied (coated) to the surface of a glass substrate manufactured by Matsunami Glass Industry by screen printing, and the conductive paste is applied. A coating film consisting of Then, the substrate and the coating film are first heated at 130° C. for 15 minutes, then at 180° C. for 30 minutes, and further at 280° C. for 45 minutes to cure the resin, thereby forming the conductive film according to each example on the substrate. formed.

The film thickness of the conductive film formed as described above was measured with a surface roughness meter (Surfcom manufactured by Tokyo Seimitsu Co., Ltd.). Using the film thickness measured in this way, the volume resistivity of the conductive film is measured by the 4-probe method using a resistivity meter (model: Loresta GX MCP-T700) manufactured by Mitsubishi Chemical Analytech Co., Ltd. did.

Based on the above results, the conductivity was evaluated by the following index. The results are shown in the "Conductivity" column of Table 1.
“A”: The volume resistivity was 1×10 ⁻⁴ Ω·cm or less.
"◯": The volume resistivity was greater than 1×10 ⁻⁴ Ω·cm and 1×10 ⁻³ Ω·cm or less.
“Δ”: The volume resistivity was greater than 1×10 ⁻³ Ω·cm and 1×10 ⁻² Ω·cm or less.
“×”: The volume resistivity was greater than 1×10 ⁻² Ω·cm.

<Comprehensive evaluation>
Based on the respective evaluations of adhesiveness, rheological properties, and conductivity obtained as described above, the conductive paste of each example was comprehensively evaluated. The evaluation indicators are as follows, and the results are shown in the column of "Comprehensive Evaluation" in Table 1.
"⊚": At least one evaluation is "⊚" and all other evaluations are "◯".
“◯”: All evaluations are “◯”.
"△": There is at least one evaluation of "△" and there is no evaluation of "x".
“×”: Even one evaluation is “×”.

As shown in Table 1, the resin component includes a thermosetting polyimide resin and a thermoplastic polyimide resin having a Td ₅ of 300 ° C. or more and a Mw of 30,000 or more, and the thermoplastic polyimide When the total of the resin and the thermosetting polyimide resin is 100% by mass, the thermosetting polyimide resin is contained at a rate of 5% by mass or more and 50% by mass or less, using the conductive paste according to Examples 1 to 15. From the results obtained, according to the above configuration, the adhesiveness of the conductive film is improved, and the conductive paste has rheological properties suitable for producing a conductive film in good condition. , was confirmed. On the other hand, in Examples 16 and 17 using a conductive paste containing only a thermoplastic polyimide resin as a resin component, and in Example 18 in which the mass proportion of the thermosetting polyimide resin exceeds 50% by mass, the adhesion of the conductive film is improved. It was not possible to achieve both the effect and the impartation of desirable rheological properties to the conductive paste.

As described above, in the conductive paste containing conductive particles, a resin component, and an organic solvent, the resin component is a thermosetting polyimide resin, Td ₅ is 300 ° C. or higher, and Mw is 30,000 or higher. and a thermoplastic polyimide resin, and when the total of the thermoplastic polyimide resin and the thermosetting polyimide resin is 100% by mass, the thermosetting polyimide resin is 5% by mass or more and 50% by mass or less. By including it, the adhesiveness of the conductive film containing the highly heat-resistant resin can be improved.

Although the present invention has been described in detail, these are merely examples and are not intended to limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

REFERENCE SIGNS LIST 1 ceramic electronic component 2 substrate 3 wiring 4 soldering layer 10 component body 12 dielectric layer 20 internal electrode 30 external electrode 32 first metal electrode layer 34 conductive film 36 second metal electrode layer 38 third metal electrode layer

Claims (6)

A conductive paste containing conductive particles, a resin component, and an organic solvent,
As the resin component,
a thermosetting polyimide resin;
A thermoplastic polyimide resin having a thermal decomposition temperature (Td ₅ ) at which the weight is reduced by 5% is 300° C. or higher and a weight average molecular weight of 30,000 or higher;
contains
Here, when the total of the thermoplastic polyimide resin and the thermosetting polyimide resin is 100% by mass, the thermosetting polyimide resin is contained at a rate of 5% by mass or more and 50% by mass or less, conductive paste. The conductive paste according to claim 1, further comprising a silicone resin as the resin component. The conductive paste according to claim 1 or 2, wherein the resin component is contained at a ratio of 5 parts by mass or more and 20 parts by mass or less when the conductive particles are 100 parts by mass. The conductive paste according to any one of claims 1 to 3, which is used in an environment of 180°C or higher and 300°C or lower. The conductive paste according to any one of claims 1 to 4, which is used for forming external electrodes of ceramic electronic components. a component body including a ceramic body and internal electrodes disposed within the ceramic body;
an external electrode provided on the surface of the component body;
with
A laminated ceramic electronic component, wherein the external electrode includes at least a portion of the dry film of the conductive paste according to claim 5 .

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