Conductive paste and its use

Abstract

To provide a technique capable of more improving stability of a conductive paste containing a polyimide resin.SOLUTION: A conductive paste contains conductive particles, a polyimide resin, and an organic solvent. The organic solvent contains a first solvent as propylene carbonate, and a second solvent having a boiling point under atmospheric pressure of 200°C or higher and an octanol / water partition coefficient logKow of larger than 0. The organic solvent has a polarization term δP of a Hansen solubility parameter of 9 (J / cm3)1 / 2 or more and 15 (J / cm3)1 / 2 or less. The organic solvent is soluble in a polyimide resin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a conductive paste and its use. [Background technology]

[0002] As electronic devices become smaller and their performance improves, ceramic electronic components mounted on them are also required to be smaller and more powerful. In particular, electronic components for automobiles are required to be compact, highly heat-resistant, and highly reliable as vehicles become more connected.

[0003] A ceramic electronic component includes, for example, a component body and external electrodes formed on a pair of opposing end faces of the component body. The external electrodes are soldered to the substrate and mounted on the substrate. It is known that, in automotive electronic devices and the like, the substrate on which the ceramic electronic component is mounted can bend due to a sudden temperature change. Because the ceramic electronic component and the substrate have different thermal expansion coefficients, thermal shock occurs in the ceramic electronic component mounted on the substrate, raising concerns that the brittle ceramic electronic component may be damaged by cracks or other damage. Therefore, a conductive film containing a resin component (resin electrode layer) is interposed between the external electrodes of the ceramic electronic component, and this resin electrode layer buffers the thermal shock applied to the ceramic electronic component.

[0004] To form a conductive film containing the resin component, for example, a conductive paste containing conductive particles, a resin component, and an organic solvent is used. The conductive film is produced, for example, by applying the conductive paste to a substrate to form a coating film of the conductive paste, and then subjecting the substrate and coating film to a heat treatment. For example, Patent Document 1 discloses the production of a conductive substrate using a conductor layer-forming composition containing a dispersion medium and inorganic particles containing a metal oxide, and a conductive adhesive composition containing a binder and conductive particles having a number-average particle diameter of 1 nm to 3000 nm. This publication proposes applying the conductive adhesive composition to a conductive substrate and thermally curing the binder in the composition to form a conductive adhesive layer, and then applying a conductor layer-forming composition to the conductive adhesive layer to form a conductor layer.

[0005] Conventional conductive pastes of this type use thermosetting resins such as epoxy resins, polyester resins, and urethane resins as their resin components. However, these thermosetting resins have a heat resistance temperature of about 150°C when used continuously at high temperatures, and there is a problem that the resin components deteriorate when exposed to temperatures higher than this.

[0006] In recent years, SiC semiconductors and GaN semiconductors have begun to become popular in order to miniaturize and improve the performance of electronic devices. It is expected that such semiconductors will be used at high temperatures (e.g., 180°C or higher and 300°C or lower). Therefore, conductive pastes containing the above-mentioned resin components are also required to have high heat resistance so that they can withstand use under such temperature conditions. Known examples of resin components with high heat resistance include super engineering plastics (super engineering plastics), such as polyimide resin, polytetrafluoroethylene, and PEEK (polyether ether ketone) resin. Among these super engineering plastics, research and development is being actively conducted on the use of polyimide resin, which has particularly high heat resistance.

[0007] Regarding the use of polyimide resins, Patent Document 2 discloses a polyimide varnish containing polyimide and a mixed solvent containing two or more solvents. This polyimide varnish is characterized in that, in the Hansen Solubility Parameter (HSP) parameters represented by the dispersion term δd, dipole term δp, and hydrogen bond term δh, the dispersion term and hydrogen bond term of the polyimide and the mixed solvent satisfy a specific relationship. The publication also describes that the use of this polyimide varnish enables the efficient production of polyimide films that are highly transparent and have flex resistance. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 5971250 [Patent Document 2] Japanese Patent Publication No. 2020-111713 Summary of the Invention [Problem to be solved by the invention]

[0009] Incidentally, the present inventors have considered that there is still room for improvement in the stability of conductive pastes containing polyimide resins.

[0010] Therefore, the present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide a technique that can further improve the stability of a conductive paste containing a polyimide resin. [Means for solving the problem]

[0011] The conductive paste disclosed herein contains conductive particles, a polyimide resin, and an organic solvent. The organic solvent contains a first solvent, which is propylene carbonate, and a second solvent, which has a boiling point of 200°C or higher under atmospheric pressure and an octanol / water partition coefficient logKow greater than 0. The organic solvent has a Hansen solubility parameter with a polarization term ΔP of 9 (J / cm 3 ) 1 / 2 More than 15(J / cm3 ) 1 / 2 The organic solvent is soluble in the polyimide resin.

[0012] In the conductive paste having such a configuration, an organic solvent containing a first solvent and a second solvent is used. The first solvent is propylene carbonate, which can reduce the water absorption of the conductive paste. On the other hand, propylene carbonate is not a solvent that dissolves polyimide. The inclusion of the second solvent can impart polyimide resin solubility to the organic solvent containing propylene carbonate. Furthermore, the boiling point and octanol / water partition coefficient log Kow of the second solvent satisfy the above-mentioned ranges, which can reduce the volatility of the organic solvent and reduce its water absorption. Furthermore, the polarization term ΔP of the organic solvent satisfies the above-mentioned ranges, which can allow the organic solvent to be contained in the polyimide resin solubility sphere. This configuration can further improve the stability of the conductive paste.

[0013] In a preferred embodiment of this conductive paste, the polarization term ΔP of the Hansen solubility parameter of the second solvent is 4 (J / cm 3 ) 1 / 2 More than 8(J / cm 3 ) 1 / 2 The second solvent having a polarization term ΔP in this range is preferable for imparting polyimide resin solubility to the organic solvent.

[0014] In another preferred embodiment of the conductive paste, the second solvent is at least one organic solvent selected from the group consisting of alcohol-based solvents, ether-based solvents, and ester-based solvents. A second solvent composed of an alcohol-based solvent, an ether-based solvent, or an ester-based solvent is preferred for achieving the effects of the technology disclosed herein.

[0015] Preferably, the second solvent is at least one organic solvent selected from the group consisting of benzyl alcohol, propylene glycol phenyl ether, and butyl benzoate, which is more preferable for achieving the effects of the technology disclosed herein.

[0016] In another preferred embodiment of the conductive paste, the content of the first solvent is 30% to 70% by weight, where the total of the first solvent and the second solvent is 100% by weight. This configuration allows the organic solvent to have appropriate polyimide resin solubility, thereby achieving a better conductive paste stabilization effect.

[0017] In another preferred embodiment of the conductive paste, the conductive particles are silver particles. With this configuration, in addition to the effects of the technology disclosed herein, the conductivity of the conductive film can be further improved.

[0018] In another preferred embodiment of the conductive paste, the polyimide resin contains a thermoplastic polyimide resin having a thermal decomposition temperature (Td5) at which a 5% weight loss occurs of 300° C. or higher. This configuration not only achieves the effects of the technology disclosed herein, but also further improves the heat resistance of the conductive film.

[0019] In another preferred embodiment, the conductive paste is used to form external electrodes of ceramic electronic components. As described above, the conductive paste has excellent stability. Therefore, suitable electrical connections can be achieved in such applications.

[0020] From another perspective, a ceramic electronic component disclosed herein includes a component body including a ceramic matrix and internal electrodes disposed within the ceramic matrix, and external electrodes provided on the surface of the component body. The external electrodes at least partially include a conductive film (e.g., a dry film) formed from the conductive paste. As described above, this conductive paste exhibits excellent stability. This makes it possible to provide an electronic component with favorable electrical connections. [Brief explanation of the drawings]

[0021] [Figure 1]FIG. 1 is a cross-sectional view schematically showing a multilayer ceramic capacitor according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the technology disclosed herein will be described. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the technology disclosed herein can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and common general technical knowledge in the relevant field.

[0023] In the following description, the term "conductive film" refers to an unfired film (dried film) obtained by applying a conductive paste to a substrate and then heat-treating (drying) it at a temperature below the thermal decomposition temperature of the resin component contained in the conductive paste (for example, below 300°C). In this specification, "conductive film" encompasses terms such as "resin electrode film" and "conductive resin for bonding." Furthermore, in this specification, "weight-average molecular weight" refers to the weight-average molecular weight measured by gel permeation chromatography (GPC) and converted using a standard polystyrene calibration curve, or the nominal value provided by the manufacturer. In this specification, the notation "A to B" indicating a numerical range means "A or more but B or less," as well as "greater than A but less than B," "greater than A but B or less," and "A or more but less than B."

[0024] <Conductive paste> The conductive paste disclosed herein (hereinafter sometimes simply referred to as "paste") can become a conductive film containing conductive particles upon drying. The conductive paste disclosed herein can contain conductive particles (A), a resin component (B), and an organic solvent (C). In this specification, the term "paste" encompasses compositions, inks, slurries, suspensions, etc. Each component will be described below in order.

[0025] (A) Conductive particles The conductive particles are prepared, for example, in the form of a powder. The conductive particles are a component that imparts electrical conductivity to the conductive film obtained after drying. The conductive particles are, for example, made of a metal. One or more of the constituent materials can be appropriately selected from the constituent materials of various metallic conductive particles used in this type of conductive paste, depending on the intended use, etc. Examples of the metal include simple metals such as aluminum (Al), nickel (Ni), copper (Cu), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), osmium (Os), iridium (Ir), platinum (Pt), and gold (Au), as well as alloys containing at least one or more of these metals. Examples of the alloy include an alloy mainly composed of silver-palladium (Ag-Pd), an alloy mainly composed of silver-platinum (Ag-Pt), an alloy mainly composed of silver-copper (Ag-Cu), an alloy mainly composed of copper-nickel (Cu-Ni), an alloy mainly composed of copper-manganese (Cu-Mn), an alloy mainly composed of copper-tin (Cu-Sn), an alloy mainly composed of copper-zinc (Cu-Zn), an alloy mainly composed of copper-aluminum (Cu-Al), etc. In this specification, "mainly composed of X" means that X accounts for approximately 80% by weight or more of the total, for example, 85% by weight or more, preferably 90% by weight or more, and more preferably 95% by weight or more.

[0026] Although not particularly limited, high electrical conductivity without firing is required for applications such as forming resin electrode films for multilayer ceramic electronic components, conductive resins for bonding, etc. Metals with such high conductivity include nickel, platinum, palladium, silver, copper, etc.

[0027] From the viewpoints of handling, cost, and electrical conductivity, the conductive particles are preferably composed of silver (Ag) particles. Here, the term "silver particles" refers to any composition that contains silver as the main component, and silver particles with the desired conductivity and other physical properties can be used. Examples of silver particles include particles composed of simple silver (Ag), particles composed of a silver-containing alloy, and silver-coated particles with a silver-containing coating layer on the surface of a core particle. Silver-coated particles include core-shell particles whose surface is composed of simple silver or a silver-containing alloy. Here, "main component" refers to the largest component among the components that make up the silver particles. Silver particles may contain unavoidable impurities, but since higher purity (content) tends to result in higher conductivity, it is preferable to use silver particles with a high purity. The purity of the silver particles is preferably 95% or higher, more preferably 97% or higher, and particularly preferably 98% or higher.

[0028] The properties of the particles constituting the conductive particles, such as particle size and shape, are not particularly limited as long as they fit within the minimum dimensions of the cross section of the desired conductive film (e.g., the thickness and width of the conductive film). The average particle diameter of the conductive particles is generally several tens of nanometers to several tens of micrometers, for example, 0.1 micrometer to 10 micrometers. In this specification, the term "average particle diameter" refers to the particle diameter corresponding to the cumulative 50% from the smallest particle diameter side in a volume-based particle size distribution determined by a laser diffraction particle size distribution analyzer.

[0029] Although not particularly limited, the average aspect ratio of the conductive particles can be 1 to 100. The average aspect ratio can be obtained by observing the conductive particles with an SEM, randomly selecting a plurality of particles (for example, 10 to 300 particles) from the obtained observation image, calculating the aspect ratio (ratio of major axis to minor axis) based on the major axis and minor axis of each particle, and obtaining the arithmetic mean value.

[0030] The conductive particles may be spherical or non-spherical. Non-spherical shapes may include, for example, plate-like, scale-like, flake-like, and irregular shapes. From the viewpoint of easily increasing the packing density of the conductive particles, spherical conductive particles having an average aspect ratio of, for example, 1.2 or less, preferably 1.15 or less, e.g., 1.1 or less, are preferably used. Furthermore, from the viewpoint of easily increasing the contact area of ​​the conductive particles, non-spherical conductive particles having an average aspect ratio of, for example, more than 1.2, preferably 1.3 or more, 1.5 or more, e.g., 1.7 or more, and more preferably 2 or more, are preferably used. From the viewpoint of synergizing the above effects, the conductive particles may be a mixture of spherical and non-spherical particles.

[0031] The content of the conductive particles is not particularly limited, but is, for example, 30% by weight or more, preferably 40% by weight or more, more preferably 50% by weight or more, and even more preferably 60% by weight or more, when the entire conductive paste is taken as 100% by weight. When the entire conductive paste is taken as 100% by weight, the content of the conductive particles is, for example, 95% by weight or less, preferably 90% by weight or less, and even more preferably 85% by weight or less. By ensuring that the content of the conductive particles satisfies the above range, a conductive film with high electrical conductivity and density can be suitably realized. Furthermore, the handleability of the paste and the workability during film formation can be improved.

[0032] (B) Resin component The conductive paste disclosed herein contains a polyimide resin. A polyimide resin is a polymeric compound containing an imide bond in its repeating unit. The polymeric compound referred to here may be, for example, a compound having a weight-average molecular weight of 1,000 or more. The polymeric compound may have a structure constituted by a large number (for example, 5 or more) of repeating units (repeat units) that are substantially or conceptually obtained and have a weight-average molecular weight of 500 or less. The polyimide resin contains, for example, a repeating unit structure represented by the following formula (1). Here, R and R' in formula (1) are independently any organic functional group or an oxygen atom.

[0033] [ka]

[0034] The polyimide resin may be, for example, a crystalline or amorphous polymer compound in which a repeating unit containing an imide bond constitutes the main chain. From the viewpoint of forming an electrode with higher adhesiveness, the polyimide resin is preferably a crystalline polymer compound. Furthermore, from the viewpoint of providing higher heat resistance, the polyimide resin may be an amorphous polymer compound. Furthermore, the polyimide resin, in a homopolymer state, may have a heat resistance temperature of 250°C or higher. For example, the glass transition point may be 200°C or higher, preferably 210°C or higher, and more preferably 220°C or higher. Although not particularly limited, the glass transition point may be, for example, 350°C or lower, or even 300°C or lower. In the polyimide resin, the proportion 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 higher (e.g., 50% to 95%), preferably 65% ​​or higher, more preferably 75% or higher, for example, 85% or higher. For example, all repeating units may be composed of units containing aliphatic or cycloaliphatic moieties.

[0035] In the polyimide resin, the type of repeating unit having an imide bond is not particularly limited. Examples of 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, 1,3,4-APB, and DDS. These may be used alone or in any combination of two or more.

[0036] The conductive paste disclosed herein may contain a thermoplastic polyimide resin (B1) as the polyimide resin. The thermoplastic polyimide resin (B1) may be a thermoplastic polyimide resin having a thermal decomposition temperature (Td5) at which a 5% weight loss occurs of 300°C or higher. The thermal decomposition temperature (Td5) of the thermoplastic polyimide resin (B1) is, for example, 350°C or higher, preferably 370°C or higher, 400°C or higher, or even 430°C or higher. From the viewpoint of the heat resistance of the conductive paste and conductive film, the higher the thermal decomposition temperature (Td5) of the thermoplastic polyimide resin (B1), the better. The thermal decomposition temperature (Td5) of the thermoplastic polyimide resin (B1) is not particularly limited, but may be, for example, 600°C or lower, 550°C or lower, or 500°C or lower. The thermal decomposition temperature (Td5) can be determined, for example, by differential thermal analysis (DTA). By including a thermoplastic polyimide resin (B1) having a thermal decomposition temperature (Td5) of 300° C. or higher as the polyimide resin, the conductive paste can be suitably used at temperatures of, for example, 180° C. or higher, or 200° C. or higher, and 350° C. or lower, or 300° C. or lower. Furthermore, by including the thermoplastic polyimide resin (B1), the formability of the coating film can be improved.

[0037] The weight-average molecular weight of the thermoplastic polyimide resin (B1) may be, for example, 30,000 or more. The weight-average molecular weight of the thermoplastic polyimide resin (B1) may be, for example, one factor for adjusting the viscosity of the conductive paste. From the viewpoint of producing a good conductive film, the weight-average molecular weight of the thermoplastic polyimide resin (B1) may be, for example, 31,000 or more, 32,000 or more, or even 33,000 or more. The upper limit is not particularly limited, but may be, for example, 1,000,000 or less, 500,000 or less, 300,000 or less, 200,000 or less, or 100,000 or less.

[0038] The thermoplastic polyimide resin (B1) is a polyimide resin obtained by, for example, reacting a tetracarboxylic dianhydride with a diisocyanate in a reaction solution. The thermoplastic polyimide resin (B1) contained in the conductive paste may be one type or two or more types.

[0039] The conductive paste disclosed herein may contain a polyimide resin (B2) different from the thermoplastic polyimide resin (B1) instead of or in addition to the thermoplastic polyimide resin (B1), as long as the effects of the technology disclosed herein are obtained. The type of polyimide resin (B2) is not particularly limited, and may be a thermoplastic polyimide resin or a thermosetting polyimide resin. The preferred range of Td5 of the polyimide resin (B2) is preferably the same as the preferred range of Td5 of the polyimide resin (B1). The weight-average molecular weight of the polyimide resin (B2) is not particularly limited, and may be the same as or smaller than the weight-average molecular weight of the thermoplastic polyimide resin (B1).

[0040] When the conductive paste contains polyimide resin (B1), the content of polyimide resin (B1) is, for example, 30% by weight or more, or may be 50% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more, when the entire resin component (B) is taken as 100% by weight. On the other hand, when the conductive paste contains both polyimide resin (B1) and polyimide resin (B2), from the viewpoint of realizing the effects of the technology disclosed herein, the content of polyimide resin (B2) is, for example, 70% by weight or less, or may be 50% by weight or less, preferably 20% by weight or less, more preferably 10% by weight or less, even more preferably 5% by weight or less, when the total amount of polyimide resins (B1 + B2) contained in resin component (B) is taken as 100% by weight. The closer to 0% by weight, the better.

[0041] The polyimide resin contained in resin component (B) can be obtained by appropriately selecting one that satisfies the above characteristics depending on the desired application from polyimide materials manufactured by, for example, JFE Chemical Corporation, Kyocera Chemical Corporation, SABIC Corporation, and PI Technical Research Institute.

[0042] The conductive paste disclosed herein may further include a silicone resin (B3) as an optional resin component. The silicone resin (B3) may be a polymeric organic compound having a main skeleton based on a siloxane bond (Si-O-Si) consisting of silicon (Si) and oxygen (O). Among polymeric organic compounds having a branched chain, the silicone resin (B3) may be a silicone rubber and / or silicone resin, excluding linear silicone oil, among siloxane compounds known as silicone oil, silicone rubber, and silicone resin. Silicone rubber is an elastomer with a low degree of branching (crosslinking) and rubber elasticity at room temperature (e.g., 25°C). Silicone resin has a high degree of branching (crosslinking) and a well-developed three-dimensional polymer structure. Of the silicone rubber and silicone resin, it is more preferable to use silicone resin as the silicone resin (B3). The silicone resin (B3) may be solid or liquid at room temperature (e.g., 25°C).

[0043] Examples of silicone resins that form the main skeleton include those represented by the general formula: HO[—Si(R)2O—] nThe silicone resin (B3) may be a polysiloxane containing a siloxane unit represented by the formula: H and R are hydrogen or any functional group; a polyalkylsiloxane in which R is any alkyl group; or a polymer obtained by polymerizing a siloxane unit with a different silicon-containing monomer. Specific examples of the silicone resin (B3) include polydialkylsiloxanes such as polydimethylsiloxane, polydiethylsiloxane, and polymethylethylsiloxane; polyalkylarylsiloxanes; and poly(dimethylsiloxane-methylsiloxane). A particularly suitable polymer constituting the main skeleton may be, for example, polydimethylsiloxane. Furthermore, the silicone resin (B3) may be a linear modified silicone in which other substituents such as polyether groups, epoxy groups, amine groups, carboxyl groups, alkyl groups, and hydroxyl groups have been introduced into the side chains, terminals, or both of the main skeleton.

[0044] It is known that silicone resins are classified into addition-curing silicone resins and dehydration-condensation-curing silicone resins. Of these, dehydration-condensation-curing silicone resins may have a negative effect on the electrode film due to the formation of water as a reaction by-product. Therefore, although not necessarily limited thereto, it is more preferable that the silicone resin (B3) be an addition-curing silicone resin.

[0045] Such silicone resins can be obtained by appropriately selecting one that satisfies the above characteristics depending on the desired application from silicone resins or silicone rubbers manufactured by Shin-Etsu Chemical Co., Ltd. or Wacker Asahi Kasei Silicone Co., Ltd.

[0046] When the resin component (B) contains a silicone resin (B3), its weight percentage, based on the total weight of the resin component (B) taken as 100% by weight, is not particularly limited, but may be, for example, 0.5% by weight or more, 3% by weight or more, 5% by weight or more, 10% by weight or more, or 20% by weight or more. However, if the weight percentage of the silicone resin (B3) is too high, the adhesiveness of the conductive film tends to decrease and the rheological properties tend to deteriorate. Therefore, the weight percentage may be appropriately adjusted. The weight percentage may be, for example, 70% by weight or less, or 65% by weight or less. From the viewpoint of obtaining a better adhesiveness-improving effect on the conductive film and realizing rheological properties suitable for producing a good coating film, the weight percentage is preferably 50% by weight or less, more preferably 30% by weight or less, and even more preferably 20% by weight or less.

[0047] Furthermore, a higher ratio of the (B) resin component to 100 parts by weight of the (A) conductive particles is preferable because it can more effectively buffer and reduce external vibrations and thermal shocks applied to the conductive film. The ratio of the resin component may be, for example, 4 parts by weight or more, preferably 5 parts by weight or more, and more preferably 8 parts by weight or more. However, an excessive ratio of the resin component is not preferable because the resin component present between the conductive particles can become a resistance. The ratio of the resin component may be, for example, 30 parts by weight or less, preferably 25 parts by weight or less, and may be, for example, 22 parts by weight or less, or 20 parts by weight or less.

[0048] The conductive paste disclosed herein may also contain other resin components as long as the above-described characteristics are not impaired. Such resin components may be one or more 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. However, among the known resin components, acrylonitrile-butadiene rubber (NBR)-based resins and acrylic-based resins do not have the effect of improving the poor adhesion of polyimide resins, as does the silicone resin described above, and therefore may not be included. From the perspective of differentiation from conventional conductive resin pastes, for example, the conductive paste may not contain epoxy-based resins or urethane-based resins. When the conductive paste contains resin components other than polyimide resin and silicone resin, the total content of these other resin components is preferably 10% by weight or less (preferably 5% by weight or less).

[0049] (C) Organic solvent As research and development of conductive pastes containing polyimide resins has become more vigorous, the use of such pastes under harsher conditions (e.g., higher humidity conditions) has been considered. While various factors contribute to the stability of conductive pastes, the present inventors have focused on the composition of organic solvents. Conventionally, N-methylpyrrolidone (NMP), γ-butyrolactone, and the like have been used as organic solvents in conductive pastes containing polyimide resins. However, considering the use of conductive pastes in higher humidity environments, for example, it was believed that there was still room for further investigation regarding the use of these organic solvents. Therefore, the present inventors considered using propylene carbonate, which has low volatility and lower water absorption than conventional organic solvents, instead of conventional organic solvents such as N-methylpyrrolidone (NMP) and γ-butyrolactone. However, propylene carbonate is not an organic solvent that dissolves polyimide resins (see the test examples below). For this reason, it was difficult to use propylene carbonate alone as an organic solvent in conductive pastes containing polyimide resins. Therefore, as a result of intensive research by the inventors, it was found that by using another organic solvent together with propylene carbonate as the organic solvent for the conductive paste, it was possible to utilize the low volatility and low water absorption properties of propylene carbonate, thereby improving the stability of the conductive paste.

[0050] The organic solvent in the conductive paste disclosed herein includes a first solvent and a second solvent. The first solvent is propylene carbonate. As the second solvent, it is preferable to use a solvent that can impart polyimide solubility to the organic solvent. This makes it possible to impart polyimide solubility to the organic solvent. In other words, by using the second solvent, propylene carbonate (first solvent), which does not have polyimide solubility, can be used as the organic solvent for the conductive paste containing a polyimide resin.

[0051] As the second solvent, from the viewpoints of workability during film formation, storage stability, etc., a high-boiling organic solvent with a boiling point of approximately 200°C or higher (200°C to 300°C) at atmospheric pressure is preferably used. Furthermore, considering the stable use of the conductive paste in a high-humidity environment with a humidity of more than 50%, a solvent with an octanol / water partition coefficient log Kow greater than 0 is preferably used as the second solvent. A solvent with a higher octanol / water partition coefficient log Kow may have lower water absorption. As the second solvent, a solvent with a higher octanol / water partition coefficient log Kow than the first solvent is preferably used. By using a solvent with lower water absorption as the second solvent in combination with the first solvent, the stability of the conductive paste can be further improved. In this specification, the "octanol / water partition coefficient" refers to a value measured according to the "shake flask method" specified in JIS Z7260-107:2000.

[0052] From the viewpoint of further enhancing the stability of the conductive paste, the octanol / water partition coefficient logKow of the second solvent is, for example, 0.1 or more, preferably 0.3 or more, more preferably 0.5 or more, even more preferably 0.75 or more, and particularly preferably 1.0 or more. The second solvent may be a single solvent or a mixed solvent of two or more solvents.

[0053] The second solvent is preferably a solvent having a smaller polarization term ΔP of the Hansen solubility parameter than propylene carbonate. By using such a second solvent, the polarization term ΔP of propylene carbonate can be buffered, and as a result, the solubility of the polyimide resin can be imparted to the organic solvent containing propylene carbonate. From this viewpoint, the polarization term ΔP of the second solvent is, for example, 12 (J / cm 3 ) 1 / 2 It is preferably 10 (J / cm 3 ) 1 / 2 More preferably, 8 (J / cm 3 ) 1 / 2 and more preferably 7 (J / cm 3 ) 1 / 2On the other hand, if the polarization term ΔP of the second solvent is too low, the polarization term ΔP of propylene carbonate cannot be sufficiently buffered. From this point of view, the polarization term ΔP of the second solvent is set to, for example, 1 (J / cm 3 ) 1 / 2 and preferably 2 (J / cm 3 ) 1 / 2 More preferably, 4 (J / cm 3 ) 1 / 2 More preferably, 5 (J / cm 3 ) 1 / 2 The Hansen solubility parameter will be discussed in more detail later.

[0054] The second solvent may be, for example, at least one solvent classified as an alcohol-based solvent, which has a boiling point of 200°C or higher at atmospheric pressure and an octanol / water partition coefficient log Kow greater than 0. In this specification, "alcohol-based solvent" refers to a solvent composed of compounds in which the hydrogen atoms of hydrocarbons are substituted with hydroxyl groups, and refers to a solvent composed of compounds represented by the general formula: R-OH. Examples of alcohol-based solvents that can be used as the second solvent include aromatic alcohols such as benzyl alcohol; monoterpene alcohols such as terpineol and dihydroterpineol (menthanol); and texanol.

[0055] The second solvent may be, for example, at least one solvent classified as an ether solvent, having a boiling point of 200°C or higher at atmospheric pressure and an octanol / water partition coefficient logKow greater than 0. In this specification, "ether solvent" refers to a solvent composed of a group of compounds having at least one ether bond (-C-O-C-) in the main chain (mother nucleus). Examples of ether solvents that can be used as the second solvent include glycol ethers such as diethylene glycol monoethyl ether, butyl carbitol (diethylene glycol monobutyl ether), triethylene glycol dimethyl ether, ethylene glycol phenyl ether, and propylene glycol phenyl ether.

[0056] The second solvent may be, for example, at least one solvent classified as an ester solvent, which has a boiling point of 200°C or higher at atmospheric pressure and an octanol / water partition coefficient logKow greater than 0. In this specification, "esters" refers to a solvent composed of a group of compounds having at least one ester bond (RC(=O)-O-R') in the main chain. Examples of ester solvents that can be used as the second solvent include isobornyl acetate, ethyl diglycol acetate, butyl glycol acetate, butyl diglycol acetate, butyl cellosolve acetate, butyl carbitol acetate (diethylene glycol monobutyl ether acetate), methyl benzoate, ethyl benzoate, propyl benzoate, and butyl benzoate.

[0057] The respective contents of the first solvent and the second solvent in the organic solvent (C) are not particularly limited as long as the organic solvent (C) is soluble in the polyimide resin and the effects of the technology disclosed herein can be achieved. From this viewpoint, when the total of the first solvent and the second solvent is taken as 100% by weight, the content of the first solvent is, for example, more than 20% by weight, preferably 25% by weight or more, more preferably 30% by weight or more, and for example, less than 90% by weight, preferably 80% by weight or less, more preferably 75% by weight or less, even more preferably 70% by weight or less, and particularly preferably 60% by weight or less.

[0058] To achieve solubility of the polyimide resin in the organic solvent (C), the organic solvent (C) can be prepared so as to satisfy a predetermined solubility parameter. By preparing the organic solvent (C) using the first solvent and the second solvent as described above, for example, the polarization term ΔP of the Hansen solubility parameter of the organic solvent (C) can be set to 9 (J / cm 3 ) 1 / 2 More than 15(J / cm 3 ) 1 / 2 The following can be satisfied: When the polarization term ΔP is in the above range, the organic solvent (C) can be contained in the dissolving sphere of the polyimide resin.

[0059] The Hansen solubility parameter is a value specific to each compound and is composed of three numerical values ​​(parameters): a dispersion term δD, a polarization term δP, and a hydrogen bonding term δH. When these three numerical values ​​are used as coordinates in a three-dimensional space (Hansen space), the closer the Hansen solubility parameter of a substance to be dissolved (here, a polyimide resin) is to the Hansen solubility parameter of a solvent (here, an organic solvent (C)), the more easily the substance tends to dissolve in the solvent.

[0060] The Hansen solubility parameter of the organic solvent (C) can be calculated, for example, from the constituent components of the organic solvent (C) and the composition ratio of the components. For this calculation, for example, software HSPiP (Hansen Solubility Parameters in Practice) can be preferably used.

[0061] On the other hand, the Hansen solubility parameter of a polyimide resin can be determined as follows: A polyimide resin is dissolved in a plurality of solvents whose Hansen solubility parameters are already known, and the Hansen solubility parameters of the solvents in which the polyimide resin is dissolved are plotted in Hansen space. When the plots of the solvents in which the polyimide resin is dissolved are gathered together, a sphere can be formed in Hansen space. The center of this sphere can be taken as the Hansen solubility parameter of the polyimide resin. The sphere formed in Hansen space as described above can be the "dissolution sphere of the polyimide resin." The Hansen solubility parameter of a polyimide resin can also be obtained using, for example, the software HSPiP.

[0062] The polyimide resin dissolution sphere can be a sphere with center coordinates (δD, δP, δH) of (18.5, 12.8, 7.7) in Hansen space and a radius (R0) of 4.4. Since the organic solvent (C) is soluble in the polyimide resin, the Hansen solubility parameter of the organic solvent (C) can be included in the polyimide resin dissolution sphere. The center coordinates and radius (R0) of the polyimide resin dissolution sphere were obtained by the inventor using the software HSPiP.

[0063] The content of the organic solvent (C) is not particularly limited, but is preferably about 70% by weight or less, for example, 5 to 60% by weight, and preferably 10 to 50% by weight, when the entire conductive paste is taken as 100% by weight. By satisfying this range, it is possible to impart appropriate fluidity to the paste and improve workability during film formation. In addition, it is possible to improve the self-leveling properties of the paste and realize a conductive film with a smoother surface.

[0064] (D) Other ingredients The paste disclosed herein may be composed solely of the above components (A) to (C), or may contain various additive components in addition to the above components (A) to (C) as needed. As additive components, those known to be usable in general conductive pastes may be used as appropriate, as long as they do not significantly impair the effects of the technology disclosed herein.

[0065] The additive components are roughly divided into inorganic additives (D1) and organic additives (D2). Examples of the inorganic additives (D1) include sintering aids and inorganic fillers. The inorganic additives (D1) have an average particle size of approximately 10 nm to 10 μm, and from the viewpoint of keeping the arithmetic mean roughness Ra of the conductive film small, it is preferably, for example, 0.3 μm or less. Examples of the organic additives (D2) include leveling agents, antifoaming agents, thickeners, plasticizers, pH adjusters, stabilizers, antioxidants, preservatives, colorants (pigments, dyes, etc.). The organic additives (D2) may or may not have an acid value. The content ratio of the additive components is not particularly limited, but may be approximately 20 wt % or less, for example, 10 wt % or less, or 5 wt % or less, when the entire conductive paste is taken as 100 wt %.

[0066] Such a paste can be prepared by weighing out the above-mentioned materials to a predetermined content ratio (weight ratio) and stirring and mixing them homogeneously. The materials can be stirred and mixed using various conventional stirring and mixing devices, such as a roll mill, a magnetic stirrer, a planetary mixer, or a disperser. The paste can be applied to the substrate by, for example, a dipping method, a dispenser supplying method, a printing method such as screen printing, gravure printing, offset printing, or inkjet printing, or a spray coating method. For example, the dipping method is suitable for forming resin electrode layers for external electrodes of multilayer ceramic electronic components. For example, the dispenser supplying method is suitable for bonding applications when mounting multilayer ceramic electronic components on substrates.

[0067] <Uses of the paste> The conductive paste disclosed herein can form a highly stable conductive film on any substrate. This conductive film hardens by drying and forms a conductive film in an unfired state. Therefore, the conductive paste disclosed herein can be preferably used as a conductive paste for forming a resin electrode layer of a ceramic electronic component that is vulnerable to temperature changes such as firing. It can also be used to form a conductive resin for bonding that replaces solder when mounting ceramic electronic components on a substrate.

[0068] In this specification, the term "ceramic electronic component" refers to an electronic component having an amorphous ceramic substrate (glass-ceramic substrate) or a crystalline (i.e., non-glass) ceramic substrate. For example, chip inductors, high-frequency filters, ceramic capacitors, low-temperature co-fired ceramic substrates (LTCC substrates), high-temperature co-fired ceramic substrates (HTCC substrates), and the like, each having a ceramic substrate, are included in the "ceramic electronic component" referred to here.

[0069] 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. 1, the ceramic electronic component 1 includes a component body 10 and external electrodes 30 formed on a pair of opposing end faces of the component body 10.

[0070] In the component body 10, multiple internal electrodes 20 are stacked with dielectric layers 12 interposed between them. Each dielectric layer 12 is made of, for example, a laminated sintered body of ceramic green sheets containing a ceramic dielectric. In an actual MLCC, the dielectric layers 12 are integrated to the extent that the junction boundaries between them are not visible. Here, portions of the internal electrodes 20 are exposed at the end faces of the component body 10 (the left and right ends in FIG. 1 ).

[0071] The external electrodes 30 are disposed on the outer surface of the component body 10. The external electrodes 30 are connected to the wiring 3 of the substrate 2 via solder 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 electrodes 30 include 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.

[0072] The first metal electrode layer 32 contains copper (Cu), a base metal, as its main component and is physically and electrically connected to the internal electrode 20. The first metal electrode layer 32 is formed continuously on a pair of left and right end faces of the component body 10 and on the outer surfaces of the four side faces connected thereto. The first metal electrode layer 32 is formed by applying and baking a conductive paste containing Cu powder to the pair of end faces of the component body 10 and on the outer surfaces of the four side faces connected thereto. The thickness of the first metal electrode layer 32 is, for example, 10 μm to 30 μm.

[0073] The conductive film 34 is a layer formed by drying and hardening the conductive paste disclosed herein. The conductive film 34 is formed by applying and drying the conductive paste disclosed herein to a pair of end faces and the outer surfaces of four side faces connected thereto of the component body 10, leaving only the peripheral edges of the first metal electrode layer 32. The drying temperature is approximately 180°C to 300°C, although this may vary depending on the resin component used (e.g., polyimide resin, silicone resin, etc.). The thickness of the conductive film 34 is, for example, 20 μm to 100 μm. This allows the conductive paste disclosed herein to harden and form the conductive film 34 as part of the external electrode 30.

[0074] The second metal electrode layer 36 contains Ni or a Ni alloy as a main component. The second metal electrode layer 36 is formed, for example, by Ni plating the surface of the first conductive film 34. The second metal electrode layer 36 has a thickness of, for example, 1 μm to 5 μm. The third metal electrode layer 38 contains Sn or a 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 a Sn alloy. The third metal electrode layer 38 has a thickness of, for example, 1 μm to 5 μm.

[0075] The ceramic electronic component 1 can be manufactured as described above. The external electrodes 30 are electrically connected to the internal electrodes 20 exposed on both end faces of the component body 10. This allows current sent from the outside to one of the internal electrodes 20 through one of the external electrodes 30 to be stored within the MLCC for insulation, rather than being sent directly to the other external electrode 30. Furthermore, when a current flows through an external load, the charge stored within the MLCC is sequentially sent to the external circuit through the external electrodes 30. The presence of the MLCC allows stable supply of charge to the external circuit even when the power supply voltage is unstable. Such an MLCC includes a highly stable conductive film 34 in the external electrode 30. Therefore, even if an electronic device incorporating the MLCC is exposed to a high-humidity environment, for example, the enhanced stability of the conductive film 34 allows the conductive film 34 to stably adhere to the second metal electrode layer 36, thereby maintaining a stable electrical connection with the component body 10. This provides a ceramic electronic component 1 that is highly reliable even in high-temperature environments (e.g., high-temperature and high-humidity environments). Such a 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.

[0076] The techniques disclosed herein include the techniques described in the following sections. Section 1: A conductive paste containing conductive particles, a polyimide resin, and an organic solvent, The organic solvent is a first solvent which is propylene carbonate; a second solvent having a boiling point of 200°C or higher at atmospheric pressure and an octanol / water partition coefficient log Kow greater than 0; It contains The polarization term δP of the Hansen solubility parameter is 9 (J / cm 3 ) 1 / 2 More than 15(J / cm 3 ) 1 / 2 is as follows: Polyimide resin soluble, conductive paste. Section 2: The polarization term ΔP of the Hansen solubility parameter of the second solvent is 4 (J / cm 3 ) 1 / 2 More than 8(J / cm 3 ) 1 / 2 Item 1. The conductive paste according to item 1, which is as follows: Section 3: Item 3. The conductive paste according to item 1 or 2, wherein the second solvent is at least one organic solvent selected from the group consisting of alcohol-based solvents, ether-based solvents, and ester-based solvents. Section 4: 4. The conductive paste according to any one of items 1 to 3, wherein the second solvent is at least one organic solvent selected from the group consisting of benzyl alcohol, propylene glycol phenyl ether, and benzoic acid butyl esters. Section 5: 5. The conductive paste according to any one of items 1 to 4, wherein the content of the first solvent is 30% by weight or more and 70% by weight or less when the total of the first solvent and the second solvent is 100% by weight. Item 6: Item 6. The conductive paste according to any one of items 1 to 5, wherein the conductive particles are silver particles. Section 7: Item 7. The conductive paste according to any one of Items 1 to 6, wherein the polyimide resin contains a thermoplastic polyimide resin having a thermal decomposition temperature (Td5) at which a weight loss of 5% is caused of 300° C. or higher. Section 8: 8. The conductive paste according to any one of items 1 to 7, which is used to form an external electrode of a ceramic electronic component. Section 9: a component body including a ceramic body and an internal electrode disposed within the ceramic body; an external electrode provided on a surface of the component body; Equipped with 9. A multilayer ceramic electronic component, wherein the external electrodes at least partially comprise a dried film of the conductive paste according to any one of items 1 to 8.

[0077] Next, test examples relating to the technology disclosed herein will be described. Note that the test examples shown below are not intended to limit the technology disclosed herein. Note that, unless otherwise specified, "%" is based on weight.

[0078] [material] The conductive particles used were flake-shaped silver powder with an average particle size of 4.7 μm (tap density 4.4 g / cm). 3 ) was prepared. The polyimide resin used was a thermoplastic polyimide resin with a Td5 of 460°C, a weight-average molecular weight of 63,000, and a glass transition temperature of 260°C to 280°C. The organic solvents used were propylene carbonate (boiling point: 240°C to 243°C, octanol / water partition coefficient log Kow: 0.017), benzyl alcohol (boiling point: 205°C, octanol / water partition coefficient log Kow: 1.1), propylene glycol phenyl ether (boiling point: 240°C to 245°C, octanol / water partition coefficient log Kow: 1.52), butyl benzoate (boiling point: 250°C, octanol / water partition coefficient log Kow: 3.84), and γ-butyrolactone (boiling point: 204°C, octanol / water partition coefficient log Kow: -0.64).

[0079] [Evaluation of polyimide resin solubility] First, the organic solvents of Examples 1 to 15 shown in Table 1 were prepared, and the solubility of polyimide resin in each organic solvent was evaluated. Here, 70 g of organic solvent and 30 g of polyimide resin were mixed for 7 hours at a temperature of 100°C while stirring. The mixed solution of the organic solvent and polyimide resin was then allowed to cool to room temperature to prepare a vehicle. The vehicle was visually observed to evaluate the solubility of the polyimide resin in each organic solvent. For each example, the solubility of the polyimide resin in the organic solvent was evaluated as "Y (Yes: polyimide resin soluble)" if the vehicle was transparent, and as "N (No: polyimide resin not soluble)" if the vehicle was not transparent. The results are shown in the corresponding column in Table 1.

[0080] The organic solvent used in each example was a solvent composed of one of the above-mentioned types alone, or a mixed solvent obtained by mixing two or more types. The blending ratio (%) of each type, when the total organic solvent is taken as 100%, is shown in the corresponding column in Table 1. Furthermore, for the organic solvent in each example, the HSP value of each value is shown in the corresponding column in Table 1.

[0081] [Evaluation of conductive paste stability] The vehicle prepared as described above, conductive particles, and an organic solvent were kneaded using a triple roller to prepare the conductive pastes of Examples 1 to 15. The "organic solvent" referred to here is the organic solvent of each example shown in Table 1, and was used as a dilution agent to prepare the conductive paste. In each conductive paste, the blending ratio (parts) of polyimide resin was 10 parts by weight when the conductive particles were taken as 100 parts. The blending amount of organic solvent in each conductive paste (the total amount of the amount used in preparing the vehicle and the amount of the dilution organic solvent) was adjusted appropriately according to the viscosity of the conductive paste, and therefore is not shown in Table 1.

[0082] Each conductive paste was applied to a glass substrate using an applicator (gap: 200 μm) to obtain a coating film (10 cm × 10 cm, paste-like). The coating film was left for 30 minutes in a room temperature (25°C) environment with a humidity of 50% or less, a room temperature (25°C) environment with a humidity of 70%, or a room temperature (25°C) environment with a humidity of 75%. The viscosity of the coating film was then measured. Specifically, the coating film was recovered, and the viscosity of the recovered coating film was measured using a Brookfield viscometer (Brookfield, DV-III ULTRA Spindle SC4-14) in a 25°C environment. The rotation speed during measurement was set to 20 rpm.

[0083] Based on the measurement results of the viscosity of the coating film, the stability of the conductive paste was evaluated using the following indexes. "E (Excellent: excellent stability)": When the viscosity of the conductive paste before application to the glass substrate is taken as 1, the viscosity of the coating film is less than 1.5, and the coating film does not gel. "G (Good: good stability)": The viscosity of the coating film was 1.5 or more, assuming that the viscosity of the conductive paste before application to the glass substrate was 1, and the coating film did not gel. "P (Poor: poor stability)": The coating film gelled. The results are shown in the corresponding columns in Table 1.

[0084] [Table 1]

[0085] From the results shown in Table 1, when Examples 1 to 8, which are conductive pastes containing conductive particles, polyimide resin, and an organic solvent, are compared with Examples 9 to 15, it was found that the conductive pastes (Examples 1 to 8) in which the organic solvent contains a first solvent and a second solvent, the polarization term ΔP of the Hansen solubility parameter is 9 or more and 15 or less, and which are soluble in polyimide resin, have excellent stability.

[0086] The technology disclosed herein has been described above, but these are merely examples and do not limit the scope of the claims. Various modifications can be made to the technology disclosed herein without departing from the spirit of the technology. [Explanation of symbols]

[0087] 1. Ceramic electronic components 2 boards 3 Wiring 4 solder layers 10 Part 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

1. A conductive paste containing conductive particles, a polyimide resin, and an organic solvent, The organic solvent is a first solvent which is propylene carbonate; a second solvent having a boiling point of 200°C or higher at atmospheric pressure and an octanol / water partition coefficient log Kow greater than 0; It contains The polarization term δP of the Hansen solubility parameter is 9 (J / cm ３ ) １／２ More than 15 (J / cm ３ ) １／２ is as follows: Polyimide resin is soluble, The conductive paste has a particle diameter of 0.1 μm or more and 10 μm or less, which corresponds to a cumulative 50% from the smallest particle diameter side in a volume-based particle size distribution based on a laser diffraction scattering method.

2. The polarization term δP of the Hansen solubility parameter of the second solvent is 4 (J / cm ３ ) １／２ More than 8 (J / cm ３ ) １／２ 2. The conductive paste according to claim 1, wherein:

3. The conductive paste according to claim 2 , wherein the second solvent is at least one organic solvent selected from the group consisting of alcohol-based solvents, ether-based solvents, and ester-based solvents.

4. 4. The conductive paste according to claim 3, wherein the second solvent is at least one organic solvent selected from the group consisting of benzyl alcohol, propylene glycol phenyl ether, and butyl benzoate.

5. 2. The conductive paste according to claim 1, wherein a content of the first solvent is 30% by weight or more and 70% by weight or less when the total of the first solvent and the second solvent is 100% by weight.

6. The conductive paste according to claim 1 , wherein the conductive particles are silver particles.

7. The polyimide resin has a thermal decomposition temperature (Td ５ 2. The conductive paste according to claim 1, comprising a thermoplastic polyimide resin having a temperature of 300° C. or higher.

8. The conductive paste according to claim 1 , which is used to form external electrodes of ceramic electronic components.

9. a component body including a ceramic body and an internal electrode disposed within the ceramic body; an external electrode provided on a surface of the component body; Equipped with A multilayer ceramic electronic component, wherein the external electrodes at least partially comprise a dried film of the conductive paste according to any one of claims 1 to 8.

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