JP2021099912A - Conductive paste - Google Patents

Abstract

To provide a conductive paste capable of forming a conductive film excellent in heat resistance and adhesiveness.SOLUTION: The conductive paste containing conductive particles, a resin component, and an organic solvent is provided. The resin component contains a polyimide resin and a silicone resin, and the ratio of the polyimide resin to the silicone resin is adjusted so as to be 95:5-50:50 on a mass basis. The silicone resin is preferably an addition-curable silicone resin. The silicone resin is also preferably a resin-based silicone resin.SELECTED DRAWING: Figure 2

Description

The present invention relates to a conductive paste. More specifically, it relates to a conductive paste suitable for forming an unfired electrode of a ceramic electronic component.

As electronic devices become smaller and have higher performance, ceramic electronic components mounted on electronic devices are also required to be smaller and have higher performance. In particular, in-vehicle electronic components are required to have both high heat resistance and high reliability in addition to miniaturization by connecting vehicles.

Ceramic electronic components generally include a component body and external electrodes formed on a pair of opposite end faces of the component body, and are mounted on the substrate by soldering the external electrodes to the substrate. Here, in in-vehicle electronic devices and the like, it is known that a substrate on which ceramic electronic components are mounted can be bent by a sudden temperature change. At this time, since the coefficient of thermal expansion differs between the ceramic electronic component and the substrate, there is a concern that the ceramic electronic component mounted on the base material may be subjected to thermal shock and the brittle ceramic electronic component may be damaged by cracks or the like. To. Therefore, a conductive film (resin electrode layer) containing a resin component is interposed in the external electrode of the ceramic electronic component, and the thermal shock applied to the ceramic electronic component is alleviated by this resin electrode layer (for example,). See Patent Documents 1 and 2). It has also been proposed to mount (bond) ceramic electronic components on a substrate using a conductive paste containing a resin component instead of solder (see, for example, Patent Document 3).

Japanese Unexamined Patent Publication No. 2018-104820 Special Table 2018-516755 Japanese Unexamined Patent Publication No. 2006-073812

By the way, a thermosetting resin such as an epoxy resin or a urethane resin is used as a resin component in the conventional conductive paste for forming a conductive film containing a resin component. However, these epoxy resins and urethane resins have a heat resistant temperature of about 150 ° C. when continuously used at a high temperature, and have a problem that the resin component deteriorates when exposed to a temperature environment higher than this. As a resin having high heat resistance, super engineering plastics represented by polytetrafluoroethylene and PEEK (polyetheretherketone) resins are known. However, super engineering plastics having high heat resistance have a problem that the adhesiveness to the base material is not sufficient. For example, a conductive film used for an electronic component that may be exposed to a high temperature environment for a long time, such as an in-vehicle ceramic electronic component, has high heat resistance and adhesiveness of about 180 ° C. or higher and 280 ° C. or lower. It is desirable to combine them.

The present invention has been made in view of the above points, and an object of the present invention is to provide a conductive paste capable of forming a conductive film containing a resin component having both heat resistance and adhesiveness. ..

The present inventors have investigated a conductive film formed from a conductive paste containing a super engineering plastic as a resin component, which can be used for a long period of time at a high temperature of 150 ° C. or higher, from various angles. As a result, it was found that the conductive film containing super engineering plastic as a resin component alone has too rigid film characteristics to obtain the desired adhesiveness. Therefore, the present inventors have focused on a polyimide resin having extremely high heat resistance among super engineering plastics, and by blending a different type of resin component with this polyimide resin, the conductive film formed has flexibility. We have conducted extensive research with the aim of improving the adhesiveness to the substrate. As a result, they have found that the adhesiveness of the conductive film can be improved by blending one resin component, which is considered to be inferior in adhesiveness, with the polyimide resin, and have completed the present invention.

That is, the conductive paste disclosed herein contains conductive particles, a resin component, and an organic solvent. The resin component contains a polyimide resin and a silicone resin, and the ratio of the polyimide resin to the silicone resin is adjusted to be 95: 5 to 50:50 on a mass basis.

According to the above configuration, the synergistic effect of the polyimide resin and the silicone resin makes it possible to form a conductive film having excellent adhesiveness, which exceeds the adhesiveness exhibited in the conductive film containing these resins alone. The paste is realized. Although the details are not clear, the polyimide resin has a rigid main skeleton based on its chemical structure, has a high glass transition point (Tg), and is difficult to soften due to temperature conditions, so that it is difficult to wet and spread on the substrate. On the other hand, it is considered that by dispersing the silicone resin in the polyimide resin, the molecular structure of the polyimide is appropriately disturbed, and the effect of softening the silicone resin and making the polyimide resin easily wet and spread on the substrate is exhibited. As a result, the conductive film obtained by drying this conductive paste preferably has high heat resistance (for example, 180 ° C. or higher and 280 ° C. or lower) and adhesiveness (for example, 4N / mm ² or higher). Be done. This provides a conductive paste capable of forming a conductive film having high heat resistance and good adhesiveness to a base material.

In a preferred embodiment of the conductive paste disclosed herein, the silicone resin is an addition-curable silicone resin. Thereby, the adhesive strength of the conductive film formed from the conductive paste ^{can be realized as, for example, 6 N / mm 2} or more, which is excellent in adhesiveness.

In a preferred embodiment of the conductive paste disclosed herein, the silicone resin is a resin-based silicone resin. Even with such a configuration, the adhesive strength of the conductive film formed from the conductive paste can be realized as being excellent in adhesiveness ^{, for example, 6 N / mm 2 or more.}

In a preferred embodiment of the conductive paste disclosed here, when the conductive particles are 100 parts by mass, the resin component is contained in a ratio of 10 parts by mass or more and 30 parts by mass or less. As a result, a conductive film having excellent electrical conductivity can be suitably formed.

In a preferred embodiment of the conductive paste disclosed herein, the conductive particles include at least one of nickel, platinum, palladium, gold, silver and copper. Even with such a configuration, a conductive film having excellent electrical conductivity can be suitably formed.

As described above, the conductive paste disclosed here can form a conductive film having both high heat resistance and adhesiveness. Such characteristics can be used, for example, to form a resin electrode layer contained in an external electrode of a ceramic electronic component used in an environment where vibration is generated at a high temperature, or a conductive resin for bonding. It can be demonstrated without any problems. For example, in a preferred embodiment of the conductive paste disclosed herein, it is used to form a resin electrode layer for an external electrode of a ceramic electronic component.

From another point of view, the ceramic electronic component disclosed herein includes a component body including a ceramic substrate and an internal electrode disposed within the ceramic substrate, and an external electrode provided on the surface of the component body. .. The external electrode includes at least a part of a conductive film (typically a dry film) formed from the conductive paste according to any one of the above. As a result, even in a high temperature environment, a highly reliable ceramic electronic component that is less likely to be peeled or damaged due to vibration from the rotating part is realized.

FIG. 1 is a cross-sectional view schematically showing a multilayer ceramic capacitor according to an embodiment. FIG. 2 is a graph showing the relationship between the composition of the silicone resin and the adhesiveness of the resin electrode layer in the conductive paste according to the embodiment.

Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than those specifically mentioned in the present specification (for example, the constitution of the conductive paste) and necessary for carrying out the present invention (for example, the method for preparing the conductive paste and the constitution of the ceramic electronic component). Etc.) can be grasped as design items of those skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in the present specification and common general technical knowledge in the art.

In the following description, an unfired film-like body obtained by applying a conductive paste onto a substrate and drying it at a temperature equal to or lower than the thermal decomposition temperature of the resin component contained in the conductive paste (for example, at 300 ° C. or lower). Is called a "conductive film". In the present specification, the "conductive film" includes the meanings of "resin electrode film", "conductive resin for bonding" and the like. Further, in the present specification, the notation of "A to B" indicating a numerical range means A or more and B or less.

≪Conductive paste≫
The conductive paste disclosed here (hereinafter, may be simply referred to as “paste”) can form a conductive film by drying. The conductive paste disclosed here contains conductive particles (A), a resin component (B), and an organic solvent (C). Further, the conductive film (typically, a resin electrode film or a conductive resin for bonding) formed from this conductive paste contains conductive particles (A) and a resin component (B). In addition, in this specification, "paste" is a term including composition, ink, slurry, suspension and the like. Hereinafter, each component will be described in order.

(A) Conductive Particles Conductive particles are typically prepared in the form of powder. The conductive particles are components that impart electrical conductivity to the conductive film obtained after drying. The type of the conductive particles is not particularly limited, and one or more of the various commonly used conductive particles can be appropriately used depending on the intended use. As the conductive particles, conductive metal powder is a preferable example. Specifically, nickel (Ni), platinum (Pt), palladium (Pd), gold (Au), silver (Ag), copper (Cu), ruthenium (Ru), rhodium (Rh), iridium (Ir), Examples thereof include simple metals such as osmium (Os) and aluminum (Al), and mixtures and alloys thereof.

Although not particularly limited, for example, in an application for forming a resin electrode film of a laminated ceramic electronic component, a conductive resin for bonding, or the like, it is required to have high electrical conductivity without firing. Examples of such highly conductive metal species include nickel, platinum, palladium, silver and copper. Of these, silver and silver alloys that are chemically stable and have excellent heat resistance are preferable.

The properties of the particles constituting the conductive particles, such as the size and shape of the particles, are limited to the minimum dimensions (typically, the thickness and / or width of the conductive film) in the cross section of the desired conductive film. There is no particular limitation. The average particle size of the conductive particles (the particle size corresponding to a cumulative 50% from the small particle size side in the volume-based particle size distribution obtained by the laser diffraction type particle size distribution measuring device. The same applies hereinafter) is approximately several tens of nm to. It is preferably about several tens of μm, for example, 1 μm to 10 μm.

The shape of the conductive particles may be, for example, spherical or non-spherical. The non-spherical shape may be, for example, a plate shape, a scale shape, a flake shape, an indefinite shape, or the like. From the viewpoint of easily increasing the packing density of the conductive particles, as the spherical conductive particles, for example, those having an aspect ratio of 1.2 or less, preferably 1.15 or less, for example 1.1 or less are preferably used. 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, for example, an aspect ratio of more than 1.2, preferably 1.3 or more, 1.5 or more, for example 1, 1. It is preferable to use 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. As a result, when the solvent is removed from the paste by drying, the plurality of conductive particles are suitably in contact with each other, and the electrical conductivity of the conductive film can be enhanced. The aspect ratio is a value calculated by (long side ÷ short side) of the minimum circumscribing rectangle of the conductive particles based on electron microscope observation.

The content ratio of the conductive particles (A) is not particularly limited, but when the total amount of the conductive paste is 100% by mass, it is approximately 30% by mass or more, typically 40 to 95% by mass, for example, 50 to 85% by mass. It should be%. By satisfying the above range, a conductive film having high electrical conductivity and high density can be preferably realized. In addition, the handleability of the paste and the workability at the time of film formation can be improved.

(B) Resin component The resin component includes a polyimide resin (B1) and a silicone resin (B2).
(B1) Polyimide resin The polyimide resin is a polymer containing an imide bond in a repeating unit. A polymer is a molecule having a large molecular weight (for example, a weight average molecular weight of 1000 or more) and a unit (repetition unit) substantially or conceptually obtained from a molecule having a small molecular weight (for example, a weight average molecular weight of 500 or less). It has a structure composed of a large number of repetitions (for example, 5 times or more). The polyimide resin typically contains a repeating unit structure represented by the following formula (1). Here, R and R'in the formula are independently arbitrary organic functional groups or oxygen atoms.

Polyimide resins are typically crystalline or amorphous polymers in which repeating units containing imide bonds make up the main chain. From the viewpoint of forming an electrode having higher adhesiveness, it may be a crystalline polymer. Further, from the viewpoint of having higher heat resistance, it may be an amorphous polymer. Further, the polyimide resin is preferably in a homopolymer state and has a heat resistant temperature of 250 ° C. or higher. For example, the glass transition point may be 200 ° C. or higher, preferably 210 ° C. or higher, more preferably 220 ° C. or higher. possible. In the polyimide resin, the ratio of the number of moles of the repeating unit containing the imide bond to the number of moles of the total repeating unit 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 an aliphatic or cyclic aliphatic.

In the polyimide resin, the type of the repeating unit of the imide bond is not particularly limited. The unit containing an imide bond is not limited to this, and is, for example, s-ODPA, i-ODPA, a-ODPA, 2,2'-BABP, 4,4'-BABP, 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, DDS and the like are exemplified. Any one of these may be used alone, or any combination of two or more thereof may be used.

As such a polyimide resin, for example, from among polyimide materials manufactured by JFE Chemical Co., Ltd., Kyocera Chemical Co., Ltd., Savik Co., Ltd., and PI Technology Research Institute, those satisfying the above characteristics are appropriately selected according to a desired application. Can be obtained.

(B2) Silicone Resin The silicone resin is a polymer organic compound having a main skeleton composed of a siloxane bond (Si—O—Si) composed of silicon (Si) and oxygen (O), and contains a branched chain. Compounds can be used. That is, among the so-called silicone oils, silicone rubbers, and siloxane compounds called silicone resins, silicone rubbers and / or silicone resins may be used, excluding linear silicone oils. Silicone rubber is an elastomer having a low degree of branching (crosslinking degree) and rubber elasticity at room temperature (for example, 25 ° C.). Silicone resin has a high degree of branching (crosslinking) and a well-developed three-dimensional polymer structure. Of the silicone rubber and the silicone resin, it is more preferable to use the silicone resin as the silicone resin. The silicone resin may be in a solid state or a liquid state at room temperature (for example, 25 ° C.).

Examples of the silicone resin forming the main skeleton portion _{include polysiloxane containing a siloxane unit represented by the general formula: HO [-Si (R) 2} O-] _n H, R is hydrogen or an arbitrary functional group; It may be a polyalkylsiloxane in which R is an arbitrary alkyl group, or a polymer obtained by polymerizing a siloxane unit and a silicon-containing monomer different from the siloxane unit. Specific examples of the silicone resin include polydialkylsiloxane such as polydimethylsiloxane, polydiethylsiloxane, and polymethylethylsiloxane, polyalkylarylsiloxane, and poly (dimethylsiloxane-methylsiloxane). The polymer constituting a particularly suitable main skeleton can be, for example, polydimethylsiloxane. The silicone resin is a linear modified silicone in which other substituents such as a polyether group, an epoxy group, an amine group, a carboxyl group, an alkyl group and a hydroxyl group are introduced into the side chain, the terminal or both of the main skeleton. You may.

Further, it is known that the silicone resin includes an addition curing type silicone resin and a dehydration condensation curing type silicone resin. Of these, in the case of a dehydration condensation curing type silicone resin, there is a risk of adversely affecting the electrode film on which water as a reaction by-product is formed. Therefore, although not necessarily limited to this, the silicone resin is more preferably an addition-curable silicone resin.

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

By blending the polyimide resin with the silicone resin even in a very small amount, the effect of improving the adhesiveness of the polyimide resin can be obtained. However, for example, ^{in the conductive paste used for forming a conductive film having a high adhesiveness of 4} N / mm 2 or more, when the total of the polyimide resin and the silicone resin is 100% by mass, the silicone resin The ratio may exceed 2% by mass, may be 3% by mass or more, and more preferably 5% by mass or more, 7% by mass or more, for example, 8% by mass or more, and further preferably 10% by mass or more. However, blending the silicone resin in an excessive ratio is not preferable in that the excellent properties of the polyimide resin may be impaired. The proportion of the silicone resin is preferably less than 60% by mass, preferably 50% by mass or less, and preferably 40% by mass or less, 30% by mass or less, and further preferably 25% by mass or less.

Further, it is preferable that the ratio of the resin component (B) to 100 parts by mass of the conductive particles (A) is larger, the vibration and thermal shock from the outside applied to the conductive film can be buffered and reduced more. The ratio of the resin component is, for example, preferably 3% by mass or more, and more preferably 5% by mass or more, 8% by mass or more, for example, 10% by mass or more. However, when the ratio of the resin component is excessive, the resin component existing between the conductive particles can be a resistance, which is not preferable. The ratio of the resin component is, for example, preferably 30% by mass or less, preferably 25% by mass or less, and may be, for example, 20% by mass or less.

As described above, this conductive paste is indispensable to contain the polyimide resin and the silicone resin. On the other hand, the market also offers block copolymers of a polyimide resin and a silicone resin in which a silicone structure is introduced into a polyimide chain. It can be understood that this silicon-modified polyimide block copolymer imparts adhesion and flexibility to polyimide. However, if the polyimide resin and the silicone resin are copolymerized, there is a big demerit that the heat resistance is impaired in the polymerized portion. Therefore, it is preferable that the polyimide resin and the silicone resin are contained in the conductive paste as a single blend rather than in the form of a copolymer. In other words, the conductive paste disclosed herein preferably does not contain a copolymer of a polyimide resin and a silicone resin.

Further, the conductive paste disclosed herein may contain other resin components as long as the above characteristics are not impaired. Such resin components include one or two kinds of known various resin components such as rubber-based resin, polyester-based resin, epoxy-based resin, urethane-based resin, polyether-based resin, polyamide-based resin, and fluorine-based resin. It can be more than that. However, among the known resin components, acrylonitrile-butadiene rubber (NBR) -based resin and acrylic-based resin are not included because they do not have the effect of improving the poor adhesion of the polyimide resin like the above-mentioned silicone resin. You may. From the viewpoint of differentiation from the conventional conductive resin paste, for example, an epoxy resin or a urethane resin may not be contained. When the conductive paste contains resin components other than the polyimide resin and the silicone resin, the ratio of these other resin components is preferably 10% by mass or less (preferably 5% or less) in total. ..

(C) Organic Solvent As the organic solvent, a solvent exhibiting compatibility with the above-mentioned polyimide resin and silicone resin can be used without particular limitation. The organic solvent is mainly composed of a high boiling point organic solvent having a boiling point of about 200 ° C. or higher, for example, 200 to 300 ° C. (a component occupying 50% by volume or more) from the viewpoint of workability during film formation and storage stability. It is good to say. As a preferred example of the organic solvent, alcohol-based solvents having a −OH group such as tarpineol, texanol, dihydroterpineol, and benzyl alcohol; glycol-based solvents such as ethylene glycol and diethylene glycol; diethylene glycol monoethyl ether and butyl carbitol ( Diethylene glycol monobutyl ether), glycol ether solvents such as 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 solvent having an ester-binding group (RC (= O) -OR'); hydrocarbon solvent such as toluene, xylene, etc .; N-methylpyrrolidone (NMP) ) Etc., aprotonic polar solvents, mineral spirits and the like can be mentioned. Among them, an organic solvent such as NMP or γ-butyrolactone can be preferably used from the viewpoint of preferably dissolving the above resin component. One of these may be used alone, or two or more thereof may be appropriately mixed and used.

The content ratio of the organic solvent (C) is not particularly limited, but when the whole conductive paste is 100% by mass, it is approximately 70% by mass or less, typically 5 to 60% by mass, for example, 10 to 50% by mass. It should be about. By satisfying the above range, it is possible to impart appropriate fluidity to the paste, and it is possible to improve workability at the time of film formation. In addition, the self-leveling property of the paste can be enhanced to realize a conductive film having a smoother surface.

(D) Other components The paste disclosed here may be composed of only the components (A) to (C) above, and in addition to the components (A) to (C) above, if necessary. It may contain various additive components. As the additive component, those known to be usable in a general conductive paste can be appropriately used as long as the effects of the techniques disclosed herein are not significantly impaired.

The additive components are roughly classified into an inorganic additive (D1) and an organic additive (D2). Examples of the inorganic additive (D1) include a sintering aid, an inorganic filler, and glass frit. The average particle size of the inorganic additive (D1) is about 10 nm to 10 μm, and is preferably 0.3 μm or less from the viewpoint of keeping the arithmetic average roughness Ra of the conductive film small. Further, as an example of the organic additive (D2), a leveling agent, a defoaming agent, a thickener, a plasticizer, a pH adjuster, a stabilizer, an antioxidant, a preservative, a coloring agent (pigment, dye, etc.) and the like. Can be mentioned. The organic additive (D2) may or may not have an acid value. The content ratio of the additive component is not particularly limited, but may be approximately 20% by mass or less, typically 10% by mass or less, for example, 5% by mass or less, assuming that the entire conductive paste is 100% by mass. ..

Such a paste can be prepared by weighing the above-mentioned materials so as to have a predetermined content ratio (mass ratio) and uniformly stirring and mixing them. The stirring and mixing of the materials can be carried out using various conventionally known stirring and mixing devices such as a roll mill, a magnetic stirrer, a planetary mixer, and a disper. Further, the paste can be applied to the base material by using, for example, a chip indip method, a dispenser supply method, a screen printing, a gravure printing, a printing method such as offset printing and an inkjet printing, a spray coating method, or the like. .. For example, the dip method is suitable for forming a resin electrode layer of an external electrode of a laminated ceramic electronic component. Further, for bonding applications when mounting a laminated ceramic electronic component on a substrate, for example, a dispenser supply method is suitable.

<Use of paste>
According to the conductive paste disclosed herein, a conductive film having excellent heat resistance and adhesiveness can be formed on an arbitrary base material. This conductive film is cured by drying and constitutes a conductive film in an unfired state. Therefore, the paste disclosed here 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, when mounting a ceramic electronic component on a substrate, it can also be used to form a conductive resin for bonding instead of solder.

In the present specification, the term "ceramic electronic component" is a term that generally refers to an electronic component having an amorphous ceramic base material (glass-ceramic base material) or a crystalline (that is, non-glass) ceramic base material. .. For example, chip inductors with ceramic substrates, high frequency filters, ceramic capacitors, low temperature co-fired ceramics substrate (LTCC substrates), high temperature co-fired multilayer ceramic substrates (LTCC substrates), high temperature co-fired Ceramics Substrate (HTCC substrate) and the like are typical examples included in the "ceramic electronic parts" referred to here.

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

In the component body 10, a plurality of internal electrodes 20 are laminated via a dielectric layer 12. Each dielectric layer 12 is composed of, for example, a laminated sintered body of a ceramic green sheet containing a ceramic dielectric. In the actual MLCC, the bonding boundaries between the dielectric layers 12 are integrated to the extent that they cannot be visually recognized. Here, a part of the internal electrode 20 is exposed on the end faces (left and right ends in FIG. 1) of the component body 10.

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

The conductive film 34 contains metal (Ag) powder as conductive particles, and is a layer formed by curing the conductive paste disclosed herein by drying. The conductive film 34 is coated with the conductive paste disclosed herein on the pair of end faces of the component body 10 and the outer surfaces of the four side surfaces connected thereto, leaving the peripheral edge of the first metal electrode layer 32. It is formed by drying. Here, the drying temperature is approximately 180 ° C. or higher and 300 ° C. or lower, although it may vary depending on the imide resin and the silicone resin used. The thickness of the conductive film 34 is, for example, 20 to 100 μm. Thereby, the conductive paste disclosed herein can be cured to form the conductive film 34 as a part of the external electrode 30.

The second metal electrode layer 36 contains Ni or a Ni alloy as a main component. The conductive film 34 is formed, for example, by Ni-plating the surfaces of the first metal electrode layer 32 and the conductive film 34. The thickness of the second metal electrode layer 36 is, for example, 1 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 thickness of the third metal electrode layer 38 is, for example, 1 to 5 μm.

As described above, the ceramic electronic component 1 can be manufactured. Here, the external electrode 30 is electrically connected to the internal electrode 20 exposed on both end faces of the component body 10. As a result, the current sent from the outside to the internal electrode 20 through one external electrode 30 can be stored in the MLCC and insulated without being sent to the other external electrode 33 as it is. Further, when a current is passed through the external load, the electric charges stored in the MLCC are sequentially sent to the external circuit through the external electrode 30. At this time, due to the presence of the MLCC, even when the power supply voltage is unstable, the electric charge can be stably supplied to the external circuit. Such a MLCC includes a conductive film 34 having excellent heat resistance and adhesiveness in the external electrode 30. As a result, even when the electronic device on which the MLCC is mounted is exposed to a high temperature environment such as a continuously traveling vehicle and the substrate on which the MLCC is mounted is bent, the conductive film 34 is the first. The metal electrode layer 32 and the second metal electrode layer 36 can be adhered to each other with good adhesion, for example, to buffer such bending, and to stably maintain an electrical connection with the component body 10. As a result, the ceramic electronic component 1 having high reliability even in a high temperature environment is provided. Although not specifically shown, the conductive paste can also be used as a bonding paste when the ceramic electronic component 1 is mounted on a substrate.

Hereinafter, some examples of the present invention will be described, but the present invention is not intended to be limited to those shown in the examples.

[Conductive paste]
The conductive pastes of Examples 1 to 19 were prepared by mixing the conductive particles, the resin component, and the solvent with the formulations shown in Table 1.
As the conductive particles, flaky Ag powder (tap density 3.1 g / cm ³ ) having an average particle diameter of 4.7 μm was commonly used in all the examples. As the solvent, γ-butyrolactone was commonly used. However, although not specifically shown, it has been confirmed that even if the types of the conductive particles and the solvent are changed, there is no significant difference in the tendency of the electrode characteristics described later.

As the resin component, 10 kinds of resins shown in Table 1 were used alone or in combination. The resins shown in Table 1 are as follows. Further, the following TD1, TD2, and TD5 mean 1%, 2%, and 5% weight loss temperatures, respectively, and Tg means the glass transition temperature.

"Polyimide resin 1": Solvent-soluble fluorine-containing polyimide resin (Tg: 360 ° C, TD 1: 500 ° C, TD 5: 540 ° C)
"Polyimide resin 2": Solvent-soluble polyetherimide resin (Tg: 260 ° C., TD1: 400 ° C., TD5: 450 ° C.)
"Silicone resin 1": Additive curing type silicone resin (two-component type)
"Silicone resin 2": Additive curing type silicone resin (one-component type)
"Silicone resin 3": Additive-curable silicone resin (phenyl silicone)
"Silicone resin 4": Condensation type silicone resin (flakes)
"Silicone resin 5": Condensation type silicone resin (flake-shaped, silicone resin 4 is a product of another manufacturer)
"Silicone resin 6": Additive curing type silicone rubber (room temperature curing type)
"Acrylic resin": Weight average molecular weight: 300,000, Tg: 56 ° C
"NBR resin": Nitrile butadiene rubber, bonded AN amount: 28.0, Mooney viscosity: 50

[Conductive film and its evaluation]
(Board adhesiveness)
The conductive paste of each of the prepared examples was applied to the tips of two copper plates (2 cm × 5 cm, no surface processing) with an area of 2 cm × 1 cm and a thickness of about 50 μm. Then, the copper plate coated with the conductive paste was first dried at 180 ° C. for 15 minutes and then dried at 280 ° C. for 45 minutes to cure the conductive paste. As a result, 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, the orientations are adjusted so that the copper plate portions are arranged on opposite sides of each other, and the conductive films are overlapped with each other. And glued. As a result, a test piece for evaluating the substrate adhesiveness of the conductive film of each example was prepared.

The copper plates at both ends of the evaluation test piece are fixed to the upper and lower chucks of a tensile tester (manufactured by Shimadzu Corporation, universal testing machine Autograph), and JIS K6850: 1999 (tensile shear bonding of rigid adherends). A tensile shear test was carried out according to the strength test method). In the tensile shear test, a tensile load (shearing force) perpendicular to the adhesive surface of the evaluation test piece is applied at a predetermined load rate, and the tensile shear load (breaking force) when the evaluation test piece breaks is used for adhesion. The strength (shear strength) was measured. The results, the case where the adhesive strength is 6N / mm ² or more "A", "B" of less than 5N / mm ² or more 6N / mm ^2, a case of less than 4N / mm ² or more 5N / mm ² ""C" and ^{less than 4N / mm 2} are designated as "D" and are shown in the "Adhesion" column of Table 1. Further, in Examples 1 to 10, the relationship between the blending amount of the silicone resin and the adhesiveness (adhesive strength) is shown in FIG.
Here, the adhesive strength of the epoxy adhesive used for producing the evaluation test piece by the direct shear test is 15 N / mm ² or more, and the epoxy adhesive portion is peeled or broken before the conductive film. There is nothing to do.

(Heat-resistant)
The conductive pastes of each of the prepared examples were first dried at 180 ° C. for 15 minutes, then dried at 280 ° C. for 45 minutes, and then held at 280 ° C. for 2 hours to measure the weight loss rate. As a result, the case where the weight loss rate was 3% or less was regarded as "OK", and the case where the weight loss rate exceeded 3% was regarded as "NG", and was shown in the "heat resistance" column of Table 1.

[Evaluation]
Examples 1 to 11 are examples in which a conductive paste was prepared by changing the amount of the silicone resin blended with the polyimide resin in the range of 0 to 100% by mass. The conductive films obtained from the conductive pastes of Examples 1 to 11 have a small weight loss rate of less than 3% when heated and held up to, for example, 280 ° C., and have heat resistance at 280 ° C. It could be confirmed.

As shown in Example 11, when the conductive paste is prepared using only the silicone resin without blending the polyimide resin, the adhesive strength of the formed conductive film is approximately 0 N / mm ^2. The conductive film has almost no adhesiveness to the substrate. Therefore, even if a conductive film (that is, a buffer layer made of a resin conductive layer) in the external electrode of the ceramic electronic component is formed by such a conductive paste, the resin conductive layer and the other external electrode are subjected to a thermal impact or the like. It can be easily peeled off and lead to disconnection.
On the other hand, in Example 1 in which the conductive paste was prepared using only the polyimide resin without blending the silicone resin, the formed conductive film exhibits an adhesive force of about ^{2 N / mm 2 due to the characteristics of the polyimide resin.} .. However, such an adhesive force is ^{less than 4 N / mm 2} , which is not sufficient to maintain the adhesion of each layer of the external electrode in an environment where a thermal shock is applied.

On the other hand, as shown in Examples 2 to 10, it was found that by blending the silicone resin with the polyimide resin, the adhesiveness of the conductive film formed changes according to the blending ratio. That is, as shown in FIG. 2, it was found that the adhesive strength of the polyimide resin itself is improved by blending the polyimide resin with the silicone resin even in a small amount.
Further, as shown in Examples 2 to 6, it was found that the effect of improving the adhesive strength was sharply increased as the blending amount of the silicone resin increased. This is because the conductive film containing a single polyimide as a resin component has relatively high rigidity, and the base material (for example, the copper layer which is the lowest layer of the external electrode) expands and contracts or moves due to, for example, thermal impact or external stress. In contrast to the fact that the change cannot be followed, the silicone resin is suitably inserted between the molecules of the polyimide resin to impart appropriate flexibility, adhesion to the substrate, and followability to the polyimide resin. Conceivable.

However, as shown in Examples 6 to 10, it was found that the effect of the silicone resin on improving the adhesive force of the polyimide resin conductive film tends to decrease when the proportion of the silicone resin becomes excessive. That is, it is considered that the presence of the excess silicone resin impairs the adhesiveness inherent in the polyimide resin.
From the above results, the proportion of the silicone resin blended with the polyimide resin should be approximately 2 parts by mass or more when the polyimide resin and the silicone resin are 100 parts by mass, and 3 parts by mass or more is appropriate. It was found that 5 parts by mass or more is preferable, and 10 parts by mass or more is more preferable. Further, it was found that the ratio of the silicone resin blended with the polyimide resin is appropriately about 50 parts by mass or less, preferably 40 parts by mass or less, and more preferably 30 parts by mass or less.

As shown in Table 1, Examples 5 and 12 to 18 are examples in which the resin components used in combination with the polyimide resin 1 are variously changed to silicone resins 1 to 6, acrylic resins, and NBR resins. Regarding the heat resistance of the conductive film formed from the conductive pastes of Examples 5 and 12 to 18, the weight reduction rate was less than 3% in all the examples, and it was confirmed that the conductive film had sufficient heat resistance.

Then, as shown in Examples 5, 12 to 16, when the polyimide resin 1 and the silicone resin are combined, the adhesive strength is 4 N / mm ² or more and the adhesiveness is excellent regardless of the type of the silicone resin. It was found that a film could be formed. Among them, when an addition-curable silicone resin is used as the silicone resin to be combined with the polyimide resin (Examples 5, 12 to 13), the adhesive strength is 6 N / mm ² or more, and the condensed silicone resin (Examples 14 and 15). It was also found that a conductive film having significantly better adhesiveness than ^{the adhesive strength of 4 N / mm 2} or more and 5 N / mm ² or less when a non-resin silicone rubber (Example 16) was used could be formed. Although the details are not clear, it is expected that the addition-curable silicone resin is easier to crosslink in the polymer structure of the polyimide resin than the condensed silicone resin or silicone rubber, and it is easier to impart flexibility to the polyimide resin. Will be done.

However, in Examples 17 and 18 in which acrylic resin or NBR resin was used as the resin component to be combined with the polyimide resin, the adhesive strength of the conductive film ^{was less than 4 N / mm 2} , and the conductive film having sufficient adhesiveness was obtained. It turned out that it could not be formed.
From the above, when a polyimide resin with high heat resistance is used for the conductive paste, the rigidity of the polyimide resin is relaxed by using it in combination with the silicone resin, and it is soft and has high adhesion to the substrate and excellent adhesiveness. It was found that a conductive film can be formed. As a result, a conductive paste capable of forming a conductive film having both heat resistance and adhesiveness is realized. It was found that the effect of relaxing the rigidity of the polyimide resin by the silicone resin was not exhibited by the acrylic resin and the NBR resin, and was an effect peculiar to the silicone resin. Further, it was found that such an effect is remarkably exhibited in the resin-based silicone resin and the addition-curable silicone resin among the silicone resins.

Example 19 is an example in which the polyimide resin 1 in the conductive paste of Example 12 is changed to the polyimide resin 2. From the comparison between Example 12 and Example 19, it was found that the same effect as described above can be obtained even when the type of the polyimide resin is changed.

The present invention has been described in detail above, but these are merely examples, and the present invention can be modified in various ways without departing from the spirit of the present invention.

1 Ceramic electronic component 10 Part body 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 (7)

With conductive particles
With resin components
With organic solvent
Including
The resin component contains a polyimide resin and a silicone resin.
A conductive paste in which the ratio of the polyimide resin to the silicone resin is adjusted to be 95: 5 to 50:50 on a mass basis. The conductive paste according to claim 1, wherein the silicone resin is an addition-curable silicone resin. The conductive paste according to claim 1 or 2, wherein the silicone resin is a resin-based silicone resin. The conductive paste according to any one of claims 1 to 3, wherein the resin component is contained in a proportion of 10 parts by mass or more and 30 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 4, wherein the conductive particles contain at least one of nickel, platinum, palladium, gold, silver and copper. The conductive paste according to any one of claims 1 to 5, which is used for forming an external electrode of a ceramic electronic component. A component body including a ceramic substrate and an internal electrode disposed in the ceramic substrate, and
An external electrode provided on the surface of the component body and
With
The external electrode is a ceramic electronic component containing at least a part of the dry film of the conductive paste according to any one of claims 1 to 6.

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