TWI846672B - Conductive paste - Google Patents

Abstract

The present invention provides a conductive paste capable of forming an electrode in which both the occurrence of sheet erosion and the penetration of conductive powder are suppressed. According to the present invention, a conductive paste is provided, which comprises conductive powder, a binder resin and an organic solvent. The organic solvent is a mixed solvent, the mixed solvent comprises a first solvent having a solubility parameter of 9.0 (cal/cm ³ ) ^0.5 or less and a second solvent having a solubility parameter of 10.0 (cal/cm ³ ) ^0.5 or more, and the solubility parameter of the organic solvent in Fedors is 9.0 (cal/cm ³ ) ^0.5 or more and 10.1 (cal/cm ³ ) ^0.5 or less.

Description

Conductive paste

The present invention relates to a conductive paste.

In the manufacture of electronic components such as sensors and capacitors, the following method is widely used: preparing a conductive paste containing conductive powder, binder resin and organic solvent, applying it to a raw material sheet through various printing methods, and drying and baking to form an electrode (see patent documents 1~4).

)。如果生片的厚度由於片浸蝕現象而局部地變薄或生片上開設有孔，則成為電極的形成不良、短路(short)的原因。關於該現象，例如專利文獻3中公開了，為了降低片浸蝕的發生而使用規定的亞烷基二醇二烷基醚和/或二亞烷基二醇二烷基醚作為有機溶劑。 As described in Patent Documents 3 and 4, when a conductive paste is applied to a green sheet, an organic solvent in the conductive paste may attack the green sheet, which is called sheet attack.

). If the thickness of the green sheet is locally thinned due to the sheet erosion phenomenon or a hole is formed in the green sheet, it becomes a cause of poor electrode formation and short circuit. Regarding this phenomenon, for example, Patent Document 3 discloses that a specified alkylene glycol dialkyl ether and/or dialkylene glycol dialkyl ether is used as an organic solvent to reduce the occurrence of sheet erosion.

[Prior art literature]

[Patent Literature]

[Patent document 1] Japanese Patent Application Publication No. 2010-516603

[Patent Document 2] Japanese Patent Application Publication No. 2012-129447

[Patent Document 3] Japanese Patent Application Publication No. 2012-231119

[Patent Document 4] Japanese Patent Application Publication No. 2012-028356

However, according to the research of the inventors, although the sheet corrosion phenomenon did not occur, why did the electronic components sometimes have a short circuit problem? The inventors analyzed the cause from various angles and found that the conductive powder was infiltrated into the green sheet together with the organic solvent, moved and diffused in the thickness direction of the green sheet, and part of it passed through to the inside of the green sheet. Moreover, it was determined that this caused the short circuit problem in the electronic components. Therefore, in the manufacture of electronic components, it can be said that not only sheet corrosion should be suppressed, but also the penetration of the conductive powder must be suppressed.

The present invention is made in view of the above aspects, and its purpose is to provide: a conductive paste that can form an electrode that can suppress the occurrence of sheet corrosion and the penetration of conductive powder.

According to the present invention, a conductive paste is disclosed, which comprises: conductive powder, binder resin and organic solvent. The organic solvent is a mixed solvent, the mixed solvent comprises a first solvent having a solubility parameter of 9.0 (cal/cm ³ ) ^0.5 or less and a second solvent having a solubility parameter of 10.0 (cal/cm ³ ) ^0.5 or more, and the solubility parameter of the organic solvent in Fedors is 9.0 (cal/cm ³ ) ^0.5 or more and 10.1 (cal/cm ³ ) ^0.5 or less.

According to the research of the inventors, the first solvent is useful for suppressing the occurrence of sheet corrosion, but when used alone, conductive powder is likely to penetrate. On the other hand, the second solvent is useful for suppressing the penetration of conductive powder, but when used alone, sheet corrosion is likely to occur. In the conductive paste of the present invention, the first solvent and the second solvent having such characteristics are included in the organic solvent, and the first solvent and the second solvent are mixed in such a way that the solubility parameter of the organic solvent as a whole becomes a predetermined range, thereby appropriately exerting the advantages of each of the first solvent and the second solvent. As a result, an electrode that can suppress both the occurrence of sheet corrosion and the penetration of conductive powder can be appropriately formed. As a result, the adverse situation of short circuit in electronic components can be better avoided.

It should be noted that the "Fedors' solubility parameter (Solubility Parameter: SP)" in this manual refers to the solubility parameter calculated by the so-called Fedors method described in R.F.Fedors, Polymer Engineering Science, 14, p147 (1974). In the Fedors method, the cohesive energy density and the molar molecular volume are considered to depend on the type and number of substituents, and the solubility parameter is expressed by the following (Formula 1). The solubility parameter is a value inherent in each compound.

δ=[ΣE _coh /ΣV] ^0.5 ‧‧‧(Formula 1)

(Here, ΣE _coh represents cohesive energy, and ΣV represents molar molecular volume.)

In addition, the solubility parameter _δa11 of the organic solvent as a whole can be calculated using the following (Formula 2).

δ _a11 (cal/cm ³ ) ^0.5 =Σ〔Intrinsic solubility parameter of each organic solvent δ(cal/cm ³ ) ^0.5 × mass ratio of each organic solvent when the whole organic solvent is set as the reference (1)〕‧‧‧(Formula 2)

In other words, first, the product of the intrinsic solubility parameter δ (cal / cm ³ ) ^0.5 of each organic solvent and the mass ratio is calculated, and these are added together to obtain the solubility parameter δ _a11 of the organic solvent as a whole. That is, the solubility parameter δ _a11 of the organic solvent as a whole is a weighted average value based on the mass standard. It should be noted that in the following description, the solubility parameter of Fedors is sometimes simply referred to as "SP value". In addition, the SI unit of the SP value is (J / cm ³ ) ^0.5 or (MPa) ^0.5 , but the conventionally used (cal / cm ³ ) ^0.5 is used in this manual. The unit of SP value can be converted using the following formula: 1(cal/cm ³ ) ^0.5 ≒2.05(J/cm ³ ) ^0.5 ≒2.05(MPa) ^0.5 ;

In a suitable embodiment, the first solvent is an acyclic compound. When the first solvent is an acyclic compound, the penetration of the organic solvent into the raw sheet can be suppressed at a higher level. Therefore, the effect of the technology disclosed herein can be better exerted. In another suitable embodiment, the first solvent is an ether. Ethers are preferred because they have excellent SP values and various properties such as printing suitability.

In a suitable embodiment, the second solvent is an ether. Ethers are preferred because they have excellent SP values and various properties such as printing suitability.

In a suitable embodiment, when the total amount of the organic solvent is set to 100 mass%, the ratio of the first solvent is 20 mass% or more and 70 mass% or less, and the ratio of the second solvent is 30 mass% or more and 80 mass% or less. Thus, the effect of suppressing sheet erosion and the effect of suppressing the penetration of conductive powder can be achieved more stably and at a high level.

In a suitable embodiment, when the total amount of the conductive paste is set to 100% by mass, the ratio of the conductive powder is 90% by mass or more. By setting the ratio of the conductive powder to the above, a dense, highly conductive, and low-resistance electrode can be suitably formed.

The above-mentioned conductive paste can be suitable for forming electrodes of inductor components, for example.

1: Laminated chip inductor

10: Main body

12: Magnetic material layer

14: Internal electrode layer

20: External electrode

FIG1 is a cross-sectional view schematically showing the structure of a stacked chip inductor according to an embodiment.

Figure 2(A) and Figure 2(B) are examples of evaluation results of Ag permeability. Figure 2(A) is a SEM-EDS image in which Ag particles are confirmed, and Figure 2(B) is a SEM-EDS image in which Ag particles are not confirmed.

The following is a description of suitable implementations of the present invention. It should be noted that features other than matters specifically mentioned in this specification (such as organic solvents) and features required for the implementation of the present invention (such as the preparation method and the imparting method of the conductive paste, etc.) can be understood based on the technical content taught in this specification and the general technical common sense of technical personnel in this field. The present invention can be implemented based on the content disclosed in this specification and the technical common sense in this field. It should be noted that the expression "A~B" indicating the range in this specification means above A and below B.

The conductive paste disclosed herein includes conductive powder, binder resin and organic solvent. The organic solvent is a mixed solvent containing at least two solvents with different SP values. The following describes each component in turn.

[Conductive powder]

Conductive powder is a component that imparts conductivity to an electrode obtained by baking a conductive paste. The type of conductive powder is not particularly limited, and a conductive powder that has been used in the conductive paste in the past can be appropriately used according to the purpose of the conductive paste. Typical examples include metals such as gold (Au), silver (Ag), platinum (Pt), palladium (Pd), aluminum (Al), nickel (Ni), copper (Cu), ruthenium (Ru), rhodium (Rh), tungsten (W), iridium (Ir), and zirconium (Os), and alloys thereof, such as silver alloys such as silver-palladium (Ag-Pd), silver-platinum (Ag-Pt), and silver-copper (Ag-Cu). Among them, silver and silver alloys are preferred in terms of low cost and high electrical conductivity.

The conductive powder may be, for example, carbon materials such as graphite and carbon black, or conductive ceramics represented by transition metal calcium-titanium oxides such as LaSrCoFeO ₃ series oxides (e.g., LaSrCoFeO ₃ ), LaMnO ₃ series oxides (e.g., LaSrGaMgO ₃ ), LaFeO ₃ series oxides (e.g., LaSrFeO ₃ ), and LaCoO ₃ series oxides (e.g., LaSrCoO ₃ ).

There is no particular limitation on the properties of the conductive powder, and it can be appropriately adjusted according to the use of the conductive paste. For example, in the use of forming an electrode of an inductor component such as an inductor, it is preferable to use a conductive powder having an average particle size of approximately 0.1 μm or more, typically 0.5 μm or more, for example 1 μm or more, and approximately 5 μm or less, typically 4 μm or less, for example 3 μm or less. By making the average particle size larger than a specified value, the aggregation of the conductive powder in the conductive paste is suppressed, and the filling property of the electrode obtained after baking can be improved. By making the average particle size smaller than a specified value, the sinterability can be improved and the resistance of the electrode can be reduced. It should be noted that the "average particle size" in this manual refers to the cumulative value 50% particle size in the particle size distribution (number basis) based on the equivalent circular diameter observed under an electron microscope.

For the conductive powder, in the volume-based particle size distribution based on the laser diffraction and scattering method, the _D10 particle size corresponding to 10 volume % of the particles with the smallest particle size is generally 1.6 μm or less, typically 1.3 μm or less, and for example, 1.0 μm or less. When the _D10 particle size is as small as this, the conductive powder is likely to pass through the green sheet. According to the technology disclosed herein, when the conductive powder has such a _D10 particle size, the conductive powder can be appropriately suppressed from passing through.

In a suitable example, from the perspective of improving the density and filling properties of the electrode, the conductive powder includes two particle groups with different average particle sizes. In other words, the particle size distribution of the conductive powder has a bimodal property. In a specific example, the average particle size of the first particle group is roughly in the range of 1 to 5 μm, for example, 2 ± 0.5 μm, and the average particle size of the second particle group is roughly in the range of 0.5 to 2 μm, for example, 0.5 ± 0.5 μm. When the particle size distribution has a bimodal property, the ratio of particles with a particle size smaller than the average particle size increases compared to the case where the particle size distribution is unimodal. The greater the ratio of small particles, the easier it is for the conductive powder to penetrate the green sheet. Therefore, the application of the technology disclosed herein is particularly effective.

The ratio of the conductive powder to the entire conductive paste is not particularly limited. In a suitable example, when the entire conductive paste is set to 100 mass%, the conductive powder is approximately 80 mass% or more, preferably 90 mass% or more, and approximately 98 mass% or less, for example, it can be 96 mass% or less. The higher the ratio of the conductive powder becomes, the easier it is for the conductive powder to penetrate the green sheet. Therefore, the application of the technology disclosed here is particularly effective. In addition, by setting the ratio of the conductive powder to the above, a dense, highly conductive, and low-resistance electrode can be suitably formed.

[Adhesive resin]

The binder resin is a component used to bind the conductive particles constituting the conductive powder to each other and the conductive particles to the components of the green sheet in the state of an unbaked coating film formed by applying the conductive paste to the raw material (green sheet) and drying it. The binder resin is preferably completely sintered at a temperature lower than the sintering temperature of the conductive powder when the conductive paste is baked. In other words, the binder resin is preferably not left in the electrode obtained after baking. There is no particular limitation on the type of binder resin, and for example, a binder resin that has been used in the conductive paste in the past can be appropriately used according to the method of applying the conductive paste, the type of green sheet, etc.

Examples of binder resins include cellulose polymers (cellulose derivatives) such as methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose, acrylic resins such as polymethyl methacrylate, polyethyl methacrylate, and polybutyl methacrylate, epoxy resins, phenolic resins, alkyd resins, polyvinyl alcohol resins, polyvinyl butyral resins, rosin, and rosin such as maleated rosin. Among them, from the perspective of excellent printing suitability when the conductive paste is applied to the green sheet, excellent combustion decomposition during baking, and environmental considerations, it is preferred to use a cellulose-based polymer, such as ethyl cellulose. As a result, an electrode with high conductivity can be suitably obtained after the conductive paste is baked. In addition, without particular limitation, the SP value of the binder resin is approximately 8 (cal/cm ³ ) ^0.5 or more, for example, 9 (cal/cm ³ ) ^0.5 or more, and further 10 (cal/cm ³ ) ^0.5 or more, and approximately 14 (cal/cm ³ ) ^0.5 or less, typically 13 (cal/cm ³ ) ^0.5 or less, for example, 11.5 (cal/cm ³ ) ^0.5 or less.

The ratio of the binder resin to the entire conductive paste is not particularly limited. In a suitable example, when the entire conductive paste is set to 100 mass%, the binder resin is approximately 0.1 mass% or more, typically 0.5 mass% or more, and approximately 10 mass% or less, typically 5 mass% or less.

[Organic solvent (mixed solvent)]

The organic solvent is a component that disperses or dissolves the conductive powder and the binder resin and adjusts the viscosity to be suitable for imparting to the conductive paste. In the technology disclosed herein, the organic solvent is a mixed solvent containing at least a first solvent and a second solvent. Moreover, the SP value of the organic solvent as a whole is adjusted to 9.0 (cal/cm ³ ) ^0.5 ~ 10.1 (cal/cm ³ ) ^0.5 . As a result, an electrode that can suppress the occurrence of sheet corrosion and the penetration of the conductive powder can be formed appropriately.

The SP value of the organic solvent as a whole may be, for example, 9.2 (cal/cm ³ ) ^0.5 or more. This can better suppress the penetration of the conductive powder when the conductive powder is micronized. The SP value of the organic solvent as a whole may be, for example, 9.9 (cal/cm ³ ) ^0.5 or less, or further 9.6 (cal/cm ³ ) ^0.5 or less. This can better suppress the occurrence of sheet corrosion.

The first solvent has an SP value of 9.0 (cal/cm ³ ) ^0.5 or less. By including the first solvent, the occurrence of sheet corrosion of the green sheet can be suppressed. The SP value of the first solvent is not particularly limited, but is generally 7.0 (cal/cm ³ ) ^0.5 or more, typically 8.0 (cal/cm ³ ) ^0.5 or more, for example 8.2 (cal/cm ³ ) ^0.5 or more, and can be 8.5 (cal/cm ³ ) ^0.5 or less. This makes it easy to adjust the SP value of the organic solvent as a whole to the above range.

The type of the first solvent is not particularly limited. For example, a solvent having an SP value of 9.0 (cal/cm ³ ) ^0.5 or less can be cited from ethers, esters, alcohols, amines, amides, hydrocarbons, etc. From the viewpoint of better suppressing the wetting and spreading of the organic solvent, the first solvent is preferably a linear or branched compound without a cyclic structural portion, that is, a non-cyclic compound. However, the first solvent may be a cyclic compound having a cyclic structural portion, such as a cyclic ether.

Ethers are compounds having at least one ether bond (-C-O-C-) on the main chain (parent nucleus). Esters are compounds having at least one ester bond (R-C(=O)-O-R') on the main chain. Alcohols are compounds having a structural part in which the hydrogen atom of a hydrocarbon is replaced by a hydroxyl group, and are compounds represented by the general formula: R-OH. Amines are compounds having a structural part in which at least one hydrogen atom of amine is replaced by a hydrocarbon residue. Amides are compounds having a structural part in which at least one hydrogen atom of amine is replaced by an acyl group (R-C(=O)-). Hydrocarbons are compounds composed of carbon atoms and hydrogen atoms. It should be noted that when there are multiple functional groups in one molecule, they are classified according to the IUPAC nomenclature. When there are ether bonds and hydroxyl groups in one molecule, they are classified as ethers, and in detail, they are classified as glycol ethers described later.

From the perspective of excellent printing suitability, it is preferred to use ethers as the first solvent. As an example of ethers, glycol ethers can be cited. The glycol ethers used as the first solvent are aliphatic compounds or alicyclic compounds in which two hydroxyl groups are bonded to two different carbon atoms, and the hydrogen of one or both of the two hydroxyl groups is substituted by a hydrocarbon residue or a hydrocarbon residue containing an ether bond. The glycol ethers include glycol monoalkyl ethers in which only one hydrogen of the hydroxyl group is substituted and glycol dialkyl ethers in which both hydrogen of the hydroxyl groups are substituted.

In addition, among ethers, non-cyclic low-order glycol ethers represented by the following general formula (Chemical 1) are preferably used because of their high boiling point and the ability to improve the workability of the conductive paste.

R ¹ -(OR ² ) _m -OR ³ ‧‧‧(Chemical 1)

(Herein, ^R1 and ^R3 are each independently a hydrogen atom or a linear or branched alkyl group having 1 to 6 carbon atoms, ^R2 is a linear or branched alkylene group having 2 to 4 carbon atoms, and m is 1 to 4.)

In the general formula (1), alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl, etc. Alkylene groups include ethylene, n-propylene, n-butylene, etc. m is typically 2 to 4.

From the viewpoint of suppressing the SP value to be low and better suppressing the occurrence of wafer corrosion, R ¹ and R ³ may each independently be a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. In addition, R ² may be an alkylene group having 2 carbon atoms, that is, an ethylene group (CH ₂ CH ₃ ).

As glycol ethers, for example, dialkylene glycol monoalkyl ethers, trialkylene glycol monoalkyl ethers, tetraalkylene glycol monoalkyl ethers, dialkylene glycol dialkyl ethers, trialkylene glycol dialkyl ethers, tetraalkylene glycol dialkyl ethers, etc. can be cited. Among them, from the viewpoint of suppressing the SP value to a lower level, it is preferred to use dialkylene glycol dialkyl ethers.

Specific ether compounds (SP value: ^0.5 cal/cm ³ ) include, for example, diethylene glycol diethyl ether (SP value: 8.2), diethylene glycol butyl methyl ether (SP value: 8.2), diethylene glycol dibutyl ether (SP value: 8.3), triethylene glycol dimethyl ether (SP value: 8.4), triethylene glycol butyl methyl ether (SP value: 8.4), and tetraethylene glycol dimethyl ether (SP value: 8.5).

As esters, glycol ether acetates can be cited, for example. Glycol ether acetates are compounds obtained by esterification of the above-mentioned glycol ethers. As an example of glycol ether acetates, non-cyclic lower glycol ethers in which at least one of R ¹ and R ³ in the above-mentioned (Chemical 1) is an acyl group can be cited. In the above-mentioned (Chemical 1), the acyl group is, for example, a straight chain or branched chain having 1 to 6 carbon atoms. The acyl group is, for example, a methyl group, an acetyl group, a propionyl group, a benzoyl group, etc. In addition, as another example of esters, a pine alcohol derivative of pine alcohol can be cited.

Specific ester compounds (SP value, unit: (cal/cm ³ ) ^0.5 ) include, for example, diethylene glycol monobutyl ether acetate (SP value: 8.9), dihydrotrivinyl acetate (SP value: 8.9) obtained by acetylation of dihydroterpineol, and dihydrotrivinyl propionate (SP value: 8.9).

Amines include, for example, primary amines substituted with only one hydrogen atom, secondary amines substituted with two hydrogen atom, and tertiary amines substituted with three hydrogen atom. Specific amine compounds (SP value, unit: (cal/cm ³ ) ^0.5 ) include, for example, di(2-ethylhexyl)amine (SP value: 8.2).

Examples of hydrocarbons include chain saturated hydrocarbons (linear alkanes) having a carbon number of 20 or less, for example, 10 to 15, and chain unsaturated hydrocarbons (linear alkenes, linear alkynes) having a carbon number of 20 or less, for example, 10 to 15. Specific examples of linear alkanes (SP value, unit: (cal/cm ³ ) ^0.5 ) include decane (SP value: 7.7), undecane (SP value: 7.8), dodecane (SP value: 7.9), tridecane (SP value: 7.9), and tetradecane (SP value: 7.9).

In a suitable example, the difference between the SP value of the first solvent and the SP value of the binder resin contained in the raw material green sheet is approximately 0.5 (cal/cm ³ ) ^0.5 or more, typically 1.0 (cal/cm ³ ) ^0.5 or more, preferably 1.5 (cal/cm ³ ) ^0.5 or more. When the SP value of the binder resin contained in the green sheet is 10.0 (cal/cm ³ ) ^0.5 or more, for example, about 10.0 to 11.0 (cal/cm ³ ) ^0.5 , the smaller the SP value of the first solvent, the better. This can better suppress the occurrence of sheet corrosion.

The second solvent has an SP value of 10.0 (cal/cm ³ ) ^0.5 or more. By including the second solvent, the penetration of the conductive powder into the green sheet can be suppressed. Without particular limitation, the SP value of the second solvent is generally 20.0 (cal/cm ³ ) ^0.5 or less, typically 15.0 (cal/cm ³ ) ^0.5 or less, preferably 13.0 (cal/cm ³ ) ^0.5 or less, further 12.0 (cal/cm ³ ) ^0.5 or less, for example, 10.5 (cal/cm ³ ) ^0.5 or less. Thus, it is easy to adjust the SP value of the organic solvent as a whole to the above range.

There is no particular limitation on the type of the second solvent. As an example, a solvent having an SP value of 10.0 (cal/cm ³ ) ^0.5 or more among ethers, esters, alcohols, amines, amides, hydrocarbons, etc. can be cited. The second solvent can be a non-cyclic compound without a cyclic structural portion, or a cyclic compound with a cyclic structural portion. From the viewpoint of improving compatibility and integrity, the second solvent can be a solvent of the same type having the same functional group portion as the first solvent. However, it can also be a different type of solvent that does not have the same functional group portion as the first solvent. It should be noted that the classification of ethers, esters, alcohols, amines, amides, and hydrocarbons is the same as that of the first solvent. Specific examples of the second solvent include the following compounds (a) to (c).

(a) Ethers

From the perspective of excellent printing suitability, it is preferred to use ethers as the second solvent. Glycol ethers are an example of ethers. It should be noted that the classification of glycol ethers is the same as that of the first solvent.

Among ethers, the lower glycol ethers represented by the following general formula (Chemical 2) are preferred because of their higher boiling points and the ability to improve the operability of the conductive paste.

R ¹¹ -(OR ¹² ) _n -OR ¹³ ‧‧‧(Chemistry 2)

(Herein, R ¹¹ and R ¹³ are each independently any one of a hydrogen atom, an alkyl group, an alkoxy group, an acyl group, and an aryl group; R ¹² is a linear or branched alkylene group having 2 to 4 carbon atoms; and n is 1 to 4.)

In the general formula (chemical 2), the alkyl group is, for example, a straight chain or branched chain with 1 to 10 carbon atoms. The alkyl group and the alkylene group are the same as those in the general formula (chemical 1). The alkoxy group is, for example, a straight chain or branched chain with 1 to 10 carbon atoms. Examples of the alkoxy group are methoxy, ethoxy, propoxy, butoxy, etc. Examples of the aryl group are phenyl, benzyl, tolyl, etc.

From the viewpoint of increasing the SP value and better suppressing the permeation of the conductive powder, one of R ¹¹ and R ¹³ may be a hydrogen atom and the other may be an alkyl group or an aryl group having 1 to 6 carbon atoms. In addition, R ² may be an alkylene group having 2 carbon atoms, i.e., an ethylene group (CH ₂ CH ₃ ). In addition, n may be 1 or 2.

Specific compounds (whose SP value is expressed in (cal/cm ³ ) ^0.5 ) include, for example, diethylene glycol (SP value: 12.1), diethylene glycol monoethyl ether (SP value: 10.2), diethylene glycol monobutyl ether (SP value: 10.5), ethylene glycol (SP value: 17.8), ethylene glycol monomethyl ether (SP value: 12.0), ethylene glycol monoethyl ether (SP value: 11.5), propylene glycol monomethyl ether (SP value: 10.2), and phenylpropylene glycol (SP value: 11.5).

(b) Alcohols

Specific examples of alcohols (whose SP value is (cal/cm ³ ) ^0.5 ) include methanol (SP value: 13.8), ethanol (SP value: 12.6), 1-butanol (SP value: 11.4), 2-butanol (SP value: 10.8), tert-butanol (SP value: 10.6), 1-octanol (SP value: 10.3), etc. Alcohols preferably have 6 or more carbon atoms, for example, 6 to 10. Alcohols are preferably linear compounds.

(c) Esters

As esters, for example, glycol ether acetates can be cited. It should be noted that the classification of glycol ether acetates is the same as that of the first solvent. As an example of glycol ether acetates, a lower glycol ether in which at least one of R ¹¹ and R ¹³ in the above-mentioned (Chemical 2) is an acyl group can be cited. The acyl group is, for example, the same as that in the general formula (Chemical 1). As specific examples of esters (whose SP value. Unit is (cal/cm ³ ) ^0.5 .), for example, 2,2,4-trimethyl-1,3-pentanediol-1-monoisobutyrate (SP value: 10.2), propylene carbonate (SP value: 13.3), etc. can be cited.

In a preferred example of the technology disclosed herein, the difference between the SP value of the second solvent and the SP value of the first solvent exceeds 1.5 (cal/cm ³ ) ^0.5 , is approximately 1.8 (cal/cm ³ ) ^0.5 or more, for example, is 2.0 (cal/cm ³ ) ^0.5 or more. Thus, the effect of the technology disclosed herein can be exerted at a higher level.

In another preferred embodiment, the difference between the SP value of the second solvent and the SP value of the binder resin contained in the conductive paste is approximately 1.0 (cal/cm ³ ) ^0.5 or less, and typically 0.5 (cal/cm ³ ) ^0.5 or less. For example, when the SP value of the binder resin contained in the conductive paste is about 10.0 to 11.5 (cal/cm ³ ) ^0.5 , it is preferred that the SP value of the second solvent is also about 10.0 to 11.5 (cal/cm ³ ) ^0.5 . This can further improve the integrity and storage stability of the conductive paste as a whole.

In addition, from the perspective of further improving the integrity and storage stability of the conductive paste as a whole, it is preferred that the second solvent is of the same type as the first solvent. For example, when the first solvent is an ether (especially a glycol ether), it is preferred that the second solvent is also an ether (especially a glycol ether).

From the perspective of improving the operability of the conductive paste and the workability during electrode formation, the boiling point of at least one of the first solvent and the second solvent (preferably both) is approximately 100°C or above, preferably 130°C or above, typically 150°C or above, for example, about 160-260°C. In addition, the molecular weights of the first solvent and the second solvent are approximately 80 or above, typically 100 or above, for example, 130 or above, and approximately 500 or below, typically 300 or below, for example, 250 or below. It should be noted that the "molecular weight" in this specification is the sum of the atomic weights of each element based on the structural formula of the compound.

It should be noted that the organic solvent may be composed of the first solvent and the second solvent, or may contain one or more third solvents in addition to the first solvent and the second solvent. As the third solvent, there is no particular limitation as long as the SP value of the organic solvent as a whole satisfies the above range, and an organic solvent conventionally used in such a conductive paste may be used appropriately. As an example, an organic solvent having an SP value of more than 9.0 (cal/cm ³ ) ^0.5 and less than 10.0 (cal/cm ³ ) ^0.5 among ethers, esters, alcohols, amines, amides, hydrocarbons, etc. may be cited.

When the total amount of the organic solvent is set to 100 mass%, the ratio of the first solvent is approximately 10 mass% or more, for example, 20 mass% or more, and approximately 80 mass% or less, for example, 70 mass% or less. In addition, the ratio of the second solvent is approximately 20 mass% or more, for example, 30 mass% or more, and approximately 90 mass% or less, for example, 80 mass% or less. In addition, the total amount of the first solvent and the second solvent is approximately 50 mass% or more, preferably 80 mass% or more, for example, 90 mass% or more, and particularly 95 mass% or more. Thus, the effect of suppressing sheet erosion and the effect of suppressing the penetration of the conductive powder can be stably combined at a higher level. Furthermore, it is easy to adjust the SP value of the organic solvent as a whole to the above range. In addition, the mixing ratio of the first solvent and the second solvent is not particularly limited. In a suitable example, the first solvent and the second solvent can be adjusted to a mass ratio of the first solvent: the second solvent = 20:80~70:30. In this way, the storage stability of the conductive paste can be better improved.

The ratio of the organic solvent to the entire conductive paste is not particularly limited. In a suitable example, when the entire conductive paste is set to 100 mass%, the organic solvent is approximately 0.1 mass% or more, typically 0.5 mass% or more, and approximately 10 mass% or less, typically 5 mass% or less. This improves, for example, the operability and printing suitability of the conductive paste, and makes it easy to form an electrode of uniform thickness on the raw sheet.

In the conductive paste, various additives can be mixed on the basis of the above-mentioned components. As an example of an additive, for example, inorganic fillers, surfactants, dispersants, viscosity regulators, defoamers, plasticizers, antioxidants, pigments, etc. can be cited. As inorganic fillers, for example, ceramic powders, glass powders, etc. can be cited. The ratio of the additives to the conductive paste as a whole is not particularly limited. From the perspective of achieving higher conductivity, it is preferably set to approximately 5% by mass or less, for example, 3% by mass or less.

The conductive paste disclosed herein can be applied to the raw material by various methods, for example, by adjusting the viscosity to an appropriate value. For example, it can be applied to the raw material by various printing methods such as screen printing, gravure printing, offset printing, inkjet printing, scraper method, spraying method, etc.

The conductive paste disclosed herein can be used, for example, to form electrodes of various electronic components such as inductor components, capacitor components, etc. It should be noted that when using the above conductive paste to manufacture electronic components, the previously known methods in the field of electronic components can be appropriately used. The above conductive paste can be appropriately used in the use of forming electrodes of inductor components such as inductors (coils), choke coils, transformers, etc.

That is, according to the inventors' understanding, for inductor components, for example, compared to capacitor components such as multi-layered ceramic capacitors (MLCC), the pores of the raw materials are relatively large and the porosity is high. Moreover, in recent years, from the perspective of low resistance, there is a tendency to micronize the conductive powder. Therefore, when the electrodes of the inductor components are formed, the organic solvent easily penetrates into the raw materials. In addition, it is also easy for the conductive powder to penetrate the raw materials. Therefore, the application of the conductive paste disclosed herein is effective. The inductor component can be in various mounting forms such as surface mounting type and through-hole mounting type. The inductor component can be of stacked type, winding type, or thin film type. In particular, the conductive paste can realize a low-resistance electrode, and is therefore suitable for forming an internal electrode layer of a stacked chip inductor used in a power supply circuit capable of passing a large current.

FIG1 is a cross-sectional view schematically showing the structure of a stacked chip inductor 1. It should be noted that the dimensional relationship (length, width, thickness, etc.) in FIG1 does not necessarily reflect the actual dimensional relationship. In addition, the symbols X and Z in the figure represent the left and right directions and the up and down directions, respectively. However, they are only directions for convenience of explanation.

The stacked chip inductor 1 has: a main body 10; and external electrodes 20 provided on both side surfaces of the main body 10 in the left-right direction X. The shape of the stacked chip inductor 1 is, for example, 1608 shape (1.6mm×0.8mm), 2520 shape (2.5mm×2.0mm), and other dimensions.

The main body 10 has a structure in which a plurality of magnetic material layers 12 are stacked and integrated in the vertical direction Z. The magnetic material layer 12 is composed of metal materials such as ferrite magnetic materials such as Ni-Cu-Zn ferrite, Fe-Cr-Si alloy, Fe-Al-Si alloy, Fe-Si-M soft magnetic alloy (where M is at least one of chromium, aluminum, and titanium).

A coil conductor serving as an internal electrode layer 14 is provided between each magnetic material layer 12. The coil conductor is formed between each magnetic material layer 12 using the above-mentioned conductive paste. Two coil conductors sandwiching the magnetic material layer 12 and adjacent to each other in the vertical direction Z are connected through a conductive hole provided in the magnetic material layer 12. Thus, the internal electrode layer 14 is formed in a three-dimensional coil shape (spiral shape). Both ends of the coil conductor are connected to the external electrode 20, respectively.

Such a stacked chip inductor 1 can be manufactured, for example, according to the following steps. That is, first, a magnetic material paste containing the above-mentioned metal material, a binder resin and an organic solvent is prepared, and it is supplied to a carrier sheet to form a raw sheet. Then, the raw sheet is pressed and cut into a desired size to obtain a plurality of magnetic material layer-forming sheets. Then, conductive holes are formed at specified positions of the magnetic material layer-forming sheets using a puncher or the like. Then, the above-mentioned conductive paste is printed at specified positions of a plurality of magnetic material layer-forming sheets in a specified coil pattern. Then, they are stacked and pressed to produce a stack of unbaked raw sheets. It is dried and baked, and the green sheet is baked as a whole to form a main body 10 having a magnetic material layer 12 and an internal electrode layer 14. Then, a suitable external electrode forming paste is applied to both ends of the main body 10 and baked to form an external electrode 20. In this way, a laminated chip inductor 1 can be manufactured.

The following describes embodiments of the present invention, but it is not intended to limit the present invention to the contents shown in the following embodiments.

(Implementation Example 1)

[Preparation of conductive paste]

Prepare the conductive paste according to the following steps (samples 1~10).

That is, first, prepare the organic solvent shown in Table 1. Table 1 also shows the SP value. Then, silver powder as a conductive powder, ethyl cellulose (EC) as a binder resin, and a single organic solvent of the type shown in Table 2 are mixed at a mass ratio of silver powder: EC: organic solvent = 92: 0.5~2: 6~7.5, and kneaded with a three-roll mill to prepare a conductive paste (samples 1~10).

[Preparation of raw film]

As the object of coating the above-mentioned conductive paste, a raw sheet is prepared. The raw sheet prepared is a raw sheet that assumes the formation of the electrode layer of the metal sensor. That is, first, Fe-Cr-Si alloy powder as a metal magnetic material, polyvinyl butyral as a binder resin and an organic solvent are mixed and kneaded with a three-roll mill to obtain a magnetic material paste. Then, the magnetic material paste is coated on the surface of a PET carrier sheet and dried to form a raw sheet.

[Evaluation of chip erosion resistance]

As mentioned above, when the conductive paste is printed on the raw sheet, the organic solvent contained in the conductive paste swells or dissolves the binder resin in the raw sheet, and sometimes the sheet becomes partially thinner or has holes, which causes sheet corrosion. In this test example, in order to evaluate the sheet corrosion resistance, the conductive paste is printed and formed on the surface of the raw sheet and dried to form an electrode layer. However, the back of the raw sheet, in other words, the side in contact with the PET carrier sheet, is observed with a microscope or a microscope to confirm whether there are holes on the back. The results are set in Table 2. It should be noted that in Table 2, the situation where holes are confirmed on the back is recorded as "×", and the situation where holes are not confirmed on the back is recorded as "○".

[Evaluation of Ag permeability]

As mentioned above, when the conductive paste is printed on the raw sheet, the organic solvent contained in the conductive paste penetrates into the raw sheet together with the silver powder, and sometimes Ag penetration occurs in which the silver powder penetrates into the inner side of the raw sheet. In this test example, in order to evaluate the Ag permeability, the conductive paste is printed and formed on the surface of the raw sheet and dried to form an electrode layer. Then, SEM-EDS (Energy Dispersive X-ray Spectroscopy) is observed from the back of the raw sheet to confirm whether there are Ag particles on the back. The results are set in Table 2. It should be noted that in Table 2, the case where Ag particles are confirmed on the back is recorded as "×", and the case where Ag particles are not confirmed on the back is recorded as "○". In addition, FIG. 2(A) and FIG. 2(B) show, as an example, SEM-EDS images of FIG. 2(A) in which Ag particles are confirmed on the back side and FIG. 2(B) in which Ag particles are not confirmed on the back side.

As shown in Table 2, it is not possible to suppress both sheet erosion and Ag penetration at the same time using only a single organic solvent. That is, in samples 1 to 9 using only an organic solvent with an SP value of 9.2 (cal/cm ³ ) ^0.5 or less, although sheet erosion was good, Ag penetration occurred in all of them. The reason is not clear, but the inventors believe that the penetration of silver powder is related to the wettability (surface tension) of the organic solvent. That is, an organic solvent with low surface tension is easy to spread on the green sheet and also easy to penetrate into the green sheet. Therefore, it is believed that the penetration of silver powder is easy to cause. In addition, according to a report on powder dispersion (Pigment dispersion and coloring materials in water-soluble acrylic resin coating systems, 62 (8) pp. 524-528, 1989 <Internet> https://www.jstage.jst.go.jp/article/shikizai1937/62/9/62_524/_pdf), surface tension is related to the solubility parameter δ of Fedors, and is expected to change in correlation with the SP value. Therefore, it is speculated that when the SP value becomes less than a specified value, the wettability of the organic solvent increases, resulting in the penetration of silver powder.

In addition, in sample 10 using only an organic solvent with an SP value of 10.5 (cal/cm ³ ) ^0.5 , although Ag permeability was good, sheet corrosion occurred. The reason is not clear, but the inventors believe that the SP value has a great influence on sheet corrosion. That is, it is estimated that when the SP value becomes a specified value or more, the compatibility with the binder resin contained in the green sheet as the raw material increases, resulting in sheet corrosion.

(Example 2)

Solvent C (diethylene glycol dibutyl ether) and solvent M (diethylene glycol monobutyl ether) were mixed at the mass ratio shown in Table 3 to prepare a mixed solvent. Conductive pastes (samples 11 to 17) were prepared using the mixed solvents, and electrode layers were formed in the same manner as in Example 1, and the sheet corrosion resistance and Ag permeability were evaluated. In addition, the printability was also evaluated. It should be noted that the SP value of the organic solvent as a whole is also shown in Table 3.

[Evaluation of printing quality]

The transferability of the conductive paste when printed on the surface of the raw sheet was evaluated. In addition, the printability of samples 3 and 10 was also evaluated in the same manner. The results are shown in Table 3. It should be noted that in Table 3, the situation where the circuit breakage caused by the blurred printing was confirmed was recorded as "×", and the situation where the circuit breakage caused by the blurred printing was not confirmed was recorded as "○".

As shown in Table 3, all samples had good printability. However, in samples 16 and 17, where the overall SP value of the mixed solvent was less than 9.0 (cal/cm ³ ) ^0.5 , although the sheet-etching property was good, Ag penetration occurred.

In contrast, in samples 11 to 15 where the SP value of the mixed solvent was 9.0 to 10.1 (cal/cm ³ ) ^0.5 , both the wafer erosion and the Ag penetration were suppressed.

(Implementation Example 3)

Various organic solvents shown in Table 4 were mixed to prepare a mixed solvent. Conductive pastes (samples 18 to 31) were prepared using the mixed solvents, and electrode layers were formed in the same manner as in Example 2. The sheet etchability, Ag permeability, and printability were evaluated. The results are shown in Table 4. It should be noted that the SP value of the organic solvent as a whole is also shown in Table 4.

[Table 4]

As shown in Table 4, the printability of any sample is good. In particular, according to the research of the inventors, when both solvents are ethers, the printing suitability is particularly excellent, and the mass ratio of the organic solvent can be further reduced.

In addition, sheet corrosion occurred in samples 18 and 19 that did not contain an organic solvent having an SP value of 9.0 (cal/cm ³ ) ^0.5 or less. On the other hand, Ag penetration occurred in samples 20 to 22 that did not contain an organic solvent having an SP value of 10.0 (cal/cm ³ ) ^0.5 or more.

In contrast, in samples 23 to 31, which contained an organic solvent having an SP value of 9.0 (cal/cm ³ ) ^0.5 or less and an organic solvent having an SP value of 10.0 (cal/cm ³ ) ^0.5 or more, and in which the SP value of the organic solvent as a whole was adjusted to 9.0 to 10.1 (cal/cm ³ ) ^0.5 , both sheet corrosion and Ag penetration were suppressed. Among them, in samples 23 to 29, which used a non-cyclic compound as the organic solvent having an SP value of 9.0 (cal/cm ³ ) ^0.5 or less, the spreading of the organic solvent was particularly well suppressed. The reason is not clear, but one of the factors is considered to be that when the first solvent is a non-cyclic (e.g., linear) compound, the first solvent is easily attracted to the polar part (δ ^- generated by the O atom) of the second solvent through hydrophobic interaction, and the wetting and spreading of the first solvent is more effectively suppressed.

These results demonstrate the significance of the technology disclosed herein.

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 its main purpose.

Claims (12)

A conductive paste is a material for forming an electrode obtained by baking, comprising: conductive powder, a binder resin and an organic solvent, wherein the binder resin comprises a cellulose-based polymer, and the binder resin is completely burned during the baking so that no residue remains in the electrode obtained after the baking, and the organic solvent is a mixed solvent, and the mixed solvent comprises: a first solvent having a solubility parameter of 9.0 (cal/cm ³ ) ^0.5 or less in terms of Fedors; and a second solvent having a solubility parameter of 10.0 (cal/cm ³ ) ^0.5 or more in terms of Fedors, and the solubility parameter of the organic solvent in terms of Fedors is 9.0 (cal/cm ³ ) ^0.5 or more and 10.1 (cal/cm ³ ) or less and ^0.5 or less, and when the entire organic solvent is set to 100 mass %, the ratio of the first solvent is 20 mass % or more and 70 mass % or less, and the ratio of the second solvent is 30 mass % or more and 80 mass % or less. The conductive paste as described in item 1 of the patent application, wherein the first solvent is a non-cyclic compound. The conductive paste as described in item 1 or 2 of the patent application, wherein the first solvent is an ether. The conductive paste as claimed in claim 1 or 2, wherein the solubility parameter of the first solvent in terms of Fedors is 7.0 (cal/cm ³ ) ^0.5 or more. The conductive paste as described in item 1 or 2 of the patent application, wherein the second solvent is an ether. The conductive paste as claimed in claim 1 or 2, wherein the solubility parameter of the second solvent in terms of Fedors is 20.0 (cal/cm ³ ) ^0.5 or less. The conductive paste as described in item 1 or 2 of the patent application scope, wherein the second solvent is at least one of ethers, linear alcohols and glycol ether acetates. The conductive paste as claimed in claim 1 or 2, wherein the difference between the solubility parameter of the Fedors in the first solvent and the solubility parameter of the Fedors in the second solvent is 1.8 (cal/cm ³ ) ^0.5 or more. The conductive paste as described in claim 1 or 2, wherein the difference between the solubility parameter of the second solvent Fedors and the solubility parameter of the binder resin Fedors is 1.0 (cal/cm ³ ) ^0.5 or less. The conductive paste as described in item 1 or 2 of the patent application scope, wherein when the entire conductive paste is set to 100% by mass, the ratio of the conductive powder is 90% by mass or more. The conductive paste as described in item 1 or 2 of the patent application scope is used to form the electrode of the inductor component. A method for manufacturing electronic components, comprising the following steps: applying a conductive paste as described in any one of items 1 to 11 of the patent application scope to a green sheet and then baking it to form an electrode.