JP6853606B2 - Conductive paste - Google Patents

Description

The present invention relates to a conductive paste.

In the manufacture of electronic components such as inductors and capacitors, a conductive paste containing a conductive powder, a binder resin, and an organic solvent is prepared, applied to a green sheet as an element by various printing methods, and dried. A method of forming an electrode by firing is widely used (see Patent Documents 1 to 4).

As described in Patent Documents 3 and 4, when a conductive paste is applied to a green sheet, a so-called sheet attack phenomenon may occur in which the organic solvent of the conductive paste erodes the green sheet. If the thickness of the green sheet is locally reduced or a hole is formed in the green sheet due to the sheet attack phenomenon, it may cause poor electrode formation or a short circuit. In this regard, for example, Patent Document 3 discloses that a predetermined alkylene glycol dialkyl ether and / or dialkylene glycol dialkyl ether is used as the organic solvent in order to reduce the occurrence of sheet attack.

Special Table 2010-516603 Japanese Unexamined Patent Publication No. 2012-129447 Japanese Unexamined Patent Publication No. 2012-231119 Japanese Unexamined Patent Publication No. 2012-028356

However, according to the study by the present inventor, even though the seat attack phenomenon has not occurred, a short-circuit defect may occur in the electronic component. When the present inventor analyzed the cause from various angles, the conductive powder newly penetrated into the green sheet together with the organic solvent, moved and diffused in the green sheet in the thickness direction, and a part of the green sheet was found. It turned out that it penetrated to the back side of. As a result, it was found that a short circuit occurred in the electronic component. Therefore, in the manufacture of electronic components, it is necessary to suppress not only the sheet attack but also the permeation of the conductive powder.

The present invention has been made in view of this point, and an object of the present invention is to provide a conductive paste capable of forming an electrode in which both generation of sheet attack and permeation of conductive powder are suppressed. ..

The present invention discloses a conductive paste containing a conductive powder, a binder resin, and an organic solvent. The organic solvent has a first solvent having a Fedors solubility parameter of 9.0 (cal / cm ³ ) ^0.5 or less and a Fedors solubility parameter of 10.0 (cal / cm ³ ) ^0.5 or more. It is a mixed solvent containing a second solvent, and the solubility parameter of Fedors is 9.0 (cal / cm ³ ) ^0.5 or more and 10.1 (cal / cm ³ ) ^0.5 or less. ..

According to the study of the present inventor, the first solvent is useful for suppressing the occurrence of sheet attack, but when used alone, the conductive powder is likely to permeate. On the other hand, the second solvent is useful for suppressing the permeation of the conductive powder, but when used alone, a sheet attack is likely to occur. In the conductive paste of the present invention, the first solvent and the second solvent having such characteristics are contained in the organic solvent, and the solubility parameter of the entire organic solvent is within a predetermined range with the first solvent. By using the second solvent in combination, the advantages of the first solvent and the second solvent are preferably exhibited. As a result, it is possible to preferably form an electrode in which both the generation of sheet attack and the permeation of the conductive powder are suppressed. As a result, it is possible to better avoid short-circuit defects in electronic components.

In addition, in this specification, "Solubility Parameter (SP) of Fedors" means the so-called solubility parameter calculated by the Fedors method described in RFFedors, Polymer Engineering Science, 14, p147 (1974). .. In the Fedors method, it is considered that the aggregation energy density and the molar molecular weight depend on the type and number of substituents, and the solubility parameter is expressed by the following (Equation 1). The solubility parameter is a value unique to each compound.
δ = [ΣE _coh / ΣV] ^0.5 ... (Equation 1)
(Here, Σ _Ecoh indicates the aggregation energy, and ΣV indicates the molar molecular content.)

The solubility parameter δ of the entire organic solvent is calculated by the following equation:
δ _all (cal / cm ³ ) ^0.5 = Σ [Inherent solubility parameter of each organic solvent δ (cal / cm ³ ) ^0.5 × Mass of each organic solvent based on the whole organic solvent (1) Ratio];
Can be calculated with. In other words, first, the product of the unique solubility parameter δ (cal / cm ³ ) ^{0.5 of} each organic solvent and the mass ratio is obtained, and these are added up to obtain the solubility parameter δ _{all of the} entire organic solvent.
In the following, the solubility parameter of Fedors may be simply referred to as "SP value". The SI unit of the SP value is (J / cm ³ ) ^0.5 or (MPa) ^{0.5 , but (cal / cm 3} ) ^0.5 , which is conventionally used in the present specification, is used. Use. The unit of the SP value can be converted by the following formula: 1 (cal / cm ³ ) ^0.5 ≈ 2.05 (J / cm ³ ) ^0.5 ≈ 2.05 (MPa) ^{0.5 ;.} ..

In a preferred embodiment, the first solvent is an acyclic compound. When the first solvent is an acyclic compound, the infiltration of the organic solvent into the green sheet is suppressed at a higher level. Therefore, the effects of the techniques disclosed herein can be better exerted. In another preferred embodiment, the first solvent is ethers. Ethers are preferable because they are excellent not only in SP value but also in various properties such as printability.

In a preferred embodiment, the second solvent is ethers. Ethers are preferable because they are excellent not only in SP value but also in various properties such as printability.

In a preferred embodiment, when the total amount of the organic solvent is 100% by mass, the ratio of the first solvent is 20% by mass or more and 70% by mass or less, and the ratio of the second solvent is 30. It is mass% or more and 80 mass% or less. Thereby, the effect of suppressing the sheet attack and the effect of suppressing the permeation of the conductive powder can be combined at a more stable and high level.

In a preferred embodiment, the proportion of the conductive powder is 90% by mass or more when the total amount of the conductive paste is 100% by mass. By setting the ratio of the conductive powder as described above, it is possible to preferably form an electrode having high density and electrical conductivity and low resistance.

The conductive paste can be suitably used for forming an electrode of an inductance component, for example.

It is sectional drawing which shows typically the structure of the laminated chip inductor which concerns on one Embodiment. It is an example of the evaluation result of Ag permeability, (A) is an SEM-EDS image when Ag fine particles are confirmed, and (B) is an SEM-EDS image when Ag fine particles are not confirmed.

Hereinafter, preferred embodiments of the present invention will be described. Matters other than those specifically mentioned in the present specification (for example, organic solvents) and necessary for carrying out the present invention (for example, a method for preparing a conductive paste, a method for applying a conductive paste, etc.) are referred to in the present specification. It can be understood based on the technical content taught and the general technical common knowledge of those skilled in the 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 addition, the notation of "A to B" indicating a range in this specification means A or more and B or less.

The conductive paste disclosed herein contains a conductive powder, a binder resin, and an organic solvent. The organic solvent is a mixed solvent containing at least two kinds of solvents having different SP values. Hereinafter, each component will be described in order.

[Conductive powder]
The conductive powder is a component that imparts electrical conductivity to an electrode obtained by firing a conductive paste. The type of the conductive powder is not particularly limited, and those used in the conventional conductive paste of this type can be appropriately used depending on the use of the conductive paste and the like. Typical examples are gold (Au), silver (Ag), platinum (Pt), palladium (Pd), aluminum (Al), nickel (Ni), copper (Cu), ruthenium (Ru), rhodium (Rh), tungsten. Metals such as (W), iridium (Ir), osmium (Os), and their alloys, such as silver-palladium (Ag-Pd), silver-platinum (Ag-Pt), silver-copper (Ag-Cu). And other silver alloys. Of these, silver and silver alloys are preferable because of their relatively low cost and high electrical conductivity.

However, the conductive powder is, for example, a carbon material such as graphite or carbon black, a LaSrCoFeO ₃ series oxide (for example, LaSrCoFeO ₃ ), a LaMnO ₃ series oxide (for example, LaSrGaMgO ₃ ), or a LaFeO ₃ series oxide (for example, LaSrFeO _3). ), LaCoO ₃ series oxide (for example, LaSrCoO ₃ ) and the like may be conductive ceramics typified by a transition metal perovskite type oxide.

The properties of the conductive powder are not particularly limited, and can be appropriately adjusted according to the use of the conductive paste and the like. For example, in an application for forming an electrode of an inductance component such as an inductor, the average particle size is approximately 0.1 μm or more, typically 0.5 μm or more, for example, 1 μm or more, and is approximately 5 μm or less, typically 4 μm. Hereinafter, for example, a conductive powder having a diameter of 3 μm or less can be preferably used. By setting the average particle size to a predetermined value or more, it is possible to suppress the aggregation of the conductive powder in the conductive paste and improve the filling property of the electrode obtained after firing. By setting the average particle size to a predetermined value or less, it is possible to improve the ease of sintering and reduce the resistance of the electrode. In addition, in this specification, "average particle diameter" means integrated value 50% particle diameter in particle size distribution (number basis) of circle equivalent diameter based on electron microscope observation.

Conductive powder is, in the laser diffraction scattering method particle size distribution based on volume-based, the D ₁₀ particle diameter corresponding to cumulative 10% by volume from the smaller particle size, generally 1.6μm or less, typically 1. It may be 3 μm or less, for example 1.0 μm or less. Thus if D ₁₀ particle size is small, transmittance of the conductive powder mentioned above is likely to occur on the green sheet. According to the art disclosed herein, when the conductive powder has such a D ₁₀ particle size also can be suitably suppress permeation of the conductive powder.

In one preferred example, the conductive powder contains two particle groups having different average particle sizes from the viewpoint of improving the denseness and filling property of the electrode. In other words, the particle size distribution of the conductive powder is bimodal. In one specific example, the average particle size of the first particle group is approximately 1 to 5 μm, for example, 2 ± 0.5 μm, and the average particle size of the second particle group is approximately 0.5 to 2 μm, for example 0. It is in the range of .5 ± 0.5 μm. When the particle size distribution is bimodal, the proportion of particles having a smaller particle size is larger than that when the particle size distribution is monomodal. The higher the proportion of small particles, the easier it is for the above-mentioned conductive powder to permeate on the green sheet. Therefore, the application of the techniques disclosed herein is particularly effective.

The ratio of the conductive powder to the entire conductive paste is not particularly limited. In one preferred example, when the total conductive paste is 100% by mass, the conductive powder is approximately 80% by mass or more, preferably 90% by mass or more, and approximately 98% by mass or less, for example, 96% by mass or less. It is good to be. The higher the proportion of the conductive powder, the easier it is for the above-mentioned conductive powder to permeate on the green sheet. Therefore, the application of the techniques disclosed herein is particularly effective. Further, by setting the ratio of the conductive powder, it is possible to preferably form an electrode having high density and electrical conductivity and low resistance.

[Binder resin]
The binder resin is an unfired coating film obtained by applying a conductive paste on an element body (green sheet) and drying it, and the conductive particles constituting the conductive powder, or the conductive particles and the green sheet. It is a component that adheres to. The binder resin preferably burns out at a temperature lower than the sintering temperature of the conductive powder when the conductive paste is fired. In other words, it is preferable that the binder resin does not remain on the electrode obtained after firing. The type of the binder resin and the like are not particularly limited, and for example, those used in the conventional conductive paste of this type can be appropriately used depending on the method of applying the conductive paste, the type of the green sheet and the like.

Examples of binder resins include cellulosic polymers (cellulose derivatives) such as methylcellulose, ethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, and carboxymethylcellulose, acrylic resins such as polymethylmethacrylate, polyethylmethacrylate, and polybutylmethacrylate, and epoxy resins. Examples thereof include phenol-based resins, alkyd-based resins, polyvinyl alcohol-based resins, polyvinyl butyral-based resins, rosins, and rosin-based resins such as rosin maleated. Among them, it is preferable to use a cellulosic polymer, for example, ethyl cellulose, from the viewpoints of excellent printability when applying the conductive paste on the green sheet, excellent combustion decomposition during firing, environmental consideration, and the like. .. This makes it possible to preferably obtain an electrode having high electrical conductivity after firing the conductive paste.

The ratio of the binder resin to the entire conductive paste is not particularly limited. In one preferred example, when the total conductive paste is 100% by mass, the binder resin is approximately 0.1% by mass or more, typically 0.5% by mass or more, and approximately 10% by mass or less. Typically, it is preferably 5% by mass or less.

[Organic solvent (mixed solvent)]
The organic solvent is a component for dispersing or dissolving the conductive powder and the binder resin to adjust the viscosity of the conductive paste to be suitable for imparting. In the technique disclosed herein, the organic solvent is a mixed solvent containing at least a first solvent and a second solvent. The SP value of the entire organic solvent is adjusted to ^{9.0 (cal / cm 3} ) ^{0.5 to} 10.1 (cal / cm ³ ) ^0.5. As a result, it is possible to preferably form an electrode in which the occurrence of sheet attack and the permeation of the conductive powder are completely suppressed.
The SP value of the entire organic solvent may be, for example, 9.2 (cal / cm ³ ) ^0.5 or more. As a result, when the conductive powder is made into fine particles, the permeation of the conductive powder can be better suppressed. The SP value of the entire organic solvent may be, for example, 9.9 (cal / cm ³ ) ^0.5 or less, and further may be 9.6 (cal / cm ³ ) ^0.5 or less. As a result, the occurrence of seat attack can be better suppressed.

The first solvent is a solvent having an SP value of 9.0 (cal / cm ³ ) of ^0.5 or less. By containing the first solvent, it is possible to suppress the occurrence of sheet attack on the green sheet. The SP value of the first solvent is approximately 7.0 (cal / cm ³ ) ^0.5 or higher, typically 8.0 (cal / cm 3) ^0.5 or higher, for example 8.2 (cal / cm ^3). ) ^0.5 or more, for example 8.5 (cal / cm ³ ) ^0.5 or less. This makes it easier to adjust the SP value of the entire organic solvent within the above range.

The type of the first solvent is not particularly limited. As an example, among ethers, esters, alcohols, amines, amides, hydrocarbons and the like, those having an SP value of 9.0 (cal / cm ³ ) of ^0.5 or less can be mentioned. The first solvent is preferably a linear or branched compound having no cyclic structural portion, that is, an acyclic compound, from the viewpoint of better suppressing the wetting and spreading of the organic solvent. However, the first solvent may be a cyclic compound having a cyclic structural portion, for example, a cyclic ether.

Ethers are compounds having at least one ether bond (-C-OC-) in the main chain (matrix). Esters are compounds having at least one ester bond (RC (= O) -OR') in the main chain. Alcohols are compounds in which the hydrogen atom of a hydrocarbon is substituted with a hydroxyl group, and are compounds represented by the general formula: R-OH. Amines are compounds in which at least one hydrogen atom of ammonia is replaced with a hydrocarbon residue. Amides are compounds in which at least one hydrogen atom of ammonia is substituted with an acyl group (RC (= O)-). Hydrocarbons are compounds composed of carbon atoms and hydrogen atoms. When one molecule has a plurality of functional groups, it is classified according to the IUPAC nomenclature, but when one molecule has an ether bond and a hydroxyl group, it is classified into ethers, and more specifically, glycol ethers described later. I decided to.

From the viewpoint of excellent printability and the like, it is preferable to use ethers as the first solvent. As an example of ethers, glycol ethers can be mentioned. 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 one of the two hydroxyl groups or A compound in which the hydrogen of two hydroxyl groups is replaced with a hydrocarbon residue or a hydrocarbon residue containing an ether bond. Glycol ethers include glycol monoalkyl ethers in which only one hydroxyl group hydrogen is substituted, and glycol dialkyl ethers in which both two hydroxyl group hydrogens are substituted.

In addition, among ethers, acyclic lower glycol ethers represented by the following general formula (Chemical Formula 1) are used because they have a relatively high boiling point and can improve the handleability of the conductive paste. preferable.
R ^1- ( ^{OR 2} ) _m- O-R ³ ... (Chemical formula 1)
(Here, R ¹ and R ³ are independently hydrogen atoms or linear or branched alkyl groups having 1 to 6 carbon atoms, and R ² is a linear or branched chain having 2 to 4 carbon atoms. It is an alkylene group of, and m is 1 to 4.)

In the general formula (Chemical formula 1), the alkyl group is, for example, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, an n-hexyl group or the like. is there. The alkylene group is, for example, an ethylene group, an n-propylene group, an n-butylene group and the like. m is typically 2-4.
From the viewpoint of suppressing the SP value to a low level and better suppressing the occurrence of sheet attack, it is preferable that R ¹ and R ³ are independently hydrogen atoms or alkyl groups having 1 to 4 carbon atoms. Further, it is preferable that R ² is an alkylene group having 2 carbon atoms, that is, an ethylene group (CH ₂ CH ₂ ).

Examples of glycol ethers include dialkylene glycol monoalkyl ethers, trialkylene glycol monoalkyl ethers, tetraalkylene glycol monoalkyl ethers, dialkylene glycol dialkyl ethers, trialkylene glycol dialkyl ethers, and tetraalkylene glycol dialkyl. Examples include ethers. Of these, the use of dialkylene glycol dialkyl ethers is preferable from the viewpoint of keeping the SP value low.

Specific compounds of ethers (and their SP value. The unit is (cal / cm ³ ) ^0.5 .) include, for example, diethylene glycol diethyl ether (SP value: 8.2) and 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), tetraethylene glycol Examples thereof include dimethyl ether (SP value: 8.5).

Examples of the esters include glycol ether acetates. Glycol ether acetates are compounds in which the above-mentioned glycol ethers are esterified. Examples of glycol ether acetates include acyclic lower glycol ethers in which at least one ^{of R 1} and R ^{3 of (Chemical Formula 1) described above is an acyl group.} In the above (Chemical formula 1), the acyl group is, for example, a straight chain or a branched chain having 1 to 6 carbon atoms. The acyl group is, for example, a metanoyl group, an etanoyl group, a propanoyl group, a benzoyl group and the like. In addition, as another example of esters, a tarpineol derivative of tarpineol can be mentioned.

Specific compounds of esters (and their SP value. Unit is (cal / cm ³ ) ^0.5 .) include, for example, diethylene glycol monobutyl ether acetate (SP value: 8.9) and dihydroterpineol acetylated. Dihydroterpinyl acetate (SP value: 8.9), dihydroterpinyl propionate (SP value: 8.9) and the like can be mentioned.

The amines include, for example, a primary amine in which only one hydrogen is substituted, a secondary amine in which two hydrogens are substituted, and a tertiary amine in which three hydrogens are substituted. And, including. Specific compounds of amines (and their SP value. The unit is (cal / cm ³ ) ^0.5 .) include, for example, di (2-ethylhexyl) amine (SP value: 8.2). Be done.

Examples of hydrocarbons include chain saturated hydrocarbons having 20 or less carbon atoms, for example 10 to 15 (straight chain alkenes), and chain unsaturated hydrocarbons having 20 or less carbon atoms, for example 10 to 15 (straight chain). Alkenes, straight chain alcohols) and the like. Specific examples of linear alkanes (and their SP value. The unit is (cal / cm ³ ) ^0.5 .) include decan (SP value: 7.7), undecane (SP value: 7.8), and dodecane. (SP value: 7.9), tridecane (SP value: 7.9), tetradecane (SP value: 7.9) and the like can be mentioned.

In one preferred example, the difference between the SP value of the first solvent and the SP value of the binder resin contained in the green sheet is approximately 0.5 (cal / cm ³ ) ^0.5 or more, typically 1. It is 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, 10.0 to 11.0 (cal / cm ³ ) ^0.5 , the first The smaller the SP value of the solvent, the more preferable. As a result, the occurrence of seat attack can be better suppressed.

The second solvent is a solvent having an SP value of 10.0 (cal / cm ³ ) of ^0.5 or more. By containing the second solvent, the permeation of the conductive powder through the green sheet can be suppressed. The SP value of the second solvent is approximately 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). 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. This makes it easier to adjust the SP value of the entire organic solvent within the above range.

The type of the second solvent is not particularly limited. As an example, among ethers, esters, alcohols, amines, amides, hydrocarbons and the like, those having an SP value of 10.0 (cal / cm ³ ) of ^0.5 or more can be mentioned. The second solvent may be an acyclic compound having no cyclic structural portion, or may be a cyclic compound having a cyclic structural portion. From the viewpoint of enhancing compatibility and integrity, the second solvent is preferably the same type of solvent having the same functional group portion as the first solvent. However, it may be a different type of solvent that does not have the same functional group portion as the first solvent. 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 viewpoint of excellent printability and the like, it is preferable to use ethers as the second solvent. As an example of ethers, glycol ethers can be mentioned. The classification of glycol ethers is the same as that of the first solvent.

Among the ethers, the lower glycol ethers represented by the following general formula (Chemical Formula 2) are preferably used because they have a relatively high boiling point and can improve the handleability of the conductive paste.
^{R 11 - (O-R 12} ) n -O-R 13 ··· ( of 2)
(Here, R ¹¹ and R ¹³ are each independently one of a hydrogen atom, an alkyl group, an alkoxy group, an acyl group, and an aryl group, and R ¹² is a linear or linear group having 2 to 4 carbon atoms. It is an alkylene group of a branched chain, and n is 1 to 4).

In the general formula (Chemical Formula 2), the alkyl group is, for example, a straight chain or a branched chain having 1 to 10 carbon atoms. The alkyl group and the alkylene group are, for example, the same as those in the general formula (Chemical Formula 1). The alkoxy group is, for example, a straight chain or a branched chain having 1 to 10 carbon atoms. The alkoxy group is, for example, a methoxy group, an ethoxy group, a propoxy group, a butoxy group and the like. The aryl group is, for example, a phenyl group, a benzyl group, a tolyl group and the like.
From the viewpoint of improving the SP value and better suppressing the permeation of the conductive powder, one of R ¹¹ and R ¹³ is a hydrogen atom, and the other one is an alkyl group having 1 to 6 carbon atoms or It is preferably an aryl group. Further, it is preferable that R ² is an alkylene group having 2 carbon atoms, that is, an ethylene group (CH ₂ CH ₃ ). Further, n is preferably 1 or 2.

Specific compounds (and their SP value. The unit is (cal / cm ³ ) ^0.5 .) include, for example, diethylene glycol (SP value: 12.1) and 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), phenylpropylene glycol (SP value: 11.5) and the like.

(B) Alcohols As specific examples of alcohols (and their SP value. The unit is (cal / cm ³ ) ^0.5 .), For example, methanol (SP value: 13.8) and 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) and the like. Alcohols preferably have 6 or more carbon atoms, for example, 6 to 10 carbon atoms. The alcohols are preferably linear compounds.

(C) Esters Examples of the esters include glycol ether acetates. The classification of glycol ether acetates is the same as that of the first solvent. Examples of glycol ether acetates include lower glycol ethers in which at least one ^{of R 11} and R ¹³ of (Chemical Formula 2) described above is an acyl group. The acyl group is, for example, the same as that of the general formula (Chemical formula 1). Specific examples of esters (and their SP value; unit is (cal / cm ³ ) ^0.5 .) Are, for example, 2,2,4-trimethyl-1,3-pentanediol-1-monoiso. Butyrate (SP value: 10.2), propylene carbonate (SP value: 13.3) and the like can be mentioned.

In one preferred example of the technique 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 and is generally 1.8 (cal / cm ³ ) ^0.5 or more, for example 2.0 (cal / cm ³ ) ^0.5 or more. As a result, the effects of the techniques disclosed herein can be exerted at a higher level.

In another preferred example, 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, typically. Is 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} , the SP value of the second solvent is also 10.0 to 11.5 (cal / cm 3). cal / cm ³ ) It is preferably about ^0.5. As a result, the integrity and storage stability of the conductive paste as a whole can be further improved.

Further, from the viewpoint of further enhancing the integrity and storage stability of the conductive paste as a whole, it is preferable that the second solvent is similar to that of the first solvent. For example, when the first solvent is ethers (particularly glycol ethers), the second solvent is also preferably ethers (particularly glycol ethers).

From the viewpoint of improving the handleability of the conductive paste and the workability at the time of electrode formation, the boiling point of at least one (preferably both) of the first solvent and the second solvent is preferably about 100 ° C. or higher, preferably. It is preferably 130 ° C. or higher, typically 150 ° C. or higher, for example, about 160 to 260 ° C. The molecular weights of the first solvent and the second solvent are approximately 80 or more, typically 100 or more, for example 130 or more, and approximately 500 or less, typically 300 or less, for example 250 or less, respectively. It would be nice to have it. In the present specification, "molecular weight" is the total atomic weight of each element based on the structural formula of the compound.

The organic solvent may be composed of the above-mentioned first solvent and the second solvent, or one or two kinds of the third solvent in addition to the first solvent and the second solvent. The above may be included. The third solvent is not particularly limited as long as the SP value of the entire organic solvent satisfies the above range, and those used in the conventional conductive paste of this type can be appropriately used. As an example, among ethers, esters, alcohols, amines, amides, hydrocarbons, etc., the SP value exceeds 9.0 (cal / cm ³ ) ^0.5 and 10.0 (cal / cm). ³ ) ^{Those less than 0.5} can be mentioned.

When the total amount of the organic solvent is 100% by mass, the ratio of the first solvent is approximately 10% by mass or more, for example, 20% by mass or more, and approximately 80% by mass or less, for example, 70% by mass or less. Good. The proportion of the second solvent is preferably about 20% by mass or more, for example, 30% by mass or more, and about 90% by mass or less, for example, 80% by mass or less. The total of the first solvent and the second solvent is preferably about 50% by mass or more, preferably 80% by mass or more, for example, 90% by mass or more, and particularly preferably 95% by mass or more. As a result, the effect of suppressing the sheet attack and the effect of suppressing the permeation of the conductive powder can be stably combined at a higher level. Further, it becomes easy to adjust the SP value of the entire organic solvent within the above range. The mixing ratio of the first solvent and the second solvent is not particularly limited, but in one preferred example, the first solvent and the second solvent are mixed in a mass ratio of the first solvent: the second solvent = 20. It is advisable to adjust between: 80 and 70:30. As a result, the storage stability of the conductive paste can be improved.

The ratio of the organic solvent to the entire conductive paste is not particularly limited. In one preferred example, when the total conductive paste is 100% by mass, the amount of the organic solvent is approximately 0.1% by mass or more, typically 0.5% by mass or more, and approximately 10% by mass or less. Typically, it is preferably 5% by mass or less. This improves, for example, the handleability and printability of the conductive paste, and facilitates the formation of electrodes having a uniform thickness on the green sheet.

In addition to the above-mentioned constituent components, various additive components can be added to the conductive paste. Examples of additive components include inorganic fillers, surfactants, dispersants, viscosity modifiers, defoamers, plasticizers, antioxidants, pigments and the like. Examples of the inorganic filler include ceramic powder and glass powder. The ratio of the additive component to the entire conductive paste is not particularly limited, but from the viewpoint of achieving higher electrical conductivity, it is preferably about 5% by mass or less, for example, 3% by mass or less.

The conductive paste disclosed herein can be applied onto the element body by various methods, for example, by adjusting the viscosity to an appropriate level. For example, it can be applied onto the element body by various printing methods such as screen printing, gravure printing, offset printing, and inkjet printing, a doctor blade method, a spray method, and the like.

The conductive paste disclosed herein can be used for forming electrodes of various electronic components such as inductance components and capacitor components. In manufacturing an electronic component using the conductive paste, a conventionally known method in the field of electronic components can be appropriately used. The conductive paste can be suitably used in applications such as forming electrodes for inductance components such as inductors (coils), choke coils, and transformers.

That is, according to the knowledge of the present inventor, in the inductance component, the pore diameter of the element body is relatively large and the porosity is relatively larger than that of the capacitor component such as a multilayer ceramic capacitor (MLCC). Is high. Further, in recent years, from the viewpoint of lowering the resistance, the conductive powder tends to be made into fine particles. Therefore, when forming the electrodes of the inductance component, the organic solvent easily penetrates into the element body. In addition, the conductive powder is likely to permeate the element body. Therefore, the use of the conductive paste disclosed herein is effective. The inductance component may be of various mounting forms such as a surface mount type and a through-hole mount type. The inductance component may be a laminated type, a winding type, or a thin film type. In particular, since the conductive paste can realize a low-resistance electrode, it is suitable for forming an internal electrode layer of a laminated chip inductor used in a power supply circuit capable of passing a large current.

FIG. 1 is a cross-sectional view schematically showing the structure of the laminated chip inductor 1. The dimensional relationship (length, width, thickness, etc.) in FIG. 1 does not necessarily reflect the actual dimensional relationship. Further, the symbols X and Z in the drawing represent the horizontal direction and the vertical direction, respectively. However, this is just for convenience of explanation.

The laminated chip inductor 1 includes a main body portion 10 and external electrodes 20 provided on both side surface portions of the main body portion 10 in the left-right direction X. The shape of the laminated chip inductor 1 is, for example, a size such as 1608 shape (1.6 mm × 0.8 mm) or 2520 shape (2.5 mm × 2.0 mm).

The main body 10 has a structure in which a plurality of magnetic material layers 12 are laminated and integrated in the vertical direction Z. The magnetic material layer 12 is, for example, a ferrite magnetic material such as Ni-Cu-Zn-based ferrite, a Fe-Cr-Si alloy, a Fe-Al-Si alloy, or a Fe-Si-M-based soft magnetic alloy (where M is. It is composed of a metal-based material such as chrome, aluminum, and at least one of titanium.).
A coil conductor as an internal electrode layer 14 is provided between the magnetic material layers 12. The coil conductor is formed between the magnetic material layers 12 by using the above-mentioned conductive paste. Two coil conductors adjacent to each other in the vertical direction Z with the magnetic material layer 12 interposed therebetween are conducted through via holes provided in the magnetic material layer 12. As a result, 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.

Such a laminated chip inductor 1 can be manufactured, for example, by the following procedure. That is, first, a magnetic paste containing the above-mentioned metal-based material, binder resin, and organic solvent is prepared, and this is supplied onto a carrier sheet to form a green sheet. Next, after rolling this green sheet, it is cut to a desired size to obtain a plurality of magnetic layer forming sheets. Next, a via hole is formed at a predetermined position on the magnetic layer forming sheet by using a drilling machine or the like. Next, the above-mentioned conductive paste is printed at a predetermined position on a plurality of magnetic layer forming sheets with a predetermined coil pattern. Next, these are laminated and crimped to prepare a laminated body of unfired green sheets. By drying and firing this, the green sheet is integrally fired, and the main body portion 10 having the magnetic material layer 12 and the internal electrode layer 14 is formed. Then, an appropriate external electrode forming paste is applied to both ends of the main body 10 and fired to form the external electrode 20. In this way, the multilayer chip inductor 1 can be manufactured.

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

(Example 1)
[Preparation of conductive paste]
Conductive pastes (Samples 1-8, 10) were prepared by the following procedure.
That is, first, the organic solvents shown in Table 1 were prepared. Table 1 also shows the SP values. Next, silver powder as a conductive powder, ethyl cellulose (EC) as a binder resin, and a single organic solvent of the types shown in Table 2 were mixed with silver powder: EC: organic solvent = 92: 0.5 to 2. : The mixture was blended in a mass ratio of 6 to 7.5 and kneaded with a three-roll mill to prepare a conductive paste (samples 1 to 8 and 10).

[Preparation of green sheet]
A green sheet was prepared as a target for applying the above conductive paste. A green sheet was prepared assuming the formation of an electrode layer of a metal inductor. That is, first, Fe-Cr-Si alloy powder as a metallic magnetic material, polyvinyl butyral as a binder resin, and an organic solvent were mixed and kneaded with a three-roll mill to obtain a magnetic paste. Next, this magnetic paste was applied to the surface of a carrier sheet made of PET and dried to form a green sheet.

[Evaluation of seat attack]
As described above, when the conductive paste is printed on the green sheet, the organic solvent contained in the conductive paste swells or dissolves the binder resin in the green sheet, and the sheet is locally thinned or punctured. A seat attack phenomenon may occur. In this test example, in order to evaluate the sheet attack property, the electrode layer was formed by printing and molding the conductive paste on the surface of the green sheet and drying it. Then, the back surface of the green sheet, in other words, the surface in contact with the PET carrier sheet, was observed with a microscope or a microscope to confirm whether or not there was a hole in the back surface. The results are shown in Table 2. In Table 2, the case where a hole was confirmed on the back surface was designated as “x”, and the case where no hole was confirmed on the back surface was designated as “〇”.

[Evaluation of Ag permeability]
As described above, when the conductive paste is printed on the green sheet, the organic solvent contained in the conductive paste permeates the green sheet together with the silver powder, and Ag permeation in which the silver powder permeates to the back side of the green sheet may occur. is there. In this test example, in order to evaluate Ag permeability, an electrode layer was formed by printing and molding the conductive paste on the surface of the green sheet and drying it. Then, SEM-EDS (Energy Dispersive X-ray Spectroscopy) was observed from the back surface of the green sheet, and it was confirmed whether Ag fine particles were present on the back surface. The results are shown in Table 2. In Table 2, the case where Ag fine particles were confirmed on the back surface was designated as “x”, and the case where Ag fine particles were not confirmed on the back surface was designated as “〇”. Further, FIG. 2 shows, as an example, SEM-EDS images of the case where Ag fine particles are confirmed (A) and the case where Ag fine particles are not confirmed (B).

As shown in Table 2, the sheet attack and Ag permeation could not be suppressed at the same time with only a single organic solvent. That is, in Samples 1 to 8 in which an organic solvent having an SP value of 9.2 (cal / cm ³ ) of ^0.5 or less was used alone, although the sheet attack property was good, Ag permeation occurred in all of them. The reason for this is not clear, but the present inventor considers that the permeability of the silver powder is related to the wettability (surface tension) of the organic solvent. That is, the organic solvent having a low surface tension easily wets and spreads on the green sheet and easily penetrates into the green sheet. Therefore, it is considered that the permeation of the silver powder is likely to occur. In addition, a report on the dispersion system of powder (pigment dispersion in water-soluble acrylic resin paint system, coloring material, 62 (8) pp.524-528,1989 <Internet> https://www.jstage.jst.go. According to jp / article / shikizai1937 / 62/9 / 62_524 / _pdf), it is predicted that the surface tension is related to the solubility parameter δ of Fedors and changes in correlation with the SP value. Therefore, when the SP value is equal to or less than a predetermined value, it is presumed that the wettability of the organic solvent is improved and the silver powder is permeated.

Further, in the sample 10 using only the organic solvent having an SP value of 10.5 (cal / cm ³ ) ^0.5 , although the Ag permeability was good, a sheet attack occurred. The reason for this is not clear, but the present inventor believes that the SP value greatly affects the seat attack property. That is, when the SP value is equal to or higher than a predetermined value, it is presumed that the compatibility with the binder resin contained in the green sheet is enhanced and a sheet attack occurs.

(Example 2)
Solvent C (diethylene glycol dibutyl ether) and solvent M (diethylene glycol monobutyl ether) were mixed at the mass ratios shown in Table 3 to prepare a mixed solvent. Using this, conductive pastes (samples 11 to 17) were prepared, an electrode layer was formed in the same manner as in Example 1, and sheet attack property and Ag permeability were evaluated. In addition, printability was also evaluated here.

[Evaluation of printability]
The transferability when the conductive paste was printed and molded on the surface of the green sheet was evaluated. The printability of Samples 3 and 10 was also evaluated in the same manner. The results are shown in Table 3. In Table 3, the case where the disconnection due to the printing blur or the like was confirmed was evaluated as “x”, and the case where the disconnection due to the printing blur or the like was not confirmed was evaluated as “〇”.

As shown in Table 3, all the samples were good in printability. However, in the samples 16 and 17 in which the total SP value of the mixed solvent was ^{less than 9.0 (cal / cm 3} ) ^0.5 , although the sheet attack property was good, Ag permeation occurred.
On the other hand, in the samples 11 to 15 in which the SP value of the mixed solvent was 9.0 to 10.1 (cal / cm ³ ) ^0.5 , sheet attack and Ag permeation were suppressed at the same time.

(Example 3)
Various organic solvents shown in Table 4 were mixed to prepare a mixed solvent. Using this, conductive pastes (samples 19 to 21, 23 to 31) were prepared, an electrode layer was formed in the same manner as in Example 2, and sheet attack property, Ag permeability, and printability were evaluated. The results are shown in Table 4.

As shown in Table 4, all the samples were good in printability. In particular, according to the study by the present inventor, when both of the two types of solvents are ethers, the printability is remarkably excellent and the mass ratio of the organic solvent can be made smaller.

Further, in the sample 1-9 SP value does not contain the 9.0 (cal ^/ cm ^{3) 0.5} or less of the organic solvent, sheet attack occurs. On the other hand, in the samples 20 and 21 containing no organic solvent having an SP value of 10.0 (cal / cm ³ ) of ^0.5 or more, Ag permeation occurred.
On the other hand, it contains an organic solvent having an SP value of 9.0 (cal / cm ³ ) of ^0.5 or less and an organic solvent having an SP value of 10.0 (cal / cm ³ ) of ^{0.5 or more.} In the samples 23 to 31 in which the overall SP value was adjusted to 9.0 to 10.1 (cal / cm ³ ) ^0.5 , sheet attack and Ag permeation were suppressed at the same time. Among them, in the samples 23 to 29 in which the acyclic compound was used as the organic solvent having an SP value of 9.0 (cal / cm ³ ) ^{0.5 or less, the wet spread of the organic solvent was particularly well suppressed.} The reason for this is not clear, but one reason is that when the first solvent is an acyclic (for example, a linear) compound, the first solvent becomes a polar part of the second solvent due to hydrophobic interaction (for example, a linear compound). ^{It is considered that it became easier to be attracted to δ −} ) by the O atom, and the wet spread of the first solvent was better suppressed.

1 Laminated chip inductor 10 Main body 12 Magnetic material layer 14 Internal electrode layer 20 External electrode

Claims (9)

A conductive paste for forming an electrode by applying it on a green sheet containing polyvinyl butyral resin as a binder and firing it.
Contains conductive powder, binder resin, and organic solvent,
The organic solvent is
A first solvent having a Fedors solubility parameter of 9.0 (cal / cm ³ ) of ^{0.5 or less,}
Solubility parameter Fedors is Ri der 10.0 (cal ^/ cm ^{3) 0.5} or more, and ethers, at least Tsudea Ru second solvent of linear alcohols and glycol ether acetates When,
The solubility parameter of Fedors is 9.0 (cal / cm ³ ) ^0.5 or more and 10.1 (cal / cm ³ ) ^0.5 or less.
Conductive paste. The first solvent is an acyclic compound.
The conductive paste according to claim 1. The first solvent is ethers.
The conductive paste according to claim 1 or 2. The second solvent is ethers.
The conductive paste according to any one of claims 1 to 3. When the total amount of the organic solvent is 100% by mass,
The ratio of the first solvent is 20% by mass or more and 70% by mass or less.
The ratio of the second solvent is 30% by mass or more and 80% by mass or less.
The conductive paste according to any one of claims 1 to 4. When the whole of the conductive paste is 100% by mass, the ratio of the conductive powder is 90% by mass or more.
The conductive paste according to any one of claims 1 to 5. The binder resin excludes heat-curable components.
The conductive paste according to any one of claims 1 to 6. Except for those containing hardeners,
The conductive paste according to any one of claims 1 to 7. Used to form electrodes for inductance components,
The conductive paste according to any one of claims 1 to 8.

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