JP7517156B2 - Conductive paste, electronic components and multilayer ceramic capacitors - Google Patents

Description

The present invention relates to a conductive paste, an electronic component and a multilayer ceramic capacitor.

As electronic devices such as mobile phones and digital devices become smaller and more powerful, there is a demand for electronic components, including multilayer ceramic capacitors, to be smaller and have higher capacity. Multilayer ceramic capacitors have a structure in which multiple dielectric layers and multiple internal electrode layers are alternately stacked, and by thinning these dielectric layers and internal electrode layers, it is possible to achieve smaller size and higher capacity.

For example, a multilayer ceramic capacitor is manufactured as follows. First, a conductive paste for internal electrodes is printed (applied) in a predetermined electrode pattern on the surface of a green sheet containing a dielectric powder such as barium titanate (BaTiO ₃ ) and a binder resin, and then dried to form a dry film. Next, the dry film and the green sheet are alternately stacked and heated and pressed to form a laminate in an integrated state. This laminate is cut, and after being subjected to an organic binder removal treatment in an oxidizing atmosphere or an inert atmosphere, it is fired to obtain a fired chip. Next, a paste for external electrodes is applied to both ends of the fired chip, and after firing, nickel plating or the like is applied to the surface of the external electrodes to obtain a multilayer ceramic capacitor.

Generally, the conductive paste used to form the internal electrode layer contains a conductive powder, a ceramic powder, a binder resin, and an organic solvent. The conductive paste may also contain a dispersant to improve the dispersibility of the conductive powder and the like. In recent years, with the thinning of the internal electrode layer, the conductive powder also tends to have a smaller particle size. When the particle size of the conductive powder is small, the specific surface area of the particle surface becomes large, which increases the surface activity of the conductive powder (metal powder), which may result in a decrease in dispersibility and a decrease in viscosity characteristics.

Therefore, attempts have been made to improve the viscosity characteristics of conductive pastes over time. For example, Patent Document 1 describes a conductive paste that contains at least a metal component, an oxide, a dispersant, and a binder resin, in which the metal component is Ni powder having a surface composition with a specific composition ratio, the dispersant has an acid site number of 500 to 2000 μmol/g, and the binder resin has an acid site number of 15 to 100 μmol/g. According to Patent Document 1, this conductive paste is said to have good dispersibility and viscosity stability.

Also, Patent Document 2 describes an internal electrode conductive paste consisting of conductive powder, resin, organic solvent, common material of ceramic powder mainly composed of _TiBaO3 , and coagulation inhibitor, the content of the coagulation inhibitor being 0.1% by weight or more and 5% by weight or less, and the coagulation inhibitor being a tertiary amine or secondary amine represented by a specific structural formula. According to Patent Document 2, this internal electrode conductive paste is said to suppress coagulation of common material components, have excellent long-term storage properties, and enable the thinning of multilayer ceramic capacitors.

On the other hand, when the internal electrode layer is thinned, it is required that the density of the dry film obtained by printing and drying a conductive paste for the internal electrode on the surface of the green sheet is high. For example, Patent Document 3 proposes a metal ultrafine powder slurry containing an organic solvent, a surfactant, and ultrafine metal particles, the surfactant being oleoyl sarcosine, the metal ultrafine powder slurry containing 70% by mass or more and 95% by mass or less of the metal ultrafine powder, and the surfactant containing more than 0.05 parts by mass and less than 2.0 parts by mass per 100 parts by mass of the metal ultrafine powder. According to Patent Document 3, by preventing the aggregation of ultrafine particles, a metal ultrafine powder slurry without aggregated particles and excellent dispersibility and dry film density can be obtained.

JP 2015-216244 A JP 2013-149457 A JP 2006-063441 A

However, as electrode patterns have become thinner in recent years, there is a demand for further improvements in viscosity characteristics over time and for improved surface smoothness of the dried film after application. In addition, as electrode patterns become thinner, a shrinkage mismatch occurs at the interface between the internal electrode layer and the dielectric layer when the laminate is fired, making structural defects such as cracks and delamination more likely to occur.

The inventors have found that one of the causes of cracks and delamination is the generation of decomposition gases derived from components contained in the conductive paste at low temperatures when firing of the laminate begins. In other words, when firing the laminate, if a certain amount of gas is generated from the dried film at a temperature lower than the temperature at which the dielectric layers (green sheets) begin to sinter, the gas will remain between the dielectric layers, generating voids, which is thought to result in cracks and delamination.

Even in conductive pastes for which problems such as cracking and delamination have not been reported in the past, when the electrode pattern is made thinner, the generation of small amounts of gas at low temperatures at the start of firing can cause cracks and delamination.

In view of the above circumstances, the present invention aims to provide a conductive paste that has high dry film surface smoothness and high dry film density, excellent dispersibility of conductive powder, very little change in viscosity over time, excellent viscosity stability, and a small amount of gas generation even at low temperatures at the start of firing.

In a first aspect of the present invention, there is provided a conductive paste comprising a conductive powder, a ceramic powder, a dispersant, a binder resin and an organic solvent, the dispersant comprising an amino acid-based dispersant represented by the following general formula (1), an amine-based dispersant represented by the following general formula (2), and a phosphoric acid alkyl ester compound, the amino acid-based dispersant is present in an amount of 0.03% by mass or more and 0.3% by mass or less relative to the entire conductive paste, the amine-based dispersant is present in an amount of 0.2% by mass or more relative to the entire conductive paste, the phosphoric acid alkyl ester compound is present in an amount of 0.05% by mass or more relative to the entire conductive paste, the total content of the amino acid-based dispersant and the amine-based dispersant is 0.5% by mass or less relative to the entire conductive paste, and the total content of the amino acid-based dispersant, the amine-based dispersant and the phosphoric acid alkyl ester compound is 0.7% by mass or less relative to the entire conductive paste.

（ただし、式（１）中、Ｒ_１は、炭素数１０～２０の鎖状炭化水素基を表す。）

(In the formula (1), R ₁ represents a chain hydrocarbon group having 10 to 20 carbon atoms.)

（ただし、式（２）中、Ｒ_２は炭素数８～１６のアルキル基、アルケニル基、又は、アルキニル基を表し、Ｒ_３はオキシエチレン基、オキシプロピレン基、又は、メチレン基を表し、Ｒ_４はオキシエチレン基、又は、オキシプロピレン基を表し、Ｒ_３及びＲ_４は、同一でもよく、又は、異なっていてもよい。また、式（２）中のＮ原子と、Ｒ_３及びＲ_４中のＯ原子とは直接結合せず、かつ、Ｙは０～２の数であり、Ｚは１～２の数である。）

(In the formula (2), R ₂ represents an alkyl group, an alkenyl group, or an alkynyl group having 8 to 16 carbon atoms, R ₃ represents an oxyethylene group, an oxypropylene group, or a methylene group, R ₄ represents an oxyethylene group or an oxypropylene group, and R ₃ and R ₄ may be the same or different. In addition, the N atom in the formula (2) is not directly bonded to the O atom in R ₃ and R ₄ , and Y is a number from 0 to 2, and Z is a number from 1 to 2.)

In addition, in the general formula (1), R ₁ preferably represents a linear hydrocarbon group having 10 to 20 carbon atoms. In addition, the conductive powder preferably contains at least one metal powder selected from Ni, Pd, Pt, Au, Ag, Cu, and alloys thereof. In addition, the conductive powder is preferably contained in an amount of 40 mass% to 60 mass% based on the entire conductive paste. In addition, the conductive powder preferably has an average particle size of 0.05 μm to 1.0 μm. In addition, the ceramic powder preferably contains a perovskite-type oxide. In addition, the ceramic powder preferably has an average particle size of 0.01 μm to 0.5 μm. In addition, the binder resin preferably contains at least one of a cellulose-based resin, an acrylic-based resin, and a butyral-based resin. In addition, the conductive paste preferably contains an amino acid-based dispersant in an amount of 0.05 mass% to 0.3 mass% based on the entire conductive paste. In addition, the conductive paste is preferably for use in an internal electrode of a multilayer ceramic capacitor.

In a second aspect of the present invention, there is provided an electronic component formed using the above-mentioned conductive paste.

In a third aspect of the present invention, a multilayer ceramic capacitor is provided having a laminate comprising an internal electrode layer formed using the conductive paste and a dielectric layer.

The conductive paste of the present invention has very little change in viscosity over time, excellent viscosity stability, and excellent dispersibility of the conductive powder, and the dried film after application has high surface smoothness and high dry film density. In addition, the conductive paste of the present invention generates little gas at the low temperature at the start of firing, so the occurrence of cracks and delamination is suppressed.

Electrode patterns of electronic components such as multilayer ceramic capacitors formed using the conductive paste of the present invention have excellent adhesion to the conductive paste even when forming thin-film electrodes, and have precisely uniform widths and thicknesses.

FIG. 1 is a perspective view and a cross-sectional view showing a multilayer ceramic capacitor according to the present embodiment.

[Conductive paste]
The conductive paste of the present embodiment contains a conductive powder, a ceramic powder, a dispersant, a binder resin, and an organic solvent. Each component will be described in detail below.

(Conductive powder)
The conductive powder is not particularly limited, and metal powder can be used, for example, powder of one or more types selected from Ni, Pd, Pt, Au, Ag, Cu, and alloys thereof. Among these, Ni or its alloy powder is preferred from the viewpoints of conductivity, corrosion resistance, and cost. As the Ni alloy, for example, an alloy of Ni and at least one element selected from the group consisting of Mn, Cr, Co, Al, Fe, Cu, Zn, Ag, Au, Pt, and Pd (Ni alloy) can be used. The Ni content in the Ni alloy is, for example, 50 mass% or more, preferably 80 mass% or more. In addition, the Ni powder may contain about several hundred ppm of S in order to suppress rapid gas generation due to partial thermal decomposition of the binder resin during the binder removal process.

The average particle size of the conductive powder is preferably 0.05 μm or more and 1.0 μm or less, more preferably 0.1 μm or more and 0.5 μm or less. When the average particle size of the conductive powder is within the above range, it can be suitably used as a paste for internal electrodes of thin-film multilayer ceramic capacitors, and for example, the smoothness and density of the dry film are improved. The average particle size is a value determined by observation with a scanning electron microscope (SEM), and is the average value obtained by measuring the particle size of each of multiple particles from an image observed with an SEM at a magnification of 10,000 times.

The content of the conductive powder is preferably 30% by mass or more and less than 70% by mass, and more preferably 40% by mass or more and 60% by mass or less, based on the entire conductive paste. When the content of the conductive powder is within the above range, the conductive paste has excellent conductivity and dispersibility.

(ceramic powder)
The ceramic powder is not particularly limited, and for example, in the case of a paste for an internal electrode of a multilayer ceramic capacitor, a known ceramic powder is appropriately selected depending on the type of multilayer ceramic capacitor to be applied. Examples of the ceramic powder include perovskite oxides containing Ba and Ti, and preferably barium titanate ( _BaTiO3 ).

The ceramic powder may be a ceramic powder containing barium titanate as a main component and an oxide as a subcomponent. The oxide may be an oxide of Mn, Cr, Si, Ca, Ba, Mg, V, W, Ta, Nb, or one or more rare earth elements. An example of such a ceramic powder is a perovskite-type oxide ferroelectric ceramic powder in which the Ba atom or Ti atom of barium titanate (BaTiO ₃ ) is replaced with another atom, such as Sn, Pb, or Zr.

In the paste for the internal electrodes, powder of the same composition as the dielectric ceramic powder constituting the green sheet of the multilayer ceramic capacitor may be used. This suppresses the occurrence of cracks due to the mismatch of shrinkage at the interface between the dielectric layer and the internal electrode layer during the sintering process. In addition to the above, such ceramic powders include oxides such as ZnO, ferrite, PZT, BaO, Al ₂ O ₃ , Bi ₂ O ₃ , R (rare earth element) ₂ O ₃ , TiO ₂ , and Nd ₂ O _3. It is to be noted that one type of ceramic powder may be used, or two or more types may be used.

The average particle size of the ceramic powder is, for example, 0.01 μm to 0.5 μm, preferably 0.01 μm to 0.3 μm. When the average particle size of the ceramic powder is in the above range, it is possible to form a sufficiently thin and uniform internal electrode when used as an internal electrode paste. The average particle size is a value determined by observation with a scanning electron microscope (SEM), and is the average value obtained by measuring the particle size of each of multiple particles from an image observed with an SEM at a magnification of 50,000 times.

The content of ceramic powder is preferably 1 part by mass or more and 30 parts by mass or less per 100 parts by mass of conductive powder, and more preferably 3 parts by mass or more and 30 parts by mass or less.

The content of the ceramic powder is preferably 1% by mass or more and 20% by mass or less, more preferably 5% by mass or more and 20% by mass or less, based on the total amount of the conductive paste. When the content of the ceramic powder is in the above range, the conductive paste has excellent electrical conductivity and dispersibility.

(Binder resin)
The binder resin is not particularly limited, and known resins can be used. Examples of the binder resin include cellulose-based resins such as methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, and nitrocellulose, acrylic resins, and butyral-based resins such as polyvinyl butyral. Among them, it is preferable to include ethyl cellulose from the viewpoint of solubility in a solvent and combustion decomposition. In addition, when used as an internal electrode paste, from the viewpoint of improving the adhesive strength with the green sheet, a butyral-based resin may be included or a butyral-based resin may be used alone. One type of binder resin may be used, or two or more types may be used. For example, a cellulose-based resin and a butyral-based resin may be used as the binder resin. In addition, the molecular weight of the binder resin is, for example, about 20,000 to 200,000.

The content of binder resin is preferably 1 part by mass or more and 10 parts by mass or less, and more preferably 1 part by mass or more and 8 parts by mass or less, per 100 parts by mass of conductive powder.

The content of the binder resin is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 6% by mass or less, based on the entire conductive paste. When the content of the binder resin is within the above range, the conductive paste has excellent conductivity and dispersibility.

(Organic solvent)
The organic solvent is not particularly limited, and any known organic solvent capable of dissolving the binder resin can be used. Examples of the organic solvent include acetate-based solvents such as dihydroterpineol acetate, isobornyl acetate, isobornyl propionate, isobornyl butyrate, isobornyl isobutyrate, ethylene glycol monobutyl ether acetate, and dipropylene glycol methyl ether acetate, terpene-based solvents such as terpineol and dihydroterpineol, and hydrocarbon-based solvents such as tridecane, nonane, and cyclohexane. The organic solvent may be used alone or in combination of two or more.

The content of the organic solvent is preferably 40 parts by mass or more and 100 parts by mass or less, and more preferably 65 parts by mass or more and 95 parts by mass or less, relative to 100 parts by mass of the conductive powder. When the content of the organic solvent is within the above range, the conductivity and dispersibility are excellent.

The content of the organic solvent is preferably 20% by mass or more and 60% by mass or less, and more preferably 35% by mass or more and 55% by mass or less, based on the entire conductive paste. When the content of the organic solvent is within the above range, the conductive paste has excellent electrical conductivity and dispersibility.

(Dispersant)
The conductive paste of this embodiment contains a dispersant. The dispersant includes an amino acid-based dispersant (amino acid-based surfactant) represented by general formula (1), an amine-based dispersant represented by general formula (2), and a phosphoric acid alkyl ester compound. The phosphoric acid alkyl ester compound is an acid-based dispersant. The dispersant may include a dispersant other than the above three types.

The inventors have investigated various dispersants for use in the conductive paste and found that by combining the above three types of dispersants in specific amounts, the conductive paste has excellent viscosity stability, the dried film after application has high surface smoothness and high dry film density, the conductive powder dispersibility is excellent, and even at low temperatures at the start of firing, the amount of gas generated is small and the occurrence of cracks and delamination can be suppressed. The dispersants used in this embodiment are described below.

The amino acid-based dispersant used in this embodiment has an N-acylamino acid skeleton and a chain hydrocarbon group having 10 to 20 carbon atoms, as shown in the following general formula (1).

（ただし、式（１）中、Ｒ１は、炭素数１０～２０の鎖状炭化水素を表す。）

(In formula (1), R1 represents a chain hydrocarbon having 10 to 20 carbon atoms.)

In the above formula (1), R ₁ represents a chain hydrocarbon group having 10 to 20 carbon atoms. R ₁ preferably has 15 to 20 carbon atoms. The chain hydrocarbon group may be a linear hydrocarbon group or a branched hydrocarbon group. The chain hydrocarbon group may be an alkyl group, an alkenyl group, or an alkynyl group. R ₁ is preferably a linear hydrocarbon group, more preferably a linear alkenyl group, and has a double bond.

The amino acid-based dispersant represented by the above formula (1) can be selected from commercially available products that satisfy the above characteristics. The amino acid-based dispersant may also be manufactured to satisfy the above characteristics using a conventionally known manufacturing method.

The amine-based dispersant used in this embodiment is a tertiary amine or a secondary amine, as shown in the following general formula (2), and has a structure in which an amine group is bonded to one or two oxyalkylene groups.

（ただし、式（２）中、Ｒ_２は炭素数８～１６のアルキル基、アルケニル基、又は、アルキニル基を表し、Ｒ_３はオキシエチレン基、オキシプロピレン基、又は、メチレン基を表し、Ｒ_４はオキシエチレン基、又は、オキシプロピレン基を表し、Ｒ_３及びＲ_４は、同一でもよく、又は、異なっていてもよい。また、式（２）中のＮ原子と、Ｒ_３及びＲ_４中のＯ原子とは直接結合せず、Ｙは０～２の数であり、Ｚは１～２の数である。）

(In the formula (2), R ₂ represents an alkyl group, an alkenyl group, or an alkynyl group having 8 to 16 carbon atoms, R ₃ represents an oxyethylene group, an oxypropylene group, or a methylene group, R ₄ represents an oxyethylene group or an oxypropylene group, and R ₃ and R ₄ may be the same or different. In addition, the N atom in the formula (2) is not directly bonded to the O atom in R ₃ and R ₄ , Y is a number from 0 to 2, and Z is a number from 1 to 2.)

In the above formula (2), _R2 represents an alkyl group, an alkenyl group, or an alkynyl group having 8 to 16 carbon atoms. When the carbon number of _R2 is within the above range, the powder in the conductive paste has sufficient dispersibility and excellent solubility in the solvent. It is preferable that _R2 is a linear hydrocarbon group.

In the above formula (2), _R3 represents an oxyethylene group, an oxypropylene group, or a methylene group, _R4 represents an oxyethylene group or an oxypropylene group, and _R3 and _R4 may be the same or different. In addition, the N atom in formula (2) is not directly bonded to the O atom in _R3 and _R4 , Y is a number from 0 to 2, and Z is a number from 1 to 2.

For example, in the above formula (2), when R ₃ is an oxyalkylene group represented by -AO- and Y is 1 or 2, the O atom in the oxyalkylene group at the end is bonded to the H atom adjacent to (R ₃ ) _Y. When R ₃ is a methylene group, (R ₃ ) _Y is represented by -(CH ₂ ) _Y- , and when Y is 1 or 2, it is bonded to the adjacent H element to form a methyl group (-CH ₃ ) or an ethyl group (-CH ₂ -CH ₃ ). When R ₄ is an oxyalkylene group represented by -AO-, the O atom in the oxyalkylene group at the end is bonded to the H atom adjacent to (R ₄ ) _Z.

In the above formula (2), when Y is 0, the amine dispersant is a secondary amine having -R ₂ , one hydrogen group, and -(R ₄ ) _z H. For example, when Y is 0 and Z is 2, the amine dispersant is a secondary amine composed of an alkyl group, alkenyl group, or alkynyl group having 8 to 16 carbon atoms, one hydrogen group, and -(R ₄ ) ₂ H, which is a dioxyethylene group or a dioxypropylene group bonded to an H element, and is -(AO) ₂ H.

In addition, in the above formula (2), when Y is 1, the amine dispersant is a tertiary amine having -R ₂ , -R ₃ H, and -(R ₄ ) _z H. And, when Y is 2, the amine dispersant is a tertiary amine having -R ₂ , -(R ₃ ) ₂ H, which is -(AO) ₂ H or -C ₂ H ₅ in which either a dioxyethylene group, a dioxypropylene group, or an ethylene group is bonded to an H element, and -(R ₄ ) _z H.

The amine-based dispersant represented by the above formula (2) can be selected from commercially available products that satisfy the above characteristics. The amine-based dispersant may also be manufactured to satisfy the above characteristics using a conventionally known manufacturing method.

Furthermore, in this embodiment, a phosphoric acid alkyl ester compound is used as an acid-based dispersant. The phosphoric acid alkyl ester compound is a phosphoric acid ester having an alkyl group, and preferably has a polyoxyalkylene structure, and may be an alkyl polyoxyalkylene phosphate compound.

The inventors have investigated various dispersants for use in conductive pastes and have found that by adding an alkyl phosphate compound to the dispersant used in the conductive paste in addition to the amino acid-based and amine-based dispersants described above, the generation of decomposition gases derived from the components contained in the conductive paste can be delayed when the laminate is fired, and the occurrence of structural defects such as cracks and delamination can be suppressed. The content of each component used as a dispersant is explained below.

The amino acid-based dispersant is contained in an amount of 0.03% by mass or more and 0.3% by mass or less based on the entire conductive paste. If the amino acid-based dispersant is less than 0.03% by mass, the conductive paste may not have sufficient dispersibility. If the content of the amino acid-based dispersant exceeds 0.3% by mass, the amount of decomposition gas generated from the conductive paste at the start of firing is large, and the dispersant removal may be insufficient. In addition, from the viewpoint of further improving dispersibility, the amino acid-based dispersant may be contained in an amount of 0.05% by mass or more and 0.3% by mass or less based on the entire conductive paste, or may be contained in an amount of 0.10% by mass or more and 0.3% by mass or less based on the entire conductive paste.

The amine-based dispersant is contained in an amount of 0.2% by mass or more relative to the entire conductive paste. If the amine-based dispersant is contained in an amount of less than 0.2% by mass, the conductive paste may not have sufficient viscosity stability or may not have sufficient dispersibility.

The amount of the alkyl phosphate compound is 0.05% by mass or more based on the total amount of the conductive paste. If the amount of the alkyl phosphate compound is less than 0.05% by mass, the conductive paste may not be able to obtain sufficient viscosity stability, and may generate decomposition gas at low temperatures at the start of sintering, which may cause cracks or delamination.

In addition, the total content of the amine-based dispersant and the amino acid-based dispersant is 0.5% by mass or less based on the entire conductive paste. If the total content of the two types of dispersants exceeds the above range, decomposition gas derived from the components contained in the conductive paste may be generated at a lower temperature when the laminate is fired, which may result in the generation of voids or poor peeling of the green sheet.

In addition, the total content of the amino acid-based dispersant, the amine-based dispersant, and the phosphate alkyl ester compound is 0.7% by mass or less based on the entire conductive paste. If the content of the three types of dispersants exceeds 0.7% by mass, the dispersants may not be sufficiently removed when the laminate is fired, and some of them may remain, resulting in structural defects such as cracks, voids, and poor peeling of the green sheet, as well as sheet attack.

The conductive paste may contain dispersants other than the amino acid-based dispersants, amine-based dispersants, and alkyl phosphate compounds described above, to the extent that the effects of the present invention are not impaired. Examples of dispersants other than the above include acid-based dispersants including higher fatty acids and polymeric surfactants, cationic dispersants other than acid-based dispersants, nonionic dispersants, amphoteric surfactants, and polymeric dispersants. These dispersants may be used alone or in combination of two or more.

(Conductive paste)
The method for producing the conductive paste of this embodiment is not particularly limited, and a conventionally known method can be used. The conductive paste can be produced, for example, by stirring and kneading the above-mentioned components with a three-roll mill, a ball mill, a mixer, or the like. In this case, if a dispersant is applied to the surface of the conductive powder in advance, the conductive powder is sufficiently loosened without agglomeration, and the dispersant is distributed over the surface, making it easy to obtain a uniform conductive paste. In addition, the binder resin may be dissolved in an organic solvent for a vehicle to prepare an organic vehicle, and the conductive powder, ceramic powder, organic vehicle, and dispersant may be added to the organic solvent for the paste, and then the mixture may be stirred and kneaded to produce the conductive paste.

When the viscosity of the conductive paste 24 hours after production is taken as the reference (0%), the viscosity after being left to stand for 28 days from the reference date is preferably within ±10%. Note that the viscosity of the conductive paste can be measured, for example, by the method described in the Examples (a method of measuring using a Brookfield B-type viscometer at 10 rpm (shear rate = 4 sec ^-1 )).

The surface smoothness of the dry film formed by printing the conductive paste can be evaluated by the surface roughness. The surface roughness of the conductive paste can be measured, for example, using a surface roughness meter. Specifically, the surface roughness of the dry film can be measured by applying the conductive paste to a glass substrate using an applicator (gap thickness 10 μm), drying the paste in air at 120° C. for 5 minutes, and measuring the surface roughness of the dry film having a thickness of 3 μm using a surface roughness meter. The surface roughness is preferably 0.05 μm or less , and more preferably 0.04 μm or less.

In addition, the dry film density (DFD) of the dried film obtained by printing and drying the conductive paste is
is preferably 5.45 g/ ^cm3 or more, more preferably exceeds 5.45 g/ ^cm3 , and even more preferably exceeds 5.5 g/ ^cm3 .

In addition, when the conductive paste is heated in a nitrogen atmosphere at a heating rate of 5°C/min and subjected to thermogravimetry (TG), the mass change (ΔTG) at 250°C is preferably less than 0.0020%/s, and more preferably 0.0015%/s or less. When the mass change is within the above range, the dispersant removal property during firing can be improved.

The conductive paste can be suitably used in electronic components such as multilayer ceramic capacitors. Multilayer ceramic capacitors have dielectric layers formed using green sheets and internal electrode layers formed using the conductive paste.

In a multilayer ceramic capacitor, it is preferable that the dielectric ceramic powder contained in the green sheet and the ceramic powder contained in the conductive paste are powders of the same composition. In a multilayer ceramic capacitor manufactured using the conductive paste of this embodiment, sheet attack and peeling failure of the green sheet are suppressed even when the thickness of the green sheet is, for example, 3 μm or less.

[Electronic Components]
Hereinafter, embodiments of electronic components and the like of the present invention will be described with reference to the drawings. In the drawings, the components may be shown diagrammatically or at a different scale as appropriate. The positions and directions of components will be described with reference to an XYZ orthogonal coordinate system as shown in FIG. 1 as appropriate. In this XYZ orthogonal coordinate system, the X and Y directions are horizontal directions, and the Z direction is vertical (up-down direction).

1A and 1B are diagrams showing a multilayer ceramic capacitor 1, which is an example of an electronic component according to an embodiment. The multilayer ceramic capacitor 1 includes a laminate 10 in which dielectric layers 12 and internal electrode layers 11 are alternately stacked, and an external electrode 20.

The following describes a method for manufacturing a multilayer ceramic capacitor using the conductive paste. First, the conductive paste is printed on a dielectric layer made of a green sheet and dried to form a dry film. A plurality of dielectric layers having this dry film on their upper surfaces are stacked and pressed together to obtain a laminate, which is then fired and integrated to produce a ceramic laminate 10 in which internal electrode layers 11 and dielectric layers 12 are alternately stacked. A pair of external electrodes 20 are then formed at both ends of the ceramic laminate 10 to produce a multilayer ceramic capacitor 1. The process will be described in more detail below.

First, a green sheet is prepared, which is an unfired ceramic sheet using a dielectric material. For example, the green sheet is prepared by adding an organic binder such as polyvinyl butyral and a solvent such as terpineol to a powder of a specific ceramic such as barium titanate, applying the resulting dielectric layer paste to a support film such as a PET film in the form of a sheet, and then drying to remove the solvent. The thickness of the dielectric layer made of the green sheet is not particularly limited, but is preferably 0.05 μm or more and 3 μm or less in view of the demand for miniaturization of multilayer ceramic capacitors.

Next, the above-mentioned conductive paste is printed (applied) on one side of the green sheet by a known method such as screen printing, and then dried to form a dry film, to prepare multiple sheets. Note that, from the viewpoint of the requirement to make the internal electrode layer 11 thin, it is preferable that the thickness of the conductive paste after printing is such that the thickness of the dry film after drying is 1 μm or less.

Next, the green sheet is peeled off from the support film, and the dielectric layers made of the green sheet and the dry film formed on one side of the green sheet are alternately stacked, and then a laminate is obtained by heating and pressing. Note that a configuration in which protective green sheets not coated with conductive paste are further placed on both sides of the laminate may be used.

Next, the laminate is cut to a predetermined size to form a green chip, and then the green chip is subjected to a binder removal treatment and fired in a reducing atmosphere to manufacture the ceramic laminate 10. The binder removal treatment is preferably performed in air or _N2 gas atmosphere. The temperature during the binder removal treatment is, for example, 200°C or higher and 400°C or lower. The temperature is preferably held for 0.5 hours or longer and 24 hours or shorter during the binder removal treatment. The firing is performed in a reducing atmosphere to suppress oxidation of the metal used in the internal electrode layer, and the temperature during firing of the laminate is, for example, 1000°C or higher and 1350°C or lower, and the temperature is preferably held for 0.5 hours or longer and 8 hours or shorter.

By firing the green chip, the organic binder in the green sheet is completely removed, and the ceramic raw powder is fired to form the ceramic dielectric layer 12. The organic vehicle in the dry film is also removed, and the nickel powder or the alloy powder mainly composed of nickel is sintered or melted and integrated to form the internal electrode layer 11, forming a multilayer ceramic sintered body in which multiple dielectric layers 12 and internal electrode layers 11 are alternately stacked. Note that the sintered multilayer ceramic sintered body may be annealed from the viewpoint of incorporating oxygen into the dielectric layer to increase reliability and suppressing reoxidation of the internal electrodes.

Then, a pair of external electrodes 20 is provided on the produced multilayer ceramic sintered body to manufacture the multilayer ceramic capacitor 1. For example, the external electrode 20 includes an external electrode layer 21 and a plating layer 22. The external electrode layer 21 is electrically connected to the internal electrode layer 11. Note that, for example, copper, nickel, or an alloy thereof can be suitably used as the material for the external electrode 20. Note that the electronic component is not limited to a multilayer ceramic capacitor, and may be an electronic component other than a multilayer ceramic capacitor.

The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited in any way by the examples.

[Materials used]
(Conductive powder)
As the conductive powder, Ni powder (SEM average particle size: 0.2 μm) was used.

(ceramic powder)
Barium titanate (BaTiO ₃ ; SEM average particle size 0.05 μm) was used as the ceramic powder.

(Binder resin)
The binder resins used were ethyl cellulose resin and polyvinyl butyral resin (PVB resin), which were prepared as vehicles by dissolving the binder resins in terpineol.

(Dispersant)
(1) As an amino acid-based dispersant, dispersant A represented by the above general formula (1) in which R ₁ =C ₁₇ H ₃₃ (straight-chain hydrocarbon group) was used.
(2) As the amine-based dispersant, dispersant B represented by the above general formula (2) in which R ₂ =C ₁₂ H ₂₅ , R ₃ =C ₂ H ₄ O, R ₄ =C ₂ H ₄ O, Y=1, and Z=1 was used.
(3) As the alkyl phosphate ester compound, dispersant C consisting of an alkyl polyoxyalkylene phosphate compound was used.

(Organic solvent)
Terpineol was used as the organic solvent.

[Example 1]
48% by mass of Ni powder, 5% by mass of ceramic powder, 3% by mass of binder resin (made of ethyl cellulose resin and polyvinyl butyral resin) in the vehicle in total, 0.10 % by mass of amino acid-based dispersant, 0.26 % by mass of amine-based dispersant , 0.10% by mass of dispersant made of alkyl polyoxyalkylene phosphate compound, and terpineol (organic solvent) as the balance were mixed to a total of 100% by mass, and these materials were mixed to prepare a conductive paste. The viscosity stability, dispersibility (dry film density, surface roughness of the dry film), and dispersant removability of the prepared conductive paste were evaluated by the following method. The evaluation results are shown in Table 1.

[Evaluation method]
(1) Viscosity stability: Amount of change in viscosity of conductive paste The time 24 hours after the manufacture of the conductive paste was set as a reference time point, and the viscosity of each sample was measured by the following method at the reference time point and after 28 days of standing at room temperature (25°C) from the reference time point. Then, the amount of change in viscosity of the sample after 28 days of standing was calculated as a percentage (%) when the viscosity 24 hours after manufacture (reference time point) was set as the reference (0%) ([(viscosity after 28 days of standing - viscosity 24 hours after manufacture) / viscosity 24 hours after manufacture] x 100), which was taken as the amount of change in viscosity. The viscosity of the conductive paste was measured at 10 rpm (shear rate = 4 sec ^-1 ) using a Brookfield B-type viscometer. It is preferable that the amount of change in the viscosity of the conductive paste is as small as possible. The viscosity stability of the conductive paste was evaluated as follows: if the change in viscosity of the conductive paste after being left standing for 28 days was 10% or less, it was marked as "○", if it was more than 10% but less than 40%, it was marked as "△", and if it was 40% or more, it was marked as "X".

(2) Dispersibility: Surface roughness of dry film, dry film density <Surface roughness>
The conductive paste thus prepared was screen-printed on a 2.54 cm (1 inch) square heat-resistant tempered glass and dried at 120° C. in air for 1 hour to prepare a 20 mm square dry film with a thickness of about 3 μm. When the conductive paste has good dispersibility, the surface of the dry film is smooth. When the dispersibility is poor, aggregation occurs in the conductive paste, the surface of the dry film becomes rough, and the surface smoothness decreases. Therefore, the surface protrusions of this dry film were measured using a contact-type surface roughness meter. Specifically, the surface roughness Ra of this dry film was measured using a surface roughness measuring device (SURFCOM480 manufactured by Tokyo Seimitsu Co., Ltd.). The smaller the surface roughness Ra value, the smoother the surface of the dry film.

<Dry Film Density (DFD)>
The conductive paste thus prepared was placed on a PET film and spread to a length of about 100 mm using an applicator with a width of 50 mm and a gap of 125 μm. The obtained PET film was dried at 120° C. for 40 minutes to form a dried body. The dried body was cut into four pieces of 2.54 cm (1 inch) square, the PET film was removed, and the thickness and mass of each of the four dried films were measured to determine the dry film density (average value). If the dispersibility of the conductive paste is low and the conductive powder aggregates, the dry film density decreases, and the electrical properties may be deteriorated. The higher the dry film density, the better the dispersibility. This indicates that.

<Evaluation of Dispersibility>
Dispersibility was evaluated as follows: when the surface roughness Ra of the above-mentioned dry film is 0.04 μm or less and the dry film density DFD is 5.45 g/ ^cm3 or more, it is marked as "○"; when the surface roughness Ra (arithmetic mean height) of the dry film is more than 0.04 μm and less than 0.05 μm and the dry film density DFD is 5.45 g/ ^cm3 or ^more , it is marked as "△"; and when either the surface roughness Ra of the dry film is more than 0.05 μm or the dry film density DFD is less than 5.45 g/cm3, it is marked as "X."

(3) Evaluation of dispersant removability The prepared conductive paste was heated in a nitrogen atmosphere at a temperature rise rate of 5°C/min, and thermogravimetry (TG) was performed to analyze the decomposition behavior due to differences in dispersants, thereby evaluating the dispersant removability. Specifically, a profile of mass change (ΔTG) against temperature was created, and the mass change (ΔTG) at 250°C was used for evaluation. It can be determined that the larger the mass change (ΔTG) at 250°C, the larger the amount of decomposition gas generated from the conductive paste at the start of firing.

250°C is the temperature at which the dielectric layer starts to sinter. When the dielectric layer starts to sinter, gaps are formed in the dielectric layer, and a certain amount of decomposition gas generated from the components contained in the conductive paste can be discharged through these gaps. On the other hand, if a certain amount of decomposition gas is generated before the firing of the dielectric layer starts, since there are no gaps in the dielectric layer, the gas is not discharged to the outside, and it is likely to remain between the dielectric layers and cause voids. Therefore, by measuring the mass change of the conductive paste during heat treatment at 250°C, it is possible to determine whether the gas generated by decomposition at the start of firing of the laminate can be discharged through the dielectric layer (good dispersant removability) or whether it remains between the dielectric layers and causes voids (poor dispersant removability).

Dispersant removal performance was evaluated as follows: when the mass change was 0.0015%/s or less, the amount of gas generated was sufficiently small, so it was rated as "○" (very good); when the mass change was greater than 0.0015%/s but less than 0.0020%/s, a certain amount of gas was generated, but the amount was such that it could be discharged through the dielectric layer, so it was rated as "△" (good); and when the mass change was 0.0020%/s or more, a large amount of gas was generated and may remain behind without being discharged to the outside, so it was rated as "×" (poor).

[Examples 2 to 6, Comparative Examples 1 to 9]
A conductive paste was prepared under the same conditions as in Example 1, except that the contents of dispersant A, dispersant B, and dispersant C were set to the amounts shown in Table 1, and the compounding ratio of the dispersants was changed. The viscosity stability, dispersibility (dry film density, dry film surface roughness), and dispersant removability of the prepared conductive paste were evaluated by the above-mentioned methods. The evaluation results are shown in Table 1.

[Evaluation results]
The conductive paste of the embodiment had good viscosity stability as shown in Table 1. The conductive paste of the embodiment had a dry film density of 5.45 g/ ^cm3 or more and a surface roughness Ra of 0.05 μm or less, and showed good dispersibility. Furthermore, the conductive paste of the embodiment had a small weight change at 250° C., and generated a small amount of decomposition gas at a low temperature at the start of firing, so there was no concern about void generation due to residual decomposition gas.

In contrast, the comparative conductive paste, in which the dispersant content is outside the range of the present invention, is found to have poor viscosity stability and low dispersibility.

The conductive paste according to this embodiment has excellent viscosity stability over time and excellent dispersibility, resulting in excellent smoothness of the dried film after application and excellent dry film density. Furthermore, the conductive paste according to this embodiment suppresses the generation of decomposition gas at 250°C, thereby suppressing the occurrence of cracks and delamination due to the generation of voids. Therefore, the conductive paste according to this embodiment can be suitably used as a raw material for the internal electrodes of multilayer ceramic capacitors, which are chip components (electronic components) of electronic devices such as mobile phones and digital devices.

Note that the technical scope of the present invention is not limited to the aspects described in the above-mentioned embodiments. One or more of the requirements described in the above-mentioned embodiments may be omitted. Furthermore, the requirements described in the above-mentioned embodiments may be combined as appropriate. Furthermore, to the extent permitted by law, the disclosures of all documents cited in the above-mentioned embodiments are incorporated by reference into this text. Furthermore, to the extent permitted by law, the contents of Japanese patent application No. 2019-022906 are incorporated by reference into this text.

REFERENCE SIGNS LIST 1 Multilayer ceramic capacitor 10 Ceramic laminate 11 Internal electrode layer 12 Dielectric layer 20 External electrode 21 External electrode layer 22 Plating layer

Claims (12)

A conductive paste comprising a conductive powder, a ceramic powder, a dispersant, a binder resin and an organic solvent,
The dispersant contains an amino acid-based dispersant represented by the following general formula (1), an amine-based dispersant represented by the following general formula (2), and a phosphoric acid alkyl ester compound,
The conductive paste contains the amino acid-based dispersant in an amount of 0.03% by mass or more and 0.3% by mass or less based on the entire conductive paste,
The conductive paste contains the amine-based dispersant in an amount of 0.2 mass% or more based on the entire conductive paste,
The conductive paste contains the phosphoric acid alkyl ester compound in an amount of 0.05 mass% or more based on the entire conductive paste,
The total content of the amino acid-based dispersant and the amine-based dispersant is 0.5 mass% or less based on the entire conductive paste,
The total content of the amino acid-based dispersant, the amine-based dispersant, and the phosphoric acid alkyl ester compound is 0.7 mass% or less based on the entire conductive paste.
Conductive paste.

(In the formula (1), R ₁ represents a chain hydrocarbon group having 10 to 20 carbon atoms.)

(In the formula (2), R ₂ represents an alkyl group, an alkenyl group, or an alkynyl group having 8 to 16 carbon atoms, R ₃ represents an oxyethylene group,
R 3 represents an oxypropylene group or a methylene group, R ₄ represents an oxyethylene group or an oxypropylene group, and R ₃ and R ₄ may be the same or different. In addition, the N atom in formula (2) is not directly bonded to the O atom in R ₃ and R ₄ , Y is a number from 0 to 2, and Z is a number from 1 to 2. The conductive paste according to claim 1, wherein in the general formula (1), R ₁ represents a linear hydrocarbon group having 10 to 20 carbon atoms. The conductive paste according to claim 1 or 2, wherein the conductive powder contains at least one type of metal powder selected from Ni, Pd, Pt, Au, Ag, Cu and alloys thereof. A conductive paste according to any one of claims 1 to 3, wherein the conductive powder is contained in an amount of 40% by mass or more and 60% by mass or less relative to the entire conductive paste. A conductive paste described in any one of claims 1 to 4, wherein the conductive powder has an average particle size of 0.05 μm or more and 1.0 μm or less. A conductive paste according to any one of claims 1 to 5, wherein the ceramic powder contains a perovskite-type oxide. A conductive paste described in any one of claims 1 to 6, wherein the ceramic powder has an average particle size of 0.01 μm or more and 0.5 μm or less. A conductive paste according to any one of claims 1 to 7, wherein the binder resin comprises at least one of a cellulose-based resin, an acrylic-based resin, and a butyral-based resin. A conductive paste according to any one of claims 1 to 8, containing 0.05% by mass or more and 0.3% by mass or less of the amino acid-based dispersant relative to the entire conductive paste. A conductive paste according to any one of claims 1 to 9, for use as an internal electrode in a multilayer ceramic capacitor. An electronic component formed using the conductive paste according to any one of claims 1 to 9. A multilayer ceramic capacitor having a laminate in which an internal electrode layer formed using the conductive paste according to claim 10 and a dielectric layer are laminated.

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