JP7053527B2 - Conductive paste - Google Patents

Description

The present invention relates to a conductive paste. More specifically, the present invention relates to a conductive paste suitable for forming an internal electrode layer of a laminated ceramic electronic component.

A multilayer ceramic capacitor (MLCC) has a structure in which a large number of dielectric layers made of ceramic and an internal electrode layer are laminated. In general, this MLCC is formed by printing a conductive paste for an internal electrode containing a conductive powder on a dielectric green sheet composed of a dielectric powder and a binder or the like to form an internal electrode layer, and the internal electrode layer is printed. It is manufactured by laminating a large number of dielectric green sheets, crimping them, and firing them. With the recent miniaturization and weight reduction of electronic devices, it is required to reduce the size and thinning of each electronic component constituting the electronic device. Therefore, in MLCC, while maintaining quality such as withstand voltage characteristics of the dielectric layer, it is possible to reduce the size and capacity by further thinning the dielectric layer and further increasing the number of layers to expand the electrode area. It has been demanded.

For example, Patent Documents 1 to 3 disclose MLCCs containing a fresnoite phase at specific sites such as inside the dielectric layer and the interface between the dielectric layer and the internal electrode layer. Bresnoite is a silicate compound having a composition represented by the general formula Ba ₂ TiSi ₂ O ₈ , and has excellent dielectric properties and optical properties. Patent Documents 1 to 3 describe that the presence of a fresnoite phase at such a site makes it possible to improve the insulation reliability of MLCC and suppress delamination.

Japanese Unexamined Patent Publication No. 2014-029978 Japanese Patent Application Laid-Open No. 2015-0622116 Japanese Unexamined Patent Publication No. 2016-035982 Japanese Unexamined Patent Publication No. 2013-021285 Japanese Unexamined Patent Publication No. 2005-203213

On the other hand, as the dielectric layer and the internal electrode layer become thinner, there is a problem that the withstand voltage and reliability of the dielectric layer tend to decrease easily. That is, for example, the flatness of the internal electrode layer is non-uniform at a level that has not been a problem in the past, so that the thinned dielectric layer is locally compressed, and the dielectric layer is formed. There is a problem that the withstand voltage is lowered as a whole. Further, for example, if there are any protrusions on the surface of the internal electrode layer, there is a problem that the protrusions easily break through the thinned dielectric layer, resulting in a product defect and a decrease in yield.

The present invention has been made in view of this point, and an object of the present invention is to provide a conductive paste for forming an internal electrode capable of suppressing a decrease in withstand voltage and constructing a high-quality MLCC.

In the production of MLCC, in order to suppress the decrease in the withstand voltage of the thinned dielectric layer, the internal electrode layer that starts sintering from a lower temperature among the co-firing dielectric layer and the internal electrode layer. It is considered that the flattening of is indispensable. The present inventors have been studying diligently for the purpose of further flattening the internal electrode layer, in order to achieve both the miniaturization of the powder used for the conductive paste and the improvement of homogeneous dispersibility. However, in the course of such research, it was discovered that there are factors that can affect the decrease in withstand voltage rather than the miniaturization of powder and its homogeneous dispersibility, and the present invention has been completed.

That is, the techniques disclosed herein provide a conductive paste used to form a conductor film. This conductive paste contains a conductive powder, a dielectric powder, a silicon-containing compound, and an organic component. In the X-ray diffraction (XRD) analysis of the calcined product of this conductive paste, the ratio of the peak intensity of the peak derived from the fresnoite phase to the peak intensity of the peak derived from the dielectric is 26 or less. It is adjusted to be. Here, the fresnoite phase is a compound phase formed by the reaction of the dielectric powder and the silicon-containing compound, and the fired product heats the conductive paste at 600 ° C. under an inert atmosphere. It was produced by treating it to remove the organic component and then firing it at 1300 ° C. in an inert atmosphere.

Among the conductive pastes, for example, pastes for forming internal electrodes of MLCCs for in-vehicle use, which are required to have higher withstand voltage characteristics, have various additives added for various purposes. And one of these additives is silica powder (see, for example, Patent Documents 4 and 5). According to the studies by the present inventors, when a silicon-containing compound typified by silica powder and other dielectric powders coexist in the conductive paste, they react at the time of firing to form a fresnoite phase. Here, we have found the fact that this fresnoite phase grows like needles under the firing conditions of the internal electrode layer of MLCC and can easily press or break through the dielectric layer. Further, such a fresnoite phase is surely formed even in a small amount at the time of firing for a conductive paste prepared under normal paste preparation conditions. However, the present inventors further adjust the paste preparation conditions appropriately so that the ratio of the peak intensities of the conductive paste is 26 or less, so that the conductivity containing the silicon-containing compound and the dielectric powder is contained. It was also found that the formation of the fresnoite phase can be remarkably suppressed even with a paste. Therefore, according to the conductive paste disclosed herein, it is possible to suppress damage to the adjacent dielectric layer and the like during firing to form a conductor film. As a result, a high-quality MLCC with a high withstand voltage can be manufactured.

In a preferred embodiment of the conductive paste disclosed herein, 0 is when the average particle size of the conductive powder based on the BET method is D ₁ and the average particle size of the dielectric powder based on the BET method is D ₂ . .03 × D ₁ ≦ D ₂ ≦ 0.4 × D ₁ is satisfied. As a result, even when a thin conductive film is formed, the dielectric particles are suitably arranged in the gaps between the conductive particles, and the abnormal grain growth of the conductive particles during firing can be suitably suppressed by the dielectric powder. ..

In a preferred embodiment of the conductive paste disclosed herein, the average particle size D ₁ of the conductive powder based on the BET method is 0.5 μm or less. Thereby, for example, a conductor film having a thickness of about 3 μm or less can be formed with high accuracy.

In a preferred embodiment of the conductive paste disclosed herein, the conductive powder is at least one of nickel, platinum, palladium, silver and copper. This makes it possible to suitably realize a conductor film having excellent electrical conductivity.

In a preferred embodiment of the conductive paste disclosed herein, the dielectric powder is at least one selected from the group consisting of barium titanate, strontium titanate, and calcium zirconate. This makes it possible to suitably realize a conductor film having excellent bondability with a dielectric layer having a high dielectric constant.

In a preferred embodiment of the conductive paste disclosed herein, it can be used to form an internal electrode layer of a laminated ceramic electronic component. For example, in the chip type MLCC, further thinning and high lamination of the dielectric layer are required. The internal electrode layer arranged between such thin (for example, 1 μm or less) dielectric layers has high surface flatness by using the conductive paste disclosed here, and damages the adjacent dielectric layer. The internal electrode layer can be suitably formed without this. As a result, it is possible to produce a small-sized, large-capacity, high-quality MLCC in which the occurrence of short circuits and cracks in the dielectric layer is suppressed.

It is sectional drawing schematically explaining the structure of MLCC. It is sectional drawing schematically explaining the structure of the MLCC main body which has not been calcined. It is an XRD pattern obtained about the fired product which concerns on the conductive paste of Example 2. It is an SEM observation image of the fired product of the conductive paste of (a) Example 1 and (b) Example 4. FIG. This is an example of an SEM observation image of Fresnoit particles.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings as appropriate. It should be noted that matters other than those specifically mentioned in the present specification (for example, the composition and properties of the conductive paste) and necessary for carrying out the present invention (for example, preparation and base of raw materials for the paste). Specific methods for application to materials, composition of electronic parts, etc.) can be carried out based on the technical contents taught in this specification and general technical common knowledge of those skilled in the art in the art. .. In this specification, the notation "A to B" indicating a numerical range means A or more and B or less.

[Conductive paste]
The conductive paste disclosed here contains (A) a conductive powder, (B) a dielectric powder, (C) a silicon-containing compound, and (D) an organic component as main constituents. The organic component is a medium called a vehicle, which is typically composed of a (D1) binder and a (D2) dispersion medium. When this conductive paste is fired, (D) the organic component disappears, (A) the conductive powder, (B) the dielectric powder and (C) the silicon-containing compound are sintered, and the conductive baking is performed. It forms a bundling (typically a conductor film). The (A) conductive powder, (B) dielectric powder, and (C) silicon-containing compound, which are the main constituents of the conductor film, are usually dispersed in a vehicle, which is an organic component, to form a paste. However, it is given appropriate viscosity and fluidity.

When a conductive paste containing (B) a dielectric powder and (C) a silicon-containing compound is fired, these react to form a fresnoite-type crystal phase (in the present specification, it may be simply referred to as a "fresnoite phase". ) Is formed. FIG. 4 shows a fresnoite (Ba ₂ TiSi ₂ O ₈ ) produced by mixing barium titanate (BaTIO ₃ : BT) powder and silica (SiO ₂ ) powder as a dielectric powder in a chemical bilateral composition and firing them. It is a scanning electron microscope (SEM) image. As can be seen in FIG. 4, since the fresnoite phase has extremely high shape anisotropy in the [001] orientation, the fresnoite compound can grow in the form of needles. Therefore, such acicular particles can be formed in the conductor film by reacting the dielectric powder with the silicon-containing compound such as silica powder when the conductive paste is fired. As shown in FIG. 4, the acicular particles grow randomly in the conductor film. Therefore, for example, when the dielectric layer is adjacent to the conductor film, the acicular particles press or damage the dielectric layer. It is not preferable because it can be squeezed.

On the other hand, the present inventors have reacted between the dielectric powder and the silicon-containing compound even in the conductive paste containing (B) the dielectric powder and (C) the silicon-containing compound, by changing the preparation state thereof. It has been found that the sex also changes and the degree of formation of the fresnoid phase can be adjusted. Therefore, in the technique disclosed here, the ease with which the fresnoid phase is formed in the conductive paste is evaluated using an index of "peak intensity rate of the fresnoite phase" so that the intensity rate is 26 or less. I try to prepare a conductive paste. In the conductive paste, when the peak intensity of the fresnoite phase is 26 or less, the growth of fresnoite particles is sufficiently suppressed. As a result, for example, compression or damage of adjacent dielectric layers can be suitably suppressed.

In the present specification, the "peak intensity ratio of the fresnoite phase" is the peak intensity of the peak derived from the fresnoite phase with respect to the peak intensity of the peak derived from the dielectric when XRD analysis is performed on the calcined product of the conductive paste. Is defined as the ratio (percentage) of. Hereinafter, the “peak intensity rate of the fresnoite phase” may be simply abbreviated as the “peak intensity rate”.
In order to obtain the "peak intensity of the fresnoite phase" of the conductive paste, a fired product is prepared in advance from the conductive paste having the same specifications as the conductive paste, and the fired product is subjected to XRD analysis. It is advisable to calculate the peak intensity rate. Such a fired product can be produced by heat-treating the conductive paste at 600 ° C. in an inert atmosphere to remove organic components and then firing at 1300 ° C. in an inert atmosphere. More specifically, the baked product of the conductive paste can be prepared, for example, based on the method disclosed in Examples described later.

Further, the "peak intensity rate of the fresnoite phase" may differ depending on the type of each constituent material of the conductive paste, its properties, the composition, and the like, as well as the preparation conditions of these constituent materials. Therefore, the "peak intensity ratio of the fresnoite phase" is, for example, the type, properties, and composition of each constituent material to be used after measuring the peak intensity ratio of the fresnoite phase in advance for a predetermined conductive paste, and the constituent components. The paste preparation conditions may be set so as to realize the desired peak intensity rate by variously changing any one or more of the stirring and mixing conditions for dispersing the powder in the organic components. As an example of preparation conditions that should be changed for adjusting the peak intensity rate, properties such as the particle size of the dielectric powder, the composition and particle size of the silicon-containing compound, their ratios, and the paste Examples include the stirring and mixing conditions of.
Hereinafter, the conductive paste disclosed herein will be described for each element.

(A) Conductive powder The conductive powder is a conductor (which may be a conductor film) having high electrical conductivity (hereinafter, simply referred to as "conductivity") such as electrodes, conductors and conductive films in electronic elements and the like. It is a material mainly for forming. Therefore, as the conductive powder, powders of various materials having desired conductivity can be used without particular limitation. Specific examples of such a conductive material include nickel (Ni), palladium (Pd), platinum (Pt), gold (Au), silver (Ag), copper (Cu), and ruthenium (Ru). , Rhodium (Rh), osmium (Os), iridium (Ir), aluminum (Al), tungsten (W) and other metal simple substances, alloys containing these metals and the like are exemplified. As the conductive powder, any one type may be used alone, or two or more types may be used in combination.

Although not particularly limited, for example, in the case of a conductive paste used for forming an internal electrode layer of MLCC, the melting point of the conductive powder is the sintering temperature of the dielectric layer (for example, about 1300 ° C.). The use of lower metal species is preferred. Examples of such metal species include precious metals such as rhodium, platinum, palladium, copper and gold, and base metals such as nickel. Of these, the use of precious metals such as platinum and palladium is preferable from the viewpoint of melting point and conductivity, but nickel is preferably used in consideration of the fact that it is more stable and inexpensive.

The manufacturing method of the conductive powder and the properties such as the size and shape of the particles constituting the conductive powder are not particularly limited. For example, in consideration of the firing shrinkage rate, it is preferable that the range is within the minimum dimension (typically, the thickness and / or width of the electrode layer) of the target conductor film. For example, the average particle size of the conductive powder is preferably about several nm to several tens of μm, for example, about 10 nm to 10 μm.
In the present specification, the "average particle size (D ₅₀ )" of the conductive powder, the dielectric powder, and the powdered silicon-containing compound is the specific surface area measured by the BET method unless otherwise specified. It means a value calculated by the following equation: D ₅₀ = 6 / (S × ρ); based on S and the specific surface area ρ of the powder. The "cumulative 90% particle size (D ₉₀ )" is the cumulative 90% from the small particle size side in the number-based particle size distribution measured based on electron microscope observation for 100 or more particles constituting the powder. It is a particle size corresponding to. A biaxial average diameter is adopted as the particle diameter measured by electron microscope observation. The specific surface area will be described later.

Further, for example, in an application for forming an internal electrode layer of a small and large capacity MLCC, it is important that the average particle size of the conductive powder is smaller than the thickness (dimension in the stacking direction) of the internal electrode layer. In other words, it is preferable that the coarse particles exceeding the thickness of the internal electrode layer are substantially not contained. From this point of view, as an example, it is preferable that the cumulative 90% particle size (D ₉₀ ) of the conductive powder does not exceed 3 μm, more preferably 1 μm or more, for example, 0.5 μm or more. The average particle size (D ₅₀ ) can be about 1 μm or less, typically 0.5 μm or less, preferably 0.3 μm or less, more preferably 0.25 μm or less, for example 0.2 μm. It should be as follows. When the average particle size is not more than a predetermined value, the conductor film can be stably formed. In addition, the surface roughness of the formed conductor film can be suitably suppressed. For example, the arithmetic mean roughness Ra can be suppressed to a level of 5 nm or less.

The lower limit of the average particle size of the conductive powder is not particularly limited, and may be, for example, 0.005 μm or more, generally 0.01 μm or more, typically 0.05 μm or more, preferably 0.1 μm or more, for example, 0. It is preferably 12 μm or more. When the average particle size is not too small, the surface energy (activity) of the particles constituting the conductive powder can be suppressed, and the aggregation of the particles in the conductive paste can be suppressed. Further, the density of the paste coating layer can be increased to preferably form a conductor film having high electrical conductivity and high density.

The specific surface area of the conductive powder is not particularly limited, but is generally 10 m ² / g or less, preferably 1 to 8 m ² / g, for example, 2 to 6 m ² / g. As a result, agglutination in the paste is suitably suppressed, and the homogeneity, dispersibility, and storage stability of the paste can be further improved. In addition, a conductor film having excellent electrical conductivity can be realized more stably. The specific surface area was calculated by the BET method (for example, the BET one-point method) based on the amount of gas adsorbed by the gas adsorption method (constant volume adsorption method) using nitrogen (N ₂ ) gas as the adsorbent, for example. The value.

The shape of the conductive powder is not particularly limited. For example, the shape of the conductive powder in the conductive paste used for forming some electrodes such as the MLCC internal electrode may be a true spherical shape or a substantially spherical shape. The average aspect ratio of the conductive powder is typically 1 or more and less than 2, preferably 1 or more and 1.5 or less. As a result, the viscosity of the paste can be kept low, and the handleability of the paste and the workability at the time of film formation for forming the conductor film can be improved. In addition, the homogeneity of the paste can be improved.
The "aspect ratio" in the present specification is calculated based on electron microscope observation, and is the length of the long side with respect to the length of the short side (a) when a rectangle circumscribing the particles constituting the powder is drawn. It means the ratio (b / a) of (b). The average aspect ratio is an arithmetic mean value of the aspect ratios obtained for 100 particles.

The content ratio of the conductive powder is not particularly limited, and is approximately 30% by mass or more, typically 40 to 95% by mass, for example, 45 to 60% by mass, when the total of the conductive paste is 100% by mass. It is good. By satisfying the above range, a moving body layer having high electrical conductivity and high density can be suitably realized. In addition, the handleability of the paste and the workability at the time of film formation can be improved.

(B) Dielectric powder The conductive paste disclosed here may contain (B) a dielectric powder in addition to the above (A) conductive powder as a component mainly constituting the conductor film after firing. .. By arranging the dielectric powder between the particles constituting the conductive powder, for example, during the firing of the conductive paste, the sintering of the conductive powder from a low temperature can be suppressed, and the heat shrinkage rate and the firing shrinkage history can be suppressed. It is a component that can adjust the thermal expansion coefficient of the conductive film after firing. The action of the dielectric powder may vary, but in particular, the dielectric powder contained in the conductive paste for the internal electrode layer of MLCC has a composition common to or similar to that of the dielectric layer, so that the dielectric layer has various actions. It is preferable because it functions suitably as a co-material that improves the sintered bondability between the material and the internal electrode layer.

The dielectric constant of the dielectric powder is not particularly limited and can be appropriately selected depending on the intended use. As an example, for a dielectric powder used in a conductive paste for forming an internal electrode layer of a high dielectric constant MLCC, the relative permittivity is typically 100 or more, preferably 1000 or more, for example 1000 to. It is about 20000. The composition of such a dielectric powder is not particularly limited, and one or more of various inorganic materials can be appropriately used depending on the intended use. Specific examples of the dielectric powder include barium titanate, strontium titanate, calcium titanate, magnesium titanate, bismuth titanate, zirconium titanate, zinc titanate, barium titanate niobate, calcium zirconate, and titanium. Metal oxides having a perovskite structure represented by _ABO3 such as barium titanate, titanium dioxide (rutyl), titanium pentoxide, hafnium oxide, zirconium oxide, aluminum oxide, forsterite, niobium oxide, neodium titanate Other metal oxides such as barium and rare earth element oxides are typical examples. In the paste for the internal electrode layer, the dielectric powder can be suitably composed of, for example, barium titanate, strontium titanate, calcium zirconate, barium zirconate titanate, and the like. On the other hand, it goes without saying that a dielectric material having a relative permittivity of less than 100 (and by extension, an insulating material) may be used.

The properties of the particles constituting the dielectric powder, such as the size and shape of the particles, are particularly limited as long as they are within the minimum dimensions (typically, the thickness and / or width of the electrode layer) in the cross section of the conductor film to be formed. Not done. The average particle size of the dielectric powder can be appropriately selected depending on, for example, the use of the paste, the dimensions (fineness) of the conductor film, and the like. From the viewpoint that it is easy to secure a predetermined conductivity for the target conductor film, the average particle size of the dielectric powder is preferably smaller than the average particle size of the conductive powder. When the average particle size of the dielectric powder is D ₂ and the average particle size of the conductive powder is D ₁ , it is preferable that D ₁ and D ₂ are usually D ₁ > D ₂ , and D ₂ ≤ 0. 5 × D ₁ is more preferable, D ₂ ≦ 0.4 × D ₁ is more preferable, and for example, D ₂ ≦ 0.3 × D ₁ may be used. Further, if the average particle diameter D2 of the dielectric powder is too small, aggregation of the dielectric powder is likely to occur, which is not preferable. In this respect, as a rough guide, 0.03 × D ₁ ≦ D ₂ is preferable, 0.05 × D ₁ ≦ D ₂ is more preferable, and for example, 0.1 × D ₁ ≦ D ₂ may be used. For example, specifically, the average particle size of the dielectric powder is preferably several nm or more, preferably 5 nm or more, and may be 10 nm or more. The average particle size of the dielectric powder may be about several μm or less, for example, 1 μm or less, preferably 0.3 μm or less. As an example, in the conductive paste for forming the internal electrode layer of MLCC, the average particle size of the dielectric powder may be about several nm to several hundred nm, for example, 5 to 100 nm.

The content ratio of the dielectric powder is not particularly limited. For example, in an application for forming an internal electrode layer of MLCC, when the total amount of the conductive paste is 100% by mass, it is generally 1 to 20% by mass, for example, 3 to 15% by mass. The ratio of the dielectric powder to 100 parts by mass of the conductive powder is, for example, about 3 to 35 parts by mass, preferably 5 to 30 parts by mass, for example, 10 to 25 parts by mass. As a result, it is possible to appropriately suppress firing of the conductive powder from a low temperature and to improve the electrical conductivity, denseness, etc. of the conductor film after firing.

(C) Silicon-Containing Compound The conductive paste disclosed here has (C) in addition to the above-mentioned (A) conductive powder and (B) dielectric powder as components mainly constituting the conductor film after firing. It can contain silicon-containing compounds. The silicon-containing compound means a compound generally containing a silicon (Si) component, and may be any of an inorganic compound, an organic compound, a metalloid, and a complex thereof. The silicon-containing compound may be a solid or a liquid (including a viscous body) at room temperature (for example, 10 to 30 ° C.). This silicon-containing compound is, for example, a component capable of adjusting the coefficient of thermal expansion of the conductive film after firing when the conductive paste is fired. At the same time, the silicon-containing compound can also serve as a component that supplies the Si component to the metal oxide constituting the dielectric powder during firing of the conductive paste and promotes the formation of the fresnoite phase.

Examples of the silicon-containing compound include oxide ceramics such as silica, zeolite and silica-alumina composite oxide, salts such as sodium silicate, and inorganic compounds such as non-oxide ceramics such as silicon nitride, silicon carbide and iron silicide. Examples thereof include organic compounds such as Si resinate, organic siloxane, and organic polysiloxane, and semi-metals containing silicon as a main component. As a typical example, the silicon-containing compound (for example, silica) as an inorganic compound may be amorphous (for example, amorphous silica) or crystalline (for example, crystalline silica). It may be a gel (for example, silica gel), a sol (for example, colloidal silica) or the like. From the viewpoint of suppressing the sintering of the conductive powder to a higher temperature, the silicon-containing compound as an inorganic compound is preferably in the form of powder. Further, as a typical example, in the case of an organic polysiloxane, for example, in the case of a linear compound, the siloxane unit (-R ₂ SiO) _n- , R is independently a hydrogen atom or an arbitrary functional group, and n is a natural number. be. ) May be an oil (oil) having a number n of 2000 or less, or a rubber-like substance having a number n of 5000 or more. From the viewpoint of lowering the peak intensity ratio described later, n is preferably an oil of 2000 or less.

When the silicon-containing compound is in the form of powder or particles, the properties of the particles constituting the silicon-containing compound, such as the size and shape of the particles, are the minimum dimensions in the cross section of the conductor film to be formed (typically, the electrode layer). There is no particular limitation as long as it fits within the thickness and / or width of. The average particle size of the silicon-containing compound powder can be appropriately selected depending on, for example, the use of the paste, the size (fineness) of the conductor film, and the like. For example, the average particle size is preferably smaller than the average particle size of the conductive powder from the viewpoint that it is easy to secure a predetermined conductivity for the target conductor film as in the case of the above-mentioned dielectric powder. When the average particle size of the silicon-containing compound powder is D ₃ and the average particle size of the conductive powder is D ₁ , it is preferable that D ₁ and D ₃ are usually D ₁ > D ₃ , and D ₃ ≤ 0. .5 × D ₁ is more preferable, D ₃ ≦ 0.4 × D ₁ is more preferable, and for example, D ₃ ≦ 0.3 × D ₁ may be used. Further, if the average particle size D ₃ of the silicon-containing compound powder is too small, aggregation of the silicon-containing compound powder is likely to occur, which is not preferable. In this respect, as a rough guide, 0.03 × D ₁ ≦ D ₃ is preferable, 0.05 × D ₁ ≦ D ₃ is more preferable, and for example, 0.1 × D ₁ ≦ D ₃ may be used. For example, specifically, the average particle size of the silicon-containing compound powder is preferably several nm or more, preferably 5 nm or more, and may be 10 nm or more. The average particle size of the silicon-containing compound powder may be about several μm or less, for example, 1 μm or less, preferably 0.3 μm or less. As an example, in the conductive paste for forming the internal electrode layer of MLCC, the average particle size of the silicon-containing compound powder may be about several nm to several hundred nm, for example, 5 to 100 nm.

The content ratio of the silicon-containing compound is not particularly limited. For example, since a typical silicon-containing compound does not have electrical conductivity and can be a resistance component, excessive content is not preferable. Therefore, the ratio of the silicon-containing compound is suitable to be about 1 part by mass or less in terms of SiO ₂ with respect to 100 parts by mass of the conductive powder, for example, in an application for forming an internal electrode layer of MLCC. It is preferably 3 parts by mass or less, and for example, 0.3 parts by mass or less. The lower limit of the content ratio of the silicon-containing compound is not limited. This is because, for example, in an application for forming an internal electrode layer of MLCC, a silicon-containing compound such as silica is widely used as a component for forming a dielectric layer even when the conductive paste itself does not contain a silicon-containing compound. Because it is included. From this point of view, the silicon-containing compound may be, for example, 0.001 part by mass or more, and may be approximately 0.01 part by mass or more, in terms of SiO ₂ with respect to 100 parts by mass of the conductive powder. It is preferably 0.05 parts by mass or more, and may be, for example, 0.07 parts by mass or more. Further, the ratio of the silicon-containing compound can appropriately suppress the firing of the conductive powder from a low temperature, and can enhance the electrical conductivity, the denseness, etc. of the conductor film after firing.

The "fresnoite phase" in the present specification is a silicate compound formed by the reaction of the above-mentioned dielectric powder with a silicon-containing compound. Therefore, the fresnoite phase can be various silicate compounds containing the elements constituting the dielectric in addition to the fresnoite represented by the general formula Ba ₂ TiSi ₂ O ₈ . Examples of such dielectric constituent elements include strontium (Sr), calcium (Ca), magnesium (Mg), bismuth (Bi), zirconium (Zr), and zinc, in addition to titanium (Ti) and barium (Ba). Examples thereof include (Zn), niobium (Nb), hafnium (Hf), aluminum (Al), iron (Fe), neodium (Ne) germanium (Ge), and rare earth elements. It is given as a typical example. The Fresnoit phase is typically described by, for example, the following equation: Ba2-x-yCaxSryTi1-zZrzSi ₂ O ₈ (0≤x <2,0≤y <2,0≤x + y <2,0≤z <1). It can be a represented compound phase and a derivative crystalline phase thereof.

(D1) Binder The binder is a material that functions as a binder among the organic components in the conductive paste disclosed herein. This binder typically contributes to the bonding between the powder contained in the conductive paste and the substrate and the bonding between the particles constituting the powder. In addition, the binder is dissolved in a dispersion medium described later and functions as a vehicle (which can be a liquid phase medium). This increases the viscosity of the conductive paste and suspends the powder component uniformly and stably in the vehicle, imparts fluidity to the powder, and contributes to improvement in handleability. This binder is a component that is premised on disappearing by firing. Therefore, the binder is preferably a compound that burns through when the conductor film is fired. Typically, the decomposition temperature is preferably 500 ° C. or lower regardless of the atmosphere. The composition of the binder and the like are not particularly limited, and various known organic compounds used for this kind of use can be appropriately used.

Examples of such a binder include rosin-based resin, cellulose-based resin, polyvinyl alcohol-based resin, polyvinyl acetal-based resin, acrylic resin, urethane-based resin, epoxy-based resin, phenol-based resin, polyester-based resin, and ethylene-based resin. Examples thereof include organic polymer compounds such as. Although it cannot be said unconditionally because it depends on the combination with the solvent used, for example, as a binder of a conductive paste containing an inorganic oxide powder and having a relatively high firing temperature, a cellulosic resin or a polyvinyl alcohol-based binder is used. Resins, polyvinyl acetal-based resins, acrylic-based resins and the like are suitable.

The cellulosic resin contributes to the improvement of the dispersibility of the inorganic oxide powder, and is excellent in the shape characteristics of the printed matter (wiring film) and the adaptability to the printing work when the conductive paste is used for printing or the like. It is preferable because of the above. Cellulose-based resin means all polymers and derivatives thereof containing β-glucose as a repeating unit at least. Typically, it may be a compound in which a part or all of the hydroxy group in the β-glucose structure which is a repeating unit is replaced with an alkoxy group and a derivative thereof. The alkyl group or aryl group (R) in the alkoxy group (RO-) may be partially or wholly substituted with an ester group such as a carboxyl group, a nitro group, a halogen, or another organic group. Specific examples of the cellulose-based resin include methyl cellulose, ethyl cellulose, propoxy cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, hydroxypropyl ethyl cellulose, carboxymethyl cellulose, carboxyethyl cellulose, carboxypropyl cellulose and carboxyethyl. Examples thereof include methyl cellulose, cellulose acetate phthalate, and nitro cellulose.

Since the polyvinyl alcohol-based resin has good dispersibility of the inorganic oxide powder and is flexible, it is excellent in adhesion and printability of the printed matter (wiring film) when the conductive paste is used for printing or the like. preferable. The polyvinyl alcohol-based resin means a whole of polymers and derivatives thereof containing a vinyl alcohol structure as at least a repeating unit. Typically, polyvinyl alcohol (PVA) having a structure in which vinyl alcohol is polymerized, polyvinyl acetal resin obtained by acetalizing such PVA with alcohol, and derivatives thereof may be used. Among them, polyvinyl butyral-based resin (PVB) having a structure in which PVA is acetalized with butanol is more preferable because the shape characteristics of the printed matter are improved. Further, these polyvinyl acetal resins may be copolymers (including graft copolymers) containing polyvinyl acetal as a main monomer and a submonomer having copolymerizability in the main monomer. Examples of the by-monomer include ethylene, ester, (meth) acrylate, vinyl acetate and the like. The rate of acetalization in the polyvinyl acetal resin is not particularly limited, and is preferably 50% or more, for example.

Acrylic resins are preferable in that they are rich in adhesiveness and flexibility, and have less firing residue regardless of the firing atmosphere. The acrylic resin means, for example, a polymer containing at least an alkyl (meth) acrylate as a constituent monomer component and its derivatives in general. Typically, a homopolymer containing 100% by mass of an alkyl (meth) acrylate as a constituent monomer component, or a copolymer containing an alkyl (meth) acrylate as a main monomer and a copolymer having a copolymerizability in the main monomer ( (Including graft copolymerization) and the like. Examples of the by-monomer include a copolymerizable monomer in which 2-hydroxyethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, a vinyl alcohol-based monomer, a dialkylamino group, a carboxyl group, an alkoxycarbonyl group, etc. are introduced. Be done. Specific examples of the acrylic resin include poly (meth) acrylic acid, vinyl chloride / acrylic graft copolymer resin, vinyl acetal / acrylic graft copolymer resin and the like. In addition, in this specification, the notation such as "(meth) acrylate" is used as a term which comprehensively means acrylate and / or methacrylate.

Any one of the above binders may be used, or two or more of them may be used in combination. Further, although not explicitly described, a copolymer obtained by copolymerizing the monomer components of any two or more of the above resins, a block copolymer, or the like may be used. Moreover, the content of the binder is not particularly limited. The content of the binder is, for example, 0.5 part by mass with respect to 100 parts by mass of the conductive powder in order to satisfactorily adjust the properties of the conductive paste and the properties of the paste print (including the dry film). As mentioned above, the ratio may be preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, for example, 2 parts by mass or more. On the other hand, the binder resin does not preferably contain an excessive amount because the firing residue may increase. From this point of view, the binder content can be 10 parts by mass or less, preferably 7 parts by mass or less, more preferably 5 parts by mass or less, for example, 4 parts by mass or less with respect to 100 parts by mass of the conductive powder. ..

(D2) Dispersion Medium The dispersion medium is a liquid medium for dispersing the powder among the organic components in the conductive paste disclosed herein, and for example, imparts excellent fluidity while maintaining the dispersibility. It is an element to do. The dispersion medium is an organic solvent that dissolves the above binder and constitutes a vehicle. This dispersion medium is also a component on the premise that it disappears by drying and firing. The dispersion medium is not particularly limited, and an organic solvent used for this kind of conductive paste can be appropriately used. For example, although it depends on the combination with the binder, from the viewpoint of film formation stability, the main component is a high boiling point organic solvent having a boiling point of about 180 ° C. or higher and 300 ° C. or lower, for example, 200 ° C. or higher and 250 ° C. or lower. (A component that occupies 50% by volume or more.)

Specific examples of the dispersion medium include scullaleol, citronolol, phytol, geranyllinarool, texanol, benzyl alcohol, phenoxyethanol, 1-phenoxy-2-propanol, tarpineol, dihydroterpineol, isobornol, butyl carbitol, and diethylene glycol. Alcohol-based solvents such as tarpineol acetate, dihydro tarpineol acetate, isobornyl acetate, carbitol acetate, diethylene glycol monobutyl ether acetate and the like; ester-based solvents such as mineral spirit and the like. Among them, alcohol-based solvents and ester-based solvents can be preferably used.

The proportion of the (C) dispersion medium in the conductive paste is not particularly limited, but when the total paste is 100% by mass, it is approximately 70% by mass or less, typically 5 to 60% by mass, for example, 30 to 50% by mass. It should be. By satisfying the above range, appropriate fluidity can be imparted to the paste, and workability at the time of film formation can be improved. In addition, the self-leveling property of the paste can be enhanced to realize a conductor film having a smoother surface.

(E) Other Additives The conductive paste disclosed herein can be used in various general conductive pastes as long as the effects of the techniques disclosed herein are not significantly impaired. Organic additives can be included. Such organic additives include, for example, dispersants, thickeners, plasticizers, pH regulators, stabilizers, leveling agents, antifoaming agents, antioxidants, preservatives, colorants (pigments, dyes, etc.). And so on. For example, when powders such as conductive powder and dielectric powder, which are the main constituents of a conductor film, are used, when the average particle size is less than 1 μm, the powder is a paste unless a special surface treatment or the like is applied. Aggregation may occur during preparation and immediately after paste preparation. This tendency becomes even more remarkable when ultrafine powder or nanoparticles (for example, powder having an average particle diameter of 0.5 μm or less) whose surface activity can be remarkably increased are used as the conductive powder or the like. Therefore, the conductive paste disclosed herein can preferably contain a dispersant as another additive.

The dispersant is a component that suppresses aggregation of particles constituting the powder when the powder is dispersed in the dispersion medium and uniformly disperses the particles in the dispersion medium. The dispersant has the function of directly adsorbing to the solid surface of the particles and stabilizing the solid-liquid interface between the particles and the dispersion medium. The dispersant preferably burns through when the conductive paste is fired. In other words, the dispersant preferably has a decomposition temperature sufficiently lower than the firing temperature of the conductive paste (typically 600 ° C. or lower).

The type of the dispersant is not particularly limited, and one or more of the various known dispersants can be used as needed. Typically, a vehicle having sufficient compatibility with a vehicle (a mixture of a binder and a dispersion medium) described later can be appropriately selected and used. Dispersants can be classified in various ways, but the dispersants include so-called surfactant-type dispersants (also referred to as low-molecular-weight dispersants), polymer-type dispersants, and inorganic-type dispersants. It may be a thing. Further, these dispersants may be anionic, cationic, amphoteric or nonionic. In other words, the dispersant is a compound having at least one functional group of anionic group, cationic group, amphoteric group and nonionic group in the molecular structure, and this functional group is typically a particle. It is preferable that the compound can be directly adsorbed on the solid surface. The surfactant is an amphipathic substance having a hydrophilic site and a lipophilic site in the molecular structure and having a chemical structure in which these are covalently bonded.

Examples of the dispersant include surfactant-type dispersants, specifically, dispersants mainly composed of alkyl sulfonates, dispersants mainly composed of quaternary ammonium salts, and alkylene oxide compounds of higher alcohols. Examples thereof include a dispersant mainly composed of a dispersant mainly composed of a polyhydric alcohol ester compound, a dispersant mainly composed of an alkylpolyamine compound, and the like. As the high molecular weight dispersant, for example, a dispersant mainly composed of a fatty acid salt such as a carboxylic acid or a polycarboxylic acid, and a polycarboxylic acid partially alkyl ester in which a hydrogen atom in a part of the carboxylic acid group is substituted with an alkyl group. Dispersant mainly composed of compounds, dispersant mainly composed of polycarboxylic acid alkylamine salt, dispersant mainly composed of polycarboxylic acid partially alkyl ester compound having an alkyl ester bond in a part of polycarboxylic acid, polystyrene sulfonic acid Dispersants mainly composed of salts, polyisoprene sulfonates, polyalkylene polyamine compounds, dispersants mainly composed of sulfonic acid compounds such as naphthalene sulfonates, naphthalene sulfonic acid formalin condensate salts, hydrophilicity such as polyethylene glycol Dispersants mainly composed of polymers, dispersants mainly composed of polyether compounds, dispersants mainly composed of poly (meth) acrylic compounds such as poly (meth) acrylic acid salts and poly (meth) acrylamide, etc. be able to. Examples of the inorganic dispersant include phosphates such as orthophosphate, metaphosphate, polyphosphate, pyrophosphate, tripolyphosphate, hexamethaphosphate, and organic phosphate, ferric sulfate, and sulfate. Iron salts such as monoiron, ferric chloride, and ferrous chloride, aluminum salts such as aluminum sulfate, polyaluminum chloride, and sodium aluminate, calcium salts such as calcium sulfate, calcium hydroxide, and dibasic calcium phosphate. Examples thereof include dispersants mainly used.

The above-mentioned dispersant may contain any one of them alone, or may contain two or more of them in combination. The type of dispersant is not particularly limited, and the repulsive effect due to steric hindrance is exhibited for the purpose of effectively dispersing finer conductive powder and dielectric powder over a long period of time by adding a small amount of dispersant. It is preferable to use a possible high molecular weight dispersant. In this case, the weight average molecular weight of the dispersant is not particularly limited, but as a suitable example, it is preferably about 300 to 50,000, for example, 500 to 20,000.

The above-mentioned organic additive may contain any one of them alone, or may contain two or more of them in combination. Further, the content of the organic additive can be appropriately adjusted within a range that does not significantly impair the properties of the conductive paste disclosed herein. For example, it can be contained in an appropriate ratio according to the properties of the organic additive and its purpose. Roughly speaking, for example, the dispersant is generally about 5% by weight or less, for example 3% by weight or less, typically 1% by weight or less, based on the total mass of the powder components, and is about 0. It is contained in a proportion of 01% by mass or more. It is not preferable to include a component that inhibits the sinterability of the conductive powder or the inorganic powder, or an additive in an amount that inhibits these. From this point of view, when the organic additive is contained, the total content of these components is preferably about 10% by mass or less of the whole conductive paste, more preferably 5% by mass or less, and 3% by mass or less. Especially preferable.

The conductive paste disclosed herein is generally prepared by mixing (D1) binder and (D2) dispersion medium, which are organic components, in advance to prepare a vehicle, and then the (A) conductive powder is added to the vehicle. , (B) Dielectric powder and (C) Silicon-containing compound can be prepared by mixing and kneading. Here, in order to adjust the peak intensity ratio of the conductive paste to 26 or less, the dispersion strength tends to be too high in the preparation using a conventional general stirring / mixing device. As described above, the stirring conditions cannot be unequivocally determined because they depend on the materials used and their properties, but when using a known stirring and mixing device, the paste should be prepared under stirring conditions in which the dispersion strength is generally relaxed. Is preferable.

The conductive paste can be supplied to a desired substrate and then fired to obtain a conductor film. For the supply of the conductive paste to the substrate, various known supply methods can be adopted without particular limitation. Examples of such a supply method include printing methods such as screen printing, gravure printing, offset printing and inkjet printing, a spray coating method, a dip coating method and the like. In particular, when forming the internal electrode layer of the MLCC, a gravure printing method, a screen printing method, or the like capable of high-speed printing can be preferably adopted. The conductive paste used for the internal electrode of MLCC can be generally fired in an inert atmosphere at the firing temperature of the dielectric layer (typically, about 1000 to 1300 ° C.).

[Use]
In the conductive paste disclosed herein, the reaction between the dielectric powder contained in the conductive paste and the silicon-containing compound is suppressed. Therefore, it is suppressed that the fresnoite phase, which is a reaction product of the dielectric powder and the silicon-containing compound, grows as needle-like particles in the conductor film. In this respect, this conductive paste can be preferably used in applications where homogeneity, surface smoothness, etc. of the conductor film after firing are particularly required. Typical applications include the formation of electrode layers in laminated ceramic electronic components. For example, when the internal electrode layer of MLCC is formed by the conductive paste disclosed here, even if the conductor film is formed under the condition adjacent to the thinned dielectric layer, it protrudes from the conductor film. It is possible to prevent the needle-shaped particles from damaging or damaging the dielectric layer. This makes it possible to manufacture a high-quality MLCC having a high withstand voltage. The conductive paste disclosed here can be suitably used for forming an internal electrode layer of a small MLCC having a side of 5 m or less, for example, 1 mm or less. In particular, it can be suitably used for producing an internal electrode of a small-sized and large-capacity type MLCC having a dielectric layer thickness of 1 μm or less.

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

Examples of the ceramic material constituting the ceramic base material include barium titanate (BaTIO ₃ ), zirconium oxide (zirconia: ZrO ₂ ), magnesium oxide (magnesia: MgO), aluminum oxide (alumina: Al ₂ O ₃ ), and silicon dioxide. Oxide-based materials such as silicon (silica: SiO ₂ ), zinc oxide (ZnO), titanium oxide (titania: TiO ₂ ), cerium oxide (ceria: CeO ₂ ), yttrium oxide (itria: _{Y2O 3 )} ; Cody Elite ( _2MgO・ 2Al _{2O 3.5SiO 2} ), Murite (3Al 2O 3.2SiO ₂ ), Forsterite (2MgO ・ SiO ₂ ) _{, Steatite (MgO ・ SiO 2 )} , Sialon (Si 3N _4－ ) Composite oxide-based materials such as AlN-Al ₂ O ₃ ), zircon (ZrO ₂ · SiO ₂ ), ferrite (M ₂ O · Fe ₂ O ₃ ); silicon dioxide (silicon nitride: Si ₃ N ₄ ), nitride Nitride-based materials such as aluminum (aluminum nitride: AlN) and boron nitride (boron nitride: BN); carbide-based materials such as silicon dioxide (silicon carbide: SiC) and boron carbide ₍ boron carbide: B4C); Hydroxide-based materials such as hydroxyapatite; and the like. These may be contained alone, as a mixture of two or more, or as a complex of two or more.

[Multilayer ceramic capacitor]
FIG. 1A is a cross-sectional view schematically showing a multilayer ceramic capacitor (MLCC) 1. The MLCC 1 is a chip-type capacitor in which a large number of dielectric layers 20 and an internal electrode layer 30 are alternately and integrally laminated. A pair of external electrodes 40 are provided on the side surface of the laminated chip 10 composed of the dielectric layer 20 and the internal electrode layer 30. As an example, the internal electrode layer 30 is connected to external electrodes 40 which are alternately different in the stacking order. As a result, a compact and large-capacity MLCC 1 in which a capacitor structure composed of a dielectric layer 20 and a pair of internal electrode layers 30 sandwiching the dielectric layer 20 is connected in parallel is constructed. The dielectric layer 20 of the MLCC 1 is made of ceramic. The internal electrode layer 30 is composed of a fired body of the conductive paste disclosed herein. Such MLCC1 is suitably manufactured, for example, by the following procedure.

FIG. 1B is a sectional view schematically showing an unfired laminated chip 10 (an unfired laminated body 10'). In the production of MLCC1, first, a ceramic green sheet (dielectric green sheet) as a base material is prepared. Here, for example, a paste for forming a dielectric layer is prepared by mixing ceramic powder as a dielectric material, a binder, an organic solvent, or the like. Next, a plurality of unbaked ceramic green sheets 20'are prepared by supplying the prepared paste in a thin layer on the carrier sheet by a doctor blade method or the like.

Next, the conductive paste disclosed here is prepared. Specifically, at least the conductive powder (A), the dielectric powder (B), the binder (C), and the dispersion medium (D) are prepared and mixed in a predetermined ratio, and the transmittance change rate is 0. A conductive paste is prepared by stirring and mixing so that the content is .003 or less. Then, the prepared paste is supplied onto the prepared ceramic green sheet 20'with a predetermined pattern and a desired thickness (for example, 1 μm or less) to form the conductive paste coating layer 30'. The conductive paste disclosed herein has significantly improved dispersion stability. Therefore, when the MLCC is mass-produced, the properties of the conductive paste are stable even when the conductive paste coating layer 30'is continuously formed (printed) on the ceramic green sheet 20'for a long time, so that the print quality is also good. It can be stabilized well.

A plurality of (for example, several hundred to several thousand) ceramic green sheets 20'with the prepared coating layer 30' are laminated and pressure-bonded. This laminated crimping body is cut into a chip shape as needed. This makes it possible to obtain an unfired laminate 10'. Next, the prepared unfired laminate 10'is fired under appropriate heating conditions (for example, in a nitrogen-containing atmosphere, at a temperature of about 1000 to 1300 ° C.). As a result, the ceramic green sheet 20'and the conductive paste coating layer 30' are fired at the same time. The ceramic green sheet is fired to form the dielectric layer 20. The conductive paste coating layer 30'is fired to become the internal electrode layer 30. The dielectric layer 20 and the electrode layer 30 are integrally sintered, and a sintered body (laminated chip 10) can be obtained. Prior to the firing, in order to eliminate organic components such as the binder and the dispersion medium, a binder removal treatment (for example, in an oxygen-containing atmosphere, a temperature lower than the firing temperature: for example, about 250 to 700 ° C.; Heat treatment) may be applied. Then, the external electrode material is applied to the side surface of the laminated chip 10 and baked to form the external electrode 40. Thereby, MLCC1 can be manufactured.

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

[Preparation of conductive paste]
The conductive paste of each example was prepared by the following procedure. In the preparation of the conductive paste, the stirring conditions were set so that the dispersion strength was four levels A to D. Each level of dispersion strength is set so that level A is the strongest and level D is the weakest in the order of A>B>C> D. Stirring under general conditions with a conventional stirrer generally corresponds to relatively "hard stirring" near level A. Further, stirring was carried out until the dry coating film obtained by the conductive paste being stirred with the above dispersion strength became a homogeneous state in which at least no particles were observed on the surface. Specifically, a small amount of conductive paste sampled during stirring is applied to a substrate with a thickness of 2 μm using an applicator, and the surface of the dried coating film obtained by drying at about 100 ° C. is microscopically viewed. The conductive paste was stirred until no particles were observed on the surface when 5 visual fields were confirmed at (200 times).

(Example 1)
A nickel (Ni) powder having an average particle size of 0.3 μm, a barium titanate (BT) powder having an average particle size of 50 nm, a slurry containing a silicon-containing compound, and a dispersant are mixed in a vehicle to disperse strength. The conductive paste of Example 1 was prepared by stirring under the condition of level A. The slurry containing the silicon-containing compound of Example 1 was prepared by previously mixing silica powder having an average particle diameter of 50 nm as the silicon-containing compound and a part of isobornyl acetate as the organic solvent. As the vehicle, ethyl cellulose as a binder and isobornyl acetate, which is a residual organic solvent, were preheated and mixed according to a conventional method. Moreover, as a dispersant, a carboxylic acid-based dispersant was used.

The composition of each material is as shown in Table 1 below. The silica powder as the silicon-containing compound was added at a ratio of 0.1 part by mass (SiO ₂ equivalent) to 100 parts by mass of the Ni powder.

(Examples 2 to 3)
The level of stirring intensity in the preparation of the conductive paste of Example 1 was changed to (Example 2) level B and (Example 3) level C, respectively, and the other conditions were the same as in Example 1, and the conductivity of Examples 2 and 3 was the same. A sex paste was prepared.

(Examples 4 and 5)
In the preparation of the conductive paste of Example 2, the addition ratio of the silica powder was changed to 0.05 parts by mass (Example 4) and 0.15 parts by mass (Example 5) with respect to 100 parts by mass of Ni powder. The conductive pastes of Examples 4 and 5 were prepared in the same manner as in Example 2 under other conditions.

(Examples 6 and 7)
Instead of the BT powder in Example 1, a finer BT powder having an average particle diameter of 10 nm was used, and the conductive paste of Example 6 was prepared in the same manner as in Example 1 under other conditions.
Further, instead of the BT powder of Example 1, a finer BT powder having an average particle diameter of 10 nm is used, the level of the dispersion strength in the preparation of the conductive paste is set to the softest level D, and the other conditions are Example 1. The conductive paste of Example 7 was prepared in the same manner as in the above.

(Examples 8 and 9)
Instead of the BT powder of Example 1, a coarser BT powder having an average particle diameter of 100 nm was used, and the conductive paste of Example 8 was prepared in the same manner as in Example 1 under other conditions.
Further, instead of the BT powder of Example 3, a coarser BT powder having an average particle diameter of 100 nm was used, and the conductive paste of Example 9 was prepared in the same manner as in Example 3 under other conditions.

(Examples 10 to 14)
Instead of the silica powder as the silicon-containing compound in Example 2, (Example 10) Si Regnate, (Example 11) Silica-containing ceramic composite oxide powder (average particle size 50 nm), (Example 12) Silicone oil 1 (Shin-Etsu Chemical Co., Ltd.) (Example 13) Silicone oil 2 (manufactured by Shin-Etsu Chemical Co., Ltd., KF-96-5000cs), (Example 14) Silicone oil 3 (manufactured by Shin-Etsu Chemical Co., Ltd.) , KF-96-50000cs), respectively, so that the amount of Si component added is 0.1 parts by mass with respect to 100 parts by mass of Ni powder when converted to SiO ₂ , and other conditions are The conductive pastes of Examples 10 to 14 were prepared in the same manner as in Example 2.

[Preparation of sample for evaluation of conductive paste]
In order to evaluate the characteristics of the conductive paste during firing, an evaluation sample consisting of a fired product obtained by firing the conductive paste was prepared by the following procedure.
First, about 10 g of the conductive paste of each example was applied onto a PET film with a film thickness of 250 μm using a film applicator. Then, a dry film was obtained by drying with a warm air dryer at a set temperature of 100 ° C. and a drying time of 15 minutes.

Next, the dried film was peeled off from the PET film, made into an appropriate size, and placed in 10 alumina crucibles (constant amount) having a capacity of 15 ml in an amount of 5.0 ± 0.1 g (N = 10). Then, using a tubular furnace (replacement furnace, inner diameter 12.16 cm × length 100 cm), two crucibles were divided into five times and fired under the following conditions to perform a binder removal treatment.
Gas replacement: 2 times before firing Atmospheric gas, flow rate: 100% N ₂ , 0.2 L / min
Temperature rise rate: 200 ° C / h
Reaching temperature, holding time: 600 ° C, 20 min
Temperature down rate: Natural cooling (cooling)

The dried membrane after the binder removal treatment was transferred from the crucible to a mortar and pestle and ground with a pestle for about 30 seconds to make a powder. Then, 1.0 ± 0.1 g of the dry film powder was separated and returned to the crucible, and two crucibles were divided into 5 times in a tube furnace and subjected to the main firing treatment under the following conditions. The powder obtained by firing in this way was taken out into a mortar again and ground with a pestle for about 30 seconds to prepare a sample (N = 10) for evaluation of the baked conductive paste of each example.
Gas replacement: 2 times before firing Atmospheric gas, flow rate: 99% N2 + 1% H ₂ , 0.2 L / min
Temperature rise rate: 200 ° C / h
Reaching temperature, holding time: 1300 ℃, 10min
Temperature down rate: Natural cooling (cooling)

[Measurement of peak intensity of fresnoit phase]
The peak intensity of the fresnoite phase in the evaluation sample of the paste-baked product of each example was measured by subjecting it to XRD analysis using the evaluation sample prepared above (N = 10). An X-ray diffraction analyzer (manufactured by Rigaku Co., Ltd., RINT-TTRIII) was used for the XRD analysis, and the measurement conditions were as follows.
X-ray source: CuKα ray (electron beam acceleration voltage 50 kV, electron beam current 300 mA)
Measurement range: 20 ° ≤ 2θ ≤ 120 °
Scan speed: 1 ° / min
Step width: 0.01 °
Measurement temperature: Room temperature (25 ° C)

Then, based on the obtained XRD pattern, the peak intensity (IF) of the peak derived from the _fresnoite phase observed near 29 ° and the peak intensity (I) of the peak derived from barium titanate observed near 22.4 °. _BT ) was read, and the peak intensity rate was calculated based on the following equation. The peak intensity rate may vary depending on the firing times. Therefore, out of the five firings, the results of the firing times in which the peak intensity rate was the maximum and the minimum were cut, and the peak intensity rate (N = 6) for the evaluation sample obtained by the remaining three firings. The arithmetic mean value of was taken as the peak intensity rate of the evaluation sample. The results are shown in Table 2 below. For reference, FIG. 2 shows the XRD patterns obtained for the evaluation sample of Example 2.

[Measurement of needle-shaped particles]
By observing with a scanning electron microscope (SEM) using the evaluation samples of Examples 1 to 9 prepared above, a needle characteristic of the fresnoite phase found in the fired product of the conductive paste. The number of shaped particles was counted.
Specifically, the powdery evaluation sample of each example was fixed on the SEM observation sample table with a silver paste, and Au vapor deposition was performed to prepare an SEM observation sample. Twenty-five pieces of SEM observation samples were prepared for each example. Then, the observation magnification was set to 5000 times, and the number of needle-shaped particles in the evaluation sample was counted. The number of needle-shaped particles in the evaluation sample of each example was counted for a total of 250 visual fields, 10 visual fields for each SEM observation sample. For reference, FIG. 3 shows SEM observation images of the evaluation samples of (a) Example 1 and (b) Example 4. As shown in FIG. 3, the needle-shaped particles are clearly anisotropy in shape as compared with other particles regardless of their dimensions. In this embodiment, particles having an aspect ratio of 2 or more are determined to be needle-shaped particles, and the number of particles is counted. The results are shown in Table 2 below.

[Insulation characteristics evaluation]
For reference, Table 2 also shows the results of evaluating the dielectric breakdown characteristics of the MLCCs prepared using the conductive pastes of Examples 1 to 3. Specifically, 50 MLCCs were prepared using the pastes of each example, and when a DC voltage (10 V) was applied for 200 hours in an atmosphere of a temperature of 85 ° C. and a humidity of 85%, the dielectric breakdown was 1 MLCC. If there is no MLCC, it is marked as "○", and if there is even one MLCC whose dielectric breakdown is present, it is marked as "x".

As shown in Examples 1 to 3 of Table 2, even if the materials and formulations used are exactly the same, the conductive paste is baked by changing the method for preparing the conductive paste (here, stirring conditions). It was found that the properties of the fired product obtained in the above process may differ greatly. Specifically, it was found that by increasing the dispersion strength at the time of preparing the paste and stirring it hard, needle-like particles are likely to be formed in the calcined product obtained by calcining the paste. It was also found that by lowering the dispersion strength and stirring mildly, needle-like particles are less likely to be formed in the calcined product obtained by calcining the paste. From the results of the XRD analysis, it was found that the sample in which more needle-shaped particles were formed tended to have a higher diffraction peak derived from the fresnoite phase and a higher peak intensity rate of the fresnoite phase. From this, it is considered that the needle-shaped particles are particles made of fresnoite and are formed by reacting the BT powder in the conductive paste with the silicon-containing compound (here, silica powder). Further, even if the type and composition of the electrode materials used are the same, the reactivity between the BT powder and the silica powder differs depending on the paste preparation conditions, and as a result, the number of fresnoites formed in the fired product also differs. I understand.

As shown in FIG. 3, since the size of the fresnoite particles to be counted is not constant, the number and the amount of the fresnoite particles do not match. However, the amount of the fresnoite phase can be evaluated by the peak intensity rate of the fresnoite phase based on the XRD analysis. Further, as shown in Table 2, a generally good correlation can be seen between the peak intensity of the fresnoite phase and the number of needle-shaped particles. From this, it can be said that the ratio of needle-like particles in the conductive paste can be appropriately evaluated by using the peak intensity rate of the fresnoite phase as an index. Further, it is considered that the MLCC produced by using the conductive paste of Example 1 had dielectric breakdown due to the increase of needle-shaped fresnoite particles.

As shown in Examples 4 and 5, the number of needle-like particles, that is, fresnoite particles, formed in the calcined product obtained by calcining the paste even when the amount of silica powder contained in the conductive paste changes. Turned out to change. Specifically, it was found that the smaller the amount of silica powder contained in the paste, the smaller the number of fresnoite particles in the calcined product, and the larger the amount of silica powder, the larger the number of fresnoite particles in the calcined product. .. It was also found that the peak intensity of the fresnoite phase in the calcined product decreases as the amount of silica powder contained in the paste decreases, and the peak intensity of the fresnoite phase of the calcined product increases as the amount of silica powder increases. rice field. From this, it was confirmed that the ratio of needle-like particles in the conductive paste can be appropriately evaluated by using the peak intensity rate of the fresnoite phase as an index.

From the comparison of Example 1, Example 6 and Example 8, when the average particle size of the BT powder is small, the peak intensity ratio of the fresnoite phase is high, the number of fresnoite particles is significantly increased, and when the average particle size of the BT powder is large, It was found that the peak intensity rate of the fresnoite phase decreased and the number of fresnoite particles decreased. It is considered that this is because the smaller the average particle size of the BT powder, the higher the surface activity and the higher the reactivity with the silica powder. Further, the result of Example 6 is that the contact point between the BT powder and the silica powder is significantly increased by reducing the BT powder to the level of several tens of nm, and the number of fresnoite particles formed is significantly increased, but the volume thereof is increased. It is in good agreement with the fact that silica does not increase so much.

Further, from the comparison between Example 6 and Example 7, it was confirmed that the peak intensity of the fresnoite phase and the number of fresnoite particles can be kept low by lowering the dispersion strength even if the BT powder having a small average particle size is used. .. Further, from the comparison between Example 8 and Example 9, it was confirmed that even if the BT powder having a large average particle size was used, the peak intensity of the fresnoite phase and the number of fresnoite particles could be kept low by lowering the dispersion strength.

Furthermore, when the average particle size of the BT powder is significantly different between 10 nm and 100 nm, it is usually better to use larger BT particles (Example 8) in the fired product, as shown in Examples 6 and 8. Is difficult to form. However, as can be seen from the comparison between Example 7 and Example 8, by setting the paste preparation conditions appropriately with a low dispersion strength so that the peak intensity ratio of the fresnoite phase is sufficiently small, the BT having an average particle size of 100 nm is larger. It was found that the number of fresnoite particles formed in the calcined product could be reduced when a smaller BT powder of 10 nm was used (Example 8) than when the powder was used (Example 8).

From the above, the conductive paste has a peak intensity of the Ni powder, BT powder and silica powder, for example, while checking the peak intensity of the fresnoite phase each time, depending on the conditions such as the particle size and blending. It can be said that the paste preparation conditions should be set so as to be sufficiently small (for example, 26 or less). Further, by using the conductive paste having a peak intensity ratio of 26 or less disclosed here, it is possible to suppress the generation of needle-shaped particles during firing and form a conductor film. This prevents needle-like particles in the internal electrode layer from penetrating the thinned dielectric layer and causing deterioration of withstand voltage characteristics, for example, in the production of MLCC. As a result, it is possible to manufacture a high-quality MLCC having excellent reliability and withstand voltage characteristics.

As shown in Examples 10 to 14, as the silicon-containing compound, Si-resinate (Example 10), which is an organic metal compound of Si (silicon), and Si is contained as a part of the metal element, in addition to the silica powder. It was found that even when a ceramic composite oxide (Example 11) and a silicone oil having a polysiloxane structure (Examples 12 to 14) were used, a fresnoite phase was formed in the calcined product of the conductive paste. Further, in this case, it was confirmed that the peak intensity ratio of the fresnoite phase in the calcined product could be suppressed sufficiently small (for example, to 26 or less) by softening the paste preparation condition to the stirring intensity B.
Although the present invention has been described in detail above, these are merely examples, and the present invention can be modified in various ways without departing from the gist thereof.

1 MLCC
10 Multilayer capacitor part 10'Unfired laminate 20 Dielectric layer 20'Ceramic green sheet 30 Internal electrode layer 30' Conductive paste coating layer 40 External electrode

Claims (4)

A conductive paste used to form a conductor film.
With conductive powder
Dielectric powder and
Silicon-containing compounds and
Contains organic ingredients
The average particle diameter D ₁ of the conductive powder based on the BET method is 0.5 μm or less.
When the average particle size of the conductive powder based on the BET method is D ₁ and the average particle size of the dielectric powder based on the BET method is D ₂ , 0.03 × D ₁ ≦ D ₂ ≦ 0.4 × D Meets ₁ and
The amount of the silicon-containing compound added to 100 parts by mass of the conductive powder is 0.01 to 0.5 parts by mass in terms of SiO ₂ .
In the XRD analysis of the fired product of the conductive paste,
The ratio of the peak intensity of the peak derived from the fresnoite phase to the peak intensity of the peak derived from the dielectric is adjusted to be 26 or less.
Here, the fresnoite phase is a compound phase formed by a reaction between the dielectric powder and the silicon-containing compound.
The fired product was produced by heat-treating the conductive paste at 600 ° C. under an inert atmosphere to remove the organic component, and then firing at 1300 ° C. under an inert atmosphere. Conductive paste. The conductive paste according to claim 1 , wherein the conductive powder is at least one selected from the group consisting of nickel, platinum, palladium, silver and copper. The conductive paste according to claim 1 or 2 , wherein the dielectric powder is at least one selected from the group consisting of barium titanate, strontium titanate, and calcium zirconate. The conductive paste according to any one of claims 1 to 3 , which is used for forming an internal electrode layer of a laminated ceramic electronic component.

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