JPH0997518A - Conductive paste and layered ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide conductive paste consisting of metal powder, ceramic powder, organic binder, and organic solvent having a large bonding strength with an element substance and cable of producing an external electrode of high resistance against moisture by using a ceramic material of such a structure as having specified particle size distribution and a mean particle size. SOLUTION: Ceramic powder contained in a conductive paste consists of a ceramic material approx. the same as the material of a dielectric substance layer of a layered ceramic capacitor element whose external electrode is prepared from such paste which is subjected to a baking process. This ceramic powder used consists in a mixture of a ceramic powder A having two peaks in its particle size distribution and a mean particle size of 0.5-1.0μm and another ceramic powder B having a mean particle size of 2.5-3.0μm, where the ratio A/B should range between 0.6-1.5. Thereby a conductive paste is obtained, which has a large bonding strength with an element substance and can produce an external electrode with enhanced resistance against moisture.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste for forming external electrodes on both ends of an element body of a laminated ceramic capacitor, and a laminated ceramic capacitor provided with the external electrodes formed by this conductive paste. is there.

[0002]

2. Description of the Related Art A monolithic ceramic capacitor includes an element body in which a large number of dielectric ceramic layers and internal electrode layers are alternately laminated,
It is composed of a pair of external electrodes formed at both ends of this element body. Here, this element body is formed by, for example, laminating a large number of unfired porcelain sheets (ceramic green sheets) on which a pattern of a conductive paste is printed, and firing them at a high temperature of about 1200 ° C. For example, it is formed by attaching a conductive paste to the end portion of the element body before firing and firing this together with the element body.

As the conductive paste forming the external electrodes, a composition composed of metal powder, ceramic powder, an organic binder and an organic solvent is generally used. Here, as the metal powder, for example, a noble metal powder such as Pd or Ag or a base metal powder such as Ni or Cu is used. The ceramic powder is used to increase the bonding strength between the dielectric ceramic layer of the element body and the external electrode. As the organic binder, for example, acrylic resin, phenol resin, alkyd resin, rosin ester, various celluloses, etc. are used. As the organic solvent, for example, alcohol-based, hydrocarbon-based, ether-based or ester-based solvents are used.

When the conductive paste is fired, the organic binder and the organic solvent in the conductive paste are first burned and removed, and then the metal powder and the ceramic powder are sintered to form an external electrode. Then, the internal electrodes in the element body are electrically and alternately connected in parallel by the external electrodes thus formed.

[0005]

By increasing the average particle size of the ceramic powder contained in the above-mentioned conductive paste, the bond strength between the element body and the external electrode is increased, but the density of the external electrode is increased. If the average particle diameter of the ceramic powder contained in the conductive paste is reduced, the external electrode density increases and the external electrode moisture resistance becomes better. However, there is a problem that the bonding strength between the element body and the external electrode is weakened.

The present invention has a large bond strength with the element body,
Moreover, it is an object to obtain a conductive paste capable of forming an external electrode having excellent moisture resistance, and to obtain a monolithic ceramic capacitor provided with such an external electrode.

[0007]

In order to solve the above problems, a conductive paste according to the present invention comprises at least a metal powder, a ceramic powder, an organic binder and an organic solvent, and the ceramic powder has a particle size distribution within its range. It has two mountains. Further, the monolithic ceramic capacitor according to the present invention includes external electrodes formed by firing the conductive paste.

Here, the ceramic powder is obtained by mixing, for example, a ceramic powder A having an average particle diameter of 0.5 μm to 1.0 μm and a ceramic powder B having an average particle diameter of 2.5 μm to 3.0 μm. It is possible to have two peaks in the distribution. In this case, the ratio of the ceramic powder A and the ceramic powder B is preferably A / B = 0.6 to 1.4. The material of the ceramic powder is preferably the same material as the dielectric ceramic layer of the manufactured multilayer ceramic capacitor (which is the same material as the dielectric ceramic layer of the element body). As the metal powder, for example, a base metal such as Ni powder can be used.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION First, a conductive paste according to the present invention comprises at least a metal powder, a ceramic powder, an organic binder and an organic solvent, and the ceramic powder has two peaks in its particle size distribution. There is.

Here, as the metal powder, for example, Pd,
It is possible to use powders of one or more noble metals selected from Pt, Ag, Au, etc. or alloys thereof, or powders of base metals such as Ni, Cu.

As the ceramic powder, any one having good wettability with the dielectric ceramic layer of the manufactured multilayer ceramic capacitor can be used, but the shrinkage rate of the external electrode is adjusted to match the shrinkage rate of the element body. Prevents cracks from occurring in the body, and makes good contact between the external electrode and the element body,
In order to reduce the influence of the ceramic powder contained in the external electrodes on the dielectric layer, it is preferable to use the same ceramic as the dielectric ceramic layer of the manufactured multilayer ceramic capacitor. The ceramic powder may be used in the range of 10 to 30 parts by weight with respect to 100 parts by weight of the metal powder.

The ceramic powder needs to have two peaks in its particle size distribution, but the ceramic powder having such a particle size distribution has, for example, an average particle size of 0.5 μm to 1.0 μm.
ceramic powder A having an average particle size of 2.5 μm to 3.
It can be obtained by mixing with 0 μm ceramic powder B. In this case, the ratio of the ceramic powder A and the ceramic powder B is preferably A / B = 0.6 to 1.4.

Examples of the organic binder include cellulosic resins, epoxy resins, aryl resins, acrylic resins,
Examples thereof include phenol-formaldehyde resin, unsaturated polyester resin polycarbonate resin, polyamide resin, polyimide resin, alkyd resin, and rosin ester, but are not limited to these and may have a property of being a binder. For example, organic compounds other than these can also be used. These organic binders can be used in the range of 8 to 12 parts by weight with respect to 100 parts by weight of the metal powder.

Examples of the organic solvent include butyl carbitol, butyl carbitol acetate, turpentine oil, α
-Terpineol, ethylene cellosolve, kerosene, butyl cellosolve, butyl phthalate and the like can be mentioned, but not limited to these, and organic compounds other than these may be used as long as they have the property of being a solvent. it can. These organic compounds can be used in the range of 50 to 80 parts by weight with respect to 100 parts by weight of the metal powder.

In addition to these organic solvents, petroleum hydrocarbons (mineral spirits, etc.) may be further used as a diluting solvent. The diluent solvent may be used in the range of 50 to 100 parts by weight with respect to 100 parts by weight of the metal powder.

The conductive paste described above is applied to both ends of the element body of the monolithic ceramic capacitor, and then 550 ° C.
By baking at a moderate temperature, it is possible to obtain a monolithic ceramic capacitor having a large bonding strength with the element body and having an external electrode excellent in moisture resistance.

[0017]

【Example】

Examples 1 to 7 First, a ceramic green sheet having a side of 10 cm and a thickness of about 20 μm was prepared, and 50 internal electrode patterns made of a conductive paste were printed on one surface by a screen printing method. Here, as the ceramic green sheet, Ba
An organic binder composed of an acrylic ester polymer, glycerin, condensed phosphate, etc. was added to and mixed with the TiO ₃ -based ceramic powder, and this was molded into a sheet to be used. As the conductive paste for the internal electrodes, 10 g of Ni powder having an average particle size of 1.5 μm and 0.9 g of ethyl cellulose dispersed in 9.1 g of butyl carbitol were used.

Next, 50 layers of the ceramic green sheets printed with the internal electrode patterns were laminated, and 10 layers of the ceramic green sheets not printed with the internal electrode patterns were laminated on the upper and lower sides thereof to obtain a laminated body. Here, the internal electrode pattern has a rectangular shape with a length of 14 mm and a width of 7 mm, and the internal electrode patterns facing each other through one ceramic green sheet are displaced by about half in the longitudinal direction during lamination. There is.

Next, the laminated body thus obtained is
These were pressed under pressure of 400 kgf / cm ² at a temperature of 00 ° C. to press-bond them, and then cut into a grid pattern for each internal electrode pattern to obtain 50 chip-shaped laminated bodies.

Next, a conductive paste for an external electrode was applied to the end of the sintered body chip where the internal electrode was exposed and dried. Here, as the conductive paste for the external electrode, 80 wt% of Ni powder having an average particle diameter of 1.5 μm, 18.9 wt% of ceramic powder co-fabricated with the dielectric ceramic layer, and Al ₂ O _{3 were used.}
0.3 wt%, ZrO ₂ 0.8 wt% and a small amount of ethyl cellulose dispersed in butyl carbitol were used. For ceramic powder, the average particle size is 0.5
~ 1.0 μm co-fabric A and average particle size 2.5-3.0
A mixture of μm co-texture B and A / B was 0.7 to 1.4 was used.

Next, this chip-shaped laminated body was placed in a firing furnace in which the atmosphere can be adjusted, and 100 ° C. /
The organic binder contained in the ceramic green sheet and the internal electrode pattern was burned and removed by heating to 600 ° C. at a rate of hr. After that, the atmosphere of the furnace was changed from the atmospheric atmosphere to the atmosphere of H ₂ (2% by volume) + N ₂ (98% by volume). Then, after keeping the furnace atmosphere in the reducing atmosphere as described above and holding the heating temperature of the laminated chip from 600 ° C. to 1150 ° C. (maximum temperature) of the firing temperature for 3 hours, 100 ° C./hr The temperature was lowered to 600 ° C., the atmosphere was replaced with an air atmosphere (oxidizing atmosphere), the temperature was kept at 600 ° C. for 30 minutes for oxidation treatment, and then the temperature was cooled to room temperature to obtain a sintered body chip.

Next, a lead wire is soldered to each external electrode portion of this monolithic ceramic capacitor, one lead wire is fixed, and the other lead wire is attached to a push-pull gauge and pulled to pull out the monolithic ceramic capacitor element. When the value when the external electrode was peeled from the body was measured, it was as shown in Table 1.

On the other hand, this monolithic ceramic capacitor 10
0 pieces were placed in a humidity resistant tank of temperature 60 ° C. and humidity 90%, 16 V which is the rated voltage of this laminated ceramic capacitor was applied and left for 1000 hours, and the number of IR less than 100 MΩ was examined. It was as shown in Table 1.

Comparative Examples 1 to 7 Multilayer ceramic capacitors were prepared in the same manner as in Examples 1 to 7 except for the condition of the particle size distribution of ceramic powder. The average particle size of the ceramic powder is 0.3 to 3.0 μm.
I used the co-fabric.

Then, the bonding strength and moisture resistance between the external electrode and the element body were examined in the same manner as in Examples 1 to 7, and Table 1
It was as shown in.

Comparative Examples 8 to 13 Multilayer ceramic capacitors were prepared in the same manner as in Examples 1 to 7 except for the condition of the particle size distribution of ceramic powder. The average particle size of the ceramic powder is 0.3 to 1.2 μm.
The co-texture A was mixed with the co-texture B having an average particle size of 2.3 to 3.0 μm so that A / B was 0.5 to 1.7.

Then, the bonding strength and moisture resistance between the external electrode and the element body were examined in the same manner as in Examples 1 to 7, and Table 1
It was as shown in.

[0028]

[Table 1]

From the results of Examples 1-7 and Comparative Examples 1-7,
If the ceramic powder contained in the conductive paste for the external electrode has two peaks in its particle size distribution, the bonding strength between the external electrode and the element body of the monolithic ceramic capacitor is increased and the moisture resistance is improved. You can see that it will improve.

Further, from the results of Examples 1 to 7 and Comparative Examples 8 to 13, the ceramic powder contained in the conductive paste for the external electrode has a peak in the range of 0.5 to 1.0 μm in its particle size distribution. It can be seen that when the peaks are in the range of 2.5 to 3.0 μm, the bonding strength between the external electrode and the element body of the monolithic ceramic capacitor becomes particularly large, and the moisture resistance is further improved.

[0031]

According to the present invention, since the ceramic powder contained in the conductive paste for the external electrode has two peaks in the particle size distribution, the external electrode and the element body of the monolithic ceramic capacitor are As the bond strength of increases,
It has the effect of improving the moisture resistance.

Claims (6)

[Claims] 1. A conductive paste comprising at least a metal powder, a ceramic powder, an organic binder and an organic solvent, wherein the ceramic powder has two peaks in its particle size distribution. 2. The conductive paste according to claim 1, wherein the ceramic powder is made of a ceramic having substantially the same quality as that of a dielectric ceramic layer of a laminated ceramic capacitor body in which the conductive paste is baked to form an external electrode. . 3. The ceramic powder has an average particle size of 0.5.
Ceramic powder A having a particle size of μm to 1.0 μm and an average particle size of 2.
The conductive paste according to claim 1 or 2, wherein the conductive paste is made of a mixture with 5 μm to 3.0 μm of ceramic powder B and ceramic A / ceramic B = 0.6 to 1.5. 4. The conductive paste according to claim 1, wherein the metal powder is a base metal powder. 5. The conductive paste according to claim 4, wherein the base metal powder is nickel powder. 6. A multilayer ceramic capacitor formed using the conductive paste according to claim 1.