JP2001023862A - Manufacture of multilayer ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the durability of a multilayer ceramic capacitor when inner electrodes B within a chip C of the capacitor is made of nickel or a nickel alloy. SOLUTION: A plurality of dielectric green sheets A1, each having an inner electrode B formed by applying nickel or nickel alloy paste to the surface thereof, are bonded by compression into a chip C. The chip C is then baked in an atmosphere of a reducing gas, after which it is baked again in an atmosphere of an oxidizing gas. Next, the resulting chip C has its left and right facets C1 and C2 polished to form external electrodes D1 and D2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a multilayer ceramic capacitor using nickel or an alloy thereof as a material of an internal electrode among multilayer ceramic capacitors.

[0002]

2. Description of the Related Art Generally, when manufacturing a multilayer ceramic capacitor of this type, a material paste for an internal electrode is screen-printed on the surface of a green sheet made of a dielectric material, and a plurality of dielectric green sheets are laminated. To a chip piece, and then this chip piece is
A method is employed in which firing is performed at a high temperature of ℃ and then external electrodes are formed on each of the left and right end faces of the chip piece.

In this manufacturing method, expensive palladium is generally used as a material for the internal electrodes. However, in some cases, less expensive nickel or an alloy thereof is used instead of the palladium. It has been proposed.

However, when the internal electrode is formed of a paste of nickel or an alloy thereof, firing at a high temperature causes
Since the nickel in the paste is oxidized in a granular state and no longer functions as an internal electrode, the firing at a high temperature is performed in an atmosphere of a reducing gas such as an N ₂ -H ₂ gas. However, if high-temperature sintering is performed in a reducing gas atmosphere, the insulation resistance of the conventional dielectric material is reduced.

Therefore, conventionally, for example, Japanese Patent Laid-Open No. Sho 53-2
As described in Japanese Patent No. 4600 or the like, the use of a dielectric having a special composition so as to have reduction resistance to high-temperature sintering as a material of the dielectric allows the dielectric insulation resistance of the dielectric to be high. It is intended to avoid a decrease by firing.

[0006]

However, a dielectric having a special composition so as to have reduction resistance to high-temperature firing,
Although there is not much price difference from a very ordinary dielectric, there is a problem that the service life is short because the insulation resistance is easily deteriorated in a high temperature load test.

An object of the present invention is to provide a manufacturing method which solves this problem.

[0008]

In order to achieve this technical object, the present invention relates to a method of forming an internal electrode by applying a paste of nickel or an alloy thereof on the surface of a green sheet made of a dielectric material. A plurality of sheets are stacked and pressed on a chip piece, and then fired in an atmosphere of a reducing gas, and then fired again in an atmosphere of an oxidizing gas. After polishing the left and right end surfaces, external electrodes are formed. "

[0009]

According to the present invention, even if the dielectric is reduced by firing in an atmosphere of a reducing gas and its insulation resistance is reduced, the dielectric having a low insulation resistance is kept in an atmosphere of an oxidizing gas thereafter. By re-firing, a dielectric having high insulation resistance can be returned.

Further, the paste of nickel or its alloy applied to the green sheet made of the dielectric material is sintered into a plate shape by firing in an atmosphere of a reducing gas at first to form one electrode. Therefore, in the internal electrode made of nickel or nickel alloy, only a part of the surface of the internal electrode is oxidized by re-firing in an atmosphere of an oxidizing gas thereafter.

Therefore, after removing the oxide film in the portions of the internal electrodes exposed at both end faces of the chip piece by polishing the both end faces of the chip piece, external electrodes are provided on both right and left end faces of the chip piece. By forming, the internal electrode can be electrically connected to the external electrode without fail.

Therefore, according to the present invention, by performing firing in an atmosphere of a reducing gas and then re- firing in an atmosphere of an oxidizing gas, the dielectric material can be used as a conventional material. Long life and high reliability because it is not necessary to use a dielectric material with high reduction resistance and to use a dielectric material that reduces the deterioration of insulation resistance in high-temperature load tests. The effect is that a multilayer ceramic capacitor having a high density can be manufactured.

In particular, the external electrode is formed by sputtering, vacuum deposition or ion plating of a metal as described in claim 2, or a temperature of 300 ° C. or less as described in claim 3. By forming by applying a conductive paste that cures in, the dielectric is reduced and the insulation resistance is reduced when forming the external electrodes,
In addition, there is an advantage that occurrence of connection failure with the external electrode due to oxidation of the internal electrode can be reliably reduced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

A paste of nickel or a nickel alloy, which is a material for forming the internal electrode B, is applied by screen printing to the surface of the green sheet A1 made of a dielectric material,
After stacking a plurality of the green sheets so that the internal electrodes B in each of them are alternately turned in the opposite direction, green sheets A2 and A3 made of a dielectric material for a cover are further stacked on the upper and lower surfaces thereof. By pressing in the stacking direction, a chip piece C as shown in FIG. 2 is obtained.

Each of the green sheets A1, A2,
A3 is made of a barium titanate-based ceramic containing BaTiO ₃ ... 99.7 wt% SiO ₂ ... 0.1 wt% MnCO ₃ . It is a dielectric and has a thickness of about 20 microns. Also,
The composition of this dielectric is general. For example, Ca, Zr, Sr and rare earth elements are used for the F characteristic, and Mg, Co, Z are used for the B characteristic.
Generally known additives such as r, Nb and rare earth elements may be added.

Then, the chip piece C is filled with 3 wt.
% Of H ₂ gas and 97 wt% of N ₂ gas in a heating furnace with a reducing gas atmosphere at a temperature of about 1250 ° C., and further heating the inside with an oxidizing gas atmosphere such as air. Refire at a temperature of about 900 ° C. in a furnace.

By firing in the atmosphere of the reducing gas, the chip C can be sintered, and at the same time, the internal electrode B made of nickel or its alloy is formed inside the chip C. Although it is possible, the dielectric is reduced by firing in the atmosphere of this reducing gas,
The insulation resistance will be reduced.

Then, after the above-mentioned sintering, by re-sintering in an atmosphere of an oxidizing gas such as air, the dielectric can be returned to a material having a high insulation resistance, while the dielectric material has a high insulation resistance. The internal electrode B made of nickel or an alloy thereof formed by firing in an atmosphere is re-fired in an atmosphere of an oxidizing gas thereafter.
Only a small part of the surface is oxidized.

Next, the left and right end faces C of the chip piece C
1 and C2 are subjected to a polishing process such as sand blasting or barrel polishing to remove an oxide film on a surface of a portion of the internal electrode B exposed to both end surfaces C1 and C2 of the chip piece C. Left and right end faces C1, C
The external electrodes D1 and D2 are formed by sputtering chromium, nickel, silver or copper on the inner electrode B.
It can be reliably electrically connected to the.

The external electrodes D1 and D2 can be formed by vacuum deposition of chromium, nickel, silver or copper, or also by ion plating. In the method, since a thermal load is less applied to the chip C, the dielectric can be maintained in a state of high insulation resistance, and at the same time, the oxidation of the internal electrode B can be prevented and the external electrode D
1 and D2 can be reduced.

Further, both end faces C1 and C2 of the chip piece C are provided.
The external electrodes D1 and D2 after the polishing process may be formed by applying a conductive paste to both end surfaces C1 and C2 and then hardening, but in this case, the hardening is performed at 200 to 300 ° C. By using the conductive paste, a thermal load is not applied to the chip piece C, so that the dielectric can be maintained in a state of high insulation resistance, the oxidation of the internal electrode B can be prevented, and the external electrode D1 can be prevented. , D2 can be reduced.

The surfaces of the external electrodes D1 and D2 are provided on the surfaces of the external electrodes D1 and D2 in order to secure the ease of soldering when soldering to a printed circuit board and the like and to prevent solder cracking. It is also possible to form a coating layer of nickel, tin or solder.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a state in which green sheets made of a dielectric material are stacked.

FIG. 2 is a perspective view showing stacked chip pieces.

FIG. 3 is a sectional view taken along line III-III of FIG. 2;

FIG. 4 is a perspective view of the multilayer ceramic capacitor.

[Explanation of symbols]

 A1, A2, A3 Green sheet B Internal electrode C Chip piece C1, C2 End face of chip piece D1, D2 External electrode

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takashi Hashiguchi 21-Family, Rohm Co., Ltd., 21 Ryozaki-cho, Ukyo-ku, Kyoto City F-term (reference) 5E001 AB03 AC09 AF06 AH01 AH03 AH06 AH08 AH09 AJ03 5E082 AA01 AB03 BC40 EE04 EE23 EE35 FG06 FG26 FG54 GG10 GG21 GG28 JJ03 JJ15 JJ21 JJ23 JJ26 LL01 MM23 MM24 PP06

Claims (3)

[Claims] An internal electrode is formed by applying a paste of nickel or an alloy thereof on a surface of a green sheet made of a dielectric material, a plurality of dielectric green sheets are laminated and pressed on a chip piece, After firing the chip pieces in an atmosphere of a reducing gas, re-fired in an atmosphere of an oxidizing gas, and then on the left and right end faces of the chip pieces,
A method for manufacturing a multilayer ceramic capacitor, comprising forming an external electrode after polishing. 2. The external electrode according to claim 1,
A method for manufacturing a multilayer ceramic capacitor, characterized by being formed by metal sputtering, vacuum deposition or ion plating. 3. The external electrode according to claim 1, wherein:
A method for manufacturing a multilayer ceramic capacitor, wherein the method is formed by applying a conductive paste that is cured at a temperature of 300 ° C. or less.