JPH1139944A - Metal paste for outer electrode of layered ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal paste for outer electrodes which give excellent connection with inner electrodes and are hard to be penetrated by a plating liquid. SOLUTION: This metal paste for outer electrodes contains a metal powder, an organic vehicle, and glassy frits as main components and is used for producing a layered ceramic capacitor comprising a capacitor main body produced by alternately laminating a plurality of dielectric layers and a plurality of inner electrodes and a pair of outer electrodes formed outside the capacitor main body while one of which being connected with a group of inner electrodes in the odd number and the other of which being connected with a group of inner electrodes in the even number. The metal powder contains copper and silver and the mixing ratio is controlled to 1-20 pts.wt. of silver to 100 pts.wt. of copper. By mixing silver with copper at the defined ratio, the sintering property of the metal paste for outer electrodes is improved and the desired purposes are realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated body comprising a capacitor body in which a plurality of dielectric layers and internal electrodes are alternately laminated, and a pair of external electrodes provided outside the capacitor body and connected to the internal electrodes. Regarding the metal paste for an external electrode of a ceramic capacitor, in particular, a nickel plating solution or the like, which is a processing agent for improving the solder wettability inside the formed external electrode and having good connectivity with the internal electrode, is provided. The present invention relates to improvement of a metal paste for an external electrode which is hardly penetrated.

[0002]

2. Description of the Related Art As this type of multilayer ceramic capacitor a, for example, as shown in FIGS. 1A and 1B, a capacitor body d in which a plurality of dielectric layers b and internal electrodes c are alternately laminated is shown. A pair of external electrodes e1 and e2 provided outside the capacitor body d, one of which is connected to the odd-numbered internal electrode c1 group and the other is connected to the even-numbered internal electrode c2 group.
It is known that the main part is constituted by.

The multilayer ceramic capacitor a
Is conventionally manufactured as follows. First, after a powdered dielectric material is formed into a sheet shape (generally called a dielectric sheet) by a doctor blade method, a metal paste for an internal electrode is formed on the surface by a screen printing method, and dry. Next, after a predetermined number of dielectric sheets on which the metal paste for internal electrodes has been formed are stacked, compressed and pressed, they are carried into an electric furnace, generally a belt furnace, and the organic binder and the internal binder in the dielectric sheets are removed. After burning the organic vehicle or the like of the electrode metal paste, sintering is performed.

Next, both ends of a multilayer body (capacitor body) obtained by alternately laminating a plurality of dielectric layers and internal electrodes obtained in this manner are polished, and the end face of an odd-numbered internal electrode group is formed on one end side. After exposing the end faces of the even-numbered internal electrode groups on the other end side, the polished end faces are immersed in metal paste for external electrodes, dried, and transported again into an electric furnace, generally a belt furnace. And sintering of the external electrode is performed continuously to form a pair of external electrodes outside the capacitor body.

Finally, the surface of the formed external electrode is subjected to nickel plating or the like in order to improve the solder wettability, thereby completing the multilayer ceramic capacitor.

Conventionally, the following materials have been selected as materials for forming the above-mentioned multilayer ceramic capacitor from the viewpoint of the capacitance of the target capacitor, the manufacturing cost, and the practicable conditions of existing manufacturing equipment. Have been.

That is, barium titanate, a perovskite oxide containing lead, or the like is generally used as the material of the dielectric. The metal paste for an internal electrode contains a metal powder such as palladium or nickel and an organic vehicle (consisting of an organic binder such as a cellulose-based or acrylic-based solvent and an organic solvent) as main components, and has a viscosity adjusted as required. A composition containing a diluting solvent or the like for the external electrode, and the metal paste for an external electrode contains a copper metal powder, an organic vehicle (same as above) and a vitreous frit as main components, and a diluting solvent or the like as necessary. The formulated composition has been applied.

The metal paste for an external electrode is prepared by mixing copper powder and vitreous frit with the above-mentioned organic vehicle, kneading with a roll mill or the like, and adding a diluting solvent such as trimethylbenzene as necessary. Have been.

[0009]

By the way, the metal paste for the external electrode of the multilayer ceramic capacitor has good connectivity with the internal electrode of the multilayer body (capacitor body), and nickel paste is formed inside the formed external electrode. A property such that a plating solution such as a plating solution does not enter is required.

This is because when the connection with the internal electrode is poor,
There is a problem that the capacitance of the intended capacitor cannot be obtained, and if the plating solution enters the inside of the external electrode, the glass contained in the external electrode is eroded by the plating solution, and This is because the adhesion strength between the body (capacitor body) and the external electrodes is greatly reduced, and the reliability of the capacitor is deteriorated.

For this reason, the conventional metal paste for an external electrode contains copper metal powder, an organic vehicle and a vitreous frit as main components from the viewpoint of satisfying these requirements and the above-mentioned conditions. Was applied.

However, despite the fact that conventional metal pastes for external electrodes have been prepared based on such requirements and conditions, conventional metal pastes for external electrodes containing copper powder, an organic vehicle and a vitreous frit as main components have been prepared. When a paste is applied to manufacture a multilayer ceramic capacitor, the desired capacitance of the capacitor cannot be obtained, or the bonding strength between the capacitor body and external electrodes decreases over time, thus reducing the reliability of the capacitor. It still had problems such as deterioration in a short period of time.

The present invention has been made in view of such a problem, and it is an object of the present invention that the connection with the internal electrode is good and the solder wettability is formed inside the formed external electrode. An object of the present invention is to provide a metal paste for an external electrode that is hardly penetrated by a nickel plating solution or the like which is a treating agent for improving the quality.

In order to solve this problem, the present inventor has conducted intensive analysis on the cause of the above-mentioned problem which occurs when the conventional metal paste for an external electrode is applied. Have come to the conclusion that the above problem is caused by insufficient sintering of copper constituting the external electrode.

That is, the firing of the external electrode is performed at about 900 ° C. as described above. However, under this temperature condition, copper is not sufficiently sintered, and the connectivity between the internal electrode and the copper and the connectivity between the copper powders in the external electrode become insufficient. As a result, a sufficient capacitance is obtained. It could not be obtained.

It was also found that the external electrode had poor sinterability, so that the surface of the external electrode was inferior, and that many fine holes were present. Then, in a plating process such as nickel plating, a plating solution enters the inside of the external electrode through this hole, so that the adhesive strength between the capacitor body and the external electrode is reduced with time.

In this case, a method of setting the firing condition of the external electrode to 900 ° C. or more in order to sufficiently sinter copper in the metal paste for the external electrode may be considered.

However, if the firing conditions are set to 900 ° C. or higher, a new problem arises in that existing manufacturing facilities cannot be used, and the structure of other constituent materials such as the internal electrode metal paste and the dielectric material is also reduced. It is not yet a sufficient way to avoid the above problems, as it creates another problem that must be changed in accordance with conditions.

Therefore, the present inventor has proposed a method for improving the sinterability of copper without changing the structure of the metal paste for internal electrodes and the dielectric material which are other constituent materials without changing the existing manufacturing equipment. As a result of intensive studies, copper 100
It has been found that by containing 1 to 20 parts by weight of silver with respect to parts by weight, sufficient sinterability is imparted to the external electrode, thereby solving the problem of insufficient capacitance and the problem of adhesive strength. The present invention has been completed through such technical studies.

[0020]

That is, the invention according to claim 1 provides a capacitor body in which a plurality of dielectric layers and internal electrodes are alternately stacked, and an odd-numbered capacitor provided outside the capacitor body. The present invention is applied to the manufacture of a multilayer ceramic capacitor having a pair of external electrodes connected to an internal electrode group and the other connected to an even-numbered internal electrode group, and an external electrode mainly composed of a metal powder, an organic vehicle, and a vitreous frit. The metal powder is composed of copper and silver, and the mixing ratio thereof is 1 to 20 parts by weight of silver per 100 parts by weight of copper.

According to the metal paste for an external electrode according to the first aspect of the present invention, 1 to 20 parts by weight of silver is mixed with 100 parts by weight of copper as a metal powder, Has improved sinterability,
The external electrodes can be sufficiently sintered under the firing conditions of about 0 ° C.

Therefore, the existing manufacturing equipment can be used as it is, and without changing the constitution of the other constituent materials such as the internal electrode metal paste and the dielectric material, the desired capacitance can be obtained and the capacitor can be obtained. It is possible to manufacture a multilayer ceramic capacitor in which the adhesive strength between the main body and the external electrode is unlikely to decrease with time.

[0023]

Embodiments of the present invention will be described below.

First, as the vitreous frit which is a constituent material of the metal paste for an external electrode according to the present invention, those generally used for a copper paste for an external electrode can be applied as they are. Further, as for an organic vehicle composed of a cellulose-based or acrylic-based organic binder and an organic solvent, those generally used for a copper paste for an external electrode can be directly applied without any particular limitation.

Copper and silver, which are constituent materials of the metal paste for an external electrode according to the present invention, include copper powder, silver powder, coat powder obtained by coating copper on silver or silver, and alloy powder of silver and copper. And these may be used as a mixture. In this case, the mixing ratio of copper and silver needs to be 1 to 20 parts by weight of silver with respect to 100 parts by weight of copper. When the compounding ratio of silver is less than 1 part by weight, the effect of improving the sinterability of copper is not seen, and when the compounding ratio of silver exceeds 20 parts by weight, the external electrodes become over-sintered and the laminate (capacitor body) This is because the external electrode may be peeled off.

In addition, the conventional method for preparing a copper paste for an external electrode can be directly applied to the preparation of a metal paste for an external electrode according to the present invention.

The reason why the sinterability of copper in the external electrode metal paste is improved by blending 1 to 20 parts by weight of silver with respect to 100 parts by weight of copper has not been elucidated yet. It is presumed that the sintering temperature is slightly lower than that of the case of using only copper by mixing silver having the low melting point in the above ratio.

[0028]

Embodiments of the present invention will be specifically described below. (1) Preparation of Organic Vehicle One part by weight of ethyl cellulose and 6 parts by weight of an acrylic resin were lightly dispersed in 93 parts by weight of terpineol, and then heated to 60 ° C. while stirring with an air motor to prepare an organic vehicle. (2) Preparation of Copper Paste for External Electrode [Example 1] 27 parts by weight of the organic vehicle, 3 parts by weight of vitreous frit, and 70 parts by weight of copper powder and silver powder each having an average particle diameter of 2 μm were 100 parts each. , And weighed according to a weight ratio of 1: 1, and kneaded with a three-roll mill to prepare 50 g of a copper paste for external electrodes according to Example 1.

Example 2 Example 1 except that the weight ratio between copper powder and silver powder having an average particle size of 2 μm was changed to 100: 10.
50 g of a copper paste for an external electrode according to Example 2 was prepared by using the same material and processing as described above.

Example 3 Example 1 except that the weight ratio between copper powder and silver powder having an average particle size of 2 μm was changed to 100: 20.
50 g of a copper paste for an external electrode according to Example 3 was prepared by using the same material and processing as described above.

[Comparative Example 1] 2 μm average particle size as metal powder
50 g of a copper paste for an external electrode according to Comparative Example 1 was prepared by the same material and processing as in Example 1 except that only the copper powder of m was applied.

COMPARATIVE EXAMPLE 2 An external electrode according to Comparative Example 2 was prepared by using the same materials and processing as in Example 1 except that the weight ratio of copper powder and silver powder having an average particle size of 2 μm was changed to 100: 0.5. 50 g of a copper paste was prepared.

Comparative Example 3 Example 1 was repeated except that the weight ratio between copper powder and silver powder having an average particle size of 2 μm was changed to 100: 25.
50 g of a copper paste for an external electrode according to Comparative Example 3 was prepared by using the same material and processing as described above. (3) Evaluation test [Evaluation test for sinterability] 13 parts by weight of ethyl cellulose was dissolved in 87 parts by weight of terpineol to prepare an organic vehicle for an internal electrode. Ni paste for an internal electrode mainly composed of this organic vehicle and nickel powder, and BaTiO using a polyvinyl butyral resin as an organic binder
Design capacitance 1μF using ₃ series dielectric green sheet
And a copper paste for an external electrode according to Examples and Comparative Examples is applied to both ends of the multilayer body and baked at 900 ° C., and then the formed external electrode is formed. The surface sinterability was observed with an electron microscope.
A sample having a good sintering state was evaluated as ○, a sample having no effect of improving the sintering state was evaluated as △, and a sample showing cracking or peeling from the sintered body was evaluated as ×. The evaluation results are shown in Table 1 below.

[Evaluation test of plating solution intrusion suppression effect] The multilayer ceramic capacitor chips according to Examples and Comparative Examples in which external electrodes were formed were subjected to barrel plating in a Ni plating solution at 45 ° C for 60 minutes. The chip was filled with resin and the cross section was cut out, and it was observed by EPMA (Electron Probe Micro Analysis) whether or not penetration of nickel plating was observed in the external electrode portion. ○: No penetration of nickel plating observed, ×: Penetration of nickel plating observed
Was evaluated. The evaluation results are shown in Table 1 below.

[Evaluation Test of Capacitance] The capacitance of the multilayer ceramic capacitor chip according to the example and the comparative example having the designed external electrode and the nickel-plated designed capacitance of 1 μF was measured using an LCR meter (42 manufactured by Hewlett-Packard Company).
78A). The measured capacitance is 0.9μ
Those with F or more were evaluated as ○, and those with 0.9 μF or less were evaluated as x. The evaluation results are shown in Table 1 below.

[Evaluation Test of Adhesive Strength] Lead wires were adhered to the external electrodes and the external electrodes of the multilayer ceramic capacitor chips according to Examples and Comparative Examples having nickel plating by soldering. Then, the strength when the lead wire was peeled off from the multilayer ceramic capacitor chip was measured by a tensile tester. If the strength is 2.5 kg or more,
Those having a weight of 2.5 kg or less were evaluated as x. The evaluation results are shown in Table 1 below.

[0037]

[Table 1] (4) Evaluation Results As is clear from Table 1 above, when the copper paste for an external electrode according to each example was applied, sinterability, penetration of plating solution,
It is confirmed that both the capacitance and the adhesive strength are good.

On the other hand, as a metal powder, the average particle size was 2 μm.
When the copper paste for an external electrode according to Comparative Example 1 using only the copper powder of m was applied, it was confirmed that the sintering property, the penetration of the plating solution, the capacitance, and the adhesive strength were all poor.

The weight ratio of copper powder to silver powder is 100:
When the copper paste for an external electrode according to Comparative Example 2, which is 0.5, was applied, no effect of improving the sinterability was observed, and penetration of the nickel plating solution into the external electrode and a decrease in the adhesive strength were confirmed. I have.

Further, the weight ratio of the copper powder to the silver powder is set to 100:
When the external electrode copper paste according to Comparative Example 3, which is No. 25, was applied, cracking and peeling, which are considered to be caused by oversintering, were confirmed.

From the results of Comparative Examples 2 and 3, the mixing ratio of copper and silver in the copper paste for an external electrode according to the present invention is in the range of 1 to 20 parts by weight of silver with respect to 100 parts by weight of copper. It was confirmed that it was necessary to set to.

[0042]

According to the metal paste for an external electrode according to the first aspect of the present invention, 1 to 20 parts by weight of silver is mixed with 100 parts by weight of copper as a metal powder, and copper in the metal paste for an external electrode is mixed. Since the sinterability is improved, it is possible to sufficiently sinter the external electrodes under the firing conditions of about 900 ° C.

Accordingly, the existing manufacturing equipment can be used as it is, and the desired capacitance and the desired capacitance can be obtained without changing the structure of the metal paste for the internal electrodes and the dielectric material which are the other constituent materials. This has the effect of producing a multilayer ceramic capacitor in which the adhesive strength between the main body and the external electrode is unlikely to decrease with time.

[Brief description of the drawings]

FIG. 1 (A) is a schematic perspective view of a multilayer ceramic capacitor, and FIG. 1 (B) is a partially cutaway sectional view of FIG. 1 (A).

[Explanation of symbols]

 a: multilayer ceramic capacitor b: dielectric layer c: internal electrode d: capacitor body e1: external electrode e2: external electrode

Claims (1)

[Claims] 1. A capacitor body in which a plurality of dielectric layers and internal electrodes are alternately laminated, and one provided outside the capacitor body, one of which is connected to an odd-numbered internal electrode group and the other is an even-numbered internal electrode group. Applied to the manufacture of a multilayer ceramic capacitor having a pair of external electrodes connected to a metal powder, and a metal paste for an external electrode mainly composed of a metal powder, an organic vehicle and a vitreous frit, wherein the metal powder comprises copper and silver A metal paste for an external electrode of a multilayer ceramic capacitor, wherein the mixing ratio is 1 to 20 parts by weight of silver with respect to 100 parts by weight of copper.