JPH03187209A - Lamination type base metal ceramic chip capacitor - Google Patents

Abstract

PURPOSE:To make field strength in a central part weaker than other parts and to improve a life by forming a dielectric layer in the central part in lamination direction thicker than other parts. CONSTITUTION:A thickness W1 of a dielectric layer 1 in a central part in lamination direction of a chip capacitor is made larger than thicknesses W2 to W4 of other parts (up and down parts in the figure). For example, the layers are made thicker as they are nearer to a center as W1>W2>W3>W4. Generally, field strength changes by changing a thickness of dielectric between opposed inner electrodes and a life is shortened remarkably as the field strength increases. Since there is a great relation between field strength and a life, a life of a chip capacitor can be improved at least twice that of a conventional one by making a dielectric layer large and field strength small in a central part wherein breakdown occures easily.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a multilayer ceramic chip capacitor in which internal electrodes are made of a base metal such as nickel or a nickel alloy.

(Prior Art) Fig. 3 is a cross-sectional view showing a conventional multilayer base metal ceramic chip capacitor. 2 are laminated by a printing method or the like, and the external electrodes 3 are formed on the side surface by baking or the like.

(Problem B to be Solved by the Invention) The conventional multilayer base metal ceramic chip capacitor described above has a shorter life under load than a multilayer noble metal ceramic chip capacitor using palladium or the like for the internal electrode 2.

By the way, there is an uneven distribution of the locations where chip breakage occurs, which shortens the lifespan. The rate of occurrence of fractures under this load is shown in percentage in the right column of FIG. As can be seen from this display of broken locations, the broken locations are concentrated in the center of the chip in the stacking direction. In other words, it is clear that the center portion of the chip in the stacking direction has a short lifespan. This is thought to be due to the fact that since nickel is used for the internal electrodes 2, firing is performed in a reducing atmosphere to prevent oxidation of the nickel. That is, this is because reoxidation occurs from the chip surface during annealing treatment after firing the chip, and reoxidation inside the chip is insufficient. In order to solve this problem, some compositional improvements have been made to prevent reduction of barium titanate-based dielectric materials, but reduction of the base material cannot be completely prevented.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a multilayer base metal ceramic chip capacitor with a long life.

(Means for Solving the Problem) In order to achieve this object, the present invention provides a multilayer ceramic chip capacitor in which internal electrodes are made of base metal such as nickel or nickel alloy. It is characterized by being thicker than the .

Further, it is characterized in that a porous dielectric layer is provided at the center in the stacking direction.

(Function) By forming the dielectric layer in the central part in the stacking direction to be thicker than other parts, the electric field strength in the central part can be made weaker than in other parts.

Furthermore, if a porous dielectric is provided in the center, reoxidation of the dielectric layer is promoted during annealing.

(Embodiment) FIG. 1 is a sectional view showing an embodiment of a multilayer base metal ceramic chip capacitor according to the present invention. This chip capacitor has a thickness W of the dielectric layer 1 at the center in the stacking direction,
The thickness of other parts, that is, the upper and lower parts in the drawing W2 ~
It is larger than W4.

In this example, the central part is thick, W,>W2>W
3 > W 4.

FIG. 4 shows that by changing the dielectric thickness between opposing internal electrodes, the electric field strength is changed and the applied voltage is increased to 200.
This shows the results of measuring the lifespan when an accelerated test was conducted at V and 200'C, and it can be seen that the lifespan decreases rapidly as the electric field strength increases.

In this way, there is a strong correlation between electric field strength and lifespan, so by increasing the dielectric layer in the central part where breakdown is likely to occur and reducing the electric field strength, as shown in Figure 1,
We were able to extend the lifespan of chip capacitors by more than twice that of conventional ones.

FIG. 2 shows another embodiment of the present invention, in which a porous dielectric layer IA is provided in the dielectric layer at the center in the stacking direction. In this way, the porous lt body layer IA is formed by laminating dielectric paste in which carbon powder or resin powder is dispersed during lamination C.

In this way, by providing the porous dielectric layer IA in the center, the dielectric layer 1 is easily re-oxidized during the annealing treatment after firing, and re-oxidation in the center is sufficient, so that unlike the above embodiment, the dielectric layer 1 is easily reoxidized. Similarly, it becomes possible to extend the service life by more than double.

The present invention provides a dielectric layer 1. lA is not only barium titanate-based, but also titanium oxide-based, barium zirconate-based,
It can also be applied to a lead composite herbskite type material, and the life extension effect can be obtained even when the internal electrode 2 is made of copper or its alloy in addition to nickel or its alloy.

(Effect of the invention) According to claim 1, since the dielectric layer in the central part is thickened,
The electric field strength in areas prone to breakdown is reduced, and the life of the capacitor is extended.

According to claim 2, by providing the porous dielectric layer in the central portion, the dielectric can be sufficiently reoxidized during annealing after firing, thereby extending the life of the capacitor.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of a multilayer base metal ceramic chip capacitor according to the present invention, FIG. 2 is a sectional view showing another embodiment of the invention, and FIG. 3 is a conventional 8I layer base metal ceramic chip capacitor. FIG. 4 is a cross-sectional view showing a chip capacitor along with a breakdown location distribution, and is a diagram showing the relationship between electric field strength and life in an accelerated test of a capacitor. 1: dielectric layer, lA: porous dielectric layer, 2: internal electrode, 3: external electrode

Claims (2)

[Claims] 1. In multilayer ceramic chip capacitors with internal electrodes made of base metals such as nickel or nickel alloys,
A multilayer base metal ceramic chip capacitor characterized by having a dielectric layer thicker in the center in the stacking direction than in other parts. 2. In multilayer ceramic chip capacitors with internal electrodes made of base metals such as nickel or nickel alloys,
A multilayer base metal ceramic chip capacitor characterized by having a porous dielectric layer in the center in the stacking direction.