JP2804325B2 - Multilayer base metal ceramic chip capacitors - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a multilayer ceramic chip capacitor having a base metal such as nickel or a nickel alloy as an internal electrode.

(Prior Art) FIG. 3 is a sectional view showing a conventional multilayer base metal ceramic chip capacitor. This capacitor has a dielectric layer 1 such as barium titanate and an internal electrode made of a base metal such as nickel or an alloy thereof. 2 are laminated by a printing method or the like and fired, and the external electrodes 3 are formed on the side surfaces by baking or the like.

(Problems to be Solved by the Invention) In the above-mentioned conventional multilayer base metal ceramic chip capacitor, the life under load is shorter than that of the multilayer noble metal ceramic chip capacitor using palladium or the like for the internal electrode 2.

By the way, there is a bias in the distribution of the locations where the chip breakage that shortens the life is generated. The percentage of occurrence of the breakage point under this load is shown in percentage in the right column of FIG. As can be seen from the display of the broken portions, the broken portions are concentrated at the center in the stacking direction of the chips. That is, it is clear that the life is shorter at the center of the chip in the stacking direction. This is considered to be caused by firing in a reducing atmosphere so that nickel is not oxidized because nickel is used for the internal electrode 2. In other words, the reoxidation occurs during the annealing process after the firing of the chip, and the reoxidation inside the chip is insufficient inside. In order to solve this problem, although some compositions have been devised to prevent the reduction of the barium titanate-based dielectric material, the reduction of the substrate cannot be completely prevented.

The present invention has been made in view of the above-described problems, and has as its object to provide a multilayer base metal ceramic chip capacitor having a long life.

(Means for Solving the Problems) In order to achieve this object, the present invention relates to a multilayer ceramic chip capacitor having a base metal such as nickel or a nickel alloy as an internal electrode. It is characterized by being formed thicker than the part.

Further, a porous dielectric layer is provided at the center in the laminating direction.

(Operation) By forming the dielectric layer at the center in the stacking direction thicker than the other parts, the electric field intensity at the center is weaker than the other parts.

Further, if a porous dielectric is provided at the center, reoxidation of the dielectric layer is promoted during the annealing process.

(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 ₁ of the dielectric layer 1 at the center in the stacking direction.
The thickness of the other parts, ie, the upper and lower parts on the drawing, W _{2 to} W ₄
It's bigger. In the present embodiment, as the central portion thicker, and the _{W 1> W 2> W 3} > W 4.

FIG. 4 shows that the electric field strength is changed by changing the dielectric thickness between the opposing internal electrodes, and the applied voltage 200
It shows the result of measuring the life when an accelerated test was performed at V and 200 ° C. It can be seen that the life is sharply reduced as the electric field intensity increases.

As described above, since the electric field strength is greatly related to the lifetime, as shown in FIG. 1, by increasing the dielectric layer and reducing the electric field strength in the central portion where destruction is likely to occur, the chip capacitor can be reduced. The service life can be extended more than twice as long as the conventional one.

FIG. 2 shows another embodiment of the present invention, in which a porous dielectric layer 1A is provided on the dielectric layer at the center in the stacking direction. The porous dielectric layer 1A is formed by laminating carbon paste or resin powder dispersed in a dielectric paste during lamination.

As described above, by providing the porous dielectric layer 1A at the center, the dielectric layer 1 is easily reoxidized at the time of annealing after firing, and the reoxidation at the center is sufficient. Similarly, it is possible to extend the life more than twice.

In the present invention, the dielectric layers 1 and 1A are not only made of barium titanate, but also made of titanium oxide, barium zirconate,
The present invention can be applied to the case of a lead composite perovskite-based material, and the life extension effect can be obtained even when the internal electrode 2 is applied to copper or its alloy in addition to nickel or its alloy.

(Effect of the Invention) According to the first aspect, since the dielectric layer in the central portion is thickened, the electric field intensity in a portion which is likely to be broken is weakened, and the life of the capacitor is extended.

According to the second aspect, since the porous dielectric layer is provided in the central portion, reoxidation of the dielectric during annealing after firing is sufficient, and the life of the capacitor is extended.

[Brief description of the 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 present invention, and FIG. 3 is a conventional multilayer base metal ceramic chip. FIG. 4 is a cross-sectional view showing the capacitor together with the distribution of breakage points, and FIG. 4 is a diagram showing the relationship between the electric field strength and the life in an acceleration test of the capacitor. 1: dielectric layer, 1A: porous dielectric layer, 2: internal electrode, 3:
External electrode

────────────────────────────────────────────────── ─── Continuing on the front page (72) Masaaki Ikeda 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Corporation (72) Inventor Yukie Nakano 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Inside (72) Inventor Michio Abe 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (58) Fields surveyed (Int.Cl. ⁶ , DB name) H01G 4/12 H01G 4/30

Claims (2)

(57) [Claims] 1. A multilayer ceramic chip capacitor in which a base metal such as nickel or a nickel alloy is used as an internal electrode, wherein a dielectric layer at a central portion in a laminating direction is formed thicker than other portions. Ceramic chip capacitors. 2. A multi-layer ceramic chip capacitor comprising a base metal such as nickel or a nickel alloy as an internal electrode, wherein a porous dielectric layer is provided at a central portion in a laminating direction.