JPS6314855B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multilayer capacitor, and particularly to a multilayer ceramic capacitor that prevents migration from occurring when a DC voltage is applied to external electrodes.

The general structure of a multilayer ceramic capacitor is
As shown in FIG. 1, a required number of dielectric layers 1 made of ceramic and internal electrodes 2 are stacked and fired to form a capacitor body 3, and external electrodes 4 and 5 are placed on both ends of this body 3. It is configured so as to be connected to an internal electrode 2 buried therein.

Conventionally, for the external electrodes 4 and 5 in the multilayer capacitor as described above, a metal containing silver as a main component, such as silver alone or an alloy of silver and palladium, has been used.

By the way, when silver is used for the external electrode, migration (diffusion) occurs electrochemically under the application of DC voltage in humidity, and the silver spreads along the surface of the capacitor body 3 between the opposing external electrodes 4 and 5. It is well known that the metal precipitates and eventually reaches the other electrode side, resulting in a shot state.

An effective way to prevent such problems is to use an alloy of silver and palladium for the external electrode and to increase the ratio of palladium in this alloy, but palladium is expensive and the amount used is limited. The disadvantage is that the material cost increases in proportion to the increase.

In addition, silver has good solderability when used alone,
Although it is possible to easily connect terminals, etc., if a large amount of palladium is mixed in, solderability deteriorates, resulting in a problem that reliability during installation is reduced.

This invention was made to solve the above-mentioned drawbacks and problems, and it has high reliability by preventing the occurrence of deterioration due to migration of the external electrode even in humidity, and is also suitable for mass production. The purpose of the present invention is to provide a multilayer capacitor that can be manufactured at low cost and suitable for

The structure of the present invention is such that a pair of external electrodes are formed of two types of metals that are electrically connected to each other, and the tip portions of both external electrodes that are attached to each other are formed of at least a metal that does not cause migration.
The main surface portions of both external electrodes are made of a metal containing silver as a main component, providing high reliability and good connectivity with terminals and the like.

Hereinafter, one embodiment of this invention will be shown in FIGS. 2 to 9.
This will be explained based on the diagram.

FIG. 2 shows the basic structure of a multilayer capacitor according to the present invention, in which a capacitor body 11 is formed by laminating a required number of ceramic dielectrics and internal electrodes.
and external electrodes 12 provided at both ends of this main body 11,
13, and the external electrodes 12 and 13 are made of a metal 14 whose main component is silver (hereinafter referred to as electrochemically stable metal) and a metal that does not easily migrate (hereinafter referred to as electrochemically stable metal). stable metal,
) 15, which are electrically conductively connected to each other.

Examples of the electrochemically stable metal 14 include platinum, gold, palladium, an alloy thereof, or an alloy of silver and palladium with a palladium content of 10% or more.
In No. 3, a metal that does not easily (or does not) cause migration can be used, and may be the same as the internal electrode.

In this invention, the mutually attached tips of the external electrodes 12 and 13 formed of two types are formed of electrochemically stable metals 14 and 14, and the main surface portions of the external electrodes 12 and 13 are electrically It is made of chemically unstable metal 15,15. Therefore, both the metals 14 and 15 in the external electrodes 12 and 13 on both sides have the same potential, and when a DC voltage is applied, a potential difference occurs between the metals 14 and 14. Therefore, the metals 14 and 15 are electrochemically unstable. The opportunity for migration of 15, 15 toward the opposing electrode is completely lost. At the same time, since the main surface portions of the external electrodes 12 and 13 are covered with unstable metals 15 and 15, the solderability of the external electrodes 12 and 13 is not impaired.

Next, FIGS. 3 to 8 show some examples of specific methods of forming external electrodes.

In the first example shown in FIG. 3 and FIG.
), from the tip of this lower layer to the capacitor body 11.
The upper layer is made of a metal 14 which is stable over time (FIG. 4).

In the second example shown in FIGS. 5 and 6, a lower layer of stable metal 14 is formed at both ends of the capacitor body 11 (FIG. 5), and an unstable metal 14 is formed on this lower layer to the extent that it does not exceed this lower layer. In this case, an upper layer of metal 15 is formed (FIG. 6).

In the third example shown in FIGS. 7 and 8, a stable metal 14 is attached in an annular manner to the peripheral surface near the end of the capacitor body 11 (FIG. 7), and the end of the capacitor body 11 is attached from above this annular body. It is formed by providing an unstable metal 15 in the portion (FIG. 8).

In addition, in any example, the external electrodes 12, 13
The stable metals 14, 14 need to be formed so that the tips of the stable metal sides facing each other are continuous with the circumferential surface of the capacitor body 11.

Next, the example shown in FIG. 9 is a case where the capacitor is applied to a feed-through type capacitor in which the through-hole 16 in the center is penetrated by the feed-through terminal 17, and the capacitor body 1 is formed in a circular shape.
8, an outer electrode 19 is provided on the outer periphery of the electrode 8, and an inner electrode 20 is provided on the inner periphery of the electrode 8, and an electrochemically stable metal 14 is formed at the tip portions of the electrodes 19 and 20 where they are attached to each other.

As described above, according to the present invention, the mutually attached tips of the external electrodes provided at both ends of the capacitor body are formed of an electrochemically stable metal, so that a DC voltage cannot be applied to the external electrodes in humidity. However, there is no electrode migration at all.
A capacitor with high reliability, especially moisture resistance and medium load characteristics can be obtained.

Further, since the main surface portion of the external electrode is formed of an electrochemically unstable metal, there is no problem in connecting the external electrode to the terminal or circuit electrode.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view showing a conventional multilayer capacitor, Fig. 2 is a perspective view showing the basic structure of a multilayer capacitor according to the present invention, and Figs. 3 to 8 each show different methods of forming external electrodes. An explanatory diagram showing an example,
FIG. 9 is a longitudinal sectional view in which the above external electrode is applied to a feedthrough capacitor. DESCRIPTION OF SYMBOLS 11... Capacitor body, 12, 13... External electrode, 14... Electrochemically stable metal, 15... Electrochemically stable metal.

Claims (1)

[Claims] 1. A multilayer capacitor in which an internal electrode is buried and a pair of external electrodes are provided on the outer surface and are electrically conductively connected to the internal electrode, wherein the pair of external electrodes are electrically conductively connected to each other. , metals 15, 19, 20 whose main component is silver,
The tip portions of both external electrodes, which are formed of these two types and which are attached to each other, are formed of the metal 14 that does not easily cause migration, and both external electrodes The main surface portion of the metal 1 whose main component is silver
1. A multilayer capacitor comprising: 5, 19, and 20.