JPS6317218B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multilayer ceramic capacitor and a method for manufacturing the same, and particularly to a distribution structure of palladium content in an external electrode portion.

Generally, this type of conventional multilayer ceramic capacitor has a dielectric green sheet 1 as shown in FIG.
The internal electrodes 2 are printed on the surface of the ceramic chip, a plurality of them are stacked in opposite directions, and after being heat-pressed and integrated, they are fired to form both ends 3 of the ceramic chip as shown in Fig. 2.
Next, a fired ceramic chip 4 in which the end surface 2a of the internal electrode 2 is exposed is made. Next, as shown in FIG. 3, silver-palladium paste or silver paste is applied as an external electrode material to both ends 3 of the fired ceramic chip 4, and after drying, the maximum firing temperature is 830-860°C.
for 10 to 15 minutes (15 minutes at 750 to 770℃ for silver paste)
After holding and firing for ~30 minutes, an external electrode 5 having a thickness of about 100 microns was formed.

In such conventional multilayer ceramic capacitors, when silver-palladium paste (containing 30% by weight of palladium) is used as the material for the external electrode 5, (a) palladium is more than 10 times more expensive than silver in terms of price; and expensive.

(b) Compared to silver, silver-palladium has 1/1 solderability.
It is worse than silver with a ratio of 5 or less.

(c) Palladium oxidizes at a temperature of 450 to 700°C, producing palladium oxide, which greatly impairs solderability. Therefore, the firing temperature and time must be controlled to minimize the amount of palladium oxide produced.

On the other hand, when only silver paste is used, the ratio of solder corrosion resistance to silver/palladium: 5 is
Silver: 1, which was worse than silver/palladium, had the disadvantage that the connection with the internal electrodes was often broken.

SUMMARY OF THE INVENTION An object of the present invention is to provide a multilayer ceramic capacitor and a method for manufacturing the same which solves the above-mentioned drawbacks of the prior art.

The laminated ceramic capacitor of the present invention has a palladium (Pd) content of 10 to 30% by weight in the lower layer that is in close contact with the external electrode layers at both ends of the capacitor element, and a palladium (Pd) content in the surface layer that decreases toward the upper layer. It is characterized by consisting of an external electrode whose main component is silver with a content of 0% by weight.

The present invention will be explained below with reference to a conventional example (FIG. 3) and an embodiment of the present invention (FIG. 4).

By the conventional method shown in FIGS. 1 and 2, internal electrodes 2 are printed on the surface of a dielectric green sheet 1, and a plurality of sheets are stacked in opposite directions, heated and pressed to integrate, and then fired. Then, a fired ceramic chip 4 is produced in which the end surfaces 2a of the internal electrodes 2 are exposed at both ends 3 of the ceramic chip. Next, both ends 3
A silver paste containing 10 to 30% by weight of palladium in the binder material, solvent, and glass frit is applied to a thickness of about 50 microns, and after drying at room temperature, the solvent, binder material, glass frit material, and silver particle size are applied on top of the paste. A silver paste that is exactly the same as the silver/palladium paste described above was applied to a thickness of about 50 microns, dried at room temperature, and then fired at a maximum firing temperature of 830 to 860°C for 10 to 15 minutes.
Hold and bake for a minute. In this firing process,
The previously applied silver and
Palladium in the palladium paste penetrates into the silver paste applied later, and an external electrode 15 shown in FIG. 4 can be obtained.

FIG. 5 is a diagram showing the concentration gradient of palladium (Pd) in the external electrode 15 shown in FIG. 4.

As described above, according to the present invention, the surface of the external electrode is covered with silver, which has very good solderability, and the content of palladium, which has good solder corrosion resistance, increases as it goes inside. )
Compared to external electrodes, (i) it is approximately 36% cheaper; (When the palladium content in the lower layer is 30% by weight) (ii) Solderability is approximately 5 times better.

(iii) Since the surface is a silver surface, the control of firing temperature, etc. to suppress the formation of palladium oxide is not so severely restricted.

Also, compared to silver external electrodes, (i) Solderability is exactly the same.

(ii) The solder corrosion resistance is good because the inside contains a large amount of palladium, which has high solder corrosion resistance, and electrode breakage does not occur.

Therefore, it has great industrial value because external electrodes can be formed economically and without impairing solderability and solder corrosion resistance.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of a dielectric green sheet printed with internal electrodes used in a conventional example and an example of the present invention, Fig. 2 is a perspective view of a fired ceramic chip used in a conventional example and an example of the present invention, and Fig. 3 is a perspective view of a conventional example. FIG. 4 is a perspective view of a multilayer ceramic capacitor with an external electrode formed thereon, FIG. 4 is a perspective view of a multilayer ceramic capacitor with an external electrode formed thereon, and FIG. 5 is a gradient diagram showing the palladium content of the external electrode of the invention. DESCRIPTION OF SYMBOLS 1... Dielectric green sheet, 2... Internal electrode, 2a... End face of internal electrode, 3... Both ends of fired ceramic chip, 4... Fired ceramic chip, 5, 15... External electrode.

Claims (1)

[Claims] 1. The palladium (Pd) content of the lower layer in close contact with the external electrode layers at both ends of the multilayer ceramic capacitor element is 10 to 30% by weight, and the palladium (Pd) content is lower toward the upper layer of the surface layer. A multilayer ceramic capacitor comprising an external electrode mainly composed of silver with a palladium content of 0% by weight. 2. Applying a first silver paste containing 10 to 30% by weight of palladium (Pd) to both ends of a multilayer ceramic capacitor element and drying it, and applying palladium (Pd) from the first silver paste onto the paste.
1. A method for manufacturing a multilayer ceramic capacitor, comprising the steps of applying a second silver paste, drying and firing to form external electrodes.