JPH0113206B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a laminated ceramic capacitor having good moisture resistance and having a silicone coating and electrode parts made of silver or silver-palladium alloy, nickel or tin-lead alloy at both ends. It is something.

Multilayer ceramic capacitors have traditionally been made smaller and larger in capacity as electronic circuits become smaller, and demand for them is currently rapidly increasing as chip components for hybrid ICs and for direct mounting on printed circuit boards.

Multilayer ceramic capacitors are generally based on a laminate obtained by alternately laminating a ceramic dielectric and thin film layers of palladium and/or platinum, and form a parallel circuit in which the dielectric is sandwiched between the internal metal thin films. The ends of the silver or silver-
It is configured to be connected to a palladium alloy electrode. The thickness of the dielectric material used in this multilayer ceramic capacitor is approximately 15 to 100 μm, and the structure is such that electrodes are provided on a flat surface of such a thin dielectric material and folded.

Generally, the capacitance of a capacitor is expressed as C=εε ₀ S/t. Here, ε is the permittivity of vacuum, ε ₀
is the dielectric constant of the dielectric, S is the electrode area, and t is the distance between the electrodes. Therefore, considering the capacitance per volume, it becomes C/V∝1/t ₂ (V is the volume of the capacitor), which is inversely proportional to the square of the thickness. Therefore, when comparing the capacitance per volume of a single-plate ceramic capacitor and a multilayer ceramic capacitor, the thickness of a multilayer ceramic capacitor can be reduced to about 1/10 or less of that of a disk-type ceramic capacitor, so it is approximately More than 100 times more capacity can be obtained with the same volume. (Please note that it is impossible to reduce the thickness of disc-type ceramic capacitors due to their strength.
Currently, the limit is around 500 μm. ) As described above, multilayer ceramic capacitors are small and have large capacitance, making them suitable for miniaturizing electronic circuits.Furthermore, by applying tin and lead alloy plating to the electrodes, they can be easily attached to printed circuit boards. Direct attachment is becoming easier.

However, such laminated ceramic capacitors have several drawbacks, one of which is defects that occur due to the thinning of the dielectric material. That is, ceramic itself is originally a polycrystalline material, and unlike a dense single crystal, it has countless pores. Such pores are also not of uniform size, and large pores also exist. Making these pores small and uniformly distributed is one of the challenges, and although much research has been done, it is still not sufficient. The effects of these pores are as follows:
It weakens moisture resistance. In particular, in processes using electrolytes such as nickel or tin-lead alloy plating, residual electrolyte may become a problem. If the electrolyte remains, the insulation resistance may decrease due to re-penetration of moisture. Such a situation significantly impairs the reliability of the product and often causes problems in the market. For this reason, special attention must be paid to multilayer ceramic capacitors provided with plated electrodes.

The present invention was achieved through various experiments in consideration of the above drawbacks.

Hereinafter, details of the present invention will be explained based on examples.

<Example> Barium titanate 71.4 parts by weight, barium zirconate 20.4 parts by weight, calcium titanate 7.4 parts by weight,
Zinc oxide 0.2 parts by weight, manganese dioxide 0.15 parts by weight,
A slurry was prepared using a binder mainly composed of ethyl cellulose from a mixed powder consisting of 0.25 parts by weight of tungsten oxide and 0.25 parts by weight of aluminum oxide, and a sheet with a thickness of 40 ± 2 μm was formed using a doctor blade method. . After punching out this sheet to a certain size, palladium electrodes were printed. After stacking and crimping the electrode-printed sheets so that the electrodes form a comb shape, 3.6 mm x 1.8
It was cut into a size of mm x 0.45 mm. This chip
Silver paste was applied to both end faces of the sintered body obtained by firing at 1370°C ± 20°C for 2 hours, and then baked at 800°C.
Silicone is adhered to the entire surface of the laminate thus prepared, and the silicone is polymerized by heat treatment in the range of 250 to 300°C for 4 to 6 hours, after which the heat-treated laminate is placed in a polypot with an inner diameter of 150 mm. The silicone on the silver electrode portions at both ends was removed by rolling at a rotational speed of 95 to 100 r.p.m. for 30 minutes.
Next, 1 to 2 μm of nickel plating was applied to the silver electrode portions at both ends from which the silicone had been removed, and then 1 to 2 μm of tin and lead alloy plating was applied thereon.

FIG. 1 shows the multilayer ceramic capacitor of the present invention thus obtained, in which 1 is a ceramic dielectric layer, 2 is a palladium electrode layer, 3 is a silver electrode, 4 is a nickel plating layer, and 5 is a tin and lead layer. 6 is an alloy plating layer, and 6 is a silicone layer.

Figure 2 shows a multilayer ceramic capacitor based on the method of the present invention and a multilayer ceramic capacitor based on the conventional method without silicone treatment (same as the method of the present invention except for the silicone treatment).
℃ and 95% relative humidity when 50V is applied. In FIG. 2, a shows the characteristics of the product of the present invention, and b shows the characteristics of the conventional product. As is clear from FIG. 2, it is clear that the moisture resistance of the multilayer ceramic capacitor based on the method of the present invention is extremely stable.

As described above, the method of the present invention is extremely significant in that it is able to solve problems such as instability in moisture resistance, which are common in laminated ceramic capacitors provided with plated electrodes.

Incidentally, in the above embodiment, a porcelain dielectric material mainly composed of barium titanate, barium zirconate, and calcium titanate was used, but it goes without saying that other dielectric materials can also be used. Further, although the case where silver electrodes are provided on both end faces has been described, silver-palladium alloy electrodes may also be used.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view of a multilayer ceramic capacitor based on the method of the present invention, and FIG. 2 is a comparison diagram of the moisture resistance characteristics of multilayer ceramic capacitors based on the method of the present invention and the conventional method. 1... Porcelain dielectric layer, 2... Electrode layer (palladium electrode layer), 3... Silver electrode, 4... Nickel plating layer, 5... Tin and lead alloy plating layer, 6... Silicone layer.

Claims (1)

[Claims] 1. Silicone is adhered to the entire surface of a laminate consisting of a porcelain dielectric layer and a comb-shaped electrode layer that are alternately laminated with silver or silver-palladium alloy electrodes on both ends, and the laminate with this silicone attached is heat treated. After that, the silicone adhering to the silver electrodes at both ends is removed, and then nickel plating is applied to the silver electrodes at both ends, and tin and lead alloy plating is applied to the nickel plating treated parts. A manufacturing method for multilayer ceramic capacitors.