JP2989319B2 - Method of forming external electrodes in multilayer ceramic capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming external electrodes in a multilayer ceramic capacitor in which dielectric ceramic layers and internal electrode layers are alternately stacked.

[0002]

2. Description of the Related Art In a multilayer ceramic capacitor, a multilayer dielectric ceramic is generally formed by interposing an internal electrode layer between dielectric ceramic layers, and an external electrode mainly composed of Ag connected to the internal electrode layer is formed on an end face of the ceramic. It is provided with a layer. When soldering such a capacitor to the board,
The so-called silver cracking, in which Ag, which is a component of the external electrode layer, is eluted in the molten solder, which significantly deteriorates the reliability of the solder joint, or the solder may have poor wettability. Various types of plating films having heat resistance and solder wettability are applied on external electrode layers. However, in the process of forming the plating film, the plating solution penetrates into fine voids (porous pores) of the external electrode layer,
Further, it diffuses to the junction interface between the dielectric ceramic layer and the internal electrode layer, causing deterioration of electrical characteristics of the capacitor such as a change in insulation resistance.

In order to further solve this problem, a multilayer ceramic capacitor has been proposed in which a plating solution is prevented from penetrating into a multilayer dielectric ceramic in a process of forming a plating film on an external electrode layer. (See JP-A-2-277205). The capacitor described in this publication has a dielectric ceramic layer 10 as shown in FIG.
A semiconductor layer 13 connected to a predetermined internal electrode layer 11 is provided on an end face of a laminated dielectric ceramic 12 in which the internal electrode layers 11 are alternately laminated.
And a plating film 15 of nickel, copper, or the like, and a plating film 16 of solder, tin, or the like are sequentially formed on the external electrode layer 14.

In this capacitor, the semiconductor layer 13 interposed between the internal electrode layer 11 and the external electrode layer 14 causes
The inner and outer electrode layers 11 and 14 are electrically connected, but are structurally separated. Therefore, when the plating films 15 and 16 are formed, the infiltration of the plating solution into the laminated dielectric ceramic 12 is prevented by the semiconductor layer 13 and the electrical characteristics are not deteriorated.

[0005]

According to the method of manufacturing a capacitor disclosed in the above publication, an end face of a laminated body in which a predetermined number of green sheets having a conductive paste layer serving as internal electrode layers and green sheets having no paste layer are laminated. Then, a semiconductor agent paste for forming a semiconductor layer is applied and dried, and then baked to simultaneously form the laminate into a ceramic and form a semiconductor layer.

However, in this manufacturing method, a laminate in which conductive paste is printed on a green sheet by a screen printing method and is laminated by thermocompression bonding is used as a bonding interface between the dielectric ceramic layer 10 and the internal electrode layer 11. (See FIG. 4) does not have sufficient adhesive strength. However,
If the semiconductive agent paste is applied to the end face of the laminate and then baked at a high temperature (about 1300 ° C.), the two layers 10 and 11 may be separated or chipped at the joint interface. Both layers 1
Once the layers 0 and 11 are peeled off, they do not rejoin even if they are fired, so that not only can a multilayer ceramic sintered body integrating the two layers 10 and 11 be obtained, but also the fired multilayer ceramic sintered body can be used. There is no effective and economical means for selecting peeling or chipping defects.

Accordingly, it is an object of the present invention to provide a method of forming external electrodes in a multilayer ceramic capacitor which does not induce peeling or chipping at a bonding interface between a dielectric ceramic layer and an internal electrode layer.

[0008]

In order to achieve the above object, a method of forming an external electrode in a multilayer ceramic capacitor according to the present invention is directed to a laminated body in which a plurality of dielectric ceramic layers and a plurality of internal electrode layers are alternately stacked. After firing, a semiconductor layer is formed and fired on the end face of the obtained laminated dielectric ceramic, and an external electrode layer is formed on the semiconductor layer and fired.

According to the formation method of the present invention, instead of applying a semiconducting agent paste to the end face of the laminate and firing it as disclosed in the above-mentioned publication, the porcelainization of the laminate and the formation of the semiconductor layer are performed simultaneously. First, the laminated body is fired to obtain a laminated dielectric ceramic, and then a semiconducting agent paste is applied to the end face of the ceramic and fired. wear. For this reason,
In addition to pressing and bonding the dielectric ceramic layer and the internal electrode layer, the laminate is fired before forming the semiconductor layer, so the bonding strength at the bonding interface between both layers is sufficient, and the two layers are integrated. A laminated dielectric ceramic is obtained. Even if a semiconductor layer is formed thereafter, a critical defect that both layers are separated or chipped at a bonding interface in the process does not occur.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for forming an external electrode according to the present invention will be described below with reference to embodiments. FIG. 1 is a cross-sectional view of a multilayer ceramic capacitor having external electrodes manufactured according to the forming method. In this capacitor, a semiconductor layer 4 is formed on a pair of end faces of a laminated dielectric ceramic 3 composed of a plurality of dielectric ceramic layers 1 and a plurality of internal electrode layers 2 alternately laminated with the ceramic layers 1. The external electrode layer 5 is formed on the layer 4. Semiconductor layer 4 and external electrode layer 5
As shown in an enlarged view of FIG. 2, a semiconductor layer 4 connected to a predetermined internal electrode layer 2 is provided on an end face of a laminated dielectric ceramic 3, and a conductive layer 51 and a base plating are provided on the semiconductor layer 4. External electrode layer 5 composed of film 52 and plating film 53
Is provided. As can be seen from FIGS. 1 and 2, the structure of the capacitor itself is almost the same as the conventional one shown in FIG.

Next, a specific production of the capacitor having the above structure will be described. First, Ba as a dielectric ceramic
A binder made of ethyl cellulose and a solvent is added to a mixture of TiO ₃ and additives of CeO ₂ , ZrO ₂ and MnCO ₂ , and the mixture is dispersed and kneaded for 15 hours to prepare a slurry. This slurry is formed by a doctor blade method to obtain a green sheet having a thickness of 20 to 40 μm. Subsequently, ink as an internal electrode agent containing Pd (palladium) as a main component is printed on the green sheet by using a screen printing method. Then, as shown in FIG. 3, a plurality of green sheets 1 'on which the ink 2' is printed are stacked, and a plurality of unprinted green sheets 1 'are stacked on and under the green sheets 1' to form a laminate. Is pressed and heated, and then cut into a predetermined size.

The following steps correspond to the method of forming an external electrode according to the present invention. That is, the laminate is first subjected to a binder removal treatment at about 500 ° C. in an N ₂ atmosphere, and then sufficiently fired at about 1300 ° C. Thereby, a laminated dielectric ceramic having a sufficient adhesive strength between the dielectric ceramic layer and the internal electrode layer can be obtained. After chamfering the dielectric ceramic, a semiconductor ceramic paste such as a positive temperature characteristic resistor (PTC) is applied to a pair of end faces of the dielectric ceramic by dipping or the like.
And sinter. At this time, P
A metal such as d or Ag may be blended. Thereby, a semiconductor layer is formed.

Next, Ag / Pd or A is used as a conductive layer agent.
A conductive paste composed of g and frit is applied on the semiconductor layer in a thick film and baked at about 800 ° C. to form a conductive layer.
Further, in order to improve the solder wettability and heat resistance during mounting on the substrate, a base plating film of Ni, Cu or the like and a plating film of solder, tin or the like are sequentially applied on the conductive layer. As described above, the semiconductor layer, the conductive layer,
A multilayer ceramic capacitor as shown in FIG. 1 in which an underlying plating film and an external electrode layer composed of a plating film are formed is completed.

[0014]

The method of forming an external electrode according to the present invention has the following effects because it is configured as described above. (1) Since the laminate is first fired, the adhesive strength between the dielectric ceramic layer and the internal electrode layer in the obtained laminated dielectric ceramic is sufficient. For this reason, even if a semiconductor layer is formed on the end face of the laminated dielectric ceramic, peeling or chipping does not occur at the bonding interface between the dielectric ceramic layer and the internal electrode layer. (2) Since the plating solution does not penetrate into the laminated dielectric ceramic due to the semiconductor layer when the plating film is formed on the external electrode layer, deterioration of the capacitor is prevented.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a multilayer ceramic capacitor having external electrodes manufactured by using the forming method of the present invention.

FIG. 2 is a partially omitted enlarged view of a semiconductor layer and an external electrode layer of the capacitor of FIG. 1;

FIG. 3 is a process chart for obtaining a laminate in the production of the capacitor as shown in FIG. 1;

FIG. 4 is a cross-sectional view of a conventional multilayer ceramic capacitor.

[Explanation of symbols]

 Reference Signs List 1 dielectric ceramic layer 2 internal electrode layer 3 laminated dielectric ceramic 4 semiconductor layer 5 external electrode layer 51 conductive layer 52 base plating film 53 plating film

Claims (1)

(57) [Claims] A semiconductor layer connected to an internal electrode layer is formed on an end face of a laminated dielectric ceramic comprising a plurality of dielectric ceramic layers and a plurality of internal electrode layers alternately laminated with the ceramic layers. A method of forming an external electrode of a multilayer ceramic capacitor, comprising forming an external electrode layer on a layer, comprising: firing a multilayer body including the dielectric ceramic layer and an internal electrode layer; Forming a semiconductor layer on the end face of the multilayer ceramic capacitor and firing the same, and further forming an external electrode layer on the semiconductor layer and firing the semiconductor layer.