JPH03246915A - Laminated ceramic capacitor - Google Patents

Abstract

PURPOSE:To prevent the formation of defects like bores on the boundary of each ceramic green sheet, by forming a protecting layer by baking a plurality of ceramic green sheets which contain admixture and is in a state of laminated layers. CONSTITUTION:In a laminated ceramic capacitor wherein a plurality of dielectric layers 11 and a plurality of layers of inner electrode 12 are alternately laminated, and a pair of protecting layers 13 is laminated on the outside of the outmost electrodes 12 out of electrodes 12, the electrodes 12 are alternately electrically connected with each other by using a pair of outer electrodes. The layer 13 is formed by baking a plurality of ceramic green sheets 14 in a state of laminated layers. Said green sheets contain admixture capable of forming liquid phase of low melting point which has low viscosity and superior wettability at the time of baking. The admixture is melted at a temperature lower than the baking temperature of the sheet 14, can permeate into bores in the layers 13, has low viscosity, and can form liquid phase excellent in wettability to the layers 13 and 11. Thereby defects like bores can be reduced, and reliability regarding humidity resistance can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a multilayer ceramic capacitor in which a plurality of dielectric layers and a plurality of internal electrodes are alternately laminated.

[Prior Art] FIG. 1 is a partially cutaway perspective view of a multilayer ceramic capacitor.

As shown in the figure, the multilayer ceramic capacitor consists of a capacitor body 10 and a pair of external electrodes 20.20 formed at both ends of the capacitor body 10.

FIG. 2 is an enlarged view of section A in FIG.

As shown in the figure, the interior of the capacitor body 10 has a structure in which a plurality of dielectric layers 11 and a plurality of internal electrodes 12 are alternately stacked.

Here, the dielectric layer 11 is made of, for example, a fired ceramic green sheet containing barium titanate powder as a main component.

Further, the internal electrode 11 is made of, for example, a fired conductive paste containing Ag--Pd as a main component.

A plurality of layers of internal electrodes 11 are formed by a pair of opposing external electrodes 20.
20 are alternately electrically connected.

A protective layer 13 is laminated on the outside of each outermost internal electrode 11 among the plurality of internal electrodes 11 in order to protect the inside of the capacitor body 10 from moisture in the atmosphere.

The protective layer 13 is made of several ceramic green sheets made of the same material as the dielectric layer 11, which are laminated, pressed, and fired, and has a laminated structure.

FIG. 3 is an enlarged view of section B in FIG.

Since the protective layer 13 has a laminated structure in this way, the boundary 15 of the laminated ceramic green sheets 14 is
Ceramic particles are in a sparse state, and defects such as bores are easily formed. Moreover, this boundary 15 is exposed on the side surface of the capacitor body 10.

Therefore, atmospheric moisture can penetrate into the interior of the protective layer through defects such as bores in this exposed boundary 15, and this moisture can also penetrate between the internal electrodes, thereby changing the electrical characteristics of the capacitor. There was a risk that it would get worse.

Therefore, it is necessary to prevent defects such as bores from being formed as much as possible at the boundaries 15 between the ceramic green sheets 14 forming the protective layer 13.

[Problem to be solved by the invention] However, in the conventional multilayer ceramic capacitor,
Due to variations in manufacturing conditions, etc., a large number of bores are formed at this boundary, resulting in the manufacture of capacitors with poor moisture resistance.

The present invention was made in order to solve the above-mentioned problems, and provides a multilayer ceramic capacitor in which defects such as bores are prevented from forming as much as possible at the boundaries between the ceramic green sheets forming the protective layer. The purpose is to obtain.

[Means for Solving the Problems] A multilayer ceramic capacitor of the present invention has a plurality of dielectric layers and a plurality of internal electrodes stacked alternately, and the outermost internal electrode among the plurality of internal electrodes is stacked alternately. In a multilayer ceramic capacitor in which a pair of protective layers are laminated on the outside of the multilayer ceramic capacitor, and the internal electrodes of the plurality of layers are alternately electrically connected by a pair of external electrodes, the protective layer has a low viscosity and does not wet when fired. It is made by firing a plurality of laminated ceramic green sheets containing additive components that can form a liquid phase with a good low melting point.

Here, the additive component is a protective layer or dielectric material that has low viscosity and can melt at a temperature lower than the temperature at which the ceramic green sheet is fired and seep into the bore in the protective layer. Any material that can form a liquid phase with good wettability to the layer can be used.

As such, for example, one or more materials selected from the following materials can be used: ■Liz 0-CaO-3iO2, ■B20s-CaO-3i02, ■5iO- .

Here, the material 2 above can form a low melting point liquid phase even when alone, and the material 2 can form a low melting point liquid phase by interaction with the material of the protective layer.

Note that when Pd is used as the internal electrode, Bi
When using low melting point components including zOa.

B i * Oyu and Pd react.

The magnitude of the influence of this reaction between B1-0- and Pd varies depending on the composition of the dielectric layer and internal electrodes, firing temperature, and firing time.

Therefore, when using a low melting point component including BiaOz,
The amount added must be suppressed to such an extent that the influence of the reaction with Pd can be ignored, and it is preferably avoided.

Further, it is preferable that the additive component is contained in the ceramic green sheet in an amount of 1 wt% or more and less than 10 wt%.

This is because if the additive content is less than 1wt%, many defects such as bores will be formed, and if the additive content is more than 10wt%, the electrical characteristics of the capacitor will deteriorate or delamination will occur, but if the additive content is less than 1wt%, Above, 10wt%
This is because within the range below, the formation of defects such as bores is suppressed, the electrical characteristics of the capacitor are good, and no delamination occurs.

As the material of the dielectric layer, any material may be used as long as it is a dielectric material, such as F characteristic material,
B characteristic materials, E characteristic materials, CH characteristic materials, SL characteristic materials, etc. can be used.

Here, the F characteristic material, B characteristic material, and E characteristic material are usually those whose main raw material is barium titanate, and CH
Characteristic material, SL characteristic material is Ti0-based or CaT
i 03 - The main raw material is rare earth.

The material for the internal electrodes is, for example, Pd.

A conductive paste containing Pt, Pd-Ag, Ni, Cu, or the like as a main component can be used.

[Function] According to the present invention, since the protective layer is formed by laminating and firing a plurality of ceramic green sheets containing a predetermined amount of a low melting point component, this added component may be used alone or as a protective layer during firing. It reacts with the layer material and has a low melting point and viscosity.
A well-wetting liquid phase is formed against the protective layer, which quickly diffuses into the sparse areas of the boundaries between each ceramic green sheet during the firing time.

[Example] Next, one embodiment of the present invention will be described.

First, commercially available F-characteristic material (BaTiO3-BaZr0m
A slurry is made using a 30 μm thick ceramic green for dielectric layer, which is coated onto a moving plastic film to a predetermined thickness using a doctor blade method, and the coated slurry is dried. Got a sheet.

In addition, 100 parts by weight of the above F-characteristic material was added with the additive components (samples 1 to 13) shown in Table 1 in the amount shown in the same table, and after thoroughly mixing in a ball mill, the above ceramic green sheet for dielectric material was prepared. In the same manner as above, a ceramic green sheet for a protective layer having a thickness of 30 μm was obtained.

Then, apply this ceramic green sheet for the protective layer to
Ten sheets were laminated and temporarily pressed to form a pair of protective layer sheets.

Next, on the dielectric layer ceramic green sheet,
A conductive paste containing Ag-Pd as a main component was printed in a pattern of 4 mm in length and 7 mm in width by screen printing to form internal electrodes.

Next, several to several tens of layers of the ceramic green sheets for dielectric layers on which internal electrodes were printed were stacked such that the internal electrodes alternately faced each other with the ceramic green sheets for dielectric layers sandwiched therebetween.

Next, the protective layer sheet is laminated on these upper and lower surfaces,
The whole of these ceramic green sheets in a laminated state were bonded together by thermocompression.

Next, these thermocompression-bonded ceramic green sheets were cut into small dice-shaped chips, and after removing the binder, they were fired at a temperature in the range of 1250 to 1350°C.

Next, a conductive paste containing Ag--Pd as a main component was applied to both end surfaces of the fired chip and baked to form external electrodes.

In the manner described above, a multilayer ceramic capacitor was formed.

Next, the cross-section of the protective layer of this multilayer ceramic capacitor was observed at at least five locations with an optical microscope, and one
The number of bores existing in the area of 00×100 um2 was determined.

When this number of bores was expressed as a ratio when the number of bores in Sample 13 to which no additive component was added was taken as 100, the results were as shown in Table 1. In addition, when we investigated the electrical characteristics of this multilayer ceramic capacitor, we found that the first
The results are as shown in the table.

Samples marked with an x are outside the scope of the present invention.

From the above results, when the above-mentioned additive components are included in the ceramic green sheets that form the protective layer, these additive components quickly diffuse into sparse areas within the firing time and are formed at the boundaries of the laminated ceramic green sheets. It can be seen that the number of bores used is reduced.

However, when the amount of these additives increases to 10% by weight, although the number of bores decreases significantly, the additives diffuse even between the internal electrodes and the electrical characteristics (e.g., ε, IR, etc.) deteriorate. Also, the difference in shrinkage of each layer became too large, resulting in delamination.

[Effects of the Invention] According to the present invention, during firing, the liquid phase formed by the additive component quickly diffuses into the sparse region of the boundary of the laminated ceramic green sheets forming the protective layer,
Since it permeates into defects such as bores, the number of defects such as bores that often exist in this region is reduced, and a multilayer ceramic capacitor with high reliability in moisture resistance can be obtained.

[Brief explanation of drawings]

Figure 1 is a partially cutaway perspective view of a multilayer ceramic capacitor.
2 is an enlarged view of section A in FIG. 1, and FIG. 3 is an enlarged view of section B in FIG. 10... Capacitor element body 11... Dielectric layer 12
...Internal electrode 13...Protective layer 14...
ceramic green sheet

Claims (1)

[Claims] 1. A plurality of dielectric layers and a plurality of internal electrodes are alternately laminated, a protective layer is laminated on the outside of the outermost internal electrode among the plurality of internal electrodes, and the plurality of internal electrodes are laminated. A multilayer ceramic capacitor comprising a pair of external electrodes electrically connected alternately, wherein the protective layer contains a predetermined amount of an additive component capable of forming a low-viscosity, wettable, low-melting-point liquid phase during firing. A multilayer ceramic capacitor characterized by being made of fired ceramic green sheets in a laminated state. 2. 2. The multilayer ceramic capacitor according to claim 1, wherein the additive component is one or more selected from materials having the following compositions (1) to (3). (1) Li_2O-CaO-SiO_2 (2) B_2O_3-CaO-SiO_2 (3) SiO_2 3. 2. The multilayer ceramic capacitor according to claim 1, wherein the additive component is contained in the ceramic green sheet in an amount of 1 wt% or more and less than 10 wt%.