JP2003092228A - Method for manufacturing laminated ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for easily manufacturing a multilayer and high capacitance laminated ceramic capacitor with its internal electrode unsevered and thin (2 μm or less after sintering), and continuously laminated. SOLUTION: A contact area between the internal electrode and a ceramic layer is regained by hot isostatic pressing, in a neutral or reducing atmosphere, the laminated ceramic capacitor primarily sintered by a densifying temperature in the reducing atmosphere, to extend the internal electrode and eliminate air hole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a monolithic ceramic capacitor, and more particularly to densification of internal electrodes of a monolithic ceramic capacitor which requires atmosphere control during firing.

[0002]

2. Description of the Related Art In recent years, monolithic ceramic capacitors have been widely used in mobile devices such as mobile phones and mobile communication devices, and have been required to be small in size and large in capacity and low in price. Conventionally, noble metal-based palladium or palladium-silver materials were used for the internal electrodes of the monolithic ceramic capacitors, but recently, with the price increase of palladium, inexpensive base metal-based nickel is being used for the internal electrodes. . However, when nickel is baked in the air atmosphere, it becomes an insulator due to oxidation and does not function as an electrode. Therefore, in order to prevent the oxidation of nickel at the time of firing, the atmosphere in the furnace is made reducible, and firing is performed, and in order to improve the reliability of the monolithic ceramic capacitor, the atmosphere is generally controlled such as reoxidation.

Conventionally, a method of manufacturing a monolithic ceramic capacitor is a green sheet having a thickness of several μm to several tens μm formed by a doctor blade method using a slurry composed of a dielectric powder, an organic binder and an organic dispersion medium. An internal electrode pattern is formed on the surface by screen printing. Next, a required number of these green sheets are laminated on each other so as to form opposing internal electrodes, thermocompression bonded, cut into a predetermined shape, and atmosphere controlled sintering to obtain a capacitor.

However, it is necessary to print the internal electrodes more accurately and thinly due to the influence of multi-layering and thinning of the multilayer ceramic capacitor. The internal electrodes are usually printed by
Although it is carried out by the screen printing method, the thin coating of the internal electrode paste includes printing pressure of the printing machine, gap, printing speed, squeegee hardness, adjustment of squeegee angle, printing screen mesh, plate making thickness, internal electrode paste. The viscosity is adjusted.

[0005]

However, in such a laminated ceramic capacitor in which the internal electrode paste is thinly coated, the internal electrodes are not formed due to the difference in melting point between the ceramic material and the internal electrode material at the densification temperature of the ceramic material. Since the holes shrink due to contraction, the contact area between the ceramic layer and the internal electrode is reduced by the area of the holes. The state of the fired ceramic capacitor is shown in FIG. This hole is shown in FIG.
When the cross section is observed from the stacking direction as shown in (b), the holes 4 are present on the internal electrode, and the internal electrode 2 appears to be cut off when observed from the cross section in the vertical direction as shown in FIG. 1 (c). When the inner electrode 2 is printed thinner than before. The breakage of the electrode became more prominent, and it was difficult to obtain the target capacitance.

As a conventional technique, in Japanese Patent No. 1595391, a method of hot isostatic pressing after primary firing in an air atmosphere has been patented, but since the primary firing is performed in the air, the nickel internal electrode is oxidized. However, it has the drawback of not becoming a capacitor.

The technical problem in the present invention is to make the internal electrodes 2 thin (2 μm or less after firing) and continuously laminated in an unbroken state. It is to provide a method of easily manufacturing.

[0008]

According to the present invention, an internal electrode is formed by subjecting a monolithic ceramic capacitor, which is primarily fired at a densification temperature in a reducing atmosphere, to hot isostatic pressing in a neutral or reducing atmosphere. This is a method of extinguishing the voids by stretching and recovering the contact area with the ceramic layer.

Further, as the ceramic material, a material that can be easily reduced such as barium titanate is used as the main component, nickel is used as the internal electrode material, and the primary firing is performed in a reducing atmosphere, and during hot isostatic pressing. , N ₂ in a neutral or reducing atmosphere. Further, reliability is improved by performing heat treatment in an oxidizing atmosphere for reoxidation after hot isostatic pressing.

[0010]

EXAMPLES The present invention will be described in detail below based on examples. As a ceramic material, a material containing barium titanate as a main component having a densification temperature of 1350 ° C. was used to manufacture a laminated ceramic capacitor by the manufacturing method of the present invention.

First, using the above dielectric powder, polyvinyl butyral as an organic binder, and methyl propylene glycol as an organic dispersion medium, a slurry was prepared, and a green sheet having a thickness of 10 μm was prepared by a doctor blade method. On this green sheet, nickel internal electrode paste was screen-printed in a predetermined pattern, and after stacking 250 sheets, thermocompression bonding was performed to form an unfired body of a laminated ceramic capacitor. After the primary firing of this green body in various temperatures and atmospheres shown in Table 1, hot isostatic pressing treatment was performed to obtain fired body chips of Examples 1 to 6. The reducing atmosphere is a mixed gas of N ₂ + H _{2 and} an oxygen partial pressure at 1300 ° C. of 10 ⁻⁹ to 10 ⁻¹⁴ [atm].
N ₂ gas was used as the neutral atmosphere gas. Furthermore, Example 7-
In No. 12, after hot isostatic pressing, heat treatment was performed in an oxidizing atmosphere to obtain a fired chip. The conditions for the hot isostatic pressing treatment were a pressure of 300 kg / cm ² , the temperature and atmosphere were variously changed as shown in Table 1, and the design value of the capacitance was 22 μF.

Cu is used as an external electrode on the fired body chip.
The paste was applied and baked to manufacture the monolithic ceramic capacitor shown in FIG. Further, in order to observe and measure electrode breakage due to holes in the internal electrode 2, cross-section observation in the lamination direction of the laminated ceramic capacitor was performed. A schematic view of the cross section is shown in FIG.

In order to quantify the breakage of the internal electrode 2 shown in FIG. 3, the ratio of the electrode breakage length to the length of the internal electrode 2 shown in the cross section BB ′ of FIG. The electrode disconnection rate is defined as follows. Electrode breakage rate [%] = sum of electrode breakage length / electrode length × 100 (1)

As is apparent from Table 1, in the conventional firing method of Comparative Example 1 in which the hot isostatic pressing is not performed, the electrode breakage rate is as large as about 15% and the capacity is as small as about 17 μF. Then, as shown in Examples 1 to 7 according to the method of the present invention, primary firing is performed at a temperature of 1300 ° C. in a reducing atmosphere of 10 ⁻⁹ and 10 ⁻¹⁴ [atm], and then in a neutral or reducing atmosphere. When the hot isostatic pressing process is performed, the electrode breakage rate is reduced to 0.28 to 0.62%, the reduction of the internal electrode holes 4 is recognized, and the electrostatic capacitance is almost equal to the design value 22μ.

Similarly, after performing primary firing in a reducing atmosphere, hot isostatic pressing is performed in a neutral or reducing atmosphere, and then heat treatment is performed in an oxidizing atmosphere for reoxidation. Examples 8 to 14 also have a cutting rate of 0.21 to
It decreased to 0.58% and the capacitance was 21.87 to 21.9.
The value was 5 μF, which was almost equal to the design value of the capacitance.

Although the effect of the present invention can be obtained without performing heat treatment in an oxidizing atmosphere, heat treatment in an oxidizing atmosphere is promoted because the reoxidation of the dielectric, which is a factor for extending the life of the device, is promoted. Is preferably performed.

In the embodiment, the densification temperature is 13
Although the dielectric material at 50 ° C. has been described, the present invention can be similarly applied to other dielectric materials, and is not limited to the dielectric materials shown in the examples.

[0018]

[Table 1]

[0019]

As described above, according to the present invention, it is possible to reduce the number of voids in the internal electrodes, which makes it possible to obtain a monolithic ceramic capacitor in which the internal electrodes are thin and continuous.

Further, since the internal electrodes can be formed thinly and continuously, it becomes possible to manufacture a large-capacity multilayer ceramic capacitor having excellent reliability even in a multi-layer ceramic capacitor.

[Brief description of drawings]

FIG. 1 is a sectional view of a monolithic ceramic capacitor in a direction perpendicular to a laminating direction.

[Fig. 2] Configuration diagram of a monolithic ceramic capacitor

FIG. 3 is a vertical cross-sectional view of a monolithic ceramic capacitor before and after HIP treatment, in which (a) is no hot isostatic pressing treatment;
(B) has hot isostatic pressing.

[Explanation of symbols]

1 Ceramic layer 2 internal electrodes 3 external electrodes 4 Internal electrode holes 5 Cut length of electrode 6 electrode length

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Claims (2)

[Claims] 1. A monolithic ceramic capacitor having a laminated structure having a plurality of internal electrode layers and ceramic layers is subjected to primary firing in a reducing atmosphere and then subjected to hot isostatic pressing in a neutral or reducing atmosphere. A method for manufacturing a monolithic ceramic capacitor, which comprises applying the same. 2. The method for manufacturing a monolithic ceramic capacitor according to claim 1, wherein heat treatment is performed in an oxidizing atmosphere after hot isostatic pressing.