JPH02220404A - Manufacture of laminated ceramic varistor - Google Patents

Abstract

PURPOSE:To acquire a low varistor voltage by forming a slurry in a sheet, thereafter by laminating the sheet and a metal thin film alternatively, and by carrying out integral junction through heat treatment. CONSTITUTION:After a slurry which consists of sintered ceramic fine powders, glass powders and organic binders having varistor characteristics is formed in a sheet, the sheet 1 and a metal thin film 2 are laminated alternatively and joined integrally through heat treatment. Then, an external electrode 3 of silver paste, etc., is applied to an end surface of the laminated body and heat treatment is carried out to manufacture a laminated ceramic varistor readily. Thereby, it is possible to manufacture a proper laminated ceramic varistor which has a low varistor voltage as in a case of a thin film sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a multilayer ceramic varistor using an improved lamination method.

[Prior art and its problems]

Ceramic varistors, whose main component is zinc oxide, have a resistance value that changes significantly depending on the applied voltage and exhibit good current-voltage nonlinearity.For this reason, they have traditionally been used for surge absorption and voltage stabilization in various electronic devices. It has been widely used as a chemical element.

In recent years, devices have become smaller and lower in voltage, and in response to this trend, multilayer ceramic varistors that are compact, have low varistor voltage, and high surge resistance have attracted attention, and various studies have been conducted.

Conventional multilayer ceramic varistors are known, for example, from Japanese Patent Application Laid-Open No. 1986-
As described in Publication No. 106894, elements obtained by cutting the sintered body after sintering and further polishing exhibit an increase in leakage current and a decrease in α, so the following method is used: Manufactured by. That is, calcined powder having a composition that exhibits voltage nonlinearity when sintered is made into a sheet by the doctor blade method, and platinum, platinum,
Internal electrodes made of a high-melting point metal such as palladium are screen printed, then laminated, thermocompressed, and cut into a predetermined shape. This is sintered in air, and external electrodes are baked on both ends of this sintered body to obtain a multilayer ceramic varistor.

In this way, in the known manufacturing method of multilayer ceramic varistors, the internal electrodes are formed at the same time as the raw sheet is sintered.
During sintering, the raw sheet shrinks, creating strain between the sheets and the internal electrodes, causing delamination between the laminated sheets, and the resulting device may not be able to provide sufficient performance. In particular, in order to achieve a low varistor voltage, it is essential to form a thin film sheet, but shrinkage of this sheet form has been a problem. Furthermore, as the internal electrode material is baked at a high sintering temperature, it is necessary to use expensive high-melting point metals such as gold, platinum, and palladium as the main component, which significantly increases the manufacturing cost of multilayer ceramic varistors. This was a major problem in practical application.

[Means for solving problems]

The present inventors conducted extensive research to solve the problems of the prior art as described above, and as a result, they arrived at the present invention.

In the present invention, a slurry made of sintered ceramic fine powder having varistor properties, glass powder, and an organic binder is formed into a sheet shape, and then the sheet and a metal thin film are alternately laminated and then heat-treated to form an integral structure. The present invention relates to a method for manufacturing a multilayer ceramic varistor characterized by bonding.

The sintered ceramic fine powder having varistor properties used in the present invention is preferably produced by the method described in, for example, Japanese Patent Application Laid-open No. 190801/1983. That is, fine particles of zinc oxide are 700 to 13
After firing at 00°C, the sintered zinc oxide
It is obtained by grinding to a particle size of 0 μm, adding 0.0001 to 10 mo1× of additives such as manganese oxide to the zinc oxide fine powder, baking at 600 to 1400° C., and then crushing and classifying. The particle size can be appropriately selected depending on the required varistor voltage, and a particle size of 1200° C. is preferably used.

The glass powder may have any glass composition as long as it can bond the sheet and the metal thin film, and specific examples thereof include glass drift having a composition of bismuth oxide, silicon oxide, and boron oxide.

The organic binder is not particularly limited, but suitable examples include methylcellulose, ethylcellulose, and polyvinyl alcohol.

The proportion of the sintered ceramic fine powder having varistor properties, the glass powder, and the organic binder used is not particularly limited, but is generally 10 to 100 parts by weight per 100 parts by weight of the sintered ceramic fine powder.

Examples of the metal thin film include an aluminum thin film, a silver thin film, and a w4 thin film. The thickness of the metal thin film is not particularly limited, but is preferably about 10 to 50 μm ###-1 mm.

One embodiment of the production method of the present invention is as follows.

First, sintered ceramic fine powder having varistor properties is prepared, glass powder and an organic binder are added to it to form a paste, and this is formed into a sheet. A plurality of these sheets and metal thin films are alternately laminated and bonded by heat treatment at a temperature of 350 to 600°C. Next, external electrodes such as silver paste are applied to the end faces of the laminate, and
A multilayer ceramic varistor can be easily manufactured by heat treatment at a temperature of about 0.000°C.

〔Example〕

Hereinafter, a method for manufacturing a multilayer ceramic varistor of the present invention will be described in detail using an example shown in FIG.

In FIG. 1, 1 is a sheet made of sintered ceramic fine powder having varistor properties. 2 is a metal thin film that serves as an internal electrode. 3 is the internal electrode 2 when laminated.
This is an external electrode connected to one end of the .

Example 1 Zinc oxide powder with a particle size of 0.05 to 1 μm was molded into pellets, fired at 1200°C for 2 hours, and then crushed and classified to obtain particles with a particle size of 1 to 20 μm.

To this zinc oxide powder, bismuth oxide, manganese oxide, cobalt oxide, antimony oxide, and aluminum oxide are added and mixed at 0.0001 to 10+solχ, respectively, and after firing at 800 to 1400'C, it is lightly pulverized. The particles were classified to have a particle size of 2 to 20 μm to obtain a sintered ceramic fine powder having varistor properties.

To 100 parts by weight of this sintered ceramic fine powder, 50 mf parts of glass frit, 5 parts by weight of ethyl cellulose, and 40 parts by weight of butyl calpitol were added and mixed to form a slurry and formed into a sheet.

Then, this sheet 1 and a 15 μm aluminum thin film 2
A plurality of layers were alternately laminated and then crimped and heat treated at a temperature of 450°C. Next, as shown in FIG. 2, silver paste was applied to the end face of the laminate to form external electrodes 3. A multilayer ceramic varistor was obtained by heat treatment at a temperature of 500°C in the atmosphere. The IN thickness of the sheet 1 of sintered ceramic fine particles having varistor properties was 20 μm.

Varistor voltage (voltage value at which 1 mA of current flows, V
1 mA) was the IOV, and the nonlinear coefficient at this time was 20.

〔Effect of the invention〕

According to the present invention, in order to manufacture a laminated ceramic varistor using a sintered ceramic fine powder exhibiting varistor properties and at a low heat treatment temperature, it is possible to manufacture a laminated ceramic varistor at a low heat treatment temperature by simultaneously firing the inner electrode and the green sheet as in the conventional manufacturing method. It is possible to obtain an element with sufficient performance without causing distortion, and in particular, it is possible to suitably manufacture a multilayer ceramic varistor having a low varistor voltage as in the case of a thin film sheet. Furthermore, materials such as aluminum and silver can be used as internal electrode materials, which can greatly contribute to cost reduction.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a laminated ceramic varistor according to the present invention, in which a sheet of fine sintered ceramic powder having varistor properties and a thin metal film are laminated, and an external electrode is applied to the end face of the laminated sheet. 1: Sheet of sintered ceramic fine powder with varistor properties, 2: Metal thin film, 3: External electrode patent applicant Ube Industries, Ltd.

Claims (1)

[Claims] After forming a slurry consisting of a sintered ceramic fine powder having varistor properties, a glass powder, and an organic binder into a sheet shape, the sheet and a metal thin film are alternately laminated and then integrally bonded by heat treatment. Characteristic manufacturing method for multilayer ceramic varistors.