JPS6387706A - Manufacture of laminated ceramic varistor - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method of manufacturing a multilayer ceramic varistor with an improved means for forming internal electrodes.

(Prior Art) Generally, the surge resistance m of a ceramic varistor is approximately proportional to the effective area (area of opposing electrodes) when the ceramic varistors have the same composition. Therefore, various types of multilayer ceramic varistors have been proposed to provide a large surge resistance without increasing the size of the varistor body.

The initial technology for laminated ceramic varistors was published in 1973
- As disclosed in Publication No. 18849, a varistor is formed by forming a pair of electrodes on both the front and back surfaces of a plate-shaped sintered body that has been sintered in advance, and forming a lead-out part on a part of the side surface continuous with the electrodes. The elements are stacked in parallel and the contact electrodes are connected via an adhesive. Since the electrode parts other than the electrode pulling part are exposed to the outside, an exterior resin is used to protect them. It is coated. However, the structure described above requires a lot of time and effort for lamination, has difficulty in protecting it from the external environment, and is difficult to reduce the thickness of the sintered body itself to 0.3 m or less. Therefore, the varistor voltage is limited and the application is naturally limited to υ1. Therefore, as a method to eliminate these drawbacks, Japanese Patent Application Laid-Open No. 54-106
There is one disclosed in Publication No. 894. This technology prints internal electrodes on a raw sheet formed using the doctor blade method.
These are stacked, pressed and sintered, and the parts other than the portions where the internal electrodes are taken out are surrounded by a sintered body, which is effective in eliminating the above-mentioned drawbacks. However, in the case of a varistor whose main component is zinc oxide 1)
Since it is necessary to sinter at a temperature of 1100° C. or higher, the internal electrode material must be mainly composed of gold, platinum, and palladium, which makes the electrode material expensive and causes an increase in cost.

2) Since the sintering temperature is 110°C or higher, varistors containing bismuth oxide and praseodymium '11 react with the internal electrodes, which are mainly composed of palladium, and corrode the electrodes, making it impossible to secure the electrode thickness. , the problem arises that the area cannot be secured. 3) Therefore, the composition of a varistor with this structure must either contain no bismuth oxide or praseodymium oxide, or must contain a very small amount of less than 0.05 mol%, but compared to the varistors currently in practical use. However, characteristics such as nonlinearity, surge resistance, load life, and environmental resistance are extremely poor, making it difficult to obtain characteristics at the level required by the market. 4) Connect the element body and internal electrodes to 1
Since simultaneous firing is performed at a high temperature of 10° C. or higher, it is necessary to control the amount of diffusion of the constituent elements of the internal electrodes into the varistor sintered body, making compositional design difficult. °5) Internal i
The linear expansion coefficient of the electrode metal is partially larger than that of the varistor sintered body, so if it is exposed to high temperatures during use, there is a risk that stress will concentrate on the internal electrode margin due to expansion of the electrode metal and cracks will occur. had the right problem to solve.

Under the above circumstances, the technique disclosed in Japanese Patent Application Laid-open No. 1501/1983 has been disclosed for the purpose of eliminating the drawback 1) above, that is, the cost increase factor due to the use of expensive noble metals as internal electrode materials. The technique disclosed in this publication is to load a ceramic varistor unfired molded body with a paste-like substance printed on its surface made of a material that is burnt out by firing or dissolved by a solvent into a car, pressurized it, and then heat-treated or solvent-treated to This is a method of manufacturing a multilayer ceramic varistor, in which the paste material is removed and then sintered, and the voids formed in layers are filled with S-electrode paint to form electrodes. However, such technology requires the use of conductive paint for the external electrodes that lead out the electrodes from the internal electrodes, which have high electrical resistance and generate heat when a surge current flows, causing the conductive paint to peel off from the ceramic.

■Due to the high resistance value of the conductive paint, the limiting voltage characteristics are very poor.

■Since conductive paint is used for the internal electrodes, when used at high temperatures for a long period of time, the organic substances contained in the paint will carbonize, making it impossible to maintain contact with the thin layer of varistor material, causing electrical discharge on the contact surface, and carbonized organic substances. It has many drawbacks and lacks reliability, such as deterioration and partial reduction of the varistor material, increased leakage current, self-heating of the varistor material, and finally thermal runaway leading to destruction.

(Problems to be Solved by the Invention) As described above, the conventionally disclosed techniques have various drawbacks and cannot be put to practical use. The present invention has been made in view of the above points, and it is an object of the present invention to provide a method for manufacturing a multilayer ceramic varistor that not only facilitates workability and contributes to cost reduction, but also exhibits excellent characteristics.

[Structure of the Invention] (Means for Solving the Problems) The method for manufacturing a multilayer ceramic varistor of the present invention includes a method for manufacturing a multilayer ceramic varistor, which includes fired particles having the same composition as the varistor composition, carbon particles, a thermoplastic resin, and a volatile component on the surface. Means for obtaining a molded sheet product by printing and drying a slit precursor paste, forming a plurality of slit precursor films, and laminating a plurality of molded sheets in such a way that one end of the slit precursor film alternately protrudes to the opposite side and bonding them under heat. , means for cutting the sheet molded body into predetermined dimensions to obtain unfired chips in which the slit precursor gI end portions are alternately led out from the opposing surface; and sintering the unfired chip at a gradually elevated temperature and high temperature to produce the slit precursor. Means for removing volatile components of a membrane and obtaining a sintered chip in which a slit having a plurality of columnar ceramic particles is formed in this part, and a porous external electrode having continuous pores on the slit lead-out surface of the sintered chip. is used as a forming means, and then preheated, immersed in molten metal, reduced pressure, and pressurized to press the molten metal into the slit.
It is characterized by comprising means for slowly cooling and forming internal electrodes.

(Function) According to the above configuration, since there is no internal electrode in the sintering process cylinder, there is no mutual reaction between the varistor composition and the internal electrode material.
Lamination of any composition becomes easy, expanding the range of compositions that can be applied to multilayer ceramic varistors. Also,
The columnar ceramic particles formed within the slits bond the laminated layers of the molded sheets, thereby preventing cracks from occurring in the internal electrode margins due to thermal stress.

Furthermore, since the internal electrodes are not baked, the range of use of the internal electrode materials is greatly expanded without being limited to precious metals such as gold, platinum, and palladium.

(Example) An embodiment of the present invention will be described in detail below.

First, calcined powder with a composition consisting of various metal oxides is ground, mixed, and dried in a ball mill using water as a solvent, and ethyl cellulose and toluene are added to the dry powder and stirred and mixed to form a similar mixture. Profit.

Ru. Thereafter, the air in this mixture is removed, and a ceramic green sheet is formed using a doctor blade method, followed by drying to obtain a formed sheet. Next, as shown in FIG.
The surface is made of the same composition as that constituting the molded sheet 1, is sintered in advance, and has a predetermined size of 5 to 100 μm).
A plurality of slit precursor films 2 are formed by printing and drying a slit out-of-plane paste composed of fired particles having the following properties, carbon particles, an acrylic thermoplastic resin, and a volatile solvent such as toluene and acetone. As shown in FIG. 3, a formed sheet 1 on which a plurality of slit precursor films 2 are formed
A plurality of the slit precursor films 2 are laminated so that one end thereof alternately protrudes toward the opposite side, and the molded sheet laminate 3 is obtained by heat-pressing. In this case, a molded sheet is used on which no slit precursor film is formed on the uppermost surface. Next, the formed sheet laminate 3 is cut along dotted lines to obtain unfired chips 4 in which the ends of the outer membrane 2 before the slits are alternately led out to the opposing surfaces, as shown in FIGS. 4 and 5.

Next, the unfired chips 4 are back-heated to 300-650°C at a heating rate of 1-20°C for 1 hour, and then heated to 300-650°C for 2 hours.
The carbon particles and volatile solvent constituting the slit precursor film 2 are decomposed and removed by holding for ~15 hours, and then held for ~15 hours.
The temperature was raised to 1000-1400°C at a heating rate of 00°C for 1 hour, and sintered at 1000-1400°C for 3.5-4.5 hours to form a formed sheet on the outer membrane 2 part before the slit as shown in Figure 6. A sintered chip 7 is obtained in which a slit 6 having a plurality of ceramic columnar particles 5 bonded between the laminated layers 11 is formed.

As shown in FIG. 1, for example, a porous silver paste having continuous pores is applied to both sides of the sintered chip 7 from which the slit 6 leads out, and after drying,
Baking at ℃ forms a porous outer electrode 8, after which Pb
, Sn, or at least one metal among Pb, and Sn as a main component.Ag, AI, and Cu.

Z" is immersed in a molten metal made of an alloy containing at least one of the following and has a melting point lower than the melting point of the lowest metal oxide constituting the molded sheet 1, the container containing the molten metal is depressurized, and then The molten metal is forced into the Surin I-6 through the porous external electrode 8 by applying pressure, and then slowly cooled to form an internal electrode 9 connected to the porous external electrode 8 within the slit 6. It is intended to do so.

According to the method for manufacturing the multilayer ceramic varistor configured as described above, the internal electrode 9 is not exposed to the sintering temperature that accompanies B reduction, so the factor of mutual reaction between the varistor composition and the internal electrode material is eliminated. There is no restriction on the usable varistor composition range, and a multilayer ceramic varistor that can satisfy the desired characteristics without deterioration of characteristics can be obtained no matter what composition is used. Further, the slit precursor 11i2 includes ceramic particles having the same composition as the varistor composition, and in the sintering process, the ceramic particles become ceramic columnar particles 5, and the molded sheets imm are bonded together via the ceramic columnar particles 5. Therefore, even if there is heat stress applied during the subsequent process or during use as a finished product, there is no risk of cranking to the internal electrode 9 machine part, and in combination with the above-mentioned effects, the conventional example Reliability is significantly improved compared to the previous one. Furthermore, the internal electrodes 9 are formed by press-fitting through the pores of the porous external electrodes 8 into slits 6 previously formed between the laminated layers of the molded sheets 1 constituting the sintered chip 7, and are sintered at high temperatures. Since it is not exposed to freezing temperatures, it has the advantage of being able to use inexpensive metals without being limited to expensive noble metals such as gold, platinum, and palladium, contributing to cost reduction.

Next, an example of comparison between an example obtained by the present invention and a reference example obtained by the prior art will be described.

Example 1 ■ Composition □ Both the present invention and the reference example have zinc oxide as the main component and B
i, Pr, La, Sb, Cr, Mg, Go, Mn, N
i respectively Bi2O3゜Pr O, La O, 5b
2o3°Cr203. MgO, Coo, MnO, N I
O.

It was calculated as follows and consisted of four types of composition ratios shown in the table below.

However, the glass in Table 1 above is SiO2,0°B2039.
0. It consists of 16.5° ZnO and 72.5% WL of PbO, and the values are weight % relative to zinc oxide.

■ Green sheet composition □ Mix each of the barista raw materials and water shown in Table 1 above for 6 hours using a fiftvJ pot and a partially stabilized zirconia ball. After dry contact and calcination at 800℃ for 2 hours, mix the calcined raw materials and water again. 20 parts by weight of trichlorethylene, ethyl alcohol, polyvinyl butyral, and polyethylene glycol were added to 100 parts by weight of the pulverized raw material obtained by crushing and drying for 16 hours using a resin pot and partially stabilized zirconia balls, and a resin pot and resin balls were added. Four types of ceramic green sheets were obtained by deaerating the slurry mixed for 24 hours using the doctor blade method.

Present invention A Molded sheet...The above configuration.

Slit precursor paste *10 parts by weight of fired particles each having a varistor composition of 26 to 37 μm.

*401m parts of carbon particles smaller than the fired particle diameter.

*Polymethyl methacrylate resin, toluene, 50 parts of octyl phthalate.

Molded sheet laminate pressing conditions...85℃100g
/ci, 1 minute.

Slit forming conditions: The temperature was raised to 600°C at a heating rate of 15°C for 1 hour, then held at 600°C for 4 hours - left to cool.

Sintering conditions: 11 at a heating rate of 100°C for 1 hour
After raising the temperature to 50°C, hold at 1150°C for 4 hours and allow to cool.

Internal electrode material and formation conditions: Pb 70%.

The alloy was melted in a container maintained at 280°C, which is higher than the melting point of the 5N30% alloy. After the container was depressurized, 15 atm was applied.

Reference example B: Japanese Patent Application Laid-Open No. 1983-1068 described in the (prior art) section above
Using a molded sheet having the structure shown in Table 1 above, the molded sheet was coated with Pd paste and cut into internal electrode formation-81FIJ.
Sintered at 50℃, coated with Ag paste on both ends, and heated to 600℃.
Baking forms the external electrode. In addition, the laminated ceramic buffster has a thickness of 3 layers, 200 μm in thickness, 3 opposing portions of internal electrodes, 1 x 5 layers, external dimensions of 5 layers x 7 layers, and the number of laminated layers is 10 A.

The results of examining various properties of Invention A and Reference Example B are shown in Table 2.

Margin below In Table 2 above, α (non-linear coefficient) is the value at ■1oA-V1mA, and C is the value when a DC'Ia pressure of ■1TrLA1/2 is applied.

As is clear from Table 2, the present invention is significantly superior in nonlinear characteristics, L, C characteristics, and voltage-current characteristics compared to Reference Example. This is because the material undergoes a diffusion reaction that changes the original composition of the varistor, and the internal electrode material is eroded.

The order of the samples in Table 2 corresponds to the order of the samples in Table 1 showing the composition, and the numerical values are the average values of 50 samples for each sample.

Example 2 Invention A using sample 11Q1 shown in Table 2 of the above (Example 1) and JP-A-56-1 described in the section of (Prior art) above
Change rate of v1TrLΔ in Reference Example B obtained by the manufacturing method disclosed in Publication No. 501 and DC in an atmosphere of 85°C
Limiting voltage characteristics when the maximum allowable circuit voltage is applied for 500 hours ■. The results of comparing the A/V and mA values are shown in FIG. 8 and Table 3.

The composition on the reference example day was the same as that used in Motobu, with polyvinyl alcohol paste used as the burned-out material and 391 paint used for the electrodes.

Table 3 As is clear from FIG. 8 and Table 3, Reference Example B had extremely poor limiting voltage characteristics and poor reliability, demonstrating the superiority of Invention A.

In the above embodiments, the varistor composition is exemplified and explained using zinc oxide as the main component, but it goes without saying that it is also applicable to varistors containing other metal oxides as the main component, such as 5rT103 or perovskite type.

Further, as shown in FIG. 7, a solution such as silver nitrate is impregnated into the slit 6 of the sintered chip 7 and applied to the inside of the slit 6 when the porous external electrode 8 is baked. 10 is effective because it improves the wettability between the molded sheet 2 and the internal electrode 9 formed by the molten metal press-fitted through the porous external electrode 8.

[Effects of the Invention] As described above, according to the present invention, it is possible to obtain a method for manufacturing a multilayer ceramic varistor that is easy to manufacture and exhibits excellent varistor characteristics regardless of the varistor composition and has high practical value.

[Brief explanation of the drawing]

1 to 6 are for explaining a method of manufacturing a multilayer ceramic varistor according to an embodiment of the present invention. 2 is a perspective view showing a molded sheet with a slit precursor film formed thereon, FIG. 3 is a sectional view showing a molded sheet laminate formed by laminating a plurality of molded sheets, and FIGS. 4 and 5 are as shown in FIG. Figure 4 is a perspective view, Figure 5 is a sectional view of Figure 4, and Figure 6 is a sintered chip obtained by cutting the formed sheet laminate shown in Figure 6. FIG. 7 is a partially cutaway enlarged sectional view showing a multilayer ceramic varistor after forming internal electrodes, for explaining a method for manufacturing a multilayer ceramic varistor according to another embodiment of the present invention. The diagram shows time-VlTrLA
It is a change rate characteristic curve diagram of. 1... Molded sheet 2... Slit precursor film 3... Molded sheet laminate 4...
... Unfired chip 5 ... Ceramic columnar particles 6 ... Slit 7 ... Sintered body chip
8...Porous external electrode 9...Internal electrode 10...Coating film patent applicant Marcon Electronics Co., Ltd. Figure 7 Time (Hr) Figure 8

Claims (3)

[Claims] (1) A means for drying a molded ceramic green sheet containing a metal oxide as a main component to obtain a molded sheet, and disposing on the molded sheet fired particles, carbon particles, and a thermoplastic resin having the same composition as that constituting the sheet. A means for printing and drying a slit precursor paste made of a volatile solvent to form a plurality of slit precursor films, and laminating and heat-pressing the plurality of molded sheets so that one end of the slit precursor films alternately protrudes to the opposite side. means for obtaining a formed sheet laminate; means for cutting the formed sheet laminate to obtain unfired chips in which the ends of the slit precursor film are alternately led out to opposing surfaces; and a means for gradually raising the temperature of the unfired chips. Means for obtaining a sintered chip in which carbon particles and volatile components constituting the slit precursor film are removed by high-humidity sintering and a slit having a plurality of ceramic columnar particles is formed in this portion, and the sintered chip and means for press-fitting molten metal into the slit through the porous external electrode to form an internal electrode. A method for manufacturing a multilayer ceramic varistor. (2) The molten metal contains at least one of Pb and Sn or at least one of Pb and Sn as a main component and contains Ag, Al
, Cu, and Zn, the method for manufacturing a multilayer ceramic varistor according to claim (1). (3) The multilayer ceramic varistor according to claim (1) or (2), characterized in that the slit is impregnated with a metal solution and a coating film is formed on the inner wall of the slit when baking the porous external electrode. manufacturing method.