JPS63100701A - Manufacture of melf type laminated chip 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 for manufacturing a Melf-type multilayer chip varistor suitable for surface mounting.

(Conventional technology) In recent years, with the expansion of applications for varistors, #? The demand for varistors of four-layer type and chip structure is increasing.

Previously proposed I! Japanese Patent Application Laid-open No. 87313/1983 describes a technology for manufacturing single-layer ceramic electronic components. The technique disclosed in this publication is to produce a prismatic laminate in which a plurality of ceramic sheets on which internal electrodes are formed are laminated and fired, and the internal electrodes are buried in layers so that they are alternately led out to opposite end faces. A cylindrical laminate is formed by grinding the circumferential side surface of the internal electrode excluding the lead-out end face, an external connection electrode is provided on the lead-out end face of the internal electrode, and a cylindrical metal is provided on both ends of the external connection electrode formation. Although the above publication relates to a ceramic capacitor, it can easily be applied to a ceramic varistor. However, since the multilayer ceramic electronic component disclosed in the above publication has a cylindrical outer shape, there is no directionality as a component, and automatic mounting on a board is easy. Since the cap is a tab, it is easy to fit the cap and a reliable connection can be obtained.Also, the presence of the metal cap eliminates the need for direct soldering to the electrode for external connection to the board. This has the effect of eliminating the fatal defect that AQ easily breaks due to mechanical stress caused by thinning of the AQ due to solder cracks and weakening of the adhesive strength with the board. This F& multilayer ceramic electronic component is worthy of attention. However, in the structure described above, the ceramic sheet and the internal electrode are sintered at the same time. For example, in the case of a varistor whose main component is normal lead oxide, the sintering temperature is over 1100°C, so the internal electrode material is also a negative metal. Limited and expensive. Furthermore, varistors containing dosmuth oxide or praseodymium oxide react with the internal electrodes and corrode the electrodes, making it difficult to form the desired internal electrodes and causing characteristic deterioration. Furthermore, since the coefficient of linear expansion of the internal electrode metal is one order of magnitude larger than that of the varistor sintered body, cracks may occur if thermal stress is applied during use, which is not a desirable method for manufacturing a laminated varistor.

Therefore, as disclosed in JP-A-56-1501, layered voids are formed in a sintered body as a means for forming internal electrodes, and the voids are filled with a conductive paint, and the conductive Ti paint is used as the internal electrode. do. In other words, it is possible to use a method that does not simultaneously bake the internal electrodes when sintering the ceramic sheet, but when the conductive paint is used at high temperatures for a long time, the organic matter contained in the paint will carbonize and the sintered body as a varistor composition may be used. It becomes impossible to maintain contact with the layer, discharge occurs on the contact surface, the carbonized organic matter changes quality, partially reduces the varistor composition, increases leakage current, generates heat, and eventually causes thermal runaway, resulting in a serious defect leading to destruction. It was dangerous and unreliable.

(Problems to be Solved by the Invention) As described above, the laminated varistors obtained with the cylindrical portion of the conventionally disclosed technology have moderate practical problems and have many problems to be solved. Ta.

The present invention has been made in view of the above points, and it not only facilitates workability and contributes to cost reduction, but also solves all of the drawbacks of the prior art described above, and provides a highly reliable Melf type without deterioration of characteristics. It is an object of the present invention to provide a method for manufacturing a multilayer chip varistor.

[Structure of the invention] (Means for solving the problems) Melf type of the present invention! The manufacturing method of the F4-layer chip varistor is to print and dry a slit precursor base consisting of fired particles, carbon particles, thermoplastic resin, and volatile solvent having the same composition as the varistor composition, and then to form a molded sheet with a slit precursor film formed on the front surface. The prismatic laminate obtained by laminating and heat-pressing a plurality of layers so that the slit precursor films are alternately led out to opposite end faces is gradually heated and sintered at high temperature, and the carbon particles and volatiles of the slit precursor film described in 114 are heated and sintered at a high temperature. A prismatic sintered body with a plurality of columnar ceramic particles formed therein by removing the slag component is obtained.

Next, the outer surface of the prismatic sintered body except for the lead-out end face of the slit is ground to form a cylindrical varistor assembly, and a porous external electrode is formed on the slit lead-out end face. The molten metal is press-fitted into the slit through the slit to form an internal electrode, and then a cylindrical metal cap is fitted onto the external electrode.

(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.
The range of varistor compositions is expanded without limiting the varistor compositions that can be used.

In addition, the columnar ceramic particles formed in the slits firmly bond the laminated layers of the molded sheets, thereby preventing the occurrence of cracks due to thermal stress during use. Furthermore, since the internal electrodes are not baked, the internal electrode materials are not limited to expensive precious metals, and IR! It is possible to select internal electrode materials within a range other than S-electrode paint, which contains organic matter that carbonizes at high temperatures and deteriorates its characteristics. By using inexpensive internal electrode materials, the characteristics do not deteriorate, contributing to cost reduction.

(Fruit eggplant example) An embodiment of the present invention will be described in detail below.

First, zinc oxide is the main component, followed by Bi, Pr, and La.

8i each of Sb, Cr, Mg, Co, ~ln, and Ni
0, Pr O, La2O3゜Sb O, Cr2
O3, Mob, Coo.

A calcined powder obtained by adding appropriate amounts in terms of Mno and Nto is ground in a ball mill using water as a solvent.
Mix to obtain a homogeneous mixture. After that, air is removed from this mixture, and a ceramic green sheet is formed by a doctor blade method and dried. Next, a pre-sintered ceramic green sheet of a predetermined size made of the same composition as that of the formed sheet is placed on the surface of the formed sheet. (5 to 100μ) fired particles, carbon particles, acrylic thermoplastic resin and toluene,
A slit precursor paste made of a volatile solvent such as acetone is stamped and dried to form a slit precursor film, and a plurality of the molded sheets are laminated. FIGS. 2 and 3 show a prismatic 8i layered body 3 obtained by laminating and heat-pressing the molded sheet 1 in such a way that the slit precursor films 2 are alternately drawn out to opposite end faces. In this case, the lowermost and uppermost surfaces are thicker than the molded sheet located between them.

Next, the temperature of the prismatic laminate 3 is raised to 500 to 650° C. at a heating rate of 10 to 650° C., and held at this temperature and humidity for 3.5 to 4.5 hours to form the slit precursor film 3.
After cooling, the carbon particles and volatile solvent constituting the carbon particles were decomposed and removed, and after cooling, the temperature was raised to 1000 to 1400 °C at a heating rate of 90 to 1400 °C, and sintered for 3.5 to 4.5 hours at this temperature increase time to form a slit. Precursor WA
As shown in FIG. 4, a prismatic sintered body 6 is obtained in which a slit 5 having a plurality of ceramic columnar particles 4 bonding the laminated layers of the formed sheet 1 is formed in the second part. Then, the outer surface of the prismatic sintered body 6, excluding both end surfaces from which the slits 5 are led out, is ground using, for example, a centerless grinder to obtain a cylindrical varistor body 7 as shown in FIG.

Next, as shown in FIG. 6, a porous silver paste, for example, is applied to both end surfaces of the cylindrical varistor body 7 from which the slit 5 is led out. The external connection electrode 8 is formed, and then at least one metal selected from Pb and Sn or Pb and S is formed.
Ag containing at least one type of n as a main component.

AI! , Cu, and Zn, and the molded sheet 1 is immersed in a molten metal whose melting point is lower than the melting point of the lowest metal oxide constituting the molded sheet 1, and the container containing the molten metal is depressurized. Then, pressure is applied to press the molten metal into the slit 5 through the pores of the porous external connection electrode 8, and then it is slowly cooled and connected to the porous external connection electrode 8 inside the slit 5. Then, as shown in FIG. 1, a cylindrical metal cap 10 is fitted onto the surface on which the porous external connection electrode 8 is formed.

According to the manufacturing method of the Melf-type multilayer chip varistor configured as described above, since the sintering step 11 in which the internal electrodes 9 are exposed to high temperatures is not performed, the factor of mutual reaction between the composition and the internal electrode material is eliminated. There is no limit to the range of varistor compositions that can be used, and 1q multilayer chip varistors can be created that can satisfy the desired characteristics no matter what varistor composition is used, and at the same time, the internal electrode material is not limited to monovalent negative metals. ,
And a! ! This makes it possible to use inexpensive metals, except for conductive paints that contain organic matter, which carbonizes at high temperatures and deteriorates the characteristics, making it possible to obtain inexpensive multilayer chip varistors without deteriorating the characteristics.

Further, in the process of forming the sintered body, the ceramic particles constituting the slit precursor film 2 become ceramic columnar particles 4, and the formed sheet 11111V! Since J is firmly connected, even if thermal stress is applied, there is no risk of cracking in the internal electrode 9 machine part.
Combined with the above-mentioned effects, the present invention has the advantage that reliability is significantly improved compared to those described in the prior art.

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

Example 1 Main component is zinc oxide, Bi2O3,5b203, M
Invention A, which uses a molded sheet with a composition containing QO, Coo, MnO, and NiO, and JP-A-61-87, which uses a molded sheet with the same composition.
As a result of examining the quality of Reference Example B consisting of a varistor obtained by applying the technology disclosed in Publication No. 313,
The results are shown in Table 1.

Table 1 The slit precursor paste in the present invention A is 26 to 3
7μm sintered particles 10!11r11 parts, carbon particles 4
0 parts, acrylic resin, toluene.

A total of 50,000 parts of octyl phthalate was used, and the internal electrode material was an alloy of 70% Pb and 30% 5N.

As is clear from Table 1, Invention A is significantly superior to Reference Example B in all of the nonlinear characteristics, LC characteristics, and υ1 limiting voltage characteristics. Each value is an average of 30 values.

Example 2 Invention A having the same configuration as used in Example 1 above,
The rate of change in VlmA in Reference Example C obtained by the manufacturing method disclosed in JP-A No. 56-1501 and the limiting voltage characteristic V2A/V1mA value when the DC maximum allowable circuit voltage is applied for 500 hours in an 85°C atmosphere are As a result of the comparison, the 8th
The results are shown in Figure and Table 2.

The composition of Reference Example C was the same as that of the present invention, and the burned-out material was polyvinyl alcohol paste, and the electrodes were made of conductive paint.

Table 2 As is clear from FIG. 8 and Table 2, Reference Example C had extremely poor limiting voltage characteristics and poor reliability, which overshadowed the superiority of the present invention.

In the above embodiments, a varistor composition mainly composed of zinc oxide has been exemplified and explained, but it goes without saying that the present invention can also be applied to a varistor composition mainly composed of other metal oxides.

Further, in the above embodiment, the width of the stacked slit precursor films 2 is the same, but as shown in FIG. By setting it so that it is wide and narrowing toward the outside and reducing the grinding allowance, it is possible to increase the number of internal 'Fi poles, so of course it is possible to obtain a small size and a large surge withstand capacity. .

〔Effect of the invention〕

As described above, according to the present invention, the Melf-type l? A method for manufacturing a single-layer chip varistor can be provided.

[Brief explanation of the drawing]

1 to 7 are for explaining a method of manufacturing a Melk-type multilayer chip varistor according to an embodiment of the present invention, FIG. 1 is an enlarged front cross-sectional view showing a Melk-type multilayer chip varistor, Figures 2 and 3 show a prismatic laminate.
The figure is a perspective view, Figure 3 is an enlarged front sectional view of Figure 2, and Figure 4 is an enlarged front sectional view of Figure 2.
The figure is an enlarged front cross-sectional view showing a prismatic sintered body with a slit formed therein, Figure 5 is a perspective view showing a cylindrical varistor body, and Figure 6 is a porous external connection to the slit lead-out end face of the cylindrical varistor body. FIG. 7 is an enlarged front cross-sectional view showing a state in which internal electrodes are formed in slits, and FIG. A perspective view showing the layered body, FIG. 8 is a time-V
FIG. 3 is a diagram showing a characteristic curve of change rate of lmA. 1... Molded sheet 2... Slit precursor film 3... Prismatic LA layer body 4... Ceramic columnar particles 5... Slit 6 ...Prismatic sintered body 7 ...Cylindrical varistor element body 8 ...Porous external connection electrode 9 ...Internal electrode 10 ... ...Patent application for cylindrical metal cap Hito Marukon Electronics Co., Ltd. 8 Enlarged front cross-sectional view of a prismatic sintered body for porous external connection Figure 4 Figure 6 Time (h) Figure 8

Claims (1)

[Claims] A slit precursor made of fired particles having the same composition as that of the molded sheet, carbon particles, a thermoplastic resin, and a volatile solvent is placed on a molded sheet obtained by drying a ceramic green sheet containing metal oxide as a main component. means for printing and drying the paste to form a slit precursor film; means for laminating and heat-pressing a plurality of the molded sheets so that the slit precursor films are alternately led out to opposite end faces to obtain a prismatic laminate; A prismatic sintered body in which the temperature of the laminate is gradually raised and the carbon particles and volatile components constituting the slit precursor film are removed by high-temperature sintering, and slits having a plurality of ceramic columnar particles are formed in this part. a means of obtaining
A means for obtaining a cylindrical varistor element body by grinding the outer surface of the prismatic sintered body except for the slit lead-out end face, and a porous external connection electrode having continuous pores on the slit lead-out end face of the element body. means for press-fitting molten metal into the slit through the porous external connection electrode to form an internal electrode; and means for fitting a cylindrical metal cap onto the porous external connection electrode forming surface. A method for manufacturing a Melf-type multilayer chip varistor, characterized by comprising: