JPH0214501A - Voltage nonlinear resistor - Google Patents

Abstract

PURPOSE:To sufficiently display a function as a varistor even when a thickness of an ineffective layer is made equal to or lower than that of an effective layer and to enhance moistureproofness by a method wherein an insulator is used as the effective layer of a laminate-type voltage nonlinear resistor. CONSTITUTION:An additive such as Bi2O3, CoO, MnO or the like is added to ZnO; they are mixed and baked temporarily; after that, an organic binder, a dispersion medium and a plasticizer are added; a green sheet 1 for effective layer use is manufactured by a doctor blade method. Then, an additive in a very small quantity is added to a metal oxide to be used as an insulator; in addition, an organic binder, a dispersion medium and a plasticizer are added; a green sheet is manufactured by the doctor blade method; this green sheet is used as green sheets 2 for ineffective layer use. Internal electrodes 3, 4 are printed on the green sheet 1 for effective layer use; they are piled up; in addition, the green sheets 2 for ineffective layer use are piled up and pressure-bonded onto the upper part and lower part; this assembly is cut to a prescribed size and sintered. Then, this assembly displays a function of a varistor even when a thickness of the ineffective layers 2 in an uppermost layer and a lowermost layer is made equal to or lower that of the effective layer 1; no problem about moistureproofness arises.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a voltage nonlinear resistor that protects electronic equipment from abnormal voltages such as inductive groups and static electricity.

(Prior Art) In recent years, electronic devices have become smaller and smaller, and the market is demanding smaller electronic components, especially chip-shaped electronic components that can be directly incorporated into printed circuit boards.

The use of chips for core components such as capacitors, resistors, and coils rapidly progressed.

It is predicted that by 1990, the chip rate of electronic components will exceed 50%. There is a strong demand for the chipping of electronic components, including voltage non-linear resistors, which are protective components, and in response to this demand, a multilayer ceramic varistor (
JP-A-54-106894) has been proposed, which basically has the same structure and manufacturing method as a multilayer ceramic capacitor. That is, zinc oxide (
ZnO) is the main component, and bismuth oxide (Bi
20. ), cobalt oxide (Coo), manganese oxide (M
n O, ), lead oxide (pbo), etc. are added, mixed, dried, and then calcined, and an organic binder and a dispersion medium are added to the calcined raw material powder.

Add a plasticizer, make a slurry, and use the doctor blade method to process 10. ~Create a uniform raw sheet membrane with zero thickness for about 200 homes. Platinum or the like is printed as an internal electrode on this green sheet film by screen printing.

A predetermined number of raw sheets with internal electrodes printed on them are stacked one on top of the other, and then raw sheets without electrodes printed on top of the other are stacked and pressed together. After this, cut it into a suitable shape with a cutter and
After baking at ~1300°C for 1 hour, silver electrodes are applied to both end faces with exposed internal electrodes and baked at 600°C. The structural diagrams are shown in FIGS. 2(A), (B), and (C). In the figure, 11 is a sintered body of a voltage nonlinear resistor whose main component is zinc oxide (ZnO). 12.1
3 is an internal electrode made of platinum (Pt) or the like; 14
．． 15 is an external electrode made of silver.
) is cut along the cutting line B-B'c-c' and the internal structure is explained using cross-sectional views (B) and (C) viewed in the direction of the arrow. It can be seen that there is an effective layer 16 that exhibits a resistance function and an ineffective layer 17 that does not. The ineffective layer 17 is formed at the top and bottom of the laminated portion.

(Problem to be Solved by the Invention) Generally, when making a multilayer voltage nonlinear resistor (hereinafter abbreviated as a multilayer ceramic varistor), one thing to be careful of is the distance between the opposing internal electrodes, that is, the effective layer thickness t
(preferably t2/11)1.
It is 3. This is because t□>1. In this case, current will not flow through the effective layer, and the varistor will not be able to sufficiently absorb and suppress abnormal voltage. For this reason, the second
As shown in the figure, when the external electrode goes around from the end face to the open plane part (when soldering directly to the printed circuit board, the external electrode goes around from the end face to the open plane part)
, it is necessary to increase the thickness of the ineffective layer, and miniaturization is not possible. Furthermore, as a sintered body, zinc oxide (
ZnO), bismuth oxide (Bi20.) and lead oxide (pb
o), the sintered body contains many pores due to the scattering of Bi and PB during the sintering process, and when moisture resistance is considered, the thickness of the ineffective layer is inevitably increased. becomes larger. Usually, the thickness of the ineffective layer is 3 to 5 times the thickness of the effective layer.

The purpose of the present invention is to eliminate the conventional drawbacks, and to provide a multilayer ceramic varistor that can fully function as a varistor even when the thickness of the ineffective layer is equal to or less than that of the effective layer, and has no moisture resistance problems. It is to provide.

(Means for Solving the Problems) The voltage nonlinear resistor of the present invention has a laminated structure of a plurality of internal electrodes, a voltage nonlinear resistance sintered body, and an insulator, and has an internal electrode and an electrical In the voltage nonlinear resistor formed by forming external electrodes that are connected to each other, at least the uppermost layer and the lowermost layer of the laminated structure are insulators.

(Function) With the above configuration, even if the thickness of the ineffective layer of the uppermost layer and the lowermost layer is equal to or less than the thickness of the effective layer, the varistor function is fully exhibited, and there is no problem in moisture resistance. The multilayer ceramic varistor's mission of miniaturization can be fully demonstrated.

(Example) An example of the present invention will be described based on FIGS. 1(A), (B), and (C).

Since the basic manufacturing method and structure of the first embodiment and the second embodiment are the same, they will be explained first.

In the present invention, first, a raw sheet for an effective layer having varistor properties after sintering is prepared. This is zinc oxide (ZnO), bismuth oxide (Bit03), cobalt oxide (CaO),
Additives such as manganese oxide (MnO) are added and mixed, and after calcining, an organic binder, a dispersion medium, and a plasticizer are added, and a green sheet is made using the doctor blade method.
A green sheet for the ineffective layer is made by adding a small amount of additives to the metal oxide that will serve as the insulator, and then adding an organic binder, a dispersion medium, and a plasticizer to create a green sheet using the doctor blade method. Make raw sheets. Then, internal electrodes are printed on the raw sheets for the effective layer and these are stacked, and the raw sheets for the ineffective layer are stacked one above the other and pressed together, and then cut into a predetermined size and sintered. For this purpose, a manufacturing method is used in which external electrodes are provided. The structure is shown in Figure 1 (A) and (B).
, shown in (C). In the figure, 1 is a sintered body forming an effective layer, 2 is an insulator forming an ineffective layer, 3 and 4 are internal electrodes, and 5.6 is an external electrode.

(Example 1) First, a raw sheet for an effective layer is prepared. Zinc oxide (Z
nO), bismuth oxide (Bi, O-), cobalt oxide (
Cod), manganese oxide (MnOt) - antimony oxide (Sb20s) + silicon oxide (s
% and mixed for 24 hours in a ball mill using pure water.

Next, it is dried, and the dried product is dry-pulverized, placed in an alumina crucible, and calcined at 800 to 950°C for 2 hours. After calcining, it is further ground again and dispersed in a solvent together with an organic binder to form a slurry. This was done by the doctor blade method for 50 minutes. Make a uniform raw sheet with a certain thickness. This raw sheet is punched out into a rectangle of 1100 mm x 80 mm, and platinum (Pt) is pasted onto this as an internal electrode by screen printing to create a zero-order invalid layer raw sheet that is screen printed to a predetermined size. 7. As a raw material.
Antimony oxide (sb,○,) in nz SiO4 powder
, silicon oxide (Sio, ) are added in small amounts, and dispersed together with an organic binder in a solvent to form a slurry.

This is made into a uniform green sheet with a thickness of about 50 doors using the doctor blade method. This raw sheet is 10100mX
80 rectangles are punched out to form a raw sheet for an ineffective layer. 6. Next, 10 raw sheets for an effective layer on which internal electrodes have been printed are stacked, and further raw sheets for an ineffective layer are stacked one above the other and pressed together.

Thereafter, it is cut with a cutter and baked at 1250°C for 1 hour.Ag-Pd electrodes are applied to both end faces with exposed internal electrodes and baked at 900°C. The sintered structure of the invalid layer is dense, and in order to investigate the moisture resistance properties of this element, we conducted a pressure couture test (leaving it at 121°C in 2 atm) and found that the rate of change in varistor voltage remained the same even after leaving it for 100 hours. It was less than 12%. On the other hand, for comparison, the device fabricated by the conventional method showed a change of -25%, and Example 1
The validity of the method was confirmed.

(Example 2) Next, a case will be described in which AJ, 03 and MgO are used as raw materials for the insulator. The method for preparing the effective layer raw sheet is the same as in Example 1. The raw sheet for the ineffective layer is AJ20. In the case of AJ, O, a small amount of boron oxide (BZ O-) and silicon oxide (SiO2) are added to the powder, dispersed in a solvent together with an organic binder, made into a slurry, and made into a slurry using a doctor blade method. Make a raw sheet of uniform thickness. The steps after lamination are the same as in Example 1. However, the firing temperature is 1350°C.

On the other hand, in the case of MgO, a green sheet for the invalid layer is prepared by adding trace amounts of boron oxide (3,03) and silicon oxide (Sin, ) to MgO powder in the same manner as in the case of Al1203. The steps after lamination are the same as in Example 1. However, the firing temperature is 1300°C. AI! 20. Also in the case of M
In the case of gO, the sintered structure of the invalid layer was also dense. In order to investigate the moisture resistance properties of this element, we conducted a pressure couture test (left at 121°C and 2 atm) and found that 10
Even after leaving it for 0 hours, the rate of change in varistor voltage is AJ20. 11% in the case of

In the case of MgO, it was -2.5%.

On the other hand, for comparison, the device made by the conventional method is 12
It showed a change of 5%, and the case of Example 2 was also effective.

(Effects of the Invention) According to the present invention, by using an insulator for the ineffective layer of a multilayer voltage nonlinear resistor, it becomes smaller than the conventional example and has excellent moisture resistance, which makes it possible to reduce the size of electronic equipment. It has great practical value as a component that is effective for development.

[Brief explanation of the drawing]

FIG. 1(A) is a perspective view of a voltage nonlinear resistor in one embodiment of the present invention, FIG. 1 CB) and (C) are the same cross-sectional views,
Figure 2 (A) is a perspective view of a conventional voltage nonlinear resistor;
Figures (B) and (C) are the same cross-sectional views. 61... Sintered body, 2... Insulator, 3.4... Internal electrode, 5
, 6... external electrode. Patent applicant Matsushita Electric Industrial Co., Ltd. Tanzu Tanzu

Claims (1)

[Claims] A plurality of internal electrodes, a voltage nonlinear resistance sintered body, and an insulator have a laminated structure, and an external electrode electrically connected to the internal electrodes is formed on the end face. A voltage nonlinear resistor, wherein at least the uppermost layer and the lowermost layer of the laminated structure are the insulator.