JPH10163009A - Manufacture of non-linear resistor dependent on voltage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a varistor which prevents clearance between a ceramic substrate and an insulating resin film. SOLUTION: A method for manufacturing a varistor comprises the process of forming a ceramic substrate exhibiting properties of a varistor, the process of making the surface of the ceramic substrate coarse, the process of forming an electrode on the ceramic substrate and the process of coating the ceramic substrate with an insulating resin film. The surface of the ceramic substrate can be made coarse by corroding with a chemical agent containing hydrofluoric acid or by sand blasting or barreling.

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 voltage-dependent non-linear resistor (hereinafter, referred to as a "varistor") having voltage non-linearity and a large dielectric constant.

[0002]

2. Description of the Related Art There are various types of varistors depending on constituent materials, and the manufacturing method differs for each constituent material. For example, a strontium titanate-based varistor is generally manufactured as follows.

First, a small amount of additives such as aluminum oxide, silicon oxide, niobium oxide and yttrium oxide are added to titanium oxide, strontium carbonate and calcium carbonate,
The raw material powder is obtained by sufficiently mixing with a ball mill.

[0004] Next, an organic binder is added to the raw material powder and granulated, and the resultant is compression-molded by a molding machine to obtain a disk-shaped molded body. Then, the molded body is fired in a reducing atmosphere composed of nitrogen and hydrogen gas to obtain a ceramic body (sintered body) which has been converted into a semiconductor and has reduced resistance.

Next, the ceramic body is reheated in the air to oxidize the grain boundaries inside the ceramic body to increase the resistance, and form a grain boundary barrier to obtain a ceramic body exhibiting varistor characteristics.

Next, a silver paste is applied to the front and back surfaces of the ceramic base and baked, lead terminals are respectively connected to the formed electrode layers, and these are left in an insulating resin while leaving a part of the lead terminals. To obtain a varistor.

[0007]

When a varistor is manufactured by the above-described method, a gap may be formed between the ceramic substrate and the insulating resin film. The varistor with the gap formed has a problem that the insulation resistance of the ceramic base is reduced, and discharge occurs along the ceramic base in the gap when abnormal voltage is absorbed, so that desired varistor characteristics cannot be obtained. Will occur.

An object of the present invention is to provide a method for manufacturing a varistor in which no gap is formed between the ceramic substrate and the insulating resin film.

[0009]

The present invention comprises a step of forming a ceramic base exhibiting varistor characteristics, a step of forming an electrode on the ceramic base, and a step of coating the ceramic base with an insulating resin film. In a method for manufacturing a varistor provided with the above, the above problem is solved by roughening the surface of the ceramic base.

Here, as a method of roughening the surface of the ceramic body, for example, a method of immersing the ceramic body in a chemical containing hydrofluoric acid to corrode the surface, a method of sandblasting the surface of the ceramic body, A method of shaving the surface of the base with a barrel can be employed.

[0011]

【Example】

Example 1 First, titanium oxide, strontium carbonate and calcium carbonate were weighed, and aluminum oxide, silicon oxide,
Additives such as niobium oxide and yttrium oxide were added in a small amount and mixed sufficiently with a ball mill to obtain a raw material powder.

Next, an organic binder is added to the raw material powder to form a granule, which is compression-molded by a molding machine to have a diameter of 9 mm.
A disk-shaped molded body having a thickness of 1.5 mm was obtained. Then, the formed body was fired in a reducing atmosphere composed of nitrogen and hydrogen gas to obtain a ceramic base (sintered body) having a semiconductor and reduced resistance.

Next, the ceramic body is reheated in the air to oxidize the grain boundaries inside the ceramic body to increase the resistance, thereby forming a grain boundary barrier to obtain a ceramic body exhibiting varistor characteristics. .

Next, this ceramic substrate is heated at room temperature in HF:
Barrel immersion was performed for 1 minute using a solution of HNO ₃ : H ₂ O = 1: 5: 50 to slightly corrode and roughen the surface of the ceramic substrate. Here, when the surface roughness Ra of the ceramic base was examined, it was as shown in Table 1.

Next, the ceramic base is washed with water and dried, and a silver paste is applied to the front and back surfaces of the ceramic base and baked, and lead terminals are connected to the formed electrode layers, and these are connected to the lead terminals. Was covered with an insulating resin except for a part of the varistor.

Next, the varistor voltage V _{1 of} this varistor
When the non-linear index α, the capacitance C, and the surge resistance ΔV ₁ were examined, the results were as shown in Table 1.

Example 2 A ceramic base was immersed in a solution obtained by adding 1% by weight of a sulfated higher alcohol surfactant as a dissolution promoter to HCl: H ₂ O = 1: 20 at 40 ° C. for 30 minutes to form a surface. A varistor was prepared in exactly the same manner as in Example 1, except that the surface was roughened. The varistor voltage V ₁ , the non-linear index α, the capacitance C, and the surge withstand voltage ΔV ₁ of this varistor were examined.

Example 3 The same procedure as in Example 1 was carried out except that the surface of the ceramic substrate was roughened by blowing sand particles (silica sand) having a particle size of 20 mesh onto the surface of the ceramic substrate using compressed air to impinge on the surface. Created a varistor. The varistor voltage V ₁ , the non-linear index α, the capacitance C, and the surge withstand voltage ΔV ₁ of this varistor were examined.

Example 4 Ceramic body and abrasive (aluminum oxide: 30 μ)
Into a hexagonal barrel so that the barrel volume ratio is 50% and the porcelain and polishing ratio is 1: 6, and the rotational speed of the barrel is 14r.
A varistor was prepared in exactly the same manner as in Example 1 except that the surface of the ceramic substrate was roughened while maintaining the varnish at pm for 10 minutes. And the varistor voltage V _{1 of} this varistor,
When the non-linear index α, the capacitance C, and the surge resistance ΔV ₁ were examined, the results were as shown in Table 1.

Comparative Example 1 A varistor was prepared in exactly the same manner as in Example 1 except that the surface of the ceramic substrate was not roughened. The varistor voltage V ₁ , the non-linear index α, the capacitance C, and the surge withstand voltage ΔV ₁ of this varistor were examined.

[0021]

[Table 1]

From the results shown in Table 1, although the surface of the ceramic substrate was not roughened, the surge withstand capability was 800 A, but the surge withstand capability of the roughened Examples 1-4 was 1
000 to 1200 A, and it can be seen that the surge resistance is improved when the surface of the ceramic substrate is roughened.

[0023]

According to the present invention, the insulating resin film is sufficiently adhered to the ceramic substrate, the electric resistance of the surface of the ceramic substrate is increased, and the insulation resistance between the electrodes is increased. There is an effect that no discharge is generated along the ceramic ground when the voltage is absorbed.

Claims (4)

[Claims] 1. A step of forming a ceramic base having varistor characteristics, a step of roughening the surface of the ceramic base, a step of forming electrodes on the ceramic base, and a step of forming the ceramic base with an insulating resin film. A method of manufacturing a voltage-dependent nonlinear resistor comprising a step of coating. 2. The method according to claim 1, wherein the surface of the ceramic substrate is roughened by corrosion with a chemical containing hydrofluoric acid. 3. The method according to claim 1, wherein the surface of the ceramic substrate is roughened by sandblasting. 4. The method according to claim 1, wherein the surface of the ceramic substrate is roughened by a barrel.