JPS5821804B2 - Atsumakubarista youdenkiyokuzairiyo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves baking zinc oxide to which nickel oxide, molybdenum oxide, magnesium oxide, barium oxide, and titanium oxide are added, and then pulverizing the resulting powder and a method for fixing this powder. This invention relates to an electrode material used in a thick film varistor made of glass frit.

BACKGROUND ART Conventionally used voltage nonlinear resistors (hereinafter simply referred to as varistors) include SiC varistors, selenium, and Si varistors, and are used for overvoltage protection.

Semiconductor elements currently in use, such as diodes, transistors, and SIRISK, have significantly lower overvoltage withstand capability than general electrical equipment, so varistors used to protect these devices from overvoltage have low limiting voltage ratios and It is desired that the nonlinearity be as large as possible.

However, the SiC varistor mentioned above is widely used because it is made of SiC particles baked and hardened at high temperature, but its structure uses particles of around 100μ, so
Those having a thickness of less than mm are difficult to manufacture and have the drawbacks of not having very large voltage nonlinearity and having a high limiting voltage.

In addition, in principle, varistors using P-n junctions of Ge or Si are limited to about 0.3V for Ge and about 0.7V for Si, so in order to obtain predetermined characteristic values, a large number of varistors are used. It is necessary to connect these elements in series, which increases the size and cost of the device.

Selenium and cuprous oxide rectifiers have similar drawbacks.

In addition, the recently developed zinc oxide varistor is manufactured by molding in the same way as the SiC varistor, and is 0.5 mm thick.
It is difficult to make a varistor with the following thickness.

In order to eliminate these drawbacks, a thick film varistor consisting of zinc oxide powder and glass frit powder bonded thereto is suitable.

This is because if it is a thick film varistor, it is possible to make a thick film of about 100 μm by screen printing, etc., and by arbitrarily changing the shape of the varistor, any desired rise voltage can be obtained. This is because it may cause disadvantages of Si varistors, selenium rectifiers, etc.

However, since Ag and Ag-Pd electrodes, which have traditionally been used as electrode materials for thick-film varistors, contain glass frit, the glass in the electrodes diffuses into the varistor film, causing changes in varistor voltage due to load. It had the disadvantage of increasing the

In order to solve the above-mentioned drawbacks of electrodes for thick film varistors, the present invention uses silver (Ag) and chromium (Cr) as electrode materials.
), using a composition consisting of bismuth oxide (Bi203),
The present invention provides a thick film varistor that reduces changes in varistor voltage due to load.

The present invention will be explained below with reference to the drawings.

In the figure, 1 is an electrically insulating substrate, 2 and 2' are electrodes, 3 is zinc oxide powder, and 4 is a binder glass.

5 includes the zinc oxide powder 3 and binder glass 4, and this is called a varistor film.

Further, the varistor shown in the figure is of a sand inch type, and has a structure in which electrodes are provided on both sides of the varistor film 5.

As is well known, the IV characteristic of a varistor is expressed by the following equation.

That is, I-(at)α where ① is the current (ampere) V is the voltage (volt) α is the nonlinear index C is a constant.

I again.

If the voltage when a milliampere current flows is vo, then
vo is electric current ■.

Defined as the varistor voltage in milliamps.

Next, to explain the present invention in detail, the present invention is based on silver (Ag) 6
5% to 99.2% by weight, chromium (Cr) 0.3 to 1
Electrode material consisting of 5% by weight and 0.5 to 20% by weight of bismuth oxide (Bi203) and 10% by weight of ethyl cellulose.
This was kneaded with terpineol containing terpineol to form an electrode ink, which was printed on a porcelain substrate by screen printing, and after drying,
It is fired at 0°C to form a lower electrode.

Next, barium oxide 0.1 mol titanium hexoxide 0 to zinc oxide
．． 5 mol%, nickel oxide 1.0 mol%, molybdenum oxide 061 mol%, magnesium oxide 0.5 mol% added and calcined at 1350°C for 1 hour Powder 40-95
Weight% and glass frit powder to fix it (
Composition where the molar ratio of BaO and B2O3 is 1:2) 5 to 60
% by weight and terpineol containing 10% by weight of ethyl cellulose are kneaded to form a varistor paste, which is printed on an electrode by screen printing, dried and then fired at 840°C to form a varistor film.

The above electrode ink is screen printed on this varistor film, dried and then fired at 760°C to form a sandwich type thick film varistor.

The reason why the composition ranges of the thick-film varistor electrode material and varistor paste are limited as described above in the present invention will be described.

The reason why silver (Ag) is limited to 65% to 99.2% by weight is that if it is less than 65% by weight, it becomes difficult for the solder to adhere to the electrode, so it is not preferable, and if it is more than 99.2% by weight, the load is This is because the improvement effect is weak.

The reason why chromium (Cr) is limited to 0.3 to 15% by weight is that
If it is less than 0.3%, the effect of improving load characteristics is small;
If it exceeds 5% by weight, the resistance value of the electrode will increase, which is undesirable.

The reason why bismuth oxide (Bi203) is limited to 0.5 to 20% by weight is that below 0.5% by weight there is little effect in improving the load characteristics, and when it exceeds 20% by weight, the electrode and hull
This is because the resistance value of the J star thickness increases, which is undesirable.

Although not directly related to the present invention, zinc oxide powder was
The reason why it is limited to 0 to 95% by weight is that below 40% by weight,
This is undesirable because the resistance value of the varistor film increases.

Moreover, if it exceeds 95% by weight, the glass component will decrease and pinholes will easily form, which is undesirable.

Hereinafter, the content of the invention will be described in more detail by giving examples.

Example 1 97.8 mol% zinc oxide (ZnO), 0.1 mol% molybdenum oxide (MoO2), 0.5 mol% titanium oxide (T i02 ), 0.5 mol% magnesium oxide, 1. Add 0 mol% nickel oxide and 0.1 mol% barium oxide and mix well to reduce the powder to 100%
It was formed at a pressure of 5° C. and fired at a temperature of 1350° C. for 1 hour.

The obtained sintered body is coarsely ground and then finely ground in a ball mill to give an average particle size of 4 microns.

As the binder glass, one with a composition of barium oxide (BaO) and boron oxide (B203) of 1:2 in terms of molar ratio was melted at 1200°C, rapidly cooled in water, coarsely pulverized, and then passed through a ball mill. to make a glass frit with an average particle size of 3 microns.

Next, as an additive, 77% by weight of bismuth oxide (B120
3) A composition consisting of 12.7% by weight cobalt oxide, 4.0% by weight magnesium oxide, and 6.3% by weight manganese oxide is thoroughly mixed to an average particle size of 4 microns.

A solid content of 80% by weight containing 60% by weight of the above zinc oxide powder, 24% by weight of glass frit, and 16% by weight of additives, and 20% by weight of a solvent containing 10% by weight of ethyl cellulose were added and kneaded well with a three-stage roller. Make barista paste.

Silver (Ag) 65% by weight, chromium (C
r) 80% by weight of powder consisting of 15% by weight, 20% by weight of bismuth oxide (B12O3) and 10% by weight of ethyl cellulose.
Add 20% by weight of a solvent containing % by weight and knead well with a three-stage roller to obtain an electrode paste.

This electrode paste is first applied onto an alumina substrate by screen printing, dried, and then fired in air through a tunnel furnace maintained at 840° C. for 10 minutes.

Then screen print the barista paste onto the electrodes,
After drying, it was fired at 840°C.

The thickness of the obtained varistor film was 25μ.

Subsequently, the same electrode paste is applied to an electrode area of 1×1 d and fired in the same manner.

The electrical characteristics (vo nonlinear index α) of the obtained sandwich-inch thick film varistor (see drawing).

Load) is shown in Example 1 of Table 1.

Here, α was calculated using the voltage when the current was between 01 mA and 1 mA.

V again. is expressed by the voltage at a current of 1 mA.

Also, the load is 1. V after 500 hours of applying OW.

(1 mA).

Example 2 Zinc oxide powder and glass frit were the same as in Example 1.

A sandwich-type thick film varistor was prepared in the same manner as in Example 1 using a composition consisting of 75% by weight of Ag, 10% by weight of Cr, and 15% by weight of Bi as an electrode paste. It is shown in Example 2 in Table 1.

Example 3 The zinc oxide powder and glass frit were the same as in Example 1.

As an electrode paste, 90% by weight of Ag, 9% by weight of Fe5
A sandwich-type thick film varistor was produced in the same manner as in Example 1 using a composition consisting of 2035% by weight of s B t , and its electrical characteristics (Vo.

α, load) are shown in Example 3 in Table 1.

Example 4 Zinc oxide powder and glass frit were the same as in Example 1.

Using a composition of 99.2% by weight of Ag, 0.3% by weight of Cr, and 2030.5% by weight of Bt as an electrode paste, a sandwich-type thick film varistor was prepared in the same manner as in Example 1, and its electrical properties ( Vo, α, negative load first
It is shown in Example 4 of the table.

Comparative Example 1 Zinc oxide powder and glass frit were the same as in Example 1.

Using a composition consisting of 99.5% by weight of Ag, 2% by weight of CrO, and 2030.25% by weight of Bl as an electrode paste, a sandwich-type thick film varistor was prepared in the same manner as in Example 1, and its electrical characteristics (V ,,α, load) as the second
It is shown in Comparative Example 1 in the table.

Comparative Example 2 Zinc oxide powder and glass frit were the same as in Example 1.

A sandwich-type thick film varistor was prepared in the same manner as in Example 1 using a composition of 55% by weight of Ag, 22.5% by weight of Cr, and 22.5% by weight of PB as an electrode paste, and its electrical characteristics (Vo , α, load) are shown in Comparative Example 2 in Table 2.

Comparative Example 3 Zinc oxide powder and glass frit were the same as in Example 1.

As an electrode paste, Ag-glass type (Ag 90% by weight, PbO-B203-Bi203 type glass 1
A sandwich-type thick film varistor was prepared in the same manner as in Example 1 using an electrode paste consisting of PbO, B2O3, and B1203 (the weight ratio of which was 60:20:10), and its electrical properties were determined. (Vo, α, and negative load are shown in Comparative Example 3 in Table 2.

As is clear from Tables 1 and 2 above, as electrode materials for thick film varistors, silver (Ag) is 65 to 99.2% by weight, chromium (Cr) is 03 to 20% by weight, and bismuth oxide (B 1203) by loading by using an electrode material according to the invention in the range of 0.5 to 20% by weight.

change is significantly improved over conventional Ag-glass based electrodes.

Furthermore, the nonlinearity index α is also improved, making it possible to provide an electrode for a thick film varistor with unprecedented characteristics.

[Brief explanation of the drawing]

The drawing is a cross-sectional view of a thick-film varistor using the electrode material of the present invention. DESCRIPTION OF SYMBOLS 1... Capacity insulating substrate, 2, 2'... Electrode, 3... Zinc oxide powder, 4... Binder glass, 5... ...Ballista membrane.

Claims (1)

[Claims] 1 Silver: 65-99.2% by weight, chromium: 0.3-15%
An electrode material for a thick film varistor, characterized in that the content of bismuth oxide is 0.5 to 20% by weight.