JPH06208908A - Electrode material for zinc oxide varistor - Google Patents

Abstract

PURPOSE:To protect a zinc oxide varistor against fracture by containing zinc oxide whiskers having specified fiber length or less by specific range of wt.% for the content of metal in electrode paste thereby preventing the electrode from peeling off the element due to abnormally high voltage. CONSTITUTION:The electrode material for zinc oxide varistor is mainly composed of zinc oxide and a sintered body itself has varistor characteristics where zinc oxide whiskers are contained by 01-10.0wt.% for the content of metal in electrode paste. Fiber length(length of needle) of the zinc oxide whisker is set at 10mum or less. The electrode paste is then printed to a zinc oxide varistor element and baked. Consequently, the electrode can be prevented from peeling off the element due to abnormally high voltage(surge) and the zinc oxide varistor can be protected against fracture.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zinc oxide varistor electrode material used for the purpose of protecting various electronic devices from abnormally high voltage.

[0002]

2. Description of the Related Art In recent years, highly integrated control circuits for consumer and industrial equipment have been rapidly developed, and semiconductor electronic components used for these control circuits are extremely vulnerable to abnormal high voltage (surge). Has become essential. Varistors are generally used as a countermeasure. Among them, the zinc oxide varistor is widely used for the purpose of protecting various electronic devices from abnormal high voltage (surge) because of its excellent voltage nonlinearity and surge absorbing ability.

Conventionally, as an electrode material used for the above zinc oxide varistor, for example, JP-A-62-290104 is used.
The gazette and the like are disclosed, the contents of which are as follows. That is, PbO is 50.0 to 85.0% by weight,
B ₂ O ₃ is 10.0 to 30.0 wt%, SiO ₂ is 5.0
~ 25.0% by weight of lead borosilicate glass powder was weighed 5.0% by weight, and A was added to a vehicle (30.0% by weight) in which ethyl cellulose was dissolved in butyl carbitol.
This is kneaded with g powder (65.0% by weight) to prepare a silver paste, which is used as an electrode material for a zinc oxide varistor.

[0004]

However, when the above-mentioned conventional electrode material for zinc oxide varistor containing glass powder made of lead borosilicate glass is used for a zinc oxide varistor, the silver electrode is oxidized by an abnormal high voltage (surge). There is a problem that the zinc oxide varistor itself is easily broken by peeling from the interface of the zinc varistor element (hereinafter referred to as element).

The present invention is intended to solve the above-mentioned conventional problems, and an object thereof is to provide an electrode material for a zinc oxide varistor, which is used in a zinc oxide varistor and exhibits excellent reliability.

[0006]

In order to achieve the above object, the electrode material for a zinc oxide varistor according to the present invention contains zinc oxide whiskers in an amount of 0.1 to 10.0% by weight based on the metal content in the electrode paste. It is configured to include.

[0007]

Therefore, by using the electrode material for a zinc oxide varistor having the above structure as an electrode of the zinc oxide varistor, the zinc oxide whiskers bite into the electrode and the element like a wedge and generate an action as an anchor, whereby the varistor itself. It is possible to improve the fatal issue of destruction of.

[0008]

EXAMPLE An example of the present invention will be described in detail below.

First, the preparation of glass powder added to the electrode material for zinc oxide varistor will be described. PbO 70.
0 wt%, B ₂ O ₃ 15.0 wt%, SiO ₂ 15.
After weighing 0% by weight, mixing and pulverizing with a ball mill, the borosilicate lead glass was obtained by melting in a platinum crucible at a temperature of 1000 ° C to 1500 ° C, rapidly cooling and vitrifying.

The lead borosilicate glass was roughly pulverized and then finely pulverized with a ball mill to obtain lead borosilicate glass powder. Next, this lead borosilicate glass powder (5.0% by weight) was added to a vehicle (30.0% by weight) in which ethyl cellulose was dissolved in butyl carbitol to obtain a silver powder (65.50 by weight).
0%) and kneaded in a three-roll mill to obtain a silver paste.

A predetermined amount of zinc oxide whiskers shown in the following (Table 1) was added to the silver paste, and the mixture was kneaded with a three-roll mill to obtain a zinc oxide varistor electrode material.

As a comparative study example, a conventional electrode material for a zinc oxide varistor in which zinc oxide whiskers were not added to the silver paste was also prepared.

In order to evaluate the electrode material for a zinc oxide varistor manufactured as described above, bismuth oxide (Bi ₂ O ₃ ),
Cobalt oxide (Co ₂ O ₃ ), manganese oxide (Mn
O ₂ ), nickel oxide (NiO), antimony oxide (S
b ₂ O ₃ ), chromium oxide (Cr ₂ O ₃ ) 0.5 mol%, Al ₂ O ₃ 0.005 mol%, and the balance zinc oxide (ZnO) (diameter 13 mm, thickness 1 0.5 mm)
Prepared. Screen printing the electrode material for zinc oxide varistor to a diameter of 10 mm on both sides of this element,
A baked electrode was formed at 10 ° C. for 10 minutes, a lead wire was soldered, and then resin-molded to obtain a sample.

To the sample thus obtained, a shock current having a standard waveform of 8/20 μS and a peak value of 5000 A was repeatedly applied in the same direction at intervals of 30 seconds, and the number of broken zinc oxide varistor was measured. (Table 1) of. The number of samples is 20 in each lot.

[0015]

[Table 1]

First, from Table 1, the relationship between the content of zinc oxide whiskers in the electrode material for zinc oxide varistor and the effect of preventing destruction of the zinc oxide varistor will be considered. With the conventional zinc oxide varistor electrode material that does not contain zinc oxide whiskers, when an impact current (surge current) was repeatedly applied under the above conditions, all zinc oxide varistor peeled from the interface between the silver electrode and the element by 4 times. And destroyed.

On the other hand, 0.1% by weight of zinc oxide whiskers
Using the zinc oxide varistor electrode material added above,
The zinc oxide whiskers bite into the silver electrode and the element like a wedge to generate an anchor effect, thereby improving the adhesive strength and preventing the varistor from being destroyed by an impact current. When an electrode material for zinc oxide varistors containing 10.0% by weight or more of zinc oxide whiskers is used, zinc oxide whiskers are deposited on the surface of the silver electrode, which deteriorates the solder wettability.
Furthermore, zinc oxide whiskers having a fiber length (length of the needle-shaped portion) of more than 10 μm have poor dispersibility in silver paste and poor printability of silver paste.

As is clear from the results of the above-mentioned examples, the optimum addition amount of zinc oxide whiskers in the electrode material for zinc oxide varistors is in the range of 0.1 to 10.0% by weight. The fiber length (the length of the needle-shaped portion) is preferably 10.0 μm or less.

In this embodiment, Ag is used as the electrode paste.
Although a paste was used, Ag-Pd, Pb, Ni, Cu,
It was confirmed that the same effect can be obtained by adding zinc oxide whiskers to a metal paste such as Al or Pt.

Furthermore, in this embodiment, lead borosilicate type glass was used as the glass powder in the electrode material for zinc oxide varistor, but glass powders of other compositions such as bismuth borosilicate type glass may also be used. The effect is the same. Further, although the case where the content of the glass powder is 5.0% by weight has been described, the effect of the present invention remains unchanged as long as the content is 1.0 to 30.0% by weight.

In this example, Z was used as the sintered element for evaluation.
nO, Bi₂O₃, Co₂O₃, MnO ₂, NiO, Sb₂O
₃, Cr₂O₃, Al₂O₃Zinc oxide varistor consisting of
Was used, Pr₆O₁₁, CaO, BaO, MgO, K₂
O, SiO₂According to the present invention to a zinc oxide varistor including
Even if the electrode material for zinc oxide varistor is applied, the effect changes.
There is no.

[0022]

As described above, the zinc oxide varistor electrode material of the present invention contains zinc oxide whiskers in an amount of 0.1 to 10.0 wt% with respect to the metal content of the electrode paste. By printing and baking this electrode paste on a zinc oxide varistor element, abnormal high voltage (surge)
It is possible to prevent the electrode from peeling off from the element and prevent the zinc oxide varistor itself from being destroyed.

Claims (2)

[Claims] 1. As an electrode material used for a sintered body containing zinc oxide as a main component and the sintered body itself having varistor characteristics, zinc oxide whiskers are added in an amount of 0.1 to 10. An electrode material for a zinc oxide varistor, which contains 0% by weight. 2. The zinc oxide whiskers have a fiber length (length of a needle-shaped portion) of 10 μm or less.
The electrode material for a zinc oxide varistor described.