JPH0897009A - Manufacture of zinc oxide varistor - Google Patents

Abstract

PURPOSE: To improve limited voltage ratio characteristics by a method wherein the electrode material, containing at least an organic metal compound selected from aluminum, indium, gallium and germanium, is diffused into an element from the surface of a fired varistor element. CONSTITUTION: The mixture, formed by kneading an aluminum organic metal compound into silver paste, is used as electrode material. First, silver paste is obtained by kneading 5.0wt.% lead borosilicate glass first, 65.0wt.% silver power and 30wt.% vehicle. Then, as an aluminum organic metal compound, the prescribed quantity of aluminum-sec-butoxide is dissolved into n-butyl carbitol, then silver paste is added thereto, and they are mixed by a mixer. Then, electrode material (silver paste) is screen-printed on both surfaces of a zinc oxide varistor sintered element 1 of 1.5mm in thickness in such a manner that the diameter of 10mm is obtained, baked at 800 deg.C for ten minutes, and an electrode 2 is formed.

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 zinc oxide varistor used for 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.

Since the semiconductor electronic components used in these control circuits are destroyed when an abnormally high voltage (surge) is applied, it is essential to take measures against them. Varistors are generally used as a countermeasure. Among them, zinc oxide varistors are widely used for protecting various electronic devices from abnormally high voltage because of their excellent voltage nonlinearity and surge absorbing ability.

Conventionally, a zinc oxide varistor in which at least two electrodes are provided on the surface of a varistor element containing zinc oxide as a main component is widely known. The material of the electrode is disclosed in, for example, Japanese Patent Application Laid-Open No. 62-290104, and its contents are as follows.

That is, lead borosilicate glass powder containing 50.0 to 85.0% by weight of PbO, 10.0 to 30.0% by weight of B ₂ O ₃ , and 5.0 to 25.0% by weight of SiO _2. Was weighed 5.0% by weight, and a vehicle in which ethyl cellulose was dissolved in butyl carbitol (30.0% by weight)
It was kneaded together with Ag powder (65.0% by weight) to prepare a silver paste, which was used as an electrode material for a zinc oxide varistor.

Then, this electrode material was applied to the surface of the burned varistor element and heated to form an electrode.

[0007]

Although the zinc oxide varistor has excellent limiting voltage ratio characteristics,
In recent years, further improvement of the limiting voltage ratio characteristic has been demanded. Therefore, an object of the present invention is to provide a method for manufacturing a zinc oxide varistor that meets the above-mentioned requirements and has further improved limiting voltage ratio characteristics and less variation in characteristics.

[0008]

In order to achieve this object, the present invention provides a varistor which has been obtained by firing an electrode material containing an organometallic compound of at least one element selected from aluminum, indium, gallium and germanium. It is applied to the element and diffused from the surface into the varistor element.

[0009]

With the above structure, the resistance value of the zinc oxide particles is low.

Generally, the voltage non-linearity of a zinc oxide varistor becomes small in a high current region, and the resistance value R of zinc oxide particles, the voltage value V between electrodes and the current value I can be approximated to V = R * I. Therefore, since the resistance value R of the zinc oxide particles becomes small, the voltage generated between the electrodes becomes small even if the surge voltage enters.

Thus, for example, when a surge voltage enters the circuit as shown in FIG. 4, the varistor 5 produces a voltage V1, but the voltage V1 produced in the varistor 5 is smaller than the surge withstand voltage V6 of the protected circuit 6. By setting it, the voltage applied to the protected circuit 6 can be limited (the voltage V1 generated in the varistor 5 at the time of this surge voltage intrusion).
Called the limiting voltage).

Therefore, when a varistor having a small resistance value of zinc oxide particles is used, the voltage generated in the varistor 5 at the time of surge voltage intrusion decreases from the conventional V1 to V2 as shown in (FIG. 5). The margin of the protection circuit 6 with respect to the surge withstand voltage V6 is increased, and the reliability is improved.

Further, the organometallic compound is dissolved in the vehicle in the electrode material paste and uniformly dispersed, so that a zinc oxide varistor having a small variation in characteristics such as a limiting voltage ratio can be obtained.

[0014]

EXAMPLE In this example, the electrode material is characterized. That is, in the present embodiment, the one obtained by kneading the organometallic compound of aluminum in the silver paste was used, and these will be described in detail below.

First, 5.0 wt% of lead borosilicate glass free
(70.0% by weight of PbO, B ₂O₃Is 15.0 weight
%, SiO₂15.0% by weight) and 65.
0 wt% silver powder was added to 30.0 wt% vehicle (n-bu
Ethylcellulose dissolved in tilcarbitol)
And kneaded together to obtain a silver paste.

A predetermined amount of aluminum tri-sec-butoxide (Chemical Formula 1) as an organometallic compound of aluminum was weighed in this silver paste according to the composition table of (Table 1) below, and this was dissolved in n-butylcarbitol. afterwards,
The mixture was added to the above silver paste and mixed by a grinder.

On the other hand, as a conventional silver paste, an electrode material was prepared without adding the above aluminum tri-sec-butoxide (Chemical Formula 1).

[0018]

[Chemical 1]

[0019]

[Table 1]

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 ₃ O ₄ ), manganese oxide (Mn
O ₂ ), nickel oxide (NiO), titanium oxide (Ti
0.5 mol% of O ₂ ) and antimony oxide (Sb ₂
O ₃ ), chromium oxide (Cr ₂ O ₃ ) 0.1 mol%, Al ₂ O ₃ 0.005 mol%, and the balance zinc oxide (Z
nO) zinc oxide varistor sintered body (varistor element 1 of FIG. 3, disk-shaped, diameter 13 mm, thickness 1.5 m
m) was prepared. The zinc oxide varistor electrode material was screen-printed on both surfaces of this sintered body so that the diameter was 10 mm, and baked at 800 ° C. for 10 minutes (electrode 3 shown in FIG. 3).
Was formed. Next, after fixing the upper end of the lead wire 3 shown in (FIG. 2) by soldering, the outer circumference of the varistor element 1 is covered with an epoxy-based insulating resin 4, and then the lead wire 3 shown in FIG. A sample was obtained in which only the lower end was pulled out of the insulating resin 4.

When the surface of the varistor element 1 is coated with the above electrode material and then heated, aluminum in the electrode material penetrates into the varistor element 1 and exhibits the effects described below.

The voltage ratio of the sample thus obtained

[0023]

[Outer 1]

The limiting voltage ratio (V _5A / V _1mA ) is shown in (Table 2) below. This voltage ratio was obtained by measuring with a DC constant current power supply.

The above voltage ratio

[0026]

[Outside 2]

Shows a voltage non-linearity, and the smaller the voltage ratio than the sample 1 of the conventional example, the smaller the leakage current until reaching the varistor voltage. That is, the V _{1 m A} indicates the voltage (varistor voltage) when a 1mA current flows between the electrodes 2,

[0028]

[Outside 3]

Those having a small value of are those in which a large amount of leakage current flows from a low voltage, which is not preferable.

The limiting voltage ratio is the voltage generated in the varistor element 1 when a surge voltage invades (current waveform 8/2 in this case).
It is the ratio of 0 μS, the voltage when a current with a peak value of 5 A flows to the varistor element 1) and the varistor voltage (V _1mA ). Therefore, the semiconductor electronic components used in the protected circuit 6 can be prevented from being destroyed.
In the above embodiment, the number of samples is 10 in each lot.

[0031]

[Table 2]

From the above (Table 1) and (Table 2), the influence of the content of the organometallic compound of aluminum in the electrode material on the voltage ratio (voltage nonlinearity) and the limiting voltage ratio characteristic will be considered.

If the amount of the organometallic compound of aluminum added is 10 ppm or more, the limiting voltage ratio characteristic becomes good.
Further, in the composition system exceeding 1000 ppm, the voltage ratio (voltage nonlinearity) is deteriorated. Therefore, it is understood that the addition amount of aluminum tri-sec-butoxide (Chemical formula 1) to the electrode material is preferably 10 to 1000 PPppm in terms of Al.

Further, aluminum is used as Al and Al ₂ O ₃
It can be seen that the characteristic variation is significantly reduced by adding aluminum by the method of the present invention as compared with the sample added in the form of.

In this embodiment, aluminum tri-sec-
Although butoxide was used, it was confirmed that the same effect was exhibited by using other organometallic compounds containing aluminum.

Further, it was confirmed that the same effect can be obtained by using an organometallic compound of indium, gallium or germanium instead of aluminum.

The electrode material for forming the electrode 2 is not limited to the paste containing silver as a main component, and other metal paste such as palladium may be used.

Further, in this embodiment, ZnO, Bi ₂ O ₃ , Co ₃ O ₄ , MnO ₂ , NiO, S were used as the sintered body for evaluation.
A zinc oxide varistor of the system consisting of b ₂ O ₃ , Cr ₂ O ₃ and Al ₂ O ₃ was used, but Pr ₆ O ₁₁ , CaO, BaO, Mg
Even if the electrode material for a zinc oxide varistor according to the present invention is applied to a zinc oxide varistor containing O, K ₂ O, SiO _2, etc., the effect remains the same.

[0039]

As described above, the aluminum of the present invention,
An electrode material containing at least one organometallic compound selected from indium, gallium and germanium,
By diffusing the baked varistor element surface into the varistor element, a limiting voltage ratio characteristic is improved and a zinc oxide varistor with a small characteristic variation can be obtained. As a result, it is possible to limit the voltage rise of the protected circuit at the time of surge voltage intrusion and prevent the destruction of the semiconductor electronic component used in the protected circuit.

[Brief description of drawings]

FIG. 1 is a front view showing an embodiment of a zinc oxide varistor of the present invention.

FIG. 2 is a sectional view of the zinc oxide varistor shown in FIG.

3 is a sectional view showing a varistor element of the zinc oxide varistor shown in FIG.

FIG. 4 is a circuit diagram showing a usage example of a zinc oxide varistor.

FIG. 5 is a characteristic diagram showing an example of current-voltage characteristics of a zinc oxide varistor.

[Explanation of symbols]

 1 Varistor element 2 Electrode 3 Lead wire 4 Insulating resin 5 Varistor

Claims (2)

[Claims] 1. A varistor element containing zinc oxide as a main component is coated with an electrode material containing an organometallic compound of at least one element selected from aluminum, indium, gallium, and germanium. Manufacturing method of zinc oxide varistor. 2. The addition amount of the organometallic compound of aluminum, indium, gallium, and germanium in the electrode material is 10 to 1000 p in terms of Al, In, Ga, Ge.
It is pm, The manufacturing method of the zinc oxide varistor of Claim 1 characterized by the above-mentioned.