JPH02241005A - Manufacture of zinc oxide type varistor - Google Patents

Abstract

PURPOSE:To stabilize varistor voltage and surge resistance characteristics by a method wherein a baking sheath having one or more penetrating hole in the bottom surface is used, a zinc oxide type varistor is mounted on the bottom surface of the baking sheath and baked, thereby uniformizing bismuth partial pressure in the baking sheaths of the upper and the lower parts. CONSTITUTION:A baking sheath 2 provided with one or more penetrating holes 3 on the bottom surface is used, and a zinc oxide type varistor 1 is mounted on the bottom surface of the baking sheath 2 and baked. For example, a molded body 1 formed by using powder wherein zinc oxide exhibiting varistor characteristics by baking is used as main component and bismuth oxide is contained as additive material. The molded body whose thickness and diameter are 1.2mm and 15mm, respectively, are stacked by 20 stages. The baking sheath 2 is provided with penetrating holes, whose diameters are 10mm, at four corners of the bottom surface. Two stages of the baking sheaths 2 are stacked. A sheath lid 4 is put on the upper stage sheath 2; a spacer 5 is arranged under the lower sheath 2, in order that gas in the sheath and atmosphere in a furnace may be able to sufficiently circulate; the molded body 1 is baked at a maximum temperature 1300 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a high-performance zinc oxide type varistor for protecting semiconductor electronic components and the like from surges.

Conventional Technology Conventionally, when firing a disc-shaped zinc oxide type varistor, it was placed inside a box-shaped firing pod with no through holes on the bottom.

Molded bodies whose main component is zinc oxide, which exhibits varistor properties when fired, are piled up in one layer or in bulk, and then fired.

Problems to be Solved by the Invention However, when firing is performed using a conventional firing pod, bismuth oxide in the upper and lower atmospheres of the pod is affected by bismuth oxide scattered from the compact during firing. There is a difference in the partial pressure, which causes a difference in the bismuth concentration in the sintered body after firing, which causes variations in the varistor voltage (Vta + A/kaku) per unit thickness of the sintered body and in the surge resistance characteristics. There was a problem.

The present invention solves the above-mentioned conventional problems, and is a method for manufacturing a zinc oxide type varistor that can stabilize the varistor voltage and surge resistance characteristics by equalizing the bismuth partial pressure in the upper and lower parts of the firing pod. The purpose is to provide the following.

Means for Solving the Problems In order to solve the above problems, the method for manufacturing a zinc oxide type varistor of the present invention uses a firing pod having one or more through holes on the bottom surface, A zinc oxide type varistor is placed on the surface and fired.

Effect: By the method described above, one or more through holes are provided in the bottom of the firing pod used when firing zinc oxide type varistors, and the gas inside the firing pod is circulated with the atmosphere in the furnace through the through holes. Therefore, the bismuth partial pressure in the atmosphere within the firing pod can be lowered and made uniform, and the varistor voltage value and surge withstand characteristics of the zinc oxide type varistor can be stabilized.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view for explaining a method of manufacturing a zinc oxide type varistor according to an embodiment of the present invention. In Fig. 1, the molded body 1 is molded from a powder whose main component is zinc oxide, which exhibits varistor properties when fired, and which contains bismuth oxide as an additive, and has a thickness of 1.2 mm and a diameter of It is made up of 20 stacks of 15 mm diameter molded wafers, and is designed so that the varistor voltage (V111A value) will be about 200 V when fired. The baking pod 2 has a height of 50 mm, a length and a width of 70 mm each, and a wall thickness of 4 mm.The four corners of the bottom have diameters of lO-φ.
A through hole 3 is provided. The firing pods 2 are stacked in two layers, a pod lid 4 with a wall thickness of 4 mm is placed on top of the upper pod 2, and the gas inside the pod and the atmosphere in the furnace are placed under the lower pod 2. A spacer 5 was placed to allow sufficient circulation of the molded body 1, and the molded body 1 was fired at a maximum temperature of 1300°C.

Further, for a comparative experiment, a circumferential firing pod without a through hole in the bottom was prepared, and the molded body 1 was fired under circumferential firing conditions. For sintered bodies manufactured by these methods.

After numbering 1 to 20 from the top and measuring the amount of Bi on the surface of the sintered body using fluorescent X-rays, electrodes mainly composed of silver were baked on both sides of the sintered body and lead wires were soldered. The entire surface of the sintered body was covered with a thermosetting resin.

Regarding the zinc oxide type varistor element thus obtained, the varistor voltage (VisA/■) value was measured, and
As the surge withstand characteristics, the peak value of 8/20 μs, 250
Table 1 shows the amount of Bi remaining on the surface of the sintered body by fluorescent X-rays, the varistor voltage (■1 .＾l■) value and rate of change of varistor voltage (Δ
V□1^ value).

〉〉〈Table 1) Residual amount of Bi, Vllll^/ll1l value and Δ
Comparison of v1゜＾ values According to Table 1, the varistor voltage (vl
, ^/■) values and surge resistance were observed,
In addition, these effects are due to the residual amount of bismuth (Bi) in the sintered body.
It can be seen that it is highly dependent on the amount

In the above experiment, the molded bodies were stacked and fired, but the same effect can be obtained even when the molded bodies are stacked and fired in bulk.

Effects of the Invention As described above, according to the present invention, by using a firing pod having a through hole in the bottom surface, the gas in the pod circulates with the atmosphere in the furnace through the through hole. Since the bismuth partial pressures above and below within the firing pod are reduced and dispersed, it is possible to manufacture a zinc oxide type varistor element with a stable varistor voltage value and improved surge resistance.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a firing sheath for explaining a method of manufacturing a zinc oxide type varistor according to an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Molded object, 2... Saya for baking, 3... Through hole, 4... Sapphire lid, 5... Spacer. Agent Yoshihiro Morimoto

Claims (1)

[Claims] 1. A method for manufacturing a zinc oxide type varistor, which uses a firing pod having one or more through holes on the bottom surface, and places a zinc oxide type varistor on the bottom surface of the firing pod and fires it.