JP2548297B2 - Varistor manufacturing method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for manufacturing a low voltage varistor for protecting semiconductor electronic components from surge current.

Conventional technology Conventionally, the main component is ZnO, Bi ₂ O ₃ , CoO, Sb ₂ O ₃ , Cr ₂ O ₃
Zinc oxide varistors containing several metal oxides as subcomponents have been widely used as devices for absorbing surge due to their excellent voltage non-linearity. This zinc oxide varistor can be applied to various voltage circuits by adjusting the rising voltage (varistor voltage: V _1mA ) per 1 mm of the sintered body. The V _1mA / mm of a zinc oxide type varistor which is currently put into practical use is about 10 to 300V. The varistor voltage of the zinc oxide type varistor depends on the number of ZnO particles in series in the sintered body, and if the thickness of the sintered body is constant, the growth of ZnO particles is hindered in order to increase the varistor voltage. On the contrary, it may be promoted in order to lower it. For example, ZnO, Bi ₂ O ₃ , CoO, S
In a zinc oxide type varistor appropriately prepared from b ₂ O ₃ , SiO ₂ , NiO, Cr ₂ O ₃ , MnO ₂ etc., the size of ZnO particles is 10 to 30 μm.
m, V _1mA / mm is 80 to 300V. On the other hand, the zinc oxide varistor with TiO ₂ added to these components has a low voltage
O particle diameter is 50 to 100 μm, and V _1mA / mm is 20 to 50V.

In recent years, progress has been made in making control circuits for home electric appliances and industrial equipment into microcomputers. As a result, the drive circuit voltage has dropped, and most of them are below 10V. However, semiconductor electronic components such as transistors and ICs are extremely vulnerable to surge currents, and countermeasures against them are essential. Due to such a background, there is a strong demand from the market for a zinc oxide type varistor for a low voltage circuit having a varistor voltage of about 10V. For this purpose, it is necessary to set the ZnO particle diameter to 200 to 300 μm.

As a method for producing the zinc oxide type varistor for the low voltage circuit, for example, the method described in Japanese Patent Publication No. 56-39526 is known. This is ZnO 99.5 mol%, BaCO ₃ 0.5 mol%
After mixing, sinter and hydrolyze Z of 30-200μm
Obtain nO crystals. Furthermore, ZnO, Sb ₂ O ₃ , CoO, MnO ₂ , NiO, Cr ₂
After mixing O _{3 and the} like, sintering is performed to obtain a spinel phase component. This spinel phase component and ZnO crystal are appropriately classified, and 1 to 50% by weight of the spinel phase component is added to a separately prepared ZnO powder.
Add 1-40 wt% of O crystal, mix, mold, sinter, V
A low voltage varistor with _1mA / mm of about 10V is created.

SUMMARY OF THE INVENTION However, according to the conventional method as described above, Zn
After firing to obtain O crystal grains, hydrolysis and classification are required, and since the same steps are required to create the spinel phase component, the number of man-hours is very large, and time and energy loss are high. It had drawbacks. Furthermore, when mixing ZnO crystal grains, spinel phase components, and ZnO powder, it is difficult to mix them uniformly due to the difference in their specific gravities, and the varistor voltage is large due to the uneven distribution of ZnO crystal grains, and there are also the drawbacks that the variation is large. Was there.

The present invention solves such problems, and an object of the present invention is to provide a method of manufacturing a low voltage varistor for protecting a semiconductor electronic component from a surge current.

Means for Solving the Problems In the present invention, in order to solve the above-mentioned conventional problems, a granulated powder of a zinc oxide varistor is used as a base material, and a granulated powder composed of MgO separately prepared in a spray dryer is granulated. It is characterized in that it is added as a growth promoter and mixed, molded and sintered.

Action By adopting the above method, 80-30
ZnO crystal grains of 0 μm are dispersedly arranged, and a low-voltage varistor having an excellent voltage non-linearity index can be easily obtained.

Examples Hereinafter, details of the present invention will be described based on Examples.

First, ZnO powder was mixed with Bi ₂ O ₃ , CoO, MnO ₂ , Sb ₂ O ₃ , NiO, Cr.
₂ O ₃ and TiO ₂ are 1.00 mol%, 0.50%, 1.00 mol%, 0.
05 mol%, 0.5 mol%, 0.10 mol%, 1.00 mol% are added, and a binder and water are added thereto and mixed to obtain a slurry. This slurry is dried and granulated with a spray dryer to obtain a base material. Next, as a grain growth promoter, MgO powder crushed to an average particle size of 1.5 μm is mixed with a binder and water, dried with a spray dryer and granulated to obtain granulated powder. At this time, the drying conditions of the spray dryer are appropriately changed and mesh cutting is performed to obtain an average particle size of 5 μm, 10 μm, 25 μm, 50 μm, 75
Five types of grain growth promoters having a size of μm were obtained. An appropriate amount of this grain growth promoter was mixed with a base material to obtain a raw material powder for a low voltage varistor. This raw material powder was pressure-molded and then sintered at 1250 ° C. for 1 to 5 hours, and the varistor voltage, the voltage non-linearity index, etc. were examined.

Figures 1 to 5 show the average particle size of 5μm, 10μm, 25μm,
The varistor voltage (V _1mA / mm) and the voltage non-linearity index (α) per unit thickness of the sample to which the grain growth promoter (MgO) mesh-cut to 50 μm and 75 μm were added in the concentration range of 0.03 to 10.00 mol% It is a characteristic view which shows a relationship. As a comparative study example, the base material and the grain growth promoter are not separated in FIG.
The characteristics of the sample in which 0.03 to 10.00 mol% of MgO was added to the starting material are shown.

It can be seen from FIG. 1 that in the sample using the grain growth promoter having an average grain size of 5 μm, V _1mA / mm decreases and ZnO grain growth occurs when the addition amount is 0.1 to 3.0 mol%. But,
At the same time, α also drops sharply, making it unsuitable as a low-voltage varistor. On the other hand, from Fig. 2 to Fig. 4, the average particle size is 10 to 50 µm.
In the sample using the grain growth promoter of No. 3, when the addition amount is 0.03 to 3.00 mol%, the target V _1mA / mm decreases to about 10V, and α
Shows a good value of 30 to 50. The addition amount is 3.0 mol%
When V is _exceeded , V _1mA / mm rather rises and α also decreases. It can be seen from FIG. 5 that when a grain growth accelerator having an average grain size of 75 μm is used, V _1mA / mm is reduced, but α is reduced to about 20. From FIG. 6, when the conventional method in which the base material and the grain growth promoter are not added separately is used, the MgO addition amount is 0.3 to
It can be seen that at 1.0 mol%, α drops to about 20 although α drops to about 10V. From the above results, when the average particle size of the grain growth promoter is 10 to 50 μm and the addition amount is 0.1 to 3.0 mol%,
V _{1 mA} / mm to about 10V, it is possible to manufacture a low-voltage varistor Arufa30～50.

As described above, according to the present invention, a granulated powder having varistor characteristics, by adding a grain growth promoter composed of MgO, low varistor voltage, high voltage non-linearity zinc oxide varistor It can be manufactured very easily.

Incidentally, ZnO in the substrate in the present _{embodiment, Bi 2 O 3, CoO,} MnO 2, Cr 2
Although O ₃ , NiO, Sb ₂ O ₃ and TiO ₂ are used, other metal oxides such as Al ₂ O ₃ , SiO ₂ and Pb which improve the characteristics as a varistor are used.
Even if O, SnO ₂ , Ag ₂ O, Pr ₆ O ₁₁ or the like is used, the effect of the present invention does not change.

[Brief description of drawings]

1 to 5 are characteristic diagrams of the present invention example and the reference example, respectively, and the average particle size is 5 μm, 10 μm, 25 μm, 50 μm, 75 μm, respectively.
Grain growth promoter addition amount and V when using other grain growth promoter
FIG. 6 is a characteristic diagram showing the relationship between _{1 mA} / mm and α, and FIG. 6 is a characteristic diagram of a varistor manufactured by a conventional manufacturing method.

Claims (2)

(57) [Claims] 1. A sintered body itself is based on a granulated powder containing zinc oxide as a main component having varistor characteristics, and MgO granulated to 10 to 50 μm by a spray dryer is used as a grain growth promoter.
A method for manufacturing a varistor, which comprises molding and sintering raw material powder obtained by mixing the above grain growth promoter with the above base material. 2. The method for producing a varistor according to claim 1, characterized in that the raw material powder contains 0.1 to 3.0 mol% of MgO.