JP2558811B2 - 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, a zinc oxide type varistor mainly composed of ZnO and containing several kinds of metal oxides such as Bi ₂ O ₃ , CoO, Sb ₂ O ₃ and Cr ₂ O ₃ as an auxiliary component has been excellent. Due to the voltage nonlinearity, it has been widely used as a device for absorbing surge. This zinc oxide type varistor has a rising voltage (varistor voltage: V
_It can be applied to various voltage circuits by adjusting _1mA ). V of zinc oxide type varistor currently in practical use
_1mA / mm is about 10-300V. 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, Sb ₂ O ₃ ,
In a zinc oxide type varistor appropriately adjusted from SiO ₂ , NiO, Cr ₂ O ₃ , MnO _2, etc., the size of ZnO particles is about 10 to 30 μm, and V _1mA / mm is 80 to 300V. On the other hand, the T
The voltage of the zinc oxide type varistor to which iO ₂ is added becomes low, and the ZnO particle size becomes 50 to 100 μm and V _1mA / mm becomes 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, a method described in Japanese Patent Publication No. 56-39526 is known. This is mixed with 99.5 mol% ZnO and 0.5 mol% BaCO ₃ and then sintered and hydrolyzed to 30-200 μm.
To obtain a ZnO crystal. Furthermore, ZnO, Sb ₂ O ₃ ,, CoO, MnO ₂ , NiO, Cr
After mixing ₂ 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% by weight 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, hydrolysis and classification are required to obtain O crystal grains, and the same steps are required to create the spinel phase component, so 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 granules made of Bi ₂ O ₃ and TiO ₂ separately prepared for this are granulated powder. The feature is that powder is added as a grain 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 contains Bi ₂ O ₃ , CoO, MnO ₂ , Sb ₂ O ₃ , NiO and Cr ₂ O _3.
0.50 mol%, 0.50 mol%, 1.00 mol%, 0.05 mol%, 0.50 mol% and 0.10 mol%, respectively, and a binder and water are added and mixed to obtain a slurry. This slurry is dried and granulated with a spray dryer to obtain a base material. Next, a binder and water are added to and mixed with the powder of Bi ₂ O ₃ and TiO ₂ mixed in an appropriate ratio as a grain growth promoter, dried by a spray dryer and granulated to obtain a granulated powder. At this time, the drying condition of the spray dryer was appropriately adjusted to change the particle size distribution of the granulated powder. Mesh-cut this granulated powder to 5μm, 10μm, 25μm,
Five kinds of grain growth promoters of 50 μm and 75 μm were prepared. Then, the base material and the grain growth promoter were mixed in appropriate amounts to obtain a raw material powder for a low voltage varistor. After pressing this raw material powder into a disk shape,
Various characteristics such as varistor voltage and voltage non-linearity index were investigated by using a sample by sintering at 50 ° C and forming ohmic electrodes on both end surfaces of the sintered body.

FIG. 1 is a characteristic diagram showing the composition of the grain growth promoter added to the base material, that is, the relationship between Bi / Ti and V _1mA / mm, α. Here, the concentration of the added grain growth promoter (total concentration of TiO ₂ and Bi ₂ O ₃ concentration) was 0.5 mol% in the raw material powder composition, and the grain size was 25 μm.
Is. From Fig. 1, it can be seen that at V _1mA / mm, Bi / Ti decreases at 1.2 or more, but when it exceeds 1.5, α decreases. FIG. 2 shows the limiting voltage ratio (V _10A / V _1mA ) of the same sample (current waveform 8/20 μs), and Bi / Ti is 1.2 or more, which shows a good limiting voltage characteristic. From the above results, it is found that the optimum value of Bi / Ti of the grain growth promoter is 1.2 to 1.5.

FIG. 3 is a characteristic diagram showing the relationship between the average particle size of the grain growth promoter and V _1mA / mm, α. Here, the value of Bi / Ti of the grain growth promoter is 1.33, and the concentration of the grain growth promoter is 0.5 mol%. When the average particle size of the grain growth promoter is 10 to 50 μm, V _1mA / m
It can be seen that m drops to 15 V or less and α also shows a value of 40 or more. FIG. 4 is a characteristic diagram showing the relationship between the amount of grain growth promoter added and V _1mA / mm, α. Here, the value of Bi / Ti of the grain growth promoter is 1.33, and the average grain size is 25 μm. And, V _1mA / mm is 8.5 to 15 when the amount of grain growth promoter added is 0.1 to 3.0 mol%.
It can be seen that the value decreases to 0 V and α also exhibits a favorable value of 35 or more.

Fig. 5 shows the conversion value of the amount of grain growth promoter added when the conventional method of adding the grain growth promoter and the substrate without separating them (0.5 mol% of Bi ₂ O ₃ contained in the substrate is _Excluded amount) and V _1mA / mm,
It is a characteristic view which shows the relationship of (alpha). From Fig. 5, the addition amount is 3.
At 0 mol%, V _1mA / mm decreases to about 15V, but does not decrease to the target of 10V, and α also tends to decrease with increasing addition amount.

From the above results, the grain growth promoter Bi / Ti ratio 1.2 to 1.5,
When the average particle size is 10 to 50 μm and the addition amount is 0.1 to 3.0 mol%, V _1mA
It is possible to manufacture a low voltage varistor having the characteristics of / mm 8.5 to 15.0 V and α about 40.

As described above, according to the present invention, the granulated powder having varistor characteristics is added with a grain growth promoter composed of a Bi ₂ O ₃ and TiO ₂ mixture, so that the varistor voltage is low and the voltage nonlinearity is high. A zinc oxide varistor having high properties can be manufactured extremely easily.

In this example, ZnO, Bi ₂ O ₃ , CoO, MnO ₂ and Cr were used as the base material.
₂ O ₃ , NiO, Sb ₂ O ₃ , TiO ₂ was used, but other metal oxides that improve the characteristics as a varistor, such as SiO ₂ , PbO, SnO ₂ , and Al.
_{Even if 2} O ₃ , MgO, Ag ₂ O, Pr ₆ O ₁₁ or the like is used, the effect of the present invention does not change.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 to FIG. 4 are characteristic charts of the present invention example and reference example, and FIG. 1 is a characteristic chart showing the relationship between the grain growth promoter composition and V _1mA / mm and α. FIG. 2 is a characteristic diagram showing the relationship between the grain growth promoter composition and the limiting voltage ratio, and FIG. 3 is a characteristic diagram showing the relationship between the average particle size of the grain growth promoter and V _{1 mA} / mm and α, FIG. Is a characteristic diagram showing the relationship between the amount of grain growth promoter added and V _{1 mA} / mm and α, and FIG. 5 is a characteristic diagram of a varistor manufactured by a conventional manufacturing method.

Claims (2)

(57) [Claims] 1. A mixture of Bi ₂ O ₃ and TiO ₂ which is granulated to have a particle size of 10 to 50 μm by a spray dryer, which is a granulated powder containing zinc oxide as a main component having a varistor characteristic. A method for producing a varistor comprising: forming a raw material powder by mixing the above-mentioned granulated powder as a grain growth promoting agent, mixing the above-mentioned base material with the above grain growing promoting agent, and molding and firing the raw material powder. 2. The concentration of the grain growth promoter (Bi ₂ O ₃ + TiO) added to the base material when the Bi / Ti ratio of the grain growth promoter is in the range of 1.2 to 1.5.
₂ ) is 0.1-3.0 mol%, The manufacturing method of the varistor of Claim 1 characterized by the above-mentioned.