JPH05190307A - Production of varistor - Google Patents

Abstract

PURPOSE:To evade the dispersion of varistor voltages, non-linear coefficients, etc., and improve a life characteristic and surge resistance by uniformizing the temperature and atmosphere at the time of thermally diffusing Na oxide, etc., in a semiconductor porcelain and removing the adhered Na compound. CONSTITUTION:When a varistor is manufactured by thermally diffusing Na oxide or Na compound in reduced and sintered semiconductor porcelain, the semiconductor porcelain and the Na oxide or the Na compound are stored in a magnetic container so as to allow thermal diffusion by rotating the container. Then the surface of the semiconductor porcelain is polished.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a varistor in which a voltage non-linear characteristic is obtained by oxidizing a ceramic grain boundary, and in particular, a temperature and an atmosphere at the time of thermally diffusing Na oxide or the like into a semiconductor ceramic are uniform. Varistor voltage,
The present invention relates to a manufacturing method capable of avoiding variations in nonlinearity coefficient and the like, and avoiding adhesion of Na compounds to improve life characteristics and surge resistance.

[0002]

2. Description of the Related Art Generally, varistors containing SrTiO ₃ -based semiconductor ceramics as a main component are widely used as surge absorbing elements and noise absorbing elements in electronic devices and the like. In this varistor, a perovskite-based polycrystalline sintered body in which SrTiO ₃ and Sr are partially replaced with Ca or Ba as main components is converted into a semiconductor by electronic valency control or reduction firing, and Na
By diffusing the oxide or the compound thereof, an electric barrier is formed at the crystal grain boundary, and thereby a large dielectric constant and a voltage non-linear characteristic are obtained. In the case of manufacturing such a varistor, conventionally, a molded body made of SrTiO ₃ based semiconductor ceramics is fired to form a semiconductor porcelain,
A general method is to apply a predetermined amount of Na oxide or its compound to the semiconductor porcelain, arrange the semiconductor porcelain in a dish-shaped box, and heat-treat the oxide in this state to thermally diffuse the oxide into the semiconductor porcelain. is there.

[0003]

By the way, in order to obtain a varistor excellent in surge absorption effect and life characteristics, in order to delicately control the diameter of semiconductor particles and the state of grain boundaries constituting the varistor, the temperature at the time of heat treatment should be controlled. It is necessary to control uniformly so that the atmosphere does not vary. However, the conventional manufacturing method described above has a limit in controlling the temperature and the atmosphere uniformly, and as a result, there is a problem in that the electrical characteristics such as the varistor voltage, the non-linear coefficient, and the capacitance easily vary. is there. Further, in the above-described conventional manufacturing method, the Na compound is likely to adhere to the surface of the semiconductor porcelain during the cooling process during the heat treatment, and thus remains in the state of being easily ionized. There is a problem that it has become.

The present invention has been made in view of the above-mentioned conventional situation. The temperature and atmosphere during heat treatment can be made uniform to avoid variations in electrical characteristics, and the adhesion of Na compounds can be avoided to improve life characteristics. It is an object of the present invention to provide a varistor manufacturing method capable of improving surge withstand capability.

[0005]

The inventors of the present invention have examined the process of heat treatment from the viewpoint that the heat treatment process of thermally diffusing Na oxide or the like into the semiconductor porcelain is an important process that determines the electrical characteristics. However, according to the conventional method, since the semiconductor porcelain is placed on the box and the box is fixed in the heat treatment furnace, the Na oxide applied to the semiconductor porcelain is increased from the temperature rise during the heat treatment to the top temperature. Are scattered, and the oxide forms a main atmosphere, and as a result, diffusion of the oxide to the grain boundaries is suppressed. From this, it has been found that the semiconductor porcelain is housed in a container to prevent the oxide from scattering, and the container is rotated to move the semiconductor porcelain, whereby variations in temperature and atmosphere can be eliminated. Further, the present invention is based on the idea that the excess Na compound attached and remaining during cooling can be removed by polishing the semiconductor porcelain after the heat treatment.

Therefore, the present invention provides a method for manufacturing a varistor in which a voltage non-linear characteristic is obtained by thermally diffusing Na oxide or a compound thereof into a semiconductor ceramic, and the semiconductor ceramic and the Na oxide or the compound. Is heat-treated in a magnetic container while rotating the container, and then the surface of the semiconductor porcelain is polished.

[0007]

According to the varistor manufacturing method of the present invention, the semiconductor porcelain, Na oxide and the like are housed in the magnetic container, and the container is heat-treated while rotating, so that the Na oxide is prevented from scattering. Oxygen diffusion to the grain boundaries can be improved, and since the semiconductor porcelain moves with the rotation of the magnetic container, the temperature and atmosphere in the container can be made uniform. As a result, variations in electrical characteristics such as varistor voltage, non-linear coefficient, and electrostatic capacitance can be prevented, a large amount of heat treatment can be performed at one time, cost can be reduced, and productivity can be improved. Further, in the present invention, since the semiconductor porcelain after the heat treatment is polished, the Na compound adhering to the semiconductor porcelain during the diffusion cooling can be removed, whereby the life characteristics and surge withstand capability can be improved. Further, by polishing the semiconductor porcelain, the effect of preventing chipping can be obtained, and the reliability of quality can be improved.

[0008]

EXAMPLES Examples of the present invention will be described below. In this embodiment, a varistor is manufactured by the manufacturing method according to the present invention,
The test conducted for confirming the effect of the varistor thus obtained will be described. First, SrTi of this example
One manufacturing method for obtaining an O ₃ -based varistor will be described. S
Raw material powders of rCO ₃ , CaCO ₃ , TiO ₂ , and Er ₂ O ₃ were respectively added to Sr _0.9 Ca _0.1 Er _0.003 TiO 2.
Mix so as to be ₃ , add pure water to this, and mix with a ball mill. This is dehydrated and dried with a filter, granulated with a mesh, and then calcined at 1200 ° C for 2 hours.

Next, the above calcined body is dry pulverized to form a calcined powder, and SiO ₂ is added to the powder in a proportion of 0.5 wt%, and polyvinyl alcohol is added as a binder to the powder.
%, At the same time, pure water is further added and mixed by a ball mill to form a slurry. Next, this slurry is dried by a spray dryer and then granulated, and a pressure of ² t / cm ² is applied to this granulated powder to form a disk-shaped compact having a diameter of 10 mmφ and a thickness of 1.5 mm.

Next, the above-mentioned molded body is heated in air from 400 ° C.
The binder is burned by heating to 600 ° C., then the atmosphere is replaced with a reducing atmosphere and firing is performed at 1400 ° C. for 2 hours to form a sintered body, whereby a semiconductor porcelain is obtained.

Then, a cylindrical alumina porcelain pot having a diameter of 150 mm is prepared, the above-mentioned semiconductor porcelain is housed in the porcelain pot, and Na ₂ CO ₃ , Ti is further placed in the porcelain pot.
An oxide powder prepared by mixing O ₂ at a molar ratio of 2: 1 is added. In this case, the shape of the alumina porcelain pot may be cylindrical or polygonal.

Then, the alumina porcelain pot is placed at 0.5 rpm.
While rotating at a rotation speed of 1, the temperature is raised to 1200 ° C. and heat treatment is performed for 5 hours. By this heat treatment, while the semiconductor porcelain is being stirred in the porcelain pot, the oxide is thermally diffused in the crystal grain boundaries of the semiconductor porcelain to form an electrical barrier.

Next, the semiconductor porcelain is housed in a pot, SiC powder is added to the pot as an abrasive, and the surface of the semiconductor porcelain is polished while the pot is rotated at a rotation speed of 20 rpm. As a result, the oxide adhering to the surface of the semiconductor porcelain is scraped off.

Finally, a diameter of 7 is formed on both main surfaces of the semiconductor porcelain.
After applying mmφ silver paste, bake at 800 ℃ for 10 minutes to form the electrode. As a result, the varistor of this embodiment is manufactured.

[0015]

[Table 1]

[0016]

[Table 2]

Tables 1 and 2 show the results of tests conducted to confirm the effect of the varistor manufactured by the method of the above embodiment. This test was carried out by rotating the semiconductor porcelain in the alumina porcelain pot while thermally diffusing it, and then polishing the surface of this Example sample No. 1 and the comparative sample No. 1 in which the semiconductor porcelain was only thermally diffused while rotating. 2, a comparative sample No. 3 in which the semiconductor porcelain was heat-diffused in a state of being fixed on the box and then surface-polished, and a conventional sample No. 4 in which the heat was diffused in a state of being fixed on the box. And created.

Then, as shown in Table 1, each of the samples N
Varistor voltage (ΔV of o.1 to No.4 after 2000A surge)
_{1 mA} ), non-linear coefficient (Δα), and rate of change of capacitance (ΔCap) were measured. This 2000A surge was applied twice with 8 × 20μsec triangular current wave at 5 minute intervals.
The characteristics after minutes were compared. Further, as shown in Table 2, the varistor voltage of each sample No. 1 to No. 4 at a temperature of 150 ° C.
A 85% DC voltage was applied for 100 hours, and the varistor voltage, nonlinear coefficient, and rate of change of capacitance of each sample after this loading were measured. In the table, the values in parentheses are 3σ / average × 100%.

As is clear from Table 1 and Table 2, in the case of the conventional sample No. 4 which was fixed on the box and thermally diffused, the varistor voltage, the non-linear coefficient and the rate of change of capacitance by the surge test were These are large at -20.2%, -14.1%, and -8.6% respectively, and the rate of change due to the life test is -5.7% and
Large at −4.4% and −24.7%. In addition, each comparative sample No.
In the case of No. 2 and No. 3, the characteristics were improved compared with the conventional sample, but the rate of change by the surge test was -12.5 to -18.3%, -8.3 to -10.0%, -4.9 to -7, respectively. .
2%, and the rate of change due to the life test is -4.
Satisfactory values of 1 to −3.3%, −1.8 to −2.1%, −18.9 to −12.3% have not been obtained. On the other hand, in the case of the sample No. 1 of this example, the change rates by the surge test were -2.3%, -3.1%, -0.3%, respectively, and the change rates by the life test were + 0.1%, respectively. −0.1%, −4.
All values are small, 1%. As described above, it is understood that both the surge withstand capability and the life characteristics can be significantly improved by performing surface polishing after thermally diffusing the semiconductor porcelain while rotating.

[0020]

As described above, according to the method of manufacturing a varistor according to the present invention, the semiconductor porcelain and Na oxide or the like are thermally diffused in the magnetic container while rotating the container, and then the surface of the semiconductor porcelain. Since it was polished, the temperature and the atmosphere during the heat treatment can be made uniform, and the effect of preventing variations in electrical characteristics such as varistor voltage, non-linear coefficient, and capacitance can be obtained, and at the same time, it has adhered to the semiconductor porcelain. There is an effect that unnecessary Na compounds are removed to improve life characteristics and surge resistance.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yasunobu Yoneda 2-26-10 Tenjin Tenjin, Nagaokakyo-shi, Kyoto Murata Manufacturing Co., Ltd.

Claims (1)

[Claims] 1. A method for manufacturing a varistor in which a voltage non-linear characteristic is obtained by thermally diffusing Na oxide or a compound thereof in a semiconductor ceramic, wherein the semiconductor ceramic and Na oxide or a compound thereof are used. A method for manufacturing a varistor, comprising: storing in a magnetic container, thermally diffusing the container while rotating the container, and then polishing the surface of the semiconductor ceramic.