JPS622696B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for insulating grain boundaries in semiconductor ceramics. Conventionally, when manufacturing grain boundary insulated semiconductor ceramic capacitors, semiconductor ceramic varistors, etc., Bi ₂ O ₃ ,
Metal oxides such as Pb ₃ O ₄ and CuO are used as insulating agents, and this is kneaded with a binder such as varnish to form a paste. After screen printing this on the surface of semiconductor porcelain, it is heated to transfer the insulating agent to the semiconductor. A method of diffusing into the surface layer and grain boundary layer of porcelain is adopted. However, this method has the problem that the amount of paste applied to the semiconductor ceramic changes over time and is highly variable, resulting in non-uniform electrical characteristics of the product and a large standard deviation. The present invention was made in order to solve this problem, and an object of the present invention is to provide a method for insulating grain boundaries of semiconductor ceramics, which makes it possible to obtain products with little variation in electrical characteristics and a small standard deviation thereof. , the gist is that the surface of semiconductor porcelain is coated with a thermoplastic binder, the semiconductor porcelain is mixed with an insulating agent powder and heated to adhere the insulating agent powder to the surface of the semiconductor porcelain, and then heat treated. A method for insulating grain boundaries in semiconductor ceramics, which comprises diffusing the insulating agent into the surface and grain boundary layers of semiconductor ceramics. As the thermoplastic binder, various thermoplastic resins such as acrylic resin, styrene resin, vinyl resin, etc. can be used. In addition, as an insulating agent, Bi ₂ O ₃ , P _b3 O ₄ ,
Conventionally known metal oxides such as CuO and MnO ₂ may be used alone or in combination, and the amount added is in the range of 0.5 to 4.0% by weight based on the porcelain. Further, in order to attach the insulating agent, heating may be performed at a temperature that softens the binder, but heating is usually performed at a temperature in the range of 80 to 110°C. As a method for coating the surface of the semiconductor porcelain with a thermoplastic binder, a spray method in which the thermoplastic resin is sprayed as it is or a solution dissolved in a solvent onto the surface of the semiconductor porcelain, or a dipping method in which the thermoplastic resin is immersed in the solution is adopted. The amount of this binder can vary depending on the individual size of the semiconductor porcelain, but is usually set so that a layer 3 to 15 microns thick is formed. This is because if the thickness of the binder layer is less than 3μ, a sufficient amount of insulating agent cannot be attached to the surface of the semiconductor porcelain, and if it exceeds 15μ, the porcelain will adhere to itself, reducing the yield of grain boundary insulation. be. The heat treatment is carried out in a neutral or oxidizing mist atmosphere, and the temperature is preferably in the range of 1000 to 1200°C, as in the conventional case. Example A binder solution consisting of 30% acrylic resin solids and 70% solvent is prepared. Next, a diameter 10 mm made of barium titanate-based semiconductor porcelain manufactured by a conventional method was prepared.
Insert 100 disc samples with a thickness of 0.4 mm and a thickness of 0.4 mm into one stainless steel mask, coat the upper and lower surfaces with the binder by spraying, dry at 60°C for 3 minutes, and apply a binder with a thickness of 7 to 10 μm. form a layer.
300 samples coated in this way were placed in a cylindrical container, and an insulating agent was added to the container.
Bi ₂ O ₃ 45% by weight, Pb ₃ O ₄ 45% by weight, CuO 10% by weight
1.5 g of mixed powder consisting of the following were added, and the container was rotated for 1 minute at a speed of 5 times per minute in a dryer maintained at 85°C. The same operation was repeated three times to create three lots of samples, each of which was heat treated in air at 1100°C for 1 hour, and then silver electrodes were baked in the usual manner to produce grain boundary insulated semiconductor porcelain capacitors. The capacitance (Cs) and standard deviation were determined for each lot. The results are shown in Table 1.

[Table] Comparative Example A paste consisting of 22.5 parts by weight of Bi ₂ O ₃ , 22.5 parts by weight of Pb ₃ O ₄ , 5 parts by weight of CuO, and 50 parts by weight of varnish was prepared, and this was applied to a porcelain plate of the same size and material as the example sample. Screen print on the surface of the disk using a conventional method, and
The samples were divided into 3 lots in chronological order, and the samples from each lot were heat-treated in air at 1100°C for 1 hour, and the silver electrodes were baked to produce grain-boundary insulated semiconductor ceramic capacitors, and the capacitances x and σ were determined. Ta. The results are shown in Table 2.

[Table] As is clear from the results in Tables 1 and 2, according to the method of the present invention, there is less variation in capacitance and the standard deviation can be reduced compared to the conventional method. can improve the quality of This also shows that according to the method of the present invention, the amount of insulating agent deposited on the surface of the semiconductor ceramic is almost uniform.

Claims (1)

[Claims] 1 Coating the surface of semiconductor porcelain with a thermoplastic binder, heating the semiconductor porcelain while mixing it with insulating agent powder to adhere the insulating agent powder to the surface of the semiconductor porcelain, and then heat-treating the surface of the semiconductor porcelain. and a method for insulating grain boundaries in semiconductor ceramics, which comprises diffusing the insulating agent into grain boundary layers.