JPH0513284A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

PURPOSE:To improve adhesive properties of solid electrolyte to a carbon layer and to reduce an impedance. CONSTITUTION:Solid electrolyte made of manganese dioxide is formed on a sintered pellet of valve operating metal powder, a carbon layer is formed on the periphery of the electrolyte, the layer is impregnated with aqueous nitric acid solution, heat treated and a silver layer is formed thereon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid electrolytic capacitor, and more particularly to a method for manufacturing a solid electrolytic capacitor having good impedance characteristics.

[0002]

2. Description of the Related Art First, a valve action metal powder such as tantalum is sintered to obtain a sintered pellet. Anode leads are previously implanted in the sintered pellets.

After forming an oxide film as a dielectric, a solid electrolyte is formed around the sintered pellet. Taking manganese dioxide (MnO ₂ ) as a solid electrolyte as an example, the sintered pellets are immersed in an aqueous manganese nitrate solution to impregnate manganese nitrate, and then pyrolyzed. The concentration of the manganese nitrate aqueous solution is gradually increased and this is repeated several times.

Then, the pellets are immersed in a carbon liquid and baked at about 150 ° C. to form a carbon layer on the solid electrolyte. Then, a silver layer is formed on the carbon layer.

[0005]

Conventionally, a solid electrolytic capacitor is manufactured as described above, but since the adhesion between manganese dioxide and the carbon layer is not sufficient, the interface resistance is high, which causes impedance failure. There was a problem that the rate was high.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances, and its structural feature is that a solid electrolyte made of manganese dioxide is formed on a sintered pellet of valve action metal powder, and In a method for manufacturing a solid electrolytic capacitor in which a carbon layer and a silver layer are sequentially formed around the solid electrolyte, a carbon layer is formed around the solid electrolyte, and then the carbon layer is impregnated with an aqueous nitric acid solution to perform heat treatment. is there.

In this case, the concentration of the nitric acid aqueous solution is 1 to 10% by volume, preferably 3 to 7% by volume. Here, when the content is 1% by volume or less, the adhesion becomes insufficient.

The temperature of the heat treatment is 150 to 300 ° C, preferably 200 to 250 ° C. When the temperature is 150 ° C. or lower, baking becomes insufficient, and when the temperature is 300 ° C. or higher, the carbon layer is peeled off and no effect is produced.

The heat treatment time is most effective for 10 to 15 minutes. The nitric acid aqueous solution may contain impurities.

[0010]

As described above, after the formation of the carbon layer, the carbon layer is impregnated with an aqueous solution of nitric acid and subjected to heat treatment, whereby the solid electrolyte (manganese dioxide) and the carbon layer are brought into close contact with each other to stabilize the interface, The value of the impedance | Z | becomes low.

[0011]

【Example】

Example 1 After forming a dielectric film on a sintered pellet of tantalum powder, manganese dioxide as a solid electrolyte was formed in the same manner as in the prior art, and a carbon layer was formed on the manganese dioxide.

After that, it was immersed in a 1% by volume aqueous solution of nitric acid for 1 minute, pulled up, and placed in a hot air circulation oven at 300 ° C. for 1 minute.
It was heat-treated (dried) for 0 minutes.

After forming the silver layer, 500 tantalum solid electrolytic capacitors having a rating of 4V and 10 μF were prototyped according to the conventional assembly process, and the impedance | Z | (Ω) at 100 kHz was measured. Was 0.5Ω. <Comparative Example 1> After forming a carbon layer, 500 pieces of tantalum solid electrolytic capacitors having a rating of 4V and 10 μF were prepared by directly forming a silver layer on the carbon layer, and the impedance | Z | (Ω) at 100 kHz was measured. The average value was 0.9Ω. Example 2 After forming a dielectric film on a sintered pellet of tantalum powder, manganese dioxide as a solid electrolyte was formed in the same manner as in the prior art, and a carbon layer was formed on the manganese dioxide.

After that, it was immersed in a 1% by volume aqueous solution of nitric acid for 1 minute, pulled up, and placed in a hot air circulation oven at 300 ° C. for 1 minute.
It was heat-treated (dried) for 0 minutes.

After forming the silver layer, 500 tantalum solid electrolytic capacitors having a rating of 4V and 2.2 μF were prototyped according to the conventional assembly process, and the impedance | Z | (Ω) at 100 kHz was measured. The average value was 0.3Ω. <Comparative Example 2> After forming a carbon layer, 500 pieces of tantalum solid electrolytic capacitors having a rating of 4V and 2.2 μF were prepared by directly forming a silver layer on the carbon layer, and the impedance | Z | (Ω) at 100 kHz was measured. However, the average value was 0.5Ω. Example 3 After forming a dielectric film on a sintered pellet of tantalum powder, manganese dioxide as a solid electrolyte was formed in the same manner as in the past, and a carbon layer was formed on the manganese dioxide.

After that, it was immersed in a 1% by volume aqueous solution of nitric acid for 1 minute, pulled up, and placed in a hot air circulation oven at 300 ° C. for 1 minute.
It was heat-treated (dried) for 0 minutes.

Then, after forming the silver layer, 600 tantalum solid electrolytic capacitors having a rating of 10V and 4.7 μF were prototyped according to the conventional assembly process, and the impedance | Z | (Ω) at 100 kHz was measured. The average value was 0.8Ω. <Comparative Example 3> After forming a carbon layer, 500 pieces of tantalum solid electrolytic capacitors having a rating of 10V and 4.7 μF according to a conventional method, in which a silver layer was directly formed on the carbon layer, were prepared, and impedance | Z | (Ω) at 100 kHz was measured. However, the average value was 1.0Ω. Example 4 After forming a dielectric film on a sintered pellet of tantalum powder, manganese dioxide as a solid electrolyte was formed in the same manner as in the past, and a carbon layer was formed on the manganese dioxide.

Thereafter, it was immersed in a 1% by volume aqueous solution of nitric acid for 1 minute, pulled up, and placed in a hot air circulation oven at 300 ° C. for 1 minute.
It was heat-treated (dried) for 0 minutes.

After forming the silver layer, 1000 tantalum solid electrolytic capacitors having a rating of 16V and 6.8 μF were prototyped according to the conventional assembly process, and the impedance | Z | (Ω) at 100 kHz was measured. The average value was 0.6Ω. <Comparative Example 4> After forming a carbon layer, 1000 pieces of tantalum solid electrolytic capacitors having a rating of 16V and 6.8 μF were prepared by directly forming a silver layer on the carbon layer, and the impedance | Z | (Ω) at 100 kHz was measured. However, the average value was 0.95Ω.

For reference, Table 1 shows the impedances | Z | (Ω; average value) of the examples and comparative examples in comparison.

[0021]

[Table 1] As can be seen from this table, according to the present invention, the impedance | Z | can be reduced by about 35% as compared with the comparative example.

[0022]

As described above, according to the present invention,
By forming a carbon layer around the solid electrolyte and then impregnating the same carbon layer with a nitric acid aqueous solution to perform heat treatment, the adhesion between the solid electrolyte and the carbon layer is improved, and the impedance | Z | is reduced. Can be achieved.

Claims (3)

[Claims] 1. A method for producing a solid electrolytic capacitor, comprising: forming a solid electrolyte made of manganese dioxide on a sintered pellet of valve metal powder; and sequentially forming a carbon layer and a silver layer around the solid electrolyte. A method for producing a solid electrolytic capacitor, which comprises forming a carbon layer around a substrate, impregnating the carbon layer with an aqueous nitric acid solution, and performing heat treatment. 2. The method for producing a solid electrolytic capacitor according to claim 1, wherein the concentration of the nitric acid aqueous solution is 1 to 10% by volume. 3. The temperature of the heat treatment is 150 to 300 ° C.,
The method for producing a solid electrolytic capacitor according to claim 1, wherein the treatment time is 5 to 20 minutes.