JPH07153650A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

PURPOSE:To obtain the solid electrolytic capacitor whose leakage current characteristic is good, which improves the impregnation property of manganese nitrate and which makes a tan delta and an impedance characteristic good. CONSTITUTION:A chemical conversion treatment by at least a phosphoric acid aqueous solution is executed to an anodic sintered substance which is formed by sintering a valve-action metal powder such as tantalum, niobium or the like, and the anodic sintered substance is then cleaned with a nitric acid aqueous solution as its posttreatment.

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 solid electrolytic capacitor having good impregnation property with manganese nitrate and good loss tangent (tan δ) and impedance characteristics. It is about the method.

[0002]

2. Description of the Related Art A method of manufacturing a tantalum solid electrolytic capacitor will be described. First, a suitable binder is mixed with tantalum powder to form a rectangular parallelepiped or a cylinder having a predetermined size, and an anode lead is implanted. Then, it is sintered to obtain a sintered pellet of tantalum (anode sintered body).

Then, an oxide film as a dielectric is formed on the sintered pellet. Usually, this oxide film is formed by a single chemical conversion treatment using a phosphoric acid aqueous solution or a nitric acid aqueous solution, or a two-step chemical conversion treatment in which chemical conversion is performed using a nitric acid aqueous solution and then phosphoric acid aqueous solution.

Next, a solid electrolyte made of manganese dioxide is formed on the sintered pellet. That is, the same sintered pellet is immersed in an aqueous solution of manganese nitrate to impregnate it with manganese nitrate and then pulled up for thermal decomposition. The concentration of manganese nitrate is sequentially increased and this is repeated several times, and re-formation is repeated several times for the purpose of repairing the oxide film damaged by the thermal decomposition process.

After that, a carbon layer and a silver layer as a cathode conductive layer are formed on the solid electrolyte.

[0006]

In this way, the capacitor element is formed, but when forming the oxide film on the sintered pellet, the leakage current characteristics are not good when the chemical conversion treatment with the phosphoric acid aqueous solution is performed. However, since the impregnation property of manganese nitrate is not sufficient in the solid electrolyte forming step, the loss tangent (tan δ) and the impedance (Z) characteristics are poor.

On the other hand, in the case of chemical conversion treatment with an aqueous nitric acid solution, the impregnation property of manganese nitrate is good and the tan δ and impedance (Z) characteristics are good, but there is a drawback that the leakage current characteristics vary.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and is characterized in that the anode sintering is obtained by sintering valve action metal powder such as tantalum or niobium. After a chemical conversion treatment with a phosphoric acid aqueous solution to the body (after a single chemical conversion treatment with a phosphoric acid aqueous solution or a two-step chemical conversion treatment with a nitric acid aqueous solution and a phosphoric acid aqueous solution), a solid electrolyte consisting of manganese dioxide is added to the anode sintered body. And a method of manufacturing a solid electrolytic capacitor in which a conductive layer for a cathode is sequentially formed, the anode sintered body is washed with an aqueous nitric acid solution as a post-treatment after the above chemical conversion treatment is performed on the anode sintered body. It is in.

In this case, the nitric acid concentration of the nitric acid aqueous solution is 0.0
It is preferably from 05 to 1.0%. The nitric acid concentration is 0.
If it is less than 005%, there is little effect, and if it is 1.0% or more, odor is generated, equipment is corroded, and the workability is significantly deteriorated.

[0010]

According to the present invention, the wettability with manganese nitrate is improved by washing the sintered pellets with an aqueous nitric acid solution after chemical conversion with an aqueous phosphoric acid solution having good leakage current characteristics. Therefore, the impregnation property of manganese nitrate is increased, and t
The an δ and impedance (Z) characteristics are improved.

[0011]

[Example] Pellet size 0.9 x 0.9 x 1.0 (m
m) using tantalum sintered pellets,
100 tantalum solid electrolytic capacitors rated at 6.3 V and 10 μF each were manufactured in accordance with No. 3 and the conventional example.
The impregnation rate of manganese nitrate, the impedance Z (Ω) at 100 kHz, and the tan δ at 120 Hz were measured.

Example 1 First, a tantalum sintered pellet of the above size was formed in an aqueous 0.1% phosphoric acid solution by applying a formation voltage four times the rated voltage to form an oxide film. Then, as a post-treatment after this chemical conversion, the same tantalum sintered pellet was washed with a 0.005% nitric acid aqueous solution.

Next, the sintered tantalum pellets were immersed in an aqueous solution of manganese nitrate to impregnate manganese nitrate, and then pulled up for thermal decomposition to form solid electrolytes of manganese dioxide on the sintered pellets of tantalum. In this case, the concentration of manganese nitrate is 20%, 40%, 70%, 100%
Then, the thermal decomposition was repeated 10 times, and re-formation was repeated 5 times with an aqueous phosphoric acid solution for the purpose of repairing the oxide film damaged by the thermal decomposition step.

Thereafter, a carbon layer and a silver layer were sequentially formed on this solid electrolyte, and after being attached to a lead frame, a resin exterior body was formed by a resin molding method.

When the impregnation rate of manganese nitrate was measured for 100 of these products, the maximum was 92.0% and the minimum was 89.
At 5%, the average value was 90.5%. Also, 10
The impedance Z at 0 kHz was a maximum of 4.9Ω and a minimum of 3.6Ω, and the average value was 4.2Ω. 120H
The maximum tan δ at z is 4.7% and the minimum is 3.5%.
The average value was 4.1%.

Example 2 Similar to Example 1, an oxide film was formed by applying a chemical conversion voltage four times the rated voltage to a tantalum sintered pellet of the above size in a 0.1% phosphoric acid aqueous solution.

Then, as a post-treatment after the chemical conversion, in Example 2, the same tantalum sintered pellet was treated with 0.05% nitric acid.
% Aqueous solution. After that, a solid electrolyte, a carbon layer, and a silver layer were sequentially formed in the same manner as in Example 1, and after attachment to a lead frame, a resin outer package was formed by a resin molding method.

When the impregnation rate of manganese nitrate was measured for 100 of these products, the maximum was 97.0% and the minimum was 94.
At 0%, the average value was 95.5%. Also, 10
The impedance Z at 0 kHz was 1.8Ω at maximum and 0.9Ω at minimum, and the average value was 1.4Ω. 120H
The maximum tan δ at z is 3.0% and the minimum is 2.1%
The average value was 2.6%.

Example 3 Similar to Example 1, an oxide film was formed by applying a formation voltage four times the rated voltage to a tantalum sintered pellet of the above size in a 0.1% phosphoric acid aqueous solution.

Then, as a post-treatment after the chemical conversion, in Example 3, the same tantalum sintered pellets were treated with 1.0% nitric acid.
It was washed with an aqueous solution. After that, a solid electrolyte, a carbon layer, and a silver layer were sequentially formed in the same manner as in Example 1, and after attachment to a lead frame, a resin outer package was formed by a resin molding method.

When the impregnation rate of manganese nitrate was measured for 100 of these products, the maximum was 98.0% and the minimum was 94.
At 5%, the average value was 96.0%. Also, 10
The impedance Z at 0 kHz was 1.7Ω at maximum and 0.9Ω at minimum, and the average value was 1.3Ω. 120H
About tan δ at z, maximum 2.8%, minimum 2.0%
The average value was 2.4%.

<Prior art example> As in Example 1, an oxide film was formed by applying a formation voltage four times the rated voltage to a tantalum sintered pellet of the above size in a 0.1% phosphoric acid aqueous solution.

However, in this conventional example, the washing step with nitric acid aqueous solution after chemical conversion is omitted, and thereafter, the solid electrolyte, the carbon layer, and the silver layer are sequentially formed in the same manner as in Example 1, and after attachment to the lead frame. A resin outer package was formed by the resin molding method.

When the impregnation rate of manganese nitrate was measured for 100 of these products, the maximum was 90.5% and the minimum was 87.
At 5%, the average value was 89.0%. Also, 10
The impedance Z at 0 kHz was a maximum of 5.7Ω and a minimum of 3.8Ω, and the average value was 5.0Ω. 120H
The maximum tan δ at z is 5.0% and the minimum is 3.5%
The average value was 4.4%.

In order to facilitate the comparison, FIG. 1 is a graph showing the measurement results of Examples 1 to 3 and the conventional example. Although the above-mentioned embodiment is for tantalum, the present invention is not limited to this, and other valve action metals may be used.

[0026]

As described above, according to the present invention,
After subjecting the anode sintered body obtained by sintering valve metal powder such as tantalum or niobium to at least a chemical conversion treatment with a phosphoric acid aqueous solution, as a subsequent treatment, the anode sintered body should be washed with a nitric acid aqueous solution. By doing so, a solid electrolytic capacitor having a good leakage current characteristic and an improved manganese nitrate impregnation property, and a good tan δ and impedance characteristic can be obtained.

[Brief description of drawings]

FIG. 1 is a graph showing characteristics of an example and a conventional example for comparison.

Claims (2)

[Claims] 1. A solid electrolyte made of manganese dioxide after subjecting an anode sintered body obtained by sintering valve action metal powder such as tantalum or niobium to at least a chemical conversion treatment with an aqueous phosphoric acid solution. And a method for manufacturing a solid electrolytic capacitor in which a conductive layer for a cathode is sequentially formed, the anode sintered body is washed with an aqueous nitric acid solution as a post-treatment after the above chemical conversion treatment is applied to the anode sintered body. A method of manufacturing a solid electrolytic capacitor, comprising: 2. The nitric acid concentration of the nitric acid aqueous solution is 0.005.
Is 1.0% or less, The manufacturing method of the solid electrolytic capacitor of Claim 1 characterized by the above-mentioned.