JP3157719B2 - Method for manufacturing solid electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 using manganese oxide for a semiconductor layer.

[0002]

2. Description of the Related Art This type of solid electrolytic capacitor is usually
A step of forming a chemical conversion film on a porous sintered body of a so-called valve action metal such as tantalum, aluminum, titanium or the like by anodic oxidation, and a step of forming a semiconductor layer made of manganese dioxide on the chemical conversion film. It is manufactured by a manufacturing process including:

In the manganese dioxide layer forming step, the operation of impregnating and adhering a manganese nitrate aqueous solution to a sintered body having a chemical conversion film formed thereon and thermally decomposing (firing) it is repeated several times to several tens of times. Do it. In the solid electrolytic capacitor thus obtained, conventionally, the capacitance value after completion as a capacitor is smaller than the capacitance value measured in the electrolytic solution after anodic oxidation during the manufacturing process, In the atmosphere, the phenomenon that the capacitance value increases with time is observed. This is because the manganese dioxide layer is difficult to uniformly adhere to the surface of the chemical conversion film. That is, a part of the chemical conversion film is not covered with the manganese dioxide layer. If moisture adheres to a portion of the chemical conversion film that is not covered by the manganese dioxide layer, the moisture acts as an electrolyte and the capacitance value increases.

[0004] The coverage of the manganese dioxide layer is related to the reaction rate of the thermal decomposition of the aqueous solution of manganese nitrate. The faster the reaction rate, the better the coverage. This is because if the reaction speed is slow,
This is because, before the manganese dioxide layer is formed, the manganese nitrate aqueous solution is aggregated in a low potential portion inside the sintered body. By utilizing this property, the reaction rate can be increased and the coverage can be improved by increasing the sintering temperature of manganese nitrate. However, this method has side effects such as an increase in leakage current as a capacitor and a decrease in reliability. This is because the higher the firing temperature, the more the thermal deterioration of the chemical conversion film becomes significant.

On the other hand, JP-A-63-31106 discloses an invention aimed at improving the coverage of a manganese dioxide layer without increasing the manganese nitrate firing temperature. In the invention described in the above publication, a substance soluble in an aqueous manganese nitrate solution, such as an ammonium salt, a carbonyl compound, or an amide compound, is added to an aqueous manganese nitrate solution used as a mother liquor for forming a manganese dioxide layer, thereby promoting a thermal decomposition reaction. , The coverage of the manganese dioxide layer is improved.

[0006]

As described above, by adding a thermal decomposition accelerator such as an ammonium salt to a manganese nitrate aqueous solution which is a mother liquor for forming a manganese dioxide layer, the manganese dioxide layer can be formed without increasing the firing temperature. The coverage can be improved.

However, in this case, if the amount of the thermal decomposition accelerator is increased to increase the effect, the adverse effect of increasing the leakage current occurs. This is because the thermal decomposition temperature of the ammonium salt in the aqueous solution of manganese nitrate is higher than the thermal decomposition temperature of the aqueous solution of manganese nitrate.If the amount of addition is large, the ammonium salt remains after the completion of thermal decomposition, and the residue causes leakage current. Is increased.

Accordingly, the present invention provides a solid electrolytic capacitor using manganese dioxide for the semiconductor layer, by increasing the coverage of the manganese dioxide layer without increasing the firing temperature, thereby allowing the capacitance value due to external moisture to increase over time. It is an object of the present invention to provide a highly reliable solid electrolytic capacitor having no change and no increase in leakage current due to the formation of a manganese nitrate layer.

[0009]

According to the present invention, there is provided a method for manufacturing a solid electrolytic capacitor, comprising the steps of forming an anodic oxide film on a porous sintered body of a valve action metal, and forming a manganese nitrate aqueous solution on the anodic oxide film. Forming a manganese oxide layer by decomposition, characterized in that in the step of forming the manganese oxide layer, a liquid obtained by adding mannite to a manganese nitrate aqueous solution in advance is used as a mother liquor. I do.

As an additive to the manganese nitrate aqueous solution ,
Sorbit can be used instead of mannite.

In the present invention, mannite or sodium manganese is added to a manganese nitrate aqueous solution which is a mother liquor for forming a manganese dioxide layer.
Rubit is added and the heat of the oxidation reaction is used to accelerate the thermal decomposition reaction of manganese nitrate. Mannit and sorbie
If the thermal decomposition temperature is lower than the thermal decomposition temperature of manganese nitrate, and if it is higher than 250 ° C, which is generally used for thermal decomposition of manganese nitrate in the production of solid electrolytic capacitors, it will completely Nothing remains. Moreover,
Handling is safe and excellent in environmental preservation.

[0012]

Next, embodiments of the present invention will be described with reference to examples.

[Example 1] Tantalum sintered pellets (powder magnification: 40,000 CV / g) rated at 16 V and 220 µF, formed at 60 V,
An aqueous solution (hereinafter referred to as liquid type A) obtained by adding 3% of mannite to an aqueous manganese nitrate solution was impregnated. For comparison, a solution containing only a manganese nitrate aqueous solution (hereinafter referred to as liquid type B) was impregnated. These were pulled up and pyrolyzed under the two temperature conditions shown in Table 1 for 10 minutes. This operation of impregnation and thermal decomposition was carried out eight times while appropriately performing re-chemical formation.
In addition, a hot-air circulation type pyrolysis apparatus was used for the pyrolysis.

Next, a carbon layer and a silver layer are sequentially formed on the manganese dioxide layer to complete three levels of solid electrolytic capacitors of Example 1, Comparative Example 1, and Comparative Example 2. The manganese layer coverage, pyrolysis reaction time, and capacitor leakage current were compared. Table 1 shows the results.

When a manganese nitrate aqueous solution is heated to cause a thermal decomposition reaction, it is considered that the following reaction occurs. Mn (NO 3) ₂ .nH ₂ O → Mn (NO ₃ ) ₂ + nH ₂ O Mn (NO 3) ₂ → MnO ₂ + 2NO _x Reaction time until manganese dioxide is obtained by thermal decomposition reaction from manganese nitrate aqueous solution by the above process Was determined from differential thermal analysis.

[0016]

[Table 1]

Referring to Table 1, in Example 1 using an aqueous solution (liquid type A) obtained by adding 3% of mannite to an aqueous manganese nitrate solution, a high coverage of 98% at a low firing temperature of 200 ° C. was gotten. At this time, the leakage current is 1.
The value was as small as 5 μA. This is considered to be the effect of shortening the reaction time by adding mannite as shown in Table 1. On the other hand, in Comparative Example 1 in which a conventional aqueous solution of only manganese nitrate aqueous solution (liquid type B) was used, the reaction rate of thermal decomposition was as low as about half, and the reaction time was longer than that in the case of adding mannite. In order to make the same approximately 120 seconds, as in Comparative Example 2, the firing temperature is set to 3 seconds.
It must be raised to 00 ° C. However, in such Comparative Example 2, although the manganese dioxide coverage is the same as in Example 1 in which mannite is added, the leakage current is increased by about 3.5 times.

Example 2 Next, an additive to an aqueous solution of manganese nitrate was added to
The solid electrolytic capacitors of Example 2, Comparative Example 3, and Comparative Example 4 were produced under the same conditions as in Example 1 except that the solid electrolytic capacitor was changed from solvit to solbit . Table 2 shows the results of comparing the capacitors of each level in the same manner as in Example 1.

[0019]

[Table 2]

Referring to Table 2, in this case also, in Example 2, the firing temperature was as low as 200 ° C. and the reaction time was 120 ° C.
Seconds, and the leakage current is as good as 1.3 μA. On the other hand, in Comparative Examples 3 and 4, the firing temperature had to be increased to 300 ° C. in order to shorten the reaction time, and the leakage current was increased.

The first and second embodiments described above are different from the first embodiment.
This is an example of adding nit or sorbite to an aqueous solution of manganese nitrate, but the additives used in the present invention are not limited to this. A substance that increases the rate of thermal decomposition of manganese nitrate by generating heat of oxidation reaction, and
As long as the oxidation reaction temperature of the additive itself is lower than the thermal decomposition temperature of the aqueous solution of manganese dioxide as the mother liquor, any additive exhibits the same effect as the embodiment. But,
Generally used for thermal decomposition of manganese dioxide aqueous solution 2
As an additive, it decomposes completely at a temperature of about 50 ° C. or more, leaving no residue, and is excellent in handling safety and environmental conservation .
Unit or sorbite would be suitable.

In the embodiment, a porous sintered body of tantalum is used. However, a solid electrolytic capacitor obtained by enlarging another valve metal, for example, aluminum foil, by another means, for example, etching or the like is used. However, it will be apparent that a similar effect can be obtained by applying the present invention.

[0023]

As described above, according to the method for manufacturing a solid electrolytic capacitor of the present invention, mannite or sol is added to a manganese nitrate aqueous solution which is a mother liquor for forming a manganese dioxide layer.
A bit is added, and the thermal decomposition reaction of manganese nitrate is promoted using the heat of the oxidation reaction.

Thus, according to the present invention, the reaction time for forming the manganese dioxide layer is shortened, and the coverage of the manganese dioxide layer on the anodic oxide film is improved. There is no increase and reliability is increased.

Further, since the reaction time can be shortened without raising the sintering temperature of manganese nitrate, deterioration of the anodic oxide film due to heating is eliminated, and the leakage current characteristics are improved.

Mannit and sorbite are safe to handle and excellent in environmental preservation, and the industrial effects of the present invention are great.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01G 9/032 H01G 9/00

Claims (3)

(57) [Claims] 1. A solid electrolytic method comprising: a step of forming an anodic oxide film on a porous sintered body of a valve metal; and a step of forming a manganese oxide layer on the anodic oxide film by thermal decomposition of a manganese nitrate aqueous solution. A method for manufacturing a solid electrolytic capacitor, characterized in that in the step of forming a manganese oxide layer, a liquid obtained by adding mannite to an aqueous manganese nitrate solution in advance is used as a mother liquor. 2. A porous sintered body of a valve metal having anodized skin
The process of forming a film, and man nitrate on the anodic oxide film
Form manganese oxide layer by thermal decomposition of gun solution
And the step of forming a manganese oxide layer,
A method for producing a solid electrolytic capacitor, comprising using a liquid obtained by adding sorbit to a liquid in advance as a mother liquor . 3. Mannit or sorbit nitrate.
3 wt. %
The solid electrolytic capacitor according to claim 1 or 2, characterized in that:
Method of manufacturing capacitor.