JPS6016745B2 - Manufacturing method of solid electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a solid electrolytic capacitor, particularly to the formation of a semiconductor layer. The purpose is to reduce the number of times of thermal decomposition and improve leakage current and withstand voltage characteristics.

Conventional sintered solid electrolytic capacitors have a structure in which a dielectric film, a semiconductor layer (for example, a manganese dioxide layer), a graphite layer, and a cathode layer are sequentially formed by molding valve action metal powder particles and instantly solidifying them. is obtained by impregnating a capacitor element by immersing it in an aqueous solution of manganese nitrate, heating it at 200 to 400 qo, and thermally decomposing the impregnated manganese nitrate.

However, it is important to form the manganese dioxide layer delicately and with a constant thickness, but in order to obtain such a manganese dioxide layer, the above-mentioned impregnation-pyrolysis process of manganese nitrate is increased from several times to one. It is necessary to repeat the attack. However, as the number of thermal decompositions increases, there are problems in terms of characteristics such as a large leakage current and a decrease in withstand voltage, as well as drawbacks in terms of work efficiency and labor due to repeating the same process. Therefore, it is desirable to reduce the number of impregnation-pyrolysis cycles of manganese nitrate as much as possible, but if the number of cycles of pyrolysis is simply reduced, a short circuit with the dielectric film may occur when graphite, which is a cathode material, is applied. The proportion increases. This is because if the number of times of thermal decomposition is small, the manganese dioxide layer is not uniformly generated and the graphite particles come into direct contact with the conductor film. The present invention has been made in view of the above points, and the graphite particles are brought into direct contact with the dielectric film by filling the gaps in the manganese dioxide layer where the graphite particles can enter with fine particles of an inorganic oxide which is an insulator. The present invention also provides a method for manufacturing a solid electrolytic capacitor with low leakage current, few short-circuit failures, and improved short circuit failure even when the number of thermal decompositions is small.

This will be explained in detail below using examples. Weight 1. A dielectric film is formed by applying 35 V to the capacitor element in an electrolytic solution to form a dielectric film by applying a 35 V to the capacitor element using a crystallized element made of tantalum powder.

Thereafter, it was immersed in an aqueous manganese nitrate solution having a concentration of 25% by weight, mixed and heated at 250°C for thermal decomposition, and then reconstituted at 25V in an electrolytic solution. After repeating the above operation twice, the process of impregnating by impregnating with a manganese nitrate aqueous solution having a concentration of 6% by weight, thermal decomposition at 25 picoC, and further reconstitution at 25V in an electrolytic solution was repeated four times. After repeating the steps up to reconstitution, 0.01, 0.05 0.01,0.050. 1
, 0.5, 1, 2, and 5% by weight were added to various aqueous dispersions.
Each tantalum solid electrolytic capacitor was heated for 18 minutes, coated with graphite and coated with silver paste, and these capacitor elements were housed in a metal case and packaged. Figure 1 shows the relationship between tan6 and the amount of silicon oxide added. In the conventional example, a capacitor element is immersed in a manganese nitrate aqueous solution, impregnated, and then thermally decomposed.The process of impregnation, thermal decomposition, and reconstitution is repeated twice for a 25% by weight manganese nitrate aqueous solution, and then the capacitor element is immersed in a manganese nitrate aqueous solution 6. The impregnation-pyrolysis-reformation process was repeated 10 times for a sample with a weight percent of As a result, the short-circuit failure rate was 2%, and tan6 was 2.8%. Other characteristics are those of the above example (shown in Figures 1 and 2).
The capacitance is 330 F, which is the same as the conventional example, but the leakage current is 0.1 rA in the above embodiment and 1.0 A in the conventional example.
Met. (Average value) As is clear from the above results, the occurrence of short circuit failures is completely eliminated when the amount of silicon oxide added is 0.1% by weight or more, and tan6 shows a rapid increase when the amount of silicon oxide added exceeds 2% by weight, indicating that oxidation The amount of silicon added is 0.1 to 2. is within the scope of the present invention. The structure of the solid electrolytic capacitor made in this way has a structure in which silicon oxide is dotted into the manganese dioxide layer, and the presence of the silicon oxide prevents the graphite particles from coming into contact with the dielectric film, resulting in short circuit failure. This is to prevent this. Therefore, as mentioned above, although the number of repetitions of the manganese nitrate impregnation to reconstitution steps is a total of 1 times in the conventional example and 6 times in the present invention, short circuit failures occur only when the addition rate of silicon oxide is 0. 1
% or more in the present invention, while in the conventional example it is 2%.
Furthermore, the leakage current has a value of approximately 1/1 brightness. As mentioned above, this leakage current characteristic increases in proportion to the thermal decomposition rate, and this is where the effects of the present invention are remarkable. In the above example, tantalum powder was used as the valve metal, but the same effect can be obtained with an aluminum solid electrolytic capacitor, and the inorganic oxide used in the aqueous dispersion has chemical and thermal properties. The condition is that the material be stable and electrically insulating.Although silicon oxide was described in the above example, similar effects have been observed with aluminum oxide, titanium oxide, zinc oxide, etc., and the use of particles of these inorganic oxides The size is desirably 0.2 mm or less, and if it exceeds 0.2 mm, the incidence of short circuit defects will be slightly higher than in the present invention. Furthermore, the manganese nitrate added to this aqueous dispersion together with the inorganic oxide has the function of a binder that fixes the inorganic oxide in the capacitor element by generating manganese dioxide by heating, and the concentration of this manganese nitrate aqueous solution is 5. A range of .about.2% by weight is desirable. The reason for this is that if it is less than 5% by weight, its function as a binder is insufficient, and if it exceeds 2% by weight, inorganic oxides will be present in the formed manganese dioxide layer, resulting in gaps between the manganese dioxide layers. This is because the effect of packing the particles is not sufficient.

[Brief explanation of the drawing]

The drawings all show the characteristics of the embodiments of the present invention. Figure 1 is a curve diagram showing the relationship between the amount of silicon oxide added and the short-circuit failure rate, and Figure 2 is a curve diagram showing the relationship between the amount of silicon oxide added and the short-circuit failure rate. It is a curve diagram showing the relationship. Figure 1 Figure 2

Claims (1)

[Claims] 1. In a method for manufacturing a solid electrolytic capacitor, which includes the steps of sequentially forming a dielectric film, a semiconductor layer, a graphite layer, and a cathode layer on a capacitor element made of a valve metal, after forming the semiconductor layer, 5 to 20% of manganese nitrate is added. 0.1 to 2% by weight of a fine particulate inorganic oxide consisting of one or a mixture of two or more of silicon oxide, aluminum oxide, titanium oxide, and zinc oxide with a size of 0.2 μm or less is added to an aqueous solution. A method for manufacturing a solid electrolytic capacitor, which comprises immersing and heating a solid electrolytic capacitor in an aqueous dispersion.