JPH0314220B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing a solid electrolytic capacitor, and particularly to a step of forming a manganese dioxide layer. In the production of solid electrolytic capacitors, an aluminum or tantalum foil or plate with an anodic oxide film formed on the surface as a dielectric is used as an anode element, and a solid electrolyte of manganese dioxide layer (MnO ₂ ) is closely attached to this as a cathode. As a means of forming a manganese dioxide layer in close contact with an anode element, the complicated cavity of the anode element is impregnated with an aqueous solution of manganese nitrate, which is thermally decomposed and replaced with manganese dioxide. However, if the specific gravity of the manganese nitrate solution impregnated into the cavity of the anode element is small, the manganese dioxide layer formed by one-time impregnation and thermal decomposition will be thin, and the impregnation and thermal decomposition must be repeated many times, which is inefficient.
Furthermore, since heat is repeatedly applied, the cavity is destroyed due to thermal distortion. Furthermore, if the specific gravity of the manganese nitrate solution impregnated into the anode element is large, it is not possible to impregnate the manganese nitrate solution up to the tip of the cavity. Therefore, it is desired to develop a method that can sufficiently form a manganese dioxide layer up to the tip of the cavity by a small number of impregnations and thermal decomposition. [Prior art] Figure 1 is an enlarged cross-sectional view of an anode element, and Figure 2 shows the specific gravity of manganese nitrate solution, the number of treatments, and tanδ.
FIG. 3 is a diagram showing the relationship between the specific gravity of the manganese nitrate solution, the number of treatments, and the capacitance. In Fig. 1, an anode element 1 has been subjected to surface expansion treatment to increase its surface area, and an anodized film 3 is applied to the surface of a complex cavity 2 formed inside the foil or plate.
is covered. In order to increase the capacitance of the capacitor per unit area, it is necessary to fill the cavity 2 up to the tip with manganese dioxide. Therefore, conventional manganese dioxide layer formation uses a manganese nitrate solution having the same specific gravity, and repeats impregnation and thermal decomposition of the manganese nitrate solution until predetermined characteristics are obtained. Figure 2 shows the specific gravity of the manganese nitrate solution and The relationship between the number of treatments and tan δ is shown, and FIG. 3 shows the relationship between the specific gravity of the manganese nitrate solution at that time, the number of times of treatment, and capacitance. In the conventional method using a manganese nitrate solution with the same specific gravity, the specific gravity of the manganese nitrate solution can reduce the number of treatments to the minimum while maintaining tan δ and capacitance, as is clear from Figures 2 and 3.
The limit is 1.8, and when the specific gravity reaches 1.9, tanδ increases rapidly and capacitance decreases suddenly. Table 1 shows the relationship between the specific gravity of manganese nitrate solution, the number of treatments, and the leak defect rate.The number of treatments and the leak defect rate decrease as the specific gravity of the manganese nitrate solution increases, but when the specific gravity is 1.8, Even if the specific gravity reaches the limit of 1.9, the number of treatments and the leak defect rate do not decrease.

[Problem that the invention seeks to solve]

As is clear from Table 1, in the conventional method using manganese nitrate solutions with the same specific gravity, even if the specific gravity of the manganese nitrate solution is increased from 1.8 to 1.9, it is not possible to reduce the leak defect rate to 2% or less. There's a problem. [Means for solving the problem] The above problem can be solved by impregnating the anode element with an aqueous solution of manganese nitrate with a specific gravity of 1.8 as a first step, thermally decomposing the aqueous solution of manganese nitrate to form a manganese dioxide layer, and then As a second step, the anode element is impregnated with an aqueous solution of manganese nitrate having a specific gravity of 1.9, and the aqueous solution of manganese nitrate is thermally decomposed to form a manganese dioxide layer.
This problem is solved by the method of manufacturing a solid electrolytic capacitor according to the present invention. [Operation] By forming the first half manganese dioxide layer using an aqueous solution of manganese nitrate with a specific gravity of 1.8, and forming the second half manganese dioxide layer using an aqueous solution of manganese nitrate with a specific gravity of 1.9, the formed dioxide The manganese layer is filled up to the tip of the cavity and has a dense composition, making it possible to significantly reduce the leak defect rate without causing a sudden increase in tan δ or a sudden decrease in capacitance. [Examples] Examples of the present invention will be described below. Factors that affect the leak failure rate in the manganese dioxide layer forming process include corrosion of the anodic oxide film by hot nitric acid and cracks that occur in the anodic oxide film. Generally, the shorter the time during which the anodic oxide film is corroded by hot nitric acid during the thermal decomposition process, the lower the leak defect rate will be. In other words, the time it takes for an anodic oxide film to be corroded by hot nitric acid is longer than for an aqueous solution of manganese nitrate with a specific gravity of 1.8.
If an aqueous solution of manganese nitrate with a specific gravity of 1.9 is used, the time will be shorter and the leak failure rate will be smaller. However, even if an anode element is impregnated with an aqueous solution of manganese nitrate having a specific gravity of 1.9 and thermally decomposed, the amount of manganese dioxide layer deposited as a cathode layer is usually at most 60%. Furthermore, since the diameter of a cavity with an average diameter of several μm is less than 1μm at the tip, even if impregnation and thermal decomposition are repeated, the entrance to the cavity is sealed in the first treatment, and a sufficiently dense manganese dioxide layer is applied to the tip of the cavity. cannot be formed. In other words, since the manganese dioxide layer is not formed up to the tip of the cavity, cracks occur in the anodic oxide film at the boundary line, causing the manganese dioxide layer to come into contact with the underlying metal foil or metal plate, resulting in a leak failure rate as shown in Table 1. Do not reduce below 2%. Furthermore, as shown in FIG. 2, tan δ is larger than in the case of an aqueous solution of manganese nitrate with a specific gravity of 1.8. On the other hand, in the conventional method using an aqueous solution of manganese nitrate with a specific gravity of 1.8, a sufficiently dense manganese dioxide layer can be formed up to the tip of the cavity, resulting in a smaller tanδ. It takes a long time for the oxide film to be corroded by hot nitric acid, and the leak failure rate is limited to 2% as shown in Table 1 and cannot be improved any further. Therefore, the method for forming a manganese dioxide layer according to the present invention differs from conventional methods in that the formation of the manganese dioxide layer is performed in a first stage and a second stage.
That is, in the first stage, in order to form a sufficiently dense manganese dioxide layer up to the tip of the cavity, treatment using an aqueous solution of manganese nitrate with a specific gravity of 1.8 is repeated twice, and in the second stage, the anodic oxide film is heated In order to shorten the time required for corrosion by nitric acid, treatment using an aqueous solution of manganese nitrate with a specific gravity of 1.9 was repeated twice. By dividing the formation of the manganese dioxide layer into the first and second stages, the specific gravity can be reduced.
The advantages of using an aqueous solution of manganese nitrate with a specific gravity of 1.8 and the advantages of using an aqueous solution of manganese nitrate with a specific gravity of 1.9 are added, and the formed manganese dioxide layer fills up to the tip of the cavity and has a dense composition. As a result, the leak failure rate can be reduced to 0.5% without causing a sudden increase in tanδ or a sudden decrease in capacitance. [Effects of the Invention] As described above, according to the present invention, the leak failure rate can be reduced without causing a sudden increase in tanδ or a sudden decrease in capacitance.
A method for forming a manganese dioxide layer that can reduce the amount to 0.5% can be provided.

[Brief explanation of the drawing]

Figure 1 is an enlarged cross-sectional view of the anode element, Figure 2 is the specific gravity of the manganese nitrate solution, the number of treatments, and tanδ.
FIG. 3 is a diagram showing the relationship between the specific gravity of the manganese nitrate solution, the number of treatments, and the capacitance.

Claims (1)

[Claims] 1. As a first step, the anode element is impregnated with an aqueous solution of manganese nitrate having a specific gravity of 1.8, and the aqueous solution of manganese nitrate is thermally decomposed to form a manganese dioxide layer.
A method for manufacturing a solid electrolytic capacitor, comprising impregnating an anode element with an aqueous solution of manganese nitrate having a specific gravity of 1.9 as a second step, and thermally decomposing the aqueous solution of manganese nitrate to form a manganese dioxide layer.