JPH09246109A - Method for manufacturing solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solid electrolytic capacitor small in a leakage current and a breakdown strength by a method wherein, on a face of a porous sintered body composed of a metal having a valve reaction, an oxide film is formed by anodigation by a compound liquid to which hydrogen peroxide water being oxidizing agent is added. SOLUTION: On a face of a porous sintered body composed of a metal having a valve reaction, an oxide film is formed by anodigation by a compound liquid to which peroxide water being oxidizing agent is added. As described above, since the compound liquid to which hydrogen peroxide water being oxidizing agent is added is used, not only hydroxyl ions but also hydrogen peroxide water become a supply source of oxygen required for a formation on of the oxide film. As the result, movement of hydroxyl ions to an anode interface is not rate-determining for forming the oxide film. For this reason, it is also possible to uniformly form the oxide film in a recess of a face of the porous sintered body or a pore inside the porous sintered body.

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 used in various electronic devices, and more particularly to an improvement in an oxide film forming method.

[0002]

2. Description of the Related Art Generally, when manufacturing a solid electrolytic capacitor of this type, an oxide film is formed on the surface of a porous sintered body made of a metal having a valve action by anodic oxidation, and the porous sintered body is oxidized. A manganese dioxide layer as a semiconductor layer is formed on the film, and a graphite layer and a silver conductive material layer are sequentially formed on the manganese dioxide layer as a cathode layer. In the past, the porous sintered body was conventionally immersed in a phosphoric acid aqueous solution which is a chemical conversion solution, and the porous sintered body was used as an anode, and the phosphoric acid aqueous solution was used as a cathode. According to the above, a predetermined DC voltage is applied and the voltage is held for a long time.

[0003]

However, according to such a conventional method, the hydroxide ion (reaction formula 1) in the chemical conversion liquid, which has a main function of supplying oxygen necessary for forming an oxide film, reaches the anode interface. Is the rate-determining step of this reaction, the thickness of the hydroxide ion-deficient diffusion layer is thicker than the unevenness of the anode surface, as shown in FIGS. The flow of hydroxide ions is concentrated and a uniform oxide film cannot be formed, and due to the bubbles generated from the porous sintered body during anodic oxidation, the chemical conversion liquid has pores inside the porous sintered body. It is difficult to permeate even up to that point, and as a result, the formation of an oxide film inside becomes insufficient, resulting in the problem that the leakage current and the withstand voltage characteristics deteriorate.

4OH ⁻ → 2H ₂ O + O ₂ + 4e ⁻ (Reaction Formula 1) The present invention solves the above-mentioned conventional problems, and a uniform oxide film is formed on the surface of a porous sintered body made of a metal having valve action. It is an object of the present invention to provide a method for manufacturing a solid electrolytic capacitor, which can form a solid electrolytic capacitor having a small leakage current and a high withstand voltage.

[0005]

In order to achieve the above object, a method for producing a solid electrolytic capacitor according to the present invention comprises a porous sintered body made of a metal having a valve action and hydrogen peroxide as an oxidizing agent. An oxide film is formed by anodic oxidation with a chemical conversion liquid containing water. According to this manufacturing method, a uniform oxide film is formed on the surface of a porous sintered body made of a metal having valve action. As a result, a solid electrolytic capacitor having a small leakage current and a high withstand voltage can be obtained.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention is anodization by a chemical conversion liquid in which peroxide water as an oxidant is added to the surface of a porous sintered body made of a metal having a valve action. It is designed to form an oxide film by means of a chemical conversion solution to which hydrogen peroxide, which is an oxidant, is added. It serves as a supply source (reaction formulas 2 and 3), and as a result, the migration of hydroxide ions to the anode interface does not become the rate-determining factor for the oxide film formation. An oxide film can be evenly formed even on the inner pores, whereby a solid electrolytic capacitor having a small leakage current and a high withstand voltage can be obtained.

2H ₂ O ₂ → 2H ₂ O + O ₂ (Reaction Formula 2) H ₂ O ₂ + 2OH ⁻ → H ₂ O + O ₂ + 2e ⁻ (Reaction Formula 3) Hereinafter, one embodiment of the present invention will be compared with a conventional example. While explaining.

(Conventional example) A tantalum powder which is a metal having a valve action is formed by a known method and sintered to form a porous sintered body of φ2.3 mm × 3.0 mm, and this porous The sintered compact was immersed in a 0.1 mol / l phosphoric acid aqueous solution, a voltage was applied at a constant current of 120 mA / g to increase the voltage to 100 V, and this increased pressure was maintained for 2 hours to carry out anodization. By doing so, an oxide film is formed on the surface of the porous sintered body. Next, a manganese dioxide layer which is a semiconductor layer, a graphite layer, a silver paste layer and a cathode conductor portion of a solder layer were sequentially formed on the oxide film, and finally a resin coating was applied to form a solid electrolytic capacitor.

(One embodiment of the present invention) The difference from the conventional example is that 0.1 mol / l phosphoric acid aqueous solution is an oxidizing agent.
A solid electrolytic capacitor was constructed in the same manner as in the conventional example except that 0 vol% hydrogen peroxide solution was used as a chemical conversion solution, and an oxide film was formed by anodizing in this chemical conversion solution. did.

The results of comparison between various electric characteristics of the solid electrolytic capacitor according to the embodiment of the present invention described above and various electric characteristics of the conventional solid electrolytic capacitor are shown in Table 1 and FIGS. 1 (a) and 1 (b). ).

[0011]

[Table 1]

As is clear from the results shown in Table 1 and FIGS. 1A and 1B, the solid electrolytic capacitor according to the embodiment of the present invention is anodized by using only the phosphoric acid aqueous solution. Further, the leakage current and the withstand voltage characteristic can be improved as compared with the solid electrolytic capacitor in the conventional example.

In the embodiment of the present invention described above, a phosphoric acid aqueous solution to which hydrogen peroxide water is added is used as the chemical conversion liquid, but the chemical conversion liquid contains hydroxide ions and hydrogen peroxide. Any solution may be used as long as it dissolves water, and the optimum addition amount at that time is determined by the amount of hydroxide ion.

[0014]

As described above, the method for producing a solid electrolytic capacitor of the present invention uses a chemical conversion solution in which hydrogen peroxide, which is an oxidizing agent, is added to the surface of a porous sintered body made of a metal having valve action. It is designed to form an oxide film by anodic oxidation.Because a chemical conversion solution containing hydrogen peroxide, which is an oxidant, is used, not only hydroxide ions but also hydrogen peroxide are necessary for forming the oxide film. It serves as a source of oxygen, and as a result, the migration of hydroxide ions to the anodic interface does not control the rate of oxide film formation.Therefore, in the recesses on the surface of the porous sintered body and pores inside the porous sintered body, It is possible to form an oxide film evenly up to this point, whereby a solid electrolytic capacitor having a small leakage current and a high withstand voltage can be obtained.

[Brief description of drawings]

FIG. 1 (a) is a characteristic diagram showing a comparison of leakage currents of a solid electrolytic capacitor according to one embodiment of the present invention and a conventional example. (B) Withstand voltage of a solid electrolytic capacitor according to one embodiment of the present invention and a conventional example. Characteristic diagram showing comparison

FIG. 2A is a schematic diagram of the surface of an anode. FIG. 2B is a characteristic diagram showing the relationship between the hydroxide ion concentration and the diffusion layer.

Front page continuation (72) Inventor Yoshiki Hashimoto 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] 1. A solid electrolysis, characterized in that an oxide film is formed on the surface of a porous sintered body made of a metal having a valve action by anodic oxidation by a chemical conversion solution to which hydrogen peroxide solution which is an oxidizer is added. Capacitor manufacturing method.