JPH04119617A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

PURPOSE:To obtain a solid electrolytic capacitor having a small leakage current and high withstand voltage by a method wherein, when an oxide film is formed by anode oxidation on the surface of a porous sintered body consisting of valve- action metal, the anode oxidation is conducted using a pulselike current. CONSTITUTION:As a pulse-like current is used for anode oxidation, a quiescent time is generated, the bubbles generated during anodic oxidation disappear in the above-mentioned quiescent time, and hydroxide ions are fully infiltrated into the recessed part of the surface of a porous sintered body and the fine holes in the inner part of the porous sintered body, and as a result, a uniform oxide film can be formed. At that point, voltage is boosted to 100V by applying pulselike voltage in such a manner that a pulse current of the conduction time of 1 second at 120mA/g and the quiescent time of 2 seconds, then anodic oxidation is conducted while pulselike voltage of 100V is being applied for two hours, and an oxide film is formed. As a result, a solid electrolytic capacitor, having small leakage current and high withstand voltage, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a solid electrolytic capacitor, and more particularly to an improvement in the method for forming an oxide film on the surface of a porous sintered body made of a valve metal. It is.

BACKGROUND ART Conventionally, as a manufacturing method for such a solid electrolytic capacitor, an oxide film is formed on the surface of a porous sintered body made of a valve metal by anodic oxidation, and the oxide film on the porous sintered body is In this process, conductive materials such as manganese dioxide as a semiconductor layer and graphite silver as a cathode layer were sequentially formed.
In forming the oxide film, the porous sintered body is immersed in a phosphoric acid aqueous solution, which is a chemical conversion liquid, and the porous sintered body is used as an anode and the phosphoric acid aqueous solution is used as a cathode.
A predetermined DC voltage corresponding to the rated working voltage was applied between the cathodes and maintained for a long time.

Problems to be Solved by the Invention However, in such conventional methods, the rate-limiting step in this reaction is the movement of hydroxide ions in the phosphoric acid aqueous solution to the anode interface, which plays a major role in the formation of an oxide film. ,
As shown in Figure 2 (a) and (b), the thickness of the diffusion layer deficient in hydroxide ions is thicker than the irregularities on the anode surface, and as a result, the flow of hydroxide ions concentrates on the convexities. A uniform oxide film cannot be formed, and the bubbles generated from the porous sintered body during anodization make it difficult for the phosphoric acid aqueous solution to penetrate into the pores inside the porous sintered body. Since the oxide film is insufficiently formed, there is a problem in that leakage current and breakdown voltage characteristics deteriorate.

The present invention solves these problems and makes it possible to form a uniform oxide film on the surface of a porous sintered body made of valve metal, thereby achieving low leakage current and high withstand voltage. It is an object of the present invention to provide a method for manufacturing a solid electrolytic capacitor that yields a solid electrolytic capacitor.

Means for Solving the Problems In order to achieve the above objects, the present invention provides that when an oxide film is formed on the surface of a porous sintered body made of a valve metal by anodic oxidation, the anodic oxidation is performed using a pulsed electric current. This is done using the .

Effects According to the method for manufacturing a solid electrolytic capacitor of the present invention described above, since a pulsed current is used for anodizing, there is a downtime, and during this downtime, there is a The generated air bubbles disappear and the hydroxide ions fully penetrate into the recesses on the surface of the porous sintered body and the pores inside the porous sintered body, making it possible to form a uniform oxide film. , a solid electrolytic capacitor with low leakage current and high withstand voltage can be obtained.

EXAMPLES Hereinafter, examples of the present invention will be explained while comparing them with conventional examples.

(Conventional example) Kuntal powder is molded using a well-known method and sintered to form φ2
．． 3ffa+X 3. Make a porous sintered body of Omm,
Then, this porous sintered body was boosted to 100 V at a constant current of 120A+A/g in a 0.1 mol/1 phosphoric acid aqueous solution, and then held at a constant voltage of IOOV for 2 hours to perform anodic oxidation. An oxide film is formed on the surface of the porous sintered body.Next, a semiconductor layer, a graphite layer, a silver paste layer, and a solder layer are sequentially formed on the cathode conductor part on this oxide film, and finally a resin exterior is applied. A solid electrolytic capacitor was obtained.

(Present Example) In the above conventional example, a constant current of 120a+A/g is used to
The oxide film was formed by boosting the voltage to V and then holding it at a constant voltage of 100 μ for 2 hours to perform anodic oxidation. Apply voltage in a pulsed manner so that a pulse current of seconds flows, increase the voltage to IOOV, and then increase the voltage to 100V.
An oxide film was formed by anodic oxidation by applying a pulsed voltage and holding it for 2 hours.

Table 1 and FIG. 1(a) show the results of a comparison between the characteristics of the solid electrolytic capacitor in this example described above and the characteristics of the solid electrolytic capacitor in the conventional example.

Table 1 As is clear from the results in Table 1 and Figures 1 (a) and (b),
The solid electrolytic capacitor of this example was able to improve the leakage current and withstand voltage characteristics of the conventional example in which anodic oxidation was performed using a constant current.

In this example, a phosphoric acid aqueous solution was used as the chemical conversion liquid, but any chemical conversion liquid may be used as long as it contains hydroxide ions, and the optimum pulse period and current value at that time will depend on the amount of hydroxide ions. It is to be determined.

Effects of the Invention As is clear from the description of the above embodiments, according to the method for manufacturing a solid electrolytic capacitor of the present invention, anodic oxidation is performed using a pulsed current. As a result, a solid electrolytic capacitor with low leakage current and high withstand voltage can be obtained.

[Brief explanation of the drawing]

Figures 1 (a) and (b) are characteristic diagrams showing a comparison of leakage current and breakdown voltage of solid electrolytic capacitors in the conventional example and the embodiment of the present invention, and Figures 2 (a) and (b) are schematic diagrams of the anode surface and It is a figure showing the relationship between hydroxyl ion concentration and a diffusion layer. Name of agent: Patent attorney Akira Okaji and two others

Claims (1)

[Claims] 1. A method for manufacturing a solid electrolytic capacitor, characterized in that when an oxide film is formed on the surface of a porous sintered body made of a valve metal by anodic oxidation, the anodic oxidation is performed using a pulsed current.