Solid electrolyte capacitor and its manufacture

Details Solid electrolyte capacitor and its manufacture Solid electrolyte capacitor and its manufacture

1998-02-18

1999-06-22

Kincaid, Kristine

Electricity: electrical systems and devices

Electrolytic systems or devices

Solid electrolytic capacitor

361525, 361528, 361532, H01G 900

Patent

active

059148527

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a solid electrolytic capacitor and a process for manufacturing the same and particularly to a solid electrolytic capacitor which employs conductive polymers as an electrolyte and to a solid electrolytic capacitor of improved impedance characteristics.


PRIOR ART

An electrolytic capacitor is comprised of an anode of valve action metals such as tantalum, aluminum and the like having fine pores or etching pits, and formed thereon with an oxide coating layer as a dielectric body from which electrodes are drawn.
The drawing of the electrode from the oxide coating layer takes place by a conductive electrolyte layer. Consequently, in the electrolytic capacitor, the electrolyte layer bears a true cathode. For example, in the aluminum electrolytic capacitor, a liquid electrolyte is used as a true electrode, and a cathode merely provides an electrical connection between a liquid electrolyte and an external terminal.
The electrolyte layer which functionates as a true electrode requires adhesive properties, denseness, uniformity and the like with the oxide coating layer. In particular, adhesive properties at the inside of fine pores or etching pit of the anode greatly affect to electrical properties and hitherto a number of electrolyte layers have been proposed.
In the solid electrolytic capacitor, a solid conductive electrolyte is used in place of a liquid electrolyte which lacks in impedance characteristics at a high-frequency region on account of ionic conduction as known by manganese dioxide and 7,7,8,8-tetracyanoquinodimethane (TCNQ) complex.
The solid electrolyte layer of manganese dioxide is formed by dipping an anode element of sintered body of tantalum into an aqueous solution of manganese nitrate for subsequent thermal decomposition at approximately 300.degree. C.-400.degree. C.
In the capacitor employing the solid electrolyte layer thus formed, the oxide coating layer is likely subjected to breakage on the thermal decomposition of manganese nitrate with a possible increment of the leakage current and further a satisfactory impedance characteristics could not be obtained because of a high specific resistance of the manganese dioxide per se.
Moreover, the lead wire damaged by a thermal treatment needed an alternate external terminal for connection as an additional step.
A solid electrolytic capacitor with use of TCNQ complex is disclosed in the Japanese Laid-Open Patent Publication 58-191414, wherein TCNQ complex is objected to the thermal melting with subsequent dipping into and coating with an anode to form a solid electrolyte layer. TCNQ complex has a high electrical conductivity with improved results in frequency and thermal characteristics.
TCNQ complex soon after molten tends, however, to transform into an insulator with difficulty in the temperature control during the manufacturing process of the capacitor and since TCNQ complex per se lacks in heat resistance a remarkable variation in the characteristics is caused by a soldering heat when TCNQ is mounted on a printing base.
In order to solve the matters to be caused by those manganese dioxide or TCNQ complex, it has been tried to use such conductive polymers as polypyrrole for a solid electrolyte layer.
The conductive polymers which are represented by a polypyrrole are mainly formed by a chemical oxidative polymerization process or a chemical polymerization or an electrolytic oxidative polymerization process or an electrolytic polymerization, but with a difficulty in forming a film with high strength and denseness.
On the other hand, the electrolytic oxidative polymerization process needs an application of a voltage to an object for forming a film with a difficulty in application it to an anode for the electrolytic capacitor formed on its surface with an oxide coating layer of an insulator. Thus, there is proposed a process of coating the oxide coating layer previously with a conductive prime coating layer of for example conductive polymer film which is chemically polymerized with an oxidizing agent

REFERENCES:
patent: 5368959 (1994-11-01), Koksbang et al.
patent: 5536601 (1996-07-01), Koksbang et al.
patent: 5766515 (1998-06-01), Jonas et al.

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