1. Field of the Invention
The present invention relates to a method of manufacturing a conductive polymer electrolytic capacitor, and more specifically, it relates to a method of manufacturing a conductive polymer electrolytic capacitor comprising a solid electrolyte containing a conductive polymer and an ionic liquid.
2. Description of the Background Art
An electrolytic capacitor employing a conductive polymer for an electrolyte and a cathode conductive layer is known in general. In relation to such a conductive polymer electrolytic capacitor, it is known that an electrolytic capacitor exhibiting a low leakage current and having high heat resistance and high moisture resistance can be manufactured by employing a dopant hardly damaging a dielectric layer consisting of an anodized film or also using a solid organic onium salt having repairability for a valve metal (refer to Japanese Patent Laying-Open No. 2003-22938, for example).
However, the conductive polymer essentially has no anodic oxidizability, whereby improvement in the withstand voltage characteristic of the conductive polymer electrolytic capacitor is limited. Japanese Patent Laying-Open No. 3-96210 (1991) describes a method of improving the withstand voltage by aging an anodic body having a solid electrolytic layer thereby performing re-repair/forming, as means for solving this problem.
However, this document, describing a method of aging the anodic body by applying a constant voltage not more than half a forming voltage, discloses that the yield is remarkably deteriorated if the forming voltage is increased. Thus, there is no technique disclosing that at least 50% of a forming voltage for a valve metal can be extracted as a normal voltage in relation to a conductive polymer electrolytic capacitor.
Further, it is known that dissociation between a forming voltage and a withstand voltage is increased when the forming voltage is increased (refer to Electrolytic Condenser Review, Vol. 53 (1), 95 (2002)). While the forming voltage and the withstand voltage are equivalent to each other up to about 30 V (however, the actual working voltage is set to about 15 V in consideration of safety), the withstand voltage is remarkably reduced at a forming voltage exceeding 30 V. The withstand voltage is 50 V and the practical voltage is not more than 24 V whether forming is performed at 100 V or 300 V. When the forming voltage is increased, further, the capacitance is unpractically reduced. In general, therefore, it is extremely difficult to manufacture an electrolytic capacitor having an actual working voltage of at least 24 V in relation to a conductive polymer electrolytic capacitor.
In order to solve this problem, it is attempted to provide an insulating layer referred to as a buffer layer on a dielectric film. If such a layer is provided, however, equivalent series resistance (ESR) or a tan δ characteristic is deteriorated, to damage the high performance of the conductive polymer electrolytic capacitor.