Electricity: electrical systems and devices – Electrolytic systems or devices – Solid electrolytic capacitor
Reexamination Certificate
2001-07-06
2002-08-06
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Solid electrolytic capacitor
C361S528000, C361S508000, C361S524000, C361S518000, C029S025030
Reexamination Certificate
active
06430032
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a solid electrolytic capacitor comprising a porous valve-acting metal substrate having formed thereon an electrically conducting polymer as a solid electrolyte layer and also relates to a method for producing the solid electrolytic capacitor.
More specifically, it relates to a high-performance solid electrolytic capacitor obtained by forming the solid electrolyte layer such that the thickness at the cut surface of the substrate and at the masking boundary part is larger than the thickness in other parts, and also relates to a method for producing the solid electrolytic capacitor, especially using a monomer solution and an oxidizing agent solution.
BACKGROUND ART
In the production of a solid electrolytic capacitor, as shown in
FIG. 1
, an oxide dielectric film layer
2
is generally formed on an anode substrate
1
comprising a metal foil subjected to an etching treatment to have a large specific surface area, a solid semiconductor layer (hereinafter referred to as a “solid electrolyte”)
4
is formed as a counter electrode in the outer side of the dielectric layer and further thereon, an electrically conducting layer
5
such as electrically conducting paste is preferably formed, thereby fabricating a capacitor basic device. This device by itself or a stacked body resultant from stacking these devices is connected with lead wires
6
,
7
and thereafter, the whole is completely molded with epoxy resin
8
or the like and then put into use as a capacitor part in electric articles over a wide range.
In recent years, with the progress of digitization of electrical instruments or high-speed processing of personal computers, a compact and large-capacitance capacitor or a capacitor showing low impedance in the high frequency region is being demanded.
As the compact and large-capacitance capacitor, electrolytic capacitors such as aluminum electrolytic capacitor and tantalum electrolytic capacitor are known.
The aluminum electrolytic capacitor is advantageous in that a large-capacitance capacitor can be obtained at a low cost but suffers from such problems that when an ion conducting liquid electrolyte is used as the electrolyte, the impedance in the high frequency region is high, the capacitance decreases accompanying the evaporation of the electrolytic solution with the passing of time and the temperature characteristics are inferior.
The tantalum electrolytic capacitor where a manganese oxide is generally used as the electrolyte, has such problems that the manganese oxide predominantly produced by the thermal decomposition of manganese nitrate cannot be evaded from the possibility of the dielectric film having damages at the thermal decomposition and due to the relatively high specific resistance, the impedance in the high frequency region is high.
In order to solve these problems, it has been proposed to use an electrically conducting polymer having electric conductivity as the solid electrolyte. For example, use of an intrinsic conducting polymer having an electric conductivity of 10
−3
to 10
3
S/cm (see, JP-A-1-169914 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) (corresponding to U.S. Pat. No. 4,803,596)) and use of a polymer such as polyaniline (see, JP-A-61-239617), polypyrrole (see, JP-A-61-240625), a polythiophene derivative (see, JP-A-2-15611 (corresponding to U.S. Pat. No. 4,910,645)) or polyisothianaphthene (see, JP-A-62-118511) are known. These electrically conducting polymers comprising a &pgr;-conjugated structure are mostly used in the form of a composition containing a dopant.
In recent years, not only the addition of a dopant but also a combination use with, for example, manganese dioxide (see, JP-B-6-101418 (the term “JP-B” as used herein means an “examined Japanese patent publication”) (corresponding to U.S. Pat. No. 4,959,753)) or filler (see, JP-A-9-320901) is employed.
With respect to the shape of the solid electrolyte, it has been proposed to weld a metal onto an aluminum foil and thereby form a starting point for growing an electrically conducting polymer by the electrolytic oxidative polymerization throughout the surface of the aluminum foil (see, JP-A-4-307917).
Also, a method of performing the alternate impregnation with a monomer solution and with an oxidizing agent solution each from 1 to 20 times and the dipping in an oxidizing solution for 5 minutes to 5 hours, thereby improving the polymerization efficiency, has been proposed (see, JP-A-11-238648).
PROBLEMS TO BE SOLVED BY THE INVENTION
These conventional methods for producing a solid electrolytic capacitor using an electrically conducting polymer as the solid electrolyte have the following problems.
(1) When monomer is used in forming a solid electrolyte layer, a mixed solution of monomer and an oxidizing agent is used and the monomer in the mixed solution is polymerized by itself due to the oxidizing action of the oxidizing agent in the mixed solution and converts into polymer. This polymer must be discarded. Therefore, monomer in the mixed solution cannot be used effectively and the use efficiency of the starting material is very bad.
(2) The mixed solution of monomer and an oxidizing agent changes in the property and therefore, the process of forming the solid electrolyte layer is unstable, for example, the oxidizing action of the oxidizing agent decreases to shorten the life of the mixed solution.
(3) In addition, even when the oxidizing agent solution and the monomer solution are separately prepared (two solutions) and the metal foil substrate is alternately dipped in these solutions, the monomer disadvantageously dissolves out into the oxidizing agent solution at the time of dipping the substrate impregnated with the monomer solution in the oxidizing agent solution for a predetermined time period, and the monomer polymerizes in the oxidizing agent solution. As a result, the life of the oxidizing agent solution is extremely shortened. Also, in the case of dipping the metal foil substrate in the oxidizing agent solution and then in the monomer solution for a predetermined time period, the life of the monomer solution is similarly shortened.
(4) In the preparation of the mixed solution of monomer and an oxidizing agent, the concentrations of and the mixing ratio between monomer and the oxidizing agent have a certain limit, therefore, the monomer concentration cannot be freely selected and for forming the solid electrolyte layer to have a desired thickness, for example, the number of times of performing the polymerization must be disadvantageously increased.
(5) According to the method of repeating the alternate dipping in the oxidizing agent solution and in the monomer solution to perform the polymerization, a washing step is generally provided after each polymerization. This washing operation every each polymerization and the time spent therefor not only lower the production efficiency of a solid electrolytic capacitor device but also decrease the strength of the polymer solid electrolyte layer part, because overlapping of the polymer solid electrolyte layers is reduced. Thus, improvement is necessary also in view of the capability of the solid electrolytic capacitor.
(6) Since the dielectric layer is formed only by an electrochemical forming treatment in the later step, the cut surface (cut end part) formed in cutting the porous valve-acting metal into a predetermined shape is weak as compared with the part other than the cut surface, and the solid electrolyte is liable to adhere thereto in a small amount.
(7) In the masking part for insulating the anode part from the cathode part of the solid electrolytic capacitor and thereby preventing the solid electrolyte from extending to the anode part, the solid electrolyte is liable to fail in satisfactorily adhering and the capacitance is disadvantageously reduced. Furthermore, the masking part works out to a part of joining anodes in stacking the solid electrolytic capacitor devices and therefore, this part is readily subject to a stress, as a res
Furuta Yuji
Monden Ryuji
Obata Tatsuo
Sakai Atsushi
Yamazaki Katsuhiko
Ha Nguyen
Reichard Dean A.
Showa Denko K. K.
LandOfFree
Solid electrolytic capacitor and method for producing the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Solid electrolytic capacitor and method for producing the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Solid electrolytic capacitor and method for producing the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2946953