Electricity: electrical systems and devices – Electrolytic systems or devices – Solid electrolytic capacitor
Reexamination Certificate
2001-07-16
2003-02-11
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Solid electrolytic capacitor
C361S530000, C029S025030
Reexamination Certificate
active
06519137
ABSTRACT:
Solid electrolytic capacitor and production method thereof, and conductive polymer polymerizing oxidizing agent solution.
1. Field of the Invention
The present invention relates to a solid electrolytic capacitor of a wound-roll type having an electrically conductive polymer as the electrolyte and a method of fabricating the same. Also, it relates to an oxidizing agent solution for polymerizing an electrically conductive polymer which is used as the electrolyte in a solid-electrolytic capacitor.
2. Background of the Invention
As a variety of electronic devices are now adapted for operating at higher frequencies, large capacitance type electrolytic capacitors are required which have favorable levels of impedance over the higher frequencies. For diminishing the impedance at higher frequencies, a solid electrolytic capacitor is introduced which employs as the electrolyte a highly electrical conductive material such as a tetracyanoquino-dimethane complex salt (referred to as TCNQ hereinafter) or any other conductive polymer. Also, for satisfying the demand of large capacitance, a wound-roll type of the solid electrolytic capacitor (having a positive foil and a negative foil separated by a separator and wound together in a roll) is proposed which is highly feasible to increase the capacitance as compared with a common electrode foil-layer type capacitor, while employing TCNQ or a conductive polymer as the electrolyte.
For use with such wound-roll type solid electrolytic capacitors, a number of methods for producing a highly conductive polymer have been developed. Among the most common methods for generating a solid electrolyte layer are electrolytic or chemical polymerization of a heterocyclic monomer solution and ah oxidizing agent solution alternately and electrolytic or chemical polymerization of a mixture of oxidizing agent solution and monomer solution for conductive polymer.
Typical examples of the heterocyclic monomer are pyrrole, thiophene, ethylene-dioxythiophene, aniline, and their derivatives. Also, examples of the oxidizing agent solution are alcohol solutions (methanol, ethanol, isopropyl alcohol, n-butanol, and ethylene glycol, etc.) containing p-toluene-sulfonic acid ferric salt, dodecyl-benzene-sulfonic acid ferric salt, naphthalene-sulfonic acid ferric salt, triisopropyl-naphthalene-sulfonic acid ferric salt, and long-chain alphatic sulfonic acid ferric salt. However, successful techniques have hardly been proposed for eliminating the effect of impurities contained in an oxidizing agent solution or a heterocyclic monomer used for chemically polymerizing a conductive polymer. Some conventional methods can simply specify the concentration of an oxidizing agent in an oxidizing agent solution.
It is known to use a separator for avoiding direct contact between the positive electrode foil and the negative electrode foil in a wound-roll type capacitor. The separator in a conventional electrolytic capacitor of a liquid electrolyte type is commonly an electrolyte-filled paper made of Manila hemp or Kraft paper.
In a wound-roll type solid electrolytic capacitor having an electrically conductive polymer as the electrolyte, an electrolyte-filled paper made of glass fiber based unwoven fabric, Manila hemp, or Kraft paper is rolled and then carbonized by baking for use as the separator (referred to as a carbonized paper hereinafter). A particular solid electrolytic capacitor is disclosed in Japanese Patent Laid-open Publication (Heisei)10-340829 where the separator is made of a synthetic unwoven fabric filled with Vinylon (a resin based on polyvinyl alcohol) or a composite unwoven fabric filled with Vinylon as a main component and other resin materials.
Also, uniquely proposed is a method of fabricating a wound-roll type aluminum electrolytic capacitor having TCNQ as the electrolyte which includes heating TCNQ to a temperature higher than its melting point to impregnate a capacitor element with melted TCNQ (comprising substantially 100% of a major component which contributes to the higher electrical conductivity) and then cooling down the capacitor element to yield a solid electrolyte layer of TCNQ between the positive electrode foil and the negative electrode foil. A related technique is provided for applying a dielectric oxide film, 2 to 5 volts, on the negative electrode foil in order to avoid inverse impression of voltage.
On the other hand, some techniques for improving a common aluminum electrolytic capacitor using a liquid electrolyte are disclosed in Japanese Patent Laid-open Publications (Showa)60-1826, (Heisei)1-304720, and (Heisei)9-186054 where providing a titanium layer or titanium nitride layer on the negative electrode foil made of a conductive metallic material such as aluminum to increase the static capacitance and prevent the electrolyte from being leaked out by the effect of electrochemical reaction over the negative electrode foil.
It is also known that solid electrolytic capacitors having a conductive polymer as the solid electrolyte, unlike common liquid electrolytic capacitors having a liquid electrolyte under an evaporating pressure, never contain a component which can easily evaporated at a higher temperature atmosphere (actually 200° C. or more) during the soldering process for surface mounting electronic devices on a printed circuit board and eliminates substantially an unwanted event of pressure increase in the shell, hence minimizing undesired effects such as expansion of the shell or injury of the sealing members and probably being favorable for use in the surface mounting.
However, such solid electrolytic capacitors having a conductive polymer as the solid electrolyte have been developed much later than popular aluminum electrolytic capacitors having a liquid electrolyte and their techniques for surface mounting fail to be successfully practiced.
One of critical disadvantages of the solid electrolytic capacitors having a highly conductive TCNQ or polymer as the solid electrolyte is that the solid electrolyte has no ionic conductivity hence disabling to repair any damaged portion of the dielectric oxide film, allowing a higher rate of the leakage current, and making frequent occasions of short-circuit during the aging process.
Also, when a glass fiber based unwoven fabric is used as the separator in a wound-roll type capacitor, its rolled form is generally low in the physical strength and its fracture may injure the dielectric oxide film thus causing current leakage or short-circuit particularly during the aging process. The glass fiber unwoven fabric has a disadvantage that its needle-like fiber pieces separated during the cutting or rolling may be scattered in all directions thus damaging the working environment.
The carbonized electrolyte-filled paper assists the TCNQ or conductive polymer to diminish the impedance at high frequencies only when the capacitor element is heated to as a high temperature as over 250° C. The heating up may however injure the dielectric oxide film and increase the leakage current. Also, as the platings (commonly of tin/lead solder) on the leads of the capacitor element are oxidized by the heating, their soldering affinity on the leads of a finished capacitor may significantly be declined. For improvement, the use of silver plated leads which are high in the resistance to oxidation shall be required, resulting in the cost up.
The composite fabric consisting mainly of Vinylon-based unwoven fabric and Vinylon-based resin is lower in the tension strength than the electrolyte-filled paper and may easily be injured during the rolling to form a capacitor element, hence causing short-circuit during the aging process. Also, as an adhesive is used for bonding resin fibers to one another to have a sheet, it may interrupt the application of the conductor polymer to the separator, thus discouraging the fabrication of a solid electrolytic capacitor having a lower impedance at high frequencies. The Vinylon-based resin is low in the resistance to heat and may possibly be decomposed during the use of the solid electrolytic capacitor un
Masumi Hideki
Mori Yoshiyuki
Morokuma Munehiro
Murata Yuki
Nakahara Takehiko
Matsushita Electric - Industrial Co., Ltd.
McDernott, Will & Emery
Reichard Dean A.
Thomas Eric
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