JP2002203751A - Solid-state electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state electrolytic capacitor having a good reflow characteristic and a good soldering characteristic. SOLUTION: The solid-state electrolytic capacitor comprises a capacitor element which is formed of a solid-state electrolyte held by a separator, and an anode foil and a cathode foil which are wound around the capacitor element through a separator, with the anode foil having an anode extracting means which comprises an anode connecting section, and an anode external connecting section and the cathode foil having a cathode extracting means which comprises a cathode connecting section and a cathode external connecting section. The anode external connecting section and the cathode connecting section are applied with metal plating having a melting point of 250 deg.C or below, and the separators are formed of heat-resistent resin, resulting in leading to a good reflow characteristic and also a good soldering characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same, and more particularly to a solid electrolytic capacitor using a conductive polymer as an electrolyte.

[0002]

2. Description of the Related Art An electrolytic capacitor is formed by forming an oxide film layer serving as a dielectric on the surface of an anode electrode made of a valve metal such as tantalum or aluminum and having fine holes and etching pits. Is drawn out. The extraction of the electrode from the oxide film layer is performed by a conductive electrolyte layer. Therefore, in the electrolytic capacitor, the electrolyte layer serves as a true cathode. Such an electrolyte layer functioning as a true cathode is required to have adhesion, denseness, uniformity, and the like with an oxide film layer. In particular, the adhesion between the micropores of the anode electrode and the inside of the etching bit greatly affects the electrical characteristics, and a number of electrolyte layers have been proposed in the past.

[0003] In recent years, the digitization of electronic devices,
With the increase in frequency, a capacitor having a small size, a large capacity, and a low impedance in a high frequency region is required.

To meet these demands, a small-sized and large-capacity battery is provided by winding a capacitor element in which a cathode foil and an anode foil are wound via a separator in a metal case and sealed with a rubber seal. Can be realized. The low impedance can be dealt with by using a granite electrolyte as the electrolyte. Such solid electrolytes include manganese dioxide and 7,7,8,8-tetracyanoquinodimethane (TCN).
Q) Complexes are known. However, these have low conductivity of the formed electrolyte itself, and the impedance characteristics of the electrolytic capacitor using the electrolyte are not sufficient.

To cope with these problems, attempts have been made to use a highly conductive polymer such as polypyrrole or polythiophene as a solid electrolyte. And
At present, attention has been paid to polyethylene dioxythiophene (PEDT), which has a slow reaction rate and excellent adhesion to the oxide film layer of the anode electrode (JP-A-2-15611). A cathode element foil is wound around a capacitor element through a separator, and a monomer and an oxidizing agent are impregnated.Polyethylene dioxythiophene, which is a solid electrolyte, is formed by a chemical polymerization reaction between the monomer and the oxidizing agent that occurs slowly thereafter. A solid electrolytic capacitor generated inside the element has been realized (JP-A-10-34).
No. 0829).

[0006]

[Problems to be solved by the invention]

[0007]

However, lead used for soldering has become a problem due to environmental problems that have been increasing recently.
Lead-free solder has been used. This lead-free solder has a high melting point and a solder reflow temperature of 200 ~
High temperatures up to 270 ° C. If solder reflow is performed under such conditions, the sealing rubber of the solid electrolytic capacitor and the metal case will swell and characteristics will deteriorate, which has been a serious problem.

On the other hand, Japanese Patent Laid-Open No. 2000-58389 discloses
As disclosed in Japanese Patent Application Laid-Open No. 2000-277385, a technique for improving the reflow characteristics by discharging gas generated during reflow by high-temperature treatment at 200 to 300 ° C. is disclosed. However, even with these methods, generation of gas at the time of reflow cannot be completely prevented, and there has been a problem that the separator and the formed polymer are damaged by the high-temperature treatment and the characteristics are deteriorated. Furthermore, silver plating must be applied to the surface so that the lead wire can withstand high temperature processing,
There is a major problem that the silver plating layer reacts with sulfur in the atmosphere to deteriorate solderability.

Accordingly, it is an object of the present invention to provide a solid electrolytic capacitor that can cope with the above-mentioned high-temperature solder reflow and that has no deterioration in characteristics.

[0010]

The solid electrolytic capacitor according to the present invention has an anode foil having an anode drawing portion comprising an anode connecting portion and an anode external connecting portion, and a cathode drawing means comprising a cathode connecting portion and a cathode external connecting portion. While winding the cathode foil and a separator made of a heat-resistant resin, a solid electrolytic capacitor provided with a capacitor element holding a solid electrolyte by the separator, the melting point of the anode external connection portion and the cathode connection portion. It is characterized by metal plating at 250 ° C. or less.

[0011] The separator made of the heat-resistant resin is a woven fabric, a nonwoven fabric, a paper, or a porous film.

Further, the solid electrolyte is polyethylenedioxythiophene formed by chemical polymerization of 3,4-ethylenedioxythiophene and an oxidizing agent.

[0013] Further, the separator made of a heat-resistant resin is made of one or more selected from aramid fiber, aramid fibrid, polyethylene terephthalate fiber, and ethoxy resin.

Further, the metal plating having a melting point of 250 ° C. or less is solder plating or tin plating.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A body electrolytic capacitor according to the present invention will be described. As shown in FIG. 1, a capacitor element 10 is formed by winding an anode electrode foil 1 made of a valve metal such as aluminum or the like and having an oxide film layer formed on its surface, and a cathode electrode foil 2 via a separator 3. I do. Then, the capacitor element 10 is impregnated with 3,4-ethylenedioxythiophene and an oxidizing agent solution, and polyethylene dioxythiophene generated by a chemical polymerization reaction in the capacitor element 10 is used as the solid electrolyte layer 5 as the separator 3. Holding in.

The anode electrode foil 1 is made of a valve metal such as aluminum. An oxide film layer serving as a dielectric is formed on the surface of the anode electrode foil 1 by applying a voltage in an aqueous solution of ammonium borate or the like. ing.

The cathode electrode foil 2 is made of aluminum or the like, similarly to the anode electrode foil 1, and has a surface subjected to an etching treatment.

An anode extraction means 4 and a cathode extraction means 5 for connecting the respective electrodes to the outside are connected to the anode electrode foil 1 and the cathode electrode foil 2 by known means such as stitching and ultrasonic welding. . These electrode extraction means 4,
5 is a connecting portion 41 between the anode electrode foil 1 and the cathode electrode foil 2;
1 and external connection portions 42 and 5 for performing electrical connection with the outside.
2 and is led out from the end face of the wound capacitor element 10.

The capacitor element 10 is formed by winding the above-mentioned anode electrode foil 1 and cathode electrode foil 2 with the separator 3 interposed therebetween. The dimensions of the bipolar electrode foils 1 and 2 are arbitrary according to the specifications of the solid electrolytic capacitor to be manufactured, and the separator 3 may have a width slightly larger than this according to the dimensions of the bipolar electrode foils 1 and 2. .

A solid electrolyte is formed in the capacitor element. It is preferable to use polyethylene dioxythiophene (PEDT) as the solid electrolyte because a solid electrolytic capacitor having a large capacity and low ESR characteristics can be obtained. This PEDT is obtained by converting 3,4-ethylenedioxythiophene (EDT) as a monomer into p-
It can be obtained by polymerizing with ferric toluenesulfonic acid. The polymerization can be carried out by injecting EDT or an EDT solution and an oxidizing agent solution into the capacitor element and heating.
It is also possible to inject a mixed solution of DT and an oxidizing agent into the capacitor element, or to immerse the capacitor element in the mixed liquid, impregnate the capacitor element, and heat.

Then, the capacitor element having the solid electrolyte formed therein is housed in a bottomed cylindrical metal case, and is caulked and sealed with sealing rubber to form a solid electrolytic capacitor (not shown).

The external connection portions 42 and 52, which are part of the electrode lead-out means, use metal-plated lead wires having a melting point of 250 ° C. or less. Examples of such metal plating include solder plating and tin plating.

In the present invention, a separator made of a heat-resistant resin is used. Examples of the separator include woven fabric, nonwoven fabric, paper, and porous film. That is, heat-resistant polymer fibers selected from aramid, polyethylene terephthalate, polyethylene naphthalate, polyphenylene sulfide, wholly aromatic polyester, polyimide, polyamideimide, polyetherimide, polytetrafluoroethylene, and polyaminopismaleimide are used. Woven fabrics, nonwoven fabrics or papers, and porous films using these heat-resistant polymers. Further, the woven fabric, nonwoven fabric or paper may contain a thermoplastic polymer fiber selected from polypropylene, nylon, rayon, ethylene 4-fluorinated ethylene, and poly (vinylidene fluoride), and further include an ethoxy resin and a phenol resin. , A polyurethane resin or a melamine resin may be used as a binder. Among these, aramid paper made of aramid fiber and aramid fibrid, nonwoven fabric made of ethylene phthalate fiber and undrawn polyethylene terephthalate fiber, nonwoven fabric made of aramid fiber and undrawn polyethylene terephthalate fiber, unwoven fabric made of aramid fiber and ethoxy resin Aramid paper comprising an aramid fiber having a high tensile strength and an aramid fibrid is particularly preferred. These separators have sufficient tensile strength to form a wound capacitor element for a solid electrolytic capacitor, and have good capacitor characteristics when a solid electrolyte is formed in the separator.

The aramid paper made of aramid fibers and aramid fibrids is a woven cloth (cloth) or a non-woven fabric (dry cloth) which is a sheet-like molded product of aramid floc and aramid fibrids produced by a dry method or a wet method. And wet), paper, film and the like. Examples of the aramid fiber include "Conex (registered trademark)" and "Technola (registered trademark)" of Teijin Limited. Aramid fibrids are film-like fine particles made of aramid and are sometimes called aramid pulp (for a description of aramid fibrids, Japanese Patent Publication No. 35-11851 and Japanese Patent Publication No. 37-5752)
No.). Since fibrids have a papermaking similar to ordinary wood (cellulose) pulp, they can be dispersed in water and then formed into a sheet by a paper machine.
Further, aramid is divided into valaramid, meta-aramid, and a copolymer thereof depending on the substitution position of the amide group on the benzene ring. As valaramid, polybaraphenylene terefucuramide and its copolymer,
Examples thereof include poly (baraphenylene) -copoly (3,4 diphenyl ether) terefucuramide. Examples of the meta-aramid include polymetaphenylene isofucuramide and a copolymer thereof. In the present invention, meta-aramid is preferably used.

The thickness of the aramid paper is preferably 20 to 60 μm. Below this range, the insulation resistance of the capacitor decreases, and above this range, the ESR of the capacitor increases. The density is preferably from 0.2 to 0.7 g / cm3.
If it is less than this range, the tensile strength is insufficient, and if it exceeds this range, the capacitance decreases and the ESR increases. Further, the tensile strength is 0.8 kgf / 15 mm or more, and further 1.5 kg
f / 15 mm or more is preferable. If it is less than this value, it is not enough to be wound together with the electrode foil as a capacitor element.

The solid electrolytic capacitor of the present invention using the separator made of the above heat resistant resin has good reflow characteristics. The reason is presumed to be as follows. When the swelling of the capacitor and the deterioration of the characteristics after the reflow were examined, it was found that the separator used for the capacitor element caused a decomposition reaction by heating at the time of the reflow, thereby generating gas. However, in the solid electrolytic capacitor of the present invention, since a separator made of a heat-resistant resin is used, a decomposition reaction is not caused even by heating during reflow, so that the reflow characteristics are good. Furthermore, it is known that in a solid electrolytic capacitor in which PEDT is formed by chemical polymerization of EDT and an oxidizing agent, the oxidizing agent remains even after the polymerization,
It was also found that the oxidizing agent accelerated the decomposition reaction of the separator during reflow. However, aramid paper consisting of aramid fiber and aramid fibrid, nonwoven fabric consisting of ethylene phthalate fiber and unstretched polyethylene terephthalate, nonwoven fabric consisting of aramid fiber and unstretched polyethylene terephthalate fiber, and nonwoven fabric consisting of aramid fiber and ethoxy resin are used. In such a case, it does not react with the remaining oxidizing agent, so that generation of gas is further suppressed, and it is considered that reflow characteristics are improved.

As described above, good reflow characteristics can be obtained without performing high-temperature treatment during the manufacturing process as in the prior art. That is, the maximum temperature of the heat treatment during the manufacturing process is less than 200 ° C., which corresponds to the polymerization process. Therefore, there is no deterioration in characteristics due to the high temperature treatment. Further, in the present invention, the melting point of the surface of the lead wire is 250 ° C.
The following metal plating, that is, solder plating, tin plating, etc., is used, but there is no alteration such as oxidation because there is no high-temperature treatment, and these metal platings react with components that form the atmosphere in the atmosphere. Since soldering does not occur, solderability is also good.

Further, when a rubber obtained by adding an alkylphenol resin as a vulcanizing agent to a butyl rubber polymer made of a copolymer of isobutylene and isoprene is used as the sealing rubber, a high hardness can be obtained. Can be prevented from swelling due to gasification.

In the present invention, since the metal case does not swell due to gas generation, there is usually no need for a safety valve formed in the metal case. In addition, manganese-
The use of an aluminum alloy improves the hardness and is suitable for higher temperature reflow tests.

Further, even in the prior art, since generation of gas cannot be completely prevented, the capacitor element is covered with resin to cope with blistering. However, this resin penetrates into the capacitor element and adversely affects the solid electrolyte, resulting in deterioration of characteristics. However, in the present invention, since no gas is generated, there is no need for resin coating, and thus the characteristics are not deteriorated.

Further, before forming the solid electrolyte, the capacitor element is immersed in a solution in which polyvinyl alcohol, vinyl acetate and a silane coupling agent are dissolved and dried, and when these are present in the capacitor element, the initial characteristics are improved. Therefore, it is preferable. The reason is not clear,
An aqueous solution of polyvinyl alcohol is preferred. The concentration of the aqueous solution is 0.005 to 1.5 wt%, preferably 0.01
The immersion temperature is preferably from room temperature to about 100 ° C., and the immersion time is preferably 5 seconds or more. The drying conditions may be such that the moisture in the capacitor element is dried.
3 minutes or more.

[0032]

Next, the solid electrolytic capacitor of the present invention will be described in detail. The anode electrode foil 1 and the cathode electrode foil 2
Made of valve metal, such as aluminum, tantalum,
The surface is preliminarily subjected to an etching treatment to increase the surface area. The anode electrode foil 1 is further subjected to a chemical conversion treatment to form an oxide film layer made of aluminum oxide on the surface. The anode electrode foil 1 and the cathode electrode foil 2
Is wound through a separator 3 to form a capacitor element 10
Get. Note that electrode lead-out means 4 and 5 are electrically connected to the anode electrode foil 1 and the cathode electrode foil 2 of the capacitor element 10, respectively, and protrude from the end face of the capacitor element 10.

Next, 3,4-
Impregnating ethylenedioxythiophene and an oxidizing agent. As the oxidizing agent, a butanol solution of ferric P-toluenesulfonate is used to generate polyethylene dioxythiophene which is a solid electrolyte.

The capacitor element 10 in which the solid electrolyte layer is formed on the separator 3 interposed between the anode electrode foil 1 and the cathode electrode foil 2 is housed in a bottomed cylindrical case, and Form a capacitor. Here, before the polymerization step, a treatment of dipping in a 0.025 wt% aqueous solution of polyvinyl alcohol at 25 ° C. for 1 minute and drying at 100 ° C. for 10 minutes was performed.

The capacitor element 10 in which the solid electrolyte layer is formed on the separator 3 interposed between the anode electrode foil 1 and the cathode electrode foil 2 as described above is housed in a bottomed cylindrical case, and is isobutylene and isoprene. A solid electrolytic capacitor is formed by sealing with a sealing rubber made of a rubber obtained by adding an alkylphenol resin as a vulcanizing agent to a butyl rubber polymer made of a copolymer of the above. The rating is 4WV-330μF.

Here, in Examples 1, 2, 4 to 6 and Comparative Examples 1 and 2, the external connection portions 4 of the electrode extraction means 4 and 5 were used.
The solder wires 2 and 52 were prepared by applying solder plating to the lead wires, and the solder wires of Example 3 were obtained by applying tin plating to the lead wires.

Examples of the separator include aramid paper made of aramid fiber and aramid fiber in Examples 1 to 3, a nonwoven fabric made of polyethylene terephthalate fiber and undrawn polyethylene terephthalate fiber in Example 4, and an aramid fiber and unwoven fabric of Example 5 in Example 5. A nonwoven fabric made of a drawn polyethylene terephthalate fiber, and a nonwoven fabric made of an aramid fiber and an ethoxy resin as Example 6 were used. In Comparative Example 1, a nonwoven fabric made of vinylon fiber and polypinyl alcohol was used. In Comparative Example 2, a high temperature treatment at 300 ° C. was performed after the polymerization step in Comparative Example 1.

In Examples 1, 3 to 6, a cathode foil having a titanium nitride layer formed on the surface was used.

Next, the characteristics of these solid electrolytic capacitors and the characteristics after reflow were measured. (Table 1)
Shown in The reflow test conditions were as follows: maximum temperature 250 ° C, 23
0 ° C. or more for 30 seconds.

[0040]

[Table 1]

As is clear from Table 1, the initial characteristics of the solid electrolytic capacitor of the example were good, and there was almost no change in the characteristics even after the reflow test using lead-free solder.
A solid electrolytic capacitor having good initial characteristics and reflow characteristics has been obtained. On the other hand, in Comparative Example 1 using vinylon, the characteristics after the reflow test were deteriorated.
In Comparative Example 2 in which the high temperature treatment was performed, the initial characteristics were deteriorated.

The first embodiment using the cathode foil having the titanium nitride layer formed on the surface has a higher capacitance than the second embodiment using the normal cathode foil.

Further, the solder wettability of the lead wire of the solid electrolytic capacitor of Example was good, but the solder wettability of Comparative Example 2 was low.

[0044]

The solid electrolytic capacitor according to the present invention comprises an anode foil having an anode drawing means comprising an anode connecting part and an anode external connecting part, and a cathode foil having a cathode drawing means comprising a cathode connecting part and a cathode external connecting part. A solid electrolytic capacitor provided with a capacitor element wound with a separator and holding a solid electrolyte by the separator, wherein a metal plating having a melting point of 250 ° C. or less is applied to the anode external connection portion and the cathode connection portion, In addition, since the separator is made of a heat-resistant resin, the reflow characteristics are good, and the soldering characteristics are also good.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a capacitor element used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Anode electrode foil 2 Cathode electrode foil 3 Separator 4 Anode extraction means 5 Cathode extraction means 41 Connection part with anode electrode foil 51 Connection part with cathode electrode foil 42, 52 External connection part 10 Capacitor element

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[Procedure amendment]

[Submission date] January 5, 2001 (2001.1.5)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

[Title of the Invention] Solid electrolytic capacitor

Claims (5)

[Claims] 1. An anode foil having an anode extraction means comprising an anode connection part and an anode external connection part and a cathode foil having a cathode extraction means comprising a cathode connection part and a cathode external connection part are wound via a separator. A solid electrolytic capacitor comprising a capacitor element in which a solid electrolyte is held by a separator made of a heat-resistant resin, wherein the external connection part of the anode and the connection part of the cathode are plated with a metal having a melting point of 250 ° C. or less. . 2. A woven fabric comprising a separator made of a heat-resistant resin,
The solid electrolytic capacitor according to claim 1, which is a nonwoven fabric, paper, or a porous film. 3. The solid electrolytic capacitor according to claim 1, wherein the solid electrolyte is polyethylene dioxythiophene formed by chemical polymerization of 3,4-ethylenedioxythiophene and an oxidizing agent. 4. The solid electrolytic capacitor according to claim 1, wherein the separator made of a heat-resistant resin is made of one or more selected from aramid fiber, aramid fibrid, polyethylene terephthalate fiber, and epoxy resin. 5. The solid electrolytic capacitor according to claim 1, wherein the metal plating having a melting point of 250 ° C. or less is solder plating or tin plating.