JPH11251193A - Solid electrolytic capacitor and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a method for manufacturing a high-reliability solid electrolytic capacitor by which the efficiency of polymerization is increased and a uniform solid electrolytic layer can be formed on the surface of metal pellet. SOLUTION: A metal pallet having a dielectric oxide film is impregnated with ethylene dioxy thiophene(EDT) or an EDT solution of specified density for a specified time to make EDT adhere on the dielectric oxide film. Then the metal pellet is impregnated with a solution of oxidant with surfactant of specified density for a specified time to make oxidants adhere to the EDT. Then the metal pellet is cleaned with wear, hot water, an organic solvent or the like and dried. These steps starting from impregnation with EDT or an EDT solution up to drying are repeated a specified number of times. After that, the metal pellet is coated with carbon and silver paste. A cathode terminal is led out with a silver adhesive. The metal pellet is housed in resin and is subjected to aging.

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 having a solid electrolyte layer formed by chemically oxidizing and polymerizing ethylenedioxythiophene (hereinafter, referred to as EDT). And a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, a solid electrolytic capacitor using a conductive polymer as a solid electrolyte of an electrolytic capacitor to reduce impedance in a high frequency region has been developed. Such a solid electrolytic capacitor is made of a film-forming metal such as aluminum or tantalum having an anodized film,
It has a structure with a solid electrolyte attached. Conventionally, manganese dioxide formed mainly by thermal decomposition of manganese nitrate has been used as a solid electrolyte of this type of solid electrolytic capacitor. However, the high heat required during the thermal decomposition of manganese nitrate and the oxidizing action of the generated NOx gas damage the metal oxide films such as aluminum and tantalum, which are dielectric materials. , The leakage current increases, and the dielectric properties deteriorate.

Therefore, a conductive polymer compound having high conductivity and good adhesion to a dielectric film has been attracting attention as a solid electrolyte for an electrolytic capacitor (Japanese Patent Publication No. 7-2).
2077, JP-A-2-15611, etc.). Note that polythiophene is known as a typical example of the conductive polymer compound. As the polythiophene, a polymer of a thiophene compound such as thiophene, 3-methylthiophene, or 3,4 ethylenedioxythiophene, or a copolymer or a mixture thereof is used.

Here, a conventional method for manufacturing a solid electrolytic capacitor using polythiophene as a conductive polymer compound will be described. That is, after a film-forming metal pellet such as aluminum or tantalum is immersed in a mixed solution of EDT and an oxidizing agent using an organic solvent as a solvent, the metal pellet is pulled up from the mixed solution and polymerized in the air. Thereafter, the solvent is quantitatively removed at room temperature, carbon and silver paste are applied, and then the cathode is pulled out with a silver adhesive, resin-covered and aged.

[0005] As described above, in the conventional method for manufacturing a solid electrolytic capacitor, the metal pellets are pulled up from the mixed solution and polymerized by evaporating the solvent of the mixed solution in air to increase the concentration of the oxidizing agent in the mixed solution. By doing so, the polymerization reaction proceeds. The mixed solution of EDT and oxidizing agent is usually prepared as follows. For example, 0.5 g of EDT as a monomer, 2.0 g of iron (III) p-toluenesulfonate as an oxidizing agent, and 5 g of a 1: 2 mixture of acetone and isopropanol as a solvent are mixed.

[0006]

However, the conventional method for manufacturing a solid electrolytic capacitor as described above has the following problems. That is, in the conventional manufacturing method, the amount of polyethylene dioxythiophene (hereinafter, referred to as PEDT) formed at the edge of the metal pellet is small, and the PEDT completely covers the oxide film on the metal pellet. When a capacitor is formed by applying a carbon or silver adhesive to the surface of the PEDT layer, a current flows through a portion where the oxide film is not covered, so that the leakage current (LC) increases, However, there is a problem that the carbon and the oxide film come into contact with each other to cause a short circuit.

It is considered that this is because the oxidizing power of the oxidizing agent is weak, so that the amount of PEDT formed on the metal pellet is small and the oxide film on the metal pellet cannot be completely covered. Further, the following points can be considered as other causes. That is, when the solid electrolyte layer is formed, the metal pellet is immersed in a mixed solution of EDT and an oxidizing agent, and then pulled up from the mixed solution and polymerized in the air. At each surface of the rectangular parallelepiped metal pellet, the surface of the liquid tends to be spherical due to the surface tension of the liquid. As a result, the adhering amount of the mixed solution at the edge of the metal pellet is smaller than that at other portions, and in particular, the amount of PEDT formed at the edge of the metal pellet is reduced, and the PEDT is oxidized on the metal pellet. This is probably because the film could not be completely covered.

The present invention has been proposed to solve the problems of the prior art as described above, and its object is to form a uniform solid electrolyte layer on the surface of a metal pellet by a highly efficient polymerization reaction. To provide a solid electrolytic capacitor having excellent electrical characteristics. Another object of the present invention is to provide a method for manufacturing a highly reliable solid electrolytic capacitor that can increase the efficiency of a polymerization reaction and form a uniform solid electrolyte layer on the surface of a metal pellet. .

[0009]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have conducted intensive studies and, as oxidizing agents to be mixed with EDT, use strong peroxidisulfates, ferric sulfate, etc. as oxidizing agents. Although they were considered to be used, these are only soluble in water, while EDT is not soluble in water, so that a mixed solution of EDT and these oxidizing agents cannot be prepared. It was not possible to use peroxodisulfate, ferric sulfate or the like having a strong oxidizing power.

Therefore, the present inventors first immersed a metal pellet having a dielectric oxide film in an EDT solution to adhere EDT on the dielectric oxide film, and then put the metal pellet into peroxodisulfate. Then, it was immersed in an aqueous solution of an oxidizing agent such as ferric sulfate having a strong oxidizing power, and the oxidizing agent was allowed to adhere to the EDT to perform oxidative polymerization. However, since EDT is not well compatible with water, the oxidizing agent did not adhere to the EDT simply by immersing the metal pellet to which EDT was attached in an oxidizing agent aqueous solution for a short time. Then, it was found that when the metal pellets were continuously immersed in the oxidizing agent aqueous solution, the polymerization proceeded favorably and a solid electrolyte layer of PEDT was formed.

However, it has been found that in the above method, the polymerization time is long and the number of times of polymerization needs to be increased. Therefore, the present inventors have further studied and completed the present invention. That is, the present inventors have found that ED
Focusing on the fact that T is not well compatible with water, and studied the addition of a surfactant to the EDT solution or oxidant solution to improve the contact state between EDT and the oxidant, the polymerization time was shortened. It was found that a good PEDT layer was formed even if the number of times was small, and that the equivalent series resistance (ESR) and the leakage current (LC) were both lower than those without the addition of a surfactant. As the surfactant to be added, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium laurate, sodium monolauryl phosphate, sodium polyoxyethylene lauryl ether sulfate, dimethyl lauryl benzyl ammonium chloride, dimethyl decyl benzyl ammonium chloride, It is desirable to use polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, dodecyl polyoxyethylene ether, or the like.

That is, a metal pellet having a dielectric oxide film is immersed in EDT or an EDT solution having a predetermined concentration for a predetermined time to cause EDT to adhere on the dielectric oxide film. Immersed in an aqueous solution of oxidizing agent for a predetermined time to allow the oxidizing agent to adhere to EDT,
Wash with water, hot water, organic solvent, etc. and dry. At this time, EDT or an EDT solution of a predetermined concentration, or
A surfactant is added to at least one of the oxidizing agent aqueous solutions. Then, the steps from immersion to drying in the EDT or EDT solution are repeated a predetermined number of times. After that, carbon and silver pastes are applied, the cathode terminal is pulled out with a silver adhesive, and a resin exterior is used to perform aging. In this case, the number of times that the metal pellet is alternately immersed in EDT or the EDT solution and the oxidizing agent aqueous solution is 1 to 20 times, preferably 3 to 10 times.
The time for immersion in the oxidizing agent aqueous solution is 5 minutes to 5 hours, preferably 15 minutes to 3 hours. Further, the concentration of the surfactant to be added is 10-3 to 10% of the oxidizing agent or EDT.
10 wt% is desirable. Incidentally, the surfactant may be added to the oxidizing agent solution, may be added to the EDT solution, or
They may be added to the element serving as the carrier.

The oxidizing agent used in the present invention is limited to an aqueous oxidizing agent, such as ammonium peroxodisulfate, sodium peroxodisulfate, and iron sulfate.
(III), iron (III) nitrate, iron (III) chloride, cerium nitrate (I
V), cerium (IV) ammonium nitrate, cerium sulfate (I
V) and cerium (IV) ammonium sulfate. The concentration of the oxidizing agent aqueous solution is preferably 5 to 60% by weight, and the temperature of the oxidizing agent aqueous solution is preferably 0 to 60 ° C.

As a solvent for the EDT solution, monohydric alcohols (methyl alcohol, ethyl alcohol, n-
Propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, etc.). The EDT solution may have any concentration.

Next, as a metal having a valve action used for the anode, a metal having a valve action such as aluminum, tantalum, niobium, titanium or an alloy using these metals as a substrate can be used. The shape of the anode is not particularly limited, such as a porous sintered body of such a metal, a plate (including a ribbon, a foil, and the like) surface-treated by etching or the like, a wire, and the like. Further, as a method of forming a dielectric oxide film on the surface of the metal pellet, a conventionally known method can be used. For example, when a sintered body of tantalum powder is used, it can be anodized in a phosphoric acid aqueous solution to form an oxide film on the sintered body.

(Effect) According to the method for manufacturing a solid electrolytic capacitor of the present invention as described above, the metal pellet is
Alternatively, it is immersed in an EDT solution and then immersed in an aqueous solution of an oxidizing agent having a strong oxidizing power, such as peroxodisulfate and ferric sulfate, and polymerized in the aqueous solution of the oxidizing agent. At this time, since the surfactant is added to at least one of the EDT or the EDT solution or the oxidizing agent solution,
The affinity between T and the oxidizing agent aqueous solution is improved, the reaction efficiency is greatly improved, and a more uniform polymer can be formed. As a result, the surface of the metal pellet can be more uniformly coated, so that the equivalent series resistance (ESR) and the frequency characteristics can be improved. Further, since the reaction efficiency is improved, the polymerization time can be shortened and the number of times of polymerization can be reduced.

Furthermore, since the oxidative polymerization is carried out in an aqueous solution of an oxidizing agent, the PEDT layers formed on the respective surfaces and the edge portions of the rectangular parallelepiped metal pellets are made uniform. PE at the edge of
Since a uniform PEDT layer can be obtained without the DT layer becoming thin, the leakage current (LC) of the capacitor can be reduced and the occurrence of a short circuit can be prevented.

Further, since the EDT solution and the oxidizing agent aqueous solution are separately prepared, it is possible to use an EDT solution having an arbitrary concentration independently of the concentration and amount of the oxidizing agent aqueous solution. Further, since there is no need to consider the life of the mixed solution of EDT and the oxidizing agent, the process of forming the solid electrolyte layer can be performed with high accuracy and high reliability.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for manufacturing a solid electrolytic capacitor according to the present invention and the initial characteristics of the solid electrolytic capacitor obtained by the method will be described below. As a comparative example, one obtained by repeating the operation of immersing in an oxidizing agent solution for 3 hours without adding a surfactant, and immersing in an EDT solution to drying six times was used. Further, as a conventional example, ED
A solid electrolytic capacitor was used in which metal pellets were immersed in a mixed solution of T and ferric p-toluenesulfonate (FePTS) in butyl alcohol, and polymerized in air.

[1. Examples of Reagents Used] Monomer: Ethylenedioxythiophene (EDT) Solvent of Monomer Solution: Monohydric alcohol (for example, methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol,
Isobutyl alcohol, sec-butyl alcohol, t
oxidant: ammonium peroxodisulfate, sodium peroxodisulfate, iron (III) sulfate, iron (III) nitrate, iron chloride
(III), cerium (IV) nitrate, ammonium cerium (IV) nitrate, cerium (IV) sulfate, cerium (IV) ammonium sulfate, etc. Surfactant: sodium dodecylbenzene sulfonate,
Sodium lauryl sulfate, sodium laurate, sodium monolauryl phosphate, sodium polyoxyethylene lauryl ether sulfate, dimethyl lauryl benzyl ammonium chloride, dimethyl decyl benzyl ammonium chloride, polyoxy ethylene nonyl phenyl ether, polyoxy ethylene octyl phenyl ether, dodecyl poly Oxyethylene ether, etc.

[2. Application conditions] Oxidant solution concentration: 5 to 60 wt% Oxidant solution temperature: 0 to 60 ° C Surfactant concentration: 10-3 to 10 wt%

[3. Manufacturing Method] As shown in the flowchart of FIG. 1, tantalum pellets (for A size, powder C)
V = 30 k, 41 FV, 6 μF) at room temperature for 2 minutes, 5
Immerse in 0% EDT in isopropyl alcohol solution.
In this EDT solution, sodium dodecylbenzenesulfonate (SDBS) as a surfactant was added in an amount of 0.5%.
g / liter. Next, the tantalum pellets are immersed in an oxidizing agent aqueous solution (water: ammonium peroxodisulfate = 2: 1 <wt>) and left to stand at room temperature for 1 hour to polymerize. After that, wash with water for 10 minutes, 100 ℃
And dry for 20 minutes. This operation was repeated four times, and after applying carbon and silver paste, the cathode terminal was pulled out with a silver adhesive, and then sealed with a resin.
Time aging was performed.

[4. Comparative Example] As a comparative example, an electrolytic capacitor which was subjected to a polymerization reaction without adding a surfactant to the EDT solution was used. The operation of dipping in the oxidizing agent aqueous solution for 3 hours and the operation of dipping in the EDT solution to drying were repeated six times. Other conditions are the same as in the above embodiment.

[5. Conventional Example] A solid electrolytic capacitor obtained by immersing a metal pellet in a mixed solution of EDT and a butyl alcohol solution of ferric p-toluenesulfonate (FePTS) and performing polymerization in room temperature air was used as a conventional example. The polymerization was performed six times. The mixed solution of EDT and the oxidizing agent is E
10 wt% DT, 36 wt% FePTS as oxidizing agent
%, And 54 wt% of butyl alcohol as a solvent.

[6. Comparative Results] Table 1 shows the electrical characteristics of the solid electrolytic capacitor (Example) obtained by the manufacturing method of the present invention, and Comparative Examples and Conventional Examples.

[0026]

[Table 1]

As is clear from Table 1, the leakage current (LC) was as high as 8.94 in the conventional example, and short-circuit occurred in 3 out of 10 cases. (LC) was significantly reduced, and no short circuit occurred. This is in the examples and comparative examples.
Since the polymerization was carried out in the liquid, PEDT was sufficiently formed also at the edge portion of the metal pellet.
Since the polymerization was performed in air, the thickness of the PEDT at the edge of the metal pellet was insufficient, and the leakage current increased.
Also, it is considered that the ratio of short-circuiting was increased.

On the other hand, when examining the examples and comparative examples, in the examples, although the polymerization time was reduced to 1 hour and the number of times of polymerization was reduced to 4, the equivalent series resistance was lower than that of the comparative example. (ESR) and leakage current (LC) were both reduced. This is because, in the examples, the addition of a surfactant to the EDT solution improves the affinity between EDT and the oxidizing agent aqueous solution, improves the reaction efficiency, and increases the amount of PEDT to be formed. It is considered that was able to be sufficiently coated.

[0029]

As described above, according to the present invention,
It is possible to provide a solid electrolytic capacitor having a uniform solid electrolyte layer formed on the surface of a metal pellet and having excellent electric characteristics by a highly efficient polymerization reaction. Further, according to the present invention, since the efficiency of the polymerization reaction can be increased, the polymerization time can be reduced and the number of times of polymerization can be reduced. In addition, by improving the efficiency of the polymerization reaction,
A highly reliable method of manufacturing a solid electrolytic capacitor capable of forming a uniform solid electrolyte layer on the surface of a metal pellet can be provided.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a method for manufacturing a solid electrolytic capacitor of the present invention.

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[Procedure amendment]

[Submission date] July 23, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 2

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Claim 7

[Correction method] Change

[Correction contents]

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction contents]

That is, a metal pellet having a dielectric oxide film is immersed in EDT or an EDT solution having a predetermined concentration for a predetermined time to cause EDT to adhere on the dielectric oxide film. Immersed in an aqueous solution of oxidizing agent for a predetermined time to allow the oxidizing agent to adhere to EDT,
Wash with water, hot water, organic solvent, etc. and dry. At this time, EDT or an EDT solution of a predetermined concentration, or
A surfactant is added to at least one of the oxidizing agent aqueous solutions. Then, the steps from immersion to drying in the EDT or EDT solution are repeated a predetermined number of times. After that, carbon and silver pastes are applied, the cathode terminal is pulled out with a silver adhesive, and a resin exterior is used to perform aging. In this case, the number of times that the metal pellet is alternately immersed in EDT or the EDT solution and the oxidizing agent aqueous solution is 1 to 20 times, preferably 3 to 10 times.
The time for immersion in the oxidizing agent aqueous solution is 5 minutes to 5 hours, preferably 15 minutes to 3 hours. The concentration of the surfactant to be added is 10 ⁻³ to 1 with respect to the oxidizing agent or EDT.
0 wt% is desirable. The surfactant may be added to the oxidizing agent solution, the EDT solution, or may be added to an element serving as a carrier thereof.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction contents]

[2. Application conditions] Oxidant solution concentration: 5 to 60 wt% Oxidant solution temperature: 0 to 60 ° C. Surfactant concentration: 10 ^{-3 to} 10 wt%

Claims (10)

[Claims] 1. A method of manufacturing a solid electrolytic capacitor in which a solid electrolyte layer is formed on the surface of a metal pellet on which a dielectric oxide film is formed by chemically oxidatively polymerizing a monomer that forms a conductive polymer compound and an oxidizing agent solution. In the above, the solvent of the oxidizing agent solution is water, and a predetermined surfactant is added to at least one of the monomer and the oxidizing agent aqueous solution, and the metal pellets are alternated with the monomer and the oxidizing agent aqueous solution, respectively. And subjecting the monomer and the oxidizing agent solution to chemical oxidative polymerization in the oxidizing agent aqueous solution. 2. The method according to claim 1, wherein the concentration of the surfactant is 10-3 to 1
2. The method according to claim 1, wherein the amount is 0 wt%. 3. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the number of times of immersion in the monomer and the oxidant solution alternately is 1 to 20 times. 4. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the time of immersion in the oxidizing agent solution is 5 minutes to 5 hours. 5. The method for producing a solid electrolytic capacitor according to claim 1, wherein the monomer is ethylenedioxythiophene (EDT). 6. A solid electrolytic capacitor in which a solid electrolyte layer is formed on the surface of a metal pellet on which a dielectric oxide film is formed by chemically oxidatively polymerizing a monomer that forms a conductive polymer compound and an oxidizing agent solution. A solvent of the oxidizing agent solution is water, a predetermined surfactant is added to at least one of the monomer or the oxidizing agent aqueous solution, and the solid electrolyte layer forms the metal pellets with the monomer and the oxidizing agent aqueous solution. Characterized in that they are formed by alternately immersing and polymerizing each of them a predetermined number of times. 7. The concentration of the surfactant is 10-3 to 1
The solid electrolytic capacitor according to claim 6, wherein the content is 0 wt%. 8. The solid electrolytic capacitor according to claim 6, wherein the number of times of alternate immersion in each of the monomer and the oxidant solution is 1 to 20 times. 9. The solid electrolytic capacitor according to claim 6, wherein the immersion time in the oxidant solution is 5 minutes to 5 hours. 10. The solid electrolytic capacitor according to claim 6, wherein the monomer is ethylenedioxythiophene (EDT).