JP2001102272A - Tantalum solid electrolytic capacitor and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve adhesion of a solid eiectrolytic layer composed of conductive high-molecular compound to a tantalum element surface. SOLUTION: A tantalum element formed at 40 V is dipped in manganese carbonate 0.01% aqueous solution at 25 deg.C for 10 minutes. After dipping, the tantalum element is heated to 400 deg.C for 30 minutes, and manganese oxide is deposited on the tantalum element. After the tantalum element is dipped in pyrrole 0.2 M/acetonitrile solution at 10 deg.C for 5 minutes, the element is dipped in paratoluene sulfonic acid 0.04 M/acetonitrile solution at 0 deg.C for 60 minutes, and polypyrrole is formed. After this operation is repeated ten times, carbon paste, silver paste and silver adhesive agent are spread on the surface, electrodes are removed, and resin mold is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tantalum solid electrolytic capacitor and a method for manufacturing the same, and more particularly, to a tantalum solid electrolyte layer made of a conductive polymer compound, which has been improved to improve the adhesion to the tantalum surface. The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same.

[0002]

2. Description of the Related Art Generally, a tantalum solid electrolytic capacitor comprises a sintered body obtained by sintering tantalum powder, a tantalum oxide film formed on the surface of the sintered body, and a solid electrolyte on the oxide film. And a conductor layer such as a graphite layer and a silver layer formed on the solid electrolyte.
This capacitor has polarity, and usually, metal tantalum serves as an anode electrode, and a conductor layer on a solid electrolyte serves as a cathode electrode.

Conventionally, manganese dioxide has been widely used as this solid electrolyte. In recent years, in order to improve the characteristics and reliability of capacitors, for example, Japanese Patent Publication No. 4-5644.
Japanese Patent Laid-Open Publication No. 5 (1999) -2005 discloses a device using a conductive polymer compound such as polypyrrole having conductivity.

As described in the above-mentioned publication, a solid electrolytic capacitor using such a conductive polymer compound as a solid electrolyte has the following excellent characteristics as compared with those using manganese dioxide. have. (1) Since the conductivity of the conductive polymer compound is several tens times larger than the conductivity of manganese dioxide, it has excellent high-frequency characteristics,
It is possible to cope with a recent increase in operating frequency of electronic equipment.

(2) In a capacitor using manganese dioxide, manganese nitrate is thermally decomposed to form manganese dioxide. Therefore, a thermal stress of 200 to 300 ° C. during the manufacturing process causes a sintered body having an oxide film formed thereon. As a result, defects may occur in the oxide film and the leakage current may increase. In contrast, capacitors using conductive polymer compounds as solid electrolytes do not require heat treatment at such high temperatures during the manufacturing process, so there is no deterioration of the oxide film, and the characteristics after long-term use. Low change and failure occurrence, and excellent reliability. (3) When the oxide film has a defect, the defect is repaired. Since the so-called self-healing temperature is lower than that of manganese dioxide, the oxide film defect is repaired in a small leakage current region. High reliability.

[0006]

In this type of solid electrolytic capacitor, there are roughly two methods of forming a conductive polymer compound as a solid electrolyte, a method by electrolytic oxidation polymerization and a method by chemical oxidation polymerization. .

The method using electrolytic oxidation polymerization forms a conductive polymer compound on the surface of a dielectric oxide film while applying a charge to a monomer to polymerize the monomer. Uses electrochemical energy. However, in the case of this electrolytic oxidation polymerization, since an oxide film as a dielectric is an electrical insulator, it is difficult to form a conductive polymer compound directly on the oxide film. For this reason, on the oxide film, for example, a precoat layer having any conductivity such as a manganese dioxide or a conductive polymer compound layer formed by a chemical oxidation polymerization method is formed, and this is used as a conductor to form an external electrode. Since the conductive polymer compound must be formed by contact, the manufacturing process is complicated.

On the other hand, in the chemical oxidation polymerization method, which is another method for forming a conductive polymer compound, (a) a sintered body having an oxide film formed thereon is alternately immersed in an oxidizing agent solution and a monomer solution. Forming a conductive polymer compound by
(B) A solution obtained by mixing the oxidizing agent and the monomer is kept at a temperature lower than the temperature at which the polymerization reaction proceeds, and the sintered body having an oxide film formed thereon is immersed in the low-temperature mixed solution, and then pulled up to perform polymerization. There is a method in which the polymerization reaction is advanced by raising the temperature to a temperature not lower than the starting temperature.

[0009] However, in these chemical oxidative polymerization methods, a conductive polymer compound is formed by an oxidation reaction of a reactant, and the chemical energy of the oxidation reaction is as follows.
Because the electrochemical energy in the electrolytic oxidation polymerization method and the thermal energy when manganese nitrate is thermally decomposed to form manganese dioxide are small, the amount of the conductive polymer compound attached to the tantalum element is reduced. In addition, the polymer was only about 2 to 3 molecules, and the intermolecular bond was weak, and it was difficult to obtain desired electric characteristics.

That is, in the tantalum solid electrolytic capacitor, after the conductive polymer compound is formed on the outer surface of the tantalum element, the cathode extracting means is formed with carbon paste or the like, but the thickness of the conductive polymer compound is small. In such a case, the carbon paste and the oxide film come into contact with each other, resulting in a short circuit or an increase in leakage current.
In particular, when polymerizing in an oxidizing agent after being immersed in a monomer or a monomer solution, the tantalum element is immersed in the monomer or the monomer solution and pulled up. Since the thickness of the corner portion of the element is reduced, the thickness of the conductive polymer compound formed in this portion is reduced, and there has been a problem that the leakage current increases and a short circuit occurs in this portion.

The present invention has been proposed in order to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a solid electrolyte layer made of a conductive polymer compound even by a chemical oxidation polymerization method. An object of the present invention is to provide a tantalum solid electrolytic capacitor capable of improving adhesion to a tantalum surface and obtaining excellent electrical characteristics, and a method of manufacturing the same.

[0012]

Means for Solving the Problems In order to solve the above problems, the present inventors have intensively studied a manufacturing method capable of improving the adhesion of a solid electrolyte layer made of a conductive polymer compound to the tantalum surface. As a result of the superposition, the present invention has been completed. That is, good results can be obtained by forming needle-like or plate-like protrusions made of a metal oxide on the surface of the tantalum element and holding the solid electrolyte layer made of a conductive polymer compound by the protrusions. It has been found to be possible.

(Needle-shaped or plate-shaped projections) As projections formed on the surface of the tantalum element, manganese dioxide,
Metal oxides such as silicon dioxide, tantalum oxide and niobium oxide are desirable. It is desirable that the size (height) of the projection is several μm to several tens μm. Needle-like or plate-like protrusions on the surface of the tantalum element are several μm to several tens μm
It has been found that, when the conductive polymer compound is adhered to and formed on the projections and the gaps between them, good electrical characteristics can be obtained. The same effect was obtained even when these projections were connected in a network.

(Method of Forming Needle-shaped or Plate-shaped Protrusions on Tantalum Element) The present inventor conducted various studies on a method of forming needle-shaped or plate-shaped protrusions on the tantalum element, and as a result, the following was obtained. It has been found that the methods (1) to (4) can be applied.

(1) A tantalum element is immersed in a solution of a metal carbonate such as manganese carbonate, and then the tantalum element is heated to thermally decompose the manganese carbonate to form manganese oxide on the outer surface of the tantalum element. This manganese oxide is deposited and formed in a projection shape. More specifically, manganese carbonate 0.005% (the applicable range is 0.001% to
(0.007%) A tantalum element formed at 40 V is immersed in an aqueous solution at 25 ° C. for 10 minutes. After the immersion, the tantalum element is heated at 400 ° C. for 30 minutes to thermally decompose manganese carbonate, thereby depositing manganese oxide on the tantalum element.
As a result, as shown in FIG. 1, it was found that needle-like or plate-like projections made of manganese oxide were formed on the outer surface of the tantalum element.

(2) The tantalum element is immersed in a solution of a metal oxide and dried, and this metal oxide is attached to the outer surface of the tantalum element. Thereafter, a process of forming a conductive polymer compound on the inside and the outside surface of the tantalum element by a polymerization reaction of the monomer and the oxidizing agent is repeated several times.

(3) A monomer is mixed with the metal oxide, the tantalum element is immersed in the solution and dried, and the mixture of the metal oxide and the monomer is adhered to the outer surface of the tantalum element. Then, an oxidizing agent is attached to the tantalum element before this step, or is attached after this step, and then polymerized. Thereafter, a process of forming a conductive polymer compound on the inside and the outside surface of the tantalum element by a polymerization reaction of the monomer and the oxidizing agent is repeated several times. When the metal oxide is contained in the monomer, the content of the metal oxide is preferably from 1.0 to 0.01%, more preferably from 0.5 to 0.05%, based on the amount of the monomer.

(4) A monomer and an oxidizing agent are mixed with the metal oxide, the tantalum element is immersed in the solution and dried, and the mixture of the metal oxide, the monomer and the oxidizing agent is adhered to the outer surface of the tantalum element. And then polymerized. Thereafter, a process of forming a conductive polymer compound on the inside and the outside surface of the tantalum element by a polymerization reaction of the monomer and the oxidizing agent is repeated several times. When the metal oxide is contained in the monomer and the oxidizing agent, the content of the metal oxide is preferably 1.0 to 0.01% based on the amount of the monomer and the oxidizing agent.
More preferably, it is 0.5 to 0.05%.

As described above, even if needle-like or plate-like projections are not formed on the tantalum element before the polymerization reaction of the conductive polymer compound, the metal or the mixture of the monomer and the oxidizing agent can be added to the metal. It was found that the oxides may be mixed, and the polymerization reaction may be advanced using this mixed solution. Note that the formation of the protrusions on the outer surface of the tantalum element may be in the middle of the conductive polymer compound forming step repeated several times,
It has been found that the effect of the present invention can be obtained even in this case.
It is desirable that the metal oxide solution has a high viscosity. The reason is that if the viscosity of the metal oxide solution is high, the metal oxide solution does not penetrate into the tantalum element, and the protrusion is formed only on the outer surface of the tantalum element.

(Method of Manufacturing Tantalum Solid Electrolytic Capacitor) Next, an example of a method of manufacturing a tantalum solid electrolytic capacitor according to the present invention will be described. That is, when polypyrrole is used as the conductive polymer compound, a tantalum element having needle-like or plate-like projections formed on the surface as described above is placed in a 0.2 M pyrrole / acetonitrile solution at 10 ° C. for 5 hours. After immersion for 5 minutes, it is immersed in a 0.04 M paratoluenesulfonic acid / acetonitrile solution at 0 ° C. for 60 minutes to form polypyrrole. After repeating this operation 10 times, a carbon paste, a silver paste and a silver adhesive are sequentially applied to the surface of the polypyrrole layer, and the electrodes are taken out and resin-molded to produce an electrolytic capacitor.

Here, the reason why the temperature for immersion in the paratoluenesulfonic acid solution is set to “0 ° C.” is as follows. In other words, since the reaction between the pyrrole monomer and the oxidizing agent is very fast, if the oxidizing agent is not penetrated into the inside of the tantalum sintered body, the oxidizing agent must be near the entrance of the pore portion of the sintered body unless the temperature is kept low. Polypyrrole is formed, this polypyrrole becomes an obstacle, the oxidizing agent cannot penetrate into the tantalum sintered body, the amount of polypyrrole formed inside the tantalum sintered body decreases, It is because.

When polythiophene is used as the conductive polymer compound, a tantalum element having needle-like or plate-like projections formed on the surface as described above is
It is immersed in a solution obtained by mixing a 4-ethylenedioxythiophene monomer and a 40% butanol solution of iron paratoluenesulfonate at a volume ratio of 1: 9 at 20 ° C. for 10 minutes.
Thereafter, polymerization is carried out in air at 40 ° C. for 2 hours. After repeating this operation seven times, a carbon paste, a silver paste and a silver adhesive are sequentially applied to the surface of the polythiophene layer,
The electrodes are taken out and molded with a resin to produce an electrolytic capacitor.

(Operation / Effect) When the projection made of the metal oxide is formed on the tantalum element as described above, the solid electrolyte layer made of the conductive polymer compound is held by the projection. The adhesion to the tantalum element is improved. In addition, since the metal oxide is uniformly formed on the surface of the tantalum element, a conductive polymer compound is generated also at the corners and edges of the tantalum element, and as a result, it can withstand the stress during molding. Therefore, it is considered that the occurrence of a short circuit can be prevented, and the leakage current can be significantly reduced.

[0024]

Hereinafter, the present invention will be described in more detail with reference to examples. In addition, the solid electrolytic capacitor according to the present invention was prepared as in Examples 1 to 4 below. Further, as a comparative example, a solid electrolytic capacitor having no needle-like or plate-like protrusions formed on a tantalum element was used.

(Example 1) A tantalum element formed at 40 V is immersed in a 0.01% aqueous solution of manganese carbonate at 25 ° C for 10 minutes. After the immersion, the tantalum element was
Heat for 0 minutes to precipitate manganese oxide on the tantalum element. This tantalum element was immersed in a pyrrole 0.2 M / acetonitrile solution at 10 ° C. for 5 minutes, and then immersed in a 0.04 M paratoluenesulfonic acid / acetonitrile solution at 0 ° C. for 6 minutes.
Soak for 0 minutes to form polypyrrole. After repeating this operation 10 times, a carbon paste, a silver paste and a silver adhesive were applied to the surface, the electrodes were taken out and resin-molded to obtain a capacitor for evaluation.

(Example 2) A tantalum element formed at 40 V was immersed in a 0.01% aqueous solution of manganese carbonate at 25 ° C for 10 minutes, and then dried with hot air at 60 ° C for 30 minutes. This tantalum element was mixed with a solution prepared by mixing a 3,4-ethylenedioxythiophene monomer and a 40% butanol solution of iron paratoluenesulfonate at a volume ratio of 1: 9,
Soak at 10 ° C for 10 minutes. Thereafter, polymerization is carried out in air at 40 ° C. for 2 hours. After repeating this operation seven times, a carbon paste, a silver paste, and a silver adhesive were applied to the surface, the electrodes were taken out and resin-molded to obtain a capacitor for evaluation.

Comparative Example 1 A polypyrrole was formed on a tantalum element formed at 40 V in the same manner as in Example 1 above, a carbon paste, a silver paste and a silver adhesive were applied on the surface, and the electrodes were taken out and a resin was formed. It was molded and used as a capacitor for evaluation.

(Comparative Example 2) Polyethylenedioxythiophene was formed on a tantalum element formed at 40 V in the same manner as in Example 2 above, and a carbon paste, a silver paste and a silver adhesive were applied on the surface, and the electrode was formed. It was taken out and resin-molded to obtain a capacitor for evaluation.

Example 3 A tantalum element formed at 40 V was immersed in a 40% solution of p-toluenesulfonic acid in acetonitrile at 20 ° C. for 10 minutes, and dried with hot air at 60 ° C. for 30 minutes. Thereafter, the tantalum element is immersed in a 0.2 M pyrrole / acetonitrile solution containing 0.01% of silicon dioxide at 0 ° C. for 60 minutes to be chemically polymerized. After repeating this operation three times, a carbon paste, a silver paste and a silver adhesive were applied to the surface, and the electrodes were taken out and resin-molded to obtain a capacitor for evaluation.

Example 4 A tantalum device formed at 40 V was immersed in a 40% butanol solution of iron p-toluenesulfonate at 20 ° C. for 10 minutes, and dried with hot air at 60 ° C. for 30 minutes. Thereafter, this tantalum element is immersed in a 100% 3,4-ethylenedioxythiophene solution containing 0.01% of silicon dioxide at 20 ° C. for 10 minutes to be chemically polymerized. After repeating this operation three times, a carbon paste, a silver paste and a silver adhesive were applied to the surface, and the electrodes were taken out and resin-molded to obtain a capacitor for evaluation.

Comparative Example 3 A tantalum device formed at 40 V was immersed in a 40% solution of p-toluenesulfonic acid in acetonitrile at 20 ° C. for 10 minutes, and dried with hot air at 60 ° C. for 30 minutes. Thereafter, the tantalum element is immersed in a 0.2 M pyrrole / acetonitrile solution at 0 ° C. for 60 minutes to be chemically polymerized. After repeating this operation three times, a carbon paste, a silver paste and a silver adhesive were applied to the surface, and the electrodes were taken out and resin-molded to obtain a capacitor for evaluation.

Comparative Example 4 A tantalum device formed at 40 V was immersed in a 40% butanol solution of iron p-toluenesulfonate at 20 ° C. for 10 minutes, and dried with hot air at 60 ° C. for 30 minutes. After that, this tantalum element is
3,4-ethylenedioxythiophene solution at 20 ° C, 10
Soak for a minute and allow for chemical polymerization. This operation is further repeated three times. Thereafter, a carbon paste, a silver paste, and a silver adhesive were applied to the surface, and the electrodes were taken out and resin-molded to obtain a capacitor for evaluation.

[Comparative Results] Table 1 shows the electrical characteristics of the solid electrolytic capacitors of Examples 1 to 4 and Comparative Examples 1 to 4 obtained by the above method.

[0034]

[Table 1]

First, Examples 1 and 2 in which manganese oxide is deposited on the surface of a tantalum element will be considered.
As is clear from Table 1, in Comparative Example 1, short-circuit occurred in 2 out of 100 cases, and in Comparative Example 2, 100 short-circuits occurred.
While short-circuit occurred in one of the examples, short-circuit did not occur at all in Examples 1 and 2.

Further, when the maximum value of the leakage current excluding the short-circuited product was examined, it was found to be “158 μA” in Comparative Example 1 using polypyrrole as the conductive polymer compound. In Example 1 using polypyrrole, the maximum value was 0.3 μA, and the maximum value of the leakage current in Example 1 was reduced to about 0.19% of Comparative Example 1.

On the other hand, in Comparative Example 2 using polythiophene as the conductive polymer compound, the maximum value of the leakage current was “560”.
μA ”, whereas in Example 2 using polythiophene as the conductive polymer similarly,“ 0.5 μA ”was used.
A ″, and the maximum value of the leakage current in Example 2 was reduced to about 0.09% of Comparative Example 2.

As described above, in the case where manganese oxide was deposited on the tantalum element, it was observed that a conductive polymer compound was also generated at the corners and edges of the element. On the other hand, in the comparative example, a situation was observed in which the amount of the conductive polymer compound attached to the corners and edges of the tantalum element was small or could not be attached. As a result, it is presumed that the comparative example was affected by the stress at the time of molding, and as a result, the occurrence of a short circuit and the leakage current increased.

Next, Examples 3 and 4 in which silicon dioxide was contained in the monomer solution will be considered. As is clear from Table 1, short-circuits occurred in three out of 100 cases in both Comparative Examples 3 and 4, whereas no short-circuit occurred in Examples 3 and 4.

Further, when the maximum value of the leakage current excluding short-circuited products was examined, it was found to be “430 μA” in Comparative Example 3 using polypyrrole as the conductive polymer compound. In Example 3 using polypyrrole, the maximum value was “1.2 μA”, and the maximum value of the leakage current in Example 3 was reduced to about 0.28% of Comparative Example 3.

On the other hand, the maximum value of the leakage current of Comparative Example 4 using polythiophene as the conductive polymer compound was “780”.
μA ”, whereas in Example 4 using polythiophene as the conductive polymer compound,“ 2.5 μA ”was used.
A ″, and the maximum value of the leakage current in Example 4 was reduced to about 0.32% of Comparative Example 4.

From this, it is considered that even when the metal oxide was mixed with the monomer, the adhesion of the conductive polymer compound to the tantalum element was increased, and the influence of the stress at the time of molding could be avoided.

[0043]

As described above, according to the present invention, the adhesion of the solid electrolyte layer made of a conductive polymer compound to the tantalum surface can be improved by the chemical oxidation polymerization method. A tantalum solid electrolytic capacitor capable of obtaining electrical characteristics and a method for manufacturing the same can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a tantalum element having a metal oxide deposited on its surface.

[Explanation of symbols]

 1: Tantalum element 2: Needle-like or plate-like projection

Claims (7)

[Claims] 1. A tantalum solid electrolytic capacitor in which an oxide film is formed on the surface of a tantalum element obtained by sintering tantalum powder, and a solid electrolyte layer made of a conductive polymer compound is formed on the oxide film. Needle-like or plate-like projections are formed on the outer surface of the tantalum element on which the oxide film is formed, and the conductive polymer compound is held by the projections. . 2. The tantalum solid electrolytic capacitor according to claim 1, wherein the protrusion is made of a metal oxide. 3. The tantalum solid electrolytic capacitor according to claim 2, wherein the metal oxide is one of manganese dioxide, silicon dioxide, tantalum oxide and niobium oxide. 4. An oxide film is formed on the surface of a tantalum element obtained by sintering a tantalum powder, and the tantalum element is immersed in a solution of a metal carbonate and heated to form a metal oxide on the outer surface of the tantalum element. To form needle-like or plate-like projections made of the product, and then, by a polymerization reaction of the monomer and the oxidant,
A method for manufacturing a tantalum solid electrolytic capacitor, comprising forming a conductive polymer compound on an outer surface of a tantalum element. 5. An oxide film is formed on a surface of a tantalum element obtained by sintering a tantalum powder, and the tantalum element is immersed in a solution of a metal oxide, dried, and then oxidized on the outer surface of the tantalum element. To form needle-like or plate-like projections made of the product, and then, by a polymerization reaction of the monomer and the oxidant,
A method for manufacturing a tantalum solid electrolytic capacitor, comprising forming a conductive polymer compound on an outer surface of a tantalum element. 6. An oxide film is formed on the surface of a tantalum element obtained by sintering tantalum powder, and the tantalum element is immersed in a mixed solution of a metal oxide and a monomer, and then dried.
A needle-like or plate-like projection made of metal oxide is formed on the outer surface of the tantalum element, and then a conductive polymer compound is formed on the outer surface of the tantalum element by a polymerization reaction of a monomer and an oxidizing agent. A method for manufacturing a tantalum solid electrolytic capacitor characterized by the following. 7. An oxide film is formed on a surface of a tantalum element obtained by sintering a tantalum powder, and the tantalum element is immersed in a mixed solution of a metal oxide, a monomer and an oxidizing agent, and then dried to obtain a tantalum element. Forming a needle-like or plate-like projection made of metal oxide on the outer surface of the tantalum element, and then forming a conductive polymer compound on the outer surface of the tantalum element by a polymerization reaction of a monomer and an oxidizing agent. Of manufacturing tantalum solid electrolytic capacitors.