JP2001167981A - Solid electrolytic capacitor and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solid electrolytic capacitor having a low leakage current, a small number of short-circuit faults and superior yield. SOLUTION: In the manufacturing method of this solid electrolytic capacitor, on the surface of an anodic body 2 having a formed dielectric oxide film layer 3, an intermediate product of a solid electrolyte layer 4 is formed through chemical oxidative polymerization, where an oxidant made of a heterocyclic monomer and an organic-acid ferric salt are used. Thereafter, an intermediate product of the solid electrolyte layer 4 is cleaned by dipping it into a solution, containing an electrolyte or by applying to it a voltage by using as an anode the anodic body 2, while dipping it into the solution containing the electrolyte. Thereby, the solid electrolytic capacitor is obtained where the solid electrolyte layer 4 made of a conductive macromolecule having an iron/concentration of not higher than 100 ppm is formed.

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 using a conductive polymer as a solid electrolyte and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, as electronic devices have become more portable and faster, solid-state electrolytic capacitors, which are electronic components, have been required to be smaller and have higher performance.

In order to meet the demands of this market, various aspects such as the surface condition of the anode, the method of forming the oxide film, the development and improvement of the solid electrolyte layer, the surface condition of the cathode, and the structure of the capacitor element have been studied.

FIG. 2 is a sectional view showing the structure of a typical solid electrolytic capacitor element. As shown in FIG. 2, a metal foil having a valve action such as aluminum or tantalum or a sintered body 11 is anodically oxidized to form a dielectric oxide film layer 12, and a transition metal such as Mn or Pb is formed on the surface of the anode body. A solid electrolyte layer 13 using an oxide is formed, and a carbon layer 14 and a silver layer 15 are sequentially laminated on the surface of the solid electrolyte layer 13 to form a cathode layer. Finally, an anode lead 16 and a cathode lead 17 are formed. Is formed by forming an exterior part (not shown) with a resin mold or the like so as to be exposed.

As an improvement measure for improving the performance of the solid electrolyte layer 13, an organic semiconductor capacitor using a TCNQ salt as a charge transfer complex, or a heterocyclic compound such as pyrrole, thiophene or furan is polymerized to make it conductive. Functional solid polymer electrolytic capacitors using conductive polymers have been put to practical use.

Since such a conductive polymer has a characteristic that its specific resistance is remarkably low, various developments have been advanced and put to practical use as a solid electrolyte layer which is effective for lowering the impedance of a solid electrolytic capacitor. .

As a method for forming the solid electrolyte layer, Japanese Patent Application Laid-Open Nos. 60-244017 and
As disclosed in JP-A-81308, a solid electrolyte layer formed by electrolytic polymerization is formed on the dielectric oxide film layer by immersing in a polymerization solution and applying a current by using the anode body on which the dielectric oxide film layer is formed as an anode. A method of forming a solid electrolyte layer by chemical oxidative polymerization by immersing the anode body in a monomer solution and then immersing it in an oxidizing agent solution such as iron p-toluenesulfonate or iron dodecylbenzenesulfonate; After that, a method of forming a conductive polymer solid electrolyte by performing electrolytic polymerization has been proposed.

[0008]

However, in the method of forming a solid electrolyte layer by chemical oxidative polymerization using the above-mentioned monomer solution and oxidizing agent, trivalent iron ions or divalent iron of the oxidizing agent not subjected to the polymerization reaction is used. Iron ions remain in the solid electrolyte layer after the polymerization reaction, so when the solid electrolyte layer is formed at a defect portion interposed in the dielectric oxide film layer,
Iron ions are reduced to iron by the oxidation-reduction potential difference with the anode body, causing leakage current failure and short-circuit failure,
There has been a problem that the yield becomes very poor in the manufacturing process.

An object of the present invention is to provide a solid electrolytic capacitor and a method of manufacturing the same which can solve the above-mentioned problems, have a low leakage current, reduce short-circuit defects, and significantly improve the yield in the manufacturing process. It is assumed that.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is directed to a dielectric oxide film layer formed on the surface of an anode body made of a metal having a valve action.
The configuration is such that a solid electrolyte layer made of a conductive polymer of not more than ppm is provided.

[0011] Further, as a manufacturing method for obtaining this solid electrolytic capacitor, a dielectric oxide film layer is formed by anodic oxidation on the surface of an anode body made of a metal having a valve action, and this anode body is formed into a heterocyclic type. The polymer solution containing the monomer and the oxidizing solution containing the oxidizing agent consisting of an inorganic ferric salt are individually impregnated and washed, and then the oxidizing solution consisting of the heterocyclic monomer and the ferric salt of an organic acid is used. After impregnating with a mixed solution containing the agent and washing, an iron concentration of 10
This is a method for forming a solid electrolyte layer of a conductive polymer of 0 ppm or less.

According to the present invention, the leakage current is low,
It is possible to obtain a solid electrolytic capacitor in which short defects are reduced and the yield in a manufacturing process is significantly improved.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention relates to a dielectric oxide film layer formed on the surface of an anode body made of a metal having a valve action, and a dielectric oxide film layer formed on the surface of the dielectric oxide film layer. A structure in which a solid electrolyte layer made of a conductive polymer having a formed iron concentration of 100 ppm or less is provided. With this structure, a leakage current is reduced, the number of short-circuit defects is reduced, and a good yield is obtained in a manufacturing process. This has the effect that a solid electrolytic capacitor can be obtained.

According to a second aspect of the present invention, in the first aspect of the present invention, the solid electrolyte layer made of a conductive polymer is formed by washing after chemical oxidation polymerization. According to the configuration, the iron concentration of the conductive polymer solid electrolyte layer formed by chemical oxidation polymerization can be reduced.

According to a third aspect of the present invention, in the first aspect of the present invention, the solid electrolyte layer comprising a conductive polymer comprises an oxidizing agent comprising a heterocyclic monomer comprising an organic and / or inorganic ferric salt. Is formed by performing a chemical oxidative polymerization reaction using
It has an effect that a conductive polymer having high chemical oxidation polymerization efficiency and high conductivity can be obtained.

According to a fourth aspect of the present invention, there is provided a polymer solution containing a heterocyclic monomer, wherein a dielectric oxide film layer is formed on the surface of an anode body made of a metal having a valve action by an anodic oxidation method. And an oxidizing solution containing an oxidizing agent consisting of an inorganic ferric salt, and then separately washed, followed by mixing containing a heterocyclic monomer and an oxidizing agent consisting of a ferric salt of an organic acid. A manufacturing method in which a solid electrolyte layer of a conductive polymer having an iron concentration of 100 ppm or less is formed by washing after being impregnated with a solution, and by this method, the iron concentration of the solid electrolyte layer is reduced to 100 ppm or less. This has the effect of reducing the leakage current, reducing the number of short-circuit defects, and obtaining a solid electrolytic capacitor with a high yield in the manufacturing process.

According to a fifth aspect of the present invention, in the fourth aspect of the invention, the step of forming the conductive polymer solid electrolyte layer comprises the step of forming the anode body with a polymerization solution containing a heterocyclic monomer and an inorganic solution. The steps of individually impregnating with an oxidizing solution containing an oxidizing agent composed of a ferric salt, washing and repairing and forming the same are repeated at least twice, followed by oxidation of the ferric salt of the heterocyclic monomer and the organic acid. The method comprises repeating the step of impregnating with the mixed solution containing the agent at least twice, and then performing washing, and this method allows the solid electrolyte of the conductive polymer to be formed on the dielectric oxide film layer with few defects. Since the layer can be formed more densely and the concentration of iron remaining in the solid electrolyte layer can be reduced, the leakage current is reduced, and the number of short-circuit defects can be reduced.

The above-mentioned washing can be carried out by using one or both of water washing and hot water washing, and the order may be reversed. However, using the hot water washing first further enhances the reduction of the iron content. be able to.

According to a sixth aspect of the present invention, in the fourth aspect of the present invention, the cleaning step is a step of immersing in an electrolyte-containing solution and / or a step of applying a voltage while using the anode body as an anode while immersing in the solution. The method includes a step of applying an ion, and by this method, it is possible to maintain an ion state in which the iron content is easily reduced by the action of the electrolyte, and it is easy to reduce the iron concentration from the solid electrolyte layer. Can be
Also, by applying a voltage using the anode body as an anode,
Since the positively charged iron ions receive a repulsive force with respect to the anode body, it has an effect that the iron concentration from the solid electrolyte layer can be more easily reduced.

A seventh aspect of the present invention is the method according to the sixth aspect, wherein the solution containing the electrolyte comprises an organic acid and a salt thereof, and comprises a molecule having both a hydroxyl group and a carboxyl group. According to this method, the function of the hydroxyl group and the carboxyl group in the molecule forms a complex of iron ions and is stable in the solution, so that the concentration of iron in the solid electrolyte layer can be easily reduced, and as a result, This has the effect that the iron concentration in the electrolyte layer can be reduced.

It is important that the electrolyte has both a hydroxyl group and a carboxyl group in the molecular structure, and it is difficult to form a complex with iron ions in an electrolyte having one or neither of them. The effect is significantly reduced.

As the electrolyte, citric acid, tartaric acid, gluconic acid and the like can be used.

According to an eighth aspect of the present invention, in the sixth aspect of the present invention, the step of applying a voltage for cleaning comprises applying a voltage 0.2 to 1 times the formation voltage of the dielectric oxide film layer. In this method, an electric field is formed by application to the anode body, and iron ions having a positive charge receive a repulsive force, which facilitates removal from the conductive polymer. As a result, since the iron concentration in the solid electrolyte layer is reduced and current concentration is reduced, the leakage current is reduced, the number of short-circuit defects is reduced, and a solid electrolytic capacitor having a good yield in the manufacturing process can be obtained. It has the action of:

If the applied voltage is less than 0.2 times the formation voltage of the dielectric oxide film, the repulsive force required to reduce the iron concentration from the solid electrolyte layer cannot be obtained sufficiently. When the applied voltage exceeds one time,
Dielectric breakdown of the dielectric oxide film occurs, and the dielectric oxide film is formed again. As a result, iron ions are taken into the dielectric oxide film, causing an increase in leakage current.

Hereinafter, specific embodiments of the present invention will be described.

FIG. 1 is a sectional view conceptually showing a configuration of a solid electrolytic capacitor according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an anode lead-out wire made of a valve metal such as tantalum wire; A porous anode body obtained by molding and sintering a valve metal fine powder in which the anode lead wire 1 is embedded so that one end of the anode lead wire 1 is exposed, and 3 is the surface of the anode body 2. A dielectric oxide film layer formed on the surface of the dielectric oxide film layer 3 by anodizing; a solid electrolyte layer of a conductive polymer formed on the surface of the dielectric oxide film layer 3 by chemical oxidation polymerization; 5 a carbon layer; The adhesive layer 7 is a cathode lead connected to the conductive adhesive layer 6. The solid electrolytic capacitor of the present invention configured as described above is configured by covering a part of the anode lead wire 1 and the cathode lead wire 7 with an exterior resin (not shown) so as to be exposed to the outside. .

Next, specific embodiments of the present invention will be described, but the present invention is not limited to these embodiments. Hereinafter, "part" indicates "part by weight".

(Embodiment 1) A tantalum metal fine powder in which an anode lead wire made of a tantalum wire is embedded so that one end thereof is exposed is molded and sintered to obtain a porous anode body.
A dielectric oxide film layer was formed on the surface of the porous anode body by anodization. Next, the anode body on which the dielectric oxide film layer was formed was attached to a pyrrole 1 which is a heterocyclic monomer.
Immersed in a solution containing 1 part of 1-propanol as a polymerization solvent and 4 parts of 1-propanol, followed by ferric sulfate 2 as an oxidizing agent.
Of the anode body at a temperature of 85 ° C and a concentration of 1.
Washing and drying were performed in a 0% citric acid aqueous solution. Subsequently, 1 part of pyrrole, which is a heterocyclic monomer, 2 parts of ferric p-toluenesulfonate, which is an oxidizing agent, and 1 part, which is a polymerization solvent,
After dipping in a mixed solution containing 4 parts of propanol and pulling up the anode body, the anode body is washed at a temperature of 85 ° C. in a 1.0% citric acid aqueous solution and dried to form a solid polymer electrolyte polymer electrolyte layer. (The iron concentration of the solid electrolyte layer at this time was 8
5 ppm). After that, a carbon layer and a conductive adhesive layer are sequentially formed, and the cathode lead is connected. Finally, the anode lead and the cathode lead are covered with an exterior resin so that a part of the lead is exposed to the outside. An electrolytic capacitor was manufactured (D size: 7.3 × 4.3 × 2.8 mm).

(Embodiment 2) In Embodiment 1, the solid electrolyte layer of the conductive polymer is formed by a solution containing 1 part of pyrrole as a heterocyclic monomer and 4 parts of 1-propanol as a polymerization solvent. The anode body was immersed and pulled up, and then immersed in an oxidizing solution containing 2 parts of ferric sulfate as an oxidizing agent and 4 parts of 1-propanol as a solvent and pulled up. Washing and drying were performed in a 0% aqueous tartaric acid solution. Subsequently, after repair formation, washing with water and drying, a mixture containing 1 part of pyrrole as a heterocyclic monomer, 2 parts of ferric p-toluenesulfonate as an oxidizing agent, and 4 parts of 1-propanol as a polymerization solvent. It was immersed in the solution, pulled up and dried. This anode body was heated at a temperature of 85 ° C. to a concentration of 1.
Washing and drying were performed in a 0% citric acid aqueous solution (at this time, the iron concentration of the solid electrolyte layer was 75 ppm). Except for this, a tantalum solid electrolytic capacitor was manufactured in the same manner as in the first embodiment.

(Embodiment 3) In Embodiment 1, the solid electrolyte layer of the conductive polymer is formed by a solution containing 1 part of pyrrole as a heterocyclic monomer and 4 parts of 1-propanol as a polymerization solvent. The anode body was immersed and pulled up, and then immersed in an oxidizing solution containing 2 parts of ferric sulfate as an oxidizing agent and 4 parts of 1-propanol as a solvent and pulled up. Washing and drying were performed in a 0% citric acid aqueous solution, followed by repair formation, washing with water, and drying. This series of steps was repeated five times. Subsequently, one part of pyrrole, which is a heterocyclic monomer, and p-
After repeating the process of dipping in a mixed solution containing 2 parts of ferric toluenesulfonic acid and 4 parts of 1-propanol as a polymerization solvent, pulling up and drying, and dipping again in the mixed solution and drying, the process was repeated three times. The anode body was washed in an aqueous tartaric acid solution having a concentration of 1.0% at a temperature of 85 ° C. and dried (the iron concentration of the solid electrolyte layer at this time was 55 ppm), and the same as in the first embodiment. A tantalum solid electrolytic capacitor was manufactured.

(Embodiment 4) In the first embodiment, the step of washing with an aqueous solution of citric acid is carried out by immersing the anode body in the aqueous solution while reducing the formation voltage of the dielectric oxide film layer to 0.1.
A tantalum solid electrolytic capacitor was produced in the same manner as in Embodiment 1 except that a double voltage was applied (the iron concentration of the solid electrolyte layer at this time was 82 ppm).

Fifth Embodiment In the first embodiment, the step of washing with an aqueous solution of citric acid is performed by applying a voltage 0.2 times the formation voltage of the dielectric oxide film layer while immersing the anode body in the aqueous solution. A tantalum solid electrolytic capacitor was produced in the same manner as in Embodiment 1 except that the solid electrolyte layer had an iron concentration of 70 ppm.

(Embodiment 6) In the first embodiment, the step of washing with an aqueous solution of citric acid is the same as that in the first embodiment except that the anode body is immersed in the aqueous solution and a voltage that is one time the formation voltage of the dielectric oxide film layer is applied. Produced a tantalum solid electrolytic capacitor in the same manner as in Embodiment 1 (at this time, the iron concentration of the solid electrolyte layer was 65 ppm).

(Embodiment 7) In the first embodiment, the step of washing with an aqueous solution of citric acid is performed by applying a voltage 1.1 times the formation voltage of the dielectric oxide film layer while immersing the anode body in the aqueous solution. A tantalum solid electrolytic capacitor was produced in the same manner as in Embodiment 1 except that the solid electrolyte layer had an iron concentration of 90 ppm.

(Comparative Example) A porous anode body was obtained by molding and sintering a fine tantalum metal powder in which an anode lead wire made of a tantalum wire was embedded so that one end thereof was exposed. A dielectric oxide film layer was formed on the surface of the anode body by the anodizing method. Next, the anode body on which the dielectric oxide film layer has been formed is immersed in a solution containing 1 part of pyrrole, which is a heterocyclic monomer, and 4 parts of 1-propanol, which is a polymerization solvent. After immersing in a solution containing 2 parts of ferric p-toluenesulfonate and 4 parts of 1-propanol as a polymerization solvent and lifting the solution, it was left at 85 ° C. for 60 minutes to form a solid electrolyte layer of polypyrrole. The iron concentration of the solid electrolyte layer at that time was 130 ppm). A carbon layer and a conductive adhesive layer are sequentially formed on the anode body, a cathode lead is connected thereto, and finally, the anode lead and a part of the cathode lead are covered with an exterior resin so that the tantalum solid aluminum is covered. Constructed electrolytic capacitor (D size:
7.3 × 4.3 × 2.8 mm).

With respect to the tantalum solid electrolytic capacitors according to Embodiments 1 to 7 of the present invention and the comparative example manufactured as described above, the iron concentration of the solid electrolyte layer, the leakage current (30 seconds after application of the rated voltage), the aging treatment Occurrence of short circuit (defective)
The results of comparing the numbers are shown in (Table 1).

The number of test pieces was 50, the iron concentration was shown by the average value of each 50 pieces, and the leakage current was shown by the average value of the samples excluding short-circuited products.

[0038]

[Table 1]

As is clear from Table 1, the tantalum solid electrolytic capacitors according to the first to third embodiments of the present invention are different from the comparative example in that the cleaning process after the chemical oxidation polymerization of the anode body is performed in a solution containing an electrolyte. By immersing in the solid electrolyte layer, the iron concentration of the solid electrolyte layer can be reduced to 100 ppm or less. As a result, the leakage current is reduced and the number of short-circuit defects is reduced.
In the manufacturing process, a tantalum solid electrolytic capacitor having a good yield can be obtained.

In the tantalum solid electrolytic capacitors according to Embodiments 4 to 7 of the present invention, a voltage was applied using the anode body having the conductive polymer solid electrolyte layer formed thereon as the anode while immersed in an aqueous solution containing the electrolyte. Because of the cleaning method, the tantalum solid electrolytic capacitor of Embodiment 4 did not provide the effect of applying a voltage. In the tantalum solid electrolytic capacitor according to the seventh embodiment, the iron concentration of the solid electrolyte layer can be reduced, but the capacitance is reduced.

Therefore, the optimum value of the applied voltage in the cleaning method in which the voltage is applied while being immersed in the solution containing the electrolyte is 0.2
A range of 1 to 1 is preferable.

[0042]

As described above, the solid electrolytic capacitor of the present invention has a structure in which the surface of the anode body on which the dielectric oxide film layer is formed
After forming a solid electrolyte layer by chemical oxidative polymerization using an oxidizing agent comprising a heterocyclic monomer and a ferric salt of an organic acid, the anode body is used as an anode while immersing or immersing in a solution containing an electrolyte. By applying and washing, a solid electrolyte layer of a conductive polymer having an iron content of 100 ppm or less is formed, the leakage current is reduced, the number of short-circuit defects is reduced, and a solid electrolytic capacitor having a good yield is obtained. It can be obtained, and its industrial value is great.

[Brief description of the drawings]

FIG. 1 is a sectional view conceptually showing a configuration of a solid electrolytic capacitor according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a configuration of a conventional solid electrolytic capacitor element.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 anode lead wire 2 anode body 3 dielectric oxide film layer 4 conductive polymer solid electrolyte layer 5 carbon layer 6 conductive adhesive layer 7 cathode lead wire

Claims (8)

[Claims] 1. A dielectric oxide film layer formed on the surface of an anode body made of a metal having a valve action, and a conductive polymer having an iron concentration of 100 ppm or less formed on the surface of the dielectric oxide film layer. A solid electrolytic capacitor comprising: a solid electrolyte layer formed of the above; and a cathode layer formed on the solid electrolyte layer. 2. The solid electrolytic capacitor according to claim 1, wherein the solid electrolyte layer made of a conductive polymer is formed by washing after chemical oxidation polymerization. 3. The solid electrolyte layer comprising a conductive polymer, wherein the heterocyclic monomer is formed by a chemical oxidative polymerization reaction using an oxidizing agent comprising an organic and / or inorganic ferric salt. 2. The solid electrolytic capacitor according to 1. 4. A dielectric oxide film layer is formed by anodic oxidation on the surface of an anode body made of a metal having a valve action, and the anode body is mixed with a polymerization solution containing a heterocyclic monomer and an inorganic ferric salt. And then immersed in a mixed solution containing a heterocyclic monomer and an oxidizing agent consisting of a ferric salt of an organic acid, and then washed. By doing, iron concentration is 100ppm
A method for producing a solid electrolytic capacitor in which a conductive polymer solid electrolyte layer described below is formed. 5. The step of forming a solid electrolyte layer of a conductive polymer comprises separately forming an anode body into a polymerization solution containing a heterocyclic monomer and an oxidation solution containing an oxidizing agent consisting of an inorganic ferric salt. , Washing and repair formation are repeated at least twice, and then a step of impregnating with a mixed solution containing an oxidizing agent comprising a heterocyclic monomer and a ferric salt of an organic acid is repeated at least twice. 5. The method for manufacturing a solid electrolytic capacitor according to claim 4, wherein the method is followed by washing. 6. The method of manufacturing a solid electrolytic capacitor according to claim 4, wherein the washing step includes a step of immersing in an electrolyte-containing solution and / or a step of applying a voltage while using the anode body as an anode while immersing in the solution. Method. 7. The method for producing a solid electrolytic capacitor according to claim 6, wherein the solution containing the electrolyte comprises an organic acid and a salt thereof, and has a molecular structure having both a hydroxyl group and a carboxyl group. 8. The solid electrolytic capacitor according to claim 6, wherein the step of cleaning by applying a voltage is performed by applying a voltage 0.2 to 1 times the formation voltage of the dielectric oxide film layer. Manufacturing method.