JPH06120086A - Method for manufacturing solid electrolytic capacitor - Google Patents

Abstract

(57) [Abstract] [Purpose] With regard to a method for manufacturing a solid electrolytic capacitor, an object thereof is to establish a method for manufacturing a low-loss capacitor. [Structure] A step of electrolytically oxidizing a porous element made of a valve metal to form an oxide film on the surface of the porous element, and immersing the porous element in a conductive polymer solution, and then performing a doping treatment to make a preliminary A step of forming an electrode layer, a step of performing electrolytic polymerization using a porous element having a preliminary electrode layer as an anode to form a cathode conductive layer on the preliminary electrode layer, and a carbon coating and silver on the cathode conductive layer. In the manufacturing process of a solid electrolytic capacitor, which consists of applying a coating material, taking out the cathode lead, and then applying a resin coating, the porous element equipped with a preliminary electrode layer is used as the anode, and the conductivity represented by pyrrole is used. A method for producing a solid electrolytic capacitor is characterized in that a surfactant is added to an electrolytic solution in a treatment step in which electrolytic polymerization is carried out using an aqueous solution containing a polymer monomer and a supporting electrolyte as an electrolytic solution. .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for manufacturing a solid electrolytic capacitor. Electrolytic capacitors include dry electrolytic capacitors and solid electrolytic capacitors, which are used as components of communication equipment.

That is, the electrolytic capacitor is aluminum
(Al) or tantalum (Ta), which uses a valve-metal that forms a high resistance oxide film on the surface by electrolytic oxidation as the anode, and the thickness of the oxide film that works as a dielectric is electrolytic. Depending on the applied voltage for oxidation, several hundred to several thousand Å
Since a very small thickness can be formed, a capacitor can be formed with the cathodes facing each other, and a large capacity can be realized.

Here, the dry electrolytic capacitor is formed by winding an anode foil provided with an oxide film so as to face a cathode foil with a separator containing an electrolytic solution in between, and a smoothing circuit requiring a large capacitance. It is used as a capacitor.

However, there are problems that the shelf life is short, the dielectric loss angle (tan δ) and the equivalent series resistance (ESR) in the high frequency region are large. On the other hand, solid electrolytic capacitors use manganese dioxide (M
Since solid electrolytes such as nO ₂ ) are used, the problem of shelf life is solved, and relatively large capacitive elements of several μF or more are widely used in communication circuits such as filter circuits.

[0005]

2. Description of the Related Art There are solid electrolytic capacitors using Al and Ta using solid electrolytic capacitors. The manufacturing method of Ta solid capacitors is as follows.

In order to increase the surface area of the electrode per unit volume, high-purity Ta powder having a particle size of 100 to 350 mesh is pressed under a pressing pressure of 1000 to 1500 kg / cm ² to form a pellet with an anode lead. Make and pellet this 1 × 10 ^-5 t
Sinter at a high temperature of 1900 to 2100 ℃ in a high vacuum below orr to make a sintered body.

Next, the pellets made of this sintered body were treated with phosphoric acid.
(H ₃ PO ₄ ) Soak in an electrolytic solution such as an aqueous solution to form an anode, apply a DC voltage corresponding to the required withstand voltage to perform chemical conversion (electrolytic oxidation), and remove it from ditantalum pentoxide (Ta ₂ O ₅ ). Forming an oxide film over the entire surface area of the sintered body.

Next, the Ta sintered body with the oxide film is vacuum impregnated with a manganese nitrate [Mn (NO ₃ ) ₂ ] solution, and pyrolyzed to obtain manganese dioxide (Mn0 ₂ ) is repeated. As a result, MnO ₂ is filled inside the sintered body.

Next, a carbon conductive paint is applied on the MnO ₂ layer to reduce the resistance and spread resistance, and
A solid state capacitor is completed by applying a silver (Ag) paint on this to make it ready for soldering, soldering the cathode lead to this, and then applying a resin mold exterior.

Here, Mn0 ₂ is an oxide having a relatively low resistance, and when Ta is used as an anode and a voltage is applied, a weak point in the oxide film (Ta ₂ O ₅ ) formed on the surface of the sintered body. As a result of the current flowing through the part (leakage current source), the generated Joule heat decomposes Mn0 ₂ to generate oxygen (O), oxidize the weak point and perform self-healing. As a result of performing sealing with Mn oxides (Mn ₂ O _3, MnO, etc.) having high resistance, it is possible to obtain an electrolytic capacitor with a small leakage current.

Although such a solid electrolytic capacitor is used as a component of a communication circuit, its equivalent series resistance is remarkably large as compared with other capacitors such as a plastic capacitor due to the presence of Mn0 ₂ layer and carbon layer. .

With the recent development of digital equipment, there is a demand for low impedance and large capacitance capacitors in the high frequency region. From this viewpoint, solid electrolytic capacitors using conductive materials instead of Mn0 ₂ have been studied. There is.

For example, it has been proposed to use a charge transfer complex such as an alkylquinolium / tetracyanoquinodimethane (abbreviated as TCNQ) complex as an organic conductive material. (For example, JP-A-58-17609 and JP-A-58-191414) However, since the organic charge transfer complex generally has a low melting point, soldering resistance is low, and it is difficult to form a chip component. is there.

Further, since the thermal stability is poor, there is a problem that a part of the complex is decomposed by the heat treatment at the time of forming the cathode layer to increase the resistance, and it is difficult to reduce the equivalent series resistance. Therefore, as an organic conductive material, a material using a conductive polymer material such as polypyrrole or polythiophene having excellent heat resistance has been proposed. (For example, JP-A-63-17331
(3 etc.) In this method, a conductive polymer film is formed by a chemical oxidative polymerization method on a film forming metal having an oxide film, and then a conductive polymer film is formed by an electrolytic polymerization method on this, and this is used as a solid electrolyte. Is used instead of.

Specifically, a film-forming metal having an oxide film (hereinafter referred to as "anode body") is immersed in a solution in which an oxidizing agent such as ammonium persulfate or iodine is dissolved to adhere the oxidizing agent to the surface of the oxide film. After that, when this anode body is immersed in a solution containing a pyrrole monomer, for example, a polypyrrole thin film is formed on the oxide film by chemical oxidative polymerization.

Next, the pyrrole monomer and supporting electrolyte (
(For example, tetrabutylammonium toluenesulfonate)
When electrolyzed by immersing it in an aqueous solution containing a and using the anode body as an anode, a black electroconductive polymer film of polypyrrole is obtained by electrolytic polymerization.

However, the problem of such a chemical oxidative polymerization method is that it can be applied to an anode body such as an etching foil which does not have a large surface magnification, a porous body having a high surface magnification such as a Ta sintered body. On the other hand, the impregnation of the solution is insufficient and a uniform polypyrrole thin film cannot be formed.

For these reasons, it is necessary to develop a manufacturing method capable of forming a low-resistance conductive polymer film by sufficiently impregnating the inside of the sintered body. As a method for solving this problem, the inventors have selected a material that is an organic compound soluble in a solvent and easily penetrates into a porous element such as a sintered element and becomes a conductive polymer by heating. As a result, the polyaniline represented by the general formula (1) was found, and after impregnating this organic compound to form a conductive preliminary electrode layer made of polyaniline even inside the porous element, a pyrrole monomer and a supporting electrolyte were formed. It is proposed that the cathode conductive layer be formed by immersing in an aqueous solution containing and performing electrolytic polymerization.

Specifically, polyaniline is dissolved in a solvent such as N-methyl-2-pyrrolidone, the porous element is immersed in this solution, and then pulled up and dried under reduced pressure to obtain polyaniline even inside the sintered body. To precipitate.

However, the polyaniline thus obtained has a high resistance and is unsuitable as an anode element for carrying out electrolytic polymerization, so that paratoluenesulfonic acid is used.
(Abbreviation pTS), naphthalene sulfonic acid (abbreviation N
S), alkylnaphthalene sulfonic acid (abbreviated to AN
S), benzene sulfonic acid (abbreviated as BS), n-alkylbenzene sulfonic acid (abbreviated as nABS), styrene sulfonic acid (abbreviated as SS) and the like, and the doping treatment is performed to lower the resistance.

Next, this porous element is immersed in an aqueous solution of pyrrole and a supporting electrolyte, for example, sodium p-toluenesulfonate, and constant current electrolysis is performed using the element as an anode.
The inside of the sintered body is filled with polypyrrole to form a cathode conductive layer.

[0022]

FIG. 2 is a cross-sectional view showing the structure of a solid electrolytic capacitor. As a method of realizing a Ta solid electrolytic capacitor having low loss and low ESR in the high frequency region, the inventors have Polyaniline is impregnated even into the inside of the porous element 2 having the oxide film 1 of the required thickness by chemical conversion to form a conductive preliminary electrode layer 3 and then immersed in a solution containing a pyrrole monomer. , A method of forming the cathode conductive layer 4 made of polypyrrole by electrolytic polymerization is proposed, whereby the low resistance polypyrrole can be filled even inside the sintered body.

Next, as in the conventional case, a carbon paint is applied on the cathode conductive layer 4 to form a carbon layer 5, and then a silver (Ag) paint is applied to form an Ag paint layer 6. The solid electrolytic capacitor is completed by soldering the cathode lead 7 to the paint layer 6 and applying the resin sheath 8.

However, the capacitor thus formed has a dielectric loss tangent and an ESR in a high frequency region as compared with a conventional solid electrolytic capacitor using MnO ₂ as a solid electrolyte.
Is big.

Therefore, this reduction is an issue.

[0026]

[Means for Solving the Problems] The above-mentioned problems are solved by using a porous element provided with a preliminary electrode layer as an anode, a conductive polymer monomer represented by pyrrole, and a supporting electrolyte represented by sodium paratoluenesulfonate. This can be solved by configuring a method for producing a solid electrolytic capacitor, which is characterized in that a surfactant is added to the electrolytic solution in a treatment step of carrying out electrolytic polymerization using an aqueous solution containing the above as an electrolytic solution.

[0027]

How to reduce the loss of the solid electrolytic capacitor depends on how to fill the inside of the sintered body with the low-resistance cathode conductive layer.

Here, polypyrrole, polythiophene,
Conductive polymer compounds such as polyaniline and polyfuran can be produced by electrolytic polymerization. However, after the chemical conversion is completed, the porous element provided with an oxide film on the surface is immersed in, for example, a pyrrole solution for electrolytic polymerization. However, polypyrrole cannot be sufficiently deposited inside.

Then, the inventors paid attention to the fact that polyaniline is soluble in a solvent, impregnating a porous element in a solution of polyaniline dissolved in the solvent, and drying it under reduced pressure to roughly deposit polyaniline on an oxide film, and then In the step of forming the cathode conductive layer, the penetration of the aqueous solution of pyrrole is facilitated.

It should be noted that polyaniline generated by drying from the solution alone has a high resistance and is insufficient to function as a current path in electrolytic polymerization, so a dopant is added to reduce the resistance.

Next, the cathode conductive layer is formed by, for example, electrolytically polymerizing pyrrole to form polypyrrole, and filling the inside of the sintered body. An ionized electrolyte is required to carry out this electrolytic polymerization. Further, since the polypyrrole produced by electrolytic polymerization has a high resistance value until then, it is necessary to add a dopant to reduce the resistance.

Here, since aromatic sulfonic acid or aliphatic sulfonic acid acts as a dopant, a sodium salt or ammonium salt thereof is used as a supporting electrolyte, and for example, an aqueous solution containing pyrrole and aromatic sulfonate as a solute is used. Electrolytic polymerization is performed to form a cathode conductive layer made of polypyrrole.

However, it is still not easy to fill the inside of the porous element with polypyrrole. Here, in order to further fill the interior with polypyrrole, it is necessary to add a surfactant to the electrolytic solution for electrolytic polymerization, use a material with a surface tension lower than that of water as the solvent, etc. However, if an organic solvent such as alcohol is used, it cannot be removed by washing if it remains inside the sintered body, and a reducing atmosphere is generated during thermal decomposition, which is not preferable.

Therefore, the inventors have been able to obtain good results by adding a surfactant. That is, the addition of a small amount of a surfactant facilitates the penetration of pyrrole, and polypyrrole can be deposited even inside the pores.

Here, there are anionic surfactants, cationic surfactants and nonionic surfactants as the surfactants, but any of these may be used. Although the surfactant remains in the porous element together with the polypyrrole, its effect on the characteristics of the polypyrrole and the quality of the solid electrolytic capacitor can be neglected because of its small amount.

[0036]

【Example】

Example 1: A Ta sintered body having an effective surface area of 10 cm ² and a concentration of 0.05
% Of H ₃ PO ₄ aqueous solution for chemical conversion to 60 V to form an oxide film on the Ta device, which is immersed in a 5% N-methyl-2-pyrrolidone solution of polyaniline whose structural formula is shown in FIG. After that, the pressure was reduced and the product was dried at 80 ° C. for 30 minutes to form a conductive layer made of polyaniline on the oxide film.

Next, this Ta element was dipped in a 1% aqueous solution of p-toluenesulfonic acid for 10 minutes to perform a doping treatment to form a preliminary electrode layer having a low resistance. Next, 0.1% of polyoxyethylene octylphenol ether as a surfactant was added to an aqueous solution of 0.06 mol of pyrrole and 0.06 mol of sodium p-toluenesulfonate per liter to prepare an electrolytic polymerization solution.

The Ta element was immersed in this aqueous solution to
Electrolytic polymerization was carried out for 1 hour at a current of 0.5 mA to form a cathode conductive layer made of polypyrrole. On top of this, apply carbon paint and Ag paint in the same manner as before, and apply 20 ° C at 120 ° C.
After drying for a minute, Ta
The solid electrolytic capacitor was completed.

The capacitance (120 Hz) of this capacitor is 2.3
μF, tan δ (120Hz) is 1.6%, equivalent series resistance (ESR) is 1
It was 0.2 Ω at MHz, and the man-hour required for manufacturing was 4 hours. Example 2: A Ta solid electrolytic capacitor was formed in exactly the same manner as in Example 1 except that sodium dodecyl sulfate was used as the surfactant added to the electrolytic polymerization solution.

The capacitance (120Hz) of this capacitor is 2.3
μF, tan δ (120Hz) is 1.3%, equivalent series resistance (ESR) is 1
It was 0.3 Ω at MHz, and the man-hour required for manufacturing was 4 hours. Example 3: A Ta solid electrolytic capacitor was formed in exactly the same manner as in Example 1, except that polyoxyethylene lauryl ether was used as the surfactant added to the electrolytic polymerization solution.

The capacitance (120 Hz) of this capacitor is 2.1
μF, tan δ (120Hz) is 1.4%, equivalent series resistance (ESR) is 1
It was 0.2 Ω at MHz, and the man-hour required for manufacturing was 4 hours. Comparative Example 1: except that the electropolymerization liquid was formed from an aqueous solution of 0.06 mol of pyrrole and 0.06 mol of sodium p-toluenesulfonate per liter in Example 1 and electropolymerization was performed without adding a surfactant. A Ta solid electrolytic capacitor was formed in exactly the same manner, but it took twice as long as when a surfactant was added in the electrolytic polymerization step.

The capacitance (120 Hz) of this capacitor is 2.0
μF, tan δ (120Hz) is 3.5%, equivalent series resistance (ESR) is 1
It was 0.7 Ω at MHz, and the man-hour required for manufacturing was 7 hours. Comparative Example 2: The same procedure as in Example 2 was carried out except that electrolytic polymerization was carried out without adding a surfactant to the electrolytic polymerization solution.
A Ta solid electrolytic capacitor was formed, but it took twice as long as when a surfactant was added in the electrolytic polymerization process.

The capacitance (120 Hz) of this capacitor is 2.3
μF, tan δ (120Hz) is 3.5%, equivalent series resistance (ESR) is 1
It was 0.6 Ω at MHz, and the number of man-hours required for production was 7 hours.

[0044]

As a result of the practice of the present invention, it is possible to manufacture a new type of solid electrolytic capacitor which has a small dielectric loss tangent value and an equivalent series resistance value in a high frequency region and has characteristics close to those of a conventional solid electrolytic capacitor using a solid electrolyte. It will be possible.

[Brief description of drawings]

FIG. 1 is a structural formula of polyaniline.

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

[Explanation of symbols]

 1 Oxide film 2 Porous element 3 Preliminary electrode layer 4 Cathode conductive layer

Claims (1)

[Claims] 1. A step of electrolytically oxidizing a porous element made of a valve metal to form an oxide film on the surface of the porous element, and a doping treatment after immersing the porous element in a conductive polymer solution. To form a preliminary electrode layer, a step of electrolytic polymerization using a porous element provided with the preliminary electrode layer as an anode, and forming a cathode conductive layer on the preliminary electrode layer, and the cathode conductive layer. In a manufacturing process of a solid electrolytic capacitor, which comprises a step of applying a carbon paint and a silver paint on the above, taking out a cathode lead, and then applying a resin coating, the porous element having the preliminary electrode layer is used as an anode. , A solid electrolytic condensate characterized by adding a surfactant to the electrolytic solution in a treatment step of performing electrolytic polymerization using an aqueous solution containing a conductive polymer monomer represented by pyrrole and a supporting electrolyte as an electrolytic solution. The method of production.