JPH10275746A - Manufacture of solid-state electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing solid-state electrolytic capacitors wherein equivalent series resistance is reduced while tan δcharacteristics is improved. SOLUTION: A solid-state electrolytic capacitor 12 is manufactured by sintering powder of valve action metal mixed with binder to form a sintered body 1, and sequentially forming an oxide coat 4 and a cathode layer on the sintered body 1. The powder of valve action metal mixed with granular binder of particle size 50 μm or smaller is used to form the sintered body 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a solid electrolytic capacitor.

[0002]

2. Description of the Related Art A solid electrolytic capacitor such as a tantalum solid electrolytic capacitor is mixed by adding a binder obtained by mixing camphor, an acrylic resin or the like with an organic solvent to fine powder of a valve metal such as tantalum or aluminum. Thereafter, a powder obtained by volatilizing and removing the organic solvent is used. Then, this powder is previously press-molded by embedding one end of an anode lead wire made of a valve metal such as tantalum. After molding, it is heated at a high temperature in a vacuum and sintered to form a sintered body. Next, an oxide film, a solid electrolyte layer made of manganese dioxide or an organic conductive polymer such as polypyrrole or polyaniline, a graphite layer and a silver layer are sequentially formed on the sintered body to form a capacitor element.

[0003]

However, in a conventional method of forming a sintered body using a powder obtained by mixing a fine powder such as tantalum and a binder obtained by mixing camphor, an acrylic resin or the like with a solvent, the conventional method is not used. Since the pore shape becomes fine, it becomes difficult to impregnate the solution, and it becomes difficult to form an oxide film or a solid electrolyte layer such as manganese dioxide. As a result, there are disadvantages that the equivalent series resistance of the solid electrolytic capacitor is hardly reduced and the tan δ characteristic is hardly improved.

It is an object of the present invention to provide a method of manufacturing a solid electrolytic capacitor which can improve the above-mentioned drawbacks, reduce the equivalent series resistance, and improve the tan δ characteristics.

[0005]

In order to solve the above-mentioned problems, the present invention sinters a valve metal powder mixed with a binder to form a sintered body, and forms an oxide film on the sintered body. And a method for manufacturing a solid electrolytic capacitor in which a cathode layer is sequentially formed, wherein a sintered body is formed using a valve action metal powder mixed with a granular binder having a particle size of 50 μm or less. Is provided.

According to the present invention, a sintered body is formed by using a valve metal powder mixed with a granular binder having a particle size of 50 μm or less, but the binder is removed during sintering. Traces of the binder remain as pores, and a sintered body easily impregnated with the solution is obtained. Therefore, it becomes easy to form an oxide film and a solid electrolyte layer on the sintered body. And the equivalent series resistance and tan δ characteristics of the solid electrolytic capacitor can be improved.

[0007]

FIG. 1 is a block diagram showing an embodiment of the present invention.
It will be described based on. First, tantalum and aluminum,
A binder in which camphor, an acrylic resin, or the like is dissolved in an organic solvent is added to fine powder of a valve action metal such as niobium and mixed. After mixing, the mixture is heated to volatilize and remove the organic solvent. After removing the organic solvent, a granular binder having a particle size of 50 μm or less is added and mixed. In this case, after removing the organic solvent, mixing the granular binder is because if the organic solvent remains, the mixed granular binder is dissolved and the granular form cannot be maintained, and the granular This is because voids cannot be formed by the binder. As the granular binder, for example, polyvinyl alcohol, polyvinyl butyral, polyvinyl acetate, polyethylene carbonate, methyl methacrylate, a polyethylene resin, a polyester resin, a methacrylic resin, and the like are used. The particle size of the binder is 50 μm or less, and preferably 5 to 50 μm. That is, when the particle size of the granular binder is smaller than 5 μm, even if pores are formed after sintering, it is difficult to form a cathode layer,
It is difficult to improve nδ characteristics and the like. Further, when the particle size of the granular binder is larger than 50 μm, the amount of powder at the time of compression molding is constant within the same product range, so that the pores formed after removing the granular binder become large. On the contrary, the other holes become smaller. Therefore, similarly, tanδ
It is difficult to improve characteristics and the like. To add and mix the granular binder, for example, container rotation type or container fixed type,
Use a container vibration type, air flow / gravity type, or other device. During this mixing, the mixing amount of the granular binder is preferably 1 to 10
wt%. That is, the mixing amount of this binder is 1 wt.
%, The effect of improving the tan δ characteristics and the like decreases. If the mixing amount is more than 10% by weight, pores formed after the granular binder removed at the time of sintering increase, but the number of pores other than the pores decreases. It is difficult to improve characteristics and the like.

Next, the powder of the valve metal after mixing the granular binder is pressed into a cylindrical or square shape by pressing an anode lead wire made of a valve metal such as tantalum. And compression molded.

After the compression molding, the sintered body 1 is formed by sintering at a high temperature in an atmosphere such as a vacuum. After sintering, a disk-shaped insulating plate 3 made of Teflon, silicone rubber, silicone resin or the like is arranged at the root of the anode lead wire 2.

Then, the sintered body 1 is immersed in a chemical solution such as nitric acid or phosphoric acid and anodized to form an oxide film 4 having a thickness of about 200 Å to 6000 Å.

After forming the oxide film 4, a solid electrolyte layer 5 made of manganese dioxide or an organic conductive polymer is formed. In order to form the solid electrolyte layer 5, the sintered body 1 is placed in a manganese nitrate solution or the like with the lead surface side of the anode lead wire 2 facing upward. And soak it so as not to exceed the insulating plate 3. Thereby, the liquid adheres to and impregnates the sintered body 1. After the impregnation, a treatment according to the type of the solution is performed to form the solid electrolyte layer 5.

That is, if the solution is a manganese nitrate solution, the sintered body 1 is immersed in the manganese nitrate solution to impregnate the solution, then thermally decomposed, and further subjected to re-chemical treatment. And by increasing the concentration of the manganese nitrate solution sequentially, these impregnations,
The steps of thermal decomposition and re-chemical treatment are repeated to form a solid electrolyte layer 5 of manganese dioxide having a predetermined thickness.

The formation of the solid electrolyte layer 5 made of an organic conductive polymer is performed by the following various methods. That is, in the first method, the sintered body 1 is immersed in a solution of the organic conductive polymer. After immersion, it is washed with an organic solvent such as alcohol. After washing, dry and evaporate the solvent. If necessary, the steps from immersion to drying are repeated to form a predetermined thickness. The second method is
The sintered body 1 is immersed in a solution of the undoped polymer. After immersion, wash and dry. The process from immersion to drying is repeated a predetermined number of times as necessary, to form a undoped polymer film having a predetermined thickness. After forming this film, the sintered body 1 is immersed in a doping solution for several tens of minutes to several hours to come into contact with it, doping the polymer film to impart conductivity, and forming an organic conductive polymer film. I do. further,
In the third method, the sintered body 1 is immersed in a solution containing doping ions in a monomer such as aniline, pyrrole, or thiophene. Next, the sintered body 1 is immersed in a solution of an oxidizing agent to cause a chemical polymerization reaction, thereby forming a film of an organic conductive polymer.
In the fourth method, the sintered body 1 is immersed in a solution of a monomer such as aniline or pyrrole containing no doping ions. Next, the sintered body 1 is immersed in a solution of an oxidizing agent to cause a chemical polymerization reaction, thereby forming a polymer film. After the formation of the polymer film, the sintered body 1 is immersed in the doping solution and brought into contact with
A film of an organic conductive polymer is formed by imparting conductivity. Note that the dopant is a substance having a dissociation constant substantially equal to or smaller than that of naphthalenesulfonic acid or a derivative thereof, and an anion of the dopant smaller than that of naphthalenesulfonic acid or a derivative thereof. Examples of such a dopant include, for example, sulfoisophthalic acid and sulfosuccinic acid, methanesulfonic acid, phenolsulfonic acid, sulfosalicylic acid, benzenesulfonic acid, benzenedisulfonic acid, alkylbenzenesulfonic acid and derivatives thereof,
Camphorsulfonic acid, sulfoacetic acid, sulfoaniline,
Acids such as diphenolsulfonic acid or salts of these acids are used. The doping solution has, for example, a composition in which a dopant or a dopant and an oxidizing agent are dissolved in an organic solvent. The concentration of the dopant or oxidizing agent in the solution is 0.01 to 1
A range of mol / l is preferred. As the organic solvent, for example, ketones, esters, alcohols, aromatic hydrocarbons, nitrile acid, cellosolves, nitrogen-containing compounds, and the like are used. Further, as the solution of the oxidizing agent, not only the oxidizing agent but also a solution to which a dopant is added or a solution of a salt of the oxidizing agent and the dopant may be used. As the oxidizing agent, a salt having an oxidation potential of 0.8 V or more with respect to the hydrogen reference electrode, such as a second iron salt, a persulfate, or a vanadate is used. By the way, when the element is formed of tantalum powder,
As the CV value of the tantalum powder increases and the capacitance per volume increases, it becomes more difficult for the liquid to be impregnated inside the element. Therefore, in order to form a conductive polymer film having good characteristics, it is necessary to use a conductive polymer solution or the like having a high concentration. And among the polymers, polyaniline has a high solubility in the solvent and can prepare a relatively high concentration solution,
It is a suitable substance.

After forming the solid electrolyte layer 5, a carbon paste is applied to form a carbon layer 6. A silver paste is applied to the surface of the carbon layer 6 to form a silver layer 7. Then, the solid electrolyte layer 5, the carbon layer 6, and the silver layer 7 are used as a cathode layer.

After the silver layer 7 is formed, a cathode terminal 9 is connected to the silver layer 7 by a silver conductive paste 8, and an anode terminal 10 is resistance-welded to the anode lead wire 2. Then, the exterior 11 is formed by a resin molding method, a resin dipping method, or the like. After the exterior 11 is formed, aging treatment is performed, and the cathode terminal 9 and the anode terminal 10 are bent along the surface of the exterior 11 to form the solid electrolytic capacitor 12.

[0016]

Next, an embodiment of the present invention will be described. First, a binder obtained by dissolving a methacrylic resin with an organic solvent is mixed with fine tantalum powder. And after mixing,
Heat to remove organic solvent. After removing the organic solvent, 1 to 10 wt% of polymethyl methacrylate having a particle size of 5 to 50 μm, which is a methacrylic resin, as a granular binder.
% Mix. Next, the tantalum powder mixed with the granular binder is press-compressed into a square shape with the tantalum anode lead wire pulled out. After compression molding, sintering at a temperature of about 2000 ° C. in vacuum,
A sintered body of mm × 1.80 mm × 1.45 mm square is formed. After forming the sintered body, a disk-shaped insulating plate made of Teflon is arranged at the root of the anode lead wire. Next, the sintered body is immersed in a nitric acid solution and anodized to form an oxide film. After forming the oxide film, the sintered body is immersed in a manganese nitrate solution to impregnate the liquid, and then thermally decomposed and re-chemically formed. The process from impregnation to re-chemical conversion is repeated several times,
A solid electrolyte layer made of manganese dioxide is formed. After forming the solid electrolyte layer, a carbon paste and a silver paste are sequentially applied to form a carbon layer and a silver layer, and the cathode layer is formed together with the solid electrolyte layer. After forming the cathode layer, the cathode terminal is connected to the silver layer with a conductive adhesive, and the anode terminal is resistance-welded to the anode lead wire. Thereafter, an exterior is formed by a transfer molding method. After the exterior is formed, it is subjected to aging treatment and the like, and the structure shown in FIG.
A tantalum solid electrolytic capacitor of 0 V, 33 μF is used.

Next, for the above embodiment, the conventional example, and the comparative example, the equivalent series resistance when an AC voltage of 100 KHz is applied, and the ta when an AC voltage of 120 Hz is applied.
nδ was measured, and the results are shown in Table 1.

The manufacturing conditions of the conventional example and the comparative example are as follows. Conventional example: Same conditions as in the example except that a sintered body is formed using tantalum powder not mixed with a granular binder. Comparative Example: In Example, the particle size of the granular binder was 1
The conditions are the same except that the thickness is set to 00 μm.

[0019]

[Table 1]

As apparent from Table 1, Examples 1 to 12 each have an equivalent series resistance of 40 to about 91.1% and a tan δ of 50 to about 97.7% as compared with the conventional example. Is declining. Also, as compared with Comparative Examples 1 to 4, the equivalent series resistance is reduced to about 31.0 to 87.2% and the tan δ is reduced to about 42.2 to 92.3%.

[0021]

As described above, according to the production method of the present invention, since the sintered body is formed using the powder of the valve action metal mixed with the granular binder having a particle size of 50 μm or less, the equivalent A solid electrolytic capacitor that can reduce series resistance and improve tan δ characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 shows a sectional view of an embodiment of the present invention.

[Explanation of Symbols] 1 ... sintered body, 4 ... oxide film, 5 ... solid electrolyte layer,
6 ... carbon layer, 7 ... silver layer, 12 ... solid electrolytic capacitor.

Claims (1)

[Claims] 1. A method for manufacturing a solid electrolytic capacitor, comprising sintering a valve metal powder mixed with a binder to form a sintered body, and sequentially forming an oxide film and a cathode layer on the sintered body. A method for producing a solid electrolytic capacitor, characterized in that a sintered body is formed using a valve action metal powder mixed with a granular binder having a particle size of 50 μm or less.