JPH11150041A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a solid electrolytic capacitor which can be minimized and in which leakage current defects or dielectric frakdown defects can be reduced. SOLUTION: In method for manufacturing a solid electrolytic capacitor 12 an oxide film 4 is formed through a chemical conversion processing of a valve action metal, and next a solid electrolytic layer 5 is formed, has features for performing steps for forming the oxide film 4 by a first chemical conversion processing and a followed by thermal processing at a temperature higher than 150 deg.C and the step of a second chemical conversion processing after the first processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid electrolytic capacitor which can be reduced in size and which can reduce leakage current failure and breakdown voltage failure.

[0002]

2. Description of the Related Art A solid electrolytic capacitor such as a tantalum solid electrolytic capacitor is manufactured by adding a binder obtained by mixing camphor, an acrylic resin or the like with an organic solvent to powder of a valve metal such as tantalum or aluminum, and mixing the powder. 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 the 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 an organic conductive polymer such as manganese dioxide or polypyrrole or polyaniline, a carbon layer and a silver layer are sequentially formed on the sintered body to form a capacitor element.

[0003] In response to the downsizing of solid electrolytic capacitors, finer powders of tantalum for forming sintered bodies have been used.

[0004]

However, when a finer powder is used, it is necessary to lower the sintering temperature. Then, in the sintered body formed at a low temperature, the number of connection points at which the powders are connected increases, and the strength of the connection points decreases. In addition, it becomes difficult to remove impurities in the sintered body, so that the connection between the powders becomes insufficient and the number of defective portions caused by the impurities increases. Then, an oxide film is formed using the sintered body, and then, when a solid electrolyte layer is formed, a heat treatment for forming the solid electrolyte layer results in
Cracks are likely to occur. Therefore, the solid electrolyte layer is formed directly on the surface of the valve metal, not on the surface of the oxide film. For this reason, there is a disadvantage that a leakage current defect and a withstand voltage defect easily occur. Further, when mounting the capacitor on a printed wiring board or the like, the capacitor is heated at a temperature of, for example, about 200 to 240 ° C. For this reason, there is a defect that a crack is generated at the weak point portion of the oxide film, and a leakage current defect and a withstand voltage defect are easily generated.

An object of the present invention is to provide a method of manufacturing a solid electrolytic capacitor which can improve the above-mentioned drawbacks, can be reduced in size, and can reduce leakage current failure and breakdown voltage failure.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method of manufacturing a solid electrolytic capacitor in which a valve metal is chemically converted to form an oxide film, and then a solid electrolyte layer is formed. Wherein a step of performing a heat treatment at a temperature higher than 150 ° C. after forming an oxide film by the first chemical conversion treatment and a step of performing a second chemical conversion treatment after this step are performed. It provides a method.

According to the present invention, after forming an oxide film, 15
Heat treatment is performed at a temperature higher than 0 ° C. That is, by this heat treatment, cracks are formed in advance in weak spots and the like. Then, after the heat treatment, a second chemical conversion treatment is performed to repair cracks formed in the oxide film. Therefore, when a solid electrolyte layer made of manganese dioxide or the like is formed thereafter, cracks can be hardly generated even if heat treatment such as firing is performed. In addition, cracks can be less likely to occur in the oxide film even by a heat treatment when mounting on a printed wiring board or the like. As a result, leakage current failure and breakdown voltage failure can be reduced.

[0008]

Embodiments of the present invention will be described below. First, a binder in which camphor, an acrylic resin, or the like is dissolved in an organic solvent is added to powder of a valve metal such as tantalum, aluminum, or niobium, and mixed. In addition, the particle diameter of the powder is preferably in the range of 0.05 to 0.5 μm as a single powder. After mixing, the mixture is heated to volatilize and remove the organic solvent. Next, the powder of the valve action metal is compression-molded by a press or the like into a cylindrical or square shape in a state where the anode lead wire made of the valve action metal such as tantalum is drawn out. After compression molding, firing at high temperature in an atmosphere such as vacuum,
A sintered body 1 as shown in FIG. 1 is formed. After the firing, 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 tip of the anode lead wire 2 drawn from the sintered body 1 is welded to a metal plate such as aluminum or stainless steel. In this state, the sintered body is immersed in an electrolytic solution in which an electrolyte such as nitric acid, phosphoric acid, sulfuric acid, or carboxylic acid is dissolved, a first chemical conversion treatment is performed by applying a voltage, and a thickness of 2
An oxide film 4 having a thickness of about 00 Å to 6000 Å is formed.

After the oxide film 4 is formed, a step of performing a heat treatment in an atmosphere such as air is performed. This heat treatment is performed for 15
The reaction is carried out at a temperature higher than 0 ° C., preferably in the temperature range of 180 to 330 ° C., and particularly preferably in the temperature range of 210 to 270 ° C. That is, when the temperature of the heat treatment is lower than 180 ° C. or higher than 330 ° C., the effect of reducing the leakage current defect and the withstand voltage defect is reduced. The heating time is preferably about 10 to 30 minutes.

After the heat treatment, the sintered body 1 is subjected to a second chemical conversion treatment. In the second chemical conversion treatment, it is preferable to use the same electrolytic solution as that used in the first chemical conversion treatment. That is,
The sintered body after the heat treatment is immersed in an electrolytic solution in which an electrolyte such as nitric acid or phosphoric acid is dissolved, and a chemical conversion treatment is performed by applying a voltage. The magnitude of the voltage applied at this time is preferably about 0.6 to 1.0 times the applied voltage at the time of the first chemical conversion treatment, and particularly preferably 0.8 to 1.0 times.
1.0 times is preferred. That is, when the applied voltage is 0.6
If it is lower than 1.0 times or higher than 1.0 times, the effect of lowering leakage current failure and the like is small. In particular, when the applied voltage is 0.8 to 1.0 times, the effect of reducing this defect becomes large.

After the second chemical conversion treatment, a solid electrolyte layer 5 made of manganese dioxide, a TCNQ salt, 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 the liquid level is slightly higher than the lead surface of the anode lead wire 2. 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 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 therewith,
A film of an organic conductive polymer is formed by imparting conductivity. As the dopant, for example, a sulfonic acid compound, a carboxylic acid compound, a phosphoric acid compound, or the like is used. The sulfonic acid compound is a substance having a dissociation constant substantially equal to or smaller than that of naphthalenesulfonic acid or a derivative thereof, and a dopant anion smaller than that of naphthalenesulfonic acid or a derivative thereof. Such dopants include, for example, sulfoisophthalic acid, sulfosuccinic acid, methanesulfonic acid, phenolsulfonic acid,
Acids such as sulfosalicylic acid, benzenesulfonic acid, benzenedisulfonic acid, alkylbenzenesulfonic acid and derivatives thereof, camphorsulfonic acid, sulfonic acetic acid, sulfoaniline, and 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 oxidant in the solution is 0.0
A range of 1 to 1 mol / l is preferred. And the organic solvent is
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 an element is formed from tantalum powder, the more the CV value of the tantalum powder increases and the capacitance per volume increases, the more difficult it is to impregnate the liquid 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. Among the polymers, polyaniline is a suitable substance because it has a high solubility in a solvent and can prepare a solution having a relatively high concentration.

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 with a conductive adhesive 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.

[0017]

Next, an embodiment of the present invention will be described. First, a binder is mixed with a fine powder of tantalum of 30 KCV / g, and the solvent is removed by heating. After removing the solvent, the tantalum powder is subjected to rectangular press compression molding with the tantalum anode lead wire pulled out. After compression molding, sintering is performed at a temperature of about 1800 to 2200 ° C. in a vacuum.
A sintered body of 10 mm × 1.80 mm × 1.45 mm square is formed. After forming the sintered body, the same plate-shaped insulating plate made of Teflon and having a thickness of about 0.1 to 0.2 mm is arranged at the root of the anode lead wire. Next, the sintered body is immersed in a phosphoric acid aqueous solution and subjected to a first chemical conversion treatment by applying a DC voltage of 24 V to form an oxide film. After forming the oxide film, the sintered body is left in the air, and is heated at a temperature of 150 to 360 ° C. for 20 minutes.
After the heat treatment, the sintered body is immersed in a phosphoric acid aqueous solution for 30 minutes, and a second chemical conversion treatment is performed by applying a DC voltage of 24 V.
After the second chemical conversion treatment, the sintered body is immersed in a manganese nitrate solution to impregnate the liquid, and then thermally decomposed and re-chemically formed. Then, the steps from impregnation to re-chemical formation are repeated several times to form a solid electrolyte layer made of manganese dioxide.
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. After forming these cathode layers, the cathode terminal is connected to the silver layer by 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 forming the exterior, aging treatment and the like are performed to form a tantalum solid electrolytic capacitor rated at 7 V and 10 μF.

With respect to the tantalum solid electrolytic capacitor of this embodiment, the defect rate of the leakage current with respect to the temperature at the time of the heat treatment was measured. Indicated.

The conventional tantalum solid electrolytic capacitor is the same as the embodiment of the present invention except that a solid electrolyte layer is formed without performing a heating treatment and a second chemical conversion treatment after forming an oxide film. It shall be manufactured by.

The comparative example is manufactured under the same conditions as in the example except that the temperature of the heat treatment after forming the oxide film is different.

The number of samples is 5000 each. Margin below.

[0022]

[Table 1]

As is clear from Table 1, the leakage current defect rate is 1.6 to 3.5% in Examples 1 to 7 and 3.7% in the conventional example and the comparative example. That is, Examples 1 to 7 are about 43.2% or more in comparison with the conventional example and the comparative example.
It is reduced to 94.6%.

Further, the defect rate of the leakage current when the temperature of the heat treatment was 270 ° C. and the voltage of the second chemical conversion treatment was changed was measured. The manufacturing conditions were the same as those in Example 4 of Table 1, except that the voltage for the formation was changed. Table 2 shows the measurement results. Table 2 shows the ratio of the voltage of the second chemical treatment / the voltage of the first chemical treatment when the voltage of the first chemical treatment is 24 V. Margin below.

[0025]

[Table 2]

As is evident from Table 2, the leakage current defect rate was 3.5% in Example 8, whereas the defect rate in Example 9 was 3.5%.
-Example 13 becomes 1.6 to 2.6%. From this, it is clear that the ratio of the voltage of the second chemical conversion treatment / the voltage of the first chemical conversion treatment being larger than 0.5 has a greater effect of reducing the leakage current defective rate. In particular, when the ratio is 0.8 or more, as is clear from Examples 11 to 13, the leakage current defect rate is lower than that in Example 8 in which the ratio is 0.5. The effect is remarkably reduced to about half or less.

[0027]

As described above, according to the production method of the present invention, after forming an oxide film by the first chemical conversion treatment,
Since the heat treatment is performed at a temperature higher than 50 ° C. and then the second chemical conversion treatment is performed, a leakage current defect and a withstand voltage defect can be reduced, and a solid electrolytic capacitor that can be reduced in size can be obtained.

[Brief description of the drawings]

FIG. 1 shows a cross-sectional view of a solid electrolytic capacitor manufactured according to 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.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hirofumi Uemura 16 Okuma Kuhei, Miharu-machi, Tamura-gun, Fukushima Prefecture Inside the Miharu Plant of Hitachi AIC Co., Ltd.

Claims (1)

[Claims] 1. A method for manufacturing a solid electrolytic capacitor in which a valve metal is subjected to a chemical conversion treatment to form an oxide film, and then a solid electrolyte layer is formed. A method for manufacturing a solid electrolytic capacitor, comprising a step of performing a heat treatment at a high temperature and a step of performing a second chemical conversion treatment after this step.