JP2000340466A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the manufacturing method of a solid electrolytic capacitor having improved leakage current characteristics and high reliability. SOLUTION: In the manufacturing process of a solid electrolytic capacitor 15, a capacitor element 10 comprising a sintered unit 1 made of valve-action metal, an oxide film 5 formed on the sintered unit 1, a conductive polymer layer 6 formed on the oxide film 5 and a cathode layer 9 formed on the conductive polymer layer 6 is covered with a covering layer 14 made of resin and subjected to an aging treatment which includes a 1st aging treatment in which a voltage not lower than a rated voltage is applied at a room temperature and a 2nd aging treatment in which a voltage not lower than the rated voltage is applied in a high temperature atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a solid electrolytic capacitor, and more particularly to a method for manufacturing a solid electrolytic capacitor having a layer made of a conductive polymer such as polyaniline or polypyrrole.

[0002]

2. Description of the Related Art A solid electrolytic capacitor such as a tantalum solid electrolytic capacitor is manufactured by, for example, the following method. That is, first, one end of an anode lead wire made of a valve metal such as tantalum is buried in advance, and powder obtained by mixing a binder with a fine powder of a valve metal such as tantalum or aluminum is press-molded. After molding, it is heated at a high temperature in a vacuum and sintered to form a sintered body. Next, the sintered body is immersed in a chemical conversion solution and subjected to a chemical conversion treatment to form an oxide film. After forming the oxide film, a manganese dioxide layer or a layer made of a conductive polymer such as polypyrrole or polyaniline is formed. Thereafter, a carbon layer and a silver layer are sequentially formed to form a cathode layer. Then, the anode terminal is connected to the anode lead wire, and the cathode terminal is connected to the silver layer. Further, the capacitor element after the formation of the silver layer and a part of the anode terminal and the cathode terminal are covered with an exterior made of insulating resin or the like. After forming the exterior, aging treatment is performed in a high temperature atmosphere of 85 ° C. or higher. A solid electrolytic capacitor having a layer made of a conductive polymer such as polypyrrole has a characteristic of low equivalent series resistance and low impedance because a substance such as polypyrrole has high conductivity.

[0003]

In the case of a solid electrolytic capacitor, the resin shrinks when forming a resin sheath, and mechanical stress is applied to the manganese dioxide layer and the conductive polymer layer. In particular, the solid electrolytic capacitor having the conductive polymer layer formed thereon has a disadvantage that the leakage current is liable to increase due to the stress as compared with the solid electrolytic capacitor having the manganese dioxide layer formed thereon.

An object of the present invention is to provide a method for manufacturing a solid electrolytic capacitor which improves the above-mentioned drawbacks, improves leakage current characteristics, reduces defects, and has high reliability.

[0005]

According to the present invention, an oxide film is formed on a sintered body made of a valve metal, and a conductive polymer layer and a cathode layer are formed on the oxide film. In a method for manufacturing a solid electrolytic capacitor in which an exterior made of resin is formed on a capacitor element sequentially laminated and then subjected to an aging treatment, a voltage equal to or higher than a rated voltage is applied at room temperature to perform a first aging treatment, and then a high-temperature The second aging process is performed by applying a voltage higher than the rated voltage in an atmosphere.

That is, according to the present invention, the first aging process is performed by applying a voltage higher than the rated voltage at room temperature, and then the second aging process is performed by applying a voltage higher than the rated voltage in a high-temperature atmosphere. By performing the processing, the leakage current characteristics can be improved, and the reliability can be improved.

[0007]

Embodiments of the present invention will be described below. First, a binder obtained by dissolving camphor, an acrylic resin, or the like in an organic solvent is added to and mixed with fine powder of a valve metal such as tantalum, aluminum, or niobium. After mixing, the mixture is heated to remove the organic solvent by volatilization. Next, the fine powder of the valve action metal is compression molded by a press or the like into a square or cylindrical shape with the anode lead wire made of a valve action metal such as tantalum pulled out. After the compression molding, sintering is performed by heating at a high temperature of about 1800 to 2200 ° C. for about 15 to 60 minutes in an atmosphere such as a vacuum to form a sintered body 1 as shown in FIG. During this sintering, impurities in the powder are also evaporated.

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. The insulating plate 3 has a thickness of, for example, less than 0.2 mm, preferably about 0.1 mm. That is, the smaller the thickness of the insulating plate 3, the larger the size of the sintered body without changing the size of the whole capacitor, the larger the capacity, and the smaller the capacity when the capacity is fixed. .

Then, as shown in FIG.
Of the anode lead wire 2 pulled out from the metal plate 4 is welded to a metal plate 4 such as aluminum or stainless steel. Metal plate 4
, A plurality of sintered bodies 1 are attached in order to improve work efficiency.
In this state, the sintered body 1 is immersed in a chemical conversion solution such as nitric acid or phosphoric acid to a predetermined level by visual observation or the like.
A direct current voltage corresponding to the rated voltage is applied to this for chemical conversion treatment. By this chemical conversion treatment, an oxide film was formed at a rate of about 16 ° / V, and finally, as shown in FIG.
An oxide film 5 of about 0 to 6000 ° is formed.

After forming the oxide film 5, a conductive polymer layer 6 is formed on the surface thereof as shown in FIG. The conductive polymer layer 6 is formed by an electrolytic polymerization method or a chemical oxidation polymerization method. For example, in the case of the latter method, it is formed as follows. That is, in the first method, first, the sintered body 1 is impregnated with a solution in which an oxidizing agent or a mixture of an oxidizing agent and a substance to which a dopant made of an acid compound or a salt compound is added is dissolved in an appropriate solvent. Thereafter, when a solution of an oxidizing agent is used, a solution consisting of a mixture of a monomer and a substance to which a dopant made of an acid compound or a salt compound is applied is impregnated,
The monomers undergo a chemical oxidative polymerization reaction to bind the dopants and impart conductivity. When a mixed solution of an oxidizing agent and a substance such as an acid compound is used, the monomer is impregnated with either a monomer or a mixed solution of the monomer and a substance to which a dopant of an acid compound or a salt compound is added, and the monomer is impregnated with the monomer. A chemical oxidative polymerization reaction is performed to combine the dopants to impart conductivity.
These impregnation processes are repeated a predetermined number of times to obtain a predetermined thickness. Thereafter, a drying treatment is performed. The second method is
First, the sintered body 1 is impregnated with a solution of a monomer or a mixture of a monomer and an acid compound or a salt compound. Thereafter, when a monomer solution is used, a solution of a mixture of an oxidizing agent and a substance to which an acid compound or a salt compound is added is impregnated to cause a chemical oxidative polymerization reaction and to impart conductivity. When a mixed solution of a monomer and an acid compound is used, an oxidizing agent or a mixed solution of an oxidizing agent and an acid compound is impregnated, and the monomer is subjected to a chemical oxidative polymerization reaction to impart conductivity. These impregnation processes are repeated a predetermined number of times to obtain a predetermined thickness. Thereafter, a drying treatment is performed. In addition, the third
Is a method of impregnating a solution obtained by dissolving a mixture of a monomer, a substance imparting a dopant of an acid compound or a salt compound, and an oxidizing agent in an appropriate solvent into a sintered body 1, causing the monomer to undergo a chemical oxidative polyreaction, thereby improving conductivity. Give. This impregnation process is repeated a predetermined number of times to obtain a predetermined thickness. Thereafter, a drying treatment is performed.

The oxidizing agent is, for example, potassium dichromate, sodium dichromate, ammonium peroxodisulfate, hydrogen peroxide, ferric chloride, potassium permanganate,
Using manganese dioxide, lead dioxide, etc., 0.1-1.0mo
Make the concentration about l / l.

As the acid compound used as a substance for imparting a dopant, a sulfonic acid compound, a carboxylic acid compound, a phosphoric acid compound and the like are used. In particular, as the sulfonic acid compound, a substance having a dissociation constant substantially equal to or smaller than that of naphthalenesulfonic acid or a derivative thereof and an anion of a dopant smaller than that of naphthalenesulfonic acid or a derivative thereof is used. Examples of such sulfonic acid compounds include, for example, sulfone isophthalic acid and sulfosuccinic acid, methanesulfonic acid, phenolsulfonic acid, sulfosalicylic acid, benzenesulfonic acid, benzenedisulfonic acid, alkylbenzenesulfonic acid and derivatives thereof, camphorsulfonic acid, and sulfoneacetic acid. An acid such as diphenolsulfonic acid is used. The concentration of this acid compound is 0.05 to
Adjust to about 1.0 mol / l. In addition, as the salt compound used as the substance imparting the dopant, an ammonium salt, a sodium salt, or a potassium salt of the above-mentioned acid compound is used. That is, in the case of a sulfonic acid compound, ammonium sulfoisophthalate, ammonium sulfosuccinate, ammonium methanesulfonate, ammonium phenolsulfonate, ammonium sulfosalicylate, ammonium benzenesulfonate, ammonium benzenedisulfonate, ammonium benzenedisulfonate, and ammonium alkylbenzene sulfonate are used as aluminum salts. And its derivatives, and salts such as ammonium camphorsulfonate, ammonium sulfone acetate, and ammonium diphenolsulfonate. Examples of the sodium salt include sodium sulfoisophthalate, sodium sulfosuccinate, sodium methanesulfonate, sodium phenolsulfonate, sodium sulfosalicylate, sodium benzenesulfonate, sodium benzenedisulfonate, sodium alkylbenzenesulfonate and derivatives thereof, and camphorsulfonic acid. Salts such as sodium, sodium sulfone acetate and sodium diphenol sulfonate are used. Further, potassium salts include potassium sulfoisophthalate, potassium sulfosuccinate, potassium methanesulfonate, potassium phenolsulfonate, potassium sulfosalicylate, potassium benzenesulfonate, potassium benzenedisulfonate, potassium alkylbenzenesulfonate and derivatives thereof, camphorsulfone Salts such as potassium acid, potassium sulfonate, sulfoaniline and potassium diphenolsulfonate are used. The concentration of these ammonium salt, sodium salt, and potassium salt compounds is 0.05 to
Adjust to about 1.0 mol / l. Further, in order to increase the solubility of the salt compound and lower the concentration in the solution, hydrochloric acid, sulfuric acid or the like may be added.

Further, as the monomer, for example, acetylene, paraphenylene, pyrrole, vinylene, phenylene, aniline, thiophene, imidazole, thiazole, furan or the like is used, and the concentration is about 0.1 to 1.0 mol / l.

Next, as shown in FIG. 1E, a graphite solution is applied to the surface of the conductive polymer layer 6 to form a graphite layer 7. After the formation of the graphite layer 7, FIG.
As shown in FIG. 5, a silver paste is applied to the surface to form a silver layer 8, which is combined with the graphite layer 7 to form a cathode layer 9, thereby forming a capacitor element 10. After forming the silver layer 8, FIG.
(G) conductive adhesive 1 such as silver conductive paste
1, the lead frame-shaped cathode terminal 12 is connected to the silver layer 8, and the anode lead wire 2 is connected to the lead frame-shaped anode terminal 13. Then, as shown in FIG. 1H, an exterior 14 made of resin is formed by a resin molding method, a resin dipping method, or the like.

After forming the exterior 12, a first aging process is performed by applying a voltage higher than the rated voltage at room temperature. Incidentally, several tens of capacitor elements are usually connected to the lead frame. Therefore, it is preferable that the first aging process is performed for each lead frame by connecting one DC power supply to one lead frame. That is, when one DC power supply is connected to a plurality of lead frames, a voltage is applied to each capacitor element, and aging processing is performed,
Aging of zero or more capacitor elements is performed at the same time, the current capacity of the DC power supply is insufficient, and each capacitor element may not be boosted to a predetermined voltage, resulting in aging failure. When the current capacity of the DC power supply is increased in accordance with the number of the capacitor elements, the voltage of the capacitor elements can be boosted to a predetermined value. However, in this case, an inrush current when a voltage is applied to each capacitor element increases, and a capacitor element having a large leakage current has a larger leakage current and may be destroyed.
The first aging process may be performed for a time period of about several seconds, and even if performed for a long time, the effect of reducing the leakage current is hardly improved. After the first aging treatment, a voltage higher than the rated voltage is applied in an atmosphere at a high temperature (for example, 85 ° C.) to perform the second aging treatment. The temperature was 85
-125 ° C is preferable, and particularly preferably 85-105 ° C, and the effect of reducing the leakage current is more remarkable. Further, the time is preferably about several hours. In a short time, the effect of reducing the leakage current is low, and when the operation is performed for a long time, the leakage current characteristic is deteriorated.

After the second aging process, FIG.
A solid electrolytic capacitor 15 is manufactured by forming the cathode terminal 12 and the anode terminal 13 as shown in FIG.

[0017]

Next, embodiments of the present invention will be described. First, a powder obtained by mixing a binder with fine tantalum powder is press-compressed into a square shape. At this time, one end of a tantalum anode lead wire is inserted into the powder, and the other end is drawn out. After compression molding, sinter in vacuum to 1.62 mm x 3.2
A sintered body of 5 mm × 3.80 mm square is formed. Next, the sintered body is immersed in a nitric acid solution and subjected to a chemical conversion treatment at a chemical conversion voltage of 25 V to form an oxide film thereon. After forming the oxide film, a conductive polymer layer made of polyaniline is formed on the surface of the oxide film by a chemical oxidation polymerization method. At this time, it is necessary to fill the inside of the sintered body with polyaniline and to laminate the conductive polymer layer to a predetermined thickness also on the outer peripheral portion, so that the chemical oxidation polymerization treatment is repeated. After forming the conductive polymer layer, it is immersed in a graphite solution to form a graphite layer. After forming the graphite layer, a silver paste is applied to form a silver layer. After forming the silver layer, the silver layer is connected to the cathode terminal portion of the lead frame with a conductive adhesive, and the anode lead wire is connected to the anode terminal portion of the lead frame by resistance welding. Then, by the same method, 30 capacitor elements after the formation of the silver layer are connected to one lead frame. Thereafter, an exterior made of epoxy resin is formed by a transfer molding method. After forming the exterior, a part of the lead frame is cut. After the cutting, the first aging process is performed at room temperature by using one DC power supply for one lead frame, applying a maximum current of 1 A, and applying a voltage of 13 V for 4 seconds. After the first aging treatment, a voltage of 11 V is continuously applied for 6 hours in an atmosphere at a temperature of 85 ° C. to perform a second aging treatment.
After this second aging treatment, the rest of the lead frame is cut, and the cathode terminal and the anode terminal are formed to produce a tantalum chip type solid electrolytic capacitor rated at 6.3 V and 150 μF. In addition, the applied voltage at the time of the first aging process and the second aging process is approximately 2.0 V of the rated voltage, respectively.
6 times and about 1.75 times.

With respect to the tantalum solid electrolytic capacitor manufactured by the method of this embodiment, each leakage current after forming the outer package, after the first aging treatment, and after the second aging treatment was measured, and is shown in FIG.

The leakage current after the aging treatment of the tantalum solid electrolytic capacitor manufactured by the method of the comparative example was measured, and is also shown in FIG. In this comparative example, the first aging treatment was omitted, and in an atmosphere at a temperature of 85 ° C., 40 lead frames each connected to 30 capacitor elements were simultaneously used by using one DC power supply. The method is the same as that of the embodiment except that a current of 5 A at maximum is applied, and a voltage of 11 V is applied for 6 hours to perform aging treatment.

The leakage current is a value 5 seconds after the application of the rated voltage. The number of samples is 60 each.

As is clear from the measurement results shown in FIG. 2, the leakage current (average value) of the embodiment is 684 μA after the outer package is formed, 46 μA after the first aging treatment, and 25 μA after the second aging treatment. On the other hand, the leakage current (average value) of the comparative example is 52 μA after the aging process. In other words, the former method has a leakage current after the second aging process, which is １ ／ or less of the latter. In addition, the former leakage current is in the range of 13 to 41 μA after the second aging process, and the latter is 19 to 1995 μA, and the former has less variation than the latter and has a leakage current defect. Absent. This is because the rush current during the aging process is large in the latter case.

[0022]

As described above, according to the production method of the present invention, an oxide film is formed on a sintered body made of a valve metal powder, and a conductive polymer layer and a cathode layer are sequentially laminated on the oxide film. In the method for manufacturing a solid electrolytic capacitor in which a resin sheath is formed on a capacitor element which has been subjected to an aging treatment, a voltage equal to or higher than a rated voltage is applied at room temperature to perform a first aging treatment, and then the aging treatment is performed at a high temperature Since the second aging process is performed by applying a voltage equal to or higher than the rated voltage, leakage current characteristics can be improved, defects can be reduced,
A solid electrolytic capacitor with improved reliability can be obtained.

[Brief description of the drawings]

FIG. 1 shows a process chart of an embodiment of the present invention.

FIG. 2 shows a graph of leakage current at each manufacturing stage.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sintered body, 5 ... Oxide film, 6 ... Conductive polymer layer, 7 ...
Graphite layer, 8: silver layer, 9: cathode layer, 10: capacitor element, 14: exterior, 15: solid electrolytic capacitor. Reference number P2511

Claims (1)

[Claims] An oxide film is formed on a sintered body made of a valve action metal, and an exterior made of a resin is formed on a capacitor element in which a conductive polymer layer and a cathode layer are sequentially laminated on the oxide film.
Then, in a method for manufacturing a solid electrolytic capacitor to be subjected to an aging treatment, a voltage equal to or higher than a rated voltage is applied at room temperature to perform the first
Aging treatment, and then applying a voltage equal to or higher than a rated voltage in a high-temperature atmosphere to perform a second aging treatment.