JPH0748454B2 - Method for manufacturing solid electrolytic capacitor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid electrolytic capacitor having excellent capacitor characteristics, particularly high frequency characteristics and reliability.

2. Description of the Related Art In recent years, along with the digitization of electric device circuits, the capacitors used therein have low impedance in the high frequency region, and there is an increasing demand for small and large capacity capacitors.

Conventionally, plastic film capacitors, mica capacitors, and laminated ceramic capacitors have been used as capacitors for the high frequency region, but it is difficult to increase the capacity because film capacitors and mica capacitors are large in size, Ceramic capacitors have the drawback that the smaller the size and the larger the capacity, the worse the temperature characteristics and the very high the price.

On the other hand, known as large-capacity type capacitors are aluminum dry electrolytic capacitors, aluminum or tantalum solid electrolytic capacitors, and the like. These electrolytic capacitors can realize a large capacity because the anodic oxide film that serves as a dielectric can be formed extremely thin, but on the other hand, the oxide film and the cathode film are easily damaged because the oxide film is easily damaged. Between them it is necessary to provide an electrolyte to repair the damage. In an aluminum dry electrolytic capacitor, an etched positive and negative aluminum foil is wound around a paper separator and a liquid electrolyte is impregnated into the separator to be used. For this reason, there are drawbacks such as decrease in capacitance and loss (increasing tan ^δ) over time due to electrolyte leakage, evaporation, etc., and at the same time, high-frequency characteristics and low-temperature characteristics are significantly deteriorated due to ionic conductivity of the electrolyte. have.

Further, in the aluminum / tantalum solid electrolytic capacitor, manganese dioxide is used as a solid electrolyte in order to improve the drawbacks of the aluminum dry electrolytic capacitor. This solid electrolyte is obtained by immersing the anode element in a manganese nitrate aqueous solution and thermally decomposing it at a temperature of 250 to 350 ° C. In the case of this capacitor, since the electrolyte is a solid, there are no defects such as electrolyte outflow at high temperatures and deterioration of performance caused by solidification at low temperatures, and it has better frequency characteristics and temperature than a capacitor using a liquid electrolyte. Although the characteristics are shown, due to the damage of the oxide film due to the thermal decomposition of manganese nitrate and the high specific resistance of manganese dioxide, the impedance or loss in the high frequency range is one digit or more compared to the multilayer ceramic capacitor or plastic film capacitor. It is a high value.

In order to solve the above problems, an organic semiconductor (7, 7,
It has been proposed to use 8,8-tetracyanoquinodimethane complex: hereinafter referred to as TCNQ complex). This organic semiconductor can be dissolved in an organic solvent, or can be impregnated and applied to the oxide film by means such as melting by heating.
As described above, it is possible to prevent damage to the oxide film due to thermal decomposition that occurs when impregnating manganese dioxide. TCNQ
The complex has high conductivity, excellent anodic oxidation property, good high frequency characteristics, and enables a large-capacity capacitor.

For example, the same applicant has filed an invention using Nn-propyl or an organic semiconductor composed of N-iso-propylisoquinoline and a TCNQ complex as a solid electrolyte (JP-A-58-17609). According to this invention, the TCNQ salt is impregnated into the wound aluminum electrolytic capacitor.
This can be done by heating and melting the salt, which achieves a strong bond between the TCNQ salt and the oxide film, and also contributes to the high conductivity of the TCNQ salt, which significantly improves the frequency characteristics and temperature characteristics. It is said that aluminum capacitors will be manufactured. The use of such an organic semiconductor based on TCNQ salt as a solid electrolyte means that TCNQ salt has higher conductivity and higher anodic oxidation ability (repairing action) than manganese dioxide. It enables superior performance in both frequency and temperature characteristics compared to capacitors. According to the present invention, the TCNQ salt having cation of isoquinolium substituted at the N-position with an alkyl group is impregnated by heating and melting in the oxide film.

Furthermore, in recent years, a solid electrolytic capacitor has been proposed in which a highly conductive polymer obtained by polymerizing a heterocyclic monomer such as pyrrole or thiophene is formed on an anode body and the polymer is used as an electrolyte. 60-37114, JP 61
−47625).

Problems to be Solved by the Invention According to electrolytic polymerization, a dense conductive polymer film can be easily formed from a solution of pyrrole, thiophene, or a derivative thereof and a suitable supporting electrolyte into a usual anode (for example, platinum, carbon, etc.). ) Can be formed on.

However, in electrolytic polymerization, it is theoretically difficult to form a conductive polymer on an anode having an oxide film because no current flows. On the other hand, it is possible to form a conductive polymer film on the surface of the valve metal not provided with an oxide film by electrolytic polymerization, but in this case, anodization must be performed through the conductive polymer film. As a result, the conductive polymer film formed in advance is deteriorated or deteriorated, and further peeled from the surface of the anode. All of these are undesirable because they deteriorate the characteristics of the capacitor.

It is also possible to synthesize a conductive polymer by oxidative polymerization, but in this case, the polymer obtained is in the form of powder, and as it is, the adhesiveness to the anode having an oxide film, coating It is difficult to use it as the electrolyte of a capacitor because of its poor property.

The present invention solves the above-mentioned conventional problems, and it is possible to form an electropolymerized polymer having excellent conductivity on a valve metal having an oxide film, and therefore, it is possible to obtain excellent reliability in high frequency characteristics and temperature characteristics. It is an object of the present invention to provide a method for manufacturing a solid electrolytic capacitor, which can manufacture a solid electrolytic capacitor having high performance, reduce the defective rate due to leakage current, and improve the manufacturing yield. To do.

Means for Solving the Problems The present invention achieves the above object, and a step of preparing a valve metal, an oxide film forming step of chemical conversion treatment of the valve metal to form an oxide film on the surface, and the oxide film A manganese dioxide film forming step of forming a manganese dioxide film by depositing manganese dioxide thereon, an immersion step of immersing the valve metal on which the manganese dioxide film is formed in an electrolytic polymerization solution, and the immersed valve metal. An arranging step of arranging the second electrode at a position apart from the first electrode while contacting the first electrode, and applying a voltage between the arranged first electrode and the second electrode. And a solid electrolytic capacitor having a polymer film forming step of forming a conductive electrolytically polymerized polymer film on the manganese dioxide film, and a re-forming step of re-forming the oxide film after the polymer film forming step. Made of It is a manufacturing method.

The valve metal is selected from aluminum and tantalum, and is etched to increase the surface area. An aqueous adipic acid solution is used to form an oxide film on the valve metal. It can be formed by a usual method.

The valve metal with the oxide film formed is immersed in an aqueous solution of manganese nitrate and then pyrolyzed in air (may be humidified) at 200 to 300 ° C to deposit manganese dioxide, for example, in the form of a film on the oxide film. Can be made.

An electrolytic polymerization film is formed on the surface of the manganese dioxide film, but even if a voltage is applied using the valve metal anode as a polymerization electrode, the dielectric oxide film intervenes, so electrolytic polymerization does not occur, and the film growth Does not happen. So, as mentioned above,
A valve metal having an oxide film on which a manganese dioxide film is formed is immersed in an electrolytic polymerization solution in a polymerization reaction vessel, and a first electrode for electrolytic polymerization is provided in contact with the surface of the manganese dioxide film, and the first electrode. The electrolytically polymerized polymer film is first formed on the first electrode by applying a voltage higher than the polymerization potential between the second electrode for electrolytic polymerization provided at a position separated from the electrode of No. Starting from this, the electrolytically polymerized polymer film can be gradually grown in the surface direction of the manganese dioxide film. The electrolytic polymerized polymer film completely covers the surface of manganese dioxide, which is a solvent that is easy to dry after the completion of the electrolytic polymerization reaction,
For example, cleaning is performed using a solvent such as water, alcohol, acetone-tolyl or ketone, and unreacted monomers, electrolytes and unstable oligomers are cleaned.

The re-formation treatment of the oxide film after the formation of the above electropolymerized polymer film is performed through the electropolymerized polymer film in water or in a dilute solution of a carboxylic acid such as adipic acid or salicylic acid of 1% or less.

The electrolytic polymerization solution is composed of an electropolymerizable monomer, a supporting electrolyte and a solvent, and the polymerizable monomer may be any as long as it gives an electroconductive polymer by oxidative polymerization, for example, pyrrole or its 3 and 4 positions. Derivatives having a substituent introduced, or dimer bipyrrole or thiophene, or derivatives having a substituent introduced at the 3- or 4-position thereof, or 2
Bimeric thiomers, trimeric tertienyl and the like can be used.

Also, a plurality of the first electrodes for electrolytic polymerization can be used.

Action As described above, it is difficult to directly attach the electropolymerized polymer onto aluminum or tantalum having an oxide film as a dielectric. However, the applicant of the present invention, after depositing manganese dioxide on the oxide film, for example, even in the form of dots, and when an electrolytic polymerization reaction occurs from a location with a certain high current density, the polymerized polymer surface starts from there. I found that I grew up in the whole area. Therefore, after the polymerized polymer has grown on the entire surface, the place that is the starting point of this polymerization reaction is removed to obtain a capacitor with less leakage current.
The repair capacity is provided by manganese dioxide. In the present invention, the electropolymerization polymer film excellent in conductivity, manganese dioxide which has been practically used so far, a state where there is no repetition of high temperature treatment when a solid electrolyte such as TCNQ salt is attached onto an oxide film. Since it is formed at room temperature and low voltage, the deterioration of the oxide film is small and a high withstand voltage capacitor can be obtained. In addition, since it is an electrolyte with excellent conductivity, it has excellent high-frequency characteristics, and because the adhesion of the electrolytically polymerized polymer film and the oxide film of the electrolytically polymerized polymer film is good, a capacitor with excellent low-temperature and high-temperature shelf life is provided. can get. In addition, since the electrolytically polymerized polymer film is formed on the oxide film in the form of a film, the shape of a thin capacitor can be easily obtained.

In addition, by forming the electrolytically polymerized polymer film and then subjecting the oxide film to chemical conversion treatment, it is possible to reduce the defect rate due to leakage current.

Examples Examples of the present invention will be described below.

1 and 2 are conceptual diagrams showing the procedure of the method for manufacturing a solid electrolytic capacitor in one embodiment of the present invention.

As shown in FIG. 1 (a), an aluminum foil 1 which is a valve metal and an anode lead electrode 2 for a capacitor attached thereto were prepared, and first, a usual etching treatment was performed in order to increase the surface area. This aluminum foil 1 is rated at 16V, 10μ
The one for F was used. Then anodizing with an aqueous solution of adipic acid on the surface of the aluminum foil 1 as shown in FIG. 1 (b) (Chemical) to Al ₂ O ₃ dielectric anodized film 3 consisting of
Was formed. Next, the aluminum foil 1 on which the oxide film 3 has been formed is immersed in a 30% aqueous solution of manganese nitrate and subjected to a thermal decomposition treatment in air at 270 ° C. for 10 minutes to form a manganese dioxide (MnO ₂ ) film 4 on the oxide film 3. did. Next, as shown in FIG. 2, an electrolytic polymerization electrode 5 made of a platinum wire for initiating polymerization is provided outside so that its tip contacts the manganese dioxide film 4, and an electrolytic polymerization counter electrode 6 is provided. Separated from. On the other hand, pyrrole (0.5 mol /
1) and an electropolymerization solution 8 consisting of tetraethylammonium paratoluenesulfonate (0.1 mol / l) acetonitonil were charged. In this, an aluminum foil 1 with an oxide film 3 having a manganese dioxide film 4 formed thereon, an electrode 5 for electrolytic polymerization
Then, the counter electrode 6 for electrolytic polymerization is immersed as shown in the figure, and a voltage of 5 V higher than the polymerization potential is applied between the counter electrode 6 for electrolytic polymerization and the electrode 5 for electrolytic polymerization to cause a reaction for 15 minutes. A polymer film (not shown) is formed on the electrode 5, and thereafter, the polymerized polymer film is gradually used as a starting point to form the manganese dioxide film 4.
Could be grown in the surface direction. After the polymerized polymer film completely covered the surface of the manganese dioxide film 4, the electropolymerization reaction was terminated, and the surface of the polymerized polymer film was washed with ethanol and dried. After forming the polymerized polymer film on the manganese dioxide film 4, the oxide film 3 was subjected to re-chemical conversion treatment in a 0.5% aqueous solution of adipic acid. After the re-formation treatment, the aluminum foil 1 was stepwise applied to the cathode from a low pressure to 20V. At this time, the flowing current gradually decreases. The voltage application was stopped when this value was saturated. After this, it was washed pure and dried. Next, apply Aquadag on the entire surface of the electropolymerized polymer film, and then
The cathode lead electrode was attached using silver paste. Next, an exterior was coated with an epoxy resin, and finally 20 V was applied at room temperature for 2 hours for aging treatment.

The following table shows the difference in the capacitor characteristics depending on the presence or absence of the re-chemical conversion treatment after forming the electrolytically polymerized polymer film. Ten samples were prepared for each.

Similar effects were obtained when the electrolytic polymerization solvent was not a non-aqueous organic solvent but an aqueous solution and the electrolyte was not only toluene sulfonate but also aromatic toluene acid such as naphthalene sulfonate.

EFFECTS OF THE INVENTION In summary, according to the present invention, an electropolymerized polymer film having excellent conductivity is formed by using a manganese dioxide treatment on an oxide film on a surface of a valve metal and using a first electrode and a second electrode. Therefore, it becomes possible to form an electropolymerized polymer film having excellent conductivity on an oxide film, and a solid electrolytic capacitor having excellent high frequency characteristics and reliability can be manufactured. Further, since the oxide film is subjected to re-chemical conversion treatment after forming the electrolytically polymerized polymer film, it is possible to prevent a decrease in defective rate due to a leakage current and improve a manufacturing yield.

[Brief description of drawings]

1 and 2 are conceptual diagrams showing the procedure of the method for manufacturing a solid electrolytic capacitor in one embodiment of the present invention. 1 ... Aluminum foil, 2 ... Anode lead electrode, 3 ... Oxide film, 4 ... Manganese dioxide film, 5 ... Electropolymerization electrode, 6 ...
Counter electrode for electrolytic polymerization, 7 ... Polymerization reaction container, 8 ... Electropolymerization solution.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masao Fukuyama Inventor Masao Fukuyama 3-10-1 Higashisanda, Tama-ku, Kawasaki City, Kanagawa Matsushita Giken Co., Ltd. (72) Susumu Yoshimura 3-chome, Higashimita, Tama-ku, Kawasaki-shi No. 10 No. 1 within Matsushita Giken Co., Ltd. (56) Reference JP-A-63-181310 (JP, A)

Claims (6)

[Claims] 1. A step of preparing a valve metal, a step of forming an oxide film on the surface by chemical conversion treatment of the valve metal, and a step of depositing manganese dioxide on the oxide film to form a manganese dioxide film. A manganese dioxide film forming step, an immersing step of immersing the valve metal on which the manganese dioxide film is formed in an electrolytic polymerization solution, and a first electrode while contacting the immersed valve metal with a first electrode. An arrangement step of arranging a second electrode at a position spaced apart from the second electrode, and applying a voltage between the arranged first electrode and the second electrode so as to increase the conductive electrolytic polymerization height on the manganese dioxide film. A method for producing a solid electrolytic capacitor, comprising: a polymer film forming step of forming a molecular film; and a re-conversion step of re-forming the oxide film after the polymer film forming step. 2. The manganese dioxide film forming step comprises a dipping step of immersing the valve metal on which an oxide film is formed in a manganese nitrate aqueous solution, and a heat treatment in air at 200 to 300 ° C. after the dipping step. The method for producing a solid electrolytic capacitor according to claim 1, further comprising a deposition step of depositing manganese. 3. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein a plurality of first electrodes are provided. 4. The method for producing a solid electrolytic capacitor according to claim 1, wherein the valve metal is aluminum or tantalum. 5. The method for producing a solid electrolytic capacitor according to claim 1, wherein the electrolytic polymerization solution comprises an electropolymerizable monomer, a supporting electrolyte and a solvent. 6. The method for producing a solid electrolytic capacitor according to claim 5, wherein the electropolymerizable monomer is pyrrole, thiophene or a derivative thereof.