JPH02219211A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION 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.

BACKGROUND OF THE INVENTION In recent years, with the digitization of electrical equipment circuits, there has been a demand for capacitors used in these circuits to have low impedance in the high frequency range, and to be small and large in capacity.

is a high school student.

Conventionally, plastic film capacitors, mica capacitors, and multilayer ceramic capacitors have been used as capacitors for high frequency regions, but film capacitors and mica capacitors have large shapes, making it difficult to increase the capacity. Ceramic capacitors have the disadvantage that the smaller and larger the capacitance, the worse the temperature characteristics and the higher the price.

On the other hand, what is known as a large capacity type capacitor,
These include aluminum dry electrolytic capacitors, and aluminum or tantalum solid electrolytic capacitors. These electrolytic capacitors can achieve large capacitance because the anodic oxide film that serves as the dielectric can be formed very thinly, but on the other hand, the oxide film is easily damaged, so the oxide film and cathode It is necessary to provide an electrolyte to repair the damage in between. In an aluminum dry electrolytic capacitor, etched positive and negative electrode aluminum foils are wound up with a paper separator in between, and the separator is impregnated with a liquid electrolyte. For this reason, capacitance decreases and loss (tan δ) increases over time due to electrolyte leakage, evaporation, etc., and at the same time, high frequency characteristics and low temperature characteristics deteriorate significantly due to the ionic conductivity of the electrolyte. It has the following disadvantages.

Aluminum and tantalum solid electrolytic capacitors use manganese dioxide as the solid electrolyte to improve the drawbacks of the aluminum dry electrolytic capacitors. This solid electrolyte is obtained by immersing an anode element in a manganese nitrate aqueous solution and thermally decomposing it at a temperature of 250 to 350 tZ'. In the case of this capacitor, since the electrolyte is solid, there are no drawbacks such as electrolyte leakage at high temperatures or performance deterioration caused by coagulation at low temperatures, and it has better frequency characteristics and temperature characteristics than capacitors using liquid electrolytes. However, due to the damage to the oxide film due to thermal decomposition of manganese nitrate and the high resistivity of manganese dioxide, the impedance or loss in the high frequency range is reduced by using a multilayer ceramic capacitor or a +57\-7 chinoku film capacitor. The value is more than an order of magnitude higher than that in comparison.

In order to solve the above problems, organic semiconductors (7, 7, 8
, 8-tetracyanoquinodimethane complex (hereinafter referred to as TCNQ)
It has been proposed to use the above-mentioned CN). This organic semiconductor can be impregnated onto an oxide film by dissolving it in an organic solvent or melting it by heating. damage can be prevented. T
CNQCN has high conductivity, excellent anodic oxidation properties, and good high-frequency characteristics, making it possible to produce large-capacity capacitors.

For example, N-n-propyl, or N-1s.

An invention has been filed by the same applicant (Japanese Patent Laid-Open Publication No. 17609/1983) in which an organic semiconductor consisting of flobylisoquinoline and TCNQCN is used as a solid electrolyte. According to this invention, T
Impregnation of CNQ salt is carried out by heating and melting TCNQ6.
A strong bond between the Q salt and the oxide film is achieved, and the high conductivity of the TCNQ salt helps to produce an aluminum capacitor with significantly improved frequency and temperature characteristics. The use of this organic semiconductor based on TCNQ salt as a solid electrolyte is possible because TCNQ salt has higher conductivity and higher anodic oxidation ability (repairing action) than manganese dioxide. Enables superior performance in both frequency and temperature characteristics compared to capacitors. According to this invention, the oxide film is impregnated with a TCNQ salt in which the cation is inquiturium substituted with an alkyl group at the N position by heating and melting it.

Furthermore, in recent years, solid electrolytic capacitors have been proposed in which highly conductive polymers obtained by polymerizing heterocyclic monomers such as pyrrole and thiophene are formed on the anode body, and this is used as the electrolyte (Japanese Patent Laid-Open No. 60-37114, JP-A-61-47625) C Problem to be Solved by the Invention 7/＼-/ According to electrolytic polymerization, a solution of pyrrole, thiophene, or a derivative thereof and a suitable supporting electrolyte. Therefore, it is possible to easily form a dense conductive polymer film on an ordinary anode (eg, platinum, carbon, etc.).

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 by electrolytic polymerization on a valve metal surface that does not have an oxide film, but in this case, anodization must be performed through the conductive polymer film. First, this causes alteration or deterioration of the conductive polymer film previously formed, and furthermore, peeling from the anode surface. All of these are undesirable because they degrade the characteristics of the capacitor.

It is also possible to synthesize conductive polymers by oxidative polymerization, but in this case, the resulting polymer is in the form of a powder, and as it is, it has poor adhesion and coating to the anode with an oxide film. Due to its poor properties, it is difficult to use it as an electrolyte in capacitors.

The present invention solves the above-mentioned conventional problems, and it is possible to form an electrolytically polymerized polymer with excellent conductivity on a valve metal with an oxide film. The purpose of the present invention is to provide a method for manufacturing solid electrolytic capacitors that can manufacture solid electrolytic capacitors with high performance, reduce the defective rate due to leakage current, and improve manufacturing yield. It is something to do.

Means for Solving the Problem The present invention achieves the above object, and its technical solution consists of chemically converting the valve metal to form an oxide film on the surface, and depositing manganese dioxide on the oxide film. A conductive electropolymerized polymer film is formed on this manganese dioxide, and after formation,
The oxide film is subjected to re-chemical conversion treatment.

The valve metal is selected from aluminum or tantalum, and is treated with Eftin 9 Henog to increase the surface area. To form an oxide film on this valve metal, an adipic acid aqueous solution or the like is used, and electrochemical treatment is performed. It can be formed by conventional means.

The valve metal on which the oxide film has been formed is immersed in an aqueous manganese nitrate solution, and then thermally decomposed in air (humidification may be used) at 200 to 300 C to precipitate manganese dioxide, for example, in the form of a film on the oxide film. be able to.

An electrolytic polymer 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, electrolytic polymerization does not occur and the film does not grow because the dielectric oxide film is present. doesn't happen.

Therefore, a valve metal with an oxide film on which a manganese dioxide film has been 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. An electropolymerized polymer film is first formed on the first electrode by applying a voltage higher than the polymerization potential between the first electrode and a second electrode for electropolymerization provided at a distant position, 10 t=-,-> Thereafter, the electropolymerized polymer film can be gradually grown from this point toward the surface of the manganese dioxide film.

After the electropolymerization reaction in which the electropolymerized polymer film completely covers the surface of the manganese dioxide, cleaning is performed using an easily drying solvent such as water, alcohol, acetone trile, or ketone solvent to remove any unreacted material. to clean monomers, electrolytes and unstable oligomers.

The reconversion treatment of the oxide film after the formation of the electropolymerized polymer film is carried out in water or in a dilute solution of 1% or less of carboxylic acid such as adipic acid or salicylic acid through the electrolytic polymer membrane.

The electrolytic polymerization solution consists of an electrolytically polymerizable monomer, a supporting electrolyte, and a solvent.The polymerizable monomer may be one that provides a conductive polymer through oxidative polymerization, such as pyrrole or its 3 and 4 positions. A derivative in which a substituent is introduced into , or a dimeric bivirol, thiophene, or a derivative in which a substituent is introduced into the 3 and 4 positions, or 2
A trimeric bithiophene, a trimeric terchenyl, etc. can be added to the base 11.

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

As mentioned above, it is difficult to apply electrolytically polymerized polymers directly to dielectric materials such as aluminum or tantalum, which have a strong oxide film. However, after depositing manganese dioxide, even in the form of dots, on the oxide film, the applicant gradually electrolytically polymerizes the polymer from a certain point where the current density is high, causing the polymer to form on the surface. Headlines are growing all over the place. Therefore, by removing the point where the polymerization reaction started after the polymer has grown over the entire surface, a capacitor with low leakage current can be obtained. The repair ability is provided by manganese dioxide. In the present invention, an electropolymerized polymer film with excellent conductivity is used after high-temperature treatment when a solid electrolyte such as manganese dioxide or TCNQ salt, which has been put into practical use in this field, is deposited on an oxide film. Since the capacitor is formed at room temperature and at low voltage without any oxidation, the deterioration of the oxide film is minimal and a capacitor with high withstand voltage can be obtained. In addition, since it is an electrolyte with excellent conductivity, it has excellent high frequency characteristics, and because it has good adhesion to electrolytic polymer membranes and oxide films of electrolytic polymer membranes, it is a capacitor with excellent low-temperature and high-temperature storage life. can get. In addition, since the electropolymerized polymer film is formed on the oxide film in the form of a film,
A thin capacitor shape can be easily obtained.

In addition, after forming the electropolymerized polymer film, the oxide film is subjected to re-chemical conversion treatment, thereby reducing the defective rate due to leakage current.

Example The present invention will be explained in detail below.

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

As shown in FIG. 1(a), a capacitor anode lead electrode 2 9 attached to an aluminum foil 1, which is a valve metal, was prepared, and first, in order to increase the surface area, it was subjected to the usual etching treatment. The aluminum foil 1 used had a rating of 16 .mu.F and a rating of 10 .mu.F. Next, as shown in FIG. 1(b), the surface of the aluminum foil 1 is anodized (chemically formed) with an adipic acid aqueous solution to form Al2O2.
A dielectric anodic oxide film 3 was formed. Next, the aluminum foil 1 on which the oxide film 3 has been formed is immersed in a 30% manganese nitrate aqueous solution and subjected to thermal decomposition treatment for 10 minutes in 270 t:' air, so that the oxide film 3 is coated with manganese dioxide (Mn
O2) film 4 was formed. Next, as shown in FIG. 2, an electrolytic polymerization electrode 5 made of a platinum wire that initiates polymerization is provided externally so that its tip contacts the manganese dioxide film 4, and a counter electrode 6 for electrolytic polymerization is placed on the electrolytic polymerization electrode 5. It was set apart from the

Meanwhile, pyrrole (0,5mo7/7) was added to the polymerization reaction vessel 7.
, tetraethylammonium paratoluenesulfone)
An electrolytic polymerization solution 8 consisting of (0.1mo7/A) acetonitrile was placed therein. In this, the aluminum foil 1 with the oxide film 3 on which the manganese dioxide film 4 was formed, the electrode 5 for electrolytic polymerization, and the counter electrode 6 for electrolytic polymerization are immersed as shown in the figure. 5V above the polymerization potential between
First, a polymeric polymer film (not shown) is formed on the electrode 5 by applying a voltage of can be gradually grown toward the surface of the manganese dioxide film 4.

After the polymerized polymer membrane completely covered the surface of the manganese dioxide membrane 4, the electrolytic polymerization reaction was terminated, and the surface of the polymerized polymer membrane was washed with ethanol and dried.

After forming the polymerized polymer film on the manganese dioxide film 4 in this manner, the oxide film 3 was subjected to reconversion treatment in a 0.5% aqueous solution of adipic acid. Aluminum foil 1 after reconversion treatment
A low pressure up to 20 V was applied stepwise to the cathode. At this time, the flowing current gradually decreases. The voltage application was stopped when this value was saturated. After that, it was washed with pure water and dried. Next, Aquada Soge was applied to the entire surface of the electropolymerized polymer membrane, and then a cathode lead electrode was attached using silver paste. Next, the exterior was covered with epoxy resin, and finally, 20V was applied for 2 hours at room temperature to perform an aging treatment.

After forming the electropolymerized polymer film, the following table shows the difference in capacitor characteristics depending on the presence or absence of reconversion treatment. Ten samples were prepared for each.

(The following is a blank space) Go to 17-7 When the electrolytic polymerization solvent is a non-aqueous organic solvent, an aqueous solution is used, and the electrolyte is not only toluene sulfonate but also aromatic toluic acid such as naphthalene sulfonate. A similar effect was obtained.

Effects of the Invention To summarize, the present invention involves forming an electrolytically polymerized polymer film with excellent conductivity on the oxide film on the surface of the valve metal by treating it with manganese dioxide. Since it is possible to form a polymeric polymer film on an oxide film, a solid electrolytic capacitor with excellent high frequency characteristics and reliability can be manufactured. However, since the oxide film is subjected to reconversion treatment after forming the electrolytically polymerized polymer film, it is possible to prevent a decrease in the defective rate due to leakage current and improve the manufacturing yield.

[Brief explanation of the drawing]

FIGS. 1 and 2 are conceptual diagrams showing the steps of a method for manufacturing a solid electrolytic capacitor in an embodiment of the present invention. 1... Aluminum foil, 2... Anode lead electrode, to 18-7 3... Oxide film, 4...; Manganese oxide film, 5...
- Electrode for electrolytic polymerization, 6... Counter electrode for electrolytic polymerization, 7... Polymerization reaction container, 8... Electrolytic polymerization solution. Name of agent: Patent attorney Shigetaka Awano and one other person Figure (cL) (b)

Claims (7)

[Claims] (1) Chemically convert the valve metal to form an oxide film on the surface, deposit manganese dioxide on the oxide film, form a conductive electropolymerized polymer film on the manganese dioxide, and after the formation,
A method for manufacturing a solid electrolytic capacitor, comprising subjecting the oxide film to a reconversion treatment. (2) After immersing the valve metal with the oxide film formed in an aqueous manganese nitrate solution, heat-treating it in air at 200 to 300°C,
2. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein manganese dioxide is deposited on the oxide film. (3) A valve metal with an oxide film formed with manganese dioxide is immersed in an electrolytic polymerization solution, and a first electrode for electrolytic polymerization provided in contact with the surface of the manganese dioxide is separated from the first electrode. 2. The method of manufacturing a solid electrolytic capacitor according to claim 1, wherein the conductive electrolytic polymer film is formed by applying a potential between the second electrodes for electrolytic polymerization provided at these positions. (4) Claim 3 in which a plurality of first electrodes for electrolytic polymerization are provided.
A method of manufacturing the solid electrolytic capacitor described. (5) The method for manufacturing a solid electrolytic capacitor according to any one of claims 1 to 4, wherein the valve metal is selected from aluminum and tantalum. (6) The method for producing a solid electrolytic capacitor according to claim 3, wherein the electrolytic polymerization solution comprises an electrolytically polymerizable monomer, a supporting electrolyte, and a solvent. (7) The method for manufacturing a solid electrolytic capacitor according to claim 6, wherein the electrolytically polymerizable monomer is selected from pyrrole, thiophene, or derivatives thereof.