JPH0550125B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for manufacturing a solid electrolytic capacitor with 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 an increasing demand for capacitors used therein that have low impedance in the high frequency range and are small and large in capacity. Conventionally, plastic film capacitors, mica capacitors, and multilayer ceramic capacitors have been used as capacitors for high frequency ranges, but film capacitors and mica capacitors are large in size, making it difficult to increase the capacitance, and multilayer ceramic capacitors 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, known high-capacity type capacitors include aluminum dry electrolytic capacitors and aluminum or tantalum solid electrolytic capacitors. These capacitors can achieve large capacitance because the anodic oxide film that serves as the dielectric can be made very thin, but on the other hand, the oxide film is easily damaged, so damage must be repaired between the oxide film and the cathode. It is necessary to provide an electrolyte for this purpose. 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 (tanδ) 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 its drawbacks. Furthermore, in aluminum and tantalum solid electrolytic capacitors, manganese dioxide is used as the solid electrolyte in order to improve the drawbacks of the above-mentioned aluminum dry electrolytic capacitors. This solid electrolyte is obtained by immersing an anode element in an aqueous manganese nitrate solution and thermally decomposing it at a temperature of 250 to 350°C. In the case of this capacitor, since the electrolyte is solid, there are no drawbacks such as electrolyte leakage at high temperatures or performance degradation caused by solidification at low temperatures, and it has better frequency and temperature characteristics than capacitors using liquid electrolytes. However, due to damage to the oxide film due to thermal decomposition of manganese nitrate and the high specific resistance of manganese dioxide, the impedance or loss in the high frequency range is more than one order of magnitude compared to multilayer ceramic capacitors or plastic film capacitors. The value is high. In order to solve the above problems, an organic semiconductor (7,7,8,8-tetracyanoxynodimethane complex: hereinafter referred to as TCNQ complex) with high conductivity and excellent anodic oxidation properties should be used as a solid electrolyte. is proposed. This organic semiconductor can be impregnated into an oxide film by dissolving it in an organic solvent or melting it by heating.
Damage to the oxide film due to thermal decomposition that occurs when impregnating with MnO ₂ can be prevented. TCNQ complexes have high conductivity and excellent anodic oxidation properties, and have good high-frequency characteristics, making it possible to create large-capacity capacitors. For example, N-n-propyl or N-iso-propylisoquinoline was developed by Shinichi Niwa.
An application has been filed for an invention that uses an organic semiconductor composed of TCNQ as a solid electrolyte (Japanese Patent Application Laid-Open No. 17609-1983).
Publication No.). According to the invention, the wound aluminum electrolytic capacitor is impregnated with TCNQ salt by heating and melting the TCNQ salt.
A strong bond between TCNQ salt and oxide film is achieved,
Thanks in part to the high conductivity of the TCNQ salt, aluminum capacitors with significantly improved frequency and temperature characteristics will be produced. The use of such an organic semiconductor based on TCNQ salt as a solid electrolyte is advantageous for solid electrolytic capacitors using manganese dioxide because TCNQ salt has higher conductivity and higher anodic oxidation ability (repairing action) than manganese dioxide. In comparison, it enables superior performance in both frequency and temperature characteristics. According to this invention, the oxide film is impregnated with a TCNQ salt whose cation is isoquinolinium substituted with an alkyl group at the N-position by heating and melting it. Problems to be Solved by the Invention Furthermore, in recent years, it has been proposed to form a polymer of a heterocyclic compound such as pyrrole or thiophene on an anode body and use it as a solid electrolyte. In the electrolytic polymerization reaction, a polymer film cannot be formed on the oxide film that serves as a dielectric without destroying the film due to the reaction process of electrolytic oxidation of monomers. Also,
Before forming the oxide film, it is possible to apply an electrolytic polymer film on the valve metal and then perform a chemical conversion reaction to form the oxide film, but in this case, the chemical reaction is carried out via the electrolytic polymer film, so It has been difficult to form a good electrolytically polymerized membrane on the valve metal because the electrolytically polymerized membrane changes in quality and its adhesion to the valve metal decreases. The present invention is intended to solve the above-mentioned conventional problems, and aims to provide a method for manufacturing a solid electrolytic capacitor using an electrolytically polymerized film, which has excellent capacitor characteristics, particularly high frequency characteristics and reliability characteristics. Means for Solving the Problems The present invention achieves the above object, and its technical means is to apply a manganese dioxide film formed on the surface of a foil made of valve metal via a dielectric film to an electrolytic polymerization solution. A potential is applied between a first electrode for electrolytic polymerization provided in contact with the surface of the manganese dioxide film and a second electrode for electrolytic polymerization provided at a position separated from the first electrode, and polymerization is performed. The method of manufacturing a solid electrolytic capacitor includes at least the step of forming a film on a manganese dioxide film. Function The present invention deposits manganese dioxide nuclei on a part of the dielectric film formed on the surface of a foil made of valve metal such as Al or Ta, and forms a polymer film from the nuclei toward the surface by electrolytic polymerization. By growing the
An electrolyte polymer film with excellent conductivity can be grown, and a solid electrolytic capacitor with excellent high frequency characteristics and reliable capacitor characteristics can be obtained. Examples Examples of the present invention will be described below. FIG. 1 shows a schematic diagram illustrating a method of manufacturing a solid electrolyte capacitor in an embodiment of the present invention.
Al foil 1, which is a valve metal, as shown in Figure 1a
A capacitor anode lead electrode 2 is attached to the capacitor, and an etching process is first performed to increase the surface area. Next, as shown in FIG. 1b, an oxide film 3 made of Al ₂ O ₃ is formed using an adipic acid aqueous solution or the like.
form. The oxide film 3 is formed by a conventional method using electrochemical means. Thereafter, the MnO ₂ film 4 is formed by immersing it in an aqueous manganese nitrate solution and subjecting it to thermal decomposition treatment in the air at 250 to 300°C. Next, an electrolytic polymer film is formed on this surface.
Even if a voltage is applied using the anode 2 of the capacitor as a polymerization electrode, electrolytic polymerization does not occur and film growth does not occur because of the presence of the dielectric film. Therefore, as shown in FIG. 2, an electrode 5 for electrolytic polymerization that initiates polymerization is provided externally so as to be in contact with the MnO ₂ film 4.
Furthermore, an electrode 6 for electrolytic polymerization was provided apart from the electrode 5 for electrolytic polymerization. In a polymerization reaction vessel 7 as shown in FIG. 2, a polymerization solution 8 consisting of an electrolytically polymerizable monomer such as pyrrole or thiophene, a supporting electrolyte, and a solvent was prepared. A polymer film (not shown) is first formed on the electrode 5 by immersing it in this as shown in the figure and applying a voltage higher than the polymerization potential between the counter electrode 6 for electrolytic polymerization and the electrode 5 for electrolytic polymerization, after that,
Gradually, using this opportunity, the polymer film was changed to manganese dioxide film 4
grows toward the surface. After the polymer film completely covers the surface of the manganese dioxide film 4, the electrolytic polymerization reaction is terminated, and the surface of the polymer film is washed and dried. Thereafter, although not shown, a lead electrode of a capacitor cathode is attached in contact with the vertical and horizontal films using carbon paste, silver paste, or the like. Finally, the exterior is treated using epoxy resin. A plurality of electrodes 5 for electrolytic polymerization may be provided. Further, the counter electrode 6 for electrolytic polymerization may be located anywhere as long as it is located apart from the electrode 5 for electrolytic polymerization, and it is desirable that the electrode 5 for electrolytic polymerization has a smaller shape than the counter electrode 6 for electrolytic polymerization. More details are provided below. As the Al foil, we used one that is normally etched and has a rating of 16V and 10μF. After applying a chemical conversion film using an adipic acid aqueous solution, it was immersed in a 30% manganese nitrate aqueous solution and heated to 270°C in air.
Thermal decomposition treatment was carried out for 1 minute. An electrolytic polymerization solution was prepared from pyrrole (0.5M/), tetraethylammonium paratoluenesulfonate (0.1M/) and acetonitrile. A platinum wire was used as the electrode at the starting point of electrolytic polymerization, and 5V was applied between this electrode and the cathode to allow the reaction to occur for 15 minutes. After that, it is washed with alcohol or the like and dried. Next, Aquadac is applied to the entire surface of the electropolymerized membrane, and then a cathode lead electrode is attached using silver paste.
Finally, the leakage current was reduced to 0.5μA by packaging with epoxy resin. Then at 80℃ in air
Aging treatment was performed by applying 20V for 2 hours. Next, the characteristics of this capacitor are shown in the table below (the average value of 5 samples, the capacitance in liquid is 10.0 μF)
(120Hz)).

[Table] As is clear from the table, the capacitance value at 120Hz, for example, is very high at 9.5μF (normal solid capacitors, such as TCNQ salt, have a capacitance of 7μF), and at 500KHz.
The series resistance (ESR) is also extremely low at 30 mΩ among Al electrolytic capacitors, and it has excellent high frequency characteristics. The leakage current also showed a very small value of 0.5μA. Furthermore, when the battery was left at 125°C without any load for 500 hours, the capacity decreased by only about -2%, and other characteristics remained unchanged. In addition, as an experiment, a commonly used Ta sintered body was used instead of Al foil to fabricate it using the same process, and the properties were equivalent to those obtained by seven times of manganese dioxide treatment. Effects of the Invention In the present invention, a dielectric film formed on the surface of a foil made of a valve metal is treated with manganese dioxide and is immersed in a polymerization solution, and then a dielectric film is formed externally in contact with a part of the manganese dioxide film. This method forms an electrolytic polymer film on a manganese dioxide film using an electrode for electrolytic polymerization, which makes it possible to form an electrolytic polymer film with excellent conductivity on an oxide film, and improves high frequency characteristics and reliability. It has the advantage of providing excellent solid electrolytic capacitors.

[Brief explanation of the drawing]

FIGS. 1 and 2 are explanatory diagrams showing the steps of a method for manufacturing a solid electrolytic capacitor in an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Al, 2... Anode lead electrode, 3... Oxide film, 4... MnO ₂ film, 5... Electrode for electrolytic polymerization, 6... Counter electrode for electrolytic polymerization, 7... Polymerization reaction vessel, 8... ...Polymerization solution.

Claims (1)

[Scope of Claims] 1. A step of forming a dielectric film on both surfaces of a foil made of a valve metal, a step of forming a manganese dioxide film on the dielectric film, and a dielectric film on which the manganese dioxide film is formed. A first electrode for electrolytic polymerization is provided in contact with the surface of the manganese dioxide film, and a second electrode for electrolytic polymerization is provided at a position separated from the first electrode. A method for producing a solid electrolytic capacitor, comprising the steps of: providing a polymer film; and applying a potential between the electrodes to form a polymer film. 2. Manufacturing the solid electrolytic capacitor according to claim 1, wherein the foil with the dielectric film is immersed in an aqueous manganese nitrate solution and heat-treated in air at 250 to 300°C to precipitate manganese dioxide to form a manganese dioxide film. Method. 3. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the electrolytic polymerization solution comprises an electrolytically polymerizable monomer, a supporting electrolyte, and a solvent. 4. The method for producing a solid electrolytic capacitor according to claim 3, wherein the electrolytically polymerizable monomer is pyrrole or thiophene. 5. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein a plurality of first electrodes for electrolytic polymerization are provided.