JPH0393214A - Manufacture of solid-state electrolytic capacitor - Google Patents

Abstract

PURPOSE:To obtain a highly reliable solid-state capacitor of good high frequency properties by forming an anode oxide film on a valve metal, by forming a film of Al2O3 and MnO2 by heat decomposition method and by forming a conducive polymer film on a surface thereof by electrolytic polymerization. CONSTITUTION:Etching is carried out to increase an area of an Al foil 1 which is a valve metal. An oxide film 3a is formed by using adipic acid water solution, etc. Then, it is immersed in aluminum nitrate water solution for heat decomposition and an Al2O3 film 3b is formed. Manganese nitrate is thermally decomposed similarly to form an MnO2 film 4. An electrolytic polymerization counter electrode 6 is arranged in a polymerization reaction container 7 and a voltage of at least a polymerization electric potential is applied to paired electrolytic polymerization electrodes 5 to carry out electrolytic polymerization by immersing a foil 1 with a film 3b and a film 4 in polymerization solution 8. Thereby, a polymerization film is formed on the electrode 5 and grows on a surface of the foil 1 which is treated by the film 4 to cover a surface of the film 4 entirely. Thereafter, armor treatment is carried out by resin and a highly reliable solid-state capacitor can be obtained in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a solid electrolytic capacitor that has excellent high frequency characteristics, low leakage current, and high withstand voltage characteristics. Conventional technology In recent years, with the digitization of electrical equipment circuits, there has been an increasing demand for capacitors used there that have low impedance in the high frequency range and are small and large in capacity.
Conventionally, as capacitors for high frequency range, plastic film capacitors, mica capacitors, multilayer ceramic capacitors, and mica capacitors have large shapes, making it difficult to increase the capacity. The disadvantage is that the temperature characteristics become worse and the price becomes very high. On the other hand, known high-capacity type capacitors include aluminum ξ 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 it is necessary to repair the damage between the oxide film and the cathode. It is necessary to provide an electrolyte for this purpose. In aluminum dry electrolytic capacitors, etched positive and negative aluminum foils are wound up with a paper separator in between, and the separator is impregnated with liquid electrolyte. For this reason, capacitance decreases and losses (tan δ
), and at the same time, it has disadvantages such as significantly inferior high frequency characteristics and low point characteristics due to the ionic conductivity of the electrolyte. Furthermore, in aluminum and tantalum solid electrolytic capacitors, manganese dioxide is used as the solid electrolyte to improve the drawbacks of the aluminum and dry electrolyte capacitors. This fixed 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 electrolytic loss at high temperatures or poor performance caused by solidification at low temperatures, and it has better frequency characteristics and better performance than capacitors using liquid electrolytes. The impedance or loss in the high frequency range is compared to that of multilayer ceramic capacitors or plastic film capacitors because the temperature characteristics are due to damage to the oxide film due to thermal decomposition of manganese nitrate and the high specific resistance of manganese dioxide. The value is more than one order of magnitude higher. In order to solve the above problems, organic semiconductors (7, 7, 8
, 8-tetracyanoquinodimethane complex). This organic semiconductor can be impregnated onto an oxide film by dissolving it in an organic solvent or melting it by heating, and MnO. This can prevent damage to the oxide film due to thermal decomposition that occurs when impregnating the oxide film.
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, Mr. Shinichi Tanba reported that N-n-probyl or Nist-probyl isoquinoline and TCNQ
An application has been filed for an invention in which an organic semiconductor consisting of According to the invention, T to a wound aluminum electrolytic capacitor is
Impregnation of the CNQ salt is carried out by heating and melting the TCNQ salt, thereby achieving a strong bond between the TCNQ salt and the oxide film, and also aiding the contribution of the high conductivity of the TCNQ salt, resulting in improved frequency characteristics and It is said that aluminum capacitors with significantly improved temperature characteristics have been manufactured. The use of such an organic semiconductor based on TCNQ salt as a solid electrolyte has already been disclosed in an invention filed by the same applicant (Japanese Unexamined Patent Publication No. 17609/1983).
Since TCNQ salt has higher conductivity and higher anodic oxidation ability (restoration effect) than manganese dioxide, it enables superior performance in terms of temperature characteristics and temperature characteristics compared to solid electrolytic capacitors using manganese dioxide. According to the invention, an oxide film is impregnated with a TCNQ salt having a cation of isoquinolium substituted with an alkyl group at the N-position by melting it under heating. Furthermore, in recent years, proposals have been made to form a film of a polymer of a heterocyclic compound such as pyrrole or thiophene on an anode body and use it as a solid electrolyte. Problems to be Solved by the Invention However, in this electrolytic polymerization reaction, it is not possible to directly attach a polymer film to the oxide film that serves as a dielectric without destroying the film due to the reaction process of electrolytic oxidation of monomers. In addition, before forming the oxide film, it is possible to apply an electrolytic polymer film on the valve metal and then perform a chemical reaction to form the oxide film. In this case, the chemical reaction is performed through the electrolytic polymer film. This may cause deterioration of the electropolymerized membrane, or
Poor adhesion with the valve metal occurs, making it impossible to obtain a good capacitor. Therefore, in order to form a good electropolymerized film on a valve metal with an oxide film, some type of electrically conductive film is required in advance. The purpose of the present invention is to improve the characteristics of leakage current and withstand voltage in a capacitor in which a manganese dioxide film is deposited on the oxide film of the valve metal and then an electrolytically polymerized film is formed. Means for Solving the Problems The present invention achieves the above object, and its technical means is to form an anodic oxide film of tantalum or aluminum on a valve metal selected from tantalum or aluminum, and then apply aluminum nitrate ξ. A solid electrolytic capacitor characterized in that an At203 and MnOt film is sequentially formed from an aqueous solution of Ni and manganese nitrate or an organic salt thereof by a thermal decomposition method, and then a conductive electrolytically polymerized polymer film is formed on the surface of the At203 and MnOt films. It provides a manufacturing method. The conductive electropolymerized polymer membrane of the present invention is prepared by providing an external electrode different from the lead electrode of the capacitor, and using this as a starting point to form an MnO. It is desirable that the material be stretched over the membrane. In addition, such conductive electropolymerized polymer membranes include virol,
Preferably, monomers selected from thiophene or their derivatives are obtained by anodic oxidation polymerization. Operation As mentioned above, the present invention is applicable to valve metals. After electrochemically creating an oxide film that will serve as an electric body, a thermally decomposed film of aluminum oxide and manganese oxide is applied, and then an electrolytic polymer film is applied to reduce defective or weak parts of the oxide film on the valve metal. As a result, leakage current and breakdown voltage characteristics are improved. EXAMPLES Examples of the present invention will be explained in detail below with reference to the drawings.
Figure 1 shows a manufacturing schematic diagram illustrating the structure of a solid electrolytic capacitor in an embodiment of the present invention. A capacitor anode lead electrode 2 is attached to an Ai foil (valve metal) as shown in FIG. 1(a), and first, an etching treatment is performed to increase the surface area. Next, Figure 1 (b)
As shown in FIG.
form. Thereafter, it is immersed in a 30% aluminum nitrate aqueous solution and thermally decomposed in air at 200 to 300°C to form AlmOsll3b. After that, 30% manganese nitrate was subjected to thermal decomposition treatment under the same conditions.
Form an nOt film 4. In this case, the concentration of the aqueous solution is 2
0 to 50% is appropriate. Al fruitium oxide precipitates,
Alternatively, if the amount of manganese oxide is small, the number of immersions in the solution may be increased. Instead of nitrates, organic acid salts such as acetate and oxalate, which are easily decomposed by heat, can also be used. Next, an electrolytically polymerized film is placed on this surface, but if the anode of a capacitor is used as an anode for the electrolytically polymerized reaction, no polymerization reaction occurs and the film does not show any length. Therefore, as shown in Figure 2, an electrode 5 for electrolytic polymerization was provided outside to initiate polymerization. In a polymerization reaction vessel 7 as shown in FIG. 2, a polymerization solution 8 consisting of an electrolytically polymerizable monomer such as virol, thiophene or a derivative thereof, a supporting electrolyte, and a solvent such as water was placed. As shown in the figure, AIlzOs film 3b%M
An with nOx film 4! A counter electrode 6 for electrolytic polymerization is placed in the polymerization reaction vessel 7 in order to perform electrolytic polymerization by immersing the flit, and by applying a voltage higher than the polymerization potential to the electrode 5 for electrolytic polymerization, the polymer membrane is electrolyzed. A polymerization film is first formed on the polymerization electrode 5, and then a polymerization film is gradually formed starting from this point, manganese dioxide! The surface of the Al foil treated with Il4 is thickened. After the polymer film completely covers the surface of the manganese dioxide film 4, the electrolytic polymerization reaction is terminated. Stability is important for the electropolymerized membrane at this time. This polymer film is formed from a virol polymer and an anion contained as a dopant. For stability, it is important that this anion is difficult to dedope in the environment in which the capacitor is used. When naphthalene sulfonate or alkylnaphthalene sulfonate is used as an anion, it was found that dedoping does not occur, so these are used. After the reaction is complete, the surface of the polymerized membrane is washed with water or alcohol, and then dried. Then, attach the cathode lead electrode using carbon paste, silver paste, etc. Finally, the exterior is treated using epoxy resin. After this, aging treatment is performed, and some effect can be seen by aging treatment in humidity after attaching the cathode or after packaging to reduce leakage current. In order to improve the withstand voltage, we also considered increasing the voltage, for example, at least three times the operating voltage, but no significant effect was seen. The most effective method for improving leakage current and breakdown voltage characteristics was the provision of a thermally decomposed film of aluminum oxide and manganese oxide.

This will be explained in more detail below. As the anode foil for the capacitor, we used a commonly used etched and chemically treated foil (rated for 16V, 1O#F). After immersing this foil in a 30% aluminum nitrate aqueous solution, it was subjected to a 10+win thermal decomposition treatment at 270°C in air. Thereafter, a MnO film was further fabricated on this oxide film using the pyrolysis method from an aqueous manganese nitrate solution under the same conditions. Virol was used as the monomer for the electrolytic polymerization reaction, and water was used as the solvent. Triisobrobylnaphthalene sulfone soda was used as the electrolyte. Concentration is 0 monomer
．． 5M/1, and the electrolytic award was 0.1M/1. The polymerization reaction was carried out by applying a DC voltage of 3 V for 15 minutes between the electrolytic polymerization electrode 5 and the electrolytic polymerization counter electrode 7 in a polymerization reaction vessel 7 as shown in FIG. After that, it was washed with pure water and dried, and a cathode was attached using carbon paste and silver paste. Furthermore, after the exterior was made of epoxy resin, aging treatment was performed at 16V. The characteristics of this capacitor were measured and were as shown in the table below. (Number of samples: 10). For comparison, we also prepared samples that were not treated with aluminum nitrate. Table When we measured the leakage current after 2wins at 16V, it was less than 1uA in all cases where an aluminum oxide film was attached instead of aluminum nitrate. However, 20% to 30% of those that do not undergo this treatment have a voltage of 1 μA or more, and some that are large are around mA. Regarding breakdown voltage, when the breakdown voltage was measured for those made from argonium nitrate to which an aluminum oxide film was attached, all of them broke at a voltage of 23 to 26V. If this treatment was not performed, there were cases where the product was destroyed at 16V or less. This effect becomes more noticeable when the rated voltage of the foil used is as high as 25 or 35V. In particular, regarding voltage resistance, aluminum nitrate to aluminum oxide film is rated at 2.
The yield of obtaining 3 to 26 V or more is very poor. Similar effects were obtained when acetic acid or oxalic acid salts were used instead of aluminum or manganese nitrates. Effects of the Invention As described above, the present invention provides Affi. 0. After attaching the film, MnO, and the film using a thermal decomposition method, an electrolytic polymer film is formed, which has excellent high frequency characteristics and low leakage current.
It has become possible to provide a highly reliable solid capacitor with little variation and high withstand voltage.

[Brief explanation of drawings]

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.

Claims (3)

[Claims] (1) Form an anodic oxide film on the valve metal, and then generate Al_2O_3 and Mn from an aqueous solution of aluminum nitrate and manganese nitrate or from these organic salts by a thermal decomposition method.
A method for manufacturing a solid electrolytic capacitor, which comprises sequentially forming an O_2 film and then forming a conductive electrolytically polymerized polymer film on the surface. (2) A conductive electropolymerized polymer film is provided with an external electrode different from the lead electrode of the capacitor, and this is used as a starting point for Mn.
The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the solid electrolytic capacitor is grown on an O_2 film. (3) The conductive electrolytically polymerized polymer membrane is obtained by anodic oxidation polymerization of a monomer selected from pyrrole, thiophene, or a derivative thereof. A method for manufacturing solid electrolytic capacitors.