JPH0719725B2 - Method for manufacturing solid electrolytic capacitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a solid electrolytic capacitor having a good performance in which a lead dioxide layer is formed on a dielectric film layer by chemical deposition at a temperature of 60 ° C. or higher. Regarding

2. Description of the Related Art A solid electrolytic capacitor using lead dioxide as a semiconductor layer is known as described in, for example, Japanese Patent Publication No. 58-21414. However, in the conventional solid electrolytic capacitor described above, the method of forming lead dioxide on the dielectric film layer is a method of thermally decomposing a reaction mother liquor containing lead ions at a high temperature of 200 to 300 ° C. However, there is a problem in that the dielectric film (oxide film) is thermally cracked or chemically damaged by the generated gas. Therefore, when a voltage is applied to this solid electrolytic capacitor, current may concentrate on the defective portion of the dielectric film, causing dielectric breakdown. Therefore, in order to increase the reliability of the withstand voltage, the formation voltage must be 3 to 5 times the rated voltage, and in order to obtain a predetermined capacity, a large anode body having a large surface area must be used. There is a problem of not getting.

In order to prevent such a defect, for example, JP-A-54-12
As described in Japanese Patent No. 447, first, manganese nitrate is thermally decomposed to form a manganese dioxide layer on an oxide film layer, and then a liquid containing lead ions and persulfate ions at an extremely low concentration is formed. In addition, a method of providing a lead dioxide layer on the manganese dioxide layer by chemical deposition is known. However, in this method, when the manganese dioxide layer is formed, manganese nitrate is thermally decomposed at a high temperature of 200 to 400 ° C., and therefore thermal cracking of the dielectric film and chemical damage due to generated gas are unavoidable.

Further, as described in JP-B-49-29374, a method of forming a lead dioxide layer on a dielectric film layer by chemical deposition is known. However, this method requires silver ions as a catalyst when chemically precipitating lead dioxide, so that there is a problem that silver or a compound of silver is attached to the surface of the dielectric film, and the insulation resistance is reduced. is there.

As a method for solving such a drawback, there is known a method of using a tetracyanoquinodimethane salt, which is an organic semiconductor, as a semiconducting material (JP-A-57-173928, etc.). The cost of methane salt is extremely high, and since it is a salt, it is unstable to moisture.

From this point of view, the inventors of the present invention did not utilize the thermal decomposition reaction in a high-pitched sound, and did not use a catalyst such as silver ion which adversely affects the capacitor characteristics, and a semiconductor of lead dioxide on the dielectric film. We proposed a method of manufacturing a solid electrolytic capacitor whose layers are formed by chemical deposition (Japanese Patent Application No. 60-1931).
No. 85). However, in the solid electrolytic capacitor obtained by this method, the leakage current value of the capacitor was not always satisfactory.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention An object of the present invention is to provide a dielectric film which is low in cost, does not utilize a thermal decomposition reaction in a high tone, and does not use a catalyst that adversely affects the performance of a capacitor, such as a silver catalyst. It is an object of the present invention to provide a method for manufacturing a solid electrolytic capacitor in which lead dioxide is formed on a layer by chemical deposition and the leakage current value is improved.

Means for Solving the Problems According to the present invention, in producing a solid electrolytic capacitor having lead dioxide as a semiconductor layer, the lead dioxide is deposited on the dielectric film layer by chemical deposition at a temperature of 60 ° C. or higher. There is provided a method for manufacturing a solid electrolytic capacitor, which is characterized in that the solid electrolytic capacitor is formed.

The dielectric film in the present invention means an oxide film of a valve metal foil such as aluminum, tantalum, niobium or a sintered body, which is well known in the art, and can be obtained by a known method.

An aqueous solution containing lead ions and persulfate ions is used as a reaction mother liquor for forming lead dioxide by chemical deposition on the dielectric film layer.

There are no particular restrictions on the lead ion species and persulfate ion species,
Representative examples of compounds that give lead ion species include lead citrate, lead acetate, basic lead acetate, lead borofluoride, and lead acetate hydrohydrate. On the other hand, typical examples of the compound that gives a persulfate ion species include ammonium persulfate, potassium persulfate, and sodium persulfate. Two or more kinds of these compounds giving the lead ion species and the persulfate ion species may be mixed and used.

Lead ion concentration in the mother liquor is 7 mol / to 0.1 mol /
, Preferably in the range of 5 mol / to 1.3 mol /. If the lead ion concentration is higher than 7 mol /
The viscosity of the mother liquor becomes too high, making it difficult to use. Also, when the lead ion concentration is lower than 0.1 mol / mole, the lead ion concentration in the mother liquor is too low, and the number of times of application must be increased. . On the other hand, the concentration of persulfate ions in the mother liquor is within the range of 3 to 0.5 in molar ratio with respect to lead ions. When the concentration of persulfate ion is more than 3 in molar ratio with respect to lead ion, unreacted persulfate ion remains, resulting in high cost, and the concentration of persulfate ion is less than 0.5 in molar ratio with respect to lead ion. If so, unreacted lead ions remain and the electrical conductivity deteriorates, which is not preferable.

The reaction mother liquor may be used by dissolving a compound giving a lead ion species and a compound giving a persulfate ion species at the same time,
Alternatively, an aqueous solution of a compound that gives a lead ion species and an aqueous solution of a compound that gives a persulfate ion species may be prepared separately and mixed immediately before use.

As a method for chemically depositing and forming a lead dioxide semiconductor layer on the dielectric film layer, a reaction mother liquor (lead ion and persulfate ion is added to a valve action metal such as aluminum, tantalum, or niobium having a dielectric film) is formed. Aqueous solution containing) is applied and held at a temperature of 60 ° C. or higher, preferably 60 to 100 ° C., more preferably 75 to 95 ° C., then washed with water and dried, or a valve having a dielectric film Immersing the working metal in the reaction mother liquor to allow the reaction mother liquor to enter the dielectric film,
A method of holding at a temperature of 60 ° C. or higher, preferably 60 to 100 ° C., more preferably 75 to 95 ° C., followed by washing with water and drying can be mentioned. In the present invention, it is essential to form lead dioxide by chemical deposition on the dielectric film at a temperature of 60 ° C. or higher. Chemically depositing at a temperature of 60 ° C or higher means maintaining the valve action metal having a dielectric film coated with the reaction mother liquor at a temperature of 60 ° C or higher as described above, or removing the valve action metal having a dielectric film. It is achieved by immersing in the reaction mother liquor and maintaining the temperature of the reaction mother liquor at a temperature of 60 ° C. or higher.

If the holding temperature for forming lead dioxide from the reaction mother liquor by chemical precipitation is less than 60 ° C, a solid electrolytic capacitor having a sufficiently high leakage current value cannot be obtained. The holding time is appropriately selected by observing the degree of lead dioxide production.

Effects of the Invention The solid electrolytic capacitor manufactured by the method of the present invention has the following advantages as compared with the conventionally known solid electrolytic capacitors.

Since the lead dioxide layer can be formed on the dielectric film layer without heating to a high temperature, there is no risk of damaging the dielectric film of the anode, and there is no need to perform anodic oxidation (reformation) for repair. Therefore, the rated voltage can be raised several times higher than before, and to obtain a capacitor with the same capacity and rated voltage,
The shape can be made smaller than the conventional one.

 Small leakage current.

 A high breakdown voltage capacitor can be manufactured.

Impedance is low because the conductivity of lead dioxide is sufficiently high at 10 ^-1 to 10 ¹ s · cm ^-1 .

 Good high frequency characteristics.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The characteristic values of the solid electrolytic capacitors of each example are shown in Table 1.

Example 1 An aluminum foil (purity 99.99%) having a thickness of 100 μm was used as an anode, and the surface of the foil was electrochemically etched by alternating use of direct current and alternating current to have an average pore diameter of 2 μm and a specific surface area of 12 m ² / g. And Then, this etched aluminum foil is electrochemically treated in a solution of ammonium borate to form a thin layer of dielectric (alumina) on the aluminum foil.
Was formed.

A reaction mother liquor was obtained by mixing an aqueous solution having a lead acetate concentration of 2.0 mol / min and an aqueous solution having a potassium persulfate concentration of 1.25 mol / min.
This reaction mother liquor was immediately applied to the above-mentioned dielectric thin layer,
When kept at 30 ° C. for 30 minutes, a lead dioxide layer was formed on the thin dielectric layer. Next, the lead dioxide layer was thoroughly washed with water and then dried under reduced pressure at 120 ° C. for 3 hours. A carbon paste was applied on the lead dioxide layer and dried, and then a silver paste was further applied and dried. An aluminum foil was used for the cathode and a resin was sealed to produce a solid electrolytic capacitor.

Example 2 In Example 1, the concentration of lead acetate trihydrate was 3.5 as the reaction mother liquor instead of the aqueous solution of lead persulfate and the aqueous solution of potassium persulfate.
A lead dioxide layer was formed on the thin dielectric layer in the same manner as in Example 1 except that an aqueous solution of mol / mol and an aqueous solution of ammonium acetate sulfate of 4.2 mol / mol were used. After washing and drying, a carbon paste was coated on the lead dioxide layer and dried, and then a silver paste was further coated and dried. Next, the lead wire was soldered and then packaged to form a solid electrolytic capacitor.

Example 3 A solid electrolytic capacitor was produced in the same manner as in Example 2 except that the holding temperature was changed to 75 ° C.

Example 4 A solid electrolytic capacitor was produced in the same manner as in Example 2 except that the holding temperature was changed to 60 ° C.

Comparative Example 1 A solid electrolytic capacitor was produced by thermally decomposing conventionally known lead nitrate at 250 ° C. to form lead dioxide on an aluminum foil having the same dielectric layer as in Comparative Example 1.

Comparative Example 2 A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the reaction mother liquor was applied to the dielectric film in Example 1 and kept at room temperature for 3 hours.

Comparative Example 3 A solid electrolytic capacitor was produced in the same manner as in Example 2 except that the holding temperature in Example 2 was 55 ° C.

Claims (3)

[Claims] 1. When manufacturing a solid electrolytic capacitor using lead dioxide as a semiconductor layer, the lead dioxide is formed on the dielectric film layer by chemical deposition at a temperature of 60 ° C. or higher, and is characterized in that it is formed by chemical deposition. Capacitor manufacturing method. 2. The method for producing a solid electrolytic capacitor according to claim 1, wherein the reaction mother liquor for chemically precipitating lead dioxide is an aqueous solution containing lead ions and persulfate ions. 3. The lead ion concentration in the aqueous solution is from 7 mol / mol.
The method for producing a solid electrolytic capacitor according to claim 2, wherein the molar ratio of persulfate ion to lead ion is in the range of 3 to 0.5 in the range of 0.1 mol / l.