JPH0722078B2 - Manufacturing method of solid electrolytic capacitor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a solid electrolytic capacitor having good performance, which has a semiconductor layer of ferric tetroxide formed on a dielectric film by chemical deposition.

Conventionally, a solid electrolytic capacitor using manganese dioxide as a semiconductor layer is known. However, in this solid electrolytic capacitor, since the method of forming manganese dioxide on the dielectric film is a method of thermally decomposing an aqueous solution containing manganese nitrate at high temperature, the dielectric film (oxide film) is thermally There is a problem that it is cracked and is 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 that there is no.

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 conductive substance (Japanese Patent Laid-Open No. 173928/1982, etc.). The cost of dimethane salt is extremely high, and since it is a salt, it is unstable to moisture.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention An object of the present invention is to provide a low cost, a low dielectric loss tangent formed by chemically depositing a semiconductor layer on a dielectric film without utilizing a thermal decomposition reaction, and a leakage current. To provide a solid electrolytic capacitor having a small performance and good performance.

Means for Solving the Problems The present inventors have conducted various studies to solve the above-mentioned drawbacks of the prior art, and by forming a semiconductor layer of ferrosoferric oxide on the dielectric film by chemical deposition, The inventors have found that the above objects can be achieved very effectively, and have completed the present invention.

That is, according to the manufacturing method of the present invention, there is provided a solid electrolytic capacitor having a semiconductor layer of ferric tetroxide formed on a dielectric film by chemical deposition.

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 iron ions is used as a reaction mother liquor for forming iron (III) tetroxide on the dielectric film layer by chemical deposition. Typical examples of the compound that gives an iron ion species include ferrous sulfate and ferric sulfate.

The iron ion concentration in the reaction mother liquor is preferably within the range of 0.01 mol / l from the concentration that gives the saturated solubility.

If the concentration of iron ions in the reaction mother liquor is lower than 0.01 mol / l, the concentration of iron ions in the mother liquor is too low, and the number of coatings must be increased. When the concentration of iron ion in the reaction mother liquor exceeds the saturation solubility,
No merit of increasing the amount is recognized.

The pH of the reaction mother liquor is preferably in the range of 4 to 9, and the pH is adjusted with a suitable pH adjuster. Reaction mother liquor
When the pH is out of the above range, the electric conductivity of the formed semiconductor layer is low, and a solid electrolytic capacitor having good performance cannot be obtained.

The solid electrolytic capacitor of the present invention is a reaction mother liquor obtained by applying a reaction mother liquor to a valve action metal having a dielectric film such as aluminum, tantalum, niobium or by immersing the valve action metal having a dielectric film in the reaction mother liquor. Is introduced into the dielectric film, left standing, washed with water and dried. Although the room temperature is sufficient as it is allowed to stand, it may be heated to 50 ° C. or higher, preferably 50 to 120 ° C. in order to accelerate precipitation. Since the standing time varies depending on the standing temperature, it cannot be determined unconditionally, but it is usually appropriately determined by observing the degree of formation of ferric tetroxide.

The solid electrolytic capacitor manufactured by the method of the present invention,
It has the following advantages over the conventionally known solid electrolytic capacitors.

Since the semiconductor layer of ferrosoferric oxide can be formed on the dielectric film without thermal decomposition at high temperature, there is no risk of damaging the dielectric film of the anode, and it is also necessary to perform anodic oxidation (reformation) for repair. Absent. Therefore, the rated voltage can be increased several times that of the conventional one, and the size of the capacitor can be made smaller than that of the conventional one to obtain a capacitor having the same capacity and the same rated voltage.

Small leakage current.

A high breakdown voltage capacitor can be manufactured.

Since the conductivity of ferric tetroxide is sufficiently high at 10 ^-1 to 10 ¹ s · cm ^-1 , its impedance is low.

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 the table.

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 saturated ferric sulfate aqueous solution whose pH was adjusted to 4.5 with an ammonium aqueous solution was applied to the above-mentioned dielectric thin layer and left at 100 ° C. for 3 hours, and a ferric oxide layer was formed on the dielectric thin layer. . Next, after thoroughly washing the ferrosoferric oxide layer with water, 11
It was dried under reduced pressure at 0 ° C. for 3 hours. A carbon paste was applied on the triiron tetraoxide layer and dried, and then a silver paste was further applied and dried. Next, the lead wire was soldered and then packaged in a mold to manufacture a solid electrolytic capacitor.

Comparative Example 1 Manganese dioxide was formed by thermally decomposing conventionally known manganese nitrate at 300 ° C. on an aluminum foil having the same dielectric layer as in Example 1 to produce a solid electrolytic capacitor.

Claims (3)

[Claims] 1. A method for producing a solid electrolytic capacitor, characterized in that ferric tetroxide is formed as a semiconductor layer on a dielectric film by chemical deposition. 2. A reaction mother liquor for chemically precipitating triiron tetraoxide is an aqueous solution containing iron ions.
A method for manufacturing a solid electrolytic capacitor as described in the item. 3. The method for producing a solid electrolytic capacitor according to claim (2), wherein the pH of the reaction mother liquor for chemically depositing ferric oxide is in the range of 4-9.