JPH03250723A - 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 solid electrolytic capacitors used in hybrid integrated circuits, electronic circuits such as electronic equipment, information equipment, and the like.

Conventional technology Conventional electrolytic capacitors, such as aluminum electrolytic capacitors, are made by applying a chemical conversion treatment to a porous aluminum foil whose effective surface area has been expanded by etching treatment, providing an oxide film dielectric material, and pasting electrolytic paper between the cathode foil and the electrolytic paper. It has a structure impregnated with liquid. In addition to exchanging electric charge between the anode and cathode, this electrolyte also has the effect of chemical formation, so it may be generated when the cut part of the anode is re-formed into an unformed oxidized skin area or when internal elements are wound. It has features not found in other capacitors, such as being able to repair defects in the oxide film dielectric of the anode body. However, the high frequency characteristics and low temperature characteristics are significantly inferior due to the ionic conduction of the charge between the anode and the cathode due to the electrolytic solution. It also has the disadvantage that its lifespan is limited due to evaporation of the electrolyte. Therefore, in order to overcome these drawbacks, solid aluminum electrolytic capacitors have been developed in which the electrolyte is replaced with a solid electrolyte made of a conductive polymer compound.

These solid aluminum electrolytic capacitors have significantly improved high frequency characteristics and low temperature characteristics by replacing the electrolyte with a solid electrolyte. Furthermore, by using a solid electrolyte made of a conductive polymer compound, its lifespan has been greatly extended.

Problems to be Solved by the Invention However, in conventional solid aluminum electrolytic capacitors, by replacing the electrolyte with a solid electrolyte made of a conductive polymer compound, one of the characteristics of the conventional solid aluminum electrolytic capacitor is that no oxide film is formed on the cut section of the anode. Since the effect of reforming the parts and repairing the defective parts caused by winding the internal elements is lost, the oxide film on the cut part of the anode is not formed before forming the conductive polymer compound. It is impossible to eliminate the oxide film formation area by re-forming the area.

Generally, after the cut part of the anode is returned to the part where the oxide film is not formed, or after etching treatment in an aqueous solution of boric acid and its salts or an organic acid salt such as ammonium adipate, the oxide film dielectric is formed by chemical conversion. Re-forming is carried out by applying the same voltage as for forming the oxide film, but because the area ratio between the area where the oxide film is formed and the area where the oxide film is not formed, that is, the area ratio of the cut part, is extremely small, the area where the oxide film is not formed is not sufficient. Since the current does not flow to the extent that a dense oxide film with few defects can be formed, it has the disadvantage that it is difficult to form a dense oxide film with few defects and a small leakage current.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for manufacturing a solid electrolytic capacitor which is small in size, has a large capacity, has excellent high frequency characteristics and low temperature characteristics, and has a small leakage current.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a method for applying porous chemical conversion as a pretreatment when reconforming a portion where an oxide film is not formed, such as a cut portion of an anode. It is characterized by the following.

Function: Since the present invention performs porous chemical conversion treatment as a pretreatment, a uniform oxide film can be obtained on the portion where the oxide film is not formed. Using the uniform oxide film formed in this pretreatment as a core, the pores called micropores distributed within the porous oxide film are filled with re-formation to create a uniform, dense anode with fewer defects. Therefore, a long-life capacitor with small leakage current and excellent high-frequency characteristics and low-temperature characteristics can be obtained.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to the drawings.

FIGS. 1 and 2 show one example of the structure of the capacitor of the present invention.

A positive electrode 1 made of etched porous aluminum was cut, and a lead 3 was joined by a caulking method in the presence of an oxide film-free portion 2 on the cut surface to obtain an anode body. Thereafter, this anode body is immersed in a chemical solution that forms a porous oxide film, such as oxalic acid or sulfuric acid, and a porous oxide film 6 is formed by constant current chemical formation, followed by boric acid and its salts, or Constant voltage and constant current chemical conversion was performed in a chemical solution of an aqueous solution of an organic acid such as ammonium adipate to obtain a reconverted oxide film 7. Thereafter, a conductive polymer compound 8 is formed by an electrolytic polymerization method or the like, resulting in a capacitor as shown in FIG.

Specific examples will be described below.

(Example 1) A 90 μm aluminum foil was subjected to AC etching in 5% hydrochloric acid to obtain an etched foil with an effective surface area increase rate of about 80 times. Subsequently, constant voltage and constant current chemical formation was performed in a 3% ammonium adipate aqueous solution under the conditions of an applied voltage of VDC and a current density of 0.01 A/d to form a dielectric oxide film. This anode foil was cut into 5×10 gg pieces, and aluminum leads were then joined by caulking to create a 5o- anode body. This anode body was heated to 1A in a 16% oxalic acid aqueous solution.
Constant current chemical formation was performed at a current density of /cd for 3 minutes, washed with water, dried, and used as a pretreatment. Subsequently, re-forming was carried out in the same chemical solution as that in which the dielectric oxide film was formed, at the same applied voltage and current density, to completely eliminate the areas where the oxide film was not formed. Next, the positive W form in which the oxide film-free part was completely removed was mixed with 0.2 mol/l of pyrrole, 0.02 mol/l of oxalic acid, and 0.2 mol/l of pyrrole.
Constant current electrolysis was carried out for 75 minutes at a current density of 0.01 A/d using the anode body as an anode and the nutless plate as a cathode in an acetone torile solution containing 0.05 mol/l of tetrabutylammonium toluenesulfonate as a dopant. As a result, a uniform black polypyrrole thin film was formed on the surface of the anode body. Aqua carbon and silver paste were then applied to this surface in that order, and an aluminum lead was bonded with silver adhesive to form the cathode lead, and the capacitor was completed by covering it with epoxy resin. The obtained capacitor characteristics were a capacitance of 5.9 μF at 120 Hz and a dielectric loss tangent (tan δ) of 1.
2%, equal series resistance (ESR) at 100 KHz
) was 121 mO, and the leakage current was 8×10 −9 A.

(Example 2) The same anode body as in Example 1 was subjected to constant current chemical formation at a current density of 0.3 A/d in a porous chemical formation stream prepared by adding a 10% sodium carbonate aqueous solution and adjusting the pH to 11 with sodium bicarbonate. The treatment was carried out for 1 minute, washed with water, and then dried as pretreatment. Thereafter, the same operations as in Example 1 were carried out to complete a capacitor. The obtained capacitor characteristics are a capacitance of 5.1 μ at 120 Hz.
The dielectric loss tangent (tan δ) was 1.2% at F, the equal series resistance (ESR) at 10KHz was 109 mQ, and the leakage current was 3×10 A.

Comparative Example An anode body similar to that in the example was reconstituted without any pretreatment, and then the same operations as in the example were carried out to complete a capacitor. The obtained capacitor characteristics are a capacitance of 6.1 μF at 120 Hz and a dielectric loss tangent (tan δ) of 1.6%.
The equal series resistance (ESR) at 100 KHz was 168 mQ, and the leakage current was 8 x 10 A.

Effects of the Invention The present invention performs porous chemical formation to obtain a uniform oxide film as a pretreatment on areas where no oxide film is formed, and then uses the uniform oxide film formed in the pretreatment as a core during porous chemical conversion flow. By re-forming the pores called micropores that are distributed in the anode, a uniform, dense, and defect-free anode body is created, resulting in a long-life capacitor with low leakage current and excellent high-frequency isochronous and low-temperature characteristics. It is possible.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part of a capacitor showing an embodiment of the present invention, and FIG. 2 is a perspective view of the same capacitor. 1...Anode, 2...Cutting part, 3...
... Anode lead, 4... Negative %i lead, 5.
... Oxide film not formed part, 6 ... Porous oxide film, 7 ... Oxide film by re-formation, 8
... Conductive polymer compound.

Claims (2)

[Claims] (1) When manufacturing a solid electrolytic capacitor consisting of an anode made of a porous valve metal oxide film as a dielectric and a cathode made of a conductive polymer compound as a solid electrolyte, oxidation of the cut portion of the anode, etc. A method for manufacturing a solid electrolytic capacitor, characterized in that a porous type chemical conversion treatment is performed as a pretreatment when performing a reconversion treatment on a portion where a film is not formed. (2) Porous chemical liquids include oxalic acid, sulfuric acid, phosphoric acid,
2. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the bath is an acidic bath such as chromic acid or an alkaline bath such as sodium carbonate.