JP5273736B2 - Manufacturing method of solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a solid electrolytic capacitor having no defect and a homogeneous oxide film. <P>SOLUTION: In a process of applying a prescribed voltage to an anode body manufactured by pressing and molding valve action metal powder such as tantalum and niobium and sintering them in an electrolyte for anodization, second anodization processing is executed by an aqueous nitrate solution with a conductivity of 50 S/m or larger after first anodization processing using an aqueous phosphate solution. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a method of manufacturing a solid electrolytic capacitor using a valve metal such as tantalum or niobium.

  For solid electrolytic capacitors that use valve action metals such as tantalum and niobium for the anode, the powder consisting of the valve action metal and the anode lead wire that acts as the anode lead are pressure-molded by the molding die and then vacuum sintered. It is known to use a sintered body produced by the above as an anode body. An oxide film of a valve metal is formed on the surface of the anode body by an anodic oxidation method, and this oxide film becomes a dielectric layer of the solid electrolytic capacitor. A solid electrolyte layer made of, for example, manganese dioxide or a conductive polymer is formed thereon, and a cathode layer is formed by further forming a graphite layer or a silver paste layer thereon to obtain a solid electrolytic capacitor element.

  In the solid electrolytic capacitor element thus obtained, the anode lead wire is connected to the external anode terminal by welding or the like, the cathode layer is connected to the external cathode terminal by a conductive adhesive or the like, and finally sealed with an exterior resin. The

  In an anodic oxidation process in which an oxide film is formed on the surface of a valve action metal, techniques using various electrolytic solutions such as phosphoric acid, nitric acid and sulfuric acid are known. In general, for example, as described in Patent Document 1, an aqueous solution containing about 0.1 to 1.0% by weight of phosphoric acid is used as an electrolytic solution. For example, as described in Patent Document 2, after anodizing with 0.001 to 0.5% phosphoric acid aqueous solution, 0.001 to 0.1% nitric acid aqueous solution is used as the electrolyte. Further, as described in Patent Document 3, a technique for anodizing with a mixed aqueous solution composed of water, phosphoric acid and sulfuric acid is also proposed.

JP 2003-338432 A JP-A-7-220982 JP 2007-242742 A

  However, with the conventional anodic oxidation as described above, it has been difficult to produce a solid electrolytic capacitor having no defects and having a uniform oxide film.

  For example, after anodic oxidation using the phosphoric acid aqueous solution described in Patent Document 1, the cross section of the formed oxide film was observed with an electron microscope. As a result, a very small crack-like defect having a width of about 5 to 10 nm ( Hereinafter, it was confirmed by analysis of the present inventors that there is a micro-crack) and that the crack has reached the valve metal part which is the anode body. Since such micro cracks may cause an increase in leakage current during the manufacturing process of the solid electrolytic capacitor, it is desirable that the number is smaller.

  In the case of a phosphoric acid aqueous solution having a concentration of 0.1 to 1.0% by weight and a liquid temperature of about 60 ° C. as in Patent Document 1, the conductivity is about 1 S / m. The electrical resistance when such low conductivity electrolyte penetrates into the microcrack part is equal to or higher than the electrical resistance value of the oxide film formed by anodic oxidation. It is considered that anodic oxidation does not occur. The same can be said for Patent Document 2 because the conductivity is similarly 1 S / m or less even in a 0.001% to 0.1% nitric acid aqueous solution.

  In addition, in the case of the manufacturing method described in Patent Document 3, there is an advantage that the leakage current value measured immediately after anodic oxidation is superior to the method described in Patent Document 1, but the solid electrolytic capacitor as a finished product is advantageous. In some cases, leakage current increased when long-term reliability evaluation was performed.

  The reason for this is that when an electrolytic solution having a high concentration and high conductivity as in Patent Document 3 is used, workability deteriorates, such as corrosion of a metal piece used to support the anode body during anodization. It is difficult to perform anodization for a long time. When the anodic oxidation time is short, it is generally difficult to form a homogeneous oxide film, which may adversely affect long-term reliability.

  In this situation, an object of the present invention is to provide a method for producing a solid electrolytic capacitor having a uniform oxide film in which the anodized film is free from defects.

  In order to solve the above-described problems, the method for manufacturing a solid electrolytic capacitor according to the present invention has a conductivity of 0.01 to 1S in the step of anodizing an anode body made of a porous body of a valve metal such as tantalum or niobium. A first anodic oxidation step of performing anodizing treatment for 3 to 20 hours using an electrolyte solution having an electric conductivity of 50 m / m, and an electric conductivity of 50 to 100 S / m after the first anodic oxidation step. And a second anodic oxidation step of performing an anodic oxidation treatment for 30 minutes to 2 hours using a certain electrolytic solution. The electrolytic solution used in the first anodic oxidation step is a phosphoric acid aqueous solution. The electrolytic solution used in the second anodic oxidation step is a nitric acid aqueous solution.

  That is, in the method for producing a solid electrolytic capacitor of the present invention, after the first anodizing step using, for example, a phosphoric acid aqueous solution having a low concentration in the anodizing step, the second anodizing is performed with a relatively high concentration nitric acid aqueous solution. By performing the process, it is possible to manufacture a solid electrolytic capacitor having no defects and having a uniform oxide film.

  As described above, according to the present invention, in the first anodizing step, a uniform oxide film is formed by performing a long-time treatment using a phosphoric acid aqueous solution having a relatively low concentration, that is, a low conductivity. In the second anodic oxidation step, it is possible to form an oxide film having no defects such as microcracks by performing a treatment using a nitric acid aqueous solution having a high conductivity of 50 to 100 S / m. .

  The reason for this is that the electrical resistance value in the second anodic oxidation step when the electrical conductivity penetrates into the microcrack portion of the electrolyte solution of 50 S / m or more is lower than the electrical resistance value of the oxide film formed by anodic oxidation. This is because anodization also occurs in the microcrack portion.

The schematic diagram of the anodizing process in the manufacturing method of a solid electrolytic capacitor. The time change of the electric current in the 2nd anodizing process by the Example and comparative example in this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  For example, a powder made of a valve metal such as tantalum or niobium and a porous body such as a sintered body produced by vacuum sintering after an anode lead wire acting as an anode drawer is pressure-molded by a molding die The material is used as the anode body of the solid electrolytic capacitor. As shown in FIG. 1, the anode body 1 is held by connecting anode lead wires 2 drawn out from the anode body 1 made of a porous body to metal pieces 3 by resistance welding or the like at appropriate intervals. Thereafter, as the first anodic oxidation step, anodic oxidation is performed using an electrolytic solution having a conductivity of 0.01 to 1 S / m. As the electrolytic solution used at this time, phosphoric acid, sulfuric acid, nitric acid or the like can be used, and is not particularly limited, but an aqueous phosphoric acid solution is desirable. The liquid temperature can be arbitrarily determined from room temperature to about 95 ° C. in consideration of the liquid type to be selected and workability. The first anodic oxidation treatment is preferably carried out for a long time in the range of 3 to 20 hours in order to form a homogeneous oxide film. By using a low concentration electrolytic solution, it is possible to perform a long-time treatment. An almost homogeneous oxide film can be formed by performing for 3 hours or more. Further, even if the anodic oxidation was continued for more than 20 hours, the current value hardly changed and the anodic oxidation did not proceed, so the upper limit was set to 20 hours. Thereafter, washing and drying are carried out to remove the adhering phosphoric acid aqueous solution, and anodic oxidation is performed using an electrolytic solution having a conductivity of 50 to 100 S / m as second anodic oxidation. As the electrolytic solution used at this time, phosphoric acid, sulfuric acid, nitric acid, or the like can be used. Although not particularly limited, an aqueous nitric acid solution having high conductivity and low viscosity is desirable. The liquid temperature can be arbitrarily determined from room temperature to about 95 ° C. in consideration of the liquid type to be selected and workability. However, when an aqueous nitric acid solution is selected, it is desirable to carry out at about room temperature in consideration of workability. The treatment time for the second anodic oxidation is preferably carried out in a short time in the range of 30 minutes to 2 hours in order to anodize only the microcrack portion. Anodization of microcracks is effective for about 30 minutes. However, if it exceeds 2 hours, corrosion of the metal due to a high concentration electrolyte is concerned, which is not preferable. Further, it is desirable that the applied voltages in the first anodization and the second anodization are the same.

  Examples of the present invention and comparative examples will be described in detail below.

(Example)
Specific examples of the method for producing a solid electrolytic capacitor of the present invention will be described. By pressing a tantalum powder (powder CV value: 150,000 μF · V / g) and a tantalum wire having a diameter of 0.5 mm to be an anode lead with a molding die, the size of the porous body portion is 2.2 mm. A molded body having a size of × 1.2 mm × 1.7 mm was produced. The pressure-molded body produced in this manner was vacuum sintered at 1,200 ° C. to obtain an anode body. Further, the anode lead wire portion of the obtained anode body was resistance-welded to a metal piece made of aluminum at a constant interval to hold the anode body.

  Next, as the first anodizing step, an aqueous solution of phosphoric acid having a concentration of 0.6% was used, the liquid temperature was kept at 80 ° C., and a DC voltage of 8 V was applied to carry out an anodizing treatment for 10 hours. The conductivity of the electrolytic solution used in the first anodic oxidation process at this time was 0.9 S / m.

  Further, after washing and drying the anode body, as a second anodizing process, an aqueous nitric acid solution having a concentration of 50% is used, the liquid temperature is set to room temperature, and a DC voltage of 8 V is applied to perform anodizing treatment for 90 minutes. Carried out. The electrical conductivity of the electrolytic solution used in the second anodic oxidation process at this time was 60 S / m.

(Comparative example)
As a comparative example, a method for manufacturing a solid electrolytic capacitor according to the prior art will be specifically described.

  As the first anodic oxidation, an aqueous solution of phosphoric acid having a concentration of 0.6% was used, and the anodic oxidation treatment was carried out for 10 hours by applying a DC voltage of 8 V while maintaining the liquid temperature at 80 ° C. The electrical conductivity of the first anodizing electrolyte at this time was 0.9 S / m.

  Further, after washing and drying the anode body, as a second anodic oxidation, a nitric acid aqueous solution having a concentration of 0.1% is used, the liquid temperature is set to about room temperature, and a DC voltage of 8 V is applied to perform an anodic oxidation for 90 minutes. Processing was carried out. The conductivity of the second anodic oxidation electrolyte at this time was 1.0 S / m.

  FIG. 2 shows a change in current over time during the anodizing process when the second anodizing is performed according to the above-described examples and comparative examples. In addition, the number of processed anode bodies was 50 each. After the treatment for 90 minutes, the current value in the example is reduced to about 1/10 compared with that in the comparative example. This is considered to be because the current value was reduced because the microcrack portion was also anodized by the treatment with the electrolyte having a high conductivity.

  As mentioned above, although the example of embodiment of this invention was demonstrated, this invention is not limited to this, Even if there is a design change of the range which does not deviate from the summary of this invention, it is included in this invention. That is, it goes without saying that various modifications and corrections can be made by those skilled in the art.

DESCRIPTION OF SYMBOLS 1 Anode body 2 Anode lead wire 3 Metal piece 4 Electrolyte solution 5 Cathode plate

Claims (3)

  In the step of anodizing an anode body made of a porous body of valve action metal such as tantalum or niobium, an anodizing treatment for 3 to 20 hours is performed using an electrolytic solution having an electrical conductivity of 0.01 to 1 S / m. A first anodizing step to be performed, and after the first anodizing step, the anode body is subjected to an anodizing treatment for 30 minutes to 2 hours using an electrolytic solution having a conductivity of 50 to 100 S / m. And a second anodizing step. A method for producing a solid electrolytic capacitor, comprising:   The method for producing a solid electrolytic capacitor according to claim 1, wherein the electrolytic solution used in the first anodizing step is a phosphoric acid aqueous solution.   The method for producing a solid electrolytic capacitor according to claim 1, wherein the electrolytic solution used in the second anodic oxidation step is a nitric acid aqueous solution.

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