JP2009206426A - Method for manufacturing solid-state electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a solid-state electrolytic capacitor in which only an oxide coating on an external surface is formed thick without causing any problem due to remaining of a solid nonconductor and an insulating liquid on an internal surface of a porous sintered body to increase the capacity while keeping a leakage current small. <P>SOLUTION: The method for manufacturing the solid-state electrolytic capacitor includes a first process of impregnating a porous sintered body element with a water-soluble impregnating liquid, a second process of cooling the sintered body element to solidify the water-soluble impregnating liquid, and a third process of dipping the sintered body element in a forming liquid while the water-soluble impregnating liquid is solidified to form an external surface of the sintered body element. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a solid electrolytic capacitor, and more particularly to a method for forming a solid electrolytic capacitor.

Solid electrolytic capacitors, especially sintered type capacitors, are provided with an oxide film formed by the chemical conversion process on the surface of the sintered body with one end of the anode lead buried in the porous sintered body of tantalum or niobium. A solid electrolyte layer made of a conductive polymer such as manganese dioxide or polypyrrole, polyaniline, polythiophene is formed on the surface, and a cathode layer made of a conductive paste is sequentially provided on the surface, and the outermost cathode layer of the sintered body In addition, the anode terminal plate is connected to the anode lead by welding or the like through a conductive adhesive made of conductive paste. Then, the capacitor element and the like are covered by a method such as a molding die with an exterior made of an insulating resin or the like, and the anode terminal plate and the cathode terminal plate are drawn out from the exterior.
As one method for improving the leakage current of the solid electrolytic capacitor, a method of increasing the thickness of the oxide film on the surface from the inside of the porous sintered body is employed in the chemical conversion step.
As a specific procedure, first, after a uniform oxide film is formed on the entire porous sintered body, only the oxide film on the outer surface of the porous sintered body is thickened (Patent Document 1), There is a method of forming a uniform oxide film on the entire surface after thickening only the oxide film on the outer surface of the sintered body, and both methods are performed by immersing the entire porous sintered body in the chemical conversion liquid.
As a method of thickening only the oxide film on the outer surface of the porous sintered body, the formation voltage is higher than the formation voltage when a uniform oxide film is provided on the whole, and the formation time when the uniform oxide film is provided on the whole. Also, a method of processing for a short time is taken.
By the way, the method of thickening only the oxide film on the outer surface of the porous sintered body is accompanied by a decrease in capacity at the same time as there are more thickened parts, so it is necessary to keep the thickened part only on the outer surface. However, in the conventional method of thickening only the oxide film on the surface, the entire surface of the porous sintered body is wetted with the chemical conversion liquid, so even if only the oxide film on the outer surface is thickened, it is thickened to the inside. The problem of being formed easily occurs.
Therefore, a method is considered in which only the outer surface of the porous sintered body is formed separately from the inner surface. As one of the methods, the porous capacitor body is anodized to form a uniform dielectric film on the entire anode body, and the anode body is impregnated with a solid non-conductor (wax, stearin, anthracene, etc.) Insulating solid is removed from the external anode surface and anodized at a voltage higher than the initial voltage on the outer surface to form an oxide film thicker than the internal anodic oxide on the outer surface. There exists a method of removing from (patent document 2). As another method, an anodized porous body electrode is impregnated with an electrolyte-insoluble insulating liquid (benzene, xylene, etc.), the insulating liquid is evaporated from the outer surface of the anode body, and the voltage is higher than the initial anodizing voltage. There is a method of forming a thick external oxide film by forming a relatively thick anodic oxide layer on the outer surface of the anode body, and evaporating the remaining solvent before processing the anode into a finished capacitor (patent) Reference 2).

Japanese Patent Publication No.58-33688 Special table 2003-512531 publication

  In order to thicken only the oxide film on the outer surface of the porous sintered body of Patent Document 2 described above, the method of separating and forming only the outer surface of the porous sintered body from the inner surface is thickened to the inside. This is an effective method because it is difficult for the problem to occur. However, as in the above-mentioned Patent Document 2, in the method of removing the solid nonconductor, the insulating liquid, etc. by impregnating the inside of the porous sintered body and then removing it, the sintered body is completely porous. It is difficult to get rid of. For this reason, the remaining solid conductor or insulating liquid shields the sintered body from the electrolyte and prevents the defect repair of the oxide film, or even a minute amount dissolves in the electrolyte to contaminate the electrolyte, or on the surface of the electrolyte layer. There is a possibility that a solution or the like bumps from the porous sintered body due to heating at the time of forming the cathode layer by the conductive paste to be provided or reflow heating after the exterior molding, and damages the capacitor element.

The present invention solves the above-mentioned problem, and does not cause a problem due to solid nonconductor or insulating liquid remaining on the inner surface of the porous sintered body, and only the oxide film on the outer surface is thickened. It is an object of the present invention to provide a method of manufacturing a solid electrolytic capacitor that can increase the capacity while forming and maintaining a small leakage current.

The present invention includes a first step of impregnating a porous sintered body element with a water-soluble impregnating liquid, a second step of cooling the sintered body element to solidify the water-soluble impregnating liquid, and the water-soluble impregnation element. A solid electrolytic capacitor manufacturing method comprising: a third step of immersing the sintered body element in a chemical conversion solution while the liquid is solidified to form an outer surface of the sintered body element.
Moreover, the manufacturing method of said solid electrolytic capacitor whose water-soluble impregnation liquid is a chemical conversion liquid or the solvent of a chemical conversion liquid is provided.

According to the present invention, there is no problem caused by solid nonconductor or insulating liquid remaining on the inner surface of the porous sintered body, and only the oxide film on the outer surface is thickened and the leakage current is kept small. However, it is possible to provide a method of manufacturing a solid electrolytic capacitor capable of increasing the capacity.

  The sintered body element described in the present invention is an anode of a sintered body having an enlarged surface area, and an oxide film is provided on the surface thereof. For example, a valve-acting metal or alloy such as tantalum or niobium made of a porous sintered body with an enlarged surface area and an anode lead embedded in one end is used.

The water-soluble impregnating liquid described in the present invention is a liquid that impregnates a porous sintered body element. It is necessary to be harmless to chemical conversion, to be in a liquid state at room temperature but to solidify upon cooling, and to be a liquid that can be easily dissolved in a cleaning liquid during or before chemical conversion. A chemical solvent, a chemical solution containing a solute, a cleaning solution during or before chemical conversion, and the like can be used.
Specific examples of the solvent for chemical conversion are water, alcohol, or a mixture thereof. As the alcohol, low molecular alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, and butyl alcohol are preferable because of low viscosity. As the solvent for the chemical conversion liquid, water is usually used, and as the solvent for the cleaning liquid, water or a mixture of alcohol and water is usually used.
A specific example of the solute for chemical conversion is usually an acid containing at least one of oxalic acid, adipic acid, boric acid, phosphoric acid, paratungstic acid and the like used for forming an oxide film layer in a solid electrolytic capacitor, or These salts (for example, ammonium salt, sodium salt) etc. are mentioned.
As the chemical conversion solution, a solution obtained by dissolving 0.05 to 10 w% of the above acid or salt in water is usually used.
The chemical conversion liquid may also be mixed with ethylene glycol, propylene glycol, isobutyl alcohol or the like as a viscosity enhancer. Viscosity enhancers are preferred because they delay the entry of the chemical conversion liquid. However, there are cases where cleaning is not easy.
The chemical conversion liquid also contains 0.01 w of a nonionic surfactant polyoxypropylene glycol and ethylene oxide block copolymer, isooctylphenol ethylene oxide adduct, and hydrogen peroxide water as an oxidizing agent. You may add about 0.1 to 0.1 w%. These additives may improve leakage current and breakdown voltage.

The above water-soluble impregnating liquid is a liquid at room temperature and is the same water-soluble as the liquid in the chemical conversion process or the solid electrolyte layer forming process, so that the impregnation work is easy and cleaning during or after chemical conversion is easy. . Further, when the impregnating liquid is a chemical conversion liquid or a solvent for the chemical conversion liquid, there is no possibility of being dissolved and causing electrolyte contamination.

  The solidification described in the present invention is a physical change that does not involve a chemical change and means that a liquid becomes a solid by cooling. By stopping cooling or heating, it can melt and return to the original liquid.

The chemical conversion described in the present invention is to form an oxide film to be a dielectric film by anodic oxidation on a sintered body element.
In the chemical conversion of the present invention, a uniform oxide film is formed on the entire anode by a normal chemical conversion step in which an anode having an enlarged surface area is immersed in the chemical conversion solution and a voltage of 2 to 4 times the rated voltage is applied. The following series of steps is added as a pre-process or a post-process of the forming process. That is, a step of impregnating the capacitor element with the impregnating liquid, a step of cooling the capacitor element to solidify the impregnating liquid, a step of immersing and forming the capacitor element in the chemical liquid while solidifying the impregnating liquid, and a solidified impregnation A step of liquefying all the liquid and a series of steps for thickening only the oxide film on the outer surface are added.
The temperature of the chemical conversion liquid at this time is 1 ° C to 60 ° C, preferably 5 ° C to 20 ° C. The temperature at which the capacitor element is cooled to solidify the impregnating liquid is about −40 ° C. to −5 ° C., preferably about −30 ° C. to −10 ° C. Moreover, the formation voltage at this time is 2 times or more, preferably 3 times or more than a normal formation voltage for forming a uniform oxide film on the entire sintered body element. Further, the formation time at this time is about 1 second to 5 minutes, preferably about 5 seconds to 3 minutes, although it depends on the weight of the sintered body element.

Hereinafter, the present invention will be described based on embodiments.
Hereinafter, the present invention will be described based on embodiments shown in the drawings.
FIG. 1 shows a method for manufacturing a solid electrolytic capacitor according to the present invention. In the process of thickening only the oxide film on the outer surface of a porous sintered body element, the porous sintered body element is added to the chemical conversion liquid. The state before immersion is shown.
Reference numeral 1 denotes an anode lead, for example, a valve action metal such as tantalum, niobium, or aluminum, which has a linear shape with a diameter of about 0.1 mm to 0.5 mm, or a strip shape with a thickness of about 0.1 mm to 0.5 mm. Is used.
Reference numeral 2 denotes a sintered body element. For example, one end of an anode lead 1 is embedded, and a binder such as acrylic or camphor is mixed with fine powder having an average particle diameter of about 1 μm of a valve metal such as tantalum, niobium, or aluminum. A sponge-like anode sintered body formed by press-pressing powder and then sintering in vacuum is used.
Thereafter, an anodized film, a solid electrolyte layer such as manganese dioxide or a conductive polymer, and a cathode layer such as a carbon layer or a silver layer are sequentially provided on the sintered body by chemical conversion.
Reference numeral 3 denotes a support holder that holds one end of the anode lead 1 and moves up and down.
4 is a chemical conversion liquid, provided in the chemical conversion tank 5, and the support holder 3 operates below to immerse the porous sintered body of the sintered body element 2.
Reference numeral 6 denotes a counter electrode, which is provided at a position not hit when the sintered body element 2 is immersed in the chemical conversion liquid. The counter electrode is a flat plate or net and is installed horizontally.
Reference numeral 7 denotes a power source, which is positive on the anode lead 1 side and negative on the counter electrode side.
A switch 8 is used to turn on / off the formation voltage application of the power source 7.

A tantalum powder having an average diameter of 0.5 μm is placed in a tantalum container and heated in a vacuum atmosphere at a temperature of 1400 ° C. for 1 hour. The heat-treated tantalum powder is bonded to each other. The tantalum powder is taken out from the container and lightly crushed, and is made into a sintered granulated powder of a predetermined size by a sieving method, a wind method or the like. Next, the crushed tantalum powder is compression-molded to a size of 1.1 × 1.5 × 0.8 mm and fired in vacuum to produce a tantalum sintered body. In this sintered body, an anode lead wire made of a tantalum wire having a diameter of 0.25 mm is embedded and the tip thereof is drawn out at the time of compression molding.
First, the sintered body is immersed in pure water for 1 minute or more, taken out, the moisture at the bottom of the sintered body element is removed by a blower, and then left in a freezer at −30 ° C. for 10 minutes or more. Next, this sintered body element is immersed in an aqueous boric acid solution having a concentration of 1% at a temperature of 40 ° C. and anodized at 80 V for 20 seconds, and the power is turned off. Next, it is washed in pure water. Next, this sintered body element is immersed in a nitric acid solution having a concentration of 0.1% at a temperature of 50 ° C. and anodized at a voltage of 26 V for 120 minutes to form an oxide film. Next, it is washed in pure water.
Next, after forming the oxide film, a solid electrolyte layer made of polyaniline is formed on the surface of the oxide film by a chemical oxidative polymerization method. That is, the formed sintered body element is immersed in an aqueous solution of 0.2 mol / l ammonium peroxodisulfate for 5 minutes. After this immersion, it is immersed for 5 seconds in a mixed solution of water and ethanol in an equal volume of 0.2 mol / l aniline and 0.1 mol / l p-toluenesulfonic acid at room temperature. Thereafter, it is left in the air for 30 minutes to carry out the polymerization treatment. Then, the process from the step of immersing in this aqueous ammonium peroxodisulfate to the standing treatment is repeated 15 times. After the repetition, it is dried at a temperature of 80 ° C. for 30 minutes to form a solid electrolyte layer made of black conductive polyaniline. After forming the solid electrolyte layer, the sintered body element is immersed in an aqueous solution of paratoluenesulfonic acid having a pH of about 1 and a concentration of 0.1 mol / l for 20 to 30 minutes. After soaking, it is dried at a temperature of 110 ° C. for about 30 minutes. After drying, a carbon paste and a silver paste are sequentially applied and cured to form a graphite layer and a silver layer. After forming the silver layer, a cathode terminal is connected to the silver layer with a silver conductive paste, and the anode terminal is welded to the anode lead wire. Then, an epoxy resin is transfer-molded to form an exterior, and then subjected to an aging process.

  As a chemical conversion method, the sintered body element is immersed in a 0.1% concentration nitric acid solution at a temperature of 50 ° C. and anodized at a voltage of 26 V for 120 minutes to form an oxide film. Next, it is washed in pure water. Next, the sintered body element is immersed in pure water for 1 minute or more, taken out, the moisture at the bottom of the sintered body element is removed by a blower, and then left in a freezer at −30 ° C. for 10 minutes or more. Next, this sintered body element was immersed in an aqueous boric acid solution having a concentration of 1% at a temperature of 40 ° C., anodized at 80 V for 20 seconds, and the power was turned off.

  As a chemical conversion method, this sintered body element is immersed in a nitric acid solution having a concentration of 0.5%, and the pressure is increased to a voltage of 20 V to perform preliminary anodic oxidation to form an oxide film. Next, the sintered body element is immersed in pure water for 1 minute or more, taken out, the moisture at the bottom of the sintered body element is removed by a blower, and then left in a freezer at −30 ° C. for 10 minutes or more. Next, this sintered body element is immersed in an aqueous boric acid solution having a concentration of 1% at a temperature of 40 ° C. and anodized at 80 V for 20 seconds, and the power is turned off. Next, it is washed in pure water. Next, this sintered body element is immersed in a nitric acid solution having a concentration of 0.1% at a temperature of 50 ° C. and anodized at a voltage of 26 V for 120 minutes to form an oxide film. Other than that was carried out in the same manner as in Example 1.

  As a chemical conversion method, first, the sintered body element is immersed in an aqueous solution of boric acid having a concentration of 1% for 1 minute or more, taken out, and moisture at the bottom of the sintered body element is removed by a blower. Then, the sintered body element is immersed in an aqueous boric acid solution having a concentration of 1% at a temperature of 40 ° C., anodized at 80 V for 20 seconds, and the power is turned off. Next, it is washed in pure water. Next, this sintered body element is immersed in a nitric acid solution having a concentration of 0.1% at a temperature of 30 ° C. and anodized at a voltage of 26 V for 120 minutes to form an oxide film. Other than that was carried out in the same manner as in Example 1.

(Comparative Example 1-4)
Freeze the sintered compact element in the freezer before anodic oxidation at 80V for 20 seconds by soaking in an aqueous boric acid solution with a concentration of 1% at a temperature of 20 ° C. The same procedure as in each example was performed except that the method was changed to the anodizing method.

As mentioned above, the capacity | capacitance and leakage current of an Example and a comparative example were measured (n = 20), and the result of Table 1 was obtained.
The increase rate of the capacity is the same as the others, and the ratio of the capacity when the sintered body element is frozen and when it is not frozen is compared. Moreover, the measuring method of leakage current was taken as the value when it took 1 minute at 10V.
From the above results, according to the present invention in which the sintered body element is frozen, the capacity can be increased from 10% to 20%, although the leakage current may increase by several%, compared with the case where it is not. That is, the capacity can be increased while suppressing an increase in leakage current.

1 shows a method of manufacturing a solid electrolytic capacitor according to the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Lead for anode 2 ... Sintered body element 3 ... Support holder 4 ... Chemical conversion liquid 5 ... Chemical conversion tank 6 ... Counter electrode 7 ... Power supply 8 ... Switch.

Claims (2)

  A first step of impregnating a porous sintered body element with a water-soluble impregnating liquid; a second step of cooling the sintered body element to solidify the water-soluble impregnating liquid; and solidifying the water-soluble impregnating liquid. A solid electrolytic capacitor manufacturing method comprising: a third step of immersing the sintered body element in a chemical conversion solution and forming an outer surface of the sintered body element.   The method for producing a solid electrolytic capacitor according to claim 1, wherein the water-soluble impregnating liquid is a chemical liquid or a solvent for the chemical liquid.

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