JP4720075B2 - Manufacturing method of solid electrolytic capacitor - Google Patents

Description

  The present invention relates to a method for manufacturing a solid electrolytic capacitor capable of preventing the occurrence of a leakage current failure in an aging process and increasing the yield.

  An electrolytic capacitor using a metal having a valve action such as tantalum or aluminum is obtained by expanding the dielectric by making the valve action metal as the anode-side counter electrode into the shape of a sintered body or an etching foil. Since it is small and a large capacity can be obtained, it is widely used. In particular, a solid electrolytic capacitor using a solid electrolyte as an electrolyte has features such as small size, large capacity, low equivalent series resistance, easy to chip, and suitable for surface mounting. It is indispensable for miniaturization, high functionality and low cost of electronic equipment.

  In this type of solid electrolytic capacitor, as a small-sized and large-capacity application, an anode foil and a cathode foil made of a valve metal such as aluminum are generally wound with a separator interposed therebetween to form a capacitor element. It is impregnated with a driving electrolyte, and has a sealed structure in which a capacitor element is housed in a metal case such as aluminum or a case made of synthetic resin. As the anode material, aluminum, tantalum, niobium, titanium and the like are used, and as the cathode material, the same kind of metal as the anode material is used.

  As solid electrolytes used for solid electrolytic capacitors, manganese dioxide and 7,7,8,8-tetracyanoquinodimethane (TCNQ) complexes are known. There is a technique (see Patent Document 1) that focuses on a conductive polymer such as polyethylenedioxythiophene (hereinafter referred to as PEDT) having excellent adhesion to an oxide film layer of an electrode.

  A solid electrolytic capacitor of a type in which a solid electrolyte layer made of a conductive polymer such as PEDT is formed on such a wound capacitor element is manufactured as follows. First, the surface of the anode foil made of valve action metal such as aluminum is roughened by electrochemical etching treatment in an aqueous chloride solution to form many etching pits, and then in an aqueous solution such as ammonium borate. A voltage is applied to form an oxide film layer serving as a dielectric (chemical conversion). Like the anode foil, the cathode foil is made of a valve action metal such as aluminum, but the surface is only subjected to etching treatment.

Thus, the anode foil having the oxide film layer formed on the surface and the cathode foil having only the etching pits are wound through a separator to form a capacitor element. Subsequently, a polymerizable monomer such as 3,4-ethylenedioxythiophene (hereinafter referred to as EDT) and an oxidizer solution are respectively discharged into the capacitor element subjected to restoration conversion, or immersed in a mixture of both. The polymerization reaction is promoted in the capacitor element, and a solid electrolyte layer made of a conductive polymer such as PEDT is generated. Thereafter, the capacitor element is housed in a bottomed cylindrical outer case, and the opening of the case is sealed with a sealing rubber to produce a solid electrolytic capacitor.
JP-A-2-15611

Conventionally, aging is performed at a constant current, but there are capacitors in which the leakage current does not decrease even if aging is continued. These capacitors cause a leakage current failure and cause a reduction in yield.
Such a problem occurs not only when EDT is used as the polymerizable monomer but also when other thiophene derivatives, pyrrole, aniline, and the like are used.

  The present invention has been proposed to solve the above-described problems of the prior art, and its purpose is to improve the yield in the aging process and improve the leakage current characteristics. It is to provide a manufacturing method.

In order to solve the above-mentioned problems, the present inventors have made various studies on the occurrence mechanism of leakage current failure in the aging process, and as a result, have reached the following conclusion.
In other words, for a plurality of solid electrolytic capacitors with different rated voltages, aging was performed at a constant current, which is a conventionally used method, and as a result of investigating capacitors that did not reduce leakage current, leakage current decreased to capacitors with lower rated voltage. It turns out that there are many things that do not.

Based on this knowledge, the present inventors have made the following hypothesis and examined it. As a result, the present invention has been completed.
In other words, the reason why the leakage current is reduced in the aging process is considered to be that current flows in the defective portion of the conductive polymer and the defective portion is insulated. In addition, it was thought that this insulation would have the minimum power required, and in the state where the rated voltage was low and the constant current was small, the insulation could not progress due to insufficient power.

  Thus, it was found that when a large current was passed at the start of aging, the leakage current failure was reduced. Further, at that time, it was found that stable characteristics were obtained when a constant voltage and a constant current were used.

This action and mechanism was considered as follows.
That is, when aging is started, since the resistance of the large defect portion is small, a current flows through that portion. In this case, if the current is small, there is not enough power to insulate the defective portion, so that the current continues to flow without the defective portion being insulated, and the leakage current does not decrease. On the other hand, when a current of a certain current or more is applied so that a large amount of power is applied, power is applied to a large defective portion to insulate, and then a current flows to the next large defective portion to insulate that portion. Therefore, it is considered that the leakage current is reduced.

(Aging conditions)
The aging voltage is preferably 1.2 to 1.5 times the rated voltage, and the lower the rated voltage, the larger the coefficient is preferable. Further, the aging current is preferably 5 to 20 mA, and it is preferable to increase the aging current as the rated voltage is lower. The reason for this is that the lower the rated voltage, the smaller the power applied during aging. Therefore, in order to obtain the energy required for insulation, the lower the rated voltage, the more power needs to be applied. .
The voltage value and current value vary depending on the rating, size, etc. of the capacitor. This is because the state of the conductive polymer varies depending on the rating, size, etc. of the capacitor, and the state of the defect also varies depending on the state, so the amount of power required for insulation varies.

(Method for manufacturing solid electrolytic capacitor)
The manufacturing method of the solid electrolytic capacitor according to the present invention is as follows. That is, an anode foil and a cathode foil having an oxide film layer formed on the surface thereof are wound through a separator to form a capacitor element, and this capacitor element is subjected to restoration conversion. Subsequently, the capacitor element is immersed in a mixed solution prepared by mixing a polymerizable monomer, an oxidizing agent, and a predetermined solvent, and a polymerization reaction of a conductive polymer is generated in the capacitor element to form a solid electrolyte layer. . And after inserting this capacitor | condenser element in an exterior case, attaching sealing rubber | gum to an opening edge part, and sealing by caulking process, the voltage of 1.2-1.5 times the rated voltage, 5-20mA Aging is performed by passing an electric current to form a solid electrolytic capacitor.

(EDT and oxidizing agent)
When EDT is used as the polymerizable monomer, EDT monomer can be used as EDT impregnated in the capacitor element, but a monomer solution in which EDT and a volatile solvent are mixed at a volume ratio of 1: 0 to 1: 3. Can also be used.
Examples of the volatile solvent include hydrocarbons such as pentane, ethers such as tetrahydrofuran, esters such as ethyl formate, ketones such as acetone, alcohols such as methanol, nitrogen compounds such as acetonitrile, and the like. Of these, methanol, ethanol, acetone and the like are preferable.

  Further, as the oxidizing agent, an aqueous solution of ferric paratoluenesulfonate, periodic acid or iodic acid dissolved in ethanol can be used, and the concentration of the oxidizing agent with respect to the solvent is preferably 40 to 65 wt%, and 45 to 57 wt%. % Is more preferable. The higher the oxidant concentration in the solvent, the lower the ESR. As the oxidant solvent, the volatile solvent used in the monomer solution can be used, and ethanol is particularly preferable. Ethanol is suitable as the oxidant solvent because it is easy to evaporate due to its low vapor pressure and the remaining amount is small.

(Chemical solution for restoration conversion)
As the chemical solution for restoration chemical conversion, phosphoric acid type chemicals such as ammonium dihydrogen phosphate and diammonium hydrogen phosphate, boric acid type chemicals such as ammonium borate, and adipic acid type chemicals such as ammonium adipate, etc. Although a liquid can be used, it is preferable to use ammonium dihydrogen phosphate. The immersion time is preferably 5 to 120 minutes.

(Other polymerizable monomers)
The polymerizable monomer used in the present invention includes, in addition to the above EDT, a thiophene derivative other than EDT, aniline, pyrrole, furan, acetylene or a derivative thereof, which is oxidatively polymerized with a predetermined oxidizing agent, and is a conductive polymer. As long as it forms, it can be applied. As the thiophene derivative, one having the following structural formula can be used.

(Action / Effect)
The reason why the yield in the aging process is improved and the leakage current characteristics are improved in the configuration of the present invention is considered as follows. That is, when a constant voltage and a current exceeding a certain current are applied so that a large amount of power is applied at the start of aging, power is applied to a large defect portion and the portion is insulated. It is considered that the leakage current is reduced because the current flows through and the part is insulated.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the solid electrolytic capacitor which can improve the yield in an aging process and can improve a leakage current characteristic can be provided.

  Subsequently, the present invention will be described in more detail based on Examples and Comparative Examples manufactured as follows.

(Example)
An electrode lead means was connected to the anode foil and the cathode foil having an oxide film layer formed on the surface, and both electrode foils were wound through a separator to form a capacitor element having an element shape of 5φ × 2.8L. And this capacitor | condenser element was immersed in ammonium dihydrogen phosphate aqueous solution for 40 minutes, and restoration | restoration conversion was performed.
On the other hand, an ethanol solution of EDT and 45% ferric paratoluenesulfonic acid is poured into a predetermined container so that the weight ratio is 1: 2, and the capacitor element is immersed in the mixed solution for 10 seconds. By heating at 120 ° C. for 60 minutes, a polymerization reaction of PEDT was generated in the capacitor element to form a solid electrolyte layer.
And this capacitor | condenser element was inserted in the bottomed cylindrical exterior case, the sealing rubber was attached to the opening edge part, and it sealed by the crimping process. Thereafter, aging was performed by flowing a current of 5.6 V and 10 mA to form a solid electrolytic capacitor. This solid electrolytic capacitor has a rated voltage of 4 WV and a rated capacity of 820 μF.

(Conventional example)
Aging was performed at a constant current of 1 mA. Other conditions and steps are the same as in the examples.

[Comparison result]
With respect to the example and the conventional example obtained by the above method, the yield in the aging process and the leakage current of the non-defective product were measured, and the results shown in Table 1 were obtained.

As is clear from Table 1, according to the example, the yield was improved while the leakage current of the non-defective product was equal to that of the conventional example. This is presumably because, in the example, the insulation of the polymer was promoted compared to the conventional example, and in the conventional example, what was not fully insulated and had a leakage current failure became a good product.
Although these conventional devices are defective, it has been confirmed that the reliability of products made good by applying the present invention is the same as the conventional products.

Claims (3)

A capacitor element in which an anode foil and a cathode foil are wound through a separator is impregnated with a polymerizable monomer and an oxidizing agent to form a fixed electrolyte layer made of a conductive polymer, and sealed in a predetermined case. A method for producing a fixed electrolytic capacitor, wherein aging is performed at a voltage 1.2 to 1.5 times the rated voltage and 5 to 20 mA at the start of aging.   The method for producing a solid electrolytic capacitor according to claim 1, wherein the polymerizable monomer is a thiophene derivative.   The method for producing a solid electrolytic capacitor according to claim 2, wherein the thiophene derivative is 3,4-ethylenedioxythiophene.