JP4529404B2 - Manufacturing method of solid electrolytic capacitor - Google Patents

Description

  The present invention relates to a method of manufacturing a solid electrolytic capacitor capable of obtaining a solid electrolytic capacitor having a high capacitance.

  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 produced 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). Similar to the anode foil, the cathode foil is made of a valve 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 mixed solution of the two. 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

  By the way, in recent years, electronic information devices have been digitized, and the driving frequency of a microprocessor (MPU) which is the heart of these electronic information devices has been increased. Along with this, the power consumption has been increasing and the problem of reliability due to heat generation has become obvious. Therefore, the drive voltage has been reduced as a countermeasure.

  In order to reduce the drive voltage, a DC-DC converter called a voltage control module is widely used as a circuit for supplying highly accurate power to the microprocessor, and the output side capacitor is used to prevent a voltage drop. Many capacitors with low ESR are used. As the capacitor having such a low ESR characteristic, the solid electrolytic capacitor as described above has been put into practical use and widely used.

However, the increase in the driving frequency of the microprocessor is remarkable, and accordingly, the power consumption further increases. In order to cope with this, further increase in the power supplied from the capacitor to prevent the voltage drop is required. That is, it is necessary to be able to supply a large amount of power in a short time, and for this reason, a large capacity is required for the solid electrolytic capacitor.
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 an object of the present invention is to provide a method of manufacturing a solid electrolytic capacitor capable of improving the capacitance. .

As a result of intensive studies aimed at improving the capacitance of the solid electrolytic capacitor, the present inventors have completed the present invention.
That is, a good result can be obtained by forming a film made of metal nitride, metal carbide or metal carbonitride on the surface of the cathode foil and immersing it in a polyimide silicone solution after the capacitor element is repaired and formed. It turns out.

(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 having an oxide film layer formed on the surface and a cathode foil having a film made of metal nitride, metal carbide, metal carbonitride, carbon, or indium tin oxide formed on the surface are wound through a separator. A capacitor element is formed by turning, and the capacitor element is subjected to repair formation. Thereafter, the capacitor element is immersed in a 0.05-20 wt% ketone-based solution of polyimide silicone, pulled up, evaporated at 40-100 ° C., and then heat-treated at 150-200 ° C.
Subsequently, the capacitor element is immersed in a mixed solution of a polymerizable monomer and an oxidizing agent to cause a polymerization reaction of the conductive polymer in the capacitor element, thereby forming a solid electrolyte layer. And this capacitor | condenser element is accommodated in an exterior case, and an opening edge part is sealed with sealing rubber | gum, and a solid electrolytic capacitor is formed.

(Metal nitride, metal carbide, metal carbonitride that forms a film)
As the metal nitride, any of TiN, ZrN, HfN, VN, TaN, and NbN is preferably used. Moreover, it is preferable to use any of TiC, WC, ZrC, HfC, VC, TaC, and NbC as the metal carbide. As the metal carbonitride, TiCN, WCN, ZrCN, HfCN, VCN, TaCN, and NbCN are used. It is preferable to use either one.
Further, the thickness of the film made of metal nitride, metal carbide, metal carbonitride, carbon or indium tin oxide formed on the surface of the cathode foil is preferably 0.05 to 5 μm, and 0.2 to 3 μm. More preferably. The reason is that if the amount is less than this range, the effect of improving the electrostatic capacity is small, and if the range is exceeded, the bonding strength between the cathode foil and the film is lowered.

(Method of forming a film on the cathode foil)
As a method of forming a film made of metal nitride, metal carbide or metal carbonitride on the surface of the cathode foil, vapor deposition is performed in consideration of the strength of the formed film, adhesion to the cathode, control of film forming conditions, etc. Of these, the cathode arc plasma deposition method is more preferable.
The application conditions of this cathodic arc plasma deposition method are as follows. That is, the current value is 80 to 300 A, and the voltage value is 15 to 20V. When titanium nitride is used, it is performed in an atmosphere where the total pressure including nitrogen is 1 × 10 ⁻¹ to 1 × 10 ⁻⁴ Torr.

(Polyimide silicone)
As a solvent for dissolving polyimide silicone, a ketone solvent having good solubility of polyimide silicone is preferable, and cyclohexanone, acetone, methyl ethyl ketone, and the like can be used.
Moreover, the density | concentration of a polyimide silicone is 0.05-20 wt%, Preferably it is 1.5-9 wt%, More preferably, it is 2-6 wt%. If the concentration is less than this range, the withstand voltage is not sufficient, and if it exceeds this range, the capacitance decreases.

(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.

  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)
As the polymerizable monomer used in the present invention, 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, 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 capacitance can be improved by the configuration of the present invention is considered as follows. That is, when a film made of metal nitride, metal carbide or metal carbonitride is formed on a cathode foil made of a conductive material, the metal nitride, metal carbide or metal carbonitride conducts with the cathode foil metal, It is considered that the capacitance component disappears, the combined capacitance of the capacitor becomes maximum, and the capacitance increases.

  Also, in the present invention, after the capacitor element is repaired and formed, it is immersed in a polyimide silicone solution, so that both the polyimide constituting the polyimide silicone and the conductive polymer such as PEDT are organic compounds, and thus have good adhesion. As a result, it is considered that the adhesion between the conductive polymer and the metal nitride is improved through the polyimide silicone layer, and the capacitance is increased.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the solid electrolytic capacitor which enabled the improvement of an electrostatic capacitance can be provided.

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

Example 1
Electrode extraction means was connected to the anode foil having an oxide film layer formed on the surface and the cathode foil having a titanium nitride film formed on the surface by vapor deposition, and both electrode foils were wound through a separator to form a capacitor element. . And this capacitor | condenser element was immersed in ammonium dihydrogen phosphate aqueous solution for 40 minutes, and restoration | restoration conversion was performed. Thereafter, the capacitor element was immersed in a 2.0 wt% cyclohexanone solution of polyimide silicone, pulled up, and then heat treated at 170 ° C. for 1 hour.
Subsequently, a 45 wt% butanol solution of EDT and ferric p-toluenesulfonate is poured into a predetermined container so that the molar ratio is 6: 1 to prepare a mixed solution, and the capacitor element is mixed as described above. The capacitor element was impregnated with EDT and an oxidizing agent by dipping in the solution for 10 seconds. Then, this capacitor element was left in a constant temperature bath at 120 ° C. for 1 hour to cause a polymerization reaction of PEDT in the capacitor element, thereby forming a solid electrolyte layer. Then, this capacitor | condenser element was accommodated in the bottomed cylindrical aluminum case, and it sealed with sealing rubber | gum, and formed the solid electrolytic capacitor. The solid electrolytic capacitor has a rated voltage of 2.5 WV and a rated capacity of 120 μF.

(Example 2)
A cathode foil on which a titanium carbide film was formed was used as the cathode foil. A solid electrolytic capacitor was prepared in the same manner as in Example 1 except for other conditions.
(Example 3)
As the cathode foil, a cathode foil on which a titanium carbonitride film was formed was used. A solid electrolytic capacitor was prepared in the same manner as in Example 1 except for other conditions.

Example 4
As the cathode foil, a cathode foil on which a carbon film was formed was used. A solid electrolytic capacitor was prepared in the same manner as in Example 1 except for other conditions.
(Example 5)
A cathode foil on which an indium tin oxide film was formed was used as the cathode foil. A solid electrolytic capacitor was prepared in the same manner as in Example 1 except for other conditions.

(Comparative example)
Using a normal cathode foil, a solid electrolytic capacitor was prepared in the same manner as in Example 1 except that the polyimide silicone treatment was not performed.

[Comparison result]
When the electrostatic capacity was investigated about the Example and comparative example which were obtained by said method, the result as shown in Table 1 was obtained.

  As is clear from Table 1, the capacitances of Examples 1 to 5 were both about twice that of the comparative example.

Claims (8)

In a method for producing a solid electrolytic capacitor in which a capacitor element obtained by winding an anode foil and a cathode foil through a separator is impregnated with a polymerizable monomer and an oxidizing agent to form a solid electrolyte layer made of a conductive polymer,
As the cathode foil, a capacitor element is formed using a cathode foil in which a film made of metal nitride, metal carbide, metal carbonitride, carbon, or indium tin oxide is formed on the surface in advance. A method for producing a solid electrolytic capacitor, wherein the capacitor element is impregnated with the polymerizable monomer and the oxidizing agent to form a solid electrolyte layer made of the conductive polymer.   2. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the metal nitride is any one of TiN, ZrN, HfN, VN, TaN, and NbN.   2. The method for producing a solid electrolytic capacitor according to claim 1, wherein the metal carbide is any one of TiC, WC, ZrC, HfC, VC, TaC, and NbC.   The method for producing a solid electrolytic capacitor according to claim 1, wherein the metal carbonitride is any one of TiCN, WCN, ZrCN, HfCN, VCN, TaCN, and NbCN.   The thickness of the film made of the metal nitride, metal carbide, metal carbonitride, carbon, or indium tin oxide is 0.05 to 3 µm. The manufacturing method of the solid electrolytic capacitor of description.   The method for producing a solid electrolytic capacitor according to claim 1, wherein the concentration of the polyimide silicone solution is 0.05 wt% to 20 wt%.   The method for producing a solid electrolytic capacitor according to any one of claims 1 to 6, wherein the polymerizable monomer is a thiophene derivative.   The method for producing a solid electrolytic capacitor according to claim 7, wherein the thiophene derivative is 3,4-ethylenedioxythiophene.