JP2008085261A - Solid electrolytic capacitor and method of manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a solid electrolytic capacitor having a high voltage withstanding characteristic. <P>SOLUTION: On the top surface of an oxide coating layer formed on the surface of an anode foil, an evaporation film of inorganic oxide, such as silicon oxide, is formed using an organic silicon compound etc. as an evaporation raw material and an inert gas, such as an argon gas and a helium gas, as a carrier gas, and further using an oxidizing gas, such as an ozone gas, and using a thermochemical vapor phase epitaxy method. In this manner, a capacitor element is formed by winding the anode foil and cathode foil, on the top surface of oxide coating layer of which a non-insulating oxide film is formed, via a separator, and the capacitor element is subjected to recovery formation. The capacitor element is immersed in a mixed liquid of polymerized monomer and oxidant, a polymerization reaction of conductive polymer is caused to occur in the capacity element and a solid electrolytic layer is formed. This capacitor element is accommodated in an outer packaging case, its opening end is sealed using sealing rubber, and thus a solid electrolytic capacitor is formed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solid electrolytic capacitor using a conductive polymer compound as a solid electrolyte, and more particularly to a solid electrolytic capacitor improved to improve withstand voltage characteristics and a method for manufacturing the same.

  An electrolytic capacitor using a metal having a valve action such as aluminum can obtain a small size and a large capacity by expanding the surface of the dielectric by making the valve action metal as an anode electrode into the shape of an etching foil or the like. It is widely used because it can. 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 and high functionality of electronic equipment.

  As the solid electrolyte used for the solid electrolytic capacitor, a conductive polymer having high conductivity and excellent adhesion to the oxide film layer of the anode electrode is used as the solid electrolyte. As this conductive polymer, for example, polyaniline, polythiophene, polyethylenedioxythiophene and the like are known.

  Among these, polyethylenedioxythiophene (hereinafter referred to as PEDOT) has attracted attention as a conductive polymer that can achieve a high breakdown voltage because the withstand voltage can be increased with respect to the thickness of the oxide film. In the capacitor using PEDOT, chemical oxidative polymerization is used, and it is manufactured as follows.

  That is, an anode foil and a cathode foil are wound through a separator to form a capacitor element, this capacitor element is impregnated with EDOT and an oxidant solution, and heated to form a PEDOT polymer layer between both electrodes. A solid electrolytic capacitor is formed (see Patent Document 1).

Such a solid electrolytic capacitor is used for in-vehicle use and inverter use, but the working voltage increases from 20 WV to 35 WV, and in order to cope with these, the capacitor element is composed of a compound having a vinyl group and a boric acid compound. It is disclosed that the withstand voltage is increased by containing a conjugate (see Patent Document 2).
Japanese Patent Laid-Open No. 9-293639 JP 2003-100560 A

  However, even with such a technique, a high withstand voltage is not sufficient, and the development of a solid electrolytic capacitor having further high withstand voltage characteristics has been desired.

  The present invention has been proposed in order to solve the above-described problems of the prior art, and an object thereof is to provide a solid electrolytic capacitor having a high withstand voltage characteristic and a method for manufacturing the same.

  In order to solve the above-mentioned problems, the present inventors have repeatedly studied solid electrolytic capacitors having high withstand voltage characteristics, tried to form various protective films on the top surface of the dielectric oxide film, and investigated the effects. As a result, it has been found that good results can be obtained by forming a non-insulating oxide film.

  The manufacturing method of the solid electrolytic capacitor according to the present invention is as follows. That is, on the upper surface of the oxide film layer formed on the surface of the anode foil, an organic silicon compound or the like is used as a deposition material, an inert gas such as argon gas or helium gas is used as a carrier gas, and ozone gas or the like is further used. Using an oxidizing gas, a vapor deposition film of an inorganic oxide such as silicon oxide is formed using a thermal chemical vapor deposition method or the like. The capacitor element is formed by winding the anode foil and the cathode foil having the non-insulating oxide film formed on the upper surface of the oxide film layer through the separator in this manner, and this capacitor element is subjected to restoration conversion.

  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, an opening edge part is sealed with sealing rubber | gum, and a solid electrolytic capacitor is formed.

  The capacitor element is impregnated with a polymerizable monomer and an oxidizing agent. The capacitor element is immersed in a mixed solution of the monomer and the oxidizing agent. The capacitor element is immersed in the monomer solution and then immersed in the oxidizing agent solution. A method of discharging the oxidant solution after discharging the monomer solution to the capacitor element can be used.

  The manufacturing method of the flat type solid electrolytic capacitor according to the present invention is as follows. That is, an anodic oxide film layer is formed on the surface of a strip-shaped aluminum foil roughened by etching or the like, and an organic silicon compound or the like is used as a raw material for vapor deposition on the upper surface of the oxide film layer. A vapor deposition film of an inorganic oxide such as silicon oxide is formed using a thermal chemical vapor deposition method or the like using an inert gas such as ozone gas and an oxidizing gas such as ozone gas.

  Then, after forming an insulating resin band for separating the anode lead portion and the cathode portion in a predetermined portion, a conductive polymer compound film is formed in the predetermined portion, and graphite is formed on the conductive polymer film. Layers and silver paste layers are sequentially formed to constitute the cathode lead portion. Thereafter, the cathode lead portion and the external cathode terminal are connected with a silver paste.

  In addition, since the predetermined anode lead portion divided by the insulating resin band is an aluminum foil that cannot be soldered, a solderable metal plate is subjected to ultrasonic welding, electrical resistance welding, laser welding, etc. Make electrical connections.

(Non-insulating oxide film)
Examples of the non-insulating oxide film formed on the dielectric oxide film include oxide films made of silicon oxide, tantalum oxide, niobium oxide, hafnium oxide, zirconium oxide, titanium oxide, and the like. However, an oxide film made of silicon oxide is more preferable. These oxide films have low insulating properties and have little influence on the electrical characteristics of the dielectric oxide film.

The specific resistance of these non-insulating oxide films is 10 ⁸ to 10 ¹¹ Ω · cm, preferably 10 ^{9 to} 5 × 10 ¹⁰ Ω · cm. If it is less than this range, the leakage current characteristics deteriorate, and if it exceeds this range, the capacitance and ESR characteristics deteriorate. The withstand voltage per unit thickness is preferably 0.01 to 0.001 V / nm.

  Note that, in order to set the specific resistance and the withstand voltage of the non-insulating oxide film within the above ranges, the film forming temperature is appropriately adjusted. Specifically, the film formation is preferably performed at 200 to 600 ° C.

  Here, the reason why the insulating property of the oxide film as described above is low will be described. For example, in a non-insulating oxide film made of silicon oxide, Si-OH is not contained in the film, as is apparent from the analysis result by the Fourier transform infrared spectrophotometer (FT-IR) shown in FIG. Exists.

  Further, according to the analysis result by glow discharge emission spectroscopy (GD-OES) of the non-insulating oxide film made of silicon oxide, as shown in FIG. Possible carbon (C) is present in the inner layer portion other than the surface layer portion of the oxide film. On the other hand, as shown in FIG. 2B, in the insulating film, carbon (C) does not exist in the inner layer portion other than the surface layer portion. From these facts, it is considered that the non-insulating oxide film made of silicon oxide has low insulating properties due to the presence of Si—OH and carbon (C).

  In addition, when the oxide film made of oxide other than silicon oxide exemplified above was similarly analyzed by glow discharge emission spectroscopy (GD-OES), carbon (which is considered to cause non-insulation) It was found that C) was present in the inner layer portion other than the surface layer portion of the oxide film.

(Method for producing non-insulating oxide film)
The non-insulating oxide film according to the present invention includes, for example, a chemical vapor deposition method (chemical vapor deposition method, CVD method) such as a plasma chemical vapor deposition method, a thermal chemical vapor deposition method, and a photochemical vapor deposition method. Etc. can be used.

  Specifically, on the surface of the dielectric oxide film, an organic silicon compound or the like listed below is used as a deposition material, an inert gas such as argon gas or helium gas is used as a carrier gas, and ozone gas is further used. A vapor-deposited film of an inorganic oxide such as silicon oxide can be formed using a thermal chemical vapor deposition method using an oxidizing gas such as.

  Moreover, it can also form by the low temperature plasma chemical vapor deposition method using a low temperature plasma generator etc., without using ozone. As a low temperature plasma generator, generators, such as high frequency plasma, pulse wave plasma, and microwave plasma, can be used, for example.

  Organic silicon compounds used as raw materials include tetramethoxysilane, tetraethoxysilane (TEOS), tetrapropoxysilane, tetraptoxysilane, trimethoxysilane (TMS), triethoxysilane (TES), triethoxyfluorosilane, hexamethyl Disiloxane (HMDS), octamethyltrisiloxane (OMTS), hexamethylcyclotrisiloxane (HMCTS), octamethylcyclotetrasiloxane (OMCTS), tetramethylcyclotetrasiloxane (TMCTS), or the like can be used. Of these, tetraethoxysilane (TEOS) is most preferable from the viewpoint of film formability.

(Polymerizable monomer)
When 3,4-ethylenedioxythiophene (hereinafter referred to as EDOT) is used as the polymerizable monomer, an EDOT monomer can be used as the EDOT impregnated in the capacitor element substrate. A mixed monomer solution can also be used.

  Examples of the volatile solvent include hydrocarbons such as pentane and hexane, ethers such as tetrahydrofuran and dipropyl ether, esters such as ethyl formate and ethyl acetate, ketones such as acetone and methyl ethyl ketone, methanol, ethanol, and propanol. Alcohols, nitrogen compounds such as acetonitrile can be used, and methanol, ethanol, acetone and the like are particularly preferable.

(Oxidant)
As the oxidizing agent, an organic sulfonic acid metal salt such as ferric paratoluene sulfonate, periodic acid or iodic acid can be used.

(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.

(Other polymerizable monomers)
As the polymerizable monomer used in the present invention, in addition to the EDOT, a thiophene derivative other than EDOT, aniline, pyrrole, furan, acetylene, or a derivative thereof, which is oxidized and 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 working mechanism of the present invention is considered as follows.
The conventional solid electrolytic capacitor has a problem that the dielectric oxide film is damaged by the oxidizing action of the oxidizing agent used for the polymerization reaction, and the withstand voltage characteristic of the oxide film is lowered.

  In contrast, in the present invention, by forming a non-insulating oxide film on the top surface of the dielectric oxide film, the dielectric oxide film is damaged by the oxidizing action of the oxidizing agent used in the polymerization reaction. Therefore, it is considered that the characteristics, capacitance, and ESR of the solid electrolytic capacitor are improved, and the leakage current characteristics are improved by the oxidation resistance of the oxide film.

  ADVANTAGE OF THE INVENTION According to this invention, the solid electrolytic capacitor which has a high withstand voltage characteristic, and its manufacturing method can be provided.

  Hereinafter, the present invention will be described in more detail based on examples. In addition, the sample of each Example and the comparative example was produced as follows, respectively.

[Test Example 1]
Samples of Example 1 and Comparative Example 2 were prepared as described below, and electrical characteristics were evaluated.

(Example 1)
(A) Substrate preparation An AC etched foil having an Al oxide film equivalent to 4 V was punched into a 1 cm ² circle having one branch. This base material was immersed in an aqueous solution (30 ° C.) composed of ammonium adipate, ammonium dihydrogen phosphate, and water (7.5 g: 0.05 g: 100 g). At a current density of 200 μA · cm ⁻² , the voltage was raised to a predetermined voltage, held for 10 minutes, and an Al oxide film corresponding to 4 V was formed on the substrate edge after punching. Thereafter, the substrate was thoroughly washed with water and naturally dried.

(B) Formation of protective film A protective film having a siloxane bond (non-insulating oxide film of the present invention) is formed on an Al oxide film by chemical vapor deposition using tetraethoxysilane, which is an organosilicon compound. It was.

(C) PEDOT formation As monomer and oxidant, 3,4-ethylenedioxythiophene (Baytron ™ registered MV2) and 54 wt% 1-butanol solution of ferric p-toluenesulfonate (Baytron ™ registered C-B54) ) Were used.

The monomer and the oxidizing agent were mixed at a volume ratio of 1: 3, and this mixed solution was dropped onto the substrate. After the dropping, spin coating was performed at 500 rpm for 5 seconds. In addition, in order to make a 1 cm < ² > circular part into a measurement part, other than this circular part was masked with the polyimide tape. These polymerizations were carried out at 60 ° C. for 30 minutes and further at 150 ° C. for 60 minutes. Electrical connection was made between the PEDOT film and the copper foil via a carbon / Ag paste.

(Comparative Example 1)
The sample of the comparative example 1 was produced without passing through the process of (b) protective film formation among the manufacturing methods of the sample of the said Example 1. Since other steps are the same as those in the first embodiment, description thereof will be omitted.

(Evaluation methods)
The electrical characteristics of the samples of Example 1 and Comparative Example 1 manufactured as described above were evaluated as follows.

  This sample was placed in a container in which dry air was kept flowing. The dew point in this container was maintained at -20 ° C to -18 ° C. When the electrical characteristics were measured after standing for 1 to 2 days, the results shown in Table 1 were obtained.

Table 1 shows a comparison of Cap (capacitance), ESR (equivalent series resistance), and LC (leakage current value). Cap is a value of f = 120 Hz, LC is a value after 1 minute when 2.5 V is applied, and ESR is a value of 1 kHz. Cap (Wet) is a value measured in an aqueous solution of 150 g / liter ammonium adipate, not facing the PEDOT cathode.

  As shown in Table 1, Example 1 having a protective film has a significantly lower leakage current and improved withstand voltage characteristics than Comparative Example 1 having no protective film, and the effect of the present application can be seen. Furthermore, since the damage of the oxide film is suppressed by the effect of the non-insulating oxide film of the present application, both the capacitance and ESR are better than those of the comparative example.

[Test Example-2]
An Al conversion foil having a protective film formed thereon was produced in the same manner as in the sample of Example 1, and used as the sample of Example 2. Moreover, as a sample of Comparative Example 2, an Al chemical conversion foil that does not form a protective film was prepared. The acid resistance of the thus formed Al chemical conversion foil was evaluated as follows.

This base material was immersed in a 0.1 mol / liter p-toluenesulfonic acid aqueous solution (60 ° C.) for 30 minutes. Thereafter, the substrate was thoroughly washed with water and allowed to dry naturally. For the acid resistance evaluation, a 150 g / liter ammonium adipate aqueous solution (30 ° C.) was used, and constant current measurement was performed at a current density of 200 μA · cm ⁻² . Table 2 shows measurement time and ultimate voltage.

  As shown in Table 2, in Comparative Example 2, after being immersed in an acidic solution, the voltage does not rise even when a voltage is applied, and the film is significantly damaged. Compared with this, it turned out that the film | membrane of Example 2 rises in 1-3 second, there is little damage of a film | membrane, and it is excellent in acid resistance.

[Test Example-3]
Samples of Example 3 and Comparative Example 3 were prepared as described below, and hydration resistance and alkali resistance were evaluated.

(Base material production and protective film formation)
A DC etched foil having an Al oxide film equivalent to 558 V was punched into a 1 cm ² circle having one branch. This substrate was immersed in a 70 g / liter boric acid aqueous solution (85 ° C.). At a current density of 200 μA · cm ⁻² , the voltage was raised to a predetermined voltage, held for 10 minutes, and an Al oxide film corresponding to 558 V was formed on the substrate edge after punching. Then, this base material was sufficiently washed with water and naturally dried. The formation conditions of the protective film are the same as in Example 1. Comparative Example 3 was produced in the same manner as Example 3 except that no protective film was formed.

(Evaluation of hydration resistance)
This base material was immersed in boiling water for 120 minutes, and then naturally dried. The evaluation of hydration resistance was carried out using a 70 g / liter boric acid aqueous solution (85 ° C.) and a constant current measurement at a current density of 200 μA · cm ⁻² . Table 3 shows measurement time and ultimate voltage.

  As can be seen from Table 3, Example 3 in which the protective film was formed is superior in hydration resistance compared to Comparative Example 3.

(Evaluation of alkali resistance)
This base material was immersed in a 0.05 mol / liter sodium hydroxide aqueous solution (room temperature) for 30 minutes. Thereafter, the substrate was thoroughly washed with water and allowed to dry naturally. For the evaluation of alkali resistance, a constant current measurement was performed using a 70 g / liter boric acid aqueous solution (85 ° C.) at a current density of 200 μA · cm ⁻² . Table 4 shows measurement time and ultimate voltage.

  As is apparent from Table 4, it can be seen that Example 3 in which the protective film was formed was superior in alkali resistance as compared with Comparative Example 3.

The figure which shows the analysis result by a Fourier-transform infrared spectrophotometer (FT-IR). It is a figure which shows the analysis result by glow discharge emission spectroscopy (GD-OES), (A) is the analysis result about the non-insulating oxide film which consists of silicon oxide, (B) is about an insulating film. Analysis results.

Claims (7)

  A solid electrolytic capacitor, wherein a non-insulating oxide film is formed on a dielectric oxide film, and a solid electrolyte layer made of an oxidatively polymerizable conductive polymer is formed thereon. 2. The solid electrolytic capacitor according to claim 1, wherein a specific resistance of the non-insulating oxide film is 10 ⁸ to 10 ¹¹ Ω · cm.   The solid electrolytic capacitor according to claim 1, wherein the non-insulating oxide film is made of silicon oxide.   The said solid electrolytic capacitor is a winding type, The solid electrolytic capacitor as described in any one of Claim 1 thru | or 3 characterized by the above-mentioned.   In the solid electrolytic capacitor, an anodic oxide film layer is formed on the surface of a foil or plate-shaped valve metal, and a solid electrolyte layer made of a conductive polymer is formed thereon. A graphite layer, silver The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the solid electrolytic capacitor is a flat plate type in which paste layers are sequentially formed to form a cathode portion.   The solid electrolytic capacitor according to any one of claims 1 to 5, wherein the solid electrolyte layer made of the conductive polymer is poly 3,4-ethylenedioxythiophene.   A method for producing a solid electrolytic capacitor, wherein an organic silicon compound is used to form a non-insulating oxide film on a dielectric oxide film by chemical vapor deposition.