JPH0378222A - Manufacture of solid tantalum capacitor - Google Patents

Abstract

PURPOSE:To improve capacitor properties and to reduce development of shortcircuit defects greatly by covering an anode lead with hydrophilic heat resistant insulator by making a surface thereof conductive and by carrying out required electrolytic polymerization. CONSTITUTION:An anode lead 7 which is connected to a sintered tantalum element 1 is covered with a dielectric oxide film 2. A part of the lead 7 is further covered with a hydrophilic heat resistant insulator 3. The insulator 3 and the film 2 are made conductive by a conductive polymer film 4 which is formed by chemical oxidative polymerization. Furthermore, a conductive high polymer film 5 is formed by electrolytic polymerization between an external cathode and an anode of a conductor 8 which is in contact with a part of the film 4, and a solid tantalum capacitor is manufactured. According to this constitution, it is possible to realize a small leak current and a large tangent of a loss angle without damaging the film 2, to produce the film 4 uniformly by the insulator 3, thereby making production of the film 5 uniform, to improve capacitor properties and to remarkably reduce development rate of shortcircuit defects.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a tantalum solid electrolytic capacitor using a conductive polymer membrane as a solid electrolyte.

(Prior art) A conductive polymer film formed by chemical polymerization and a conductive polymer film formed by electrolytic polymerization are sequentially formed on the surface of a tantalum sintered body on which a dielectric oxide film is formed. A solid electrolytic capacitor having a structure in which a carbon layer and a conductive coating film are formed on a conductive polymer film has been proposed. Compared to conventional solid electrolytic capacitors, this capacitor has features such as a large capacitance and good temperature and frequency characteristics, but there are some issues that require improvement, such as a large leakage current or a large tangent of the loss angle (tanδ). In addition, there were other problems such as damage to the dielectric oxide film due to contact with the conductor (power supply electrode) during electrolytic polymerization.

(Problem to be Solved by the Invention) The applicant proposed providing a heat-resistant insulator in the part where the conductor comes into contact in order to prevent damage to the dielectric oxide film, but the heat-resistant insulator is Generally, due to poor hydrophilicity, the formation of a chemically oxidized polymer film may be uneven, and this has caused a problem in that the formation of an electrolytically oxidized polymer film is uneven.

The present invention has been made to solve the above problems,
An excellent solid electrolytic capacitor with a structure in which a conductive polymer film is formed as a solid electrolyte on the surface of a tantalum sintered body on which a dielectric oxide film is formed, with low leakage current and a small loss angle tangent. The purpose of the present invention is to provide a method for manufacturing tantalum solid electrolytic capacitors with specific characteristics.

[Structure of the Invention] (Means for Solving the Problem) As a result of intensive research, the present inventors have come to invent a method for manufacturing a tantalum solid electrolytic capacitor that can achieve the above object.

That is, a dielectric oxide film is formed on the surface of the tantalum sintered element to which the anode lead is connected, a part of the anode lead is covered with a hydrophilic heat-resistant insulator, and the surface of the heat-resistant insulator and the dielectric oxide are coated. A conductive polymer film formed by chemical oxidation polymerization is formed on the film, and a conductor in contact with a part of the conductive polymer film formed by chemical oxidation polymerization formed on the surface of the heat-resistant insulator is used as an anode and an external cathode. This is a method for manufacturing a tantalum solid electrolytic capacitor, characterized in that a conductive polymer film is formed by electrolytic polymerization on a conductive polymer film by chemical oxidative polymerization.

Conductive polymers include polypyrrole, polythiophene,
Polyfuran and polyaniline are used, and polypyrrole is preferred from the viewpoint of stability of the conductive polymer.

Next, specific examples of the present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a schematic sectional view of a capacitor in which an anode lead is taken out by a tantalum wire from the center of a tantalum sintered element. A dielectric oxide film (2) is formed on a part of the sintered element (1) made of tantalum and the anode lead (7) made of tantalum wire by anodic oxidation. Next, a portion of the anode lead (7) is covered with a hydrophilic heat-resistant insulator (3).

The covered area is a part of the anode lead, preferably a part of the anode lead that is in contact with the element.

Next, the heat-resistant insulator (3) and the dielectric oxide film (2)
) is immersed in an oxidizing agent or a solution containing an oxidizing agent, and further immersed in a conductive polymer monomer or a solution containing the monomer to form a heat-resistant insulator (3) surface and a dielectric oxide film (2). A conductive polymer film (4) is formed thereon by chemical oxidative polymerization.

A conductor (8) is brought into contact with a part of the chemical oxidation polymerized conductive polymer film (4) formed on the heat-resistant insulator (3), and an electrolytic solution containing a supporting electrolyte and a conductive polymer monomer is applied. conductor(
6) is immersed so that a portion of the conductor (6) is submerged, and electrolytic polymerization is performed between the conductor (6) as an anode and an external cathode. A conductive polymer film (5) is formed. In this electrolytic oxidation polymerization, if the heat-resistant insulator (3) is not present, the dielectric oxide film (2) may be damaged due to contact with the conductor (6), and as a result of the damage, the leakage current of the completed capacitor becomes large. and the tangent of the loss angle also increases.

The hydrophilic heat-resistant insulator used in the present invention is a combination of heat-resistant polymers such as silicone resin, epoxy resin, polyimide, fluororesin, and polyphenylene sulfide resin, and mineral inorganic substances such as calcium sulfate, magnesium carbonate, silica, and alumina. A mixture can be used, and the mixture can be coated directly on a part of the anode lead and cured, or by dissolving it in a suitable solvent, coating it, drying and curing it. A mixture of epoxy resin and fine silica powder is preferable because it has low water repellency and good adhesion of the chemical oxidation polymer film.

The method of chemical oxidative polymerization involves uniformly dispersing a solution containing at least 0.01 mol/l of a conductive monomer on the surface of a sintered element, and then adding an oxidizing agent of 0.001 mol/l to 10 mol/l.
Conductive polymer film (
4) to make the surface conductive.

Oxidizing agents used in chemical oxidative polymerization include halogens such as iodine, bromine, and bromine iodide, arsenic pentafluoride, antimony pentafluoride, silicon tetrafluoride, phosphorus pentachloride, phosphorus pentafluoride,
Metal halides such as aluminum chloride and molybdenum chloride, protonic acids such as sulfuric acid, nitric acid, fluorosulfuric acid, trifluoromethanesulfuric acid, and chlorosulfuric acid, oxygen-containing compounds such as sulfur trioxide and nitrogen dioxide, persulfuric acid,
These include persulfates such as ammonium persulfate, peroxides such as hydrogen peroxide, and peracetic acid.

Electrolytic polymerization uses a supporting electrolyte of 0,01 mol/1 to 2
mol/I and conductive polymer monomer 0.01 mo
The test is carried out in an electrolytic solution containing 1/1 to 5 mol/I.

The supporting electrolyte used in the electrolytic polymerization of the present invention includes anion such as a halide anion such as hexafluoroline, hexafluoroline, or tetrafluoroborine, a halogen anion such as iodine, bromine, or chlorine, a perchlorate anion, or a benzenesulfonic acid anion. , a sulfonic acid anion such as alkylbenzenesulfonic acid, and the cation is an alkali metal cation such as lithium, potassium, or sodium, or a quaternary ammonium cation such as ammonium or tetraalkylammonium. As a compound, LIPFe,
L IAs F e, L I C104, L I B F
4, K I , NaPF61NaC104, sodium toluenesulfonate, tetrabutylammonium toluenesulfonate, and the like.

The element on which the conductive polymer has been formed in this way is immersed in colloidal carbon to form a carbon layer on the surface.

Furthermore, a conductive coating film is formed using a conductive paste on top of the coating film, and a lead wire for drawing out the cathode is connected to a part of the coating film. Silver bar as a conductive paste. Paste, copper paste, aluminum paste, etc. can be used. A solid electrolytic capacitor is obtained by applying an exterior covering to the capacitor element configured as described above, such as by sealing it in a resin mold, a resin case, or a metal case.

(Function) The capacitor using the conductive polymer as a solid electrolyte and produced by the saw-bag of the present invention has superior electrical properties as compared to the solid electrolytic capacitor produced by a conventionally known method.

This is because the conductor does not damage the oxide film during electrolytic polymerization, the leakage current is extremely small, and the tangent of the loss angle (
A capacitor with a small tan δ) can be obtained.

In addition, since a hydrophilic heat-resistant insulator is used, the insulator will not melt at high temperatures and impair capacitor characteristics.
The chemical oxidation polymer film adheres well, and the yield rate during mass production is high.

(Example) Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 A tantalum sintered element with an anode lead taken out was heated to 150 cm.
A dielectric oxide film was formed by anodic oxidation.

As shown in Figure 1, a part of the anode lead is coated with epoxy resin (
A hydrophilic heat-resistant insulator made of a 1=1 mixture of SUMIMAC 9060 (manufactured by Sumitomo Bakelite) and Nlica fine powder (reagent grade silicon dioxide) is coated.
It was cured and coated by heating for a minute. The element was heated with 10vt of hydrogen peroxide.
% and 2 wt % of sulfuric acid at room temperature for 10 minutes so that the hydrophilic heat-resistant insulator was submerged halfway.

Next, the element was quickly immersed in the virol monomer stock solution.
The reaction was held for 0 minutes. When the device was removed from the pyrrole monomer, washed, and dried, a polypyrrole layer was formed by chemical oxidation polymerization halfway up the surface of the heat-resistant insulator on the anode lead and on the dielectric oxide film.

Next, a stainless steel wire was connected to a part of the polypyrrole produced by chemical oxidation polymerization on the surface of the hydrophilic heat-resistant insulator to serve as an anode.
The stainless steel wire was submerged in a stainless steel beaker containing an acetonitrile solution containing ol/I, and electrolytic polymerization was performed for 30 minutes at a constant current of 1 mA using the stainless steel beaker as a cathode. As a result, a polypyrrole film formed by electrolytic polymerization was formed on a polypyrrole film formed by chemical oxidative polymerization.

After removing the stainless steel wire, washing and drying, the device was coated with colloidal carbon and silver paste, an anode lead was attached, and molded with epoxy resin to obtain a tantalum capacitor with a rated voltage of 35 V and a nominal capacitance of 1.5 μF. Table 1 shows the capacitance of the completed capacitor, the tangent of the loss angle (tan δ), the negative current value (LC) at 35 cm, and the short-circuit failure rate.

Table 1 Comparative Example 1 A tantalum solid electrolytic capacitor was completed according to Example 1 except that only epoxy resin was applied instead of the 1=1 mixture of epoxy resin and fine silica powder. Table 1 shows the capacitance, tan δ, leakage current (LC), and short-circuit failure rate of the completed capacitor.

Epoxy resin alone has poor hydrophilicity, so even when immersed in an aqueous solution containing 10 wt% hydrogen peroxide and 2 wt% sulfuric acid during chemical oxidative polymerization, it does not adhere well to the epoxy resin, resulting in uneven formation of a chemical oxidative polymer film. be. For this reason, the electrolytically polymerized film also becomes non-uniform, tan δ and leakage current increase, and the incidence of short circuit failures also increases.

[Effects of the Invention] A part of the anode lead is coated with a hydrophilic heat-resistant insulator, the surface of the heat-resistant insulator is made conductive, and a conductor is brought into contact with the surface and electrolytically polymerized to form a dielectric material. The leakage current is extremely small without damaging the oxide film, and the ta
A tantalum solid electrolytic capacitor with a small nδ could be obtained. In addition, since it is coated with a hydrophilic heat-resistant insulator, the chemical oxidation polymer film is uniformly formed on the surface of the heat-resistant insulator, and as a result, the electrolytic polymer film is uniformly formed, improving capacitor characteristics. The incidence of short circuit failures is significantly reduced.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of a capacitor in which an anode lead is taken out by a tantalum wire from the center of a tantalum sintered element. 1. Tantalum sintered element 2. Dielectric oxide film
3. Hydrophilic heat-resistant insulator 4. Conductive polymer film by chemical oxidation polymerization 5. Conductive polymer film by nakago depolymerization 6. Conductor 7. Hand anode lead

Claims (3)

[Claims] 1. A dielectric oxide film is formed on the surface of the tantalum sintered element to which the anode lead is connected, a part of the anode lead is covered with a hydrophilic heat-resistant insulator, and the surface of the heat-resistant insulator and the dielectric oxide film are coated. A conductive polymer film formed by chemical oxidation polymerization is formed on the surface of the heat-resistant insulator, and a conductor that is in contact with a part of the conductive polymer film formed by chemical oxidation polymerization formed on the surface of the heat-resistant insulator is used as an anode and connected to an external cathode. 1. A method for manufacturing a tantalum solid electrolytic capacitor, the method comprising: electrolytically polymerizing a tantalum solid electrolytic capacitor, and forming a conductive polymer film by electrolytic polymerization on a conductive polymer film by chemical oxidative polymerization. 2. 2. The method for manufacturing a tantalum solid electrolytic capacitor according to claim 1, wherein the conductive polymer is polypyrrole. 3. 2. The method for manufacturing a tantalum solid electrolytic capacitor according to claim 1, wherein the hydrophilic heat-resistant insulator is a mixture of a heat-resistant polymer and a mineral inorganic material.