JPH1050561A - Solid state electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the withstanding voltage characteristic and leak current characteristic by providing an insulative resin layer on the surface of a thin portion of a solid state electrolytic layer. SOLUTION: An anode 1 uses a square sintered block of a valve-action metal fine powder or a roll of laminated valve-action metal foils with an oxide film 2 on the surface. A solid state electrolytic layer 4 is formed on the oxide film 2 and made of a conductive polymer or MgO2 . An insulative resin layer 7 is formed on the entire lower part of the anode 1 with the electrolytic layer 4, including its corners 5 and ridge 6. The resin layer 7 covering these corners 5 and ridges 6 is prepared, because the electrolytic layer 4 is often too thin or formed too little.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a solid electrolytic capacitor.

[0002]

2. Description of the Related Art A solid electrolytic capacitor uses an anode body formed by anodizing a foil or sintered body of a valve metal such as aluminum or tantalum to form an oxide film and drawing out an anode lead wire such as tantalum. I have. Then, a solid electrolyte layer made of manganese dioxide or a conductive polymer is formed on the surface of the oxide film of the anode body, and further a carbon layer or a silver layer is overlaid to form a cathode layer. It has a structure in which external terminals are connected to form an exterior.

[0003]

By the way, when the anode body is square, the thickness of the solid electrolyte layer is reduced at the corners and the twill lines when the anode body is cylindrical, and at the twill lines when the anode body is cylindrical. In particular, the solid electrolyte layer made of a conductive polymer is formed by a chemical oxidation polymerization method, a gas phase oxidation polymerization method, an electrolytic polymerization method, or the like. For this reason, the conventional solid electrolytic capacitor has a drawback that the withstand voltage characteristics are reduced, and the cathode layer is in direct contact with the oxide film, and the leakage current is increased.

An object of the present invention is to provide a solid electrolytic capacitor capable of improving the above-mentioned drawbacks and improving the withstand voltage characteristics and the leakage current characteristics.

[0005]

According to a first aspect of the present invention, there is provided a solid electrolytic device comprising: an anode body having an oxide film formed on a valve metal; and a solid electrolyte layer and a cathode layer provided sequentially on the anode body. It is an object of the present invention to provide a solid electrolytic capacitor characterized in that an insulating resin layer is provided on a surface of a thin portion of a solid electrolyte layer in a capacitor. The invention according to claim 2 is a solid electrolytic capacitor in which a solid electrolyte layer and a cathode layer are sequentially provided on an anode body in which an oxide film is formed on a valve action metal, and the surface of the cathode layer where the solid electrolyte layer is not formed is insulated. A solid electrolytic capacitor provided with a resin layer is provided.

According to the present invention, after the solid electrolyte layer is provided on the anode body, the insulating resin is applied to the corner portions and the twill wire portions where the thickness of the solid electrolyte layer is thin or the solid electrolyte layer may not be provided. Since the layers are provided, the withstand voltage of the corner portions, the twill lines, and the like is improved, and the leakage current from these portions can be reduced.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. First, tantalum, aluminum, or the like is used as the valve metal. Further, as shown in FIG. 1, the anode body 1 has a square (or cylindrical) shape made of fine powder of valve action metal.
Or a material obtained by laminating or winding a valve metal foil and having an oxide film 2 formed on the surface thereof. An anode lead wire 3 such as tantalum is drawn from the anode body 1. On the surface of the oxide film 2, a solid electrolyte layer 4 is provided. The solid electrolyte layer 4 is made of a simple substance such as polyaniline, polypyrrole, polythiophene, polyparaphenylene, or polyacetylene, or a conductive polymer obtained by mixing these with a polymer such as polystyrene, polyethylene, polymethyl methacrylate, or polyacrylonitrile butadiene-styrene. Or manganese dioxide.

Then, an insulating resin layer 7 is provided on the entire lower portion including the corner portion 5 and the twill wire portion 6 of the anode body 1 provided with the solid electrolyte layer 4. It is to be noted that the insulating resin layer 7 is provided on the corner portion 5 and the twill wire portion 6 because the thickness of the solid electrolyte layer 4 is reduced in these portions or the solid electrolyte layer 4 is not formed in many cases. It is. Therefore, if there is another portion where the thickness of the solid electrolyte layer 4 is small, the insulating resin layer 4 may be provided in that portion as well. Further, as shown in FIG. 2, the insulating resin layer 8 may be provided only on the lower corner portion 5 of the anode body 1 where the solid electrolyte layer 4 is provided. And FIG.
As shown in (1), the insulating resin layer 9 may be provided on all corners 5 of the anode body 1 where the solid electrolyte layer 4 is provided. Furthermore, a) only the upper corner portion and the twill line portion or the entire upper portion including these portions; b) the upper corner portion only; c) only the upper portion or lower portion when the anode body is cylindrical. , An insulating resin layer may be provided on the entire corner portion and the whole including the traverse line portion. As the insulating resin, an epoxy resin, a phenol resin, a urethane resin, a melamine resin, an alkyd resin, an unsaturated polyester resin, or the like is used.

A carbon paste is applied to the surfaces of the solid electrolyte layer 4 and the insulating resin layer 7 to form a carbon layer 10. Further, a silver paste is applied to the surface of the carbon layer 10 to provide a silver layer 11. This carbon layer 10 and silver layer 11
Together to form a cathode layer. Then, a cathode terminal 13 is connected to the silver layer 11 by a silver conductive paste 12. An anode terminal 14 is welded to the anode lead wire 3. Further, the entirety is covered with an exterior 15 made of an insulating resin. The tips of the cathode terminal 13 and the anode terminal 14 are drawn out of the exterior 15, provided with plating, and bent along the exterior 15.

Next, a method of manufacturing the solid electrolytic capacitor 16 of the above embodiment will be described. First, the anode body 1 is formed by forming a rectangular or cylindrical sintered body using a fine powder of a valve action metal such as tantalum or aluminum, or by laminating or winding an etched valve action metal foil. Form. For example, when using tantalum powder, the anode lead wire 3 of tantalum or the like is drawn out, this powder is formed into a predetermined shape, and then sintered at a high temperature in a vacuum to form the anode body 1. I do. Then, the anode body 1 is anodized using an aqueous solution of nitric acid, phosphoric acid or the like to form an oxide film 2. After the oxide film 2 is formed, a solid electrolyte layer 4 made of a conductive polymer or manganese dioxide is formed. The formation of the solid electrolyte layer 4 from the former substance is performed as follows. That is, a) the anode body 1 is immersed or sprayed in the conductive polymer solution to apply the conductive polymer solution to the surface of the oxide film 2. After the application, it is washed with an organic solvent such as alcohol. After washing, dry and evaporate the solvent. If necessary, the steps from coating to drying are repeated to form a predetermined thickness. Also,
(B) The anode body 1 is immersed in a solution of the undoped polymer, or the solution is sprayed on the anode body 1 to apply the polymer solution to the surface of the oxide film 2. After application, it is washed and dried. The process from coating to drying is repeated a predetermined number of times as necessary, to form a undoped polymer film having a predetermined thickness. After forming this film, the anode body 1
Is immersed in a doping solution for several tens of minutes to several hours to make contact with it, thereby imparting conductivity by doping a polymer film to form a conductive polymer film. Further, (c) the anode body 1 is immersed in a solution containing doping ions in a monomer such as aniline, pyrrole, or thiophene, or this solution is sprayed. Next, the anode body 1 is immersed in a solution of an oxidant,
A chemical polymerization reaction is performed to form a conductive polymer film on the surface of the oxide film 2. D) The anode body 1 is immersed in a solution of a monomer such as aniline or pyrrole that does not contain doping ions, and the solution is applied. Then, a polymer film is formed. After the formation of the polymer film, the anode body 1 is immersed in a doping solution or the like to make contact therewith, thereby imparting conductivity to form a conductive polymer film. Note that as the polymer, polyaniline, polypyrrole, polythiophene, polyparaphenylene, polyacetylene, or the like, or a mixture of such a polymer with polystyrene, polyethylene, polymethyl methacrylate, polyacrylonitrile butadiene-styrene, or the like is used. The dopant is a substance whose dissociation constant is almost the same as or smaller than that of naphthalenesulfonic acid or a derivative thereof, and whose anion is smaller than that of naphthalenesulfonic acid or a derivative thereof. Such dopants include, for example, sulfoisophthalic acid, sulfosuccinic acid, methanesulfonic acid, phenolsulfonic acid, sulfosalicylic acid, benzenesulfonic acid,
Acids such as benzenedisulfonic acid, alkylbenzenesulfonic acid and derivatives thereof, camphorsulfonic acid, sulfoacetic acid, sulfoaniline, and diphenolsulfonic acid, or salts of these acids are used. The doping solution has, for example, a composition in which a dopant or a dopant and an oxidizing agent are dissolved in an organic solvent. The concentration of the dopant or oxidizing agent in the liquid is preferably in the range of 0.01 to 1 mol / l. And the organic solvent is, for example, ketones, esters, alcohols,
Aromatic hydrocarbons, nitriles, cellosolves, nitrogen-containing compounds and the like are used. Further, as the solution of the oxidizing agent, not only the oxidizing agent but also a solution to which a dopant is added or a solution of a salt of the oxidizing agent and the dopant may be used. As the oxidizing agent, a salt having an oxidation potential of 0.8 V or more with respect to a hydrogen reference electrode, such as a ferric salt, a persulfate, or a vanadate, is used. By the way, when an element is formed from tantalum powder, the more the CV value of the tantalum powder increases and the capacitance per volume increases, the more difficult it is to impregnate the liquid inside the element. Therefore, in order to form a conductive polymer film having good characteristics, it is necessary to use a conductive polymer solution or the like having a high concentration. Among the polymers, polyaniline is a suitable substance because it has a high solubility in a solvent and can prepare a solution having a relatively high concentration. The formation of the solid electrolyte layer 4 from the latter manganese dioxide is performed as follows. That is, the anode body 1 is immersed in a manganese nitrate solution to impregnate the solution. After the impregnation, it is thermally decomposed and then subjected to re-chemical treatment. And raise the concentration of the manganese nitrate solution,
These steps of impregnation, thermal decomposition and re-chemical treatment are repeated to form a solid electrolyte layer 4 of manganese dioxide having a predetermined thickness.

After the formation of the solid electrolyte layer 4, the insulating resin layer 7 is formed by dipping, spraying, or screen printing the anode body 1 in a molten insulating resin such as an epoxy resin.

After forming the insulating resin layer 7, a carbon paste is applied to form a carbon layer 10, and a silver paste is applied to the surface of the carbon layer 10 to form a silver layer 11. After the silver layer 11 is formed, the silver layer 11 is
And the anode terminal 14 is welded to the anode lead wire 3. Then, the exterior 15 is formed by a resin molding method, a resin dipping method, or the like. After the exterior 15 is formed, plating is provided on the tips of the cathode terminal 13 and the anode terminal 14 and bent to form a solid electrolytic capacitor 16.

[0013]

Embodiments of the present invention will be described below. Example 1: Rated 16 V, 3.3 μF of the structure shown in FIG.
Tantalum chip type solid electrolytic capacitor. That is, tantalum powder is used as the valve metal. The tantalum powder is drawn out of an anode lead wire of tantalum, compression-molded, and then vacuum-sintered at a temperature of 1400 to 1500 ° C. to obtain a square anode having a size of 0.8 mm × 1.1 mm × 1.2 mm. Body. Further, the anode body is immersed in an aqueous acid solution and anodized to form an oxide film. A solid electrolyte layer made of conductive polyaniline is provided on the surface of the oxide film.
In addition, this solid electrolyte layer is formed as follows. That is, first, the anode body after forming the oxide film is immersed in a 2.5 wt% polyaniline solution. After immersion, the anode body is taken out, washed, and dried at a temperature of 60 to 120C. The process from immersion to drying is repeated about 15 to 20 times to form a polyaniline film. Thereafter, the anode body is immersed in a sulfonic acid solution for several hours to dope, thereby forming a solid electrolyte layer made of a conductive polyaniline film. Then, the entire surface of the anode body, including the surface of the anode body opposite to the surface from which the anode lead wire is pulled out, and the corners and the twill lines connected to the surface are immersed in a molten epoxy resin and thermally cured to a thickness of 0.1 mm. An insulating resin layer of 1 mm or less is provided. Further, a carbon layer and a silver layer are provided on the surfaces of the solid electrolyte layer and the insulating resin layer. Then, the whole is covered with an epoxy resin by a molding method to form an exterior.

Example 2 The conditions are the same as in Example 1 except that an anode body provided with an insulating resin layer having a structure as shown in FIG. 2 is used.

Embodiment 3 The conditions are the same as in Embodiment 1 except that an anode body provided with an insulating resin layer having the structure shown in FIG. 3 is used.

Next, the leakage current value and the withstand voltage failure of the tantalum chip type solid electrolytic capacitors of Examples 1 to 3 were measured together with the conventional example. The conventional example is the same as Example 1 except that the insulating resin layer is not provided. The number of samples is 20 for each of the leakage current cases and 1000 each for the case of the withstand voltage failure. As is apparent from the measurement results shown in FIG.
Is about 0.015 to 0.1 μA and about 0.01
5-1 μA. That is, Examples 1 to 3 have a lower leakage current and smaller variations than the conventional example. The number of withstand voltage defects was 5 for each of the first to third embodiments.
8, 8 and 37 in the conventional example. That is, the withstand voltage failure of the former is about 13.2 of that of the latter conventional example.
It has fallen to 5% to 21.6%.

[0017]

As described above, according to the present invention, the insulating resin layer is provided on the surface of the thin portion of the solid electrolyte layer or on the surface of the cathode layer where the solid electrolyte layer is not formed.
A solid electrolytic capacitor that can reduce withstand voltage failure, reduce variations in leakage current, and reduce the overall value can be obtained.

[Brief description of the drawings]

FIG. 1 shows a sectional view of an embodiment of the present invention.

FIG. 2 is a cross-sectional view of an anode body provided with a cathode layer used in another embodiment of the present invention.

FIG. 3 is a cross-sectional view of an anode body provided with a cathode layer used in another embodiment of the present invention.

FIG. 4 shows a graph of leakage current.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Anode body, 2 ... Oxide film, 4, 8 ... Solid electrolyte layer, 5 ... Corner part, 6 ... Twill wire part, 7, 8, 9 ... Insulating resin layer, 10 ... Carbon layer, 11 ... Silver layer, 16 ...
Solid electrolytic capacitor.

Claims (2)

[Claims] 1. A solid electrolytic capacitor in which a solid electrolyte layer and a cathode layer are sequentially provided on an anode body having an oxide film formed on a valve metal, and an insulating resin layer is provided on a surface of a thin portion of the solid electrolyte layer. A solid electrolytic capacitor characterized by being provided. 2. A solid electrolytic capacitor in which a solid electrolyte layer and a cathode layer are sequentially provided on an anode body in which an oxide film is formed on a valve metal, and an insulating resin layer is provided on the surface of the cathode layer on which no solid electrolyte layer is formed. A solid electrolytic capacitor characterized in that: