JP2001176759A - Solid electrolytic capacitor and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor which can reduce the occurrence of leakage currents, and to provide a method of manufacturing the capacitor. SOLUTION: A capacitor element is manufactured, in such a way that a square sintered body 10 containing an anode lead 11 embedded in one wall is formed of valve action metal powder (a) and an oxidized film 17 is formed by thermally oxidizing the surface embedding the lead 11 (hereinafter called the 'upper surface') of the sintered body 10 (b). In addition, coating oxidized films 14 are formed around the metal powder and on the outer periphery of the sintered body 10 by anodic oxidation (c), and manganese dioxide layers 15 are formed around the metal powder and on the outer periphery of the sintered body 10 (d). Finally, metal layers 16, composed of graphite layers, silver layers, etc., are formed on manganese dioxide layers 15 (e).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolytic capacitor comprising a sintered body of a valve metal powder such as a tantalum powder and a method for producing the same. More particularly, the present invention relates to a highly reliable solid electrolytic capacitor in which a leak defect that is likely to occur near the root of an anode lead is reduced, and a method for manufacturing the same.

[0002]

2. Description of the Related Art In order to manufacture a capacitor element 1 built in a solid electrolytic capacitor such as a conventional tantalum electrolytic capacitor, as shown in FIG.
A powdered anode lead 1 on one wall such as Ta wire
Create a rectangular or cubic shaped body with embedded 1
Sinter in a vacuum atmosphere. A dielectric layer (oxide film) 1 such as Ta ₂ O ₅ is formed around the powder and the outer periphery of the sintered body 10.
4 and a manganese dioxide layer 15 are formed. Further, a metal layer 16 composed of a graphite layer, a silver resin layer, etc.
Are formed respectively. As a result, the outer peripheral wall is
It has become. Reference numeral 13 denotes a Teflon ring which is provided to prevent the liquid from rising toward the anode lead 11 when immersed in the liquid for forming the manganese dioxide layer 15 and the like.

As shown in FIG. 3 (b), the anode lead 11 of the capacitor element 1 is electrically connected to the first external lead 2 by electric welding or the like. Are electrically connected to the second external leads 3 via wires 4 having a fuse function, and the periphery thereof is molded with a resin and covered with a resin package 5. Is formed. The first and second external leads 2 and 3 are cut and separated from the lead frame after the resin package 5 is formed by molding, and are formed into a structure shown in FIG. 3B. Have been.

[0004]

As described above, the capacitor element has an oxide film formed by anodic oxidation on the outer periphery of metal powder, a manganese dioxide layer formed on the surface thereof, and a cathode on the outer periphery of the sintered body. Are formed. But,
For some reasons, the leakage current between the anode lead 11 and the cathode 12 is large. A capacitor is essentially a complete insulator against direct current, and there is a problem in that a leak current flows between the anode and the cathode and the electrical characteristics are reduced, which is a major drawback in the characteristics.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a solid electrolytic capacitor capable of reducing a leak current and a method of manufacturing the same.

[0006]

The inventor of the present invention has conducted intensive studies on the cause of the occurrence of leakage current in a solid electrolytic capacitor such as a tantalum capacitor. It has been found that most leak defects occur on the upper surface in which the anode lead is embedded due to cracks in the film. After further intensive studies, the oxide film and manganese dioxide layer were anodized by immersing the sintered body in an aqueous phosphoric acid solution or impregnated by immersion in an aqueous manganese nitrate solution. It is formed by the method of decomposing manganese, and the top surface of the capacitor element is the top surface of the immersion solution (it cannot be immersed up to the anode lead), so the oxide film on the top surface is formed thicker than other parts by anodic oxidation On the other hand, it has been found that the upper surface is caused by an extremely large number of opportunities to apply an external force, such as welding of the anode lead to an external lead.

By increasing the thickness of the oxide film by thermally oxidizing only the upper surface of the capacitor element (the surface where the anode lead is embedded), the leakage current can be significantly reduced without substantially affecting the characteristics of the capacitor. I found that I can do it.

[0008] A solid electrolytic capacitor according to the present invention comprises a sintered body of metal powder, an anode lead embedded in one wall surface of the sintered body, and an oxide film of metal powder formed on the inside and outer periphery of the sintered body. An oxide film formed thicker than the oxide film on the one wall surface of the sintered body, a manganese dioxide layer formed outside the oxide film, and a metal layer provided outside the manganese dioxide layer. A capacitor element is formed.

The method for manufacturing a solid electrolytic capacitor according to the present invention comprises the steps of (a) forming a sintered body in which an anode lead is embedded in one wall surface with valve metal powder, and (b) embedding the anode lead of the sintered body. Thermally oxidizing only the surface and (c) anodizing to form an oxide film on the inside and the outer periphery of the sintered body; (d) forming a manganese dioxide layer on the outside of the oxide film; The capacitor element is formed by forming a metal layer on the manganese dioxide layer on the outer periphery.

According to this structure and the manufacturing method, the oxide film formed on the surface where the anode lead is particularly susceptible to external force is not only an oxide film formed by anodic oxidation but also a thick oxide film formed by thermal oxidation. Since the oxide film becomes thick and the oxide film is formed thickly, cracks and the like hardly occur in the oxide film even with an external force applied from the anode lead, so that a leak current can be prevented.

The method of thermally oxidizing only the surface in which the anode lead is embedded is performed by exposing only one wall surface of the capacitor element in a container having a concave portion corresponding to the outer peripheral shape of the sintered capacitor element. In this way, the entire surface of the sintered body can be thermally oxidized by thermal oxidation, and the oxide film does not become unnecessarily thick in the other parts. , While reducing the leakage current.

If the container is made of alumina coated with carbon on the surface, there is an advantage that the heat resistance is particularly excellent and the oxidation of the surface other than the exposed upper surface can be prevented by reduction with carbon.

[0013]

Next, a solid electrolytic capacitor of the present invention and a method for manufacturing the same will be described with reference to the drawings. The solid electrolytic capacitor of the present invention, as shown in FIG. 1 is a flowchart of a method of manufacturing a capacitor element according to an embodiment of the present invention and a cross-sectional explanatory view of the capacitor element. A rectangular or columnar sintered body 10 having an anode lead 11 embedded therein is formed. By thermally oxidizing only the surface of the sintered body in which the anode lead 11 is embedded (hereinafter, also referred to as the upper surface), an oxide film 17 thicker than the oxide film 14 formed by anodic oxidation described later is formed. Then, oxide film 14 is formed inside (around the metal powder) and outer periphery of sintered body 10 by anodizing sintered body 10. Further, a manganese dioxide layer 15 is formed outside the oxide film 14, and a metal layer 16 made of a graphite layer, a silver layer, or the like is provided on the outer manganese dioxide layer 15, thereby forming the capacitor element 1. Next, a detailed description will be given in the order of the manufacturing steps with reference to FIG.

(A) First, a valve metal powder made of, for example, tantalum powder is formed into a size of about 0.3 mm cubic to several mm cubic (or may be a rectangular parallelepiped or a column), and the anode lead 11 is formed on one wall surface. For example, the thickness is 0.2
A molded body is produced by embedding a tantalum wire of about mmφ (S1). As the valve metal, metals such as niobium and molybdenum can be used in addition to tantalum. Then, by sintering in a vacuum at 1400 to 2300 ° C. for about 20 to 30 minutes, a sintered body 10 having the anode lead 11 embedded in one wall surface is formed (S2).

(B) Next, the anode lead 1 of the sintered body
Only the upper surface embedded with 1 is thermally oxidized to form an oxide film 17
I do. This thermal oxidation is performed only on the upper surface of the sintered body 10,
Thermal oxide film on the side and bottom surfaces of metal and around the metal powder inside
Is performed so as not to form. For example, as shown in FIG.
Made of alumina, etc., concave according to the size of the sintered body
The anode lead 11 is embedded in the container 20 in which the portion 21 is formed.
Insert the sintered body 10 and expose only the upper surface of the sintered body.
And put in a heating furnace at about 1000 ° C for 20 minutes
Perform a degree of thermal oxidation. By performing this degree of thermal oxidation,
As a result, the surface of the Ta powder is oxidized to, for example, 0.1 to 0.3.
A tantalum oxide film (Ta _TwoO_Five)
An amorphous metal oxide film 17 is formed (S3).

In the container 20 used for oxidation, a concave portion 21 is formed in such a size that the outer periphery of the sintered body almost coincides, and the outer surface thereof is coated with carbon. This recess 2
The reason why the size 1 is formed so as to substantially match the outer periphery of the sintered body 10 is to prevent the outer periphery of the sintered body from being oxidized by contact with air. By doing this,
It is possible to prevent an oxide film from being formed around the outer and inner metal powders without applying an antioxidant to the outer periphery of the sintered body. The thickness of the surrounding oxide film can be increased to prevent the capacity from decreasing. Further, the reason why the surface of the container 20 is coated with carbon is to prevent oxidation of a portion other than the upper surface such as the side wall of the sintered body due to the reducing action of carbon.
The carbon coating can be performed by, for example, burning the container 20 with fire.

(C) Next, in the same manner as in a normal tantalum capacitor manufacturing process, anodization is performed to form an oxide film 14 around the metal powder and the outer periphery of the sintered body 10 (S4). Specifically, a Teflon ring 13 is put on the base of the anode lead 11, and the tip of the anode lead 11 embedded in one wall surface of the sintered body 10 is attached to a stainless bar formed of, for example, a stainless steel plate by several tens. Weld about pieces. Then, the portions welded to the stainless steel bar are collectively immersed in, for example, a phosphoric acid aqueous solution and subjected to anodic oxidation using the anode lead 11 as an anode, so that Ta ₂ powder is formed around the tantalum powder and around the sintered body 10. An oxide film (dielectric layer) 14 made of O ₅ is formed (chemical conversion treatment) (S4). The formation of the oxide film 14 is usually 20 to 10
This is carried out by applying a voltage of 0 V, and 0.04 to 0.0.
It is formed to a thickness of about 2 μm. An oxide film is further formed on the surface on which the above-described thermal oxide film is formed by anodic oxidation.

(D) Next, a manganese dioxide layer 15 is formed around the metal powder and around the sintered body 10. Specifically, the above-described sintered body is immersed in a manganese nitrate solution while being welded to a stainless steel bar, and impregnated into the sintered body. Then, while evaporating the water in the furnace, it is decomposed until the nitrous acid gas disappears to form a manganese dioxide layer on the oxide film (S5). In this case, the manganese dioxide layer 15 is formed not only on the inside of the sintered body 10 but also on the oxide film 14 on the outer periphery of the sintered body 10. In the step of forming the manganese dioxide layer, a portion where the above-mentioned oxide film 14 is damaged occurs. Therefore, the same step as the above-mentioned chemical conversion treatment is performed again, and this step is repeated several times (re-chemical conversion treatment). In order to form the manganese dioxide layer 15 on the outer periphery of the sintered body 10, the manganese nitrate is decomposed by immersion in an aqueous manganese nitrate solution in which fine particles of electrolytic MnO ₂ are dispersed, thereby heating the sintered body. Outer manganese dioxide layer 15 on the outer periphery
Is formed to a thickness of about 20 to 30 μm.

(E) Next, the outer manganese dioxide layer 1
Metal layer 1 composed of graphite layer and silver layer on 5
By forming 6, a capacitor element is manufactured. Specifically, the sintered body 1 having the manganese dioxide layer 15 formed therearound while being welded to the stainless steel bar described above.
The graphite solution is applied to the outer periphery by dipping 0 in an aqueous graphite solution and then pulling it up. Then, it is placed in a furnace and baked at about 130 ° C., for example, to form a graphite layer on the manganese dioxide layer 15 to about 1 μm to several μm.
Dip in the same manner and apply silver paste on the
By drying at about ° C, a metal layer 16 such as a silver layer is formed to a thickness of about 50 μm, and the cathode 12 is used to form the capacitor element 1.

Thereafter, as shown in FIG. 3B, an anode lead and a cathode are electrically connected to external leads such as a lead frame, and the periphery thereof is molded with a resin to form a package. Thereby, the solid electrolytic capacitor of the present invention is obtained.

According to the present invention, the oxide film on the upper surface of the capacitor element (the wall surface on which the anode lead is embedded), which is apt to be stressed particularly by welding of the anode lead, is not only an oxide film formed by ordinary anodic oxidation, but also a thermal film. Since the oxide film formed by oxidation is provided, a thick and very strong oxide film (oxide film) can be formed. As a result, cracks and the like do not occur in the oxide film even with stress caused by welding of the anode lead and the like, and generation of leak current can be prevented.

[0022]

According to the present invention, it is possible to greatly reduce defects due to leakage current and the like, to improve the yield, and to prevent the leakage current from increasing in the subsequent use state and to achieve a very high reliability. improves.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a manufacturing process of an embodiment of a manufacturing method according to the present invention, and a cross-sectional explanatory view of a capacitor element.

FIG. 2 is an explanatory view of an example of oxidizing the upper surface of a sintered body by the manufacturing method according to the present invention.

FIG. 3 is a structural explanatory view of a conventional solid electrolytic capacitor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Capacitor element 10 Sintered body 11 Anode lead 14 Dielectric layer (oxide film) 15 Manganese dioxide layer 16 Metal layer

Claims (4)

[Claims] 1. A sintered body of a metal powder, an anode lead embedded in one wall surface of the sintered body, an oxide film of the metal powder formed on the inside and the outer periphery of the sintered body, An oxide film formed thicker on the one wall surface than the oxide film;
A manganese dioxide layer formed outside the oxide film,
A solid electrolytic capacitor in which a capacitor element is formed from a metal layer provided outside the manganese dioxide layer. 2. A sintered body in which an anode lead is embedded in one wall surface by valve action metal powder, and (b) only the surface of the sintered body in which the anode lead is embedded is thermally oxidized.
(C) anodizing to form an oxide film inside and around the sintered body; (d) forming a manganese dioxide layer outside the oxide film; and (e) forming a manganese dioxide layer around the periphery. A method for manufacturing a solid electrolytic capacitor in which a capacitor element is formed by forming a metal layer thereon. 3. A method of thermally oxidizing only the surface in which the anode lead is embedded, wherein only one wall surface of the capacitor element is formed in a container having a concave portion that matches the outer peripheral shape of the sintered capacitor element. 3. The method according to claim 2, wherein the container is exposed and thermally oxidized together with the container. 4. The method according to claim 3, wherein the container is made of alumina having a surface coated with carbon.