JP2000091163A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To materialize the manufacture of a solid electrolyte capacitor which can raise leaked current property and can suppress the inferiority. SOLUTION: This is the manufacture of a solid electrolytic capacitor 16 which forms a sintered substance 1 by burying one end of a lead wire 2 for a cathode and sintering the powder of metal for valve action and forms an oxide film 5 and a cathode layer in order in this sintered substance 1 and forms a package 15 next. This is manufacture of a solid electrolytic capacitor 16 which performs the processing of bringing the cathode layer of a capacitor element 9 into contact with the electrode member consisting of a lump of ceramic granular matter which is provided with a metallic layer on the surface and applying positive voltage to the capacitor element 9 after formation of the cathode layer and besides before formation of the package 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a solid electrolytic capacitor, and more particularly to a method for manufacturing a solid electrolytic capacitor with improved defects such as leakage current characteristics.

[0002]

2. Description of the Related Art A solid electrolytic capacitor such as a tantalum solid electrolytic capacitor is manufactured by, for example, the following method.
That is, first, a powder obtained by mixing a binder with fine powder of a valve metal such as tantalum or aluminum is embedded in advance at one end of an anode lead wire made of a valve metal such as tantalum to form a sintered body. Next, the plurality of sintered bodies are connected to an elongated metal plate such as stainless steel at the tips of the anode lead wires. Then, in this state, the sintered body is immersed in a chemical conversion solution and anodized to form an oxide film. After forming the oxide film, a cathode layer is formed by sequentially stacking a conductive layer made of manganese dioxide or a conductive polymer such as polyaniline or polypyrrole, a carbon layer, and a silver layer. Then, the anode lead wire is cut, and the capacitor element after the formation of the cathode layer is separated from the metal plate. After the separation, the anode terminal is connected to the anode lead wire, and the cathode terminal is connected to the cathode layer. After this,
An exterior made of an insulating resin or the like is formed to cover the capacitor element and a part of the anode terminal and the cathode terminal.

[0003]

When or after forming a casing by covering a capacitor element with an insulating resin or the like, the insulating resin or the like shrinks, thereby damaging an oxide film or the like and increasing leakage current. However, there is a disadvantage that leakage current defects increase.

An object of the present invention is to provide a method of manufacturing a solid electrolytic capacitor which can improve the above-mentioned drawbacks, improve the leakage current characteristics, and reduce the defects.

[0005]

According to the present invention, in order to solve the above-mentioned problems, one end of an anode lead wire is embedded,
The powder of the valve metal is sintered to form a sintered body, and an oxide film and a cathode layer are sequentially formed on the sintered body. And a process of applying a positive voltage to the capacitor element by contacting the cathode layer of the capacitor element with an electrode member made of a lump of ceramic granular material provided with a metal plating film on the surface before forming the exterior. And a method for producing a solid electrolytic capacitor.

That is, according to the present invention, since the process of applying a positive voltage to the capacitor element is performed before forming the exterior, the leakage current characteristic is improved. And even if an exterior is formed after that, the increase in leakage current failure can be reduced.

[0007]

Embodiments of the present invention will be described below. First, a binder obtained by dissolving an acrylic resin or the like in an organic solvent is added to and mixed with fine powder of a valve metal such as tantalum, aluminum, or niobium. After mixing, the mixture is heated to volatilize and remove the organic solvent. Next, the valve metal powder is compression-molded into a shape such as a cylinder or a square by a press or the like. At this time, one end of an anode lead wire made of a valve metal such as tantalum is inserted into the powder, and the other end is drawn out. After the compression molding, firing is performed at a high temperature in an atmosphere such as a vacuum to form a sintered body 1 as shown in FIG. Thereafter, a disk-shaped insulating plate 3 made of Teflon, silicone rubber, silicone resin, or the like is disposed at the root of the anode lead wire 2. Then, as shown in FIG. 1B, a plurality of the sintered bodies 1 are connected to an elongated metal plate 4 made of stainless steel or the like at the locations of the anode lead wires 2. Sintered body 1
Is connected to a metal plate 4, the sintered body 1 is immersed in a chemical solution such as nitric acid or phosphoric acid and anodized to form an oxide film 5 having a thickness of about 200 to 3000 mm as shown in FIG. To form

After the oxide film 5 is formed, as shown in FIG. 1D, a conductive layer 6 made of manganese dioxide, a conductive polymer, or the like is formed.
To form In order to form the conductive layer 6, the sintered body 1 is placed in a manganese nitrate solution or the like with the lead surface side of the anode lead wire 2 facing upward, and the liquid level is slightly above the lead surface of the anode lead wire 2. Immersion so as not to exceed the height of the insulating plate 3. Thereby, the liquid adheres to and impregnates the sintered body 1. After the impregnation, processing is performed according to the type of the solution to form the conductive layer 6.

That is, if the solution is a manganese nitrate solution, the sintered body 1 is immersed in the manganese nitrate solution to impregnate the solution, then thermally decomposed, and further subjected to re-chemical treatment. Then, the concentration of the manganese nitrate solution was gradually increased to impregnate these
Repeat the steps of dehydration, thermal decomposition and re-chemical treatment,
A conductive layer 6 of manganese dioxide having a predetermined thickness is formed.

The conductive layer 6 made of a conductive polymer is formed by, for example, the following various methods. That is, in the first method, first, the sintered body 1 is immersed in a conductive polymer solution. After immersion, it is washed with an organic solvent such as alcohol. After washing, dry and evaporate the solvent. Then, if necessary, the steps from immersion to drying are repeated to form a predetermined thickness. In the second method, first, the sintered body 1 is immersed in a solution of the undoped polymer. After immersion, wash and dry. The process from immersion to drying is repeated a predetermined number of times as necessary,
A undoped polymer film having a predetermined thickness is formed. After forming this film, the sintered body 1 is placed in a doping solution for several tens of minutes.
It is immersed in contact for several hours to bond the ion of the dopant to the polymer to impart conductivity, thereby forming a conductive polymer film. Further, in the third method, first, the sintered body 1 is immersed in a solution containing a monomer such as aniline, pyrrole, or thiophene and a dopant ion. Next, the sintered body 1 is immersed in a solution of an oxidizing agent to cause a chemical polymerization reaction to form a conductive polymer film. In the fourth method, first, the sintered body 1 is immersed in a solution of a monomer such as aniline or pyrrole. Next, the sintered body 1 is immersed in a solution of an oxidizing agent to cause a chemical polymerization reaction, thereby forming a polymer film. After the formation of the polymer film, the sintered body 1 is immersed in a doping solution and brought into contact with the sintered body 1 to impart conductivity to form a conductive polymer film. Note that as the dopant, a substance having a dissociation constant substantially equal to or smaller than that of naphthalenesulfonic acid or a derivative thereof and an anion of the dopant smaller than that of naphthalenesulfonic acid or a derivative thereof is used. Such dopants include, for example, sulfoisophthalic acid, sulfosuccinic acid, methanesulfonic acid, phenolsulfonic acid,
Acids such as sulfosalicylic acid, benzenesulfonic acid, benzenedisulfonic acid, alkylbenzenesulfonic acid and derivatives thereof, camphorsulfonic acid, sulfoacetic acid, sulfoaniline and diphenolsulfonic acid, and 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 oxidant in the solution is 0.0
A range of 1 to 1 mol / l is preferred. And the organic solvent is
For example, ketones, esters, alcohols, aromatic hydrocarbons, nitrile acid, 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. And 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 second iron salt, persulfate, or vanadate is used.
By the way, when an element is formed from tantalum powder, as the CV value of the tantalum powder increases and the capacitance per unit volume increases, the inside of the element becomes more difficult to impregnate with a liquid. 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. And polyaniline in the polymer,
It is a suitable substance that has a high solubility in a solvent and can prepare a relatively high-concentration solution.

After forming the conductive layer 6, a carbon paste is applied to form a carbon layer 7 as shown in FIG. Further, as shown in FIG. 1F, a silver paste is applied to the surface of the carbon layer 7 to form a silver layer 8 to obtain a capacitor element 9.

The conductive layer 6, the carbon layer 7, and the silver layer 8
After the cathode layer made of is formed, the anode lead wire 2 side is made positive and the cathode layer side is made negative, and a voltage is applied to the capacitor element 9 in the positive direction. At this time, the ambient temperature is preferably in the range of room temperature to about 200 ° C., particularly about 120 to 150 ° C., and the leakage current can be further reduced. The voltage application time is given by the following equation
0 minute to several hours, preferably about 1 hour.

In order to apply a voltage to the capacitor element 9, an electrode is connected to the metal plate 4 and the cathode layer is brought into contact with the electrode member.

This electrode member is made of ceramic granular material having a metal plating film on the surface. Ceramic materials include zirconia-silica, alumina, silicon nitride,
Silicon carbide or the like is used. Also, as the metal plating film,
A nickel plating film, a gold plating film, a copper plating film or a combination thereof is used. Further, the granular material is a sphere, an ellipse, a cylinder, or the like. The average particle size of the granular material is preferably smaller than 10.0 mm, particularly preferably smaller than 6 mm, and the effect of improving the leakage current characteristics is remarkable.

Then, for example, as shown in FIG.
A granular electrode member 11 is placed on the surface of the
A part of the capacitor element 9 is embedded in 1. Then, a positive voltage is applied to the capacitor element 9 using the metal plate 4 side to which the anode lead wire 2 is connected as an anode and the metal plate 10 side on which the electrode member 11 is mounted as a cathode.

In addition, rubber, sponge, glass wool, or cotton, which has been provided with conductivity by being coated with a metal foil or the like, is interposed between the metal plate 10 on the cathode side and the granular electrode member 11. You may. In this case, when the capacitor element 9 contacts the granular electrode member 11 as compared with the case of FIG.
The mechanical force applied to the capacitor element 9 can be further reduced. After a voltage is applied to the capacitor element 9, the lead wire for the anode is cut to separate the capacitor element 9 from the metal plate 4. Then, as shown in FIG. 1 (g), the cathode terminal 13 is connected to the silver layer 8 by the silver paste 12, and the anode terminal 14 is connected to the anode lead wire 2 by welding or the like. Next, as shown in FIG. 1H, the exterior 15 is formed by a resin molding method, a resin dipping method, or the like, and the capacitor element 9 is covered with an insulating resin. After the exterior 15 is formed, it is subjected to an aging treatment, and further, the cathode terminal 13 and the anode terminal 14 are
To form a solid electrolytic capacitor 16.

[0017]

Next, an embodiment of the present invention will be described. First, a powder obtained by mixing a binder with a fine powder of tantalum is press-molded into a square shape. At this time, one end of the tantalum anode lead wire is inserted into the powder, and the other end is pulled out. After compression molding, sinter in vacuum, 2.60mm
A sintered body of × 2.32 mm × 1.52 mm square is formed. Next, the sintered body is immersed in a nitric acid solution and subjected to anodizing treatment at a formation voltage of 17 V to form an oxide film. After forming the oxide film, a conductive layer made of any one of manganese dioxide, conductive polypyrrole, and conductive polyaniline is formed. After forming the conductive layer, a carbon paste and a silver paste are sequentially applied to form a carbon layer and a silver layer. After forming the silver layer, a DC voltage of 9 V is applied to the capacitor element for one hour in an atmosphere at a temperature of room temperature to 200 ° C. At this time, the pressing force of the capacitor element against the electrode member is 10 kg / cm ²
And The electrode members are as shown in Table 1. After applying the voltage, the cathode layer of the capacitor element is connected to the cathode terminal of the lead frame with silver paste, and the anode lead wire is welded to the anode terminal of the lead frame.
Thereafter, an exterior is formed by a transfer molding method. After forming the exterior, the lead frame is cut at a predetermined position, subjected to aging treatment, and the cathode terminal and the anode terminal are formed to produce a tantalum solid electrolytic capacitor rated at 7 V and 100 μF.

The defective rate of leakage current was measured for the tantalum solid electrolytic capacitors manufactured by the method of the above embodiment and the tantalum solid electrolytic capacitors of the comparative example and the conventional example, and the results are shown in Table 1.

The tantalum solid electrolytic capacitors of Comparative Examples 1 and 2 were prepared in the same manner as in Examples 1 to 2 except that the conditions of the electrode members used when applying a voltage after forming the cathode layer were as shown in Table 1. Assume that it was manufactured under the same conditions as in Example 16.

The conventional tantalum solid electrolytic capacitor is manufactured under the same conditions as in Examples 1 to 16, except that the process of applying a voltage before forming the exterior is omitted.

The leakage current is determined by connecting a 1 KΩ resistor in series to the sample, applying a DC voltage of 7 V between the sample and the resistor in an atmosphere at a temperature of 25 ° C., and setting a current value after a lapse of 1 minute. And the commonly used product rating standard value 0.0
A value obtained by multiplying 1 CV (μA / μF · V) by 0.25, that is, 0.25 × 0.01 CV as a reference value, is good if the leakage current is smaller than this value, and is bad if the leakage current is equal or larger. The rate was determined.

The electrode member is a sphere, and its material, melting point, density, average particle size before plating film formation, surface roughness (maximum height Rm when reference length is 0.1 mm), plating film and Table 1 also shows the material of the conductive layer.

[0023]

[Table 1]

As is clear from Table 1, the defective rate of the leakage current is 0.8 to 5.1% in Examples 1 to 16 and 5.8 to 6.7% in Comparative Examples 1 and 2. And the conventional example is 7.
2%. That is, according to Examples 1 to 16, the size is reduced to about 12 to 88% as compared with Comparative Examples 1 and 2, and about 11 to 71% as compared with the conventional example. Has declined. In addition, comparing Example 1 to Example 14 and Example 15 to Example 16 with respect to the defect rate of the leakage current, the former is reduced to about 16 to 78% of the latter. Therefore, the average particle size of the granules is 6.0.
It is clear that mm or less is more preferable.

In addition, when the capacitor element was burned out due to short-circuit failure, it was measured whether or not the electrode member was melted and deformed. As a result, no deformation was observed in Examples 1 to 16 and Comparative Example 2, but Comparative Example 1
In the case of it was deformed.

[0026]

As described above, according to the manufacturing method of the present invention, one end of the anode lead wire is embedded, and the valve metal powder is sintered to form a sintered body. After sequentially forming the oxide film and the cathode layer, and before forming the exterior, the cathode layer side of the capacitor element is brought into contact with an electrode member made of a lump of ceramic granular material provided with a metal plating film on the surface, thereby forming the capacitor element. Since a positive voltage is applied to the capacitor, leakage current characteristics and the like can be improved, defects can be reduced, and a highly reliable solid electrolytic capacitor can be obtained.

[Brief description of the drawings]

FIG. 1 shows a process chart of an embodiment of the present invention.

FIG. 2 is a structural diagram showing a state in which a voltage is applied to a capacitor element after a metal layer is formed according to the embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sintered body, 2 ... Lead wire for anode, 4, 10 ... Metal plate, 5 ... Oxide film, 6 ... Conductive layer, 7 ... Carbon layer,
8: Silver layer, 9: Capacitor element 15: Exterior, 16: Solid electrolytic capacitor. Reference number P2469

Claims (1)

[Claims] A sinter is formed by sintering a valve metal powder by embedding one end of an anode lead wire, forming an oxide film and a cathode layer on the sintered body in order, and covering the exterior. In the method for manufacturing a solid electrolytic capacitor, the cathode layer of the capacitor element is brought into contact with an electrode member formed of a lump of ceramic granular material provided with a metal plating film on the surface after forming the cathode layer and before forming the exterior. Performing a process of applying a positive voltage to the capacitor element.