JP2002222742A - Method of manufacturing electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing electrolytic capacitor by which dielectric layers can be formed advantageously in both cost and working efficiency. SOLUTION: In this method of manufacturing an electrolytic capacitor 1 in which the dielectric layers 3 are formed in the respective pores 20 of a porous conductor 2, sol-gel treatment which is performed for forming metal oxide layers by gelling a sol of a metal hydroxide by dehydrating the sol after the sol is impregnated in the conductor 2, and heat-treating the obtained gel is included in a step of forming the dielectric layers 3. Preferably, the dielectric layers 3 are formed by performing anodic oxidization on the conductor 2 after the sol-gel treatment. It is preferable to perform the dehydrating treatment and heat treatment in the same step by heating the porous conductor 2 impregnated with the sol for 0.5-2 hours at a temperature of 100-200 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electrolytic capacitor in which a dielectric layer is formed in each hole of a porous conductor.

[0002]

2. Description of the Related Art As an electrolyte capacitor, for example, there is a solid electrolyte capacitor as shown in FIG. In the solid electrolyte capacitor 1 shown in this figure, a dielectric layer 3 of, for example, Ta ₂ O ₅ is provided in each hole 20 of a porous sintered body 2 obtained by sintering a compact of a metal powder such as tantalum. And a solid electrolyte layer 4 of MnO ₂ . One end of a metal wire 5 as an anode is buried and integrated with the porous sintered body 2, and a buffer layer 6 and a metal layer 7 as a cathode are formed on the apparent surface of the porous sintered body 2. Is formed.

[0003] The dielectric layer 3 of such a capacitor 1 comprises:
Usually, the porous sintered body 2 is formed by anodizing (chemical formation). More specifically, as shown in FIG.
The phosphoric acid solution (0.01 to 1) held in the metal container 80
%), The porous sintered body 2 is immersed in a state where the porous sintered body 2 is supported via the SUS bar 81, and a current is passed between the porous sintered body 2 and the metal container 80. It is provided by forming an oxide film on the inner surface of each hole 20.

[0004]

The porous sintered body 2 includes:
As shown in FIG. 3, a constant current is applied until the voltage value reaches a predetermined value, and thereafter a constant voltage is applied. Therefore, the resistance value increases as the dielectric layer (oxide film) 3 grows, and the current flowing through the porous sintered body 2 decreases with time. Therefore, in the method of growing the dielectric layer 3 by anodic oxidation (chemical formation), the growth rate of the dielectric layer 3 decreases over time, so that it takes a long time to obtain the dielectric layer 3 having the desired dielectric constant. For example, it may take 10 hours or more, which is disadvantageous in terms of cost and work efficiency.

The present invention has been conceived under such circumstances, and provides a method of manufacturing an electrolytic capacitor capable of forming a dielectric layer advantageously in terms of cost and work efficiency. Is the task.

[0006]

DISCLOSURE OF THE INVENTION The present invention employs the following technical means to solve the above-mentioned problems. That is, the method for manufacturing an electrolyte capacitor provided by the present invention is a method for manufacturing an electrolyte capacitor in which a dielectric layer is formed in each hole in a porous conductor, and the step of forming the dielectric layer includes: After impregnating the porous conductor with a sol of a metal hydroxide, the porous conductor is subjected to a dehydration treatment to form a gel, and the gel is subjected to a heat treatment to form a metal oxide layer. I have.

[0007] The sol-gel treatment comprises the treatment of impregnating the porous conductor with the sol, gelling the sol, and heating the gel. In these processes, it is not necessary to energize the porous conductor as in anodic oxidation, so that the electric resistance of the dielectric layer does not affect the formation time of the dielectric layer. On the other hand, the total time of each treatment of sol impregnation, gelation of the sol, and heating of the gel is at most about several hours, and in order to achieve the desired dielectric constant, it is assumed that the sol-gel treatment is repeated. Also, the working efficiency is better than that of anodic oxidation.

The dielectric layer may be formed only by the sol-gel processing, or may be formed by performing the sol-gel processing and then performing the anodic oxidation of the porous conductor. In anodic oxidation, it takes a long time to grow a dielectric layer, but if it is used in reverse, fine control of the film thickness becomes possible. In other words, if the final step in the process of forming the dielectric layer is performed by anodic oxidation, the film thickness is roughly brought closer to the target value by sol-gel treatment, and then the film thickness is gradually reduced to the target value by anodic oxidation. , And precise control of the dielectric constant becomes possible.

Although the dehydration treatment and the heat treatment may be performed in separate steps, these treatments are preferably performed in the same step. In that case, the porous conductor impregnated with the sol may be heated at, for example, 100 to 200 ° C. for 0.5 to 2 hours. If the dehydration treatment and the heat treatment are performed in the same step, the time required for forming the dielectric layer can be further reduced.

As the metal hydroxide, for example, a hydroxide of a valve metal is used, and the porous conductor is formed, for example, by compressing and molding a valve metal powder and then sintering the powder. Is done. Valve metal includes, for example, tantalum, aluminum, and niobium.

[0011] Other advantages and features of the present invention will become more apparent from the following description of embodiments of the present invention.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be specifically described below with reference to FIG. Figure 1
The cross-section of the solid electrolyte capacitor to which the present invention is applied and its main part (the part circled in the figure)
Is shown in an enlarged scale.

In the solid electrolyte capacitor 1 shown in FIG. 1, a dielectric layer 3 and a solid electrolyte layer 4 are formed in each hole 20 of the porous conductor 2. One end of the metal wire 5 is buried and integrated with the porous conductor 2, and a buffer layer 6 and a metal layer 7 are formed on the apparent surface of the porous conductor 2.

The porous conductor 2 is formed by compressing a valve metal powder such as tantalum, aluminum or niobium into a rectangular parallelepiped and sintering it in a high vacuum state.

The dielectric layer 3 literally functions as a dielectric, and the capacitance of the solid electrolyte capacitor 1 is
It is determined by the total area and thickness of the dielectric layer 3.

Such a dielectric layer 3 can be formed by a sol-gel process. More specifically, the dielectric layer 3 is formed by impregnating the porous conductor 2 with a sol of a metal hydroxide and then performing a dehydration treatment to form a gel, and then heating the gel to form a metal oxide layer. Formed by

As the metal hydroxide, for example, it is preferable to use a hydroxide of the same kind of metal as the metal constituting the porous conductor 2. For example, a hydroxide of a valve metal such as tantalum, aluminum or niobium is preferably used. Is used.

It is efficient that the dehydration treatment and the heat treatment are performed in the same step. For example, the porous conductor 2 impregnated with the sol may be placed in an electric furnace maintained at 100 to 200 ° C. for 0.5 to 2 hours. It is performed by heating for about an hour. As a result, the metal hydroxide is dehydrated to obtain a metal oxide, which is attached to the inner surface of each hole 20 of the porous conductor 2.

The sol-gel treatment may be performed a plurality of times until the desired film thickness is obtained, or the sol-gel treatment may be performed to roughly bring the film thickness closer to the desired film thickness. After that, the target film thickness may be adjusted by anodic oxidation.

In the anodic oxidation, for example, a phosphoric acid aqueous solution (0.01 to 1%) is held in a metal container 80 functioning as a cathode as shown in FIG. 2, and the porous conductor 2 is immersed in the aqueous solution. In this state, current is supplied between the porous conductor 2 and the metal container 80. As described above, in anodic oxidation, as the formation of the dielectric layer 3 proceeds, the resistance value increases, and the formation speed of the dielectric layer 3 decreases.
Therefore, a dielectric layer 3 having a dielectric constant of, for example, 90 to 99% of a target dielectric constant is formed by sol-gel processing, and a dielectric layer 3 having a target film thickness is formed by anodic oxidation. By using the sol-gel treatment, the time for forming the dielectric can be shortened, and the dielectric layer having the desired dielectric constant can be obtained by gradually approaching the target film thickness by anodic oxidation. 3 can be formed more reliably.

The solid electrolyte layer 4 is provided by forming, for example, a manganese oxide layer (MnO ₂ ) in the hollow portion of the porous conductor 2 that remains after the formation of the dielectric layer 3. More specifically, the solid electrolyte layer 4
It is formed by performing a heat treatment after impregnating the porous conductor 2 with a manganese nitrate solution.

The impregnation and the heat treatment are preferably performed until each hole 20 in the porous conductor 2 is completely filled. For this purpose, the impregnation and the heat treatment are usually performed plural times.

The metal wire 5 functions as an anode, and is formed of, for example, the same kind of metal as the metal constituting the porous conductor 2. Such a metal wire 5
For example, when the porous conductor 2 is compression-molded, one end thereof is buried at the same time, or after the porous conductor 2 is compression-molded, one end is buried in the porous conductor 2 so that the porous conductor 2 is buried. It is integrated.

The buffer layer 6 is made of graphite or the like, and is provided for the purpose of reducing the resistance between the solid electrolyte layer 4 and the metal layer 7 when the contact resistance between them is large. For example, when the solid electrolyte layer 4 is made of MnO
_The buffer layer 6 is provided when the metal layer 7 is made of silver or the like. for that reason,
The buffer layer 6 is an optional one provided as needed.

The metal layer 7 functions as a cathode, and is provided by, for example, performing a plating process to form a conductor layer of silver or the like.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a solid electrolyte capacitor.

FIG. 2 is a schematic diagram for explaining a conventional method (anodic oxidation) for forming a dielectric layer of the solid electrolyte capacitor shown in FIG.

FIG. 3 is a time chart of an applied voltage and an anode (porous sintered body) current in the anodic oxidation described with reference to FIG. 2;

[Description of Signs] 1 solid electrolyte capacitor 2 porous conductor 20 holes (of porous conductor) 3 dielectric layer

Claims (5)

[Claims] 1. A method for manufacturing an electrolyte capacitor in which a dielectric layer is formed in each hole of a porous conductor, wherein the step of forming the dielectric layer comprises: A method for producing an electrolytic capacitor, comprising: a sol-gel treatment in which a conductor is impregnated, dehydrated to form a gel after being impregnated, and the gel is heated to form a metal oxide layer. 2. The method for producing an electrolytic capacitor according to claim 1, wherein in the step of forming the dielectric layer, the porous conductor is anodized after performing the sol-gel treatment. 3. The dehydration treatment and the heat treatment are performed in the same step by heating the porous conductor impregnated with the sol at 100 to 200 ° C. for 0.5 to 2 hours. 3. The method for producing an electrolyte capacitor according to claim 1. 4. The method according to claim 1, wherein said metal hydroxide is a hydroxide of a valve metal. 5. The method for manufacturing an electrolytic capacitor according to claim 1, wherein said porous conductor is formed by sintering a valve metal powder after compression molding.