JP2007311629A - Method for manufacturing solid-state electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that in the case where, when a solid-state electrolytic capacitor is manufactured, a dielectric film covering near a surface of a sintered body is selectively thickly formed, and a basic anode oxidizing liquid is used in an anode oxidizing process for preventing a deterioration of a leakage current characteristic caused by a damage of the dielectric film occurred by a stress or mechanical stress, in a cathode forming process or armoring process without reducing a capacity of a capacitor, a conductivity of the anode oxidizing liquid is easy to reduce by a volatilization of an ammonia group in the anode oxidizing liquid, the dielectric film is not stably formed, and variations of an electric characteristic occur. <P>SOLUTION: In a step of forming the dielectric film in a porous sintered body composed of a metal having a valve action, this step contains the steps of: anode-oxidizing by use of a basic solution having a temperature of 30-50°C, and anode-oxidizing by use of an acid solution. It is preferable that this basic solution has a pH of 8-10. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a solid electrolytic capacitor used in various electronic devices, and more particularly to an improvement in a method for anodizing a solid electrolytic capacitor.

A conventional solid electrolytic capacitor pressurizes a metal powder having a valve action such as tantalum or niobium to form a porous molded body, and sinters the porous molded body to form a porous sintered body. In this porous sintered body, a dielectric film is formed, and a solid electrolyte layer made of a conductive polymer or manganese dioxide as a cathode, a graphite layer as a cathode lead layer, a cathode silver layer, and the like are sequentially formed. .
In general, when forming the dielectric film, the porous sintered body is immersed in an acidic electrolyte solution such as phosphoric acid, which is an anodizing solution maintained at 60 to 80 ° C., and a voltage is applied in the electrolyte solution. The method of forming by this was used.

  On the other hand, since the dielectric film is very thin and easily damaged, the dielectric film on the surface of the sintered body is damaged by the stress and mechanical stress in the cathode forming process and the exterior process, resulting in deterioration of leakage current characteristics. is there.

In order to solve the above problem, the dielectric film is formed thick by using a basic anodic oxidation solution maintained at 60 to 80 ° C., so that the dielectric is generated by stress or mechanical stress in the cathode forming process or the exterior process. It is known that leakage current characteristics can be prevented from deteriorating due to damage to the film. (For example, see Patent Document 1)
Japanese Patent Laid-Open No. 58-190016

However, in the above conventional method, since the base contained in the basic anodic oxidation solution volatilizes, the conductivity of the anodic oxidation solution decreases with time, and the dielectric film is not stably formed. However, the dielectric film formed of the anodized liquid with reduced conductivity has a problem that the leakage current value is deteriorated.
The present invention solves the above-mentioned conventional problems, and forms a dielectric film stably and thickly, and leak current characteristics due to damage to the dielectric film caused by stress or mechanical stress in the cathode forming process or the exterior process. The purpose of the present invention is to provide a method for producing a solid electrolytic capacitor having a small leakage current when a solid electrolytic capacitor is used over a long period of time even when a basic anodizing solution is used for a long time It is what.

The method for producing a solid electrolytic capacitor of the present invention capable of solving the above-mentioned problem is that a dielectric film, a solid electrolyte layer, and a cathode lead are formed on a porous sintered body obtained by pressure-molding and sintering a valve action metal powder. A method for producing a solid electrolytic capacitor including a capacitor element in which layers are sequentially formed,
The step of forming the dielectric film by anodic oxidation of the method includes a step of performing anodic oxidation using a basic solution and a step of performing anodic oxidation using an acidic solution.

  The present invention is also characterized in that, in the method for producing a solid electrolytic capacitor having the above-described characteristics, the temperature of the basic solution is 30 to 50 ° C.

  Furthermore, the present invention is characterized in that, in the method for producing a solid electrolytic capacitor having the above-described characteristics, the pH of the basic solution is 8 to 10.

  The present invention is also characterized in that, in the method for producing a solid electrolytic capacitor having the above-described characteristics, the basic solution contains ammonium borate or ammonium carbonate.

According to the method for manufacturing a solid electrolytic capacitor of the present invention, the above-described conventional problems can be solved. In other words, after anodizing with a basic solution and then anodizing with an acidic solution, the dielectric film can be stably and thickly formed. It is possible to stably prevent the deterioration of the leakage current characteristic due to the damage of the generated dielectric film.
Therefore, a solid electrolytic capacitor having a small leakage current can be obtained even when the basic anodizing solution is used for a long period of time.

Hereinafter, each process in the manufacturing method of the solid electrolytic capacitor of this invention is demonstrated.
First, a porous sintered body was produced by sintering a porous molded body formed by pressing metal powder having a valve action such as tantalum or niobium.

Then, anodic oxidation is performed using a basic solution having a temperature of 30 to 50 ° C., which is a first step of forming the dielectric film by anodizing the surface of the metal having a valve action.
At this time, when the temperature of the basic solution is lower than 30 ° C., the leakage current tends to increase. Conversely, when the temperature of the basic solution is higher than 50 ° C., the solid electrolytic capacitor is used for a long time. It is not preferable because the leakage current value tends to be high when used over a wide range. In the present invention, as the basic solution, for example, ammonium borate, ammonium carbonate, and ammonium succinate are preferable, and the conditions for anodization are preferably in the range of 35 to 40 ° C., 10 to 150 V, and 5 to 120 seconds.

Furthermore, anodization is performed using an acidic solution, which is the second step.
In general, anodization is performed under conditions of 40 to 90 ° C., 6 to 140 V, and 0.5 to 10 hours. As the acidic solution, phosphoric acid, nitric acid, adipic acid, citric acid, acetic acid, succinic acid, tartaric acid, and boric acid are suitable.
EXAMPLES Hereinafter, although an Example of this invention is given and this invention is demonstrated, this invention is not limited to these.

[Example 1]
After the porous molded body obtained by pressure-molding tantalum powder is vacuum-sintered at a high temperature, a voltage is applied as an anodizing solution in an aqueous ammonium borate solution having a temperature of 30 ° C. and a pH of 8, and an elapsed time of 0 h. 60 V was applied for 30 seconds to anodize the porous sintered body.
Subsequently, an anodic oxidation voltage of 20 V was applied in an aqueous phosphoric acid solution for 3 hours to further form a dielectric film made of an acidic solution on the dielectric film made of a basic solution, and impregnated with an aqueous manganese nitrate solution. Thermal decomposition at 400 ° C. was repeated a plurality of times to sufficiently form a manganese dioxide layer on the dielectric film.
Furthermore, it was immersed in a graphite liquid in which graphite powder was suspended, dried in a thermostatic bath, and then immersed and dried in a silver paste to form a cathode lead layer to constitute a capacitor element.

  Thereafter, the anode lead wire and the anode terminal are connected by welding, the cathode lead layer forming the capacitor element and the cathode terminal are connected by a conductive adhesive, and then transfer molding is performed, so that the chip-type tantalum solid electrolytic capacitor is 100. Individually produced.

[Example 2]
A chip type tantalum solid electrolytic capacitor of Example 2 was obtained in the same manner as in Example 1 except that the ammonium borate aqueous solution used for 168 h was used as the anodizing solution.

[Example 3]
A chip-type tantalum solid electrolytic capacitor of Example 3 was obtained in the same manner as in Example 1 except that the temperature of the anodic oxidation solution was 50 ° C. and an aqueous ammonium borate solution used for 168 h was used.

[Example 4]
A chip-type tantalum solid electrolytic capacitor of Example 4 was obtained in the same manner as in Example 1 except that an anodic oxidation solution was an ammonium borate aqueous solution having a pH of 10 and 168 hours passed.

[Example 5]
After producing the porous sintered body, the same procedure as in Example 1 was performed, except that anodic oxidation was performed using an aqueous ammonium carbonate solution after 168 hours as the anodizing solution in the first step. 5 chip-type tantalum solid electrolytic capacitors were obtained.

[Conventional example 1]
As an anodic oxidation step using a basic solution, an aqueous solution of ammonium borate having a liquid temperature of 60 ° C. was used, and the anodization step using an acidic solution was not performed. The chip type tantalum solid electrolytic capacitor was obtained.

[Conventional example 2]
The chip type tantalum solid electrolytic capacitor of the conventional example 2 is manufactured by the same means as the conventional example 1 except that the aqueous solution of ammonium borate which has passed 168 hours in the anodizing tank is used as the anodic oxidation step with the basic solution. Obtained.

[Comparative Example 1]
A chip type tantalum solid electrolytic capacitor of Comparative Example 1 was obtained in the same manner as in Example 1 except that an aqueous solution of ammonium borate having a liquid temperature of 20 ° C. was used.

[Comparative Example 2]
A chip type tantalum solid electrolytic capacitor of Comparative Example 2 was obtained in the same manner as in Example 1 except that an ammonium borate aqueous solution having a pH of 7 was used.

[Comparative Example 3]
A chip type tantalum solid electrolytic capacitor of Comparative Example 3 was obtained in the same manner as in Example 1 except that an aqueous ammonium borate solution having a pH of 11 was used.

  Table 1 shows the results of comparing the average values of the leakage current values after 2000 hours for the chip-type tantalum solid electrolytic capacitors of the above examples and comparative examples at the initial time and high temperature load (85 ° C./RV).

As is clear from Table 1, Examples 1 and 2 were able to obtain good leakage current values as compared with Conventional Examples 1 and 2. This is because the basic anodic oxidation solution is kept at 30 ° C., so that less base is volatilized in the anodizing tank for a long time than when kept at 60 ° C., and the anodic oxidation by the basic solution is performed. This is probably because an anodic oxide film was formed on the film with an acidic solution.
Moreover, even if anodization is performed using a solution that has passed for a long time after fabrication, a good leakage current value can be obtained, and the superiority of the present invention has been demonstrated.

Further, as is clear from Table 1, Example 5 was able to obtain characteristics with substantially the same leakage current value as compared with Example 2.
Therefore, it was demonstrated that the effect of the present invention can be obtained by using any basic anodizing solution of ammonium borate solution or ammonium carbonate solution.

  Further, as is clear from Table 1, the leakage current value of Example 1 was better than that of Comparative Example 1. Therefore, it was demonstrated that better characteristics can be obtained by holding the basic anodic oxidation solution at 30 ° C. than at 20 ° C.

  As is clear from Table 1, Example 1 and Example 4 had better leakage current values than Comparative Example 2 and Comparative Example 3. Therefore, it was demonstrated that the dielectric film is stably formed and good characteristics can be obtained by setting the pH of the basic anodizing solution to 8 to 10.

  In this example, tantalum was used as the metal having a valve action, but it was confirmed that the same effect as in the case of tantalum can be obtained even in the case of a metal having a known valve action such as niobium or aluminum. It was.

Claims (4)

A method of manufacturing a solid electrolytic capacitor including a capacitor element in which a dielectric film, a solid electrolyte layer, and a cathode lead layer are sequentially formed on a porous sintered body obtained by pressure-molding and sintering a valve action metal powder. And
The step of forming a dielectric film by anodic oxidation of the method includes a step of performing anodic oxidation using a basic solution and a step of performing anodic oxidation using an acidic solution. Manufacturing method. 2. The method for producing a solid electrolytic capacitor according to claim 1, wherein the temperature of the basic solution is 30 to 50 ° C. 3. The method for producing a solid electrolytic capacitor according to claim 1, wherein the pH of the basic solution is 8 to 10. The method for producing a solid electrolytic capacitor according to claim 1, wherein the basic solution contains ammonium borate or ammonium carbonate.