JP3388639B2 - Manufacturing method of capacitor element - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a sintered body element used in an electrolytic capacitor using a valve metal such as tantalum or niobium.

[0002]

2. Description of the Related Art Fine particles of a valve metal are most effective for increasing the capacity of a capacitor, and a method for increasing the surface area of the valve metal is known.

As the surface area of the valve metal increases, the natural oxide film and adsorbed oxygen on the surface of the valve metal increase, so that the oxygen concentration of the whole sintered body element increases.

When the oxygen concentration of the sintered body element is increased, the mechanical strength of the valve action metal wire for drawing out the electrode is deteriorated and the defective portion of the dielectric oxide film is increased.
It is known that leakage current becomes high.

Further, if the strength of the wire-embedding portion is weak, there is a problem that leakage current becomes high. Therefore, after the wire is welded once after the sintering, the wire is re-sintered, whereby the sintered body and the wire There is known a technique for improving the binding force of.

In the capacitor element for welding the wire, the oxygen concentration increases during the wire welding, and the leakage current increases greatly as the valve action metal becomes finer as described above. Therefore, the wire should be welded. Was not possible from the aspect of characteristics.

[0007]

There is a positive correlation between the number of defective portions and the leakage current as shown in FIG. 1, and the more defective portions, the higher the leakage current. In addition, the larger the number of defective portions, the worse the result of the life test, such as an increase in leakage current.

The oxygen concentration and the leakage current of the sintered body element, and the oxygen concentration and the mechanical strength of the valve action metal wire have a correlation as shown in FIGS. That is, when the oxygen concentration of the sintered body element is high, the leakage current increases and the mechanical strength of the valve action metal wire deteriorates.

On the other hand, the oxygen concentration of the sintered body element is proportional to the surface area of the valve action metal powder or the surface area of the sintered body element. The oxygen concentration of the body element is increased.

In order to solve the above problems, the present invention reduces the oxygen concentration of the sintered body element to improve the mechanical strength of the valve action metal wire and to improve the defective portion of the dielectric oxide film. The purpose is to reduce leakage current, improve withstand voltage, and improve reliability of life test.

[0011]

[Means for Solving the Problems] In order to achieve the above object,
In the method for producing a sintered body element according to the present invention, the element formed of the valve action metal powder is sintered in vacuum after removing the binder used in the forming process in vacuum if necessary. Thereafter, the valve action metal wire is welded, the sintered body element is reduced with a reducing material, the reducing material is acid-cleaned, and then again sintered in vacuum at a temperature higher than the temperature at the time of reduction. Composed.

[0012]

By carrying out the reduction treatment of the present invention as described above, a sintered body element having a low oxygen concentration can be obtained, and as a result, the mechanical strength of the valve action metal wire is improved and the leakage current characteristic of the capacitor is improved. Can be improved. Further, after the reduction of the present invention, if the acid cleaning is not carried out, the reducing material remains and the leakage current characteristic is deteriorated.

[0013]

[Embodiment 1] An embodiment of the present invention will be described below.

Tantalum powder-150 mg is 3.0 mmφ × 4.5 mm
After pressure molding into a cylindrical shape, the molded element was sintered at 1350 ° C for 10 minutes in a vacuum of 0.0133 Pa or less, and then tantalum wire was resistance-welded, and sintered with 2% by weight of magnesium relative to the element weight. Put the element in a sintering dish, 1000 ℃ in a vacuum of 0.133Pa or less.
Was heat-treated for 60 minutes to reduce oxygen in the device.

After that, the element was acid-washed with sulfuric acid and then again.
Sintering was performed at 1350 ° C. for 10 minutes in a vacuum of 0.0133 Pa or less. still,
The acid cleaning may be performed with nitric acid, hydrochloric acid or the like.

The sintered element was held at 50 V for 2 hours by the method shown in EIAJ RC-2361 (Japan Electronic Machinery Manufacturers Association Standard) for anodic oxidation to form a dielectric oxide film. Then, a voltage of 35 V was applied to the thus constituted capacitor element, the capacitor element was charged for 2 minutes, and then the leakage current was measured. Further, the relationship between the bending strength of the tantalum wire and the oxygen concentration of the sintered element was measured.

The results are shown in Table 1.

[0018]

[Table 1]

As is clear from the results of Table 1, the sintered body element subjected to the reduction treatment of the present invention has improved leakage current characteristics in the liquid and bending strength of the tantalum wire as compared with the conventional method. . Also, the oxygen concentration of the sintered element is reduced.

Thereafter, a semiconductor layer, a carbon layer, and a silver layer are sequentially formed on the dielectric oxide film, and then a cathode lead for external extraction and an anode lead are drawn out, and then an outer package. Resin was applied to form a tantalum electrolytic capacitor.

Then, this tantalum electrolytic capacitor 12
The sample was subjected to a high temperature load life test of applying 5 V at 16 V for 1000 hours. The result is shown in FIG. As is clear from FIG. 4, 10
After 00 hours, the leakage current of the tantalum electrolytic capacitor using the conventional sintered body element is increased 10 times, but the tantalum electrolytic capacitor using the sintered body element of the embodiment of the present invention leaks. It has been demonstrated that there is little increase in current, which improves the reliability of the high temperature load life test.

In the present embodiment, the binder was not mixed with the tantalum powder when the molded element was manufactured. However, when the binder was mixed to improve the moldability, the binder was pressed after the pressure molding. It is advisable to perform reduction after removing − in vacuum and then performing sintering. Further, even if the sintering is performed at a temperature equal to or lower than the reduction temperature, magnesium remains in the tantalum element, resulting in poor leakage current characteristics.
In order to remove magnesium in the tantalum element, it is preferable to sinter at a temperature higher than the reduction temperature. Although magnesium was used as the reducing material in the examples, the same effect can be obtained by using aluminum.

[0023]

As described above, the capacitor of the present invention can significantly improve the mechanical strength of the tantalum wire and the leakage current characteristics as compared with the conventional manufacturing method, and the high temperature in an actual product can be improved. The reliability when subjected to the load test can be remarkably improved. Further, in the present invention, since the valve action metal wire is reduced after being welded, the increase in oxygen concentration of the element at the time of welding can be reduced and the capacitor element having better leakage current characteristics can be manufactured.

[Brief description of drawings]

FIG. 1 is a relationship diagram between the number of defects in a dielectric oxide film of a capacitor element and a leakage current.

FIG. 2 is a diagram showing the relationship between the oxygen concentration of a sintered body element and the leakage current of a capacitor element.

FIG. 3 is a diagram showing the relationship between the oxygen concentration of the sintered body element and the number of bendings of the valve action metal wire.

FIG. 4 is a leakage current characteristic result diagram in a high temperature load test.

Front Page Continuation (72) Fumio Katayama Inventor Fumio Katayama 4th floor, Uehara Building, 3rd floor, Uehara Building, No. 191, Nakaboricho, Oike Dori, Kaikemaru Higashiiri, Nakagyo-ku, Kyoto (56) , A) JP-A-4-223318 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01G 9/00 H01G 9/052

Claims (2)

(57) [Claims] 1. A valve-acting metal powder is pressure-molded, then sintered in a vacuum, and a valve-acting metal wire for drawing out an electrode is welded to form a sintered body element. A method for manufacturing a capacitor element, which comprises reducing the material using a reducing material and then performing sintering again in a vacuum and at a temperature higher than the temperature at the time of reduction. 2. The method of manufacturing a capacitor element according to claim 1, wherein after the reduction, the reducing material attached to the capacitor element is washed with an acid and then sintered again.