JPS6053454B2 - Manufacturing method of sintered capacitor element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a capacitor element for an electrolytic capacitor in which metal powder having a valve action is sintered into a porous shape.

Generally, an electrolytic capacitor element is manufactured by molding and sintering a metal powder having a valve action, such as tantalum, niobium, or aluminum, into a porous shape.

For example, this manufacturing was conventionally performed as follows. First, an organic binder such as camphor is mixed with the metal powder at a ratio of about 1 part to 3% by weight via a solvent.

Then, a predetermined amount of this mixture powder is put into a mold having a cylindrical cavity, and a metal wire having a valve action is planted in the mixture powder in the cavity. Next, the mixture powder in the cavity is press-molded using upper and lower molding punches, and as shown in FIG. 1, a capacitor element 2 formed by press-molding the mixture powder onto a metal wire 1 is obtained. Note that metal powder alone has poor fluidity, and therefore it is very difficult to automatically introduce a certain amount of metal powder alone into the cavity of a mold. However, if a binder is mixed with the metal powder, the fluidity will improve and the above operations will become smoother.

This is one reason why a binder is mixed into the metal powder. Next, the pressure-molded capacitor element 2 has a diameter of approximately 70 mm.
It is pre-sintered at a low temperature of 00 to 800°C, during which most of the binder and solvent are scattered and removed.

Then, main sintering is performed in vacuum at a high temperature of 1400 to 2000'C to obtain a porous sintered body made of metal powder. In other words, as the binder scatters, the portions of the binder that were present become pores, thereby obtaining a porous sintered body. This is another reason to mix the binder into the metal powder. After that, the sintered body is immersed in a chemical liquid and energized to form an oxide film on the entire surface of the sintered body, then immersed in a semiconductor mother liquor such as manganese nitrate solution, and then thermally decomposed. A semiconductor layer is formed on the oxide film.

Furthermore, an electrode lead layer consisting of a polymerized layer of a graphite layer and a silver paste layer is formed on this semiconductor layer, a negative external lead wire is soldered to this electrode lead layer, and a positive external lead wire is soldered to the metal wire 1 described above. are welded, and then the entire capacitor element is sheathed with resin. By the way, the capacitor element which has undergone the above-mentioned firing, chemical formation and thermal decomposition has a sintered structure as shown in FIG.

That is, T is applied to the surface of the metal sintered body 3, such as Ta, which has a valve action.
An oxide film 4 is formed on a2O5, etc., and Mn is further formed on it.
A semiconductor layer 5, such as O2, is deposited. In addition, 6 in FIG. 2 are pores after the binder has been scattered, and the chemical solution and semiconductor mother liquid penetrate into the interior through these pores 6, and the oxide film 4 and semiconductor layer 5 are formed inside. become. However, in reality, all binders do not scatter during sintering.
In particular, as shown in FIG. 3, the binder inside the element sometimes became an impurity of carbon 7 and adhered to the metal sintered body 3 during the main sintering. In this case, the oxide film 4 may not be formed on the surface of the metal, and only the semiconductor layer 5 may be formed, so at this carbon 7, the semiconductor layer 5 on the negative electrode side and the metal sintered body 3 on the positive electrode side. A short circuit occurred, which worsened the capacitor's leakage current characteristics. or,
In order to improve this leakage current, it is necessary, for example, to increase the degree of vacuum and perform sintering at high temperature for a long time, which reduces equipment capacity. Another drawback was that the capacity was reduced due to baking at high temperatures. In order to solve these problems, for example, Japanese Patent Publication No. 52-50381 discloses a method in which a metal powder having a valve action is mixed with an insulating oxide powder such as aluminum oxide, silicon dioxide, titanium oxide, etc., and the mixture is press-molded. , discloses a method for manufacturing an electrolytic capacitor that undergoes chemical conversion treatment without sintering.

According to this method, since oxide powder that does not need to be removed is used instead of the binder, it is possible to increase the capacitance of the capacitor and improve leakage current. Since the element is not sintered, cracks and chips are likely to occur during the manufacturing process, which remains a problem that must be resolved.

The present invention is an improvement on the above-mentioned conventional drawbacks, and will be described below.

The present invention is a method in which no binder is used at all, and a mixture of a metal powder having a valve action and a metal oxide powder having a valve action is used as the raw material powder.

The ratio of this metal powder to its oxide powder is 1:0.1~0
．． 5 weight ratio. The method of the present invention will now be described in the case where the metal powder is Ta (tantalum) powder and the metal oxide powder is powder. First, Ta powder vs. Ta2
The O5 powder is mixed at a weight ratio of 1:0.1 to 0.5.

In addition, although Ta powder alone has poor fluidity, 'Ta2
By mixing O5 powder, the fluidity of the mixed powder is improved. Therefore, it becomes easy to automatically supply a certain amount of metal powder to the mold. In other words, Ta2O5 powder acts in the same way as a conventional binder. Next, when the pressure molding of the mixed powder is completed, the molded product is main sintered at once without pre-sintering, that is, in a vacuum at about 1700C for about 30 minutes.
Sinter for a minute. At this time, the Ta2O powder is reduced and oxygen is scattered, and only the remaining Ta component is sintered together with the previous Ta powder. Then, the portion occupied by the oxygen ejected from the Ta2O5 powder remains as a space, and this space is formed as a part of the pore. In fact, this Ta2O
When the 5 powder is sintered and reduced, the volume of the sintered body that remains after reduction is reduced by about 20% compared to the volume before reduction, and this reduced volume remains as pores, resulting in a porosity that is lower than that of the conventional method. and the mechanical strength has also been significantly improved. Also, if Ta2
Even if a part of the α powder is not reduced and remains as Ta2O5, it is still an insulator, so even if a semiconductor layer is deposited on its surface in a later step, no short circuit problem will occur. Incidentally, post-processes such as chemical conversion treatment and thermal decomposition treatment are performed in the same manner as conventional methods.
Now, the powder is mixed at a weight ratio of 100 parts of Ta powder to 20 parts of Ta2O5 powder, and the diameter is 1. Due to the leakage current of the capacitor manufactured by planting a 0.5mφ metal wire with a height of 1.8m, pressure forming, and sintering, and chipping of the element after forming. When comparing the defect rate with conventional capacitors of the same size (using a binder), we obtained the results shown in the table below.

As is clear from this table, in the case of the present invention, since impurities such as carbon are not produced during the main sintering, the leakage current is reduced to about 1'3 compared to the conventional method.

In addition, since pores are created by the reduction of metal oxides such as Ta2O5, the pressure during pressure molding can be relatively large, which increases the mechanical strength of the sintered capacitor element and lowers the defective rate compared to conventional methods. It became about 113. In addition, it is best to mix the metal powder and metal oxide powder at a weight ratio of 1:0.1 to 0.5. If the weight ratio of the metal oxide powder is less than 0.1, it is too small and the mixed powder Good fluidity cannot be obtained.

Furthermore, if the weight ratio of the metal oxide powder exceeds 0.5, the mechanical strength of the element after sintering will be weakened and properties will likely deteriorate. Furthermore, as mentioned above, the metal powder having a valve action and the metal oxide powder having a valve action mixed therein are T.
In addition to the combination of a and Ta2O5, different combinations such as Ta and niobium oxide or titanium oxide may be used. As explained above, according to the present invention, since metal oxide powder is used in place of the conventional binder, a binder removal process such as preliminary sintering before main sintering can be omitted, and the number of steps can be simplified.

In addition, since metal oxides are insulators, they are reduced to metals during sintering, but even if some of the metal oxides are not reduced and remain, there is no risk of short circuiting as with binders. Therefore, leakage current can be improved. Furthermore, when a metal oxide is reduced to a metal, pores are formed in the pores that remain, making it possible to produce a porous capacitor element with a higher degree of porosity than conventional capacitor elements. Furthermore, since no binder is used,
It is possible to increase the pressure applied during pressure molding, thereby reducing problems such as chipping and cracking after molding, and reducing the defective rate.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a sintered capacitor element, FIG. 2 is an explanatory view of the inside of the element in a normal state after thermal decomposition, and FIG. 3 is an explanatory view of the inside of an abnormal location according to the conventional manufacturing method shown in FIG.

Claims (1)

[Claims] 1 A mixture of a metal powder having a valve action and an oxide powder of a metal having a valve action at a weight ratio of 1 to 0.1 to 0.5 is press-molded and then sintered. A method for manufacturing a sintered capacitor element characterized by reducing oxide powder during sintering.