JPS6035816B2 - Manufacturing method of solid electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for manufacturing a solid electrolytic capacitor.

In general, a solid electrolytic capacitor is a capacitor element A made by press-molding a metal powder having a valve action such as tantalum, niobium, aluminum, etc. into a cylindrical shape, as shown in Figures 1 and 2. A metal wire having a pre-effect is placed in a tub as an anode lead B, and a first external lead member C is welded to the protruding portion of this anode lead B.
The second external lead part D is soldered to the electrode lead layer formed on the outer surface of the capacitor element A via the oxide layer E, the semiconductor layer F, and the graphite layer G, and then the capacitor element The entire circumferential surface of A is covered with a resin material K.

By the way, this capacitor element A is manufactured by a process in which a required amount of a mixed powder consisting of a metal powder having a valve action, an organic binder such as camphor, and a solvent is supplied to a molding die, and then pressure-formed using upper and lower punches. Body 700-80
It is made porous through a step of preliminary sintering at a temperature of 0° C. to remove the binder and solvent, and then a main bonding step in a vacuum at a high temperature of 1,400 to 2,000° C.

However, most of the binder in capacitor element A is removed during the preliminary binding process and the main binding process, but a small portion of it remains as carbon M, as shown in Figure 2. It's facing the mirror.

However, unlike the metal powder constituting the capacitor element A, this carbon M has no valve action at all, and therefore the oxide layer E cannot be formed on the surface of the capacitor element A during the chemical conversion treatment.

Furthermore, since the carbon M is in close contact with the surface of the metal powder a, the oxide layer E cannot be formed on the portion of the metal powder a where the carbon M is in close contact. Therefore, when a semiconductor layer F, a graphite layer G, etc. are polymerized and formed on carbon M, the semiconductor layer F having a cathode function is formed by carbon M.
Since the capacitor is resistively connected to the metal powder a having an anode function through the capacitor, there is a problem in that leakage current increases during operation, and the characteristics and reliability of the capacitor are impaired.

For this reason, in order to completely remove the binder of the condensation element A so that no carbon M remains as a residual component, attempts have been made to raise the dawning temperature even higher or to lengthen the dawning time. However, since carbon M has a high boiling point, it is extremely difficult to remove it within the normal vacuum temperature range.

In view of these points, the present invention provides a method for manufacturing a solid electrolytic capacitor that can easily and effectively remove carbon residue from a capacitor element without making any particular changes to firing conditions. A manufacturing method will be explained.

First, a required amount of mixed powder consisting of a metal powder with a valve action, an oxide of the metal powder with a valve action, an organic binder, and a solvent is supplied to a forming die, and the mixture is press-formed into a cylindrical shape using upper and lower punches. .

Next, this molded body is set in a vacuum condensation furnace, and the furnace temperature is set to 700 to 80,000. Then, most of the binder and solvent in the molded body are removed. Next, the furnace temperature is raised to 1,400 to 2,000 oo and the main competition is carried out. At this time, the oxide of the metal powder having a valve action is thermally decomposed into pure metal and oxygen, resulting in a slight oxygen atmosphere inside the molded body. A part of the oxygen reacts with the remaining carbon, resulting in C○,
C02 gas is produced. This gas is removed together with oxygen from the molded body through the pongee hole into the vacuum system. After cooling, the condenser element is obtained by taking it out from the phosphorization furnace. In this way, the metal powder with valve action contains an appropriate amount of oxide of the metal powder with valve action, so even if the binder is not removed sufficiently in the preliminary sintering process and carbon remains. In the main sintering process, metal oxide powder reacts with oxygen due to thermal decomposition, resulting in C○
, can be easily removed as CO2 gas.

Therefore, resistance connection due to carbon between the semiconductor layer and the metal powder can be prevented, and leakage current characteristics can be improved. In particular, carbon residue in the capacitor element is gasified and removed using oxygen generated by thermal decomposition of metal oxide powder, so the sintering temperature must be raised or the sintering time lengthened. There's no need.

Therefore, it is not only possible to streamline the freezing work, but also to maintain good porosity of the capacitor element.
Desired capacitor characteristics can be obtained. In this regard, the present inventor uses tantalum powder (Ta powder) as the metal powder.
Various mixed powders using tantalum oxide (Ta205) as the metal oxide powder, mixing 3% by weight of Vanida with Ta powder, and mixing Ta2Q powder in a range of 0 to 2% by weight with respect to Ta powder. A 20V, 22rF capacitor was manufactured using a conventional method, and its leakage current characteristics were measured, and the results shown in FIG. 3 were obtained.

As is clear from the figure, the leakage current characteristics are improved by mixing Ta23 powder with Ta powder.

In particular, the improvement effect is remarkable when the mixed amount is 2% or more, and while the conventional product (0%) has an output of 1.3 rA, the product of the present invention has reduced it by half to 0.6 rA. In addition, the binder T
No significant difference was observed in the leakage current characteristics even when the amount mixed with respect to the a powder was varied in the range of 1 to 5% by weight.

This is considered to be due to the fact that most of the binder is removed during the preliminary sintering process. However, Ta20
If the mixed amount of the 5 powder exceeds 2% by weight, it will take a long time to remove the decomposed oxygen in the vacuum system, resulting in a decrease in workability, which is undesirable.

Therefore, the proportion of Ta205 powder in Ta powder is 2~
A weight percent of 2 is preferred. In addition, in the present invention, the metal powder having a valve action can be an alloy in addition to a single metal, and the metal oxide powder may be an oxide of a metal having a valve action different from the metal powder. can do.

As described above, according to the present invention, by mixing the oxide of the metal powder that has a valve action, the force of the binder can be gasified and removed easily and reliably, so that the leakage current characteristics can be effectively reduced. can be improved.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of a conventional solid electrolytic capacitor, FIG. 2 is an enlarged sectional view of the main part of FIG. 1, and FIG. 3 is a characteristic diagram of changes in leakage current with respect to the amount of oxide mixed in tantalum powder. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A solid that is characterized in that a mixed powder containing a metal powder having a valve action, an oxide of the metal powder having a valve action, an organic binder, and a solvent is pressure-molded into a desired shape and sintered in a vacuum. Method of manufacturing electrolytic capacitors.