JPH0614502B2 - Sintered barium titanate capacitor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact and large capacity sintered barium titanate capacitor using barium titanate as a dielectric.

2. Description of the Related Art Recently, a sintered barium titanate capacitor, which uses an anode body obtained by sintering titanium metal powder and performs chemical conversion treatment on this anode body in an aqueous solution of barium hydroxide to form a barium titanate dielectric, has been announced. , The dielectric constant of this capacitor is 30
Since it is 0 or more, and a capacity about 10 times that of a conventional tantalum capacitor can be obtained, it has been noted that the size can be reduced to about 1/8 to 1/5.

Problems to be Solved by the Invention It is conceivable that manganese dioxide is formed as a counter electrode on a barium titanate dielectric in the same manner as in a tantalum capacitor in this capacitor. After impregnation with the sintered body, it is necessary to thermally decompose and bake at a temperature of 250 to 300 ° C. At this time, since the dielectric film deteriorates,
After baking the manganese dioxide, it is necessary to restore the film in the re-formation process while applying the voltage again in the barium hydroxide aqueous solution. Also, in order to impregnate the details of the porous sintered body with the manganese nitrate solution, the work of initially impregnating with a dilute solution and then thermally decomposing, and then impregnating with a concentrated solution and thermally decomposing several times are repeated. The workability was poor in the number of steps.

Means for Solving the Problems The present invention is characterized by using corodyl carbon as a counter electrode without using manganese dioxide.

In the capacitor of the present invention, when a DC voltage is applied to an anode body obtained by sintering titanium metal powder in a pressure vessel containing a barium hydroxide aqueous solution, a barium titanate dielectric film is formed on the surface of the anode body. This anode body is immersed in an aqueous suspension of colloidal carbon and degassed under reduced pressure. After defoaming, it is dried, then immersed in a silver paste and dried to form a silver electrode on the surface of carbon.

When the titanium metal powder used has a fine particle size, the carbon concentration is adjusted as necessary, and the application is repeated a plurality of times. The colloidal carbon is preferably 1.0 μm or less, and it is preferable to use an aqueous suspension prepared by adding an adhesive such as carboxymethyl cellulose as a binder and adding alcohol or ammonia water as a dispersant. If the amount of adhesive is small, the characteristics of the capacitor will be weakened by mechanical and thermal stress, and if it is too large, the electrical resistance will be large and the tan δ and impedance characteristics will be poor. The silver paste may be a commercially available one, but the binder is preferably a thermoplastic one rather than a thermosetting one. After applying the silver paste, a resin mold or resin dip exterior can be applied as in a general capacitor.

Example After molding a titanium metal powder, the anode body 1 sintered in vacuum was immersed in a Ba (OH) ₂ aqueous solution (concentration 0.2 N) to
Applying DC voltage at 20 ℃ and 2 atm, current 200m
A, flow for 60 minutes and form a dielectric film 2 of BaTiO _{3 on} the surface of titanium. A titanium wire 8 is embedded in the anode body 1 at the time of molding, and serves as a power supply terminal when a DC voltage is applied, and serves as a connecting wire for an anode lead terminal 9 of a capacitor.

The dielectric film 2 is formed up to the inside of the porous anode body 1,
Immersing this anode body 1 in an aqueous suspension of colloidal carbon,
Immerse under reduced pressure. This colloidal carbon water suspension suspends carbon particles (0.5% by weight) of 1 μm or less in a 2% aqueous solution of methyl cellulose. At this time, in order to improve the dispersibility, a small amount of ammonia water is dropped and PH8-9 is added.
Adjust to.

The concentration of methyl cellulose and the concentration of colloidal carbon may be appropriately adjusted depending on the size of the anode body, the porosity, and the size of the pores.

After soaking in colloidal carbon, it is dried at 150 ° C. for 20 minutes, and impregnation and drying are repeated a plurality of times as necessary to form the carbon layer 3. Silver paste 4 on this carbon layer 3
Is dried, and the cathode lead wire 7 is brought into close contact with the capacitor element and fixed with solder 5. Thereafter, the entire capacitor element is dipped in a liquid epoxy resin to form the outer package 6.

The characteristics of the 33 μF capacitor manufactured as described above and the conventional capacitor are shown in the table below.

Effects of the Invention In the capacitor of the present invention, by using colloidal carbon as the counter electrode of the capacitor, the manganese dioxide baking step in the tantalum capacitor can be omitted and tan δ can be improved.

Comparing the conventional manganese dioxide baking process with the carbon coating process of the present invention As described above, the process is simplified and the yield is improved.

[Brief description of drawings]

 FIG. 1 is a sectional view of the present invention. 1: Sintered body, 2: Barium titanate dielectric film, 3: Carbon layer, 4: Silver layer, 5: Solder layer, 6: Exterior resin, 7: Cathode terminal, 8: Titanium wire, 9: Anode terminal.

Claims (1)

[Claims] 1. An anode body in which a metal powder of titanium is sintered to derive a titanium wire, a barium titanate dielectric layer is formed on the anode body, and colloidal carbon as a counter electrode is formed on the dielectric layer. A layer and a silver paste layer are provided to form a capacitor element, an anode terminal is connected to the titanium wire, a cathode terminal is connected to the capacitor element, and the capacitor element is packaged with a packaging resin. Type barium titanate capacitor.