JPH09167719A - Tantalum solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a high frequency characteristic by providing a conductive layer made from the fine powders of gold which have the particle diameters in a specified range, on a carbon layer formed on the surface of a manganese dioxide layer, avoiding the occurrence of a gap and making an equivalent series resistance to be small. SOLUTION: A carbon layer 4 is formed on the surface of the manganese dioxide layer 3 deposited on the surface of a porous pellet 2. A tantalum capacitor element 7 where the conductive layer 5 of gold is formed by applying liquid in which the fine powders of gold, which have the particle diameters of 0.01-0.1μm, are dispersed in toluene to the surface of the carbon layer 4 and they are dried is provided. The necessary part of an anode lead line 1 which is led is remained and the line is cut. Then, an external electrode 8 is fitted to the tip and an anode external electrode 8A is provided. Then, the external electrode 8 is fitted to the conductive layer 5 of gold and a cathode external electrode 8B is provided. An armor 14 is formed with mold resin, a lead frame is formed and it is set to be a chip. Thus, the equivalent series resistance becomes less than the half of a conventional one and the high frequency characteristic can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tantalum solid electrolytic capacitor.

[0002]

2. Description of the Related Art As shown in FIG. 3, in a tantalum solid electrolytic capacitor, a lead wire 1 for an anode is embedded in fine powder of tantalum metal, and the fine powder of tantalum metal is compression molded into pellets. An oxide film that is a dielectric is formed on the surface of the sintered porous pellet 2, and the porous pellet 2 that forms this oxide film is immersed in a manganese nitrate solution,
Next, heat is applied to the porous pellets 2 to which the manganese nitrate solution is attached to thermally decompose the manganese nitrate solution to deposit the manganese dioxide layer 3. Thereafter, the manganese nitrate solution is dipped in the porous pellet 2 → the pyrolysis of manganese nitrate → the precipitation of the manganese dioxide layer 3 is performed, and these operations are repeated several times.

Next, a carbon paste is applied to the surface of the manganese dioxide layer 3 deposited on the surface of the porous pellet 2 and then dried to form a carbon layer 4. Next, a silver paste is applied to the surface of the carbon layer 4 to form a silver paste layer 6
To form a tantalum capacitor element 7. After cutting the anode lead wire 1 derived from the tantalum capacitor element 7 while leaving a necessary portion, the external electrode 8 which is a lead frame made of nickel silver is resistance-welded 9 by resistance welding 9 to the tip of the anode lead wire 1 of the tantalum capacitor element 7. Attached to the part Anode external electrode 8A
And Next, the external electrode 8 is attached to the tantalum capacitor element 7 by soldering 10 to form a cathode external electrode 8B.
Then, the outer casing 11 is made of epoxy resin by transfer molding, the lead frames other than those used as the external electrodes 8 are cut, and then the lead frame that is the external electrode 8 is formed along the outer casing 11 to form a tantalum solid electrolytic capacitor. And

[0004]

Recently, the performance of tantalum solid electrolytic capacitors has been required to be improved as the performance of equipment has been improved, and there has been an increasing demand for tantalum solid electrolytic capacitors having excellent high frequency characteristics. . Therefore, there is an increasing tendency to improve high frequency characteristics by reducing the equivalent series resistance. However, in the conventional tantalum solid electrolytic capacitor, as shown in FIG. 4, since the surface of the manganese dioxide layer 3 forming the cathode layer is uneven, the surface of the carbon layer 4 is also uneven. For this reason, the silver paste layer 6 formed on the carbon layer 4 is provided with a silver paste having a relatively high grain size, so that the silver paste cannot sufficiently enter into the recesses 12 of the carbon layer 4 and the carbon layer 4 and the silver paste are There is a problem in that a void 13 is easily formed between the layer 6 and the layer 6, the effective connection area is reduced, the equivalent series resistance is increased, and the high frequency characteristics are deteriorated.

[0005]

In order to solve the above problems, the present invention, as shown in FIG. 1, embeds an anode lead wire 1 in a fine powder of tantalum metal, sinters the pressed pellets, and porosity. Porous pellets 2, an oxide film that is a dielectric is formed on the porous pellets 2, and the porous pellets 2 that have an oxide film that is a dielectric are immersed in a manganese nitrate solution, and then manganese nitrate is attached to the porous pellets 2. Quality pellets 2
Is heated to thermally decompose manganese nitrate to deposit the manganese dioxide layer 3. The operations of immersing the porous pellet 2 in a manganese nitrate solution → thermal decomposition of manganese nitrate → precipitation of the manganese dioxide layer 3 are repeated several times.

Next, a carbon paste is applied to the surface of the manganese dioxide layer 3 deposited on the surface of the porous pellet 2 and then dried to form a carbon layer 4. Next, a liquid in which fine gold powder having a particle diameter of 0.01 to 0.1 μm is dispersed in an organic liquid having a molecular weight of 74 to 154 and a boiling point of 58 to 220 ° C. is applied onto the carbon layer 4 and dried. However, by forming the gold conductor layer 5, as shown in FIG. 2, the organic liquid in which gold is dispersed has a small particle size, so that it easily enters into the concave portion 12 of the manganese dioxide layer 3, and thus a void is formed. Without doing so, the equivalent series resistance becomes small and the high frequency characteristics are improved. In addition,
A silver paste may be further applied to the surface of the gold dielectric layer 5 to form a silver paste layer.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. 1 by taking a chip type tantalum solid electrolytic capacitor as an example. A tantalum metal fine powder having an average particle diameter of 3 μm and a secondary particle diameter of about 100 μm is used, a tantalum wire serving as an anode lead wire 1 is embedded in the tantalum fine powder, and the tantalum fine powder is compression-molded by a press to obtain tantalum. Pellet. The tantalum pellets are sintered in a vacuum of 1500 to 1600 ° C. to form porous pellets 2. Then, the porous pellets 2 are washed with pure water and then immersed in a 0.1% nitric acid solution,
Anode lead wires 1 and 0.
A voltage is applied between 1% nitric acid solutions to perform chemical conversion to form an oxide film of tantalum pentoxide, which is a dielectric. Next, the porous pellets 2 having the oxide film formed thereon are immersed in a manganese nitrate solution, and then the porous pellets 2 to which the manganese nitrate solution is attached are heated to thermally decompose the manganese nitrate solution to deposit a manganese dioxide layer 3. Let

The operations of immersing the porous pellets 2 in a manganese nitrate solution → thermal decomposition of manganese nitrate → precipitation of the manganese dioxide layer 3 are repeated several times. Next, a carbon paste is applied to the surface of the manganese dioxide layer 3 deposited on the surface of the porous pellet 2 and then dried to form a carbon layer 4. Then, on the surface of the carbon layer 4, a solution in which fine gold powder having a particle diameter of 0.01 to 0.1 μm is dispersed in toluene is applied and dried at about 250 ° C. to form the gold conductor layer 5. Then, the tantalum capacitor element 7 is formed. In addition to toluene, xylene or α-terpineol may be used for the solution in which the fine gold powder is dispersed.

Next, the anode lead wire 1 led out from the tantalum capacitor element 7 is cut while leaving a necessary portion, and an external electrode 8 which is a lead frame made of nickel silver is resistance-welded 9 by resistance welding 9. 7 anode lead wire 1
The anode external electrode 8A is attached to the tip of the anode. Then
The external electrode 8 is attached to the tantalum capacitor element 7 by soldering 10 to the gold conductor layer 5 to form a cathode external electrode 8B. Next, a package 14 made of epoxy resin is formed by transfer molding, the lead frame other than the one used as the external electrode 8 is cut, and then the lead frame that is the external electrode 8 is formed along the package 13. A chip type tantalum solid electrolytic capacitor is manufactured. The tantalum capacitor element 7 may be formed by forming the gold conductor layer 5, applying silver paste on the surface of the gold conductor layer 5, and forming the silver paste layer 6.

[0010]

Since the tantalum solid electrolytic capacitor of the present invention is manufactured as described above, it has the following unique effects. As shown in FIG. 5, the equivalent series resistances of the product of the present invention and the conventional product are compared at a measurement frequency of 100 KHz. As shown in this figure, the average value of the equivalent series resistance of the conventional product is 0.13Ω, whereas the average value of the equivalent series resistance of the product of the present invention is 0.55Ω, which is equivalent to that of the conventional product. The resistance became 1/2 or less, and the high frequency characteristics were significantly improved.

[Brief description of the drawings]

FIG. 1 shows a sectional view of the present invention.

FIG. 2 shows a detailed cross-sectional view of the cathode of the present invention.

FIG. 3 shows a conventional cross-sectional view.

FIG. 4 shows a detailed cross-sectional view of a conventional cathode.

FIG. 5 shows equivalent series resistance values of the present invention and a conventional one.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Anode lead wire 2 ... Porous pellet 3 ... Manganese dioxide layer 4 ... Carbon layer 5 ... Gold conductor layer 6 ... Silver paste layer 7 ... Tantalum capacitor element 8 ... External electrode 8A ... Anode external electrode 8B ... Cathode external electrode 9 ... Resistance welding 10 ... Soldering 11 ... Exterior 12 ... Recesses 13 ... Voids 14 ... Exterior

Claims (2)

[Claims] 1. A pellet is obtained by embedding an anode lead wire in fine tantalum metal powder, press-molding the fine tantalum metal powder, and using this pellet as a sintered porous pellet, which has a dielectric on the surface. A tantalum solid electrolytic capacitor in which an oxide film is formed and a manganese dioxide layer and a carbon layer are sequentially formed on the oxide film, and a gold conductor having a particle size of 0.01 to 0.1 μm on the manganese dioxide layer. A tantalum solid electrolytic capacitor having a layer. 2. The tantalum solid electrolytic capacitor according to claim 1, further comprising a silver paste layer on the gold conductor layer.