JPH09129512A - Tantalum solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a clearance between a carbon layer and a silver paste layer from being caused and enhance high frequency characteristics by a method wherein a metal layer composed of a fine powder of gold or silver or palladium or a fine powder of these mixtures is formed between a carbon layer and a silver paste layer. SOLUTION: Liquid in which a fine powder of gold or silver or palladium or a fine powder of these mixtures is dispersed in organic liquid at molecular weight of 74 to 154 at boiling point of 58 to 220 deg.C is applied onto a carbon layer 4, to form a metal layer 6 dried and formed. Next, silver paste is applied onto the metal layer 6 to form a silver paste layer 5 to make a tantalum capacitor element 7. As viscosity of the metal layer 6 is low, it is easy to enter a recess of the carbon layer 4, so that a clearance cannot be caused and equivalent series resistance is small. Accordingly, high frequency characteristics 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, an anode lead wire 1 is embedded in fine tantalum metal powder, and the fine tantalum metal powder is compressed into pellets by a press, which is then sintered into a porous structure. An oxide film that is a dielectric is formed on the surface of the porous pellet 2, and the porous pellet 2 that has formed the oxide film that is a dielectric is immersed in a manganese nitrate solution,
Then, the porous pellet 2 to which the manganese nitrate solution is attached
Is heated 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 on the surface of the carbon layer 4 to form a silver paste layer 5 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, an external electrode 8 which is a lead frame made of nickel silver is resistance-welded 9 to the anode lead wire 1 of the tantalum capacitor element 7. It is attached to the tip and used as the anode external electrode 8A. Next, the external electrode 8 is attached to the tantalum capacitor element 7 by soldering 13 to form a cathode external electrode 8B. Then, the outer casing 10 is formed by a mold resin made of epoxy resin by a trans mold, the lead frame other than the one used as the external electrode 8 is cut, and then the lead frame which is the external electrode 8 is formed along the outer casing 10 by tantalum. Manufacture solid electrolytic capacitors.

[0004]

Recently, the performance of tantalum solid electrolytic capacitors has been required to be improved as the performance of equipment has improved, and there has been an increasing demand for tantalum solid electrolytic capacitors having excellent high frequency characteristics. Therefore, there is an increasing trend 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 has irregularities, the surface of the carbon layer 4 also becomes irregular and is formed on the carbon layer 4. Since the silver paste layer 5 to be used is a silver paste having a relatively high viscosity, the silver paste cannot enter the recesses 11 of the carbon layer 4, and a void 12 is easily formed between the carbon layer 4 and the silver paste layer 5 so that it is actually formed. There is a problem that the connection area becomes small, the equivalent series resistance becomes large, and the high frequency characteristics deteriorate.

[0005]

In order to solve the above problems, the present invention, as shown in FIG. 1, embeds anode lead wire 1 in tantalum metal fine powder and press-presses the pellet to sinter the porous pellet. 2, the porous pellets 2 are formed with an oxide film which is a dielectric, and the porous pellets 2 having an oxide film which is a dielectric are immersed in a manganese nitrate solution, and then a manganese nitrate solution is attached to the porous pellets 2. Heat is applied to the pellets 2 to thermally decompose manganese nitrate to deposit the manganese dioxide layer 3. Immersing a manganese nitrate solution in the porous pellet 2 → thermal decomposition of manganese nitrate → 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,
The carbon layer 4 is formed.

Next, a liquid in which fine powder of gold, silver or palladium or a fine powder of a mixture thereof 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 on the carbon layer 4. Then, by forming the metal layer 6 formed by drying, as shown in FIG.
Has a low viscosity, it is easy to enter the recess 11 of the carbon layer 4 and voids are not formed, so that the equivalent series resistance becomes small and the high frequency characteristics are improved.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described by taking a chip type tantalum solid electrolytic capacitor as an example. Average particle size 3μ
m, a tantalum metal fine powder having a secondary particle diameter of about 100 μm is embedded with a tantalum wire serving as the anode lead wire 1 and compression molded by a press to obtain a tantalum pellet. 1 tantalum pellet
The porous pellets 2 are formed by sintering in a vacuum of 500 to 1600 ° C. Then, the porous pellets 2 are washed with pure water and then immersed in a 0.1% nitric acid solution to obtain the porous pellets 2.
A voltage is applied between the anode lead-out wire 1 and the 0.1% nitric acid solution, which is led out, to perform chemical conversion to form an oxide film of tantalum pentoxide as a dielectric. Next, the porous pellets 2 having an oxide film formed thereon are dipped in a manganese nitrate solution, and then 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. .

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. About 3 μm to 1 on this carbon layer 4
A solution of 0 μm fine gold powder dispersed in toluene is applied and dried at about 250 ° C. to form the metal layer 6. The metal layer 6 may be coated with a solution prepared by dispersing fine powder of silver or palladium or a mixture of gold, silver and palladium in toluene in addition to the above gold.

Next, a silver paste is applied on the metal layer 6 to form a silver paste layer 5 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, an external electrode 8 which is a lead frame made of nickel silver is resistance-welded 9 to the anode lead wire 1 of the tantalum capacitor element 7. It is attached to the tip and used as the anode external electrode 8A. Next, the external electrode 8 is attached to the tantalum capacitor element 7 by soldering 13 to form an electrode 8B outside the cathode. Next, the outer casing 10 is formed by a mold resin made of epoxy resin by transfer molding, and the lead frame other than the one used as the external electrode 8 is cut,
Next, the lead frame which is the external electrode 8 is formed along the exterior 10 to manufacture a tantalum solid electrolytic capacitor.

[0010]

Since the tantalum solid electrolytic capacitor of the present invention is manufactured as described above, it has a unique effect as described below. FIG. 5 compares the equivalent series resistances of the conventional product and the product of the present invention at a measurement frequency of 100 KHz. As shown in Fig. 5, the average equivalent series resistance of the conventional product is 0.13Ω.
On the other hand, the average value of the equivalent series connection of the product of the present invention is 0.055Ω, the equivalent series resistance is 1/2 or less as compared with the conventional product, and the high frequency characteristics are 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 a comparison between the present invention and a conventional equivalent series resistance value.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Anode lead wire 2 ... Porous pellet 3 ... Manganese dioxide layer 4 ... Carbon layer 5 ... Silver paste layer 6 ... Metal layer 7 ... Capacitor element 8 ... External electrode 8A ... Anode external electrode 8B ... Cathode external electrode 9 ... Resistance welding 10 ... Exterior 11 ... Recess 12 ... Void 13 ... Soldering

Claims (2)

[Claims] 1. A pellet obtained by embedding an anode wire in tantalum metal fine powder and press-compressing, and sintering the pellet,
On the surface of the porous pellet, an oxide film which is a dielectric is formed, and a manganese dioxide layer, a carbon layer, and a cathode layer of a silver paste layer are sequentially formed on this oxide film, in the tantalum solid electrolytic capacitor, A tantalum solid electrolytic capacitor characterized in that a metal layer made of fine powder of gold, silver or palladium or a fine powder of a mixture thereof is provided between a carbon layer and a silver paste layer. 2. The fine powder according to claim 1, having a molecular weight of 7
A tantalum solid electrolytic capacitor, characterized in that a metal layer is formed by using a liquid dispersed in an organic liquid having a boiling point of 58 to 220 ° C. and a boiling point of 58 to 220 ° C.