ECIA EIA-809

Introduction

Solid electrolytic tantalum capacitors are those devices havinga sintered tantalum anode that incorporates a solid electrolytecounter-electrode layer.

They are polar devices, having distinct positive and negativeterminals, and are offered in a variety of styles that include bothmolded and conformal coated versions of radial, axial and surfacemount configurations.

These devices typically offer capacitance values from 0.1 µF to1000 µF in voltage ratings from 2 V to 50 V (with a maximumcapacitance-to voltage combination of approximately 22 µF @ 50 Vfor leaded styles or 22 µF @ 35 V for surface mount). Primecharacteristics include excellent temperature stability, volumetricefficiency and compatibility with all automated assemblysystems.

The capacitor element, usually referred to as the “anode”, is ofthe same basic construction for all body styles.

Taking high-purity tantalum powder and pressing into anappropriately shaped pellet makes the anode. The pellet isgenerally cylindrical for axial and radial capacitors, andrectangular in cross-section for surface-mounted capacitor. A puretantalum wire (the anode connection) is attached either byinsertion into the pellet before sintering, or welding aftersintering.

The sintering operation (where the anodes are heated up to2000°C under a high vacuum or inert atmosphere) causes theindividual tantalum powder particles to interconnect and form asingle electrode of extremely high surface area in a verysmall volume.

Tantalum is a valve metal whose amorphous oxide called tantalumpentoxide (Ta₂O₅), can be formed to anextremely uniform thickness over the entire anode surface byelectrolysis.

Although the tantalum pentoxide dielectric constant is high foran electrolytic capacitor, it is much lower than achieved byceramic technologies. However, the relative thinness of thedielectric (about 0.02 micrometers per volt) and the high surfacearea (typically 250 cm² for a 22 µF/25 V rating)results in highly volumetric-efficient devices.

Edition:

99

Published:

06/01/1999

Number of Pages:

28

File Size:

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