Introduction

Solid electrolytic tantalum capacitors are those devices having a sintered tantalum anode that incorporates a solid electrolyte counter-electrode layer.

They are polar devices, having distinct positive and negative terminals, and are offered in a variety of styles that include both molded and conformal coated versions of radial, axial and surface mount configurations.

These devices typically offer capacitance values from 0.1 µF to 1000 µF in voltage ratings from 2 V to 50 V (with a maximum capacitance-to voltage combination of approximately 22 µF @ 50 V for leaded styles or 22 µF @ 35 V for surface mount). Prime characteristics include excellent temperature stability, volumetric efficiency and compatibility with all automated assembly systems.

The capacitor element, usually referred to as the "anode", is of the same basic construction for all body styles.

Taking high-purity tantalum powder and pressing into an appropriately shaped pellet makes the anode. The pellet is generally cylindrical for axial and radial capacitors, and rectangular in cross-section for surface-mounted capacitor. A pure tantalum wire (the anode connection) is attached either by insertion into the pellet before sintering, or welding after sintering.

The sintering operation (where the anodes are heated up to 2000°C under a high vacuum or inert atmosphere) causes the individual tantalum powder particles to interconnect and form a single electrode ofextremelyhigh surface area in a very small volume.

Tantalum is a valve metal whose amorphous oxide called tantalum pentoxide (Ta₂O₅), can be formed to an extremely uniform thickness over the entire anode surface by electrolysis.

Although the tantalum pentoxide dielectric constant is high for an electrolytic capacitor, it is much lower than achieved by ceramic technologies. However, the relative thinness of the dielectric (about 0.02 micrometers per volt) and the high surface area (typically 250 cm² for a 22 µF/25 Vrating) results inhighly volumetric-efficient devices.

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