Progress in High CV Ta Capacitors

摘要

For more than 45 years of the history of Ta capacitors, progress in their most critical parameter, volumetric efficiency, was chiefly provided by the powder makers, developing new powders with finer primary particles and, thereby, larger specific surface area. This way has practically ended with the only exception, very low rated voltage capacitors. Across the major range of the rated voltages, Ta capacitors are facing high voltage and low voltage limits preventing further CV increase. These limits come from size effects when the thickness of the anodic oxide film becomes comparable with the thickness of the necks connecting the powder particles, the size of pores between the particles, and the thickness of the natural thermal oxide on the Ta surface. The new way of sintering Ta anodes with existing powders, Y-sintering, pushes CV beyond current limits and allows making capacitors with record high volumetric efficiency and improved DC and AC characteristics. This is due to low oxygen in Y-sintered anodes, improved morphology (thick necks and open pores), strong lead-to-pellet bonding without shrinkage, and low thickness of the thermal oxide on Ta surface. As an example, A-case 25V rated voltage capacitors with conventional sintering have maximum 4.7 μF capacitance, while the Y-sintering provides 10μF -25V CV in the same case-size or double volumetric efficiency.rnThe Y-sintering is only the first step in the new high CV technology where major manufacturing steps are designed on the base of uniform physical model. With this technology, Ta capacitors will continue to improve their volumetric efficiency and other critical parameters, keeping a strong position on the market of the passive electronic components.