Reliability of High-Voltage MnO2 Tantalum Capacitors

While tantalum polymer capacitors are making significant penetration into many applications previously dominated by MnO2 tantalum capacitors, the present reality is that significantly more capacitors are manufactured with MnO2 as the cathode material than are made with conducting polymer. There are reasons other than market inertia for the good market performance of MnO2 capacitors. These include lower cost, good reliability, and robustness against high temperature and humidity. Recent work reported at CARTS focused on the reliability of tantalum polymer capacitors which display very long predicted lifetime. This work featured accelerated lifetesting of capacitors at various voltages and temperatures, and formulation of acceleration models that predict lifetime at normal use conditions. Even while the polymer capacitors were receiving this needed attention, improvements continued to be made in MnO2 capacitors. The most improvement is seen in MnO2 capacitors rated from 25 to 50V. The present work involves accelerated lifetesting of these improved high-voltage MnO2 capacitors. The test strategy is similar to that employed with the polymer capacitors. Time-to-failure data are presented that were collected over a range of voltages and temperatures. Trends in the data are identified and models for voltage and temperature acceleration are discussed. Median lifetime at rated conditions is estimated, and comparisons and contrasts are drawn between MnO2 and polymer capacitors and their underlying degradation mechanisms.