Surge voltage and surge current characterization of solid tantalum chip capacitors

Solid tantalum chip capacitors are widely used in spacecraft systems for different applications like filtering, bypassing and coupling in electrical circuits. In spite of using established reliability component, many field failures of these capacitors are being reported. Generally, during such failures a substantial amount of energy is released by exothermic reaction of the tantalum pellet with oxygen generated by the overheated manganese dioxide cathode. As such, the failure mechanism is most likely the breakdown of the dielectric when exposed to a specific critical stress for the first time. Manufacturers usually attribute electrical failures of solid tantalum capacitors to stresses such as higher DC voltage application, surge voltage and surge current. Failure reasons of higher DC voltage stress are properly understood and could be simulated, which reveals that a solid tantalum capacitor fails in short mode when double the rated voltage is applied to the device. Where as, for surge voltage and surge voltage current related failures, even though several literatures are available, the failure mechanisms are not yet understood fully. The most common explanation is that surge current facilitates unlimited current supply, which in turn does not allow the self heating mechanism of MnO 2 (used as cathode in solid tantalum capacitor). Such condition increases the temperature of the capacitor, which leads to dielectric breakdown and subsequent catastrophic failure in the capacitor. In this paper an effort has been made to characterize the surge voltage and surge current threshold level of solid tantalum chip capacitor which feeds as useful data to understand their failure mode. Surge voltage test was also carried out on solid tantalum chip capacitor under different environmental and electrical conditions. SEM (Scanning Electron Microscope) and ED AX (Energy Dispersive Analysis of X-rays) analysis were carried out to understand the internal construction of good capacitor. Chip capacitor type CWR-06/22μ F/20V, which exhibited more failure in recent times has been chosen for study.