The Solid Tantalum Capacitor - A 'Solid' Contributor to Reliability

The predominant failure mode experienced in solid tantalum capacitors is the electrical short caused by impurities in the tantalum slugs and imperfections in the dielectric. These defects result in a phenomenon commonly called scintillation, the momentary short at dielectric imperfections. Scintillations can result in the capacitor (1) healing itself, (2) forming high leakage current, or (3) permanently shorting. The lack of understanding and the random nature of these scintillations have caused users to incorporate extreme application derating, experience higher system costs, incur long purchasing lead times, and specify physically larger components. Characterization of the failure modes and mechanisms resulted in deeper understanding of the physics of the component. By establishing an effective closed-loop failure analysis system, the failure modes and mechanisms were examined, applications were studied, and corrective actions developed and implemented. This paper demonstrates that by correctly applied screening methods, pre-failure and post-failure analyses, and voltage and temperature derating (without an extra derating for < 3 ohms/volt applications) the solid tantalum capacitor can be made to demonstrate extremely low failure rates in a variety of applications. Data presented fit a Weibull distribution with a decreasing failure rate, and establish a curve which can be used as a small lot reliability indicator.