NASA Electronic Parts and Packaging Program (NEPP) Reliability of Tantalum Capacitors Effect of Inductance and Requirements for Surge Current Testing of Tantalum Capacitors Alexander Teverovsky QSS Group, Inc. Code 562, NASA GSFC, Greenbelt, MD 20771
[email protected] October 2005 Abstract. Surge current testing is considered one of the most important techniques to evaluate reliability and/or screen out potentially defective tantalum capacitors for low- impedance applications. Analysis of this test, as it is described in the MIL-PRF-55365 document, shows that it does not address several issues that are important to assure adequate and reproducible testing. This work investigates the effect of inductance of the test circuit on voltage and current transients and analyzes requirements for the elements of the circuit, in particular, resistance of the circuit, inductance of wires and resistors, type of switching devices, and characteristics of energy storage bank capacitors. Simple equations to estimate maximum inductance of the circuit to prevent voltage overshooting and minimum duration of charging/discharging cycles to avoid decreasing of the effective voltage and overheating of the parts during surge current testing are suggested. I. Introduction. High current spikes caused by power supply transients might result in short-circuit failures of tantalum capacitors and cause catastrophic consequences for electronic systems, including igniting the system. The probability of this type of failure is especially high for low-impedance circuits when inrush currents are limited mostly by the impedance of the capacitor itself [1]. Recently, these problems have gained yet more importance due to proliferation of distributed- power architecture systems and low-voltage DC-DC converters.