Robustness of Surface-Mount Aluminum Electrolytic Capacitors When Subjected to Pb-Free Reflow SURFACE-MOUNT ELECTROLYTIC CAP A CITORS

In addition to a change in materials, the movement to Pb-free will also result in significantly higher temperatures during surface-mount assembly. Initial attempts at surfacemount reflow have noted the initiation of case deformation aluminum liquid electrolytic capacitors in a surface-mount configuration (V-chip). Of special concern is not only the visually observable change in component dimensions, but the possibility of damaged capacitors escaping into the field and inducing widespread field returns. To assess this issue, a wide range of V-chip capacitors was subjected to two series of experiments. In the first set, capacitors of various size and electrolyte formulation were exposed to a modified reflow condition, where the peak temperature was maintained until deformation of the aluminum housing was observed. Based on time to deformation determined in this experiment and the reflow parameters defined in J-STD-020C, a more limited population of V-chip capacitors was exposed to simulated reflow conditions and then subjected to highly accelerated life tests. Results suggest that the strongest predictor of deformation is the volume of the capacitor, with the smallest and largest case sizes having the potential to deform during reasonable Pb-free reflow conditions. When exposed to elevated temperature conditions designed to accelerate electrolyte evaporation, V-chip capacitors showed limited differentiation in time to failure as a function of reflow conditions or the presence or absence of case deformation.