The Impact of Reflowing A Pbfree Solder Alloy Using A Tin/Lead Solder Alloy Reflow Profile On Solder Joint Integrity

The electronics industry is undergoing a materials evolution due to the pending Restriction of Hazardous Substances (RoHS) European Directive. Printed wiring board laminate suppliers, component fabricators, and printed wiring assembly operations are engaged in a multitude of investigations to determine what leadfree (Pbfree) material choices best fit their needs. The size and complexity of Pbfree implementation insures a transition period in which Pbfree and tin/lead solder finishes will be present on printed wiring assemblies. Ball grid array is one component style that has generated concern with respect to mixed finish scenarios. To better understand the reliability effect of mixed surface finish manufacturing, an investigation was conducted to evaluate the solder joint integrity impact of reflowing a Pbfree solder alloy using a tin/lead reflow profile. In this study, ball grid array components with tin/silver/copper (SAC) solder spheres were processed using a tin/lead reflow profile and then subjected to thermal cycle testing from -55ºC to +125ºC. Solder joint life measurements and failure analysis revealed premature solder joint failures due to non-uniform microstructure and poor wetting characteristics. BACKGROUND