Assessment of long-term reliability in lead-free assemblies

This paper explains that to assess long-term reliability, an experimental plan must include assessing the interactions among the applications conditions. The interacting influences include the growth of intermetallics at the solder joints due to high temperature exposure, electro-chemical degradation of electronics assemblies due to the exposure to humidity and atmospheric contaminants, formation of tin pest due to extended exposure to low temperature and the effects of combined thermo-mechanical loading conditions on the electronics assemblies. The test vehicle designs incorporate commercial variations in PCB pad finishes, and component lead finishes. Three PCBs designs were developed to assess the reliability of surface mount assemblies and single sided through-hole assemblies. The PCB materials include FR4, polyimide for SMT assemblies and paper-phenolic type (CEM-1) for through-hole assemblies.