Abstract:

The European Union's Restriction on Hazardous Substances (RoHS) Directive, imposed on electronics manufacturers in 2006, banned the use of certain toxic substances such as lead and cadmium in components and assemblies. Removal of lead which was used in solder, die attaches and surface finishes has introduced reliability risks such as thermomechanical fatigue, tin whiskers, tin pest, electro-chemical migration, and corrosion. Due to these concerns, certain reliability-critical industries such as medical, defense, and automotive were either exempted or excluded from these restrictions. Since the commercial electronics sectors have switched to lead-free materials, few suppliers now produce leadbased solders and surface finish boards. Hence there is a growing supply chain pressure on these exempted and excluded industries to switch to lead-free materials. However, they are hesitant to transition to lead-free due to previously said reliability concerns remaining with lead-free assemblies

This study analyses possible failure modes and mechanisms to assess these reliability risks in this transition. The critical failure mechanisms included thermal and mechanical fatigue and tin whiskers. Simulation was conducted using CalcePWA software to compare the reliability between tin-lead and SAC305 solder under temperature cycling and vibration loading in addition to assessing the risk due to tin whiskers. The discussion is mainly focused on concerns about the changes in manufacturing practices, effects of storage and handling conditions on manufacturing defects, while susceptibility to other failure mechanisms are briefly discussed. The study provides assessment and important factors to be considered and monitored during lead-free transition.