Risk Assessment of Transition to Lead-Free Electronics Assembly

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 have introduced reliability risks such as thermomechanical fatigue, tin whiskers, tin pest, electrochemical 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 lead-based solders and surface-finished 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. A 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 is briefly discussed. The study provides assessment and important factors to be considered and monitored during the lead-free transition.

 

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