Effect of intermetallic phases on performance in a mechanical drop environment: 96.5Sn3.5Ag solder on Cu and Ni/Au pad finishes

Mechanical drop test reliability risk due to incompatibility between component and board surface finishes of thin (30-100 μm) 96.5Sn3.5Ag solder joint assemblies is examined in this study. Failures in test components with ENIG plated interposers occurred owing to inhibition of any Ni-Sn(Cu) intermetallic phase growth at the interposer/solder interface on account of Cu migration from the solder/ceramic interface, i.e. a coupling effect between the two interfaces of the solder joint and consequently the lack of a metallurgical bond between solder and interposer. Results of this study demonstrate that interface reaction coupling phenomena play a critical role in determining the performance of thin lead-free solder joints under mechanical loading.