Written by the United Test & Assembly Center Ltd (UTAC) in Singapore this paper explores the reliability of Lead versus Lead free soldered IC’s during drop testing.
The influence of different package types and the impact of PCB surface finishes for OSP and ENIG (electroless nickel immersion gold) were studied. The drop test results showed that lead- free solder joints with ENIG finish have weaker drop reliability performance than the case for OSP surface finish. The different solder alloy-to-surface finish type combination results in different intermetallics formed and contributed to different failure sites and mode of failure.
The formation of the brittle intermetallics (Cu-Ni-Sn) for Pb-free solder (Sn-4Ag-0.5Cu) with ENIG pad led to detrimental interfacial fracture of the PBGA solder joints. For both lead-based and Pb-free solders with copper-pad and OSP surface finish, the formation of Cu6Sn5 intermetallics resulted in a different failure site and mode. The failures migrated to the PCB copper traces and resin layers.
The small size (VQFN) package is most resistant to drop impact failures, due to it’s small size, weight and larger solder volume. The compliant leads for the PQFP is more resistant to drop failures compared to the PBGA solder joints.