Reliability of various Pb-free solders under vibration and elevated temperature environments

In this study, the vibration reliability at elevated temperature was evaluated on Pb-free solders (Sn-3.5Ag, Sn-0.7Cu, and Sn-5.0Sb). Daisy-chained BGA chips with ENIG finish was assembled on FR-4 PCB with OSP finish. After fabrication of test modules, vibration test was performed under resonant frequency with acceleration of 3G-level at 150°C. To understand the difference of reliability among three solders, IMC morphologies, thickness and failure locus were observed by SEM and EDS analysis. In chip side, IMCs of Sn3.5Ag and Sn5.0Sb were (Ni, Cu)₃Sn₄ or (Cu, Ni)₆Sn₅ and that of Sn0.7Cu was (Cu, Ni)₆Sn₅. In board side, all of IMCs were Cu₆Sn₅. The IMC thickness of Sn0.7Cu was the thinnest among three solders. After vibration test, crack initiated at interface IMCs and solder matrix and then propagated within solder and in interface between IMCs and solder. The lifetime of Sn5.0Sb was longest and that of Sn3.5Ag was shortest among three solders under vibration at high temperature. Considering lifetime, Sn5.0Sb and Sn0.7Cu was the most stable on vibration test among three solders.