Isothermal aging effects on the dynamic performance of lead-free solder joints

Isothermal aging effects on lead-free solders have been extensively investigated in recent studies. There is researches show that aging effects will significantly degrade the mechanical properties of lead-free solders. However, very little work been done on the study of aging effects on the board level dynamic performance of lead-free solder joints, especially for large flip-chip BGA packages for ASICs. Due to the extreme sensitivity of aging effects on lead-free solders, it is crucial to investigate the aging effects on the board level dynamic performance of lead-free solders. In this study, dynamic performance of lead-free solder joints has been characterized and the isothermal aging effects have been investigated. It was found that dynamic shock performance of the lead-free FCBGA packages significantly degraded up to 20-35% after aging at varies elevated temperatures. It has also been discovered that aging at 100 degC shows more dramatic degradation than that of aging at 75 degC and 150 degC. It is a very critical finding due to the fact of that many electronic products operate at the 100 degC range for long period of time. The results will provide crucial guidelines in implementation of lead-free solders based on the products end-use conditions. The unique finding of aging effects is related the growth of Cu₃Sn and Cu₆Sn₅ intermetallics after aging. Even though the failure analysis shows mixed failure of pad cratering and intermetallic compounds (IMC) failures, the IMC growth is the most sensitive factor to contribute to the failure observed in this study.