SUMMARY

This research aims to understand the reliability of SnAgCu solder interconnects used in plastic ball grid array (PBGA) packages using microstructure evolution, laser moiré interferometry and finite-element modeling. A particle coarsening based microstructure evolution of the solder joint material during thermal excursions will be studied for extended periods of time lasting for several months. The microstructure evolution and particle coarsening will be quantified, and acceleration factors will be determined between benign field-use conditions and accelerated thermal cycling (ATC) conditions for PBGA packages with different form factors and for two different lead-free solder alloys. A new technique using laser moiré interferometry will be developed to assess the deformation behavior of SnAgCu and SnPb based solder joints during thermal excursions. This technique will be used to estimate the fatigue life of solder joints quickly in a matter of few days instead of months and can be extended to cover a wide range of temperature ranges. Finite-element analysis (FEA) in conjunction with experimental data from the ATC for different lead-free PBGA packages will be used to develop a fatigue life model that can be used to predict solder joint fatigue life for any PBGA package. The proposed model will be able to predict the mean number of cycles required for crack initiation and crack growth rate in a solder joint.