A severity metric is developed to predict the life of SnPb and SnAg solder joints in PBGA packages by quantitatively estimating the changes in damage arising from different board configurations and accelerated thermal cycle tests (ATC). Damage measures include time-dependent creep, time-independent plastic deformation, and an effective stress that is computed from the ATC parameters of temperatures, dwell-time, and ramp rates and from package geometries on the printed wiring board. Life prediction using this severity metric has been applied to 24 sets of test data on SnPb and SnAg solder joints in 357-PBGA packages and include three post-processing conditions (aged at 150/160°C, quenched at 0°C, and air-cooled), three ATC test conditions (0–100°C, −40–125°C, and −55–125°C), and four package-on-board geometric configurations. Statistical analysis is provided to compare the life predictions based upon the severity metric and from ATC testing—predicted joint life is well within one standard deviation of the experimental mean value of life for most of the 24 cases. The severity metric can be used to quantify the effects of design and manufacturing choices on joint life.

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