Comparisons of Solder Joints Fatigue Life Predictions and Several Long-Term Testing Results

Solder fatigue phenomena on lead-free solder joints have been subject of numerous studies. In most cases, reference was made to test cycling conditions. To address the reliability of solder joints subjected to service conditions, long-term studies have been made using two test setups. The first used a standard industrial board with either SAC 305 or Innolot joints and cycling conditions 22°C/95° C, 6 hours, and the other one a test board with SAC 357 joints and cycling conditions 18°C/80°C, 7.1 hours. Both cyclic conditions have been applied for approximately ten years. The tests have reached solder fatigue failure for the most critical components, which are reported in the paper. Acceleration factors are additionally reported for these components related to test cycling results performed in parallel. Two predictive methodologies were applied to evaluate the acceleration prediction by the testing results: analytical models of Norris/Landzberg type and numerical modeling (FEA). It is shown that the estimates of acceleration factors from published Norris/Landzberg formulas result in a wide span of predictive results. The solder damage prediction based on FEA is finally shown to be on the safe side, but its usefulness also for service conditions is obvious.