Solder Fatigue Analyses and Predictions for PCB Mounted Components after Thirteen Years of Thermal Field Cycling

A long-term temperature cycle test has been running for more than 13 years to answer the most challenging questions about dominating failure modes and degradation processes caused by thermal cycle loadings close to service conditions. Test boards with components QFN40, QFN36,FBGA48, TQFP100, FBGA227 and chip capacitors/resistors size 0201 have been subjected to temperature cycles 18°C/80°C, 7.1 hours. The latter three were analyzed by Finite Element Analysis (FEA) and compared to damage observed from cross sectioning up to damage states at approx. 15.700 cycles (13 years). SAC357 (Sn3.5Ag0.7Cu) was used. Solder fatigue was clearly the dominating failure mechanism for all components except the 0201 ceramic chip capacitors/resistors.SAC solder fatigue is briefly discussed from a microstructural and continuum mechanical perspective. Fatigue life evaluation results based on averaged cyclic creep strain and creep dissipation are compared to testing results. The fatigue life prediction model based on the secondary/primary creep law tends to predict fatigue life reasonably well for test cycling but underestimates it for field cycling. Simulation inherent issues like the use of a combined secondary/primary creep model vs. two Anand’s models from the literature are also addressed.Some failure modes apart from standard ductile solder fatigue are discussed for thermal test-and field-conditions.