Flip chip solder joint fatigue life model investigation

In recent years, many solder fatigue models based on strain-range and energy density methods have been developed to predict the fatigue life of solder joints. The application of these fatigue models to flip chip solder joint reliability has been investigated. In this study, the solder joint fatigue life of non-underfill and underfilled flip chip on board (FCOB) assemblies was assessed by numerical simulation and experimental testing under two - 40/125°C thermal cyclic test profiles: i) TC1 (15 min dwell/5 min ramp), and ii) TC2 (5 min dwell/3 min ramp). A 3D-slice finite element model was established using two different solder (Sn-37Pb) material constitutive models, namely state variable viscoplastic and elastic-plastic-creep analysis. The accumulated inelastic response at the critical joint location, calculated from the volume averaging method, was used as a failure parameter for fatigue life prediction. Mixed mode failure, consisting of UBM delamination and solder joint cracking, were observed in the non-underfill FCOB assembly for both TC1 and TC2 test profiles. However, only solder joint fatigue failure mode was observed for the underfilled FCOB assembly. The mean time to failure (MTTF) of the non-underfill FCOB assembly for TC1 and TC2 profiles is 79 and 89 cycles respectively. With underfilling, the MTTF after TC1 and TC2 profiles was improved to 2437 and 3507 cycles, respectively. For the FCOB assembly with underfill, the solder joint life prediction using the creep-fatigue model has good correlation between the modeling and experimental result.