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With the increasing requirement for lead-free solders, it is desired to know how different solder alloys affect on reliability of microelectronic assembly. Some fatigue life models for Sn-Ag-Cu (SAC) solder have been developed by researchers. The Ni-dopant lead free solder is increasingly used in electronic packages due to its good drop performance. Currently, it lacks the fatigue life model for Ni doped SAC solder. In this paper, thermal cycling test and finite element simulation were conducted for 5 FBGA (Fine pitch BGA) assemblies with Sn-Ag-Cu-Ni (SACN) lead free solder. The thermal fatigue life prediction model was developed for FBGA assemblies with SACN solder by combining experimental and simulation results. The good correlation between predicted and experimental lives was achieved. In addition, the effect of geometry and loading condition on solder joint predicted life was investigated based on the finite element simulation result and the developed life model.