In this work, a deep analysis of the reliability of lead-free (SnAgCu) solders in comparison with conventional tin-lead (SnPb) solders was done for a particular aerospace application. Creep properties of this solder composition were investigated, and results were validated with a thermal shock test. A 0805 resistor was considered to simulate creep deformation, an electronic board was used for a thermal shock test to check continuity of the circuit for the specified mission, and finally a detailed metallographic study was done to examine microstructure of solder joints after thermal shock test. Main constitutive relations were implemented in commercial finite-element analysis software (ABAQUS 6.5), to predict creep strain accumulation under thermal loads. Moreover, effects of implementing different constitutive relations in compare with life prediction models were investigated. Overall, both solders are highly reliable with this number of thermal cycles; however, SnAgCu shows higher life time under this type of loading.