A deep analysis of the reliability of lead-free (SnAgCu) solders in comparison with tin-lead solders have been done for a particular aerospace application, SwissCube’s motherboard (MB). Since 2006, using Pb in consumer electronics has been banned. Aerospace applications are not included in this legislation, however, sooner or later aerospace industry should comply with the general trend in the electronic industry because it is dependent on the whole industry for its components. Searching for a lead-free solder which presents high-reliability properties is still continued. SnAgCu solders have become popular in the electronics industry, because of the price and their mechanical properties. The creep properties of this solder composition, as the most important deformation mechanism under thermal loads, has been investigated in this thesis, and results have been validated with a thermal shock test. To simulate creep de- formation in 2-dimension, one small electronic package, resistor, of SwissCube’s motherboard was selected. Main constitutive relations have been implemented in a finite-element analysis software, to calculate creep strain evolution under thermal loads. The results of simulation suggest using, the new kind of solder, SnAgCu, would be even better for this type of package. For 3-dimensional analysis, one of the largest packages of the SwissCube’s motherboard was simulated, using a conservative assumption in terms of constitutive relation from 2-dimensional analysis. The risk of failure for this package is not high, and it was not predicted to see a total failure after one thousand test cycle. Again, both solders show a good resistance to creep deformation, although SnAgCu shows a higher number of life cycles to failure from simulation results. Finally, a thermal shock test was performed to evaluate the reliability of solder joints practically. The test was performed for one thousand cycles. Temperature and output current were monitored. No cut in voltage was seen, while temperature followed a very close trend to thermal simulation result. Microstructural analysis has also been performed using metallography process and optical microscopy. Results of this investigation also shows that both solders are safe to be used up to one thousand cycles. Overall, both solders are highly reliable with this number of thermal cycles, however, SnAgCu shows higher life time under this type of loading.