Comparison of isothermal mechanical fatigue properties of lead-free solder joints and bulk solders

Low-cycle isothermal mechanical fatigue testing of bulk solders and solder joints of eutectic Sn-37 wt% Pb, Sn-3.5 wt% Ag and Sn-4.0 wt% Ag-0.5 wt% Cu were carried out at room temperature over a wide range of strains (1-10%). The fatigue results of both bulk and solder joints were compared; the eutectic Sn-37 wt% Pb was used as reference. Concerning bulk solders and solder joints, the two lead-free solders showed better fatigue properties than Sn-37Pb. For all three solder alloys tested, bulk solders showed better fatigue performance than solder joints when subjected to higher strains. The situation was the opposite at lower strains, resulting in bulk solders depicting larger values for the Coffin-Manson fatigue exponent and ductility coefficient compared to solder joints.