Creep of lead-free Sn-3.8Ag and Sn-3.8Ag-0.7Cu solder alloy as replacements of Sn-Pb solder used in microelectronic packaging

Creep behavior of the tin-based lead-free Sn-3.8Ag and Sn-3.8Ag-0.7Cu alloys together with Sn-37Pb, as the material for comparison, was studied by impression and indentation creep testing at room temperature. Stress exponent values in the range 5.1 to 9.7, obtained by the two methods, were in good agreement with each other and with those determined by room-temperature creep testing of the same materials reported in the literature. Among all tested materials, as indicated by their steady-state creep rates, Sn-3.8Ag-0.7Cu showed the highest creep resistance followed by Sn-3.8Ag and Sn-Pb. The formation of Ag₃Sn and Cu₆Sn₅ intermetallics in Sn-3.8Ag-0.7Cu, and Ag3Sn in Sn-3.8Ag are the main cause of improved creep resistance of the alloys over the eutectic Sn-Pb alloy.