2008 Volume 49 Issue 5 Pages 1175-1179
Tensile properties of several Sn-Ag-Cu lead-free solders have been investigated by micro size specimens. For as-cast specimens, tensile strength increases with increasing content of Cu and Ag. After aging at 120°C for 168 h, however, tensile strengths are similar among eutectic and hypereutectic alloys. The similar tendency was observed among hypoeutectic alloys. Moreover, negligible change was found in tensile strength between specimens aged at 120°C for 168 h and 504 h in all solders. The strength change with aging corresponds to microstructural change of the solder. In the cases of eutectic and hypoeutectic alloys, as-cast microstructures are composed of coarsened primary Sn phases and finer eutectic phases of Sn and intermetallic compounds. The primary Sn phases and the eutectic phases are homogenized upon aging. In contrast, finer Sn and eutectic phases are formed in as-cast hypereutectic alloys. The finer phases are coarsened upon aging. After aging, homogenization of the Sn phases and the eutectic phases occurred in all solders.
