Comparative tests for lead-free solder bumps

Lead-free solders around the Sn-Ag-Cu eutectic point offer many choices of parameters critical to assembly, such as melting point or range, thermal expansion coefficient, ductility or hardness. Published results with such systems are difficult to compare, as differences in geometry (solder volume, aspect ratio bump height to bump base, maximum bump width) as well as test conditions affect the results. The present study analyzes different lead-free solder bumps of identical volume and pad structure under shear test, hot - and cold pull test and the results are compared to eutectic lead solder. The results indicate Sn-3%Ag-0.5%Cu and Sn-0.7%Cu bumps to have very similar parameters, whereas those from Sn-3%Ag-0.7%Cu to show significantly higher strength.