Nanoindentation study of the Pb-free solders in fine pitch interconnects

Sn-Ag/Au/Ni-P/Cu, Sn-Ag-Cu/Au/Ni-P/Cu, Sn-Ag-Bi/Au/Ni-P/Cu diffusion couples were prepared and subjected to solid stage aging at temp 170/spl deg/C for 45 days. The intermetallic compound (IMC) formed at the interface of solder/substrate were characterised using SEM and their mechanical properties were measured at different strain state by using instrumented nanoindentation technique. The hardness and Young's modulus of different IMCs formed during reflow and aging were calculated from their load-displacement data. The deformation mechanisms operating at the small length scales of IMCs has been studied in the present work.