Experimental characterization and mechanical behavior analysis on intermetallic compounds of 96.5Sn-3.5Ag and 63Sn-37Pb solder bump with Ti-Cu-Ni UBM on copper chip

This study investigated the mechanical behavior of flip-chip lead-free solder bumps affected by solder/UBM intermetallic compound formation in the duration of isothermal aging. To attain the objective, test vehicles of Sn-Ag (lead-free) and Sn-Pb (lead-containing) solder bump systems were used to experimentally characterize and analyze their mechanical behavior. By way of metallurgical microscopy and SEM observation, the interfacial microstructure of test vehicles were measured and analyzed. In addition, a bump shear test is utilized for the strength determination of solder bumps. The results indicated that after isothermal aging treatment at 150°C for over 1000 hours, the Sn-Ag solder revealed a better maintenance of bump strength than that of Sn-Pb solder, and the Sn-Pb solder showed a higher intermetallic compounds growth rate than that of Sn-Ag solder. In terms of the solder bump volume and the UBM size effects, both the Sn-Ag and the Sn-Pb solders showed no significant effect on the intermetallic compounds growth rate.