Effect of activators and surfactants in halogen-free fluxes on wettability of Sn-0.7Cu-0.05Ni solder on Cu substrate

The effect of the activators and surfactants in halogen-free fluxes on the wettability of Sn-0.7Cu-0.05Ni solder on Cu substrate (or under bump metallization, UBM) was investigated in this study. The spreading area of Sn-0.7Cu-0.05Ni solder on Cu substrate was used to estimate the wetting performance of the solder influenced by the activators with different amounts added in halogen-free fluxes. The wetting time (t) and wetting force (F_max) of Sn-0.7Cu-0.05Ni solder on Cu substrate were used to evaluate the wetting performance of the solder influenced by the surfactants with different amounts added in halogen-free fluxes. The results show that the flux formula with a composition design of “citric acid: glutaric acid: adipic acid = 1: 3: 6” provides the best activity for soldering, and 0.10% surfactant dosage could be the optimal concentration in halogen-free fluxes. Moreover, fluorosurfactant (FC4430) performs much better in improving the wettability of the solder in terms of wetting time and wetting force than both cetrimonium bromide (CTAB) and sodium dodecyl surfactant (SDS) when the dosage is more than 0.10%.