Effect of iron and indium on IMC formation and mechanical properties of lead-free solder

In recent years, because of environmental concerns, lead solders have been replaced by lead-free solders. One of the numerous lead-free solders developed in the past several years is the Sn–Ag–Cu (SAC) eutectic solder. This work explored the effects of adding iron and indium to the reliability of SAC solder. Four different solders have been fabricated by adding Fe or In into the solder, i.e., Sn3.6Ag0.9Cu (SAC–E), SAC–Fe02, SAC–Fe06 and SAC–InCe. DSC results showed that adding indium decreased the melting point of SAC, and the single eutectic peak was maintained in all cases. Solders were reflowed on bare Cu and electroless Ni–P-coated substrates. It was found that the SAC–E and SAC–InCe gave the highest and the lowest IMC thickness, respectively among all solders. The same pattern was observed in the wetting angle measurement. Shear strength results showed that the SAC–Fe06 and SAC–Fe02 solder displayed the highest strength, followed by SAC–InCe and the SAC–E solder had the lowest strength. Results suggest that adding small amounts of Fe and In&Ce improved the wettability and shear strength of the SAC solder. Also, the Coefficient of thermal expansion measurement showed a possible decrease in thermal expansion mismatch with the addition of In&Ce and Fe into the SAC eutectic solder.