This study investigated the effects of adding Bi and In to Sn-3Ag Pb-free solder on undercooling, interfacial reactions with Cu substrates, and the growth kinetics of intermetallic compounds (IMCs). The amount of Sn dominates the undercooling, regardless of the amount or species of further additives. The interfacial IMC that formed in Sn-Ag-Bi-In and Sn-In-Bi solders is Cu(6)Sn(5), while that in Sn-Ag-In solders is Cu(6)(Sn,In)(5), since Bi enhances the solubility of In in Sn matrices. The activation energy for the growth of IMCs in Sn-Ag-Bi-In is nearly double that in Sn-Ag-In solders, because Bi in the solder promotes Cu dissolution. The bright particles that form inside the Sn-Ag-In bulk solders are the zeta-phase.
