Sn-Bi-Ag-(In) solder alloys have been extensively studied in the study. The experimental results reveals that the liquidus temperatures of Sn-(1-5) Bi-(2-3.5) Ag-(0-10) In solders are between 201.7 and 225.3degreesC, which were higher than that of the most popular eutectic Pb-Sn solder (183degreesC). Additions of (5-10) wt% In into Sn-Bi-Ag solders can effectively decrease the melting point of the solder alloy. However, the gap between T-s and T-L temperatures increases with the additions of Bi and In into Sn- Bi- Ag-( In) solders. Although there is no flux applied during soldering, most Sn- Bi- Ag-( In) solder alloys can well bond the Au/Ni metallized copper substrate. 94Sn-3Bi-3Ag solder demonstrates the lowest wetting angle of 45degrees among all test samples. Thermal expansion coefficients of both 94Sn-3Bi-3Ag and 90Sn-2Bi-3Ag-5In solders are slightly less than that of 63Sn-37Pb. Both 90Sn-2Bi-3Ag-5In/substrate and 94Sn-3Bi-3Ag/substrate interfaces demonstrate similar reaction kinetics in the experiment. The stability of the interface is greatly impaired during 90degreesC aging. Some locations of the electroless Ni layer break down, and new phases are formed nearby the interface during aging treatment. Initially, the growth of Ni-rich (Ni, Cu)(3)Sn-4 phase dominates the interfacial reaction. However, the growth of Cu-rich (Cu,Ni)(6)Sn-5 phase will dominate the reaction layer for specimens aged at 90degreesC for long time periods. (C) 2003 Kluwer Academic Publishers.