Abstract
The Au/Sn/Cu structure is frequently encountered in flexible electronics. Interfacial reactions in Au/Sn/Cu sandwich specimens with limited Sn supply were examined. The thickness of the Sn layer varied from 5, 8, 14, 17, 27-32 μm and the reaction temperature was at 210 °C. The reaction intermetallic phases were determined and found to evolve with reaction time. Initially, the reaction path in the Au/Sn/Cu specimen is Au/AuSn/AuSn 2 /AuSn 4 /Sn/Cu 6 Sn 5 /Cu 3 Sn/Cu. With longer reaction time, the (Cu,Au) 6 Sn 5 phase is formed on the Au side as well. The (Cu,Au) 6 Sn 5 phase is the Cu 6 Sn 5 phase with Au solubility. The (Cu,Au) 6 Sn 5 phases at the Cu and Au sides merge together after the Sn layer is entirely consumed. The path evolution is Au/AuSn/AuSn 2 /AuSn 4 /(Cu,Au) 6 Sn 5 /Sn/(Cu,Au) 6 Sn 5 /Cu 3 Sn/Cu, Au/AuSn/AuSn 2 /AuSn 4 /(Cu,Au) 6 Sn 5 /Cu 3 Sn/Cu, Au/Au 5 Sn/AuSn/AuSn 2 /(Cu,Au) 6 Sn 5 /Cu 3 Sn/Cu, and Au/Au 5 Sn/AuSn/(Cu,Au) 6 Sn 5 /Cu 3 Sn/Cu. The evolution will continue until the reactants are completely reacted, and the reaction system reaches phase equilibrium. In addition, in the AuSn 4 matrix, a ternary Au 25 Sn 50 Cu 25 phase was found, which merits further characterization. © 2009 Elsevier Ltd. All rights reserved.