Abstract
Cu 6 Sn 5 is the dominant intermetallic compound at the Sn/Cu joint interface. The crystal structure of Cu 6 Sn 5 varies with temperature. After reflow at 250 °C, interfacial Cu 6 Sn 5 revealed a hexagonal structure (η-Cu 6 Sn 5 ). During aging at 150 °C, hexagonal η-Cu 6 Sn 5 transforms into monoclinic η′-Cu 6 Sn 5 . X-ray diffraction and differential scanning calorimetry analyses show that doping small amounts of Zn (0.8-2.1 at.%) into Cu 6 (Sn,Zn) 5 can stabilize the hexagonal structure during the thermal aging process. Thermodynamic calculation also demonstrates that Zn stabilizes the hexagonal Cu 6 (Sn,Zn) 5 . © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.