Kinetics of intermetallic compound formation at 91Sn-8.55Zn-0.45Al lead-free solder alloy/Cu interface

The kinetics of intermetallic compounds (IMCs) formation at the 91Sn-8.55Zn-0.45Al lead-free solder alloy/Cu substrate interface during soldering and subsequent aging have been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), transmission electron microscopy (TEM) and electron diffraction (ED). From the XRD results, gamma-Cu5Zn8 and Cu6Sn5 are found in the eutectic 91Sn-8.55Zn-0.45Al solder alloy/copper interface, but no gamma'-Cu9Al4 is formed in the wetted samples aged at 423 K for 250 h. However, by TEM observation and ED analysis, gamma'-Cu9Al4 is found at the interface of the solder alloy and the Cu substrate, and the IMC growth can be expressed as X = (Dt)(1/2). The activation energy of the gamma-Cu5Zn8 layer growth in 91Sn-8.55Zn-0.45Al solder alloy/Cu interface is determined as 53.77 kJ/mol. (C) 2004 Published by Elsevier B.V.