Electrochemical behavior of a lead-free SnAg solder alloy affected by the microstructure array

The aim of this study is to evaluate the electrochemical corrosion behavior of a Sn-Ag solder alloy in a 0.5 M NaCl solution at 25 degrees C as a function of microstructural characteristics. Different microstructure morphologies, which can be found in Sn-Ag solder joints and that are imposed by the local solidification cooling rate, are evaluated and correlated to the resulting scale of the dendritic matrix and the morphology of the Ag3Sn intermetallic compound. Cylindrical metallic molds at two different initial temperatures were employed permitting the effect of 0.15 degrees C/s and 0.02 degrees C/s cooling rates on the microstructure pattern to be experimentally examined. Electrochemical impedance spectroscopy (EIS) diagrams, potentio-dynamic polarization curves and an equivalent circuit analysis were used to evaluate the electrochemical parameters. It was found that higher cooling rates during solidification are associated with fine dendritic arrays and a mixture of spheroids and fiber-like Ag3Sn particles which result in better corrosion resistance than coarse dendrite arrays associated with a mixture of fibers and plate-like Ag3Sn morphologies which result from very slow cooling rates. (C) 2011 Elsevier Ltd. All rights reserved.