Experimental Studies and Thermodynamic Assessment of Ternary Cu-Pd-Sn Phase Relations Focusing on the Sn-Rich Alloys

Abstract

Recently, Pd surface finishes over Cu substrates have been widely used in microelectronic packaging to prevent pad oxidation before soldering and to improve the bondability with Cu wires. The interfacial reactions between these newly developed Pd-based substrates and Pb-free solders, particularly Sn-based solders, are of practical importance. To completely understand interfacial reactions and phase transformation phenomena, phase equilibrium information on solders, intermetallics, and substrate materials are required. In this study, the phase equilibria of the Cu-Pd-Sn ternary system at 200°C was investigated by scanning electron microscopy, electron probe microanalysis, and electron backscatter diffraction. Particular emphasis was placed on the Sn-rich corner of the isothermal section. To analyze the experimental results, a thermodynamic assessment was performed using the computer coupling of phase diagrams and thermochemistry method.