The effect of Pd and Cu in the intermetallic growth of alloy Au wire

Abstract

This is the new wire evaluation work for the reliability of the wire-bonding process. There is a trend for the plastic integrated-circuit package to function at higher junction temperature with thinner wire. New alloy Au wires have been developed to meet the reliability requirements. Two types of alloy Au wires, Au-Pd and Au-Cu, were evaluated in this study. These samples were aged between 155°C and 205°C under air from 0 h to 3,000 h. According to this study, the phase-formation sequence of Au2Al, Au5Al2, and Au4Al intermetallic is similar to the pure Au wire. There is a Pd-rich layer working as a diffusion barrier to slow down the growth rate of intermetallic phases in the Au-Pd wire. The Au-Cu wire also slowed down the growth rate with a different mechanism. Both wires have better reliability based on the microstructure examination. The reliability test results show longer working life at higher temperatures in comparison with the regular Au wire.