Effects of Temperature and Pd Concentration on the Corrosion Behavior of Pd-Doped Cu and Cu9Al4 at the Cu–Al Ball-Bond Interface

Abstract

Corrosion-induced failure along the Cu and Cu9Al4 interface is a major reliability concern for the Cu-wire-bonded packages. The open circuit potential, $E_{\text {oc}}$ , and the corrosion current density, $i_{\text {corr}}$ , of Cu and Cu9Al4 with varying amounts of Pd addition were characterized using the potentiodynamic polarization method at 25 °C, 45 °C, and 65 °C. At a given temperature, Pd addition to Cu caused the value of $E_{\text {oc}}$ to increase and the value of $i_{\text {corr}}$ to decrease due to the higher nobility of Pd. For the Cu9Al4 intermetallics, although Pd addition caused an increase in the value of $E_{\text {oc}}$ attributed to the high nobility of Pd, the value of $i_{\text {corr}}$ increases with small amounts of Pd addition due to high cathodic activity of Pd. To further evaluate the effect of Pd addition in preventing the corrosion of Cu wire bonds, galvanic current densities, $i_{g}$ , between Cu and Cu9Al4 and their Pd-doped couples were also measured. At 25 °C and 45 °C, the stabilized value of $i_{g}$ decreases with an increasing amount of Pd addition. At 65 °C, the stabilized value of $i_{g}$ was not lower until 9 wt.% Pd was added. The results of both self-corrosion and galvanic corrosion suggest that the amount of Pd needs to be above a critical value to effectively prevent Cu wire corrosion regardless of the operating temperature.