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

Corrosion-induced failure along the Cu and Cu
₉
Al
₄
interface is a major reliability concern for the Cu-wire-bonded packages. The open circuit potential, E
_oc
, and the corrosion current density, i
_corr
, of Cu and Cu
₉
Al
₄
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
_oc
to increase and the value of i
_corr
to decrease due to the higher nobility of Pd. For the Cu
₉
Al
₄
intermetallics, although Pd addition caused an increase in the value of E
_oc
attributed to the high nobility of Pd, the value of i
_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 Cu
₉
Al
₄
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.