Electrochemical studies of Pd-doped Cu and Pd-doped Cu-Al intermetallics for understanding corrosion behavior in wire-bonding packages

摘要

This study investigated the electrochemical characterizations in the field of wire metallurgy (Pd concentration) and molding compound chemistry (chloride concentration) to find ways to reduce metallic entities' susceptibility to corrosion at ball-pad interfaces. The open circuit potentials and potentiodynamic polarization curves of various metallic entities found in a Cu(Pd)-Al bonding interface were obtained in near-neutral electrolytes of 100 ppm, 20 ppm, and 1 ppm of NaCl in high-purity water. From X-ray diffraction spectra, it was found that Pd could be homogeneously incorporated into Cu9Al4, the Cu-rich intermetallic compound (IMC) also referred to as gamma but not into CuAl2, the Al-rich IMC also referred to as theta for arc-melted specimens. For Cu-Pd alloys, at a given chloride concentration, increasing Pd concentration causes the value of open-circuit potential (E-oc) to increase and corrosion current density (i(corr)) to decrease. Likewise, for a given amount of Pd in Cu-Pd alloy, decrease in the NaCl concentration causes the value of E-oc to increase and i(corr) to decrease. Interestingly, for high concentration of Pd as in the case of Cu-9Pd, E-oc and i(corr) became less sensitive to the NaCl concentrations investigated. This can be attributed to the Pd enrichment on the corroding surface that reduces the anodic dissolution rate of Cu. For Pd-doped gamma intermetallics, increasing Pd concentration causes a systemic increase in the value of E-oc, but at a lower concentration of Pd, the value of i(corr) was increased. The addition of Pd to gamma causes an increase in the cathodic current density due to the high cathodic activity of Pd, while the passivation of Al in gamma reduces the extent of the anodic current density reduction due to the addition of Pd, which leads to a higher value of i(corr) at a low Pd concentration. This is true even when the NaCl concentration is as low as 1 ppm. On the other hand, the influence of NaCl concentration on the E-oc and i(corr) of gamma IMC was always observed, even with Pd addition. (c) 2017 Elsevier Ltd. All rights reserved.