Abstract
Copper wire bonding has increasingly being preferred in place of the more expensive gold wire for chip-to-substrate or chip-to-leadframe interconnects. The copper wire has a higher propensity for corrosion, higher hardness, narrow process window, thinner intermetallics and a higher propensity for cratering owing to a highe splash. Electronics in automotive underhood applications may be routinely expected to function reliability for 10-years, 100K miles. There is lack of foundational data for the assessment of Cu-Al wirebond reliability under humidity and contaminants including Bromine and Chlorine. Exposure to high temperature has been shown to appearance of two new intermetallics Cu85Al15 and Cu94Al6 never studied before for their propensity for corrosion. In this paper, the Cu85Al15 and Cu94Al6 intermetallics have been methodically fabricated using an arc-melter. Polarization curves of the intermetallics have been measured versus operating temperature, annealing duration at 250C, and changes in the pH. For each use-case, the effect of open circuit corrosion current density, open circuit corrosion potential, anodic and cathodic slopes have been quantified. Corrosion rate has been computed for both the intermetallics. The experimental data has been used to formulate a Multiphysics model for the prediction of propensity for corrosion using the Butler-Volmer and Nernst Planck Equations.
