Effect of Chlorine-Bromine pH and Temperature on the Corrosion Propensity of the Cu-Al WB System

The lower cost and lower resistivity of copper wire has fueled industry migration away from gold wire used previously. Copper has a higher hardness than gold wire, produces a higher splash, and has a narrow process window. Recently, palladium-coated copper and gold flash palladium-coated copper have appeared. Prolonged exposure of copper wire to high temperatures may result in increased consumption of the aluminum-pad layer and deterioration of the interface's shear strength and robustness. The corrosion resistance of copper wire bonds may vary with environmental exposure. This paper has studied the effect of temperature, pH, chlorine concentration, and bromine concentration on the polarization curves of the Cu-Al intermetallics. The EMC used to encapsulate chips and interconnects can vary widely in formulation, including pH, porosity, diffusion rate, the composition of contaminants, and contaminant concentration. A predictive model that considers ambient factors, operating environment, and EMC exposure is required to reflect the expected wire bond reliability accurately. Different EMCs were used in this work in a high-temperature current environment with temperatures ranging from 60°C to 100°C and different pH values from 4 to 10. The anodic slope, cathodic slope, open-circuit corrosion current density, and then-circuit potential of the Cu-Al intermetallics have been reported for various operating conditions. In order to build a multiphysics model, diffusion dynamics based on the Nernst-Planck Equation for chlorine ion transport were combined with the Butler-Volmer Equation for corrosion dynamics. The diffusion coefficient and flux have been measured by analyzing the chlorine, bromine, and sulfur weight percentage obtained from SEM/EDS machine for the pristine EMC sample and 66 hours sample. Measurements of polarization curves were used to extract Tafel parameters.