Reduction of Cu-Ni-Pd pad discoloration caused by Cu re-deposition

Cu-Ni-Pd bonding pads are used extensively in high current wirebonded devices. However in certain cases, there is a susceptibility to discoloration caused by copper re-deposition on the palladium surface. To prevent this mechanism, the best solution is to remove the Cu ions or the electrolyte. Initial evaluations were done using a surfactant with a chelating agent to prevent Cu ions from re-depositing. While the process was successfully used, one drawback given the acidic nature of the surfactant is reduced saw blade life and correspondingly reduced manufacturability. A design solution is also proposed to ensure that the occurrence of copper re-deposition, and subsequently pad discoloration, is prevented through robust die design.