Methodology to determine high precision variation in the electrical resistance of copper wires due to corrosion

In reliability testing, integrated circuit (IC) packages are subjected to accelerated stress test according to the Joint Electron Device Engineering Council (JEDEC) standards to predict the lifetime under the operating conditions. Accelerated stress test on copper wire under the influence of moisture causes corrosion which leads to increase in electrical resistance. This paper describes a methodology to measure small resistance change across the bond wires. An approach of using ceramic packages to study bond wire resistance is introduced. Customized wire bonding layout is designed using bare copper wire bonded directly on the gold-plated lead frame. Four-wire measurement setup is applied to eliminate the unwanted test lead resistance. Two types of experiments are carried out to emulate different level of corrosion, namely unbiased highly accelerated temperature and humidity stress test (uHAST) and exposure to salt-acid solution. Physical characterization such as scanning electron microscopy (SEM) inspection, transmission electron microscopy (TEM) inspection and energy dispersive x-ray spectroscopy (EDX) mapping are conducted to characterize the changes that cause the increase in electrical resistance. By using finite element method (FEM) simulation, bond wire resistance is calculated using the effective diameter of copper wires. The values from measurement and simulation are comparable with maximum deviation of 0.32%. The proposed methodology provides an accurate and reliable data collection method for corrosion effect study of copper wire bond.