Abstract: An incrementally coupled "thermal-mechanical-ultrasonic"(T-M-U) model was developed to simulate the thermosonic wire bonding process using two types of wires(copper and gold) and three thicknesses of Ag coatings(4,8,16 μm).The results showed that the gold wire was better than copper wire for stress condition in the silicon substrate,and the stress concentration zone for the gold wire was closer to the center than that for the copper wire.In addition,the thicker the Ag coating,the lower the stresses in the silicon substrate.Hence,thicker coating is better for reducing substrate damages.