Present study investigates the effects of the electrical fatigue test on the microstructures, electrical properties and elemental distribution of gold (Au)-coated Ag-4Pd (ACA4P) alloy wire. The electrical fatigue test is an important method for estimating the reliability of electronic devices to cyclic thermal stress caused by bias-induced Joule heat. In the bias test, the thermal diffusion behavior of Au atoms on the wire surface was more intense with increasing current density. The Au atoms diffused along the grain boundary of the wire and finally distributed throughout the wire matrix. In the bias fatigue test, the electrical resistances of the wire and ball bond decreased, and then increased as the bias cycle increased to 6000 cycles. An increase in grain size of the wire and ball bonded wires by bias-induced thermal energy caused their electrical resistances to decrease. Poisson's effect caused the diameter of the wire to decrease, and thus increased the resistance of the wire. The growth of Ag2Al intermetallic compounds (IMCs) at the bonding interface was responsible for the increase in the resistance of the ball bonded wire.
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