Microstructure, Tensile Mechanical Properties and Electrical Fatigue Mechanism of a Microalloyed Copper Wire

In this study, trace quantities of silver, palladium, and gold were added to 5 N pure copper wires to prepare microalloyed copper (MAC) wires. The mechanical properties and electrical fatigue mechanisms of original wires and wire bonding specimens were compared to assess the differences between MAC and Au/Pd-coated copper (CPA) wires. The results indicate that the solid-solution strengthening achieved by the addition of trace alloy elements improved the microhardness and tensile properties of the wires; thus, the overall mechanical properties of the MAC wires were superior to those of a CPA wire. Moreover, after wire bonding, the MAC wires exhibited a higher first bond strength than the CPA wire. In terms of electrical properties, the addition of trace alloying elements increased resistance marginally, which resulted in MAC wires with higher dynamic resistance than the CPA wire in the early stage of electrification. At high currents, CPA wires are affected by Joule heat. The palladium atoms in the coating layer diffuse into the wire matrix, which causes the resistance to increase rapidly and thus results in a decreased fusing current. In a power cycling test, the coefficients of thermal expansion of the coating layers were different from that of the wire; thus, the CPA wire was susceptible to thermal fatigue, which led to its failure. The MAC wires had a higher power cycle life than the CPA wire. Because of their superior mechanical and electrical properties, MAC wires can replace CPA wires in the electronic packaging industry.