Effects of Current Stressing on the Grain Structure and Mechanical Properties of Ag-Alloy Bonding Wires with Various Pd and Au Contents

Ag-alloy bonding wires containing various Pd and Au elements and traditional 4 N Au and Pd-coated 4 N Cu bonding wires were stressed with a current density of 1.23 ˆ 105 A/cm2 in air. The amounts of annealing twins in the Ag-alloy wires were much higher than those in Au and Pd-coated Cu wires. The percentages of twinned grains in these Ag-alloy wires increased obviously with current stressing. However, the grains in Ag-3Pd and Ag-15Au-3Pd grew moderately under current stressing, in contrast to the dramatic grain growth in the other bonding wires. In addition, the breaking loads and elongations of the various Ag-alloy wires changed slightly, similar to the case of Au wire. The results implied that degradation of the mechanical properties of these annealing twinned Ag-alloy wires due to electromigration was limited. Pd-coated Cu wire was severely oxidized after current stressing for only 1 h in air, which drastically degraded both the breaking load and elongation.