Enrichment of annealing twins in an Ag-4Pd bonding wire for electronic packaging

Annealing twins have been reported to have beneficial effects on the mechanical properties of structural materials. For electronic applications, it has also been reported that electromigration can be retarded by one order of magnitude in a Cu thin film under current stressing. Due to its low stacking fault energy, it is expected that Ag alloy can be produced as a bonding wire with a high percentage of twinned grains for IC and LED applications. This paper presents a new method of multiple drawing and annealing procedures for further enhancing the formation of annealing twins. The experimental results indicate that the twinned grain percentage of an Ag-4Pd wire increases from 15.8% to 35.3% during multiple drawing and multiple annealing treatments as the wire diameters decrease from 30 μm to 17.6 μm, and further increases to values over 50% after aging at 600 °C or current stressing at 1.23×10⁵ A/cm² for 3 hrs. In comparison to the conventional grained Ag-alloy wires with the same alloy compositions, such twin-rich bonding wires exhibit higher thermal stability of the grain structure and longer mean failure time under current stressing.