Abstract
In the present study, the neck fracture properties of annealed wire with φ=20 μm (0.8 mil) at 225°C for 1 hour and un-annealed wire were compared. In addition, the microstructural characteristics, the mechanical properties and the texture transition using EBSD methods before and after an electric flame-off (EFO) process were also studied. Experimental results indicate that the recrystallization temperature of the as-drawn wire was ∼225°C, and the annealed copper wires possessed a fully annealed structure. Through recrystallization, the matrix structure transferred from long, thin grains to equiaxed grains and a few annealed twins. The microstructure of the free air ball (FAB) after an EFO process consisted of column-like grains, and grew from the heat-affected zone (HAZ) to the Cu ball. For the annealed and un-annealed wires, their preferred orientations on the wire and the neck were ⟨100⟩||AD. Under the thermal effect of EFO, the orientation of the Cu balls were mainly ⟨101⟩||AD and ⟨111⟩||AD for annealed wires. Additionally, the hardness of the Cu balls and the strength of the neck sites of the EFO wires were able to affect the reliability of the copper wire bonding.
