Recrystallization, Electric Flame-Off Characteristics, and Electron Backscatter Diffraction of Copper Bonding Wires

Abstract

In the present study, the neck fracture properties of annealed wire with ¿ = 20 ¿m (0.8 mil) at 200°C ~ 300°C for 1 h and unannealed wire were compared. The microstructural characteristics, the mechanical properties and the texture transition using electron back scatter diffraction methods before and after an electric flame-off (EFO) process were also studied. Experimental results indicate that the annealing temperatures of more than 225°C, the 20 ¿m copper wires possessed a fully annealed structure, the tensile strength and the hardness decreased, and the elongation was raised. 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 225°C annealed and unannealed 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.