The microstructure evolution of copper and gold bonding wires during annealing

Copper and gold bonding wires were characterized and compared using electron backscatter diffraction (EBSD). During drawing, < 111 > and < 100 > fiber textures are the main components in the wires and shear components are mainly located under the surface. Grain average misorientation (GAM) and scalar orientation spread (SOS) of the < 100 > component in copper and gold bonding wires are lower than those of the < 111 > or other orientations. The bonding wires experience three stages of microstructural changes during annealing. The first stage is subgrain growth to keep elongated grain shapes overall and to be varied in aspect ratio with annealing time. The grain sizes of the < 111 > and < 100 > components increase during annealing. The volume fraction of the < 100 > component increases whereas that of the < 111 > decreases. The second stage is recrystallization, during which equiaxed grains appear and coexist with elongated ones. The third stage is grain growth which eliminates the elongated grains and enlarges equiaxed grains. The < 111 > and < 100 > grains compete with each other and the < 111 > grains grow faster than the < 100 > grains during the third stage.