Investigation of recrystallization and grain growth of copper and gold bonding wires

Abstract

Copper bonding wires were characterized using electron backscatter diffraction (EBSD). During drawing, shear components are mainly located under the surface and ,111. and ,100. fiber texture components develop with similar volume fractions. Grain average misorientation (GAM) and scalar orientation spread (SOS) of the ,100. component are lower than those of the ,111. or other orientations. Also, ,100. components grow into other texture orientations during recrystallization. Copper wires experience three stages of microstructure change during annealing. The first stage is subgrain growth to keep elongated grain shapes overall and to be varied in aspect ratio. The grain sizes of the ,111. and ,100. components increase. 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. The ,111. and ,100. grains compete with each other, and the ,111. grains grow faster than the ,100. grains during the third stage. Comparison of recrystallization and grain growth processes in copper and gold wires reveals many common microstructural features.

Evolution of microstructure and texture of cold-drawn polycrystalline Ag with low stacking fault energy

“…grain subdivision near the sample surface is more evident than that at the center, as shown in Figures 2(a) and (b). However, work hardening can reduce deformation inhomogeneity along the radial direction of wires [7,23], which leads to that the difference of grain subdivision along the radial direction of wires disappears at the strains higher than 0.58, as shown in Figures 2(c)-(f).…”

“…Cold drawing can be used to prepare ultra-fine crystal materials [1,2] and super-fine bonding wires [5]. Therefore, in order to understand their properties, microstructure and texture of cold-drawn metal wires have received wide attention [6][7][8].…”

Experimental and numerical investigations of the texture evolution in copper wire drawing

“…The plastic strain increment is computed based on the shear strain γ of each active slip system α A, activated. A rate independent crystal plasticity case is considered here where the determination of active slip systems is based on Kuhn-Tucker criteria [26] as defined by (9), (10), and (11). The slip systems with shear strain γ α < 0 are not considered for the yield function validation during that particular time step and are excluded.…”

“…The coefficient of friction between the die and the copper wire was kept constant at a value of 0.05 for all the drawing simulations conducted. The friction in diamond die has been considered to be negligible during modeling by Cho et al [10] and Park et al [28,29]. They assumed 0.001 as Coulomb coefficient of friction between the die and wire.…”

“…The manufacturing of these polycrystalline wires requires an understanding of the relation of the role of deformation induced anisotropy on the plastic flow behavior of the material. In polycrystalline materials, the crystallographic orientations of individual grains, play an important role in the plasticity of the material [9,10]. In face centered cubic material (FCC), i.e., silver, gold, copper, and brass undergoing rolling or extrusion, the grains rotate toward a preferential orientation, leading to deformation induced crystallographic texture.…”