Recrystallization and grain growth of cold-drawn gold bonding wire

Abstract

Recrystallization and grain growth of gold bonding wire have been investigated with electron backscatter diffraction (EBSD). The bonding wires were wire-drawn to an equivalent strain greater than 11.4 with final diameter between 25 and 30 mm. Annealing treatments were carried out in a salt bath at 300 °C, and 400 °C for 1, 10, 60 minutes, and 1 day. The textures of the drawn gold wires contain major ͗111͘, minor ͗100͘, and small fractions of complex fiber components. The ͗100͘ oriented regions are located in the center and surface of the wire, and the complex fiber components are located near the surface. The ͗111͘ oriented regions occur throughout the wire. Maps of the local Taylor factor can be used to distinguish the ͗111͘ and ͗100͘ regions. The ͗111͘ oriented grains have large Taylor factors and might be expected to have higher stored energy as a result of plastic deformation compared to the ͗100͘ regions. Both ͗111͘ and ͗100͘ grains grow during annealing. In particular, ͗100͘ grains in the surface and the center part grow into the ͗111͘ regions at 300 °C and 400°C. Large misorientations (angles Ͼ40 deg) are present between the ͗111͘ and ͗100͘ regions, which means that the boundaries between them are likely to have high mobility. Grain average misorientation (GAM) is greater in the ͗111͘ than in the ͗100͘ regions. It appears that the stored energy, as indicated by geometrically necessary dislocation content in the subgrain structure, is larger in the ͗111͘ than in the ͗100͘ regions.

Recrystallization Textures of Metals and Alloys

“…Figure 24 shows the grain size and the volume fraction of the <111> and <100> grains as a function of annealing time at 300 and 400 o C. These values are based on EBSD measurements. The aspect ratio of grain shape was in the range of 1.5 -2, which is little influenced by annealing time and temperature [36]. The grain growth occurs in whole area of the wire and is more rapid at 400 o C than at 300 o C as expected for thermally activated motion of grain boundaries.…”

“…The annealing textures obtained at 700 °C is not the primary Rex texture. Cho et al [36] measured the drawing and Rex textures of 25 and 30 µm diameter Au wires of over 99.99% in purity, which had dopants such as Ca and Be that total less than 50 ppm by weight. The Au wires were made by drawing through a series of diamond dies to an effective strain of 11.4.…”

Recrystallization and grain growth of cold-rolled gold sheet

“…Recently, Cho et al reported recrystallization and grain growth of gold bonding wire during isothermal annealing at 300 °C and 400°C using electron backscatter diffraction (EBSD). [25] In cold-rolled gold sheet, the authors found that deformation textures consist of the general ␤-fiber (Brass-S-Copper) and some shear textures on the surface. Annealing textures have the same ␤-fiber in addition to cube and random orientation.…”

A Preliminary Electron Backscatter Diffraction Study of Microstructures and Microtextures Evolution during Au Stud and Flip Chip Thermosonic Bonding

“…The results are agreement with other studies. [3][4][5] As shown in the orientation map and the inverse pole figure of the wire, the two fiber components <111> + <100> were observed. It is evident that the <111> component is much stronger than the <100>.…”

“…So far, several researchers have applied this technique to study wire drawing and gold wire bonding. [3][4][5] Jae-Hyung Cho 3 investigated the recrystallization and grain growth of gold bonding. Wulff 4 demonstrated the characterization of gold bonding wires at various stages of processing, from casting through wire drawing.…”