Au-induced improvements in the grain stability and mechanical properties of Ag-based alloy wires under electrical current stressing
The evolutions of the surface morphologies, cross-sectional microstructures, and mechanical properties of two types of Ag-based alloy wires with different Au contents under a 105 A/cm2 electrical current density across various times were compared in this study. Ag-based alloy wires that contain 8 wt% Au and 15 wt% Au with 3 wt% Pd were produced via rapid drawing and multiple annealing processes to replace commercial Au-bonded wires in the electronic packaging industry. The surface morphologies of these wires were revealed by scanning electron microscopy (SEM), and cross-sectional microstructures were analyzed by electron back scattering diffraction (EBSD). The SEM observations showed grain- and step-like structures in the Ag–8Au–3Pd and Ag–15Au–3Pd wires after a 5-h treatment, respectively. EBSD results revealed a change in the main preferred orientation from <001> slender grains to <111> equiaxed grains because the high-angle grain boundaries (HAGB) were reduced, and the twin boundaries (TB) were multiplied along the drawing direction. In terms of mechanical properties, Ag–15Au–3Pd wire showed better breaking loads and elongations than Ag–8Au–3Pd wire. The Au effect in Ag-based alloy wires reduced the atomic diffusion to stabilize grain structures and induce a dislocation accumulation, which subsequently improved the mechanical properties by retaining and forming HAGBs, LAGBs, and TBs under high current stressing.
The authors gratefully acknowledge the financial support for this research by the Ministry of Science and Technology of Taiwan under Grant No. NSC 106-2221-E-005-026-MY3. The present work was also supported in part by the Center for Micro/Nano Science and Technology of the National Cheng Kung University and Innovation and Development Center of Sustainable Agriculture (IDCSA).
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