Study on the preparation of Au-Sn eutectic alloy solder for electronic packaging and gold purification

Au-Sn eutectic alloy has emerged as a critical lead-free solder material in advanced electronic packaging due to its superior thermal conductivity, low melting point, and excellent wettability. However, challenges persist in achieving uniform microstructures during fabrication and efficiently recovering high-purity gold from alloy scraps. This study presents an integrated approach for the preparation of Au-Sn eutectic alloy sheets and a three-step chemical purification method for gold recovery. The alloy fabrication process involves vacuum melting, directional solidification, homogenization heat treatment, and warm rolling, which yield fine-grained, crack-free solder sheets. For gold purification, sequential tin removal steps—copper powder replacement, hydrochloric acid leaching, and hydrolysis—are combined with sodium sulfite reduction to achieve a purity of 99.99% gold. Experimental results demonstrate that the optimized process parameters (e.g., 20.0~20.5 wt.% Sn, 1100~1200 °C melting, and 230~260 °C homogenization) significantly enhance alloy ductility and solder performance. The developed methods offer scalable solutions for industrial applications, aligning with sustainable manufacturing and resource recycling goals.