关键词: 激光喷球键合, 尺寸效应, β-Sn晶粒, 显微硬度

Abstract: To address the issues of substrate thermal warpage deformation caused by conventional reflow soldering and performance variability due to anisotropy in Sn-based solder joints, Sn-3.0Ag-0.5Cu(SAC305)/Cu ball grid array (BGA) joints with sizes ranging from 400 to 760 µm were fabricated via laser jet solder ball bonding (LJSBB) technology in this study, and the size effect on microstructure and microhardness evolution was systematically investigated. The results indicated that all the LJSBB joints exhibited a β-Sn<110> preferred orientation, especially in large joints. As joint size increased, the average grain size of β-Sn on the transverse section increased from 42.0 µm to 66.2 µm. Meanwhile, the volume fraction of low-angle grain boundary (LAGB) decreased from 71.9% to 55.6%, and strain reduced from 0.8° to 0.5°. This joint size effect could be attributed to the rapid-gradient cooling characteristic of the LJSBB technology. Small-sized joints demonstrated “fine grain-high LAGB-high strain” features due to short interfacial reaction duration and strong geometric constraints. The microhardness decreased from 17.2 HV to 13.9 HV with joint size increased. Hall-Petch analysis confirms that grain refinement strengthening is the core mechanism of hardness regulation. Compared to conventional soldering joints, the LJSBB joints exhibited over 9.6% higher hardness and significantly improved performance stability.

Key words: laser jet solder ball bonding, size effect, β-Sn grain, microhardness