Temperature Gradient Induced Orientation Change of Bi Grains in Sn–Bi57–Ag0.7 Solder Joint

Sn-Bi-X solders are widely used in electronic packaging industry. However, thermomigration (TM) behaviors of solder joints and the orientations change Bi grains under temperature gradient rarely reported. In this study, Sn-Bi57-Ag0.7/Cu were to conduct a TM test 625 °C/cm for 400 h, an isothermal aging at 85 °C was also conducted comparison. The microstructural evolution after reflow, analyzed by scanning electron microscopy (SEM), transmission (TEM) probe microanalysis (EPMA). results indicated that Sn/Bi areal ratio did not significantly whether hot end (from 46.78%/52.12% 50.90%/48.78%) or cold 50.25%/49.64% 48.71%/51.16%) compared with as-reflowed samples due insufficient thermal energy. thickness intermetallic compound (IMC) (2.49 μm) very close IMC (2.52 μm), which aged samples. addition, preferred Sn different Sn–Bi–Ag resulting from conditions (reflow, aging) characterized backscatter diffraction (EBSD). obtained demonstrated both had no orientation reflow aging, while sample changed random direction c-axis ([0001] direction) parallel heat flow. Ag3Sn could hinder gradient, corresponding mechanism systematically illuminated. This study firstly revealed would have profound guiding significance enhancing reliabilities joints.