Effect of Zn doping on SnAg solder microstructure and electromigration stability

A comprehensive study on the effect of Zn-doped SnAg solders on microstructure and electromigration (EM) is reported. Minor Zn doping, about 0.6 wt%, in a SnAg solder alloy is found to be effective in stabilizing solder microstructure and improving EM reliability. Early EM failure modes in Zn-doped solders are significantly suppressed, resulting in a longer EM lifetime with tight distributions. Analyses using optical microscopy, scanning electron microcopy, transmission electron microscopy, electron microprobe analysis, and electron backscattering diffraction were conducted. Zn addition in SnAg leads to significant changes in solder microstructure, grain structure, and thermal and EM stabilities. The strong reaction of Zn with Cu atoms effectively slowed down the Cu diffusion in Β -Sn grains, thus improved the EM stability of Sn-rich solder joints. © 2009 American Institute of Physics.