Growth behavior of tin whisker and hillock on Cu/Ni/SnAg micro-bumps under high temperature and humidity storage

It is the first time that tin whisker was observed to grow from shallow surface grains on Cu/Ni/SnAg micro-bumps under high temperature and humidity storage. Stress difference formed by oxidation and intermetallic compound (IMC) reaction was the driving force for whisker formation. Interrelated twins with uniform orientation slowed down the diffusion rate of tin atoms and large Ag3Sn bulk on the shallow surface restricted the whisker grain boundary migration, impacting significantly on the morphology of whisker and hillock. Based on the results, formation mechanism of tin whisker and terrace-like hillock was proposed. The findings are of great significance to the study of tin whisker and hillock on isolated Sn-based solders and provide insights into the reliability of 3D electronic packaging.