New challenges of miniaturization of electronic devices: Electromigration and thermomigration in lead-free solder joints

The continuous improvement of electronic device performances and the advancement of packaging technology have brought greater challenges to the reliability of solder joints in integrated circuits (ICs). In view of the increase of chip integration and the reduction of micro-bump size in 3D ICs, the high current density and excessive Joule heat will result in serious reliability issues of electromigration (EM) and thermomigration (TM) respectively, which evidently shorten the lifetime of solder joints. This article reviewed the influence of EM, TM and their coupling effect on microstructure evolution and properties of different joints soldered with pure Sn, SnAgCu, SnBi and SnZn solder. What's more, the increase of EM and TM resistances of micro-joints by microalloying, particle reinforcement and substrate improvement was explored. Finally, the shortcomings of current studies and the future research directions were summarized to further improve the EM and TM reliability of micro-joints, which promotes the application of lead-free solders in 3D ICs package. (C) 2020 The Authors. Published by Elsevier Ltd.