Aging effect on microstructure and properties of SAC305/Cu column interconnect obtained by friction plunge welding

The influence of aging treatment at 393 K on microstructure and properties of SAC305/Cu column interconnect obtained by friction plunge welding (FPW) was investigated. Analysis showed that a thin Ag-rich adhering layer formed at the interface after welding. With increase of aging time, Cu6Sn5 and Cu3Sn layers successively formed at the interface and the outermost Ag-rich layer gradually disappeared. Interface layer thickness is much lower than that of traditional reflow soldering joints within aging time of 600 h. Tests revealed that indentation hardness of thermal-mechanically affected zone and reflow soldering zone decreased after aging due to the coarsening of solder and wetting of β-Sn grain boundary by intermetallic compound (IMC). Stir zone softened by recrystallization during FPW, after aging its hardness increased to that of reflow soldering microstructure, which may be that sufficient atom diffusion improved wetting of IMC particles in β-Sn matrix and dispersion strengthening effect of IMC. Corresponding to above results, pull-out load of aging joint has also doubled. For solid-phase micro-welding with insufficient diffusion such as wire bonding and the FPW, joint performance can be improved by a suitable aging treatment because aging is similar to the post-weld heating. © 2020 Elsevier B.V.