Phase-Field Modeling and Experimental Observation of Microstructures in Solidifying Sn-Ag-Cu Solders

A multiphase-field model coupled to a thermodynamic database has been successfully applied to model the microstructure evolution during solidification of ternary Sn-Ag-Cu solders, revealing up to five different phases. Simulations were performed in two dimensions (2D) in the bulk volume of the solder as well as at the interface with a copper substrate, addressing the length scales of both dendritic and eutectic structures. Primary dendrite spacing and secondary arm spacing of Sn dendrites in the bulk solder volume match well with experimental observations. The eutectic spacing of Ag3Sn lamellae and their thickness also match experimental data, while the thickness of the Cu6Sn5 lamellae is slightly larger than found by experiment. Nucleation and growth of Cu6Sn5 on a Cu substrate lead to superficial dissolution and roughening of the substrate, with the size of the Cu6Sn5 largely determined by its nucleation conditions.status: publishe