Influence of trace Mn doping on the high-speed shear performance of lead-free alloy/copper solder joints: Experimental and first principles investigation

This study aims to investigate the mechanical properties changes and the underlying reasons caused by Mn addition to the Cu6Sn5 intermetallic compounds (IMC). For this purpose, 0.07 wt.% Mn doped SnAgCu (SAC)305/Cu joint were prepared to observe its shear performance at a high speed of 1000 mm/min after aging at 170°C for 750 h. The mechanical properties of Mn-doped samples exhibited a smaller decline after aging, in comparison to the undoped samples. Notably, the fracture location transitioned from the interior of the SAC joint to joint interface after doping. Nanoindentation experiments demonstrated a significant increase in the modulus and hardness of the Mn doped Cu3Sn and Cu6Sn5 phases. To gain a deeper understanding of the underlying mechanisms driving the changes in IMC properties, first principles calculations were employed. The introduction of Mn resulted in a strengthened bonding due to the hybridization of Mn and Sn atoms in the high-energy regions, leading to the formation of charge-enriched areas and improved mechanical properties of the IMC. The results obtained from both computational and experimental approaches exhibit similar trends in these changes. Moreover, the integration of computational and experimental methods provides a guidance for advancing IMC research and enhancing our understanding of their behavior.