First-principles and experimental investigations on the mechanical properties of Co particles modified Sn-1.0Ag-0.5Cu solder

• The First-principles calculations revealed that the (Cu, Co) 6 Sn 5 exhibited superior thermodynamic stability compared to Cu 6 Sn 5 . • The introduction of Co particles provided additional heterogeneous nucleation sites at the interface layer, leading to grain refinement. • The addition of Co particles was found to improve solder wettability. • Co incorporation was found to significantly improve the shear strength (peaking at 30.64 MPa) and microhardness (reaching 16.1 HV) This study systematically investigated the influence of Co particles addition on the properties of Sn-1.0Ag-0.5Cu (SAC105) solder through a combined approach of first-principles calculations and experimental characterization. First-principles calculations revealed that the adding Co particles significantly increased in the elastic modulus of SAC105 solder. In addition, the (Cu, Co) 6 Sn 5 intermetallic compound (IMC) exhibited superior thermodynamic stability compared to conventional Cu 6 Sn 5 . Microstructural analysis showed that the adding Co particles resulted in both interfacial morphology smoothing and grain refinement. Significantly, this modification process was found to promote the growth of the interfacial layer. The analysis revealed the conversion of Cu 6 Sn 5 to (Cu, Co) 6 Sn 5 within the IMC layer, accompanied by the formation of blocky (Cu, Co) 6 Sn 5 near the IMC layer. Experimental results demonstrated that incorporation of Co particles into SAC105 solder induced no significant alteration in the thermal properties of the solder alloys. Nevertheless, the wettability and mechanical properties of composite solder showed improvement. The best shear strength was obtained at Co content of 0.06 wt %. At the Co content of 0.1 wt %, the composite solder achieved superior wettability, exhibiting a reduced contact angle of 24.03°