Viscoplastic behavior of Sn-3.0Ag-0.5Cu-xBi low-melting-point lead-free solder alloys and the thermal fatigue reliability of their packaging interconnections
Abstract：As electronic products become more pervasive, issues of thermal reliability during their service period have attracted extensive attention. Rate/temperature-dependent mechanical behavior of low-melting-point lead-free solder alloy and thermal reliability study of its packaging interconnection are an important foundation for the lead-free, high equipment quality and reducing energy consumption requirements in the field of electronics industry. Firstly, uniaxial tensile tests of three low-melting-point lead-free solder alloys, namely Sn-3.0Ag-0.5Cu-xBi (x = 0 wt.%, 1.5 wt.%, 2.5 wt.%), are conducted at different temperatures and strain rates using an Instron universal material testing machine. The influence of temperature, strain rate, and Bi element content on the tensile deformation behavior (elastic modulus, saturation stress) of the three solder alloys are analyzed. Additionally, the thermal expansion coefficients of the three solder alloys are obtained through thermal expansion tests and the melting points of three solder alloys are measured by Differential Scanning Calorimetry. Based on nonlinear fitting, the unified viscoplastic Anand constitutive parameters for three solder alloys are obtained and compared with the experimental data to verify the validity of the obtained parameters. Furthermore, combined with the obtained viscoplastic parameters and numerical simulation, the thermal fatigue reliability of SAC305-xBi low-melting-point lead-free solder alloys in packaging interconnections is analyzed. The positions of key solder joints during the temperature cycling process are determined, and the effects of Bi element content on the maximum equivalent stress and maximum equivalent plastic strain of key solder joints were analyzed. Finally, the thermal fatigue life of critical solder joints is evaluated based on the modified Coffin-Manson fatigue model considering plastic deformation. Results show that the addition of Bi element can lower the melting point and improve the thermal fatigue reliability of SAC305 solder alloy in packaging interconnection. The related research is of great significance for the system design of low-melting-point lead-free solder alloys and the improvement of their thermal reliability in packaging interconnections.
2025, Vol. 46 
