Thermodynamic Investigation On The Ag-Ni-Pd-Sn Solder System

Due to their excellent comprehensive properties,Ag-Sn solder is replacing the traditional Pb-Sn solder and widely used in electronic circuit and electronic packaging field.Ni/Pd metal coating can effectively improve the reliability and the service life of solder joints.Accurate thermodynamic investigation can help the effective design of the solder composition,optimization of the solder process parameters and improvement of the reliability of the solder joints.Based on the CALPHAD（CALculation of PHAse Diagram）method,this work performed thermodynamic investigation of the Ag-Ni-Pd-Sn solder system.The main works and results are as follows:（1）The Ag-Sn and Ni-Sn systems were re-optimized and the obtained thermodynamic parameters can accurately reproduce the phase diagrams and the thermodynamic data of the two binary systems,especially on the heat capacity of the Ag₃Sn phase,temperature dependence of enthalpies of mixing of liquid in the Ni-Sn system,and the allotropy transformation of the Ni₃Sn₂ phase.Considering the reported thermodynamic parameters of the Ag-Ni system and the experimental data on the ternary system in literature,the Ag-Ni-Sn system was systematically optimized.The calculated isothermal sections and vertical sections as well as thermodynamic properties using the obtained thermodynamic parameters showed reasonable consistency with the experimental data.The liquidus projection of Ag-Ni-Sn system was further calculated and the Scheil reaction scheme was constructed.（2）Isothermal sections at 523 K and 673 K in the Sn-rich corner of the Ag-Pd-Sn system were experimentally determined and the as-cast microstructure of the alloys were analyzed.No ternary compounds were observed and the solubilities of the third component in binary compounds were limited in this system.The Ag-Pd and Pd-Sn binary systems were re-optimized and the obtained thermodynamic parameters refined the description on the phase diagram and the enthalpies of mixing of FCC phase at 600 K in the Ag-Pd system,and invariant reactions in the Sn-rich corner of Pd-Sn system.Based on the re-assessed Ag-Pd and Pd-Sn binary systems and the obtained experimental data,the Ag-Pd-Sn system was systematically optimized and a set of self-consistent thermodynamic parameters of the Ag-Pd-Sn system was obtained.（3）The Ni-Pd system was re-optimized and the obtained self-consistent thermodynamic parameters of the system refined the description on the enthalpies of mixing of FCC phase at 1173 K.Then the Ni-Pd-Sn system was systematically optimized based on the available experimental data of the ternary system and the thermodynamic parameters of the sub-binary systems.The calculated Sn-corner isothermal sections using the obtained thermodynamic parameters were in reasonable agreement with the experimental data,and the measured homogeneity range of the Ni₃Sn₄phase region was accurately reproduced.