Fatigue Damage Study And Numerical Simula-tion Of SnAgCu Lead-free Solders

Due to the threats of the lead and the lead alloy’s toxicity to the environment and health of the human being, and the restrictions of the global lead-free legislation, it has become an inevitable trend to use lead-free solder in the microelectronics packaging. The solder joints are the welding materials of the thermal, mechanical and electrical connection between the components and the PCB boards, whose reliability is very important for the service life of the electronic products. Therefore, it is very urgent to master the mechanical response, constitu-tive behavior, and failure mechanisms of the lead-free solder.In this thesis, the lead-free solder SnAgCu is chosen as the object to research. According to the data getting from the constant strain rate uniaxial tensile experiments under different temperatures and different strain conditions, seven materials parameters of the lead-free sol-der SnAgCu in partitioned constitutive model are determined, and the numerical simulation is also carried out. On the basis of data getting from the tensile-compression cycling fatigue ex-periment of the lead-free solder SnAgCu, the evolution law of the solder fatigue damage is analyzed, and the damage parameters are also determined. Using the partitioned damage con-stitutive model, the Fortran Language, and the nonlinear incremental approach, the stress-strain behavior of the solder under cycling and loading is programmed and simulated, and the influence of the loading conditions to the stress amplitude, plastic strain amplitude and cumulative plastic work of the solder is also analyzed and discussed.The nonlinear finite element numerical simulation of the BGA packaging structure vibra-tions is carried out by the finite element software, and the stress and strain distribution of the overall lead-free solder joints in the BGA package is observed. Meanwhile, the influence of temperature, load frequency and amplitude to the simulation results is also discussed. Using the Engelmaie fatigue model, the longevity of the lead-free solder joints in the BGA package structure is predicted, and the influence of the loading conditions to the longevity of the solder joints is also analyzed.