Finite Element Analysis For Thermal Fatigue Reliability Of Lead-free Solder Joints In The Plastic Ball Grid Array Package

With the advance of miniaturization and integration of electronic devices, solder joints, which are used for electrical connections and mechanical connections, become more in numbers and smaller in sizes .The failure of a solder joint can endanger the function of the system, so many researches and attentions are focused on the issue of the reliability of solder joints. Based on the FEA software ANSYS and ABAQUS, a finite element model simulating the typical plastic ball grid array package (PBGA) is established, the thermal fatigue life of lead-free solder joints is predicted, and the reliability analysis for the lead-free solder joints is completed. The thesis consists of three parts:First, the mechanical behavior of the lead-free solder joints is described based on the Anand constitutive model.The stress-strain distribution in the solder joints, failure modes, and their mechanisms under the temperature cycles are studied. For the key solder joint, we give their hysteresis loops of the equivalent stress and plastic strain and the strain energy density curve.The periodic variation of temperature with the equivalent stress and plastic strain is analysed. In terms of the Manson-Coffin model, the thermal fatigue life of the lead-free solder joints is predicted.Second, based on ABAQUS software, the Thermal–Elastoplasticity– Creep– Damage constitutive model is used to describe the mechanical behaviors of the solder joints in PBGA. The distribution of stress, strain and damage in the solders joints are given. The failure modes of the solder joints under the thermal cycles are studied. The key solder joints in PBGA are determined. For the key solder joints, we give their hysteresis loops of the equivalent stress and plastic strain and the strain energy density curve .The periodic variation of temperature with the equivalent stress,plastic strain and damage is analysed. In terms of the evolution of damage, the thermal fatigue life of the key solder joint is predicted.Finally, the Monte Carlo Method and finite element simulation are used to analyse the influences of the random distribution of initial defects on the reliability of the solder joints. The results show that if the initial defects obey the normal distribution, the thermal fatigue life of the solder joints also obeys the same distribution. This conclusion is benefit to evaluating the reliability of PBGA.