Experimental Research On Solder's High Temperature Mechanical Property And Thermal Cycle Numeric Simulation Of Solder Joints In Electronic Package

Under running condition, the solder joints endure stress and strain cycles because of the cyclic variation of inner power dissipation and environment temperature plus the thermal expansion mismatch among different material, which result in cracks in high stress and strain spot in solder joints and destroying of the whole component. So it's significant to study high temperature mechanical property of solder and solder joints thermal cycle reliability.The research is sponsored by Chinese National Natural Science Foundation(No.50376076) entitled "Heat design and optimization research based on coupled multi-physical fields of air cooling electronic packaging". Solder mechanical property and solder joint thermal cycle reliability were studied by experiment and numeric simulation.Firstly, high temperature tensile tests of solder 63Sn37Pb were conducted, obtaining stress-strain curves and tensile properties under different temperature and strain rate. The viscoplastic Anand model parameters were fitted based on the experiment data, and functions of parts of the parameters versus temperature were fitted. Compared with the model in literature and experiment data, it indicated that the prediction ability was enhanced with this modified Anand model. At the same time, the experiment and its data processing method will be used in the study of lead-free solder.Low cycle fatigue experiment for solder 63Sn37Pb was done at large temperature and strain range, the effects of temperature on fatigue property and fatigue life were analysed, and the Coffin-Manson model parameters at different temperature were fitted. The model is used to forecast fatigue life in the finite element simulation.Secondly, tensile tests at higher temperature were done for lead-free solder 96.5Sn3.5Ag. The results indicate that deformation and tensile properties of this solder are related to temperature and strain rate, and better creep resistance property is recognized compared with solder 63Sn37Pb. Anand model was fitted by experiment data, and was verified by comparing the results of model prediction and experiment data.Finally, Anand models were applied to the thermal cycle finite element simulation of the CBGA package. The results show that during the thermal cycle, the outmost solder joint from the symmetrical center endures the highest stress and strain which fluctuate as the thermal cycle proceeds. By analyzing the hysteresis loops, the equivalent plastic strain range was calculated and used to forecast solder joint thermal fatigue lives based on the fatigue model both from the literature and experiment. Results showed that the fatigue model in this paper can be used under the experimental condition, and the lead-free 96.5Sn3.5Ag solder joint had larger fatigue life than that of the 63Sn37Pb solder joint according to different models in literatures.In this paper, the precision of Anand model was enhanced by the experimental study on 63Sn37Pb solder, tensile property data at higher temperature and Anand model for lead-free solder 96.5Sn3.5Ag were supplied. The excellent packaging performance of lead-free solder 96.5Sn3.5Ag was verified based on the numeric simulation.