倒装焊Sn—Pb焊点的热疲劳失效

对倒装焊Sn-Pb焊点进行了热循环实验，结合三维全局有限元模拟的结果，研究了Sn-Pb焊点热疲劳失效，结果表明，充胶后焊点内塑性应变范围减小近一个数量级，从而显著降低焊点的疲劳损伤后，由于底充胶改变了Sn-Pb焊点应力、应变分布，使得充胶前后焊点裂纹位置发生改变，Sn-Pb焊点热疲劳裂纹萌生于粗化的富Sn相，并穿过富Pb相沿Sn相生长，Sn和Pb晶粒的非均匀粗化趋势与模拟给出的剪切应变轴向分布一致。

THERMAL FATIGUE FAILURE OF Sn-Pb SOLDER JOINTS OF FLIP CHIP ON BOARD

By thermal cycling test and three-dimensional global finite element simulation, the thermal fatigue failure of Sn-Pb solder joints of flip chip on board was investigated. The results show that the plastic strain range in solder joints decreased to nearly an order of magnitude, which degrades thermal fatigue failure of the solder joints subsequently. Since the thermal stresses and strains in the solder joints were redistributed due to the application of underfill, the conditions of thermal fatigue crack initiation and propagation in the solder joints were changed. The initiation and propagation of thermal fatigue crack occurred in the coarsened Sn-rich phases while the crack propagated also across Ph--rich phases intergranularly. Moreover, heterogeneous coarsening in the Sn-rich and Pb-rich phases is coincident with the simulation results of axial distribution of shear strains in the solder joints.