倒装焊SnPb焊点热循环失效和底充胶的影响

采用实验方法，确定了倒装焊SnPb焊点的热循环寿命．采用粘塑性和粘弹性材料模式描述了SnPb焊料和底充胶的力学行为，用有限元方法模拟了SnPb焊点在热循环条件下的应力应变过程．基于计算的塑性应变范围和实验的热循环寿命，确定了倒装焊SnPb焊点热循环失效Coffin-Manson经验方程的材料参数．研究表明，有底充胶倒装焊SnPb焊点的塑性应变范围比无底充胶时明显减小，热循环寿命可提高约20倍，充胶后的焊点高度对可靠性的影响变得不明显．

Thermal Cycle Failure of SnPb Solder Joint for Flip Chip Package and Effects of Underfill Material

The thermal cycle lifetimes of SnPb solder joints for flip chip package were determined experimentally.With viscoplastic and viscoelastic materials representing the mechanical behavior of SnPb solder and underfill,respectively,the stress/strain responses of SnPb solder joints under thermal cycling with finite element method are simulated.Based on the calculated plastic strain ranges and the experimental thermal cycle lifetimes,the material constants in Coffin-Manson empirical equation were then obtained.The results show that,the plastic strain ranges of solder joints with underfill decrease distinctly and the thermal cycle lifetimes are approximately 20 times larger than that in the case without underfill.Moreover,the influences of solder joint height on solder joint reliability are weakened for the flip chip package with underfill.