底充胶及其材料模型对倒装焊热循环可靠性的影响

对倒装焊电子封装可靠性进行了热循环实验和有限元模拟，结果表明，有底充胶（underfill)时，SnPb焊点的热循环寿命可提高约16倍，并确定了Coffin-Manson半经验方程的参数，采用3种底充胶材料模型，亦即定常弹性模型，温度相关弹性模型和粘弹性材料模型，描述了底充胶U8347－3的力学性能。模拟结果表明，材料模型影响计算得到的SnPb焊点的塑性应范围，封装形变以及底充胶／芯片界面应力，采用弹性材料模型可能过高估计了SnPb焊点的热循环寿命和界面应力。

The influence of underfill and its material models on the reliability of flip chip package under thermal cycling

In this paper, the reliability of flip chip in electronic package was investigated with both experimental thermal cycling tests and finite element simulation. The results show that the thermal fatigue lifetime of SnPb solder joint is increased approximately 16 times with the use of underfill, and the material constants of Coffin Manson empirical equation were also determined. Three different material models, i.e. constant elastic, temperature dependent elastic and viscoelastic, were employed to represent the mechanical properties of underfill U8437 3. The simulation results revealed that the material models of underfill play a role in the plastic strain range of SnPb solder joint, the deformation of package and the interfacial stresses at underfill/chip interface. It could be concluded that the constant elastic material models for underfill may overestimate the thermal fatigue lifetimes of SnPb solder joints and the interfacial stresses.