倒装芯片封装中下填充流场渗透率的数值分析

Numerical Analysis of Permeability of Underfill Flow Domain in Flip-Chip Packaging

倒装芯片封装中的下填充流场可以假设为多孔介质流场,其渗透率的求解对研究下填充流动过程至关重要。根据下填充流场所具有的周期性结构,通过单胞数值模拟的方法得到了下填充流场的渗透率。通过对渗透率数据的分析,发现了渗透率和下填充流场参数之间的关系,并建立了计算渗透率的幂律模型。其中幂律模型的底是下填充流场的孔隙率,系数仅与芯片和基板的间隙有关,指数仅与芯片和基板的间隙相对于焊球直径的比值有关。通过实例分析表明,与其他模型相比,用基于幂律模型的渗透率所计算出的填充时间更符合实验结果。

The underfill flow domain in flip-chip packaging can be regarded as a porous medium flow domain. It is critical to gain the permeability of the porous medium. According to the periodic structure of the underfill flow domain, the numerical simulation method of unit cell was used to acquire the permeability of the underfill flow domain. Based on the results of the numerical simulations, the relationship between the permeability and the parameters of the underfill flow domain was found. And a power law model was established to calculate the permeability. The base of the power law model is the porosity of the underfill flow domain. And the coefficient is only relevant to the gap between chip and substrate. The exponent is only related to the ratio of the gap between chip and substrate to the diameter of solder bump. The analysis of an example indicates that the permeability calculated using this power law model gives more reasonable prediction of the filling time as compared with other models.