功率循环下CSP封装结构焊点的寿命预测分析

采用非线性有限元方法，分析了CSP封装形式的焊点在给定功率循环下的应力应变．单一内变量的统一粘塑性Anand本构方程，描述了63Sn37Pb焊料的粘塑性变形行为．考虑封装体内温度梯度的存在，更加真实地模拟芯片实际发热机制，采用间接法将CSP功率循环模拟方法具体分为瞬态热分析和热应力分析两个阶段．热分析得到的温度场分布结果作为热应力分析的栽荷．通过基于以能量为基础的疲劳寿命预测公式预测焊点的失效循环数．对1／8CSP模型作寿命预测，并和简化模型作比较分析．结果表明，两者焊球温度分布和等效应力基本一致，焊球失效循环数相差不起过5％．

Solder joint fatigue life predictions for CSP package under power cycling

The three-dimensional nonlinear finite element modeling is used to analyze stress-strain response of solder joint under certain power cycling loading condition. A unified viscoplastic Anand constitutive model is applied to represent the nonlinear deformation behavior of 63Sn37Pb solder. Considering the thermal gradients in the whole assembly, the actual heating of chip is simulated factually on the power cycling condition. The method consists of transient thermal simulation and thermal-structure analysis of the assembly. The thermal analysis results is taken for the nodal load for structure analysis. Number of failure cycles is calculated depending on fatigue life prediction equation based on the energy analysis. The 1/8 CSP fatigue life prediction is studied and compared to the simplified model. The result show that temperature distribution and equivalent stress of the two solders are basically same. The difference between the two numbers of failure cycles is not more than 5 %.