基于数值模拟的多圈QFN封装热疲劳可靠性试验设计方法

Design of Experiment Methodology for Thermal Fatigue Reliability of Multi-row QFN Packages Based on Numerical Simulations

提出一种基于数值模拟的试验设计方法,研究材料属性和几何结构对多圈四边扁平无引脚(Quad flat no-lead,QFN)封装热疲劳寿命的影响,并进行最优因子的组合设计,以提升热疲劳可靠性。采用Anand黏塑性本构模型描述无铅钎料Sn3.0Ag0.5Cu的力学行为,建立三维有限元模型分析焊点在温度循环过程中的应力应变,采用Coffin-Manson寿命预测模型计算多圈QFN封装的热疲劳寿命。采用Taguchi试验设计(Design of experiment,DOE)方法建立L27(38)正交试验表进行最优因子的组合设计。采用有限元分析方法对最优因子组合设计结果进行验证。结果表明,印制电路板(Printed circuit board,PCB)的热膨胀系数、焊点的高度和塑封料的热膨胀系数对热疲劳寿命的影响最为显著;初始设计情况下多圈QFN封装的热疲劳寿命为767次;最优因子组合设计情况下的热疲劳寿命提高到4 165次,为初始设计情况下的5.43倍。

A design of experiment （DOE） methodology based on numerical simulation is presented to improve thermal fatigue reliability of multi-row quad flat non-lead （QFN） packages. The influences of material properties, structural geometries and temperature cycling profiles on thermal fatigue life are evaluated. Anand constitutive model is adopted to describe the viscoplastic behavior of lead-free solder Sn3.0Ag0.5Cu. The stress and strain in solder joints under temperature cycling are studied by 3D finite element model. Coffin-Manson model is employed to predict the fatigue life. A L27（38） orthogonal array is built based on Taguchi method to figure out optimized factor combination design for improving thermal fatigue reliability. The optimized factor combination design derived from DOE methodology is verified by finite element analysis. Results indicate that the coefficients of thermal expansion （CTE） of printed circuit board （PCB）, the height of solder joints and CTE of epoxy molding compound （EMC） have critical influence on thermal fatigue life. The fatigue life of multi-row QFN package with original design is 767 cycles, which can be substantially improved by 5.43 times to 4 165 cycles after the optimized factor combination design based on the presented method.