Abstract: 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.

Key words: multi-row QFN package;numerical simulation;thermal fatigue life;design of experiment