The reliability of novel Quad Flat No-Lead (QFN) package design with multi-row lead fmgers has not been well analyzed yet The thermal characterization, warpage performance and board level solder joint reliability of dual row and conventional QFN packages are investigated in this paper for comparison. Flotherm Computational Fluid Dynamics (CFD) software is employed to predict the package thermal performance. Warpage performance is studied by FE modeling, and correlates with analytical results from Timoshenko's bi-layer beam model. In board level solder joint reliability comparison study, 3D-Quarter fmite element (FE) model, steady-state creep hyperbolic sine constitutive model for SnAgCu solder and Zhu's energy based fatigue model are used. The results show that thermal performance and board level solder joint fatigue life of conventional QFN are slightly greater than that of dual-row QFN. Warpage results based on bi-Iayer beam theory basically agree with FE modeling results.

A design of experiment (DOE) methodology based on numerical simulation is presented to improve thermal fatigue reliability of multirow quad flat nonlead (QFN) packages. In this method, the influences of material properties, structural geometries, and temperature cycling profiles on thermal fatigue reliability are evaluated, a L27(38) orthogonal array is built based on Taguchi method to figure out optimized factor combination design for promoting thermal fatigue reliability. Analysis of variance (ANOVA) is carried out to examine the influence of factors on the thermal fatigue reliability and to find the significant factors. 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 (FE) model. The modified Coffin–Manson model is employed to predict the fatigue life of solder joints. Results indicate that the coefficients of thermal expansion (CTE) of printed circuit board (PCB), the height of solder joint, and CTE of epoxy molding compound (EMC) have critical influence on thermal fatigue life of solder joints. The fatigue life of multirow QFN package with original design is 767 cycles, which can be substantially improved by 5.43 times to 4165 cycles after the optimized factor combination design based on the presented method.

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Quad Flat non-lead(QFN) packages known with many outstanding properties. However the thermal stresses and plastic strain accumulation in solder joints during temperature and power cycling can be induced due to the significant mismatch in the coefficients of thermal expansion (CTE) of dissimilar materials. The damage caused by these stresses and plastic strain accumulation, which are induced during accelerated temperature cycling due to the CTE mismatch between the various materials that encompass the QFN package, ultimately cause the failures of solder joints. In this paper the ANSYS software is adopted to build a quarter of model about QFN, which is sUbjected to the thermal recycling of -40� 125°C. The thermal fatigue life of QFN is calculated based on the maximum strain range and the Coffin-Manson equation. Anand's viscoplastic material model is used to describe the constitutive equation of the solder joints in this study. A L27(3 8 ) orthogonal array is built based on Taguchi Method to figure out the optimized conditions. Besides, in order to avoid accidental error, ANOV A is carried out to estimate the error and find the most important factors. The results indicate that only five material and structural factors are the most important ones, and the other factors are selected by price or convenience. Finally, the fatigue life after optimal design by Taguchi method has 3.43 folds on the fatigue life over the original design.

A DOE (Design of Experiment) methodology based on finite element analysis is presented to investigate thermal fatigue reliability of multi-row QFN packages. In this method, the influences of material properties, structural geometries and temperature cycling profiles on thermal fatigue reliability are evaluated, a L27(3 8 ) orthogonal array is built based on Taguchi method to figure out optimized factor combination design for promoting thermal fatigue reliability. 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. The modified Coffin-Manson model is employed to predict the fatigue life of solder joints. Results indicate that CTE of PCB board, the height of solder joint and CTE of epoxy molding compound have critical influence on thermal fatigue life of solder joints. The fatigue life of multi-row QFN package with original design is 767 cycles, which can be substantially improved by 5.43 times to 4165 cycles after optimized factor combination design.