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.

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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.

The research on surface texture is developing from single macro-texture to composite micro-nano texture. The current research on the anti-friction mechanism and theoretical models of textures is relatively weak. Studying the characteristics of different types of surface textures and determining the applicable working conditions of each texture is the focus of current research. In this paper, a mathematical model of hydrodynamic lubrication is established based on Navier–Stokes equations. The FLUENT software is used to simulate and analyze the four texture models, explore the dynamic pressure lubrication characteristics of different texture types, and provide data support for texture optimization. The key variable values required by the mathematical model are obtained through the simulation data. The friction coefficient of the texture under different working conditions was measured through friction and wear experiments, and the mathematical model was verified by the experimental results. The research results show that circular texture is suitable for low to medium speed and high load conditions, chevron texture is suitable for medium to high speed and medium to high load conditions, groove texture is suitable for high speed and low load conditions, and composite texture is suitable for high speed and medium to high load conditions. Comparing the experimental results with the results obtained by the mathematical model, it is found that the two are basically the same in the ranking of the anti-friction performance of different textures, and there is an error of 10%−40% in the friction coefficient value. In this study, a mathematical model of hydrodynamic lubrication was proposed, and the solution method of the optimal surface texture model was determined.

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.

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The thermal fatigue reliability of solder bumps in TSV interposer package is analyzed by finite element method. The 3D finite element model of TSV interposer package is established in ANSYS software. Anand constitutive model is adopted to describe the viscoplastic behavior of Sn3.0Ag0.5Cu lead-free solder bumps. The influences of material properties and structural geometries on thermal fatigue reliability are evaluated by Taguchi method. The optimized factor combination design for promoting thermal fatigue reliability is obtained and validated by finite element analysis. The finite element modeling results show that the critical solder bump is located at the corner of solder bump array. Both the maximum von Mises stress and accumulated nonlinear strain energy density are located at the top layer elements of the critical solder bump. It is found that the material properties of underfill have the most important influence on thermal fatigue reliability of solder bumps. The higher Modulus and lower CTE improves the thermal fatigue life greatly. It is validated by finite element analysis that the optimized factor combination design can successfully improve the thermal fatigue reliability of solder bumps.

This paper established a mathematical model of hydrodynamic lubrication through theoretical analysis, solved the key variables of the mathematical model through simulation and validated the mathematical model using the experimental results. The purpose is to summarize a set of surface texture theory and optimal selection equations for complex working conditions. After comparing the experimental results with the results obtained by the mathematical model, it is found that the two are basically the same in the ranking of the anti-friction properties of different textures, and there is an error of 10%-40% in the friction coefficient value.