Evaluation of the effect of stress relief slots on QFN strip warpage using finite element analysis

Abstract

QFN (Quad Flat No-lead) packages become popular in recent years because they provide many advantages over conventional leadframe packages.Due to CTE (Coefficient of Thermal Expansion) mismatch of different materials applied in the package, significant warpage will be generated during QFN packaging process, and may cause yield and reliability issues. In this paper, the warpage of a QFN strip induced by molding process was simulated using finite element analysis (FEA). Effect of stress relief slots design of the leadframe was evaluated, and the influence of material properties was also studied with three different types of EMC (Epoxy Molding Compound). Simulation results indicated that CTE of the EMC had a considerable effect on the warpage direction and magnitude, and the existence of stress relief slots only slightly reduced warpage magnitude.

Modeling Study on the Impact of Mold Thickness on Strip Warpage of a Molded Leadframe Package

“…Some are using FEA techniques for improved prediction like the inclusion of cure shrinkage [4] or using the anisotropic viscoelastic shell modeling technique performed on the warpage simulations for a full microelectronic package with a multilayer PCB [9]. Other semiconductor package strip warpage studies use FEA in analyzing the effect of stress relief slots [10], mold compound fillers and die thickness [11], and the combination of mold cap thickness, substrate thickness and mold compound [12]. A simple and efficient imagebased approach for simulating strip warpage as a function of temperature is also studied with FEA [13].…”