Comprehensive design analysis of QFN and PowerQFN packages for enhanced board level solder joint reliability

Board level solder joint reliability is a critical issue for Quad Flat Non-lead Package (QFN), a type of leadframe CSP, during the thermal cycling test. However, currently there are very few papers available on fatigue modeling and thermal cycling test of QFN on board. In this paper, a parametric 3D FEA sliced model is built for QFN (4/spl times/4, 5/spl times/5, 6/spl times/6, 7/spl times/7, and 8/spl times/8) and PowerQFN-8/spl times/8 on board with considerations of detailed pad design, realistic shape of solder joint and solder fillet, and non-linear material properties. It has the capability to predict the fatigue life of solder joint during the thermal cycling test. The fatigue model applied is based on Darveaux's approach with non-linear viscoplastic analysis of solder joints. The solder joint damage model is used to establish a connection between the strain energy density (SED) per cycle obtained from the FEA model and the actual characteristic life during the thermal cycling test. Higher SED leads to shorter fatigue life. For the test vehicles studied, the maximum SED is observed mostly at the top corner of peripheral solder joint.