Effects of Thermomechanical Properties on Interface Edge Singular Thermal Stresses of Quad Flat Package Solder Joints

摘要

The thermomechanical properties of the pin, printed circuit board (PCB) and solder of a QFP solder joint are often different, singular stresses, which are an inducement of interfacial delamination, will occur at the interface edges of the QFP solder joint under thermal loading. In order to evaluate the local mechanical behavior of the QFP solder joint, in the paper, singular thermal stresses as well as the corresponding generalized stress intensity factors (GSIFs) at the interface edge of an arbitrary bi-material wedge is determined numerically based on the analytical solution and the FEM. Firstly, A ad hoc FE eigenanalysis method is used to solve the eigensolusions of singular stress fields, i.e., the orders of stress singularities and the angular variations of stresses, and these eigensolusions together with a constant stress term under thermal loading are used to established the expression of the singular stress field near the interface edge. Secondly, the GSIFs for thermal loading are solved by the FE technique and the least square method. Finally, the effects of elastic modulus, poisson's ratios and thermal expansion coefficients on generalized stress intensity factors (GSIFs) at the interface edge of the QFP solder joint are investigated, and suitable material constants for the solder and the PCB are recommended to improve the local stress states.