THE THERMO-MOIST MECHANICAL GENERALIZED HYBRID/MIXED SINGULAR FEA OF GBA PACKAGING STRUCTURES WITH SMT STRESSES AND SEALING CRACKS

摘要

The initiation and propagation of yielding failure in BGA structures with SMT solder joints subjected to thermal cycling loads are complicated issues, while the first key step to predict solder joint reliability is to locate the yielding iniation and accurately determine the amount of thermal surface mount stresses (SMS). The constrained moisture can, in principle, be considered by converting it into expanding mechanical loads to start cracks at corners in finite element analysis. From viewpoint of computational mechanics with temperature change considered, the advanced multivariable generalized hybrid/mixed finite element formulation is further reconstructed for improved and singular thermo-stress analysis, and applied to coupling study of thermal loading and temperature-dependent solder materials for prediction of the thermal SMS in electronic packaging structures, in order to analyze and pinpoint the yielding failure initiation and most dangerous solder joints in an electronic BGA structure based on Von Mises SMS stresses and deformations. The assumed stress FEA method adopted and its element reliability are numerically tested and computationally applied. Different from other general commercial FEA codes, some interesting numerical and computational results of a free surface solder and a three solder GBA structure are provided for further theoretical and test investigations.