Robustness of BGAs: Parametric study of voids' distribution in SAC solder joints

摘要

The study aims at evaluating by simulation the impact of voids on the mechanical behaviour of a BGA solder joint. The Finite Element (FE) method is adapted to achieve such a task where an infinite number of different void distributions is possible. The modelling process involves a global calculation of a thermal load and a refined sub model. The global model represents a quarter of an electronic package soldered to a piece of PCB while the submodel is limited to a single ball with coper pads and defects under investigation i.e. intermetallic compounds (IMC) and voids. Creep properties are taken into account to model mechanical response of the lead-free solder SAC 305. The simulation of a thermal cycle is performed on the global model with only elastic properties. The nodal displacements are extracted from the results to be applied to the submodel's mesh. True viscoplastic mechanical behaviour is simulated in this refined model to get the RoHS solder material response with respect to different defects' considerations. The void distribution is handled with 4 parameters driving the height and thickness of the layer of apparition, the size and the proximity of voids. Simulating the effects of these parameters can afford to sort them for future reliability assessments via Finite Element methods.