Sequential processing mechanics modeling for a model IC package

In this paper, a nonlinear finite element framework was established for processing mechanics modeling of electronic packaging assemblies and layered manufacturing. In particular, topological change was considered in order to model the sequential steps during a typical integrated circuit (IC) package assembly. Geometric and material nonlinearity, temperature dependent material properties were considered. Different stress free temperatures for different elements in the same model were used to simulate practical manufacturing process-induced thermal residual stress field in the chip assembly. As comparison, two finite element method (FEM) models (processing model and nonprocessing model) of an encapsulated IC package considered, associated with different processing schemes, were analyzed. From the finite element analysis, it is found that due to the coefficient of thermal expansion (CTE) mismatch between the solder and silicon chip, the substrate and the solder, there exists very high stress field near these interfaces when the encapsulated IC package is cooled down to room temperature after processing for these two models. But in contrast with the stresses near the edges of all interfaces obtained from nonprocessing model, the stresses near the edges of all interfaces corresponding to processing model are generally higher than those obtained from nonprocessing model. In particular, the Von Mises stress at the edge of silicon chip/solder interface obtained from processing model is nearly 50% higher than that obtained from nonprocessing model. It is shown that processing model which is based on the FEM framework established in this paper can more realistically simulate a series of practical manufacturing processes in the chip assembly, whereas a larger error can be caused by using nonprocessing model in the analysis of process-induced residual stress field in the packaging assemblies due to the negligence of the bonding process during cooling from 250°C to 160°C