Investigation on FBGA block warpage by Finite Element Simulation

Warpage is a major reliability concern for IC packages. Package structure, material property and assembly process will all impact warpage behavior, which can be characterized by 3D Finite Element Analysis (FEA). Traditionally, the FEA simulation will only analyze warpage of a free standing package with thermo-mechanical stress induced by Coefficient of Thermal Expansion (CTE) mismatch during cooling process of Epoxy Molding Compound (EMC) from cure temperature to room temperature. In this paper, a dedicated FEA model has been developed to simulate a strip type Fine-Pitch Ball Grid Array (FBGA) package. Different from conventional simulation, effect of both EMC chemical shrinkage due to polymerization conversion during post molding cure and actual measurement operation on warpage have been taken into consideration in the FEA model. Parametric study with different package layout, die area and die thickness has been performed. Result showed package layout of the strip can significantly impact warpage; and die area had more influence on warpage than die thickness. Warpage performance can be improved by optimizing these parameters. Compare to measurement, the simulation result is in good agreement with actual package warpage.