Modeling of cure-induced warpage of plastic IC packages

The accurate prediction of warpage induced during manufacturing processes is important for the optimal design of both package structure and process conditions. In this paper, a cure-dependent viscoelastic constitutive model is established to model the cure-induced warpage after the map-mould manufacturing process. In the model, the relaxation moduli of the silica particle-filled polymer during the curing process are considered to be the sum of two parts, i.e. the cure-dependent equilibrium moduli and the transient parts. The equilibrium moduli are modeled with a model based on scaling analysis. The relaxation behavior of the transient part is described by the cure-dependent relaxation amplitude and reduced relaxation times, which are based on the time-conversion superposition principle. The cure-dependent parameters are characterized by using an integrated approach of DMA and DSC measurements. The chemical shrinkage strain is measured with an online density measuring setup. The viscoelastic parameter-functions of the resin, measured by DMA and DSC, have been incorporated in the MARC finite element code. Finite element modeling is carried out for three configurations of a carrier package map-mould and the warpage induced during the curing process and cooling down is predicted. The results show that warpage induced during the curing process has a significant contribution on the total warpage of the map.