Prediction of process-induced warpage of IC packages encapsulated with thermosetting polymers

One critical issue for manufacturing of map-molded packages is the warpage induced during the molding process. To minimize the warpage, first of all, process-dependent material models need to be established and the related parameters should be properly characterized before optimization of the package design and process condition can be realized. In this paper, a cure-dependent viscoelastic constitutive model is established to describe the evolution of material properties during the curing process of a thermosetting polymer. The equilibrium modulus is 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. A new method based on ultra-low frequency DMA is developed to acquire the evolution of the rubbery moduli. 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 conducted 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 significant contribution on the total warpage of the map.