Modelling methodology for linear elastic compound modelling versus visco-elastic compound modelling

Finite element (FE) simulations take an important place in predicting the thermo-mechanical plastic-package behaviour. Several studies in both industry and research cover this topic since the mechanical impact of the epoxy moulding compound (EMC) behaviour is of major impact on package reliability and the understanding of the material behaviour is limited. In the history of package modelling, large differences in thermo-mechanical stresses are found between (temperature dependent) elastic calculations and time dependent calculations, such as visco-elastic calculations. Visco-elastic compound behaviour is often recommended to take into account to predict stresses reliably, but takes significant effort and time for material characterization. In this paper the origin of stress differences was analyzed for different EMC material models in different realistic process conditions. By understanding the impact of realistic compound behaviour during real process conditions, an effective modelling approach was proposed which took less material characterisation and less calculation time. The modelling method was applied on a package simulation analyzing 3 different compounds and is verified by visco-elastic simulations.