In order to establish the possible influence of residual stress and strain fields after cure on the failure prediction of electronic packages, cure-dependent viscoelastic constitutive relations for the applied polymers are required. This paper gives an overview of progress in the field of viscoelastic modeling and characterization of applied polymers over the past few years. It also discusses limitations and needs for future development.@en

Package warpage, interface delamination and thermal fatigue are the major reliability concerns for micro-electronic packages, caused by mismatch in thermal expansion together with residual stress originating from the curing process of the packaging polymers. To investigate the influence of the residual stress- and strain fields on the failure predictions and to optimise the product for reliability, cure-dependent viscoelastic constitutive relations for the applied polymers are required. The present paper gives an overview of recent progress in establishing such relations. A model moulding compound is used for cure dependent characterization and is subsequently used for QFN package moulding. The modelled and the experimentally obtained warpage have been compared.@en

Reliability calculations of the microelectronic packages require cure dependent viscoelastic constitutive relationship for the packaging polymers in order to predict residual stress and strain fields in the final product. The residual stresses can result in the product failure due to warpage, interfacial delamination, thermal fatigue etc. The previous work in the same group (Ernst et al. 2006, 2003) towards complete viscoelastic model development was done using "approximate fully cure dependent" model in order to predict warpage of the QFN package. The relaxation shear modulus was accurately established but due to measurement limitation only estimated values of bulk modulus could be used. In the present work, a high pressure dilatometer (Gnomix PVT apparatus) was used to establish the time, temperature and pressure dependence of bulk modulus. The bulk modulus shows negligible time dependence which suggests that bulk modulus is not a viscoelastic but merely a temperature dependent linear elastic parameter. A material model for time, temperature and pressure dependency of the bulk Modulus is developed.@en