Cure-Dependent Viscoelastic Behaviour of Electronic Packaging Polymers: Modelling, Characterization, Implementation and Applications

Abstract

Polymers are widely used in electronic packaging as encapsulants, underfills, adhesives, insulators, and dielectrics, etc. Generally these materials are thermosetting polymers that have to be cured during the fabrication process at elevated temperatures. The curing process will introduce residual stress and warpage in the microelectronic devices, due to the polymerization shrinkage and subsequent cooling down from the curing temperature. During cure these polymers gradually transform from the more or less liquid state into a viscoelastic solid with a relatively high glassy modulus, accompanied with chemical shrinkage. Due to the cross-linking reaction and thermal shrinkage under continuing stiffness increase, stresses will arise in areas where shrinkage is partly prevented by geometrical constraints. Furthermore, if the cross-linked product is cooled down to ambient temperature, the difference in thermal expansion between matrix and adjacent materials will cause additional stresses and deformation. In order to be able to conduct reliable prediction of the process-induced stress and warpage in electronic packaging, cure-dependent viscoelastic constitutive relations for thermosetting polymers are required. Furthermore, material characterization and numerical implementation of the constitutive models into commercial FEM programs are important for providing a base for large scale thermo-mechanical FEM modelling of electronic packaging. And then a simulation-based optimization on the design for package structure, material parameters, and process conditions can be carried out…Electrical Engineering, Mathematics and Computer Scienc