A Fracture Mechanics Evaluation of the Cu-Polyimide Interface in Fan-Out Redistribution Interconnect

In this study, the risk of debonding failure of the Cu-polyimide structure prepared by using realistic redistribution processes were investigated. The constitutive behavior of the polyimide thin film was first evaluated under tensile loading conditions at various temperatures. It was shown that the polyimide thin film with low glass transition temperature exhibits obvious viscoelastic response. A generalized Maxwell model was adopted to describe the thermoviscoelastic behavior. The debonding growth behavior of the Cu-polyimide interface was then investigated by using the double cantilever beam fracture mechanics tests. A finite-element based numerical model was then developed to evaluate the debonding growth at the Cu-polyimide interface and to investigate the effects of inelastic energy dissipations in the Cu and polyimide layers on the debonding response of the layered structure. The model can be applied to consider complex fan-out designs and would allow development of design rules for extending the Cu-polyimide based redistribution interconnect technology to the regimes of higher I/O densities.