Adhesion and reliability of underfill/subtrate interfaces in flip chip BGA packages: metrology and characterization

This paper discusses the methodologies of fracture mechanics that are used to study interfacial delamination by modeling delamination as a crack propagating along the interface between two materials. Specifically, adhesion and subcritical debonding at interface between silicon nitride passivated Silicon die and silica/alumina filled epoxy underfill are investigated. Adhesion was measured in terms of a critical value of the applied strain energy release rate, G (J/m²). Subcritical debond growth rates were characterized as a function of applied G. Adhesion and subcritical debonding were studied by varying interfacial chemistry, process and environmental factors. Interfacial chemistry was modified by using different adhesion promoters and by varying the COOH acid content. Process variable such as filler bead settling was studied. The effects of environmental variables were studied with temperature and humidity controlled environments.