Characterization of underfill/passivation interfacial adhesion for direct chip attach assemblies using fracture toughness and hydro-thermal fatigue measurements

Delamination of underfill/passivation interface is a major cause for failure of direct chip attach (DCA) assemblies during reliability testing. We have used a modified asymmetric double cantilever beam (ADCB) testing for measuring the fracture toughness of the interface and a newly developed hydro-thermal fatigue testing (based on noncontact fiber optic displacement sensor) for measuring the fatigue crack growth rate along the interface. We have developed and used a simple anhydride cured model underfill epoxy (that captures the basic chemistry of the underfills) and a commercially available PMDA/ODA passivation for this study. Both the fracture toughness (determined through ADCB testing) and the fatigue crack growth rate (determined through hydro-thermal fatigue testing) are dependent on the mechanical phase angle under which the crack grows.