Interfacial Failure of Thin Epoxy Films

Interface adhesion is a key factor in controlling the reliability of thin films. It is particularly important in components with thin polymer films on metal substrates where changes in composition and structure during processing and service can lead to interfacial failure. There is also a move to thinner bond lines than we have used before. Nevertheless, our understanding of interfacial failure in these systems is limited. We have therefore begun a program to determine the fracture susceptibility of Epon 828/T403 on aluminized glass substrates. The films were spin coated onto aluminized substrates to four thicknesses ranging from 24 nm to 11.8 mm. Nanoindentation test techniques were combined with deposition of highly stressed overlayers to induce delamination and blister formation from which interfacial fracture energies were obtained using mechanics-based models. The resulting fracture energies decreased with film thickness and approached a lower limit for films less than 200 nm thick. However, this limit is significantly higher than the true work of adhesion for this film system. This suggests that inelastic or plastic dissipation processes operate even in the thinnest films we can test. In this presentation, the test and analysis techniques will be discussed and used to show that practical works of adhesion can be obtained for the very thin polymer films used in this study.