Thin-film Adhesion and Adhesive Failure—A Perspective

A practical definition of “good adhesion” is that the interfacial region (or nearby material) does not fail under service conditions nor at unacceptably low stress levels under test conditions. Adhesion is a macroscopic property that depends on the chemical and mechanical bonding across the interfacial region, the intrinsic stress and stress gradients, and the adhesive failure mode. The failure mode depends on the interfacial structure and the stress to which the interface is subjected. Good adhesion is promoted by: (1) strong bonding across the interfacial region, (2) low stress gradients, either from intrinsic or applied stress, (3) absence of easy fracture modes, and (4) no long-term degradation modes. Adhesion testing must take into account the possible deformation and fracture modes, and a testing program must be devised to test all aspects of adhesion.