Effects of surface roughness of AlN ceramic substrate on the interface mechanical behavior of AlN/Ag structures

The effects of surface roughness and microtopography of AlN substrate on the interface mechanical behavior of AlN/Ag structures were studied by experimental and numerical simulation methods. Fracture toughness and adhesive strength of the Ag thick film metallized AlN substrate were evaluated by four-point bending tests. Interfacial damage evolution and failure mechanism were simulated and analyzed by using finite element method. The results showed that the AlN substrates with rougher surface and deeper pits were beneficial for improving interface mechanical properties of AlN/Ag structures. After the raw AlN substrate was ground by a 240 mesh sandpaper, the maximum peeling stress σmax and shear stress τmax of the AlN/Ag interface were increased by 82% and 92.5%, respectively. More importantly, the interfacial fracture toughness was increased by approximately 125%. The convex grain faces on the surface of raw AlN substrate, however, had an adverse effect on the interface mechanical properties of AlN/Ag structure due to the weak mechanical interlocking effect. The concave interfaces on the rougher AlN substrate could act as a buffer zone for crack propagation. The direction change of interface cracks propagation along with rough interface effectively delayed the interface damage process of AlN/Ag structures.