The fracture toughness of thin metal films confined between elastic layers, a geometry prevalent in electronic packaging applications, was found to depend strongly on the metal film thickness and on residual stress. Here, a 2-dimensional discrete dislocation (DD) model was used to predict the dependence of fracture toughness on both residual stress and film thickness. The fracture toughness was found to be nearly independent of cohesive strength once the cohesive strength exceeds ~900MPa, and predictions for systems with nearly zero residual stress agree well with experiments. The fracture toughness was found to decrease significantly with increasing residual stress, and again the predictions were in qualitative agreement with experiments. The DD model predicts that the effect of residual stresses was independent of the sign of the stress, tension versus compression, in contrast to continuum plasticity models. Overall, this demonstrated the power of dislocation-based modelling in handling multiple scale-dependent plasticity phenomena simultaneously.

Effect of Residual Stress on Fracture in Confined Thin Films - a Discrete Dislocation Study. A.C.Chang, W.A.Curtin, A.A.O.Tay, K.M.Lim: Modelling and Simulation in Materials Science and Engineering, 2008, 16[1], 015002 (19pp)