Simulation of delamination initiation and subsequent propagation using cohesive zones

Delamination is one of the main problems in electronic packaging due to the relatively weak adhesion strength of interfaces. Delamination failure includes two processes: crack initiation and crack propagation. Various experimental setups and theories have been built to study these processes. Among these studies the cohesive zone method being implemented in various finite element packages is becoming a popular tool for crack propagation modelling. In our previous work [1–4] the efficient use of cohesive zone modelling of the delamination propagation process of pre-cracked samples was discussed. Here also an appropriate method to establish the cohesive zone parameters was given. Among this a fitting method to establish the critical energy release rate through cohesive zone modelling was presented. Although the modelling of delamination propagation for packages with assumed pre-cracks at various spots now is quite feasible, in the thermal-mechanical designing of packages the initiation of delamination (without assumed pre-cracks) is much more important. Therefore, the present work primarily focuses on applying the cohesive zone method for the modelling of the initiation of delamination, followed by the subsequent delamination propagation. The paper will primarily investigate the crack initiation (without pre-crack) for a chosen interface. The influences of mesh size, number of loading increments and the critical stress values are investigated and discussed in detail. The computing time is considered and compared for various settings, such as to overcome convergence problems. The present study will help to make proper choices for future correct and economically feasible simulations of delamination initiation and subsequent propagation.