Power semiconductors play a crucial role in energy efficiency and sustainable energy consumption and can be found in most electronic devices. Consequently, their reliability is a topic of great interest. In this context, physics-of-failure lifetime models (PLM) show great potential for designing more reliable products. Herein, a PLM for simulating the formation and propagation of fatigue cracks in the copper (Cu) metallization layer of power semiconductors subjected to repeated power pulses is presented. The presented approach is an enrichment of the continuum damage mechanics based fatigue model presented in [Springer et al. 2018]. The enrichment allows the damage susceptibility of certain microstructural features such as triple points [Kleinbichler et al. 2021] to be taken into account without explicitly modeling the microstructure. To achieve this, a spatially varying variable is introduced into the damage onset criterion accounting for the local influence of triple points and their misorientation angles. The damage evolution law remains unchanged. The approach is implemented within the finite element method (FEM) using the averaged stress and strain states at the center point of the elements. Fully damaged elements are deleted, allowing to simulate the emergence and propagation of macroscopic fatigue cracks. Furthermore, a procedure for determining the required material parameters from experiments on specialized test chips [Moser et al. 2019] is presented. FEM simulations on a bi-layer system reveal that the parameter controlling the influence of the misorientation angles on the damage onset has a strong impact on both the number of cycles until a so-called through-film crack emerges and the amount of emerging secondary damage in the form of macro voids and small fatigue cracks. The distribution of triple points has minor influence on the overall amount of predicted fatigue damage and no influence on how quickly damage and, as a result, cracks occur. These findings can serve as basis for further studies on the relationship between certain microstructural features and fatigue damage in metallization layers. Acknowledgment: This work was funded by the Austrian Research Promotion Agency (FFG, Project No. 881110).