The structure of the TSV itself is exposed to instability caused by stress. Within this chapter the situations which arise from processing or device operation and which can be dangerous for the TSV are discussed. Local features’ effects, such as Bosch scallops, are investigated as well as mechanical effects during wafer handling. Particular attention is paid to thin films, especially because of the lack of available information for such systems. A deep look into the stress relaxation of metal films is presented and a scheme to couple FEM simulation with relaxation models is provided.