Effects of Bosch scallops on stress reduction in metal layers of an open TSV technology were studied. Two possibilities were evaluated for an explanation of the phenomenon, including a weak adhesion of the scallops’ bottom and the geometry of the scallops themselves. The latter causes most of the stress reduction, while weak adhesion is only a secondary mechanism. The manner in which the scallop geometry modifies the stress was described. Additionally, valleys between scallops were identified as potential failure regions due to increased stress in pinch-off sites. It was also shown that the equibiaxial stress assumption on the via walls in the presence of scallops is invalid. This information is vital for the proper evaluation of the simulation and experimental results. Finally, the simulations have shown to be consistent with experimental data, validating the setup for further studies.