In this paper, we propose a fast and accurate chip/package thermomechanical stress co-analysis tool for through-silicon-via (TSV)-based 3-D ICs. We use our tool for full-stack mechanical reliability as well as stress-aware timing analyses. First, we analyze the stress induced by chip/package interconnect elements, i.e., TSV, μ-bump, and package bump. Second, we explore and validate the principle of lateral and vertical linear superposition of stress tensors (LVLS), considering all chip/package elements. The proposed LVLS method greatly reduces the complexity of stress calculation compared with the conventional finite element analysis method with high enough accuracy for full-chip/package-scale stress simulations and reliability analysis. In addition, we build hole and electron mobility variation maps based on LVLS. Finally, we study the mechanical reliability issues and provide full-stack timing analysis results in practical 3-D chip/package designs including wide-I/O and block-level 3-D ICs.