Effect of microstructure on thermal-mechanical stress in 3D copper TSV structures

Electronic packaging technologies have developed into the 3D packaging era and the TSV structure is one of the possible technological routes. TSVs of small scales such as submicron or even nano scales are envisioned for 3D packaging. From a material point of view, microstructure and its related micro-processes involved at such small scales will have important impacts on the performance of the electronic packages. This paper focuses on modeling the microstructural effects on the thermal-mechanical behavior of Cu-TSVs. In the microstructural models, Cu grains inside the vias are simulated using the Voronoi algorithm. The Young´s moduli and Poisson´s ratios of different grains are determined by their crystallographic orientations. A coupled thermal-mechanical finite element analysis is then carried out to study the microstructural effects. The temperature distribution is not significantly affected by the non-uniform thermal conductivities in this study. The stress distribution in the anistropic model exhibits considerable differences from that of the reference model in which the vias are treated as bulk materials. The stress within the vias varies significantly and there are sites where the stress is as high as 240 MPa, which has not been found in the reference model. Therefore, the effects of microstructures inside the Cu TSV are obvious and the microstructures should be among the design factors for reliable 3D electronic packaging.