Reliability Assessment of Through-Silicon Vias in Multi-Die Stack Packages

A thermo-mechanical reliability study of through-silicon vias (TSVs) is presented in this paper. TSVs are used to interconnect stacked dies to achieve 3-D packages. As the core of the TSV contains high coefficient of thermal expansion (CTE) copper surrounded by low-CTE SiO₂ and Si materials, the thermo-mechanical reliability of TSVs is a concern. When dies with such TSVs are stacked and packaged, the presence of additional structures and associated materials could introduce different thermo-mechanical concerns compared with free-standing wafers. This paper presents 3-D finite-element models for studying the thermo-mechanical stresses in TSVs in free-standing wafers and in stacked dies, which are packaged. Warpage measurements have been used to validate the finite-element modeling approach. The results from the finite-element models show that the TSV stresses in a packaging configuration are typically lower than the TSV stresses in a free-standing wafer configuration. In addition, it is seen that the microbumps connecting adjacent dies experience high magnitude of inelastic strain, indicating that such locations are of reliability concern.