Effective thermo-mechanical properties and deformation characteristics of through-glass-via (TGV) structures in microelectronic packaging

Through-glass-vias (TGVs) are emerging as an alternative to conventional interconnect technology for advanced microelectronic packaging. Due to glass's tunable thermo-mechanical properties, dimensional stability, and low electrical loss, it surpasses organic substrates for its ability to contain high-density vertical interconnections. When numerically analyzing the deformation behavior of a complex package structure, it is frequently desirable to treat the substrate containing fine features as one material with representative effective properties, for the purpose of computational efficiency. In this study the effective coefficient of thermal expansion (CTE), Young's modulus, and Poisson's ratio of the glass substrate containing copper TGVs are obtained using finite element modeling. A three-dimensional unit-cell approach is undertaken, which takes into account periodically distributed TGVs in the glass matrix. The simulated effective properties with various TGV concentrations are compared with analytical expressions based on the fiber-composite theories. Deviations from the ideal square array of TGVs are found to only moderately affect the effective thermal expansion and elastic properties. Issues important for the determination of effective properties are discussed. Local stress and deformation fields induced by thermal cooling and in-plane mechanical loading are also examined, where plastic yielding of copper is observed to take place in the interface region near the free surfaces. The evolution of internal stress and deformation fields are used for identifying potential reliability concerns of the glass substrate.