Location-Dependent Microstructure and Mechanical Properties Evolution of TGV-Cu via an EBSD-Nanoindentation Co-Localization Characterization

Abstract

As 2.5D/3D advanced packaging moves toward higher interconnect density, glass substrates are attractive for their electrical performance and dimensional stability. However, high aspect ratio, fine pitch through-glass vias (TGVs) are prone to thermo-mechanical failures under long-term thermal shock, and microscale reliability assessment is hindered by costly microstructural characterization and the lack of models capturing long-term microstructural evolution and property degradation. Here, fully copper-filled TGV-Cu structures were fabricated on Schott AF32 glass and subjected to thermal-shock cycling from - 40 ℃ to 125 ℃ (0, 700, 1400, and 2100 cycles). Results show a non-monotonic, location-dependent hardness evolution with pronounced heterogeneity, where the mid-via region exhibits stronger late-stage softening by nanoindentation. EBSD shows grain diameter increases from 0.61 μm to 0.91 μm, while GND density decreases by recovery and then re-accumulates preferentially near the via bottom, evidencing competition between grain-growth softening and dislocation hardening. Hybrid Potts-phase field simulations further predict continuous grain growth and stress relaxation (declining von Mises stress) inside the via; including the glass substrate and interface constraints raises the stress level but preserves the relaxation trend. Moreover, the phase field simulations results of equivalent plastic strain (PEEQ) reveal progressively intensified cyclic plastic localization near the top/bottom caps (Cu/glass intersections), providing mechanistic support for cracking localized at the via mouths.