Multiscale phase-field fracture modeling of sintered porous silver nanoparticles within a unified creep-plasticity framework

Sintered silver nanoparticle (AgNP) materials are increasingly used in high-power and high-temperature electronic packaging; however, predicting their fracture behavior remains challenging due to their porous microstructure and strongly coupled time- and temperature-dependent deformation. In this work, a unified multiscale computational framework is developed to characterize deformation, damage, and fracture in porous sintered AgNP. The framework employs a temperature- and rate-dependent unified creep-plasticity (UCP) model as the common inelastic constitutive model and compares two alternative failure descriptions: a reference local UCP-damage formulation, in which a scalar damage variable produces distributed constitutive degradation, and a coupled UCP-phase-field fracture (UCP–PFF) formulation, in which the scalar damage variable is inactive and fracture is represented explicitly by a gradient-regularized phase-field variable. Mesoscopic pore morphologies, reconstructed via Gaussian random field (GRF) techniques and calibrated with SEM-derived two-point correlation functions, are utilized to link pore-scale fracture mechanisms with the macroscopic mechanical response. At the macroscopic scale, results demonstrate that conventional scalar damage models (UCP with entropy-based damage), even after calibration, predict diffuse stiffness degradation and smooth post-peak softening under the loading conditions considered. In contrast, the coupled UCP–PFF framework accurately predicts crack initiation and propagation following a distinct localization transition. At the mesoscopic scale, fracture preferentially initiates at pore clusters and narrow sintering necks, where viscoplastic dissipation accumulates and localizes. Increasing porosity redistributes dissipation among multiple weak regions, promoting a transition from a single dominant crack path to a multi-zone fracture involving branching and coalescence. These results demonstrate that fracture evolution in sintered AgNP is governed by mesostructure-dependent energy localization rather than averaged stress measures. The proposed framework provides a predictive tool for assessing fracture and reliability in AgNP-based interconnect systems.