The mechanical reliability of sintered silver joints, widely used in power electronics packaging, is critical for long-term applications such as electric vehicle converters. However, conventional homogeneous modeling often oversimplifies internal microstructural variations and limits the accuracy of stress prediction, especially under thermal cycling. In this study, a region-refined modeling framework is proposed to account for epoxy-regulated porosity and mechanical inhomogeneity across the joint. Pressureless die-attach joints were prepared using submicron silver pastes with varying epoxy contents (0∼4 wt%). The joint was divided into five sub-regions from the center to the fillet for localized characterization. Nanoindentation, SEM, and EDS analyses were conducted to assess region-specific mechanical properties and microstructure. Power-law constitutive models were extracted for each region and implemented into finite element simulations of thermal cycling (−55 ∼ 150 °C, 2 cycles/h, 250 h). The sub-region FEM model more accurately captured local stress concentrations and identified failure-prone areas, particularly near the fillet, compared to conventional homogeneous models. Experimental validation confirmed a good correlation between simulated stress zones and observed degradation. This sub-region strategy provides a robust framework for reliability prediction and design optimization of sintered silver joints in high-performance, large-area packaging applications.

Pressureless sintered silver pastes composed of submicron particles represent a promising, cost-effective interconnect solution for power electronics. While epoxy additives are often introduced to modify solvent behavior and enhance mechanical integrity, they can simultaneously degrade electrical and thermal performance, leading to critical trade-offs. In this work, five custom-formulated pastes with varying epoxy contents (0–4 wt%) and two commercial benchmarks were systematically evaluated in terms of shear strength, resistivity, thermal conductivity, and coefficient of thermal expansion (CTE). To optimize across multiple criteria, the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) was employed. The paste containing 2 wt% epoxy achieved the highest composite score, offering a favorable combination of mechanical, thermal, and electrical properties. Long-term reliability was further validated through high-temperature storage and thermal cycling tests. These results highlight that epoxy modulation, when integrated with an optimization framework, offers a viable strategy for tailoring high-performance, reliable sintered silver joints for next-generation power electronic packaging.