Although silver sintering is widely used in die attach, its reliability under low-pressure and pressureless sintering conditions remains a challenge, and the degradation mechanism needs to be addressed urgently. This study investigates the degradation mechanisms of silver sintered die attach subjected to thermal shock (TS) (−45 °C to 125 °C), revealing its microstructural evolution, degradation of mechanical properties, and pore dynamics. After 1500 cycles, the average porosity did not decrease and remained at approximately 10%, but the porosity distribution exhibited significant heterogeneity, forming three characteristic regions of high porosity, low porosity, and crack regions. With the porosity evolution, the grain size increased by a factor of 2.1–2.8, with the largest grain sizes in the crack region, and the recrystallization fraction decreased significantly, from 89.6 % to a range of 37.3 %–72.1 %. Additionally, the combination with the decrease in both statistically stored dislocation density and total dislocation density reveals a decline in hardness and yield strength of silver sintered layer from 1.05 GPa and 326 MPa to 0.92 GPa and 231 MPa, respectively, gradually diminishing their ability to impede pore migration and merging. Thermal-mechanical coupling simulations based on the actual porous structure images show that the mismatch in the coefficient of thermal expansion induces alternating tensile and compressive thermal stresses, driving pore evolution and crack propagation. The kinetic Monte Carlo (KMC) Potts model based on Kawasaki dynamics combined with pore conservation can effectively predict the long-term pore evolution in this case. These findings provide important guidance for optimizing the sintering process and improving the application of silver sintering materials in high-reliability electronic packaging.

Investigating the interconnection and strengthening mechanisms of die-attach layers is instrumental for advancing die attach process toward low-pressure and, ultimately, pressureless sintering while maintaining reliability. This study compares the microstructure and micromechanical heterogeneity of the pressure-assisted and pressureless regions in SiC die attach to elucidate the interconnection and strengthening mechanisms. Recrystallized grains make up 71.7 % of the pressureless region, markedly lower than the approximately 90 % observed in the pressure-assisted region, resulting in a higher porosity in the former. Evidence of both continuous dynamic recrystallization and discontinuous dynamic recrystallization is identified throughout the sintered layer. Microhardness reveals that the pressureless zone exhibits a hardness of 0.373 GPa, significantly lower than left (0.745 GPa) and right (1.832 GPa) of pressure-assisted region. All three regions share an average grain size of 400 ± 50 nm, and geometrically necessary dislocation density in pressureless zone exceeds that in pressure-assisted areas, neither of which can account for the difference in micromechanical performance. In contrast, the statistically stored dislocation (SSD) densities on the left and right of the pressure-assisted region are approximately 4.74 × 10¹⁴ m⁻² and 2.88 × 10¹⁵ m⁻², respectively—substantially higher than the 2.88 × 10¹⁴ m⁻² measured in the pressureless region. Collectively, these findings demonstrate that dislocation strengthening, and particularly SSD density, constitutes the dominant strengthening mechanism in silver sintered layers. This work not only provides new insights for enhancing reliability under low-pressure and pressureless sintering but also establishes a theoretical foundation for optimizing sintering material formulations.