Micro-nano cooperative diffusion in bayberry-like porous Ag microparticle pastes enabling 125 °C ultralow-temperature sintering

Silver sinter-based interconnection is attractive for advanced electronic packaging, but the high sintering temperature of conventional Ag nanoparticle (AgNP) pastes and the high Young’s modulus of the sintered layer restrict use in temperature-sensitive and high-reliability devices. Here, we develop a micro-nano bimodal silver (AgPs-BM) paste composed of bayberry-like porous Ag microparticles (AgMPs) and AgNPs, enabling high-quality interconnections at 125 °C, well below the conventional 200 to 250 °C. Under 125 °C, 15 MPa, and 10 min in air, the bimodal paste produced a denser and more interconnected network than microparticle-only or nanoparticle-only pastes. The joints achieved a shear strength of 37.82 MPa and a film resistivity of 9.85 μΩ·cm. Extending the sintering time to 20 min further increased the shear strength to 60.15 MPa. Notably, AgPs-BM paste also achieved an average shear strength of 21.19 MPa under pressureless sintering at 125 °C for 60 min. Mechanistically, the porous microparticles carry a thin, readily desorbed organic layer and abundant surface features that anchor nanoparticles and accommodate organic residues. The nanoparticles create kinetically favorable contacts and diffusion bridges, shifting densification from self-sintering and spheroidization of microparticles to synergistic interparticle neck growth. Twins, low-angle grain boundaries, and dispersed nanopores retained in the microparticles after low-temperature sintering act as pinning sites during dislocation slip, yielding a favorable combination of high yield strength and low elastic modulus. This work provides a materials design strategy for low-thermal-budget, high-reliability Ag interconnects for next-generation electronic packaging.