Synergistic optimization of conductivity and interfacial performance via humidity-assisted sintering of silver nanoparticle ink

High-reliability flexible and conformal electronic devices demand interconnects that simultaneously exhibit high conductivity and robust interfacial strength, as both are indispensable for ensuring efficient signal transmission and long-term operational stability under mechanical deformation. Nevertheless, existing sintering methods often struggle to achieve this dual optimization, thereby constraining their practical deployment in high-reliability electronic applications. Traditional thermal sintering process has an inherent trade-off between high conductivity and strong interfacial shear strength (IFSS) that cannot be achieved using silver nanoparticle ink (Ag NP). To address this, a humidity-assisted sintering (HAS) strategy (150 °C, 85 % relative humidity) is proposed and validated. This study presents a systematic investigation into the conductivity and interfacial performance of Ag NP ink printed on glass and polyimide (PI) substrates under various sintering conditions. Conductivity increases with rising temperature while shear testing across different sintering temperatures reveals a non-monotonic IFSS trend—an initial increase followed by a decline—on both substrates. This behavior stems from a mismatch between the thermal decomposition of insulating layers and the curing kinetics of the resin in thermal sintering, which hampers the concurrent optimization of conductivity and interfacial performance. In contrast, HAS allows for low-temperature sintering while simultaneously enhancing conductivity and interfacial performance, achieving values of 1.76 × 10⁷ S/m and 1.27 × 10⁷ S/m, comparable to those achieved at 250 °C and high IFSS of 20.5 MPa and 16.3 MPa (286.8 % and 50.9 % increase), on glass and PI substrates, respectively. Under bending fatigue tests, serpentine circuits fabricated with conventional sintering show a resistance increase of up to 352 % after 2000 cycles, whereas HAS-treated samples exhibit only a 10.8 % increase. These findings demonstrate that humidity-assisted sintering not only preserves high electrical performance but also significantly improves interfacial robustness and fatigue resistance, offering a viable route toward high-reliability flexible and conformal electronic devices.