<p>Cu nanoparticles exhibit excellent properties as high-temperature-resistant, conductive, heat-dissipating, and connecting materials. However, their susceptibility to oxidation poses a major challenge to the production of high-quality sintered bodies in the air, severely limiting their widespread adoption in power electronics packaging. This study presents a novel approach to the synthesis of Cu nanoparticles capped with oleylamine ligands. By employing a simple solvent-cleaning process, effective control of the density of oleylamine ligands on particle surfaces was achieved, resulting in high-performance Cu nanoparticles with both oxidation resistance and air-sintering susceptibility. Moreover, through our research, the solvent-cleaning mechanism was clarified, a model for the oleylamine ligand decomposition was developed, the air-sintering behavior of Cu nanoparticles was analyzed, and the impacts of both the sintered bodies and interfaces on the sintering performance were explained. Additionally, Cu nanoparticles subjected to 5 cleaning rounds followed by sintering at 280&#xa0;°C and 5&#xa0;MPa in air were confirmed to be able to produce the highest shear strength (49.2 ± 3.51&#xa0;MPa) and lowest resistivity (6.15 ± 0.32&#xa0;μΩ·cm). Based on these results, flexible capacitive pressure sensors with Cu sintered electrodes were fabricated and demonstrated a stable pressure–capacitance response over the temperature range of 25–250&#xa0;°C. These findings underscore the impressive robustness and durability of sintered structures and the potential for high-temperature applications of oleylamine-capped Cu nanoparticles. Our study provides reliable application demonstrations for the low-cost manufacture of high-performance power electronics packaging structures that can operate in high-current–density, high-heat-flow-density, high-temperature, and high-stress environments.</p> Graphical abstract <p></p>