Development of high-performance Cu nanoparticle paste and low-temperature sintering for Cu–Cu bonding

The sintering technology of Cu nanoparticle paste has significant potential for application in wide bandgap semiconductor devices. In this study, a high-performance and multi-scale Cu nanoparticle paste is proposed to solve the critical issues of easy oxidation during preparation and storage, as well as high sintering temperature. The multi-scale Cu nanoparticles with sizes ranging from 20 to 140 nm were synthesized simply and efficiently using a liquid-phase reduction method. These nanoparticles were subsequently mixed with a reducing composite solvent to develop a Cu nanoparticle paste. Based on this paste, pressure-assisted Cu–Cu bonding experiments were conducted at various temperatures and durations. The Cu–Cu joints achieve an average shear strength of 33.3 MPa after sintering at 240 °C in a nitrogen atmosphere and even exceed 60 MPa when the temperature is raised to 280 ℃. Additionally, with a reductive surface coating, the multi-scale Cu nanoparticles can be stored for over 20 days under ambient air condition. Besides, the enhanced bonding strength and dense microstructure are attributed to the close-packing effect of multi-scale nanoparticles and the facilitation of small size nanoparticles. The proposed multi-scale Cu nanoparticle paste exhibits excellent oxidation resistance and low-temperature sintering performance, which demonstrates significant potential for application in power device packaging and interconnection.