Reduction Behavior of Surface Oxide on Submicron Copper Particles for Pressureless Sintering Under Reducing Atmosphere

The reduction behavior of the surface oxide on Cu particles under a reducing gas atmosphere was investigated for a pressureless sinter joining. We conducted x-ray thermodiffraction analysis and simultaneous thermogravimetry, differential thermal analysis, and mass spectroscopy (TG–DTA–MS) under a reducing atmosphere to investigate the reduction and subsequent sintering behaviors of copper particles at different oxygen concentrations. The shear strength of the pressureless sinter joint decreased with increasing oxygen concentration. The thermodiffraction results revealed that the reduction onset of Cu2O started at the same temperature (220°C), whereas the reaction markedly persisted at higher oxygen concentrations. Cu sintering progressed significantly after the reduction due to generation of Cu nanoparticles. The TG–DTA–MS results indicated that H2O formation temperature associated with the reduction depends on the oxygen concentration, consistent with the thermodiffraction results. The surface oxides were found to play an important role in pressureless sinter joining via nanoparticle formation, while the presence of a large amount of oxide delayed the reduction and subsequent sintering.