Enhancement of Cu-to-Cu bonding property by residual stress in Cu substrate

This study investigated the use of copper nanoparticles (Cu NPs) as a novel material for interconnecting joints in advanced electronic packaging technology. Cu NPs offered a promising alternative due to their excellent electrical and thermal properties. Cu NPs were characterized as single crystals by a transmission electron microscope, and electron backscatter diffraction confirmed that the grain size of the Cu substrate was about 11 μm and only became slightly larger after thermal annealing. Surface diffusion was determined to be the dominant kinetic path for Cu NP sintering on the substrate. An additional driving force for sintering was validated by measuring the stress state using X-ray diffraction. The characterization results provided evidence for proposing a mechanism to explain how residual stress influenced atomic behavior during the sintering process. High residual stress enhanced the strength of the Cu NP joints and improved the reliability of electronic devices.