Low-Temperature Cu-Cu Bonding by Using Cu₂O Nanoparticle Coated Hierarchical Structure

To solve the problems of high cost of Cu nanoparticles (NPs) and high bonding temperature of Cu microparticles (MPs), a Cu
₂
O NP-coated hierarchical structure (Cu-MP@Cu
₂
O-NP) was proposed and fabricated for low-temperature Cu–Cu bonding. The Cu-MP@Cu-NP particles were obtained by Cu MPs through preoxidation and
in situ
reduction process, which formed a Cu particle with micro–nano core–shell hierarchical structure. The effect of preoxidation temperature on morphological features of Cu-MP@Cu
₂
O-NP particles and mechanical properties of bonded joints were investigated. After reduction process, the generated Cu
₂
O NPs on the surface of the hierarchical structure were reduced to Cu NPs completely. The surface NPs significantly enhanced the sinterability and structure density. After sintering at 300 °C, the shear strength of the bonded joints improved to 23.7 MPa, which is higher than that of Cu MPs without hierarchical structure. A sintering mechanism of Cu-MP@Cu-NP particles was proposed, revealing the surface NP layer is the key factor in this bonding process.