Robust Cu–Cu Bonding with Multiscale Coralloid Nano-Cu3Sn Paste for High-Power Electronics Packaging

In this work, a multiscale coralloid nano-Cu3Sn composed of a bimodal structure (∼55 and ∼120 nm) has been successfully synthesized to meet low-cost and Pb-free packaging demands for high-power electronic application. Owing to the excellent oxidation resistance of the Cu3Sn intermetallic compounds (IMCs) and the protection of solvent poly(ethylene glycol)-400 (PEG-400) at high temperature, the full-Cu3Sn joints sintered in air have a comparative shear strength with the joints acquired in vacuum when the sintering temperature is no more than 300 °C. The full-Cu3Sn joints acquired at 300 °C in air achieve a high bonding strength of 40.4 MPa, which is superior to those of traditional Sn-based solder joints (19 MPa) and full-Cu6Sn5 joints (17.7 MPa). The electrical resistivity of the sintered Cu3Sn films reaches 29.1 μΩ·cm in air. Cu3.02Sn0.98 is formed at the interface between the Cu substrate and sintered Cu3Sn layer, contributing to the exceptional bonding strength of the full-Cu3Sn joints. The bonding strength of the joints after high-temperature storage (HTS) tests reveals that the prepared full-Cu3Sn joints possess outstanding long-term thermal stability with a shear strength of 47.9 MPa after 800 h of storage at 250 °C. Our work breaks through the synthesis bottleneck of nano-Cu3Sn IMCs and provides the underlying insights needed to guide the design of highly stable full-IMC joints for high-temperature electronic packaging.