One-Step Wet Chemical Treatment for Fluxless Cu-Sn Thermocompression Microbump Bonding

A new one-step wet chemical treatment has been developed for fluxless Cu-Sn microbump bonding. This treatment simultaneously removes native oxide from the Cu surface and deposits a functional layer on the cleaned surface. The treatment passivates the surface against re-oxidation and activates it for thermocompression bonding (TCB) between Cu and Sn without applying a flux agent. This paper discusses oxide layer removal from the Cu surface and the stability of the formed functional layer for up to 45 weeks. Die-to-die (D2D) microbump bonding was also evaluated through conductivity tests after thermal stress. Additionally, the uniformity of the layer formation on a 300-mm wafer-level application was assessed using dipping and spinning methods.