Room temperature bonding of Au plating through surface smoothing using polyimide template stripping

Room temperature bonding of Au plating offers various applications in electronics packaging, but smoothing of the bonding surface is a critical challenge. In this study, we propose and demonstrate the additive smoothing of the plated Au surface by combining the template stripping and surface activated bonding techniques for direct Au bonding at room temperature. The surface roughness of the Au plating is reduced from 21 nm to 5 nm in RMS by transferring Au films from the polyimide (PI) template three times. It is found that the transferred Au films from the PI template compensate the surface asperity of the Au plating, resulting in fewer gaps at the interface than using a SiO₂ template. The smoothed Au plating is also bonded through surface activated bonding at room temperature, exhibiting as high bonding strength as bulk fracture. The presented method enables room temperature bonding of plated Au without conventional polishing processes.