A method and apparatus for performing metal-to-metal bonding for an electrical device and an electrical device produced thereby. For example and without limitation, various aspects of this disclosure provide a process that comprises depositing a thin metal layer on a copper pillar and then mating the copper pillar with another copper element. Atoms of the thin metal layer may, for example, form a substitutional solid solution or intermetallic compounds with copper. A concentration gradient is introduced by the thin metal layer, and diffusion at the Cu—Cu interface begins immediately. The thin metal film and the copper may, for example, diffuse until the interface disappears or substantially disappears.