Cu-Cu Bonding Alternative to Solder based Micro-Bumping

High strength Cu-Cu thermo-compression bonds have been obtained at temperatures as low as 210degC. The bonded Cu surfaces were prepared by diamond bit cutting from electroplated structures. The electrical yield of bump chains depends on bonding temperature and bump size. At bonding temperatures of 300degC and over, bumps of 15 and of 20 mum diameter are bonded with high yield. Below 300degC, the yield decreases strongly for the larger bumps. However, chains made up of 15 mum bumps show high yield when bonded at 250 or 230degC, and still show 70% yield when bonded at 210degC. The electrical resistance of the bonded interface was too small to be determined separately. In shear testing, failure of the bumps does not occur at the bonded interface but after strong plastic deformation or as delamination of another interface.