A thermal mechanical process for bonding a flip chip die to a substrate. The flip chip die includes a plurality of copper pillar bumps, each copper pillar bump of the plurality of copper pillar bumps having a copper portion attached to the die and a bonding cap attached to the copper portion. The process includes positioning the die on the substrate such that the bonding cap of each copper pillar bump of the plurality of copper pillar bumps contacts a corresponding respective one of a plurality of bonding pads on the substrate, and thermosonically bonding the die to the substrate.