Abstract: A process for bonding a flip chip (20), of the type having an active face provided with conductive bumps, to a substrate (22) so that its active face is oriented toward the substrate (22). The flip chip (20) is coupled through a vacuum to the distended end (32) of an ultrasonic horn (30) and then lowered onto the substrate (22) so that the bumps (20b) align with a bonding pattern on the substrate (22). A bias force is applied through the ultrasonic horn (30) to the backside of the flip chip (20), in a direction normal to the substrate (22) so that minimal lateral displacement of the flip chip (20) and the substrate (22) results. The ultrasonic horn (30) is then activated while the bias force is applied such that the ultrasonic energy is isothermally transferred in a direction normal to and across the flip chip (20) to the substrate (22) for creating a diffusion bond therebetween.