In the forms of a flip-chip package in which the contact elements of the chip are ultrasonically welded to the contact elements of the substrate, either the chip or the substrate or both are provided, prior to juxtaposition, with a bonding material which can be ultrasonically activated. During the ultrasonic welding process in which the contact elements of the chip and substrate are bonded together, the bonding material provides an additional attachment between the chip and substrate and eliminates the need for underfilling.