Abstract: A system for mounting VLSI devices on a substrate is disclosed, offering a high contact density. Each package consists of a semiconductor device having protruding elongated contact pin (2) on its surface and a wiring substrate having a cavity (3) on its surface. The cavities are filed with a conductive material (7) of a low melting point composition and sealed with a thin non-conductive foil (4). During packaging, the contact pins are made to penetrate the foil, and extend into the conductive alloy, thus making electrical contact therewith. To ease the penetration of the foil, the contact pins could be set into oscillating motion by means of an ultrasonic generator.