Laser-assisted bump transfer for flip chip assembly

This paper describes a novel laser-assisted bumping technique for flip chip assembly. Copper bumps, with gold bonding layers and intermediate nickel barriers, are fabricated by UV lithography and electroplating on quartz wafers with pre-deposited polyimide layers. The bumps are thermosonically bonded to their respective chips and then released from the carrier by laser machining of the polyimide layer, using laser light incident through the carrier. Bump fabrication, parallel bonding, and chip release have been successfully demonstrated for test chips having 28 peripheral I/Os on 127 μm pitch. Visual inspection of bump cross-sections and individual bump shear test measurements have been carried out for chips bumped by the new method