Fluxless flip chip bonding on flexible substrates

Flip chip (FC)-technology on flexible circuits is of increasing interest for application in consumer oriented products. In particular, fluxless processes are in demand for compatibility with underfill materials and for improved reliability performance. This paper presents two approaches to a fluxless process based on soldering techniques using Au-Sn metallurgy and on adhesive joining techniques using gold and nickel gold bumps. Soldering is performed with a thermode and with a laser based system. For these FC joining processes, alternative bump metallurgies based on electroplated gold, electroplated gold-tin, mechanical gold and electroless nickel-gold bumps are applied.