Low temperature fluxless flip chip technology for fine pitch bonding

This paper describes a flip chip technology representing a technological breakthrough compared with conventional method such as soldering or the bonding through conductive adhesives. Electrical connections are performed by the insertion of metallic micro-tips in ductile solder material. As low temperature and fluxless technology, this method is adapted to fine pitch and large devices. Here we present our technological investigations to perform electrical conductive micro-tips such as plasma etching, chemical etching, lift-off, and an innovated use of nanoimprint technology of metallic materials. Gold appears as a good choice of material for micro-tips performing, because an intermetallic phase is formed with solder materials such as tin, lead, or indium based solder and ensures the mechanical and electrical contact. Finally we present the bonding results of our test vehicle which validate the principle of the electrical connection through insertion for a 15mum pitch. The resistance value of such a connection has also been measured for a 30mum pitch