Assembly of ultra thin and flexible ICs

The Fraunhofer Institute for Reliability and Microintegration in Munich has developed a process for manufacturing ultra thin ICs with a thickness down to 10 μm. These very thin ICs offer several advantages like low package height, flexibility and low topography for interconnection. These properties make them an ideal candidate for their integration in flexible substrates like polymer foil or even paper. Possible applications for such systems are electronic labels, tickets or security papers. For these systems different die bonding and electrical interconnection methods can be used. Dies are bonded by adhesive. Due to low topography ultra thin ICs can then be interconnected just by screen printing of polymer paste or by using the flip chip technique with anisotropic conductive adhesive. The paper describes new fundamentals for interconnection of ultra thin ICs and systems to flexible substrates. Accurate dosing of adhesive for die bonding with a thickness of adhesive of approx. 5 micron was developed. Solutions for handling of ultra thin and flexible ICs was found. An optimal process flow was developed by investigations at different types of substrates (paper, polymer foil, electronic flex substrates), different adhesives (epoxy, cyanacrylates) deposition methods (dispensing, stamping and dipping) and interconnection techniques. The properties of the assembled test systems, in due to reliability under mechanical and thermo mechanical stresses have been evaluated and are discussed