Development of high-density interconnection techniques for contactless smart cards

Summary form only given. This paper deals with techniques that are used for fabricating high density and thin assemblies with emphasis on materials, implementation and reliability. Moreover, a new potential interconnection and packaging technique being particularly suitable for contacting ultra-thin chips is also introduced. In the production tests electroless fine-pitch Ni/Au bumped chips were bonded with solder paste but the results were not satisfactory. Commercial isotropically and anisotropically conductive adhesives allowing denser interconnections than conventional soldering gave markedly better results and are now used in volume production of contactless cards. A new type of ACA containing fusible filler particles was employed for bonding flip chip bumps on the substrate with metallurgically compatible contact pads. The results proved to be very promising especially from the electrical continuity point of view. A solderless interconnection technique, which is especially suitable for producing very fine pitch interconnections, was employed successfully for fabricating contactless smart cards. In this technique, in which the substrate conductors are chemically deposited on shallow bumps of the embedded chips, high reliability of the interconnections can be achieved.