ACF bonding technology for paper- and PET-based disposable flexible hybrid electronics

In light of the necessity to introduce reliable interconnection technologies for the development of disposable diagnostic kits, fine-pitch flip-chip integration of bare silicon dies on the paper and polyethylene terephthalate (PET)-based substrates have gained increasing importance. As the key-enabler of a hybrid electronic system, the interconnection technology should provide reliable electrical and mechanical properties. Paper and PET are temperature- and pressure-sensitive, and are not compatible with the conventional flip-chip bonding technologies, i.e., soldering and thermo-compression bonding. In this study, the feasibility of implementing Anisotropic Conductive Films (ACF) in hybrid integration was assessed, in which bare silicon dies with the thicknesses of 30 µm and 730 µm were bonded to screen-printed paper and PET substrates. As an alternative to direct bare die bonding, the integration of PET- and paper-based interposers to printed substrates was also addressed here. Correspondingly, the long-term reliability of the ACF-bonded samples was assessed via dynamic bend cycling tests. It was shown that ACF provides robust and reliable interconnects on both substrates with a failure cycle of more than 45,000 cycles.