Direct Current Response of Inkjet-printed Flexible Interconnects

Flexible electronic circuits greatly depend on reliable interconnects joining circuit elements. Inkjet printing has been an attractive large area rapid printing technology for manufacturing of such interconnects. An understanding of the response of interconnects to applied direct current stress and subsequent failure is important to improve the reliability of them. Therefore, this study focuses on the application of stepwise direct current pulses to inkjet-printed interconnects fabricated on flexible polymer substrates. The interconnects were printed with commercial silver conductive ink (Metalon JS-B25P) on a Polyethylene Terephthalate (Novele IJ-220 - PET) substrate, employing an EPSON L130 desktop document printer. The interconnects were subjected to direct current step pulses starting from small currents and increasing until failure. The resistance and the peak temperature of the interconnects were recorded. Printed interconnects, which were conductive as-printed, showed minimal improvement in conductivity followed by applying the step currents. However, SEM images showed neck formation and subsequent growth in domains of the silver micro-structure. Further increase of the current resulted in failure of the interconnect and is mainly attributed to delamination of silver from the substrate due to evaporation of the ink binder and alterations of the chemical structure in the substrate. Therefore, the results suggest the need for careful consideration of peak current passing through an interconnect to ensure optimal reliability.