Laser Engineered Fatigue Response of Flexible Interconnects

Printing of conductive nanoparticle inks on to flexible substrates is a promising method to manufacture flexible electronics. Most of such conductive inks need post thermal curing that can be achieved using laser sintering. The mechanical characteristics of such interconnects highly depend on sintering parameters. Here, we report on the use of laser sintering to manufacture an interconnect with predetermined fatigue response. Conductive interconnects were printed on substrates (Novele IJ-220-PET) using Epson L130 Inkjet printer loaded with silver nanoparticle ink (NOVACENTRIX JS-B25P). They were sintered using Cobolt 08-01 series 785 nm continuous wave laser. The laser power, the sintering speed, and the number of sintering passes were optimized to yield interconnects with different fatigue responses. The interconnects were subjected to bending over a 2'' mandrel under a load of 200 g. Two-probe in-situ resistance measurements were recorded using a Keithley multimeter. We demonstrated the fabrication of interconnects showing 2%, 7.5%, 18% and 30% increase in relative resistance after 700 bending cycles by sintering with 350, 400, 450, and 500 mW laser powers, respectively. The possibility to fabricate interconnects with predetermined fatigue response is mainly attributed to selective evaporation of the ink binder which is confirmed by Scanning Electron Microscopy (SEM) images. Hence, we propose laser sintering as a technique to manufacture interconnects with predefined fatigue response.