Sustainability and Life Cycling Investigation of Buck Charging Circuits Printed using Gravure Offset Printing

Conductive inks for additive fabrication of flexible circuits typically comprise metal nanoparticles and several solvents for carrier fluid, surfactants, catalysts, and curing agents. Increased emphasis on sustainability has resulted in the emergence of water-based inks to replace volatile organic solvents. Flexible electronics have the potential for closer integration of form and function while lowering product weight and bulk. In this paper, the use of sustainable inks for the fabrication of additive battery charging circuits has been studied. The objective of this paper is to examine the use of water-based inks with surface mount components for an application with sustained current exposure of a battery charging circuit. The Gravure offset printing technique has been used to print switch mode buck battery charging circuits using water-based silver conductible ink. Component attachment for the circuits has been performed using electrically conductive adhesive (ECA) and low-temperature solder (LTS). The charging circuits have been subjected to accelerated life cycling to study the effect of usage on trace resistance evolution. The output charging current of the circuit has been monitored to track its evolution correlated with line resistance. The printed circuits were subjected to a repairability study wherein the attached components were manually removed; the component pads then underwent site redressal using conductible ink and the respective component attachment material (ECA/ LTS), which were dispensed manually. This was followed by the attachment of new components and subsequent curing. The performance of the repaired charging circuits was also tested and compared with that of the pristine circuits. Finally, the switch mode buck charging circuits were also printed using non-sustainable silver ink, i.e., inks not using water as the primary solvent, to compare their pre- and post-repair performance with the circuits printed using sustainable water-based ink. Elemental analysis of printed circuit interconnects has been performed to corroborate the differences in performance seen within sample types.