The Resistor Network Approach to Modeling Screen-Printed Silver Ink Under Uniaxial Stretch

Flexible electronic devices are used in a wide variety of applications that utilize their unique ability to stretch, bend, and twist. Experimental methods were developed for evaluating the piezoresistive behavior of printed conductive inks under uniaxial strain. DuPont 5025 screen-printed silver ink on Kapton and Melinex substrates was stretched until substrate failure. Kapton samples were found to rupture at around 60% strain and have a relative resistance, R/R0, of about 30-40 at substrate rupture. On Melinex substrates, the ink was found to electrically fail before the substrate ruptured but could be stretched to strains exceeding 130% or higher before failing. The relative resistance values for these high strains in the Melinex samples were erratic and could exceed 1000 and in one case more than 30,000. The ink strain to failure exhibited a dependence on conductor width with narrower conductors failing before wider ones. Finally, a 2.5D RVE model that accounts for ink filler volume fraction, particle size distribution, contact resistance, and electron tunneling was developed that accurately predicts the piezoresistive behavior of 5025 ink up to 60% axial strain. An initial parametric study found that increasing the volume fraction of the RVE results in improved electrical performance.