Improving Printed and Thermoformed Conductors on Polycarbonate with a Thin-Film BNNT Interlayer for Next-Generation In-Mold Electronics.

The processes of thermoforming 2D-printed electronics into 3D structures can introduce defects that impact the electrical performance of conductors, making them more susceptible to thermal failure during high electrical power/current applications on temperature-sensitive substrates. We therefore report the use of a thin-film boron nitride nanotube (BNNT) interlayer to directly reduce heat stress on linear and serpentine metallic traces on polycarbonate substrates thermoformed to 3D spherocylindrical geometries at varying elongation percentages. We demonstrate that the BNNT interlayer helps to improve the electrical conductivity of highly elongated thermoformed 3D traces in comparison to traces on bare polycarbonate. Further, we correlate localized substrate thinning at high elongation areas with increases in the local trace resistance. These resistance increases create localized "hot spots" in the traces when high voltages and currents are applied to them. BNNT interlayers provide thermal protection to the underlying substrate and enable them to endure localized temperatures 1.5 times higher than those on bare substrates, as high currents are applied to the silver traces. Overall, this study demonstrates the use of BNNT interlayers as valuable thermal management materials to facilitate the development of more reliable and higher-performing conductive metal traces for use in 3D electronics and in-mold electronics applications.