Towards out-of-chamber damage-free fabrication of highly conductive nanoparticle-based circuits inside 3D printed thermally sensitive polymers

Combining metal nanoparticle (NP) printing and additive manufacturing has high potential for integration of 3D conductive elements and electronic devices inside objects. Current processes used to achieve desired electrical resistivity of the printed NP circuits entail a compromise between resistivity, throughput, and thermal damage of the structure. We aim to break this tradeoff. We explore the mechanisms underlying the combination of Fused Filament Fabrication (FFF) of Acrylonitrile Butadiene Styrene (ABS) and Polylactide (PLA) polymer structures, printing of silver NPs (mixed nanowires and nanospheres), and out-of-chamber Intense Pulsed Light (IPL) sintering of the printed circuits. IPL of only-nanosphere based circuits on the FFF-made structure thermally damages the polymer without any resistivity reduction. In a significant advance, the addition of nanowires achieves a resistivity several times lesser than the state-of-the-art (13.1 μΩ-cm or 8 x bulk silver) without any thermal damage and within 0.75 s of IPL. Electromagnetic analysis and Molecular Dynamics simulations show that nanowire addition concurrently reduces IPL temperature and accelerates the kinetics of resistivity reduction. Subsequent FFF over the post-IPL conductive pattern causes a non-monotonic change in resistivity, surprisingly effecting a resistivity reduction down to 11.8 μΩ-cm. The mechanisms underlying this observation are discussed. The developed approach is used to demonstrate multilayer sensing of internal temperature and a light sensing circuit with embedded interconnects. Finally, we discuss how these insights may guide the creation of a machine tool that creates a seamless form of the proposed process.