Additive integration of 3D electrical circuits with off-the-shelf electronic devices inside 3D printed polymer parts, i.e., structural electronics, can enable new paradigms in miniaturized multifunctional structures. This paper investigates a hybrid printing process called Flash Light Assisted Manufacturing of structural Electronics (FLAME) which integrates Fused Filament Fabrication (FFF) of polymers with printing and Intense Pulsed Light sintering (IPL) of silver nanoparticles. The effect of IPL parameters and nanoparticle shape on conductivity is quantified, revealing that using NWs with IPL allows greater conductivity with lesser sintering-induced polymer damage. The conductivity of planar circuits is characterized during over-FFF, i.e., during FFF of the polymer on the sintered circuit. An unexpected finding is that over-FFF increases the conductivity in a complex and nonmonotonic manner that depends on the over-FFF parameters. A multi-layer IPL strategy is introduced for through-plane circuits, in which NWs are deposited in increments smaller than the circuit's total height and IPL is performed after each increment. Electromagnetic and thermal simulations reveal why through-plane circuits have lesser conductivity than planar ones and uncover the key role of multi-layer IPL in increasing the conductivity of through-plane circuits. Overall, FLAME increases the conductivity by 300 % for planar circuits and by 170 % for through-plane circuits as compared to state-of-the-art nanoparticle printing-based methods, even for low-thermal-tolerance polymers, in less than 10 s for each polymer layer. These advances break the performance-material-throughput tradeoff that plagues existing nanoparticle-based printing methods for fabricating 3D structural electronics.
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