Boron Nitride Nanotube Coatings for Improved Thermal Management and Mechanical Durability of Flexible Printed Conductors

Large-scale production of flexible conductors hinges on developing economically viable printable materials that can be formed under rapid processing. To decompose and convert the ink to its metallic state, sintering techniques with high irradiative and thermal requirements, such as photonic sintering, can be used to form conductive traces on a millisecond timescale. However, utilizing intense processing techniques with low-temperature substrates like polyethylene terephthalate (PET) or polylactic acid (PLA) can lead to warping of the substrate and subsequently poor trace morphology due to the uneven heat accumulation at the interface between the substrate and the printed trace. To combat this issue, incorporating an electrically insulating film interposed between the substrate and the printed feature can aid in spreading heat laterally away from the substrate-feature interface without sacrificing conductive performance or flexibility of the plastic substrate. Boron nitride nanotubes (BNNTs) exhibit high thermal conductivity and impressive mechanical robustness, and therefore present a promising platform to minimize thermal and mechanical degradation of the printed feature and the substrate over time.<br/><br/>We present the use of modified boron nitride nanotubes (BNNTs) as a heat dissipating layer to mitigate deformation and thermal damage to PET and PLA substrates upon curing of silver molecular inks through IPL and UV sintering. Conductive traces were printed onto BNNT-coated substrates of varying surface concentrations and exposed to a wide range of sintering energies to fully investigate the effects of increasing thermal heat generation across varying trace designs. The inclusion of the BNNT thin-film at the substrate-trace interface resulted in reduced warpage of the substrate, as well as improved trace morphology and subsequent conductivity at increasing BNNT surface concentrations, confirmed through scanning electron microscopy (SEM), 2D scan profilometry, and energy-dispersive x-ray spectroscopy (EDS). Thermal infrared imaging observed a decrease in average peak temperature of the features at high BNNT surface concentrations, owing to the lateral heat diffusive properties of the BNNT network. Furthermore, incorporating the BNNT interlayer into thermoformed structures assists in normalizing the conductivity at elongated stress points due to the mechanical durability of the underlying BNNT network. The BNNT interfacial film as a thermal management tool successfully maintains the structural integrity of conductive traces upon rapid processing techniques, and holds promise for integration into wearable electronics platforms to extend operational lifetime.