Photonic Curing of Copper Ink Films on Liquid Crystal Polymer Substrate
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.287
Photonic Curing of Copper Ink Films on Liquid Crystal Polymer Substrate Andrew Luce1, Guinevere Strack1*, Oshadha Ranasingha1, Edward Kingsely1, Craig Armiento1, and Alkim Akyurtlu1* 1
Printed Electronics Research Collaborative (PERC), Raytheon–UMass Lowell Research Institute (RURI), Department of Electrical and Computer Engineering, University of Massachusetts Lowell, Lowell, MA 01854
*Corresponding authors:[email protected] and [email protected]
Abstract
The application of intense pulsed light (IPL) to printed copper nanoparticle (CuNP) films enables rapid curing on low temperature substrates in ambient conditions. In this work, we printed CuNP ink on liquid crystal polymer (LCP; Vectra A resin) and then cured the films using a high energy density light pulse. High-resolution SEM images of the cured films revealed that the CuNPs on LCP were fused together. Optimal curing parameters were a 5 ms pulse, 75% duty cycle, and an energy density range of 4.2–5.2 J·cm-2. Sheet resistance, Rs, values as low as ~0.1 Ω·sq-1were obtained. The LCP substrate took on a yellowed appearance after the application of five pulses and exhibited a surface free energy increase. A filter that blocked wavelengths 500° C in a 2 to 3 milliseconds. Therefore, physical changes that occur during the thermal analysis processes might not reflect the in situ curing process.
Figure 2 TGA (left; black trace) and DSC (right: blue trace) thermal profiles of copper nanoparticle ink.
Single layers of CuNP ink were printed on Kapton and LCP and subjected to light pulses. Applied energy density optimization was performed on CuNP films printed on LCP substrates. Average Rs of printed CuNP ink films on LCP with respect to a range of applied energy densities, 3.1–5.9 J·cm-2, are displayed in Figure 3A. Films comprised of one printed layer exhibited gaps; therefore, a second layer of ink was printed on top of the first layer to compensate for discontinuity. Energy densities that provided the lowest Rs, ~0.1 Ω·sq-1, ranged from 4.2–5.2 J·cm-2. Low energy density (5.2 J·cm-2) slightly increased Rs. Figure 3B displays photographs of the printed copper films after curing. The lowest applied energy density produced copper films with relatively high Rs. The black colour of the printed copper film indicates the presence of Cu(II) oxide. High energy density pulses appeared to breakdown the copper film or produce ‘burnt’ areas, which contributed to slightly higher resistance.
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Figure 3 Average Rs of layers of CuNP ink printed on LCP vs. respect to a range of applied energy densities, 3.1 to 5.9 J· cm-2 (A). Photographs of the corresponding cured copper ink films on LCP with energy densities equal to 3.1 (1), 3.8 (2), 4.2, (3), 4.5 (4), 5.2
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