Photonic Curing of Copper Ink Films on Liquid Crystal Polymer Substrate

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 <450 nm was placed over the printed copper film on LCP. As expected, the presence of the filter decreased the total energy density and produced a cured film with high Rs; however, when the energy density was increased in the presence of the filter, the Rs remained high (0.95 Ω⋅sq-1). This preliminary work indicates that additional studies are required not only to understand low thermal budget curing on LCP, but also to elucidate the properties of substrates that enable low Rs.

Copper inks for printed electronics: a review

“…121 For substrates with low T g and thermal conductivity, using multi-pulse IPL sintering with the same energy density can effectively prevent a rapid increase in temperature. 94,115,244,245 Copper particle ink printed on paper substrate using a fixed energy density of 15.6 J cm −2 and three pulses of IPL with 80% duty cycle within 2 ms exhibited a resistivity of 2.8 × 10 −7 Ω m. 94 In addition, Chu et al obtained conductive films with low resistance (5.12 μΩ cm) by sintering copper–silver hybrid inks on PI substrates using an energy density of 7 J cm −2 , pulse time of 1 ms, off time of 9 ms, and 20 pulses. 129 Recently, Lee et al developed a bidirectional IPL (B-IPL) sintering method that maintains uniform heating of the system by simultaneously radiating photon energy from both front and back sides, avoiding the layering and empty cavities caused by local heat conduction inside the copper film by single-way pulsed light sintering.…”

Selective laser sintering of conductive patterns on a novel silver–barium strontium titanate composite material

“…Devices made using AM techniques require dimensional control for device functionality, especially for discrete structures used for applications in the radio frequencies (RF) and microwave (MW) frequencies, and higher [5]. Printing capabilities and dimensional control depend on the ink composition and the printing method; therefore, development of functional inks that can be used in printed/additively manufactured devices is a significant and necessary step to advance this technology [3,4,[6][7][8]. Non-contact direct-write printing technologies such as aerosol jet printers are suited to print fine features as small as 10 µm.…”