Thermal Dynamics Effects using Pulse-Shaping Laser Sintering of Printed Silver Inks

Abstract

In recent years, additive manufacturing has been evolving towards flexible substrates for the fabrication of printable electronic devices and circuits. Generally polymer-based, these emerging substrates suffer from their heat sensitivity and low glass-transition temperatures. As such they require new highly-localized sintering processes to treat the electronic inks without damaging the polymer-based substrate. Laser-based sintering techniques have shown great promises to achieve high-quality sintering locally, while controlling the heat penetration to preserve the polymer substrates integrity. In this report, we explore new optimization pathways for dynamic laser-based sintering of conductive silver inks. Multiple passes of a pulsed laser are first performed while varying pulse train frequencies and pulse energies as an attempt to optimize the properties of the silver inks. Then, time-domain pulse shaping is performed to alter the properties of the conductive inks. Together, these pathways allow for the careful control of the time-domain laser energy distribution in order to achieve the best electronic performances while preserving the substrate’s integrity. Sheet resistance values as low as 0.024Ω/□ are achieved, which is comparable to conventional 1-hour oven annealing, with the processing time dramatically reduced to the milisecond range. These results are supported by finite element modeling of the laser-induced thermal dynamics.

Silver Nanoparticles Based Ink with Moderate Sintering in Flexible and Printed Electronics

“…Yeo et al [89] sintered the R2R printed Ag NPs layer by laser to a conductivity up to 20% of bulk Ag on PET substrates. Bolduc et al [90] indicated that controlling the incident laser pulse’s energy distribution in the time-domain was paramount to optimizing sintering process in Ag NPs based ink. A multi-step microsecond-pulsed laser process and a time-domain pulse-shaping modulation sintering caused a uniform and high conductive printed Ag trace on polymer substrates.…”

Laser sintering of gravure printed indium tin oxide films on polyethylene terephthalate for flexible electronics

“…The laser sintering approach heavily relies on the optical properties of nanoparticles in the film; one has to choose the radiation source according to their absorption spectrum. This can be easily achieved for the most commonly used metal nanoparticles (Au 38 , Ag 39 , Cu 31 ), whose plasmon resonance peaks are located in the visible part of the spectrum 40 , however sintering of TCO particles becomes a challenging task due to their high transparency in that spectral region. Nevertheless, it has been shown that effective sintering of such nanoparticles is feasible using UV excimer lasers by specifically adding compounds to the ink with high absorption at the incident beam wavelength 41–43 .…”

Contactless In Situ Electrical Characterization Method of Printed Electronic Devices with Terahertz Spectroscopy

“…The jetting frequency was set at 500 Hz. We used a commercially available conductive silver ink DGP 40TE-20C (ANP, Pleasanton, CA, USA) that contains silver nanoparticles (Ag NPs) of sizes around 50 nm with 30–35 wt.% in triethylene glycol monomethyl ether solvent [39]. The substrate used for printing was a heat-stabilized polyethylene terephthalate (PET) polyester film (Melinex ST505, New Berlin, WI, USA).…”