Laser selective sintering and patterning of printed silver nanoparticle inks on temperature-sensitive polymeric substrates for flexible electronicsTuesday (23.06.2020) 11:50 - 12:10 Room 2
Thin flexible electronics are gaining interest, among others, due to the possibility of bringing cost-effective digital traceability and interactivity to everyday objects, when employing radio-frequency identification (RFID) or near-field communication (NFC) technologies.
Laser processing with short and ultra-short laser pulses can be applied to a number of steps in the microfabrication processes related to those technologies, such as printing, sintering and patterning of micrometric-sized wide conductive tracks. Direct laser printing allows creating metallic tracks following predesigned paths with a relatively simple setup and resolution down to a few micrometres. The selective nature of the laser sintering process allows in addition employing cost-effective flexible substrates, which would otherwise degrade when employing traditional non-selective sintering techniques, e.g. oven sintering. Further, laser patterning can be exploited for opening relief holes by ablating conductive material at desired locations, without causing damage to underlying functional layers. This facilitates making further vertical interconnections. All this becomes possible thanks to the highly confined exposure of the material to the laser radiation. Particularly when using ultra-short laser pulses, the undesired heat affected zone is limited to a few micrometres or less. Highly integrated modern laser sources with advanced CNC and fast optical scanning systems offer also an accuracy in positioning and steering a laser beam in the range of just a few micrometres across large areas, which can typically reach several hundreds of millimetres.
In this work, the combined application of these laser technologies for creating conductive patterned micrometric sized tracks on a flexible polymeric substrate is shown. Laser Induced Forward Transfer (LIFT) is applied to transfer nanoparticle silver inks according to a designed pattern onto the polymeric substrate. Selective laser sintering is afterwards employed to process the printed tracks and make them electrically conductive, without damaging the underlying substrate. The electrical resistance of the resulting tracks is afterwards measured, to ensure sufficient conductivity for the circuit to be functional. The laser printed, sintered and patterned tracks show a measured sheet resistance below 30mΩ/sq and a resistivity below 10x bulk silver.