Thermal behavior estimation during thermal sintering of inkjet-printed silver nanoparticles via modulated laser beam and electrical sintering

Abstract

We studied rapid sintering of inkjet-printed Silver (Ag) Nanoparticles (NPs) by pulsed laser sintering and electrical sintering methods. A numerical model for pulsed laser sintering was developed in which temperature-dependent Thermophysical properties of Ag Nisswa’s adopted. An algorithm for treating the Thermophysical properties of the heated Ag NPs in a region by a previous laser shot was devised for the improvement of the temperature field estimation. The developed model was aimed towards the improvement and accuracy of the temperature calculation during a pulsed laser sintering. Furthermore, we applied the temperature field estimation model to study the pulsed overlapping characteristics during pulsed laser sintering of Ag NPs at 30%, 50%, 70%, 80%, and 90% pulse overlaps (POs) with 100 ms, 1 Hz and 3470 W/cm2 laser parameters. A detail electrical resistivity, thermal analysis, and surface morphology analysis for each pulse overlap (PO) case revealed that the 70% PO provided the best results among the three characterization categories, consequently producing the lowest Ag NPs line resistivity with the highest degree of consistency. The study was aimed to establish the parameters for an effective pulsed laser sintering operation. The algorithm was further used to calculate the temperature field induced during a to-and-fro (double scan) CW laser scan. The results predicted that double scanning provides with an even end-to-end sintering of the Ag NPs lines. The experimental investigations confirmed the predictions of the model and better electrical performance was observed with double CW laser scans as compared to single scans. During electrical sintering, with the help of a novel stepwise current increment sintering (SCIS) technique a stable Ag NPs line sintering was made possible avoiding thermal damage. In less than 0.15s a line resistivity as low as 6.8 μΩcm was obtained which was comparable with the furnace sintered line resistivity of 6.13 μΩcm at 250°C for 600s. In an attempt to lower the obtained line resistivity, the current supply duration at the final-step current was explored. Constant final-step currents of 0.4A and 0.5A with various time intervals was applied to the printed Ag NPs lines. While the 0.5A final step current damaged the printed line at a comparatively shorter time duration, the 0.4A final-step current prevented the line damage at longer durations subsequently producing comparatively better Ag NPs line resistivity at 3.59 μΩcm in 5000 ms. Numerical temperature estimation and SEM surface morphology analysis revealed that a comparatively lower estimated temperature and lower surface porosity at the final-step current of 0.4A prevented the line damage and enabled a prolonged current supply to boast the sintering and lower the Ag NPs line resistivity. Keywords: Laser sintering, Electrical sintering, Temperature calculation, Pulse overlapping.