Selective laser sintering of Ag nanoparticles ink for applications in flexible electronics

In this study the potential of three different laser sources (continuous wave (cw) or pulsed nanosecond (ns) and picosecond (ps)) operating at 532 and 1064 nm is investigated, as efficient tools for selective laser sintering of Ag nanoparticle (NP) ink layers on flexible substrates. Theoretical simulations indicate that picosecond (ps) laser pulses restrict the heat affected zone to a few micrometers only around the irradiated regions of the ink layer. For longer duration pulses or continuous wave operation, the laser beam profile and average power must be taken into account in order to avoid undesirably high temperatures reaching the substrate. These predictions were confirmed experimentally at 1064 nm and with ps pulses, efficient Ag ink sintering was achieved with no evidence of substrate degradation. On the contrary longer pulses may sinter Ag NPs in a broad wavelength range but inflict substrate damage over a wide laser fluence regime. Continuous wave mode may inflict damage to the low Tg polymers when applying laser power higher than 20 W, but it is the most flexible tool for sintering micro-patterns of homogeneous metallic features. The characteristics and the underlying mechanisms of each configuration are discussed.