## 1 Introduction  
When forming electronic elements by printing with nanoparticles (NP), an important process that ensures the electronic properties of these elements is the sintering of NP arrays deposited on the substrate. In recent years, studies and applications of local laser sintering of NP arrays on substrates have been developing, which significantly expands the possibilities of micron-size printing methods in the areas of heat-sensitive plastic substrates and a variety of NP materials used [1, 2]. In particular, the method of laser sintering of micron-size conductors from silver NPs and organic thin-film transistors on polyethylene naphthalate (PEN) substrates was studied in [3, 4]. Most metals used for the synthesis of NPs, e.g., copper or aluminum, have a high oxidation reactivity in ambient conditions. It results in the formation of oxide insulating film 1-3 nm thick on a surface, preventing the high conductivity between particles. To minimize the oxygen flow to the surface of NPs a layer of noble metal or other inert coating substance (thiol, polymer) may be applied [5, 6]. Also, to prevent oxidation processes, it is possible to form samples in a high vacuum or in an inert gas environment [7]. The use of laser sintering for micron-size elements formed by the developing aerosol printing technology, which is based on selective deposition of aerodynamically focused NP streams onto the substrate is promising. In the first implementation of the technology samples were being formed by microdrops from the dispersion of NPs (inks) [8]. Aerosol printing allows to form functional elements on the substrates with a minimum line width of around 10 \(\upmu\)m, which is much lower than while using inkjet and screen printing technologies [9]. However, when NPs are delivered to the substrate as a part of the ink, solvent and other organic additives must be removed before sintering. This makes the sintering process of NP array dependent on the composition of the ink used. In the last decade, many studies have been done in the field of conductive lines formation by selective laser sintering of NP arrays formed by ink printing, mainly on heat-sensitive substrates (PET, PEN, polyamide), e.g., [10; 11; 12; 13]. Sintering processes were studied using continuous (CW) and pulsed nanosecond and picosecond laser sources operating at 248, 532 and 1064 nm. The processes of laser radiation absorption by silver NPs and energy transfer to the substrate were studied experimentally and by computer simulation. The high specific conductivity of sintered silver NP arrays, 4-6 times smaller than for bulk silver, was demonstrated in studies using inks of silver NPs of less than 50 nm in size and a mass fraction of 34-75 wt% and with the use of nanosecond pulsed laser sources with a wavelength 532 nm [10; 12]. Special attention was paid to the process of removing solvents and other additives from the ink deposited on the substrate, as this procedure improves the laser sintering efficiency of the silver NP arrays. In recent articles the time spent on drying of deposited inks at 60-80 \({}^{\circ}\)C has been reduced from 24 hours to 30-60 min. The use of ink with a high mass fraction of silver NPs (70-75 wt%) was a fundamentally new step in this direction. It allowed to evaporate the solvent and the volatile additives from the ink at room temperature, by leaving the ink to dry for 1 h [12]. However, the problem of drying the ink deposited on the substrate remains. Recently [14; 15; 16] a new approach in aerosol printing has been proposed with no ink used. In this approach, NPs just before being used are synthesized in the processes of a spark discharge in a flowing gas between electrodes of the material desired [17]. The aerosol stream of NPs is focused and delivered to the treated surface, the particles are deposited in a dry form without a solvent. Recent studies have shown a high efficiency and productivity of dry aerosol printing in comparison with the other additive technologies [18; 19; 20; 15].