Improving the conductivity of metal particle inks is a hot topic of scientific research. In this paper, a method for preparing metal-filled particles was proposed. By adding filled particles to the ink, the size distribution of particles could be changed to form a bimodal distribution structure in accordance with Horsfield’s stacking model. The filling particles had small volume and good fluidity, which could fill the gaps between the particles after printing and improve its electrical conductivity without significantly changing the metal solid content in the ink. Experimental results show that the silver content of the ink slightly increased from 15 wt% to 16.5 wt% after adding filled particles. However, the conductivity of the ink was significantly improved, and after sintering, the resistivity of the ink decreased from 70.2 μΩ∙cm to 31.2 μΩ∙cm. In addition, the filling particles prepared by this method is simple and has a high material utilization rate, which could be applied to the preparation of other kinds of metal particle inks.

The liquid phase reduction method has a wide application prospect because of its simple equipment and low cost. However, the disadvantages, such as uneven particle size distribution and easy agglomeration of particles, make it difficult to prepare high-concentration nanoparticle ink by this method, which limits its application in the manufacture of high-resolution electronic products. This paper presents a printing and sintering process for low-concentration ink prepared by the liquid reduction method. First, the set pattern is printed by the near-field electrohydraulic printing method. At the same time as multi-layer printing, the substrate is heated by the collecting plate to accelerate the evaporation of the solvent in the printed pattern. Then, the printed multi-layer micro-conductive pattern is solidified by a hot/pressure sintering machine. This method can overcome the edge diffusion effect caused by poor ink viscosity effectively and obtain printing patterns with high thickness, high conductivity, and high resolution. The drying time of different ink layers, the pressure and temperature of hot/pressure sintering, and other parameters were studied in this paper. The electrical conductivity and reliability of the pattern with different printing layers are also analyzed, which provides a reference for the printing and sintering of low-concentration ink in the future.

Resistivity is considered a significant parameter for printing a conductive pattern and nano-ink. Nevertheless, the resistivity of a sintered printing pattern varies with the performance of the pattern and nano-ink. The cross section or non-uniformity of the printing pattern is not taken into consideration, and the changes in resistivity are not measured during the whole sintering process. In this work, the cross section uniformity of the pattern is improved, which is attributable to the standard sample template fabricated by laser engraving. First, the ink containing 50 wt. % silver nanoparticles (AgNPs) with sizes ranging from 30 to 100 nm was prepared. Second, the prepared ink and commercial ink containing 50 wt. % AgNPs with an average size of 5 nm were separately injected into two standard sample templates. Finally, a four-probe platform was employed to carry out the sintering process at different temperatures. We studied the effects of sintering temperature on pattern resistivity and the subsequent performance of the prepared ink. Furthermore, the thermal conductivities of inks were calculated through the optimized Wiedemann–Franz law for different temperatures. The results showed that electrical resistivity of two inks changed after sintering, presenting the same trend of an initial linear increase, then a linear decrease, followed by a period of stability, and finally a linear increase as the sintering temperature increased. In addition, when the ink was sintered completely, the porosity observed using an optical microscope with 1000× magnification and resistivity and thermal conductivity of the prepared ink were 80.13%, 69.48%, and 66% smaller than those of commercial ink, respectively. The methods proposed in this paper lay the foundation for further research on nano-ink.