Low-temperature Sintering And Performance Study Of Composite Nanosilver Particle Inkjet Printed Patterns

With the progress of technology and the updating of electronic product structures,the flexibility of electronic products has gradually become one of the development directions.Flexible electronic technology is required to support applications such as health monitoring and flexible displays.Among the popular materials for printed electronics manufacturing,nanosilver particles can be sintered into good conductors at relatively low process temperatures.Furthermore,inkjet printing technology offers the flexibility of design and suitability for various substrate materials.Therefore,inkjet printing of nanosilver particle ink is the best solution for rapid manufacturing of printed circuit samples.However,issues such as low temperature tolerance of polymers,large surface wetting fluctuations of polymers,difficulty in forming chemical bonds between metals and polymers,and poor contour accuracy of inkjet printed patterns have affected the quality of the nanosilver inkjet printing patterns.Therefore,it is necessary to conduct further research on material design methods that obtain denser sintered structures under low-temperature sintering conditions,mechanisms for substrate modification to improve the bonding strength of nanosilver printed patterns,and the laws governing the influence of different factors on inkjet printing pattern accuracy in order to comprehensively solve the current difficulties.This thesis proposes a design method for mixing nanosilver particles of different sizes in ink,which reduces the stacking porosity of the particles,and develops a solvent system suitable for inkjet printing requirements.By improving the wettability of the ink on different substrate surfaces through substrate modification and combining with chemical sintering,high conductivity and high bonding strength of inkjet printed patterns under low-temperature processes are achieved.The ink droplet deposition forming process in inkjet printing is numerically simulated,and the influence of various factors on ink droplet deposition forming is systematically studied.The effectiveness of patternization processing in improving the contour accuracy of inkjet printed patterns is also analyzed.Firstly,the optimization of the inkjet printed nano-silver particle ink was carried out by using composite particles of different sizes to reduce the random packing porosity of the particles.A calculation model of binary mixture random packing porosity was established by taking the average number of small particle layers(n)between large particles as a variable.The model comprehensively considers the packing porosity and low-temperature sintering ability of composite particles,which can be used to guide the optimization of particle size and quality ratio of nano-silver particles in ink.Nano-silver particles with sizes of 12 nm and100 nm were prepared by chemical reduction method and composite according to the optimized ratio,and dispersed in a solvent mixture of propylene glycol-dimethylformamide-methanol selected by Aspen Plus calculation,to form inkjet ink.The ink met the performance requirements of inkjet printers and had good particle dispersion stability and inkjet stability.Secondly,the conductivity of sintered patterns printed by inkjet under different low-temperature sintering processes and the bonding strength of sintered patterns with different substrate surface modification processes were comprehensively studied.In terms of low-temperature sintering process,the use of composite particles with n=0.58 can achieve the best low-temperature sintering conductivity by soaking in a 1 M Na Cl solution for 90 s,with a relative specific resistance of the pattern of 4.3 compared to bulk silver,and a 34% decrease in resistance compared to single-sized nano-silver particle sintered patterns.In terms of substrate modification process,the use of atmospheric plasma cleaning combined with polyvinyl alcohol(PVA)/silane coupling agent(KH550)mixed coating can effectively reduce the ink contact angle on the surface of polymer substrates such as polyethylene terephthalate(PET)and polyimide(PI),and can also enable the printed patterns to obtain good bonding strength after chemical sintering in Na Cl solution,with good universality.As a result,nano-silver particle sintered patterns with good conductivity and bonding strength were obtained on various polymer substrates.Furthermore,the influence of various factors on the ink droplet deposition process was systematically studied through numerical simulation methods.In terms of the simulation model,the mathematical model of the boundary conditions of the Volume of Fluid(VOF)method was modified based on the frictional tension viewpoint of the contact angle hysteresis phenomenon,thereby introducing frictional effects to improve the accuracy of the simulation results.Based on the simulation results,it was clarified that the essence of ink droplet deposition is the movement of the contact line,and the surface tension/viscosity value and contact angle determine the speed of contact line movement,while the size of the ink droplet determines the distance of contact line movement.Simulation and summarization were conducted to determine whether ink droplets could form straight continuous lines using different printing parameters under different conditions,and the summarized results could be used to guide inkjet printing parameter optimization.To further improve the accuracy of inkjet printing patterns,the effect of substrate pattern treatment on ink droplet deposition was studied,and the role of pattern treatment in reducing the minimum print line width and improving the smoothness of pattern contours was analyzed.Finally,the method for controlling the accuracy of inkjet printing patterns was discussed,which integrated the substrate surface modification process and the chemical sintering process of printing patterns with substrate pattern treatment.In order to maintain the designability of inkjet printing technology patterns,a patterned hydrophobic layer was created using a carbon dioxide laser marking machine and transparent paint to achieve rapid substrate patterning.Inkjet printing patterns on the patterned substrate exhibited higher accuracy in terms of oblique and curved contours as well as pattern corners compared to those on unpatterned substrates.Finally,the process scheme was extended to successfully produce multilayer circuits and curved circuits,demonstrating its high practical value.