Research On Droplet Formation And Deposition Of Nano-silver Inkjet Printing

Printed electronics technology is a process that produce electronic devices by means of printing.The intended function of the printed electronics is achieved by selectively depositing functional ink on the substrate.It has broad application prospects in the fields of wearable devices and radio frequency identification.Inkjet printing technology has the advantages of low cost,no contact with the substrate,simple molding,material saving,and is an ideal process for manufacturing printed electronics.In the inkjet printing process,the ejection and deposition of ink droplets are important factors that influencing the morphology of inkjet printing patterns.The stable ink jetting is beneficial to improve the accuracy of ink droplet deposition and reduce the characteristic size of the printed circuits.The uniform deposition of ink droplets helps to improve the conductivity of the printing line and enhance the performance of the printed device.In order to achieve stable injection and uniform deposition,this paper takes nano-silver ink as the research object,and combines experimental and finite element simulation to study the conditions of ink droplet forming process and stable injection.Aiming at the problem that the rheological properties of particle-suspended ink will change with the change of shear rate,a variable viscosity inkjet printing model is established by fitting the rheological parameters.The trend of ink viscosity during high shear rate spraying is investigated.The causes of the instability of the ink droplets are analyzed,and the conditions that the ink stable injection needs to be satisfied are summarized.Based on the above work,the printing parameter settings satisfying the uniform deposition are studied.The main work and summary of this paper is as follows:(1)The inkjet process is simulated by using COMSOL Multiphysics.The ink is affected by factors such as nozzle and air resistance,and has a high shear rate.Affected by this,most of the ink droplets maintain their extreme viscosity during the injection process.(2)By analyzing the relationship between the droplet velocity distribution and the droplet morphology,it is pointed out that capillary force is an important factor affecting the stable injection of ink.The pressure on the neck of the droplet is greater than the head of the droplet,causing the ink to accelerate toward the main droplet.(3)The number of capillaries and the Z value are used as parameters for judging the stable injection of the ink.Based on the experimental and simulation data,the ink printability window is summarized.By analyzing the position of the ink injection parameters in the printability window,the injection parameters are adjusted,and the conclusion is verified by the inkjet printing experiment.(4)The ink deposition is adjusted based on the mathematical model of droplet deposition and the spreading process of a single drop of ink in the simulation.Only when the print resolution is greater than 400 dpi can the droplets overlap each other to form a uniform pattern.(5)Sintering is used as a post-treatment method.At a resolution of 1000 dpi,a sintering temperature of 180 °C,and a sintering time of 30 min,the printed circuit has a lower resistance.