Application Cases

Experimental Title: Experimental Study on an Air-Assisted Electrostatic Focusing Electrohydrodynamic Printhead

Test Equipment: High-voltage amplifier, function generator, precision flow pump, laser scanning confocal microscope, and ultra-depth-of-field optical microscope, etc.

Experimental Process:

Figure 1: Experimental platform: (a) Schematic diagram of the experimental platform; (b) Physical image of the experimental platform.

The experimental platform used in the experiment is shown in Figure 1. The substrate is mounted on a motion stage, and the printhead is installed directly above it. Software controls the motor to drive the motion stage. Parameters such as stage speed, trajectory, and printhead height can be adjusted via the software. Bitmap files of the pattern to be printed and motion trajectory files can be imported into the platform software, which reads the files and directly controls the motion stage to follow the predetermined pattern, enabling the printing of various custom patterns. A precision flow pump supplies solution to the printhead. An air pump supplies airflow to the printhead; the input air pressure is controlled by adjusting a pressure regulator valve. Simultaneously, a pressure gauge is installed at the printhead's air inlet to monitor pressure changes in real-time, ensuring stability. The equipment used includes a pressure regulator valve and a digital pressure gauge. A high-voltage power supply provides high voltage to the various electrodes of the printhead. This high-voltage power supply consists of a function signal generator and a high-voltage amplifier. The function signal generator is used to generate various forms (DC, AC, pulse, etc.) of voltage signals. The high-voltage amplifier amplifies the voltage signal output from the function signal generator (by a factor of 1000) and outputs it to the high-voltage electrode of the printhead. An observation camera is set up on the experimental platform to monitor the printing process in real-time. The printed results on the substrate are observed using microscopes, specifically a laser scanning confocal microscope and an ultra-depth-of-field optical microscope.

Experimental Results:

Figure 2: Silver paste printing results on an insulating substrate: (a) Printing results using conventional electrohydrodynamic printing; (b) Printing results using the printhead's electrostatic focusing function; (c) Line width variation with substrate speed.

The results of conventional electrohydrodynamic printing on an insulating PI film substrate are shown in Figure 2(a). Influenced by the substrate, the printed silver paste lines appear curved, and adjusting the nozzle-to-substrate distance does not resolve this issue. In the electrostatic focusing electrohydrodynamic printing experiments, a glass nozzle with a radius of 20 µm was used, and nano-silver paste solution was printed on both insulating polyimide (PI) substrates and glass substrates. The electrostatic lens structure used was an electrode aperture structure with an inner diameter of 2.2 mm. Figure 2(b) shows the printing results of the nano-silver paste solution on glass and PI substrates. Figure 2(c) shows that the printed line width of the silver paste solution decreases as the substrate speed increases. At a substrate speed of 300 mm/s, the line width on the PI substrate can reach 20 µm, and on the glass substrate, it can reach 10 µm. This demonstrates that the printhead achieves good printing results on insulating substrates when utilizing the electrostatic focusing function.

Figure 3: Printing results on an inclined substrate: (a) Observation diagram of the printing process; (b) Variation of error coefficient with tilt angle.

To demonstrate that the printhead with the electrostatic focusing function can improve printing accuracy on inclined substrates, experiments were conducted comparing the printing performance of the electrostatic focusing electrohydrodynamic printhead and conventional electrohydrodynamic printing on inclined substrates, as shown in Figure 3. For easier camera observation, a metal nozzle with a radius of 150 µm was used in this experiment, and nano-silver paste solution was printed on both inclined conductive silicon substrates and insulating polyimide (PI) substrates. The electrostatic lens structure used was a sapphire disc structure with an inner diameter of 4 mm. The parameters used for printing are shown in Figures 3(a) and (b). When printing on the conductive silicon substrate, the inclined electric field formed between the nozzle and the substrate in conventional electrohydrodynamic printing caused significant jet deflection. In contrast, with the electrostatic focusing electrohydrodynamic printhead, the focusing effect of the electrostatic lens significantly reduced the jet deflection. Here, ds represents the distance between the jet's landing point on the substrate and the printhead's central axis, and hs represents the distance from the printhead to the point where its central axis intersects the substrate. The error coefficient (ds/hs) is used as an evaluation of printing error on the inclined substrate. The experimental results are shown in Figure 3(c). On the conductive silicon substrate, the error coefficient (ds/hs) of the electrostatic focusing electrohydrodynamic printhead is significantly smaller than that of conventional electrohydrodynamic printing. On the insulating PI substrate (relative dielectric constant of 3.5), stable printing was difficult to achieve with conventional electrohydrodynamic printing. The electrostatic focusing electrohydrodynamic printhead not only enabled stable printing but also achieved a smaller error coefficient than that on the silicon substrate. When the substrate tilt angle was less than 30°, the error coefficient was less than 0.03. This indicates that the printhead, when employing the electrostatic focusing function, achieves higher printing accuracy on both insulating and inclined substrates.

High-Voltage Amplifier Recommendation: ATA-7050

Figure: ATA-7050 High-Voltage Amplifier Specifications and Parameters

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