Additive Manufacturing Technologies Compared: Morphology of Deposits of Silver Ink Using Inkjet and Aerosol Jet Printing

Abstract

We report about a detailed comparison of the additive manufacturing methods inkjet printing (IJP) and aerosol jet printing (AJP). Both technologies are based on the direct-writing approach enabling the non-contact deposition of various materials in flexible patterns, e.g., for printed electronic applications. The deposited pattern elements were classified as (i) drops (IJP) or splats (AJP), (ii) lines, and (iii) squares. These elements can be considered as basic elements of the deposition systems and also of printed electronics. The pattern elements were deposited with IJP and AJP using the same silver nanoparticle ink. After printing, the layers were characterized regarding their morphology by optical and topographical measurement methods as well as regarding their electrical characteristics. It turned out that drops deposited with IJP and splats deposited with AJP can have similar dimensions. However, the shapes of the deposits differ widely. In the case of lines, AJP enables narrower line widths and thinner line thicknesses in comparison to IJP. In IJP, the line morphology varies depending on the direction of the deposition. Finally, the morphology of the deposited lines determines the electrical conductivity. For printed squares, the IJP layers show much higher layer thickness and a different layer topography compared with AJP as result of a higher volume per area deposition of materials

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“…Like IJP, AJP also shows the coffee-ring effect [31], indicating that similar evaporation processes take place for both printing methods. However, no work has shown successful mitigation of this effect to date for AJP.…”

“…However, no work has shown successful mitigation of this effect to date for AJP. Despite the difference in nozzle sizes between IJP and AJP, both methods achieve decreased feature sizes with a decrease in nozzle diameter [31,36]. AJP demonstrates a splatter effect [31] rather than cleanly defined droplets due to the mist of particles, and this can be detrimental to achieving finer patterns and tighter print spacing.…”

“…A pattern is created by overlapping the droplets so that a continuous line is formed. The characteristics of the print may be altered by changing the overlap percentage or the print direction [31]. The spacing must be less than 65% overlap [32] in order to prevent bulging of the printed line, and the ultimate resolution is a function of the droplet diameter as well as the spreading upon contact with the substrate surface [19,31,33].…”

“…The characteristics of the print may be altered by changing the overlap percentage or the print direction [31]. The spacing must be less than 65% overlap [32] in order to prevent bulging of the printed line, and the ultimate resolution is a function of the droplet diameter as well as the spreading upon contact with the substrate surface [19,31,33]. Currently, the smallest achievable feature sizes of 25-50 μm are comparable to or even better than processes such as screen printing and photolithography [33].…”

“…Dimethylformamide (DMF) when mixed with water as a solvent for Ag NPs has been shown to be effective in reducing the coffee-ring phenomenon [35]. Furthermore, printing lines counter to the nozzle direction have been shown to reduce the coffee-ring effect and create a more uniform lateral profile [31].…”