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Direct printing methods have been used as manufacturing tools for printed electronics applications due to their cost effectiveness. In this review, the piezo-driven inkjet is discussed in detail since it is a mature technology and suitable for the production printing of printed electronics. In addition, other printing methods are considered for using higher viscosity ink and for producing smaller printed feature size. Various direct printing methods are compared in terms of jet mechanism, printing algorithm, and their applications. In particular high resolution printing methods using high viscosity inks, such as electrohydrodynamic jet, aerosol jet and micro-plotter are reviewed. To understand the recent status of industrial printing applications, display (liquid crystal display and organic light emitting diode) materials and printing issues are discussed. Finally, a brief overview of nano-particle metal based conductive inks is included because these inks have been widely used for printed electronics applications.

This paper describes the design and initial results from the "Cambridge Trimaster," a recently developed high speed filament stretch and break-up device that can be used for viscoelastic fluids with shear viscosities as low as 10 mPa s. Extensional viscosity and filament break-up behavior were studied optically using a high speed camera and extensional viscosity values determined for a series of mono-disperse polystyrene solutions up to a weight concentration of 5 wt % were measured as a function of the polymer loading. The transient stretching and break-up profiles recorded with the apparatus were observed and correlated with drop formation for drop-on-demand inkjet printing fluids. This allowed the filament break-up behavior to be ranked in terms of satellite drop and droplet filament behavior. Correlation with previous work on the jetting of similar low viscosity viscoelastic polymer solutions demonstrated the ability of this apparatus to characterize

This article links measurements of ink jetting performance in drop-on-demand printing with the high-frequency rheological properties of model viscoelastic fluids containing linear polymers with various molecular weights. Jet formation and evolution were studied for solutions of polystyrene in diethyl phthalate. Ligament length, initial jet ejection speeds, and ligament extension and retraction rates were determined by high-resolution imaging with high time resolution. For these fluids, the viscosity measured under low shearrate conditions showed no correlation with their jetting performance. The jetting behavior was, however, well correlated with high frequency rheological properties measured at 5 kHz using a piezoelectric axial vibrator rheometer. This study shows that high frequency rheometry can provide useful predictive data about the jettability of fluids, and differentiate between inks that have similar low shearrate viscosity yet show different jetting behavior. A phenomenological model has been proposed and fitted to the evolution of the average ligament length from emergence, through break-up and into the final state of unmerged drops and associated satellites in order to help discuss the influence of viscoelastic behavior on the fixed speed drop-on-demand jetting and printability of fluids. The values of the parameters of this model obtained from the fitting are shown to have a consistent correlation with the rheological properties of the jetted fluids.

Droplet, printer nozzle, drop on demand and continuous jet.