Inkjet Printing of Microcomponents: Theory, Design, Characteristics and Applications

Inkjet printing technology has been invented and used in the form of continuous jets for typewriting and recording over 50 years. However, this kind of printing technique becomes truly popular within twenty years for the public at homes and offices greatly thanks to the consumer products of desktop inkjet printers developed and marketed in the middle of the 1980s. Those leading manufacturing companies including Hewlett-Packard (HP), Canon, and Seiko Epson et al. have been celebrated around the world for the evolution of the modern digital printers since then. Compared to the mechanical typewriters in the past, the new inkjet printers perform the printing by dye or pigment-based ink droplets jetted through micro-electro-mechanical actuators, which feature non-impact and digital-control merits, thereby generating less noise and power consumption. Furthermore, as operating in called drop-on-demand (DOD) mode, their droplets with sub-nanoliter volume form the dot-matrix patterns onto medium surfaces, rendering static images for human sight with resolution from low to more than 1200 dot per inch (dpi). To achieve high quality ink printing on various substrates, dispensing the micro droplets precisely from nozzles to underlying medium propose some technical difficulties concerning fluidic issues such as the variations in droplet volume, flight direction, and deposition morphologies. In terms of microfluidic flow, a stream of micro droplets significantly undergo high speed flying in air, impacting on a solid substrate, forming and drying above a substrate surface. Through the whole process, the issues about transition and stability of flow from liquid channels to individual droplets, and vice versa, will be frequently encountered in theory, which need to be delicately dealt with in advance of various applications. For instance, undesirable satellites from main droplets may be generated due to Rayleigh instability; similarly, it is possible to form irregular bulges within a lengthy liquid channel on a nonpenetrable substrate (e.g., glass substrate) instead of porous paper. Moreover, nonuniform evaporation can be caused in nature for volatile sessile droplets placed on flat surfaces, in which the called coffee-ring effect often seen for diluted fluids (Deegan et al., 1998) should be avoided for the requirements of uniform thickness. Besides the conventional dye and pigment inks, almost the materials in solution involve the complexity of evaporable droplets, when applying to the inkjet printing processes that rely heavily on the full understanding of droplet behaviors on various surfaces from wet to dry stages.