Inkjet technology is a method for depositing liquid droplets on a substrate. It was originally developed for the publishing industry, but has become a popular method in digital fabrication of electronic and mechanical devices. Although both terms, "inkjet technology" and "inkjet printing", are commonly used interchangeably, inkjet printing usually refers to the publishing industry, used for printing graphical content, while inkjet technology usually refers to the general purpose fabrication via inkjetting.
Video Inkjet technology
Applications
- soldering
- deposition of passive electronic components, which can be used for simple sensing such as gas, strain, humidity, temperature, touch, and more.
- mechanical components and actuators.
Inks must have high conductivity, high oxidation resistance and low sintering temperature.
- optical devices.
Personalized medications
Maps Inkjet technology
Drop formation
Various drop formation technologies exist, and can be classified into two main types: continuous inkjet (CIJ) and drop-on-demand (DOD).
While CIJ has a straightforward drop creation and sophisticated drop trajectory manipulation, DOD has sophisticated drop creation and no trajectory manipulation.
Drop-on-demand (DOD)
In this method, drops of ink are released individually, on demand, by a voltage signal. Released drops fall vertically without any trajectory manipulation. Commercial printheads can have tens to thousands of nozzles.
The two leading technologies for forcing ink out of a nozzle on demand are thermal DOD and piezoelectric DOD. Additional technologies include electrospray, acoustic discharge, electrostatic membrane and thermal bimorph.
Piezoelectric DOD
Piezoelectric DOD was invented in the 1970s. One disadvantage of the piezo-DOD method is that jettable inks must have viscosity and surface tension within a relatively strict range.
Thermal inkjet (TIJ) DOD
Thermal DOD was introduced in the 1980s by Canon and Hewlett-Packard.
One disadvantage of this method is that the variety of inks compatible with TIJ is essentially limited, because this method is compatible with inks that have high vapour pressure, low boiling point and high kogation stability. Water being such a solvent, limited the popularity of this method for non-industrial photo printing only, where water-based inks are used.
Continuous inkjet (CIJ)
In this method, a column of ink is released continuously from the nozzle. The ink column spontaneously breaks into separate drops due to the Plateau-Rayleigh flow instability. The formed ink drops are either deflected by an electric field towards the desired location on the substrate, or collected for reuse. CIJ printheads can be either have a single jet (nozzle) or multiple jets (nozzles).
One disadvantage of the CIJ method is the need for solvent monitoring. Since only a small fraction of the ink is being used for actual printing, solvent must be continually added to the recycled ink to compensate the evaporation that takes place during flight of the recycled drops.
Another disadvantage is the need for ink additives. Since this method is based on electrostatic deflection, ink additives, such as potassium thiocyanate, may deteriorate the performance of the printed devices.
The printhead
The printhead must have heating capability to print metallic alloys such as lead, tin, indium, zinc and aluminium. The process of printing of low-melting point metals is called "direct melt printing".
Photo inkjet printhead
Tandem printheads
Multiple printheads
Fabrication approaches
The printed material is sometimes only one step in the process, which may include deposition of a precursor followed by a catalyst, sintering, photonic curing, electroless plating etc., to give the final result.
- Direct deposition
- Mask printing
- Etching
- Inverse printing
- Powder bed
Additive inkjet fabrication
Subtractive inkjet fabrication
Inkjettable materials
The ink must be liquid, but may also contain small solids if they do not cause clogging. The solid particles should be smaller than 1/10 of the nozzle diameter to avoid clogging.
Drop formation is governed by two physical properties: surface tension and viscosity. The surface tension forms ejected drops into spheres, in accordance with Plateau-Rayleigh instability. The viscosity can be optimized at jet time by using an appropriate printhead temperature.
Generally, lower viscosity allows better droplet formation and in practice only liquids with viscosities of 2-50 mPa s can be printed. More precisely, liquids whose Ohnesorge number is larger than 0.1 and smaller than 1 are jettable.
- Metals:
- Indium, tin, lead, zinc.
- Gold, silver and copper can be printed if made into nanoparticle inks, which have lower sintering temperatures than in bulk, and can therefore be used with a larger range of temperature sensitive substrates.
- Printing ascorbic acid followed by silver nitrate can be used for conductive traces.
- Ceramics:
- Lead zirconate titanate (PZT)
- Barium strontium titanate
- Cerium oxide
- Alumina (Al2O3)
- Silicon nitrate (Si3N4)
- Titania (TiO2)
- Polymers:
- PEDOT
- PSS
- PEDOT:PSS
- Biological materials (living cells, ...)
References
Further reading
- Hutchings, Ian M.; Martin, Graham D., eds. (December 2012). Inkjet Technology for Digital Fabrication. Cambridge: Wiley. ISBN 978-0-470-68198-5.
- de Gennes, Pierre-Gilles; Brochard-Wyart, Françoise; Quéré, David (2004). Capillarity and Wetting Phenomena. Springer New York. doi:10.1007/978-0-387-21656-0. ISBN 978-1-4419-1833-8.
Source of article : Wikipedia
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