28/07/21

Inkjet Printing of Conductive Structures – How Do You Solve Nozzle Clogging?

Inkjet printing is something we know perfectly well from everyday life, because office and home printers are based on this technique. This technology is now being adapted for high-tech applications, because inkjet printers are relatively cheap and allow for rapid prototyping. The problem with inkjet printing is that it’s very fast up to the moment when the process is stopped—by a clogged printing nozzle!

In this short guide, we’ll tell you how to safeguard your printing process against the slowdowns generated by the major problem of clogging printing nozzles. Let’s start with understanding where the problem comes from.

Fundamentals – how does inkjet printing work?

The working principle of inkjet printing is based on the ejection of a fixed volume of ink from the reservoir through nozzles in the printing head. The operation of the printing head is controlled by a computer, and when the electronic control system sends an electric pulse to the head, the released ink takes the form of droplets and falls onto the substrate.

The proper generation of ink droplets creates a fundamental aspect of inkjet technology. In order to provide accurately deposited structures with smooth edges, the ejected droplets should be single and spherical.

If you want to achieve appropriate jetting performance for your use case, you need to control the rheological properties of your ink, as well as printing process parameters.

(we discussed rheological properties in conductive ink design in this article)

Optimizing printing process conditions

To optimize the conditions of your printing process to provide stable and efficient jetting, you need to:

Consider the printhead specification (nozzle diameter, channel length),
Carefully select processing parameters (frequency of the drop ejection, driving voltage, dwell time, repetition rate, and internal pressure).

If these factors aren’t designed and matched well, you might encounter problems in the ink-jetting process:

Clogging of the printhead nozzle,
Non-uniform droplet volume generation,
Formation of ink filaments or satellite droplet formation.

Image of satellite droplet formation created when printing conductive patterns with inkjet printer becomes disturbed

These issues have a detrimental effect on the quality of printed features, because they damage the precision and resolution with which the structures are deposited.

When it comes to nozzle clogging, this is a problem where proper ink design for stable jetting plays a crucial role. It’s especially visible in case of particle-loaded inks that are additionally exposed to the risk of particle aggregation.

Nozzle clogging is a complex phenomenon that might happen due to various reasons:

Size exclusion clogging – when a particle or aggregate size is in the range or even larger than the nozzle diameter.
Fouling – when the ink builds up on the interior surface of the nozzle with time during printing, thus reducing the nozzle diameter over time.
Solvent drying clogging – when the evaporation rate of the ink solvents is too high at the printhead operation temperature.
Hydrodynamic bridging – when the nozzle is blocked with small particles reaching the nozzle exit at the exact same time.
Shear-induced gelation – this may occur in polymer suspensions when bridges between polymer chains are created due to shear forces.

Accordingly, the particle size (and particle size distribution) appears to be another critical parameter that you absolutely must control.

It’s generally known that the size of the printed features depends on the volume of the droplets generated by the head. The larger the ejected droplet volume, the larger the diameter of the structures deposited on the substrate. So, if you need higher printing resolution, finer droplets are better.

On the other hand, to generate smaller droplets you’d need to apply narrower printing nozzles — but decreasing nozzle size carries with it an increase in the viscosity and surface tension of the ink formulation. This may lead to clogs in the printing nozzle.

To avoid particle aggregation, particle size distribution should be uniform, providing great stability of the functional formulation. This highlights the complexity of the optimization of an efficient jetting that yields high-performance patterns.

Chart of particle size distribution - a parameter influencing inkjet printing efficiency

Practical ways to reduce nozzle clogging

One potential way to reduce the risk of nozzle clogging, especially for nozzles with decreased diameter, is to decrease the concentration of the functional component in the ink formulation.

However, this won’t solve the problem completely, because reduced functional material concentration results in lower volume of the active material deposition on the substrate. For electrically conductive structures, this means a limited aspect ratio and diminished electrical conductivity of the printouts. So, it’s highly desirable to maintain concentration of the active material in the ink formulation.

Another way to solve this problem is to use non-clogging inks. Ink processability affects the resolution of the obtained structures. This is of great interest because there’s growing demand for high aspect ratio conductive components of higher resolution (down to a single micron in scale) in the field of microelectronics.

The right conductive inkjet ink for your use case

Conductive inkjet inks for high-resolution printing in electronics applications are characterized by:

uniform particle size distribution,
excellent stability,
non-clogging behavior.

The optimal formulations should deliver high solid content to ensure no compromises on exhibited electrical conductivity. Moreover, making inks compatible with nozzles of small diameter can help overcome the challenging aspect of improving the printing resolution possible with inkjet technology.

All in all, nozzle clogging when printing conductive patterns is a complex issue, but the occurrence of this problem can be reduced. It should be first well understood—so take the advice above as a starting point.

Thank you for reading this article! Here are a few additional resources you can check out:

Check out anti-clogging XTPL Ag Nanoink IJ36 for inkjet printing,
Read about how conductive inks are designed,
Check out technical papers about our nanoprinting technology,
Contact us and tell us about your printing needs.

Written by:

Daria Więcławska, Business Development Specialist at XTPL

References:

Kwon, K. Rahman, T. H. Phung, S. D. Hoath, and S. Jeong, “Review of digital printing technologies for electronic materials,” Flex. Print. Electron., vol. 5, no. 043003, 2020.
Yan, J. Li, L. Pan, and Y. Shi, “Inkjet printing for flexible and wearable electronics,” APL Mater., vol. 8, no. 12, p. 120705, 2020.
Waasdorp, O. Van Den Heuvel, F. Versluis, B. Hajee, and M. K. Ghatkesar, “Accessing individual 75-micron diameter nozzles of a desktop inkjet printer to dispense picoliter droplets on demand,” RSC Adv., vol. 8, no. 27, pp. 14765–14774, 2018.
P. Yin, Y. A. Huang, N. Bin Bu, X. M. Wang, and Y. L. Xiong, “Inkjet printing for flexible electronics: Materials, processes and equipments,” Chinese Sci. Bull., vol. 55, no. 30, pp. 3383–3407, 2010.