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Electrohydrodynamic Printing: Breaking the Limits of Inkjet

EHD is one of the most exicintg developments in the additive electronics field. It offers several key advantages over traditional inkjet: (1) it can achieve lower resolutions beyond current capabilities of inkjet, (2) can handle a wider range of ink viscosities, and (3) can cover non-flat topographies.

EHD can print drops with <500nm diameters. It can reach 1-10um resolution, which standard inkjet would struggle to achieve. Furthermore, it can handle pastes with viscousities of some 1000 Cp. Given that the principle is based upon particles being pulled out by electrostatic force, whereas being pushed out by mechnical force as is the case with inkjet, the trajectory of the particles can be controlled, enabling one to print on 3D or non-flat topographies. These are all important technological steps forward.

In the second slide, you can see examples of printing lines, droplets, and other patterns, demonstrated by Enjet. In the case of lines, one can see L/S ranging from 2/2um to 80/80um, demonstrating both the versality and also ultrafine line printing capabilities of this technology. In the inset, digital printing over a non-flat surface is shown, demonstraing good step coverage.

A challenge for this technology is that it is slow. Most systems are R&D systems with a single head. However, companies are now developping industrial-scale mult-head printing. The embedded video shows a multi-bozzle array printing of 0.5-1um Ag NP lines by Scrona. This is a fantastic result because it shows a pathway towards industrial scale printing at ultra fine lines, beyond what inkjet achieves.

Final slides show some applications. The application space is in fact broad and expanding. The EHD can be used to digital print micropads for placement of ever shrinking microLEDs (is the die attach a particle free Ag ink??); it can be used to print quantum dots (QDs) onto ever shrinking microLED dies, enabling color conversation; it can be used to repair printed metallizations and wrap-around edge electrodes for microLEDs or repair TFTs post production; it can be used in semiconductor packaging to digital print inteconnects or shielding; etc etc

Join the TechBlick Innovation Festival (24 June- free | online) here to learn more. At this festival, Fraunhofer IAP will present the latest on EHD of QDs for display applications and DoMicro will present its perspectives on EHD printing, perhaps for die-first integration.

0.5- 1um Ag NP lines with multi-head EHD


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