On October 31, 2018, Dutch researchers at the University of Twente developed a new metal 3D printing technology that allows laser devices to print metal structures, including pure gold, drop by drop, with print accuracy reaching a few microns.
Generally, metal structures can be manufactured by photolithographic methods, casting, selective laser sintering or melting. However, these new methods are not yet applicable to 3D printing of metals with feature sizes smaller than about 10 μm, which would be very interesting for electronic devices.
The researchers' new technology, called laser-induced forward transmission (also known as "LIFT"), uses ultra-short laser pulses to melt tiny metals in nano-thick films. This forms droplets of molten metal that can be sprayed to the target location and solidified. Thanks to this technology, UT researchers were able to build a spiral microstructure with copper and gold droplets drop by drop. The two metals have similar melting points, in which case copper acts as a support on which gold can form.
Laser printing technology: By printing copper and gold in sequence, the copper is etched away to produce an independent spiral of pure gold
The volume of metal droplets is only a few liters (one trillionth). Drops are made by irradiating metals with ultra-short pulses of green laser light. This precise droplet generation enables the structure to be carefully constructed, with a height of only a few tens of micrometers, with details less than 10 μm, and minimal surface roughness (about 0.3 to 0.7 micrometers). For researchers, a key question is whether the two metals will mix at their interface: this will affect the quality of the etched product. Researchers wrote in additive manufacturing that there was no sign of mixing between the metals.
Once the structure was completed, the researchers used chemical etching in ferric chloride to completely remove the copper scaffold. By doing so, they left a pure gold independent spiral composite.
The ability to create completely independent and overhanging structures is essential for printing complex 3D devices. The use of LIFT in combination with chemical etching can show the possibility of generating these types of structures on a small scale.
LIFT technology is also a promising technology for other metals and metal combinations. Researchers expect opportunities for materials used in 3D electronic circuits, micromechanical devices, and sensing, such as biomedical applications. Therefore, it is a powerful new production technology on a very small scale: an important step towards "functionalization" of 3D printing.
The study was completed by the Solids, Surface and Systems Mechanics (MS3) and Design, Production and Management (DPM) departments, both of which are part of the Department of Engineering and Technology at the University of Twente. The researchers collaborated with the University of Twente's spin-off company DEMCON.