Improving Compactness of 3D Metallic Microstructures Printed by Laser-Induced Forward Transfer

Abstract

Laser-induced forward transfer (LIFT) has been shown to be a useful technique for the manufacturing of micron-scale metal structures. LIFT is a high-resolution, non-contact digital printing method that can support the fabrication of complex shapes and multi-material structures in a single step under ambient conditions. However, LIFT printed metal structures often suffer from inferior mechanical, electrical, and thermal properties when compared to their bulk metal counterparts, and often are prone to enhanced chemical corrosion. This is due mostly to their non-compact structures, which have voids and inter-droplet delamination. In this paper, a theoretical framework together with experimental results of achievable compactness limits is presented for a variety of metals. It is demonstrated that compactness limits depend on material properties and jetting conditions. It is also shown how a specific choice of materials can yield compact structures, for example, when special alloys are chosen along with a suitable donor construct. The example of printed amorphous ZrPd is detailed. This study contributes to a better understanding of the limits of implementing LIFT for the fabrication of metal structures, and how to possibly overcome some of these limitations.

Direct Writing of High‐Resolution, High‐Quality Pure Metal Patterns on Smooth Transparent Substrates by Laser‐Induced Forward Transfer Followed by a Novel Laser Treatment

“…The microstructure is fairly compact, and grain boundaries can be observed. We expect, in agreement with previous work, [48] that the internal compactness of the structure will result in higher mechanical strength.…”

“…Typically, LIFT-printed structures tend to have lower rigidity (Young's modulus) than the bulk material and be quite brittle. [48,49] Thermal annealing post-treatment may improve the mechanical properties, as it does to the electrical properties. [47] LIFT-printed metals are typically both polycrystalline and porous.…”

“…Moreover, the intrinsic characteristics of the donor play a significant role during the printing stage, and the morphology of the printed line will dominate the formation of the melt pool during post‐treatment. These will affect the density/porosity and the occurrence of voids due to dynamically limited wetting or trapped air, [ 46 ] high disorder at the interface between LIFT‐printed droplets, [ 47 ] surface oxidation around voids due to trapped air, [ 47 ] cracking and lack of melting at droplet interfaces, [ 46,48 ] delamination due to shear stresses that develop during droplet solidification on the metal substrate, [ 48 ] high surface roughness, [ 49 ] etc. Ultimately, understanding the correlations among all of these defects, the solidification mechanisms and the processing conditions are not easy tasks, and much research is being put into that.…”

Printed Cu–Ag Phases Using Laser‐Induced Forward Transfer

“…Yet, to achieve high‐quality printing, in the cap regime (clear and clean droplets), the work window is limited. As mentioned previously in this study, we used the optimal energy for printing [ 12 ] the samples. The wavelength of the laser in the process affects the absorption of the light in the metal.…”

“…In addition, the structure that was printed using cosputtered donor leads to the most compact printed structure with minimum voids and delaminations. In a previous work [ 12 ] the advantage of using a layered donor to obtain compact structures was mentioned. In part, due to the associated high heat of mixing, Cu–Ag is quite unusual as the mixing enthalpy is positive.…”