Digital & 3D Additive Manufacturing of Electronics, Sensors, Photovoltaics, Displays, etc

Over the last decades, printed electronics has gained importance as a cost-effective alternative to silicon-based electronics. Capitalizing on the conventional techniques from the graphics industry has allowed printing all the required materials (including metals, polymers, dielectrics, or ceramics) necessary to produce functional components and devices. Among them, direct-write techniques such as inkjet printing are particularly interesting since they allow printing inks on-demand directly from a digital file without the need for expensive pre-fabricated stencils or masks. However, high-viscosity inks, or those containing large particles in suspension, result in clogging of the nozzle output, which limits the range of printable materials. Alternatively, laser-induced forward transfer (LIFT), a more recently developed digital printing technique, has barely any of these constraints.

LIFT is a digital method for printing almost all kinds of inks regardless of their rheology. In LIFT, a thin layer of ink containing the desired functional material is extended on a donor substrate, which is placed facing the receiver substrate at a certain gap. Then, a laser pulse focused on the donor film induces a cavitation bubble that propels the material forward, which results in the material finally being deposited on the receiver substrate. The lack of nozzle in LIFT allows printing inks featuring low and high viscosities (0.001-100 Pa·s) and particles up to several tens of micrometers.

In this presentation, we explore the versatility of LIFT as a printing technique for printed electronics applications. Special attention is devoted to the transfer of conductive pads to be used as interconnects, the fundamental component in electronic devices. In particular, to demonstrate the potential of LIFT, we put into perspective three different cases. First, the LIFT of silver nanowire inks for producing transparent electrodes. Second, the LIFT of high solid content silver screen printing ink to be used as low-resistivity interconnects on regular paper. These two inks are particularly interesting since their rheology makes them unprintable using other digital printing techniques like inkjet. And, third, a striking concept consisting of the LIFT of a silver nanoparticle ink with continuous-wave laser radiation. In each one of these studies, the capabilities of LIFT with printed electronics applications are demonstrated by printing functional components and devices.

Additive printing technology has evolved to realize functional electric pattern on various type of substrates and form factor to create novel electronic device. While there is a broad range of Polymer Thick Film (PTF) inks for additive technologies including ink-jet, micro-dispensing and screen printing, choice of material depends on not just printing method but applications. In this presentation, we will discuss a ink-jet printable conductive ink and micro-dispensable polyimide series inks by introducing their technical features and potential applications.

While the uses of ceramics in electronic devices are multiple, the manufacturing processes are also varied. Whereas conventional and strong processes are still used and need many steps, digital printing processes that emerged can path the way to new 3D complex shapes as well as reducing the number of steps.
Two additive manufacturing processes for substrates fabrication are especially interesting: laser stereolithography (SLA) and robocasting. SLA is a process based on the photopolymerization, by mean of a UV source, lighted on a liquid or paste surface. Usually, the liquid or paste contains a photopolymerizable resin loaded with ceramic particles. Starting from a CAD file, the ceramic pieces are produced layer by layer to obtain the green body of the piece. Starting from a CAD file as well, robocasting method is based on the extrusion of a filament trough a nozzle. The material filament can be obtain from a high viscous paste charged with ceramic fillers or else a thermoplastic filament heated to reach a semi-liquid state. At this stage the material is extruded and deposited into thin layers. Both green parts obtained by SLA and robocasting process need post-printing steps: debinding and sintering.
Once ceramic substrates are produced it is necessary to make them functional. The functionalization means the deposition of metallic traces and lots of processes can be used to do so. The presentation will focus on disruptive technologies like Aerosol Jet Printing (AJP) or micro-dispensing. AJP is a well-known conformal printing method where an aerosol is generated from a low viscous ink. The aerosol is then carried to the nozzle where it is concentrated by mean of an auxiliary gas. The AJP process produces high resolute lines with very low thickness. Micro-dispensing process may then appear to be complementary to AJP. Indeed, this process produces thick lines with higher current carrying capability. Micro-dispensing is a process using positive pressure on the ink that is transferred to a nozzle with a small aperture diameter. While AJP is a non-contact process, micro-dispensing is a different approach where the ink needs to be in permanent contact with substrate to be correctly deposited. Antennas, strain gauge or passive components can therefore be manufactured.
From those different digital technologies, one idea can emerge: their hybridization.