The recent developments in the field of large area, flexible and printed electronics have fueled substantial advancements in Laser Printing and Laser Sintering, which have been attracting interest over the past decade. Resulting applications, ranging from flexible displays and sensors, to biometric devices and healthcare, have already showcased transformational advantages in terms of form factor, weight and durability. In HiperLAM project, Laser-Induced Forward Transfer (LIFT), combined with high speed laser micro-sintering are employed, as digital microfabrication tools for the demonstration of fully functional RFID antennas and fingerprint sensors based on highly viscous Ag and Cu nanoparticle inks. Having previously successfully demonstrated complex structures, this work’s focus is on increasing the process throughput and yield by increasing the laser repetition rate (up to 40 kHz) and scanning speed (up to 2 m/s), without compromising reliability and resolution. In order to gain insight into the effects of the incremented repetition rate on the printing procedure, the latter was monitored in real time via a high-speed camera, able to acquire up to 540.000 fps, coupled to the setup. Examples of resulting structures comprise well-defined interdigitated and spiral micro-electrodes with post-sintering electrical resistivity lower than 5 x bulk Ag and 3 x bulk Cu. The aforementioned results validate the compatibility of laser based processing with the field of flexible RFID tags and OTFT based fingerprint sensors and foster the wider adoption of LIFT and laser micro-sintering technology for laboratory and industrial use.
Laser induced forward transfer (LIFT) is a freeform, additive patterning technique capable of depositing high resolution
metal structures. A laser pulse is used to generate small droplets from the donor material, defined by the spot size and
energy of the pulse. Metallic as well as non-metallic materials can be patterned using this method. Being a contactless,
additive and high resolution patterning technique, this method enables fabrication of multi-layer circuits, enabling bridge
printing, thereby decreasing component spacing. Here we demonstrate copper droplet formation from a thin film donor.
The investigation of the LIFT process is done via shadowgraphy and provides detailed insight on the droplet formation.
Of particular importance is the interplay of the droplet jetting mechanism and the spacing between donor and receiving
substrate on a stable printing process. Parameters such as the influence of laser fluence and donor thickness on the
formation of droplets are discussed. An angle deviation analysis of the copper droplets during flight is carried out to
estimate the pointing accuracy of the transfer. The possibility of understanding the droplet formation, could allow for
stable droplets transferred with large gaps, simplifying the process for patterning continuous high-resolution conductive