Investigation into the Effects of Pulsed Laser Sintering on Inkjet-Printed Functional Materials for Printed Electronics

Inkjet printing is a technology available since the late 90’s, and has shown widespread adoption in various fields beyond graphics printing, including printed electronics due to the rising availability of functional materials such as metallic nanoparticle-based inks. However, the functional materials require some level of heat treatment, and recently, since the early 2000’s, alternative methods of delivering that particular thermal energy have been explored, including the use of lasers for their ability to deliver localised thermal energy. The thesis describes the novel use of pulsed laser sintering combined with inkjet printing of functional materials of a conductive nature (e.g. metallic nanoparticle-based silver and copper inks), with the aim of forming interconnects after laser irradiation. The printed copper patterns were successfully made conductive at ambient conditions by optimising the laser processing parameters, and also without showing any structural degradation of the substrate. Furthermore, thermo-sensitive substrates such as PET and paper were explored to demonstrate the novelty and feasibility of this alternative manufacturing method. The effects following the laser treatment on the printed patterns and the substrates were investigated, namely the electrical performance and mechanical properties such as the adhesion, morphology, heat affected zone and structural integrity. It was found that the patterns achieved comparable electrical performance up to 38.7 % and 24.9 % bulk conductivity of copper and silver, respectively, on the thermo-sensitive substrates at ambient conditions. The adhesion was evaluated by an improved standardised test method which incorporated a digital perspective to eliminate subjective bias, and the samples were categorised as 3B and above, hence targeting mid-range electronics applications. The outcome of this innovative fabrication method was applied to a scenario where copper sensors in the form of multi-layer inductance coils were applied to carbon fibre actuators to detect strain for structural health monitoring purposes, and compared to commerciallyavailable sensors. The results indicated superior performance of the inkjet-printed coils.