Qualification of NIR, UV and Laser Irradiation as Alternative Photonic Sintering Methods for Printed Electronics

Printed Electronics creates new areas of applications with a new manner of manufacturing electronics. Due to its technical and 3D design freedom, new markets and innovative products arise that were initially unthinkable. However, the focus of research is currently on mastering and improving the printing process. The subsequent process step of drying and densifying the printed structures to achieve high conductivities in the shortest possible time is up to now hardly considered. This paper treats the inquiry of fitted and optimized parameters of alternative promising photonic sintering methods for printed electronics compared to the much more time-intensive state of the art sintering process in a furnace. These photonic sintering methods comprise the near infrared, ultraviolet light as well as laser irradiation of the printed structures. Photonic sintering promises faster and more efficient curing and sintering due to the direct and selective application of energy to the printing structures without damaging the temperature-sensitive substrates. As substrate materials ABS and PC-ABS, as well as a glass material were used. Both polymer materials are standard and technical thermoplastics which are available at the market in huge quantities at low price. For the manufacture of printed circuits, a dispense printer was used, in order to process a low-cost silver-based micro particle paste. The evaluation of the sintering result was carried out based on the electrical conductivity of the printed conductor path and the adhesion strength on the substrate. In addition, the sintering time required for the curing of the structures as well as impacts on the substrate or the printed tracks due to photonic treatment were taken into account. To perform the experiments, two different print layouts were set up in order to be able to assess the electrical properties on the first layout and the adhesion on the second layout. To obtain a detailed statement on the exploration on the photonic sintering methods, a fully factorial design plan was conducted. For the near-infrared irradiation, the important parameters were the irradiation duration and the irradiation power. While sintered by ultraviolet light, the parameters were irradiation time, as well as the distance between the sample surface and the UV emitter. In the treatment by means of laser radiation, laser power and the motion speed were identified as the relevant parameters. In order to be able to draw a comparison to the mainly used sintering method, samples were also sintered in a furnace. The results show a significant reduction of the sintering time to a few seconds with comparable and even significantly better electrical and mechanical properties.