Product Code: ICAL08_M108

Utilization of 515 nm Pulsed Fiber Laser for Low Temperature Nanoparticle Sintering
Authors:
Jussi Pekkanen, Tampere University of Technology - Department of Electronics; Tampere Finland
Tero Kumpulainen, Tampere University of Technology - Department of Production Engineering; Tampere Finland
Presented at ICALEO 2008

Printed electronics is a promising new technology to produce low-cost electronics. Electronic devices can be printed using nano-scale metal particle inks, which can revolutionize the electronics industry in a near future. Due to a small particle size metallic nanoparticles can be sintered to homogeneous electrically conductive traces at rather feasible temperatures e.g. 220 C. However, evaporating the solvent and sintering the printed structures successfully takes a relatively long time in a convection oven, typically from one to two hours. Thus an exposure to high thermal stresses causes a big reliability risk for a product, especially if a circuit consists of several layers and different materials. Laser sintering has been studied as an alternative to a sintering process for inkjet printed silver nanoparticles to overcome above-mentioned challenges. A drop-on-demand printer was used to print conductive patterns with metallo-organic silver nanoparticles on a flexible polyimide substrate. Sintering studies were made with a 515 nm pulsed fiber laser. Laser processing is a selective method to implement solvent evaporation and sintering. Processing can be programmed to affect only required areas precisely. Thus it will induce only a minimal thermal load to ambient materials. Sintering process was carried out by changing incident laser power, beam translation speed and interaction time. Properties of laser sintered samples were compared to reference samples sintered according to the standard sintering procedure in a convection oven. Sintered samples were examined using an optical and a scanning electron microscope to compare differently sintered structures. Additionally electrical properties of samples were examined after sintering. Results show that laser techniques provide a promising alternative for controlled sintering of printed nano-metal circuits. The variety of materials can be increased due to the better controlled sintering process, which enables manufacturing of more complicated electronic modules. Also a wider range of materials can be used, because thermal stresses induced to materials during the sintering process can be reduced.