Investigation of Different Sintering Methods on Ink-Jet-Printed Conductive Structures

Abstract

Over the last decades ink-jet-printing has developed in many applications. The di-rect writing of materials such as silver (for conductive circuits) or polymers (for insulation or second layer) is an attractive method to reduce costs and save raw materials. For conductor paths silver inks with nanoparticles are used. To ensure a good dispersion the nanoparticles are mostly covered with organic compounds. To guarantee electrical conductivity the organic compounds have to be removed and the particles have to be sintered to minimize resistivity. This is done by heating up the silver structures. In this article we compare different meth- ods of sintering conductive paths printed using a silver ink with a particle size of ≤ 50 nm. The methods of sintering are the established thermal sintering in an oven, and alternatively laser sintering as well as electrical resistive sintering. Laser sintering is carried out with a semiconductor laser with a wavelength of 408 nm and different feeding speeds so the energy input in the structures can be varied. For electrical resistive sintering a DC-current is injected to the structures whereby they are heated up by the current. During electrical sintering the actual value of the resistance of the hot structures can be observed. Thereby the sintering can be stopped, when a certain value (of the hot structure) is reached. The best parameters for both sintering alternatives are identified. The conductivity and the deviation of the conductivity of the sintered paths are determined and compared with the results achieved for thermal sintering. As a result, it can be stated, that both alternatives pro-vide specific advantages over thermal sintering such as lower deviations of the measured values or significantly lower process times. On the other hand, specific limitations might occur when using laser or electrical sintering. Additionally, the individual amount of energy input for the three respective sintering pro-cesses is calculated and compared with each other to determine the most energy efficient sintering method. Also the process of direct contacting electrical devices with ink-jet-printing is compared with the standard process wire bonding related to the consumption of material and energy.