Piezo inkjet printing and microwave sintering of conductive paths on non-planar substrates – selected examples

Printed electronics (PE) has not only established itself as one of the key technologies in electronics, but also for many types of electrically controlled components. Components made of different materials can be functionalized by applying conductive structures using various printing techniques. These structures may serve as conductive tracks to control electronic components or as heating elements. For the final adjustment of the conductivity of the printed structures, a downstream sintering process of the conductive inks is required, which is usually carried out in conventional ovens by heating directly the components. The research objective is to reach the energy input into different semi-finished products by means of irradiation with microwaves. By inducing eddy currents in the conductive structures through an external electromagnetic field, those can be selectively heated and thus sintered. The range of materials which can be functionalized by ink-jet printing can be extended by this approach to temperature-sensitive substrates, which need to be microwave-transparent. These should remain largely unaffected by the microwaves and experience heating at most locally in the immediate vicinity of the conductor paths to be sintered. This concept has two advantages: Substrates with low thermostability can functionalized by means of piezo inkjet printing and subsequent microwave irradiation without significant harming the substrates. Furthermore, there is considerable potential for energy savings, particularly in the case of large substrates with a low conductor density, as the entire component does not have to be heated. The electrical conductivity was chosen as a characteristic value for comparison and determined using the four-point method. For a better comparison, time-resolved measurement series were carried out in the oven.