RF Characterization of the Homogeneity of Sintered Micro- and Nanoparticle Silver Inks for Printed Electronics

A significant problem of printed electronics which is hardly considered in science is the inhomogeneous sintering of printed conductive silver micro- and nanoparticle inks. This so called skinning effect as well as its consequences such as accompanying economically suboptimal processes, reduced conductivity, poor surface quality and possible mechanical reliability problems have not yet been investigated. On the other hand, there is a lack of characterization methods to analyze this effect with sufficient accuracy so that it can be observed at all in order to optimize existing processes, materials and thus end products. In this paper the concept of a novel electrical characterization method is presented. The basis of the method is the skin effect, not to be confuse with the skinning of the ink, which describes the penetration of electromagnetic fields in metals that decreases with frequency, thus enabling a correlation between electrical transmission properties and the conductivity profile of printed and sintered lines. This allows for characterization of the effects from various sintering parameters on printed structures by means of appropriate measurement technology. The expected measurement frequencies are in the three-digit MHz range, depending on the DC conductivity. If additional measurements at higher frequencies are available, the penetration depth is so small that conclusions about surface roughness of the sintered structure can be drawn.