Abstract-The sintering of elements performed with the inkjet printing technique is one of the stages of flexible printed circuit manufacturing process. It is a crucial factor to determining the printed paths conductivity playing often an important role in the printed circuit. In this paper the study of the influence of thermal sintering conditions (temperature, time) on the resistance of paths made with inkjet printing on flexible substrates by using two electrically conductive inks was presented. The results of the investigations show that the sintering temperature is the main factor determining the paths resistance. Therefore, in some applications the sintering temperature higher than the one specified by the ink manufacturer can be used to decrease the paths resistance and to improve some circuit parameters. However, it should be noticed that the effective resistance decrease occurs only up to a certain temperature due to the appearance cracks in the printed paths.

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Purpose This paper aims to study the packing density of printed paths on different substrate materials. It presents problems which appear when the necessity of printing one or more narrow paths occurs. Design/methodology/approach A piezoelectric printhead containing nozzles with a diameter of 35 µm was used for printing nanoparticle silver ink on different polymer substrates which were treated by plasma or not treated at all. The shape, defects, resistance and printing parameters for the printed paths were analysed. Findings The obtained results allow the identification of the sources of the technological problems in obtaining a high packing density of the paths in a small area of substrate and the repeatable prints. Research limitations/implications The study could have limited universality because of the chosen research method; printhead, ink, substrate materials and process parameters were arbitrarily selected. The authors encourage the study of other kinds of conductive inks, treatment methods and printing process parameters. Practical implications The study includes practically useful information about widths, shapes, defects and the resistance of the paths printed using different technological parameters. Originality/value The study presents the results of original empirical research on problems of the packing density of inkjet printed paths on a small area of substrate and identifies problems that must be resolved to obtain effective interconnections in the inkjet technology.

Purpose The purpose of this paper is to study the repeatability of path manufacturing in the drop on demand inkjet printing process and the influences of environmental and application factors on path resistance. Design/methodology/approach Paths were printed as multiline paths in packets one-, two- and three-layer paths on polyimide substrates using nanoparticle silver ink. The sintering conditions were determined experimentally. The paths were subjected to climatic and shock exposures and to bending processes. The resistance, profile and width of the paths were measured and analyzed. The temperature distribution for electrically heated paths was measured to identify the defects. Findings This research shows the repeatability of printing processes and identifies the sources that cause diversification in path parameters after the whole technological process. The influence of shock, climatic and mechanical exposures on path electrical properties is indicated. An effective method for identifying defects thermally is shown. Research limitations/implications The research could have limited universality by arbitrarily use of substrate material, ink, printhead, process parameters and kind of sample exposures. Practical implications The research includes practically useful information about the width, thickness, defects and resistances and their changes during a typical application for a path printed with different technological parameters. Originality/value This research presents the results of original empirical research on problems concerning the manufacture of paths with uniform parameters and shows how path parameters will change under exposures that may occur in a typical application. The research combines both production and application aspects.

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