System analysis of a DoD print head for direct writing of conductive circuits

The inkjet-printing principle is becoming more and more important for new applications besides conventional graphic printing. The target at our institute is to print conductive silver lines and areas of different widths and thicknesses. Based on a drop-on-demand (DoD) micro feeding system, a colloidal ink printer was developed to print conductive circuits. The printer has a stationary piezo-driven print head with a nozzle diameter of 100 mu m. With such a nozzle, conductive paths with a width between 110 and 250 mu m can be realized. A waveform generator is used to actuate the print head's piezo actuator. The most common control signal is a nearly rectangular voltage pulse. Shape, duration, and amplitude of the piezo control signal influence the stability of the printing process and thus the quality of the printed electrical structures significantly. Different rise and dwell times or pulse shapes can be considered to optimize the printing process. In this article, the piezo control signal's shape is analyzed, varied and the print head's system behavior is characterized. In a performance and signal analysis, the influence of the piezo input signal's shape on the transient behavior of the piezo output energy signal is identified. An optimized piezo control signal shall be achieved. In conclusion, a method is presented to measure droplet parameters such as radius, speed, and volume.