Determination of the Stability of Low Viscous Particle Inks

Abstract

Inkjet printing is a flexible contactless deposition method for a variety of materials and applications in microelectronics. For a reliable printing process the stability of the ink is essential and verification of the stability of a suspension remains a demanding task. After presenting some fundamentals of ink preparation, several methods of determining the stability of inks considering different particles are discussed. In a stable suspension no sedimentation occurs i.e. the solid content remains constant over a long period. The simplest way of evaluating the stability is supposed to be visual inspection however this method yields no measurable information about the stability. Standard photometric methods deliver a measurement signal but the signal does not contain any information about the sedimentation processes. Scanning photometry compensates this deficit and provides furthermore information about the distribution of the solid content over the sample. Therefore a method of determining the solid content of a sample from transmission and backscattering measurement data is introduced. However, these contactless photometric methods work only with certain particles. If photometric methods fail, the evaluation of samples from the suspension is required. With non-contactless methods sample taking has to be performed very carefully and due to small sample amounts weighting of the samples in order to determine the solid content requires very precise measurement systems. For small sample amounts flame absorption spectrometry has been found to be a good method to receive reliable measurement results. In conclusion the application of rheological methods for the determination of stability is discussed.