The importance of shear thinning, thixotropic and viscoelastic properties of thick film pastes to predict effects on printing performance

Abstract

Highly concentrated ceramic polymer suspensions (thick film pastes) are used in many fields of hybrid technology and micro systems packaging. Thereby, in dependence of the used printing technologies like screen printing or micro-dispensing, different requirements are set on the ceramic suspensions. For example, to reach similar structural resolutions for both technologies the suspensions can differ strongly in their solid content, their organic polymer suspension and, above all, in their viscosity. This results in the fact that it is enormously important for paste development to study the requirements and for successful deposition to adjust them by means of targeted variation of the paste components. These components are for a typical ceramic suspension: a solvent, a polymer and inorganic fillers. Such complex fluids exhibit a broad spectrum of rheological features attributable to the various components and making effective controls over their printing properties a formidably challenging task. However, understanding the rheological properties is crucial for setting an optimal high-precision printing. Previous works have tried to correlate rheological properties of commercial thick film pastes [1,2] to screen printing behavior, but these results didn't allow correlations to the particular components and no specific adjustments for the formulation of suspensions are possible. This study will show how rheological parameters can be adjusted by specific paste composition variations in order to adjust the deposition behavior according to the printing technology. Results of the pastes development, in which the particle type, shape, size, but also the polymer-solvent system were systematically varied, are shown in order to deposit high-resolution structural functional layers. Both shear thinning and thixotropic as well as viscoelastic properties of the paste systems are considered and correlated with their effects on printing performance.