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2015
Poster
Titel
Rheological properties of silver filled polymer suspensions and their effects on printing performance
Titel Supplements
Presented at the 10th Annual European Rheology Conference, AERC 2015, April 14-17 2015, Nantes, France
Abstract
Screen printing of pastes is the major structuring approach in the ceramic thick film technology by which narrow conductor, resistor and isolation layers are assembled to highly integrated sensors and microsystems. Thereby a paste is a suspension by a solvent, a polymer and an inorganic filler. Understanding the rheological properties is crucial for setting an optimal high-precision printing. Previous works have shown that the measurements of flow curves1 or the considerations of oscillation analysis2 of thick film pastes correspond to the printing behavior. However, the basic knowledge regarding correlations between therheological data and the paste recipe is still limited. For example different polymer types and their effect on the printing performance have not been studied in detail. To evaluate these parameters two polymers (ethyl cellulose (EC) & polyacrylate (PA)) were investigated, where each having a chain length variation. The polymers were solved in an organic fluid and formulated with silver powder to model thick film pastes (solids content of 40 vol%). Rotational (0.1-1000 rad/s) and capillary viscosimetry (1000-6000 /s) were carried out. A significant difference regarding viscosity and shear thinning can be observed. The PA system is more shear thinning at <100/s than the EC system and shows even a stronger deviation at >1000/s. Using time-dependent rheological experiments, relations between shear stress induced dispersion configurations were examined. The measured rheological curves were fitted with several equations to reflect a relationship between polymer, chain length and filler. Correlations are discussed in terms of polymer chain lengths, shear rate-dependent viscosities and printing resolution.
Author(s)