Aerosol jet printing of two component thick film resistors on LTCC
Aerosol jet printing is a rather new technology for the deposition of thick film structures offering high line and space resolution. This offers a high potential for miniaturization for thick film structures. The advantages of this technology could be shown with inks carrying single solid powder (e.g. silver, platinum, ceramic or glass powder). Challenging is printing of solid powder mixtures due to the differences in the aerodynamic properties of different powders. Those differences result in changes of the mixing ratio within the aerosol jet and therefore poor reproducibility in the final film properties is obtained. In this work, thick film resistors consisting of RuO2 with particle size < 1 mm as the conducting phase and different glass powders with particle size around 1 mm as the isolating phase were investigated. One glass had a density rather close to RuO2, the other glass significantly lower. Inks were made from RuO2/glass powder mixtures, a solvent and organic additives. After manufacturing the inks are printed on LTCC and the microstructures of the dried and the fired films were visualized by FIB preparation and SEM. The resistances as well as the temperature coefficients of the resistors were measured and compared to resistor films with an identical solid composition manufactured by conventional screen printing. The results of the obtained resistors are presented and discussed in terms of powder properties, ink dispersion and printing parameters.