Screen-printed polymer-based microfluidic and micromechanical devices based on evaporable compounds
We investigate in this work the fabrication of polymer fluidic and mechanical devices based on evaporable compounds as sacrificial layers using the screen-printing process. The combination of thermosetting polymer resins with evaporable compounds as sacrificial layers allows straightforward fabrication of polymer microfluidic and micromechanical devices. Channel, cavities and spacings are first defined by sacrificial material layers. This is followed by polymer resin deposition and polymerization / solvent removal. Removal of the sacrificial layers is then accomplished by heating at their decomposition / evaporation temperature. This process does not require an ulterior dissolution step, and systems exist where the sacrificial layer molecules escape by diffusion through the polymer at high temperature: we are therefore not limited to open structures. Furthermore, the use of screen- printed thick-film compositions is very advantageous regarding process cost and flexibility. The selected sacrificial layer must be stable at the polymer processing temperature, yet decompose / evaporate cleanly at a temperature low enough to avoid degradation of the polymer. In this work, we used polymers such as ethylcellulose and silicone resins filled with graphite to impart electrical conductivity and improve mechanical stability. The selected sacrificial materials were polyol-based and were formulated to sublime rather than evaporate, in order to preserve the structures. They were formulated as thick-film pastes using a suitable cyclohexanol-based solvent mix.