Lift-off processes are very well known in the field of microelectronics: A cleaned substrate is typically spin-coated with photoresist. Subsequently the exposure using a patterned mask and the resist development results in a specific photoresist pattern left on the substrate. After a coating (e.g., PVD) and the dissolution of the remaining resist with the coating on top, a micro-patterned coating remains on the substrate. Feature size dimensions are typically in the range of microns.
Obviously, these process steps are hard to apply when using architectural substrate dimensions in the range of square meters. However, on the other hand, for most large area applications a feature size of about 100µm up to one millimeter is fully sufficient.
For this reason, an efficient masking can be provided by available printing processes. In case of high-volume identical mask patterns screen printing is preferable, while digital printing provides a maximum flexibility of printed patterns. In this large area process the desired uncoated area is just masked by printing, the PVD coating is applied and the printed mask with the coating on top is washed off right after the coating process. By iteratively applying these steps different color coatings can be arranged side by side.
In this contribution the challenges of the different process steps of the large area lift-off procedure are discussed in detail and potential architectural applications are presented ranging from patterned colored BIPV modules to brilliantly reflecting company logos in large glass facades.
