Precision control of cylindrical stamp contact in a continuous roll-to-roll microcontact printing machine

Abstract

Microcontact printing is a form of soft lithography that uses a molded elastomeric stamp to print patterns with micron and sub-micron scale features. This is an effective low-cost technique for replicating master patterns onto substrates. However, the traditional embodiment of using a planar stamp with a planar substrate is limited in both scale and speed. In order to achieve higher production rates, the lab scale plate-to-plate microcontact printing method must be developed into a roll-based manufacturing process. The marriage of the precision of microcontact printing with the speed of traditional press printing will fill a niche in manufacturing capabilities. Large area, high rate patterning of micron and sub-micron scale features will help to enable the economic manufacturing of a wide range of emerging technologies. Specifically, this continuous microcontact printing process could be used to make flexible displays, thin film photovoltaic cells, transparent conductors, desalination membranes, and other large-scale surface modifications. This thesis details the development of a precision roll-to-roll microcontact printing machine. This pilot-scale web-handling machine serves as the platform for research on the continuous microcontact printing process. Specific consideration is given to the design of a precision print head that is capable of maintaining consistent contact pressure even while printing at high speeds. As well, a novel camera system is developed to achieve in-situ real-time inspection of the contact region between the stamp and the substrate. The visual data from this sensor is used as feedback for the controller, enabling the print head to maintain the desired evenly distributed pressure along the entire stamp width. Results show that the closed-loop control of print contact is able to compensate for eccentricities and disturbances in the system, significantly decreasing variation in print pressure. These tests show promise for the usefulness of this novel process control technique, rather than traditional downstream sensing. As well, this pilot-scale machine succeeds in serving as a platform for continuous roll-to-roll microcontact printing research that will help to guide the scale-up of the process into a high rate manufacturing technique.