This paper will discuss recent developments in making of passive and active matrix OLED devices on polyethylene napthalate (PEN) which has been improved for the use in display device applications. The improved film properties are meeting many of the desired needs and specifications for display and process applications as they are understood today. Improvements to the film's surface quality, and its inherent properties make PEN a good choice for OLED applications. Processing the plastic substrate through the OLED device making process can contribute to small changes in the substrate dimensions. Photolithography process is a critical part of the OLED device making process, knowing to compensate for substrate size does address technical challenges in overlay registration.