Before the digital age of data processing and storage, PCB designers created and stored the designs on Mylar/BoPET drafting films, which were used in the photo-resistive fabrication process for circuit boards. These films were oftentimes the only copy of the design data for the board. While their primary use was in the manufacturing of PCBs they also doubled as their own storage media. Ultimately these films can disintegrate with time and use, so the design must be imaged and converted to vector formatting in order to be used for future fabrication. The reverse engineering of film sets is roughly the same process as reverse engineering a PCB - each layer is imaged, and Gerber/vector data is created for the different circuit layers.
