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12 The PCB Magazine • June 2014 Introduction Polyester film substrates have been widely used in making membrane touch switches and other flexible and printed electronic devices for more than 30 years. However, the early 2000s brought about an explosion of interest in ad- ditive printed electronics to replace subtractive etched circuitry in terms of materials develop- ment and device technologies aimed at defin- ing new business opportunities. The opportu- nity to exploit flexible substrates in roll-to-roll production has gained the interest of the plastic films and associated film processing and coat- ing industries. This next generation of flexible electronics technologies has required materials suppliers to deliver improved functionalities to the device developers in fields as wide as elec- trophoretic displays, backplanes, barrier films, photovoltaics, sensors, and more. The terms flexible and printed electronics can be defined in many ways, but these defini- tions will not be debated here. It is commonly understood that commercial polyester film sub- strate technology provides a key cost-effective building block for devices requiring deposition of functional materials. However it is less com- monly known that there are many varieties of polyester film, and that the polymers and film coatings can be tailored to meet the end user's evolving film requirements. It is now possible to compare and contrast the vision of what the early thoughts on mate- rial requirements were and how the technology might be exploited, with what has emerged. by Scott gordon, William MacDonald, Robert Rustin, Duncan Mackerron, John Flett, Valentijn von Morgen, Robert Eveson and Karl Rakos duPont teijin Films Substrates: Polyester Film for the Flexible Electronics Industry F e a t u r e