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14 The PCB Magazine • June 2014 SUBSTRATES: PoLyESTER FILM FoR THE FLExIBLE ELECTRoNICS INDUSTRy continues Physical Form/Manufacturing Route Initially, the potential to prepare displays based on a flexible substrate opened up the pos- sibility of thin, robust, rollable, color displays based on OLED technology, but the technical difficulties in developing a high barrier on a flexible substrate has limited the development of flexible color displays. The prototype rolla- ble and flexible displays sampled to the market have been based on electrophoretic black and white displays, which were superseded by the introduction of the smart phones and tablet based devices. The consumer now expects the sophistication of full color displays, and the public acceptance of the tablet form has mostly negated the desire for a rollable display concept. Despite this and the fact that present day glass- based displays remain largely flat, ruggedness and light weight remain desirable attributes that displays on flexible substrates can offer. In terms of manufacture, the vision of a roll of film at one end and devices emerging at the other end was postulated. Although R2R is used ex- tensively for specific steps in substrate produc- tion including film manufacture, conductive coatings and barrier coatings, device manufac- ture is still largely batch based, partly because this fits best with the semiconductor industry's existing manufacturing tooling equipment. Film in Use Films now find use in a much broader range of application areas than the OLED displays that were originally envisioned (e.g., printed circuit- ry, printed memory, electrophoretic displays, sensors, OLED lighting and flexible PV devices). In addition, flexible film is used extensively in rigid electronic devices (e.g., touchscreen) and in light management films in LCD displays. These evolving trends have influenced flex- ible substrate development throughout the past decade, so this article will take a high-level overview of the substrate evolution for flexible electronics, exploring the issues associated with substrate development and selection. We will then discuss the latest polyester film develop- ments in support of the flexible electronics and PV industry. Figure 1: common substrate films for flexible electronics.