Flexible OLED screens are made of organic self-emissive materials that emit light when powered, eliminating the need for an additional backlight layer or color filter. Compared to LCD screens, they offer significant advantages such as large size, ultra-thinness, flexibility, transparency, low power consumption, and fast response, making them widely used in smartphones, tablets, and television screens.
However, flexible OLED screens suffer from a short lifespan. This is mainly due to two factors: first, the organic thin film is sensitive to moisture and oxygen, easily aging and deteriorating, leading to decreased brightness and lifespan; second, the cathode uses a low work function metal, which is prone to oxidation, further reducing device lifespan. Therefore, it is essential to package the sensitive material with the highest precision to isolate it from oxygen and moisture, especially given the increasing demand for foldable phones and full-screen displays, which places higher demands on packaging technology.
Both flexible OLED screens and their wiring materials are flexible and bendable. To achieve a full-screen effect, COF or the more advanced COP process is required to fold the wiring and IC chips under the screen, reducing the bezels and achieving a full-screen effect.
The packaging process can be either COF or COP. COF (Chip On Film) packaging technology integrates the IC chip onto a flexible PCB board, bending it under the screen to reduce bezels and increase screen-to-body ratio. Most mid-to-high-end full-screen and notch-screen phones use COF packaging, such as the OPPO R15, vivo X21, and APEX full-screen concept phone.
COP (Chip On Pi) packaging technology is specifically designed for flexible OLED screens. It bends and packages a portion of the screen, integrating the ribbon cable and IC chip under the screen to achieve a near-bezel-less effect. However, phones using this technology are generally expensive, such as the iPhone X, iPhone XS, iPhone XS Max, OPPO Find X, and Samsung's flagship phones of the past two years.
In summary, both COF and COP packaging technologies can be applied to flexible OLED screens. COP packaging can minimize the screen module's footprint on the "chin" (bottom bezel), but from an economic perspective, COP packaging technology is mostly used in high-end smartphones.
