PACKAGING TECHNOLOGIES FOR OLED DISPLAYS AND LIGHTING PRODUCTS

摘要

Solid State Lighting (SSL) is an emerging technology in the world of lighting, which has been dominated by traditional incandescent and fluorescent lighting technologies. Light Emitting Diodes (LEDs) are leading the way as robust, efficient, and long-lived solid-state sources of light and are finding increasing acceptance in general lighting applications. Organic LEDs (OLEDs) have provided a superior alternative to LCD display technology and are becoming more popular as the display of choice in high-end mobile products such as smartphones. OLEDs are now following inorganic LEDs into the SSL market, where both technologies are generating great excitement as the next generation of lighting technology. In addition to being highly efficient and having long lifetime, LEDs and OLEDs have other inherent benefits that make them attractive alternatives to traditional lighting. With their solid-state nature, they are more resistant to handling and impact, and can withstand a wider range of operating environments. Also, they do not contain mercury, which is a hazardous material present in all fluorescent (FL) and compact fluorescent (CFL) lamps. Both LEDs and OLEDs are typically operated at low voltages and are thus considered safe electrical devices, and both are easily dimmable. But with all of these commonalities between these SSL technologies, there are a number of important differences. LEDs are intense point sources of light, where a high amount of current is driven through a small area device typically around 1mm~2. With this high current density, usually in the hundreds of milliamperes per square centimeter, comes extreme heating, which must be dissipated properly in order to keep the critical internal junction temperature of the LED package low enough to maintain long term reliability. Thermal management is therefore a key system consideration when designing an LED luminaire, which consists of the LED die assembled into a package, along with optics, drive electronics, and heat sink technology. Unlike their inorganic cousins, OLEDs are flat, large-area, diffuse sources of light and can be operated at a much lower current density. Typical OLED SSL panels are 50-200 cm~2 in area, and can be driven at current densities below 10 mA/cm~2, thereby keeping heating effects to a minimum. As the name implies, OLEDs are constructed of carboncontaining organic layers which are sensitive to oxygen and moisture, and thus have stringent requirements around encapsulating and packaging the device to protect it from the damaging environment. The encapsulation technology used to protect the packaged OLED panel is similar for both display and SSL applications. However, the driving methods, assembly, and interconnect technologies have different requirements for each application, and therefore different solutions have been realized. This paper discusses the latest trends in OLED technology and provides insight into the challenges and opportunities that are encountered as OLEDs are manufactured and assembled into display and SSL products.