Degradation Mechanisms of Mid-power White-Light LEDs

In this chapter, the optical degradation mechanisms of mid-power white-light LED packages have been studied by using high-temperature operation life test (HTOL), wet-high-temperature operation life (WHTOL) test, and highly accelerated temperature-humidity test (HAST). As a result, it was found that (1) for LED packages aged under HTOL, the major degradation mechanism is different for samples aged at 55 °C and ambient temperature higher than 85 °C, with which lead frame deterioration is the major degradation mechanism at 55 °C, while Ohmic contact deterioration is the major degradation mechanism at 105 °C for the aged LED packages; (2) for LED packages aged under WHTOL, both deterioration of the Ohmic contacts of the blue chip and yellowing of the package encapsulant are considered as the major degradation mechanisms; (3) and for LED packages aged under HAST, the failure mechanism is considered as the result of blue light over-absorption, which generates very high temperature inside the silicone bulk, resulting in serious carbonization.