Rapid Degradation of Mid-Power White-Light LEDs in Saturated Moisture Conditions

Serious silicone carbonization has been reported in mid-power white-light LEDs during highly accelerated temperature and humidity stress test, although the junction temperature of the LED chip is much lower than the critical temperature of silicone carbonization (300 degrees C). This paper presents a comprehensive investigation, through which the effects of Joule heating and phosphor self-heating have been eliminated as main failure mechanisms. As a result, the over-absorption of blue lights by silicone bulk is considered as the root cause for silicone carbonization. This is mainly due to the scattering effect of water particles inside the silicone materials, which can increase the silicone temperature significantly. Furthermore, finite-element thermal simulation has also been performed, confirming the validity of the failure mechanism.