We report on the degradation mechanisms and dynamics of silicone encapsulated ultraviolet A (UV-A) high-power light-emitting diodes (LEDs), with a peak wavelength of 365nm. The stress tests were carried out for a period of 8665 hours with forward currents between 350mA and 700mA and junction temperatures up to 132°C. Depending on stress condition, a significant decrease in optical power could be observed, being accelerated with higher operating conditions. Devices stressed at a case temperature of 55 °C indicate a decrease in radiant flux between 10-40% varying with measurement current, whereas samples stressed at higher case temperatures exhibit crack formation in the silicone encapsulant accompanied by electromigration shorting the active region. The analyzed current and temperature dependency of the degradation mechanisms allows to propose a degradation model to determine the device lifetime at different operating parameters. Additional stress test data collected at different aging conditions is used to validate the model's lifetime predictions.

We report on the degradation dynamics and mechanisms of the commercially available chip-on-board (COB) high-power light-emitting diode (LED) modules with an electrical power of 175 W. Due to the associated thermal load, the temperature dependence of the aging processes is additionally analyzed within the scope of this work. The aging tests were performed for a period of 6000 h at four different case temperatures between 55 °C and 120 °C. The results of the accelerated stress tests indicate a temperature-Activated aging process, which severely limits the lifetime of the modules. In addition, the following key findings can be reported: 1) a significant decrease in optical power occurs within 6000 h of operation; 2) depending on the stress test condition the accompanying color shifts exceed a limit of $\Delta {u}\,'{v}\,'={0}.{007}$ ; and 3) the limiting degradation mechanism can be attributed to the package of the device and can be accelerated with temperature, current, and chemicals. Reported findings can be manifested by additional optical material inspections, allowing to use the results for optimizations of future module generations.