Failure analysis on reflector blackening between lead frame electrodes in LEDs under WHTOL test

• We report a new blackening failure mode of commercial LEDs.
• Delamination and corrosive de-flash agent are the root causes of the failure.
• Reflector cup corrosion and Ag migration are the features of the failure.
• The effect of the blackening failure to LED performance is estimated.

Blackening induced lumen decay in a QFN LED after WHTOL reliability test was reported and analyzed in this paper. A new LED blackening failure mechanism was proposed based on solid experimental results. We concluded that the failure process underwent delamination between lead frame and reflector polymer composites followed by chemical penetration, composite corrosion, silver migration, and finally caused blackening failure. Delamination and corrosive de-flash agent were the key factors for the failure mode. Besides, we also estimated the influence of the failure to the optical performance through simulation. Apart from other reported factors, this study highlighted that both composite corrosion and Ag migration could generate serious illumination decrease as well. The outcome of this study is valuable for LED manufacture and quality control in the future.