Field Failure Investigation of Power LEDs caused by Bond Wire Defect

Abstract

LED lighting is an energy-efficient, durable, and eco-friendly solution that has become increasingly important in recent years. Advancements in LED technology have greatly improved the longevity of LED lights and they have become an indispensable part of lighting solutions, making them a popular choice for residential, commercial, and industrial applications. Although LEDs are known to have a long service life, in practice the occurrence of various degradation mechanisms can significantly shorten the lifetime. Factors such as humidity, electrostatic discharge damage and an unstable power supply can accelerate the degradation process. In this study, an LED spotlight that had failed prematurely under real operating conditions was examined to determine the failure mechanism. The structural degradation of the LEDs was qualified and located by ultraviolet illumination with optical microscopy and detailed analysis using scanning electron microscopy. VI characteristics measured for each individual LED revealing the integrity and higher current in the low-forward-bias for damaged LEDs. These damaged LEDs were not detected by electroluminescence spectrum analysis. The investigation showed that two LEDs were not functional and at least one LED driver was defective. One defect LED showed a broken phosphor layer. This LED, as well as the LEDs in the immediate vicinity, showed a white structure on the phosphor layer with strongly reduced or absent photoluminescent properties. The defects detected indicate destruction by a current/voltage spike, assumed to be caused by voltage peaks on the mains side.