Early degradation of high power packaged LEDs under humid conditions and its recovery — Myth of reliability rejuvenation |
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Affiliation: | 1. Department of Electronics Engineering, Chang Gung University, Wenhua 1st Rd., Guishan Dist., Taoyuan City 33302, Taiwan, ROC;2. Centre for Reliability Science and Technology, Chang Gung University, Wenhua 1st Road, Guishan Dist, Taoyuan City 33302, Taiwan, ROC;1. Research scholar, Department of Physics, Jawaharlal Nehru Technological University, Kakinada, India;2. Department of Physics, Vasireddy Venkatadri Institute of Technology, Nambur, Andhra Pradesh, India;3. Department of Physics, JNTUH College of Engineering, Kukatpally, Hyderabad, India;1. Institute for Integrated Systems, Technical University of Munich, Munich, Germany;2. Huawei Technologies, European Research Center, Munich, Germany |
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Abstract: | A sharp rise in lumen degradation was observed for packaged high power LEDs during the initial period of operation under high humidity and temperature conditions, and the degradation reaches a peak value, followed by a “recovery” in lumen output, a sign of reliability rejuvenation. The time to reach the peak degradation is shorter with higher relative humidity. Scanning acoustic microscopy (SAM) tomography is employed to study the effect of moisture at different time intervals. With the help of moisture diffusion modeling using ANSYS simulation, the phenomenon is found to be due to the increasing moisture absorption of silicone resulting in subsequent light scattering as light is emitting from the dice. The “recovery” is the result of moisture absorption by die attach material that sucks the moisture from the silicone. Thus the “recovery” of lumen degradation is actually associated with the degradation in the internal structure of the LED package which is not reversible. C-SAM results are in accordance with the simulation and experimental results. The implication of this finding on temperature–humidity test of high power LEDs is described, and the material parameters of silicone to reduce this initial degradation are also presented. |
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