PROJECT TITLE :
Investigation on Some Parameters Affecting Optical Degradation of LED Packages During High-Temperature Aging
The mechanism of optical degradation for the sunshine emitting diode (LED) packages in the light bars beneath the high-temperature aging condition, one of the accelerated life tests, is studied experimentally and numerically. Some parameters, as well as junction temperature, encapsulant materials, delamination, leadframe surface degradation, and encapsulation, are closely investigated. It's found that the encapsulants (with or while not phosphors) and interface delamination don't have any effect on the optical degradation throughout the high-temperature aging. On the contrary, junction temperature, leadframe surface degradation, and encapsulation play important roles on this degradation. Optical degradation of the LED packages is found to be mainly caused by silver chloride, which is generated on the leadframe surfaces with an exposure of silver finish in lightweight and heating conditions once interface delamination happening throughout the high-temperature aging. The high junction temperature could speed up the generation of silver chloride. Moreover, the blue LED package with an encapsulant (silicone) surprisingly provide a lower lumen maintenance than one without encapsulant throughout the high-temperature aging, as a result of of a lot of light absorption on the darkening leadframe surface by total light reflection from silicone encapsulant. Some vital parameters affecting the thermal reliability of the LED packages are identified and therefore the corresponding optical degradation mechanism has been clarified.
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