Comparation of thermal and hygro effects on the degradation of LED package

Abstract

Humidity test is common to all the packaged integrated circuits, few works have been reported on the study of the humidity effects combined with high temperature on packaged LEDs. Moreover, the packaged LEDs are also subjected to moisture environment in many of their applications. In this work, the high temperature-humidity (95°C-85% RH) aging test is used to evaluate the reliability of the packaged LEDs with respect to their optical output properties. The degradation of two kinds of commercial packaged light-emitting diodes (LEDs) are investigated using high temperature aging combined with fast moisture diffusion method, which is quatitively calculated by simulation. First, the tested LED devises is put in the chamber for 84 hours at 95°C/85%RH, then the temperature is set to 85°C in order to know the effects of moistute loss, and then the LED devises are under stress conditions 65°C/85%RH for 50 hours. At last sample are put in the oven for 25 hours at 105 °C. An optical measurement system consisting of a one-meter diameter integrating sphere and a spectroradiometer is set up to measure the luminous flux of the LEDs. The spectral flux responsivity of the measurement system is calibrated at the start and the end of the measurement of LEDs to achieve high measurement accuracy. During the optical measurement, the LED under test is powered up with a nominal constant current as recommended by the manufacturers of the packaged LEDs. Temperature and moisture has effects on both type of epoxy packaged LED the luminous flux, temperature color but almost no effectsof the color purity, peak wave length and half wave width. Further study are still onging to investigated the relation between aging time and optical degradation and also relation between moisture content and optical degradation.