Junction Temperature Study During Degradation Process of High Power Light-Emitting Diodes

High junction temperature accelerates the degradation of the chips and the package materials of high power light emitting diodes (LEDs). In this paper, two experiments were conducted to investigate the fluctuation of junction temperature in the aging process. At the ambient temperature of 65 degrees C, the samples from four different types of LED packages were used to investigate the variation of junction temperature, and four kinds of impact factors were proposed to explain the changes with temperature. It can be found that the annealing effect of materials on the upper interface of the packaged LED was the most important factor for the declined junction temperature in the early accelerated aging process. In addition the thermal mismatch between the epilayer of chip and the substrate of package raised junction temperature in the later aging time.