Design Of The Flexible Packaged LED Modules And Reliability Studies

LEDs offer design flexibility, from zero-dimensional lighting (dot-scalelighting) to three-dimensional lighting Flexible packaged LED modules haveadvantages of flexible application, well-adapted and so on, which have a widelyapplication prospect. At the same time, the flexible packaged LED modules facesome issues, for instance, the bad thermal management, poor operationalreliability.In this paper, a high power flexible LED module with polyimide flexiblesubstrate was designed. The heat pipe with aluminum fin was used as the heatsink. The juncton temperature was measured below70℃under the condition ofnatural convection. The PI substrate has better theraml performance comparedwith DBC substrate. The packaged module has lower thermal resistance. Thestrcture of the heat sink,such as radius,distance, number and thickness of the tin,has been discussed by numerical simulation using ANSYS software and aslooptimized the heat emission structure.A low power flexible LED module has been designed with transmittancesilicone gel. Large area curved surface light source could be achieved bymultichip arrays packaging. To research the reliability of the LED module,thermal aging test and thermal/humidity aging test were performed. Thedegradation of YAG phosphor is the main reason of the degradation of opticaloutput in thermal aging test. However, the main failure mechanism is theyellowing of the silicone in thermal humidity aging test. We have analyzedstatistically degradation time of luminous flux by means of Weibull distribution.Peck model was used to establish the life prediction model of the flexible LEDmodules. The general operation situation of the LED modules is45℃/50%RH,we calculates the failure time was13232hours in this work condition.The moisture diffusion process in the silicone was analyzed by the secondFike’s law. The moisture diffusion coefficient and coefficient of moistureexpansion were measured. Moisture diffusion process in the silicone andhygroscopic swell were studied by numerical simulation method. The wet stressmay be caused delamination between silionce and copper substrate in the LEDmodule.