Different LED device has different failure mechanism. The reliability of the study of high power white LED should be based on other LED device and the achievements of the predecessors as well as the LED characteristics. At present, all the high power white LED device used in commerce adopts WBG GaN material to produce the blue chip, and then use light transformation material, such as fluorescent powder, the yellow light transformed from the blue light and the fluorescent powder, and the white light. Therefore, the development of reliability study should be under the precondition of understanding the white LED chip materials and structure. The reliability of some other LED devices doesn’t adapt the white LED. For example, after the observation and understanding of the aging chip, it is not suitable for white light, because the blue chip in the white light is coated with fluorescent powder. Recently, the reliability analysis of high power white LED can be mainly divided into two parts: the reliability analysis of the blue chip and the fluorescent powder. However, they are not independent, but related to each other.
At present, we often adopt the following methods: the contrast test of packing blue light and white LED ( use the same blue chip).
Creditability forcast based on engineering reliability
High power white LED device has the life service as long as 100 thousand hours. According to the present speed of the development of the semiconductor materials and device, it is still time consuming and energy consuming if though we conduct the accelerated aging test. Based on the reliability prediction mechanism of the engineering reliability, it is a method to realise the quantitative prediction of LED reliability without the long-time test. This kind of method can reduce the LED test time, save the LED life test cost. Through the tube initial performance index test, we can analyze the characteristic value related to the later failure so as achieve the purpose of predicting the device performance. At the same time, according to initial test value, we can use the computer simulation technology to conduct the later simulation, which has very important practical value.
Characteristic curve related to the reliability of high-power LED can be classified into the following parts:
(1) Voltage-current curve
(2) Electricity derivative characteristic curve
(3) Light output characteristic curve
(4) Spectrum characteristic curve
(5) LED thermal characteristic curve