The Reliability Study Of Power LED Driver On And Off Underhigh Temperature And COB Temperature Cycle

LED which is an important invention on the course of human civilization becomes the protection of pursuit of energy conservation and low-carbon environment effective. Because of long life, high efficiency, high environmental protection, reliability and brightness advantages, LED lighting has been widely used in areas such as lighting and display. In the future LED will further instead the traditional way of lighting, and the market is still growing, so the heat of LED lighting problem is concerned about will not be weakened. And the reliability problem can’t be ignored. Aiming street lighting system on the LED driver and COB light, reliability studies were done in this paper. Because LED can’t be used directly, there must be a special driver to power it, in which case the quality of LED driver not only directly affects the use of the entire lighting system, but also brings additional stress lamp beads. COB is a result of the development of high-power and small size, but the heat problem has cropped up, so how to effectively dissipate heat in a timely manner is a challenge. For electrolytic capacitors in the LED drive power failure problems and high reliability of the solder layer of COB, LED driver on and off under high temperature experiments and COB temperature cycling experiments were designed. Basically has the following work:1. LED driver including EMC filter, PFC converter, PWM control and DC/DC converter module, in which the weakest point is the electrolytic capacitors of DC/DC converter modules. Electrolytic capacitors working in the long term will lose the electrolyte, which led to decreased capacity, filtering degradation and failure phenomenon occurs. LED driver power supply has been the lack of uniform standards, which brings the assessment problems to the driver. During the experiment, the important parameters of LED driver were recorded and the conclusion of the changes can be got to assess the overall driver in this paper. After the experiment, removing the key parts of the diver to have assessment important parameters of the electrolytic capacitors and finally analysis the main reasons for degradation which has important significance for future research.2. For COB packaged LED, comparative experiments of different forms and different power were done. The stress of cyclic temperature was applied to the COB sample in accelerate experiments. Different temperature was controlled by different current, and each experiment was conducted about 12000 cycles. A noninvasive approach is used to study the die attach layer of chip-on-board(COB) packaged light-emitting diodes(LEDs) after temperature cycling. Failure analysis of the die attach layer is performed by monitoring the changes in the thermal resistances in differential structure function curves of the COB. The results suggest that delamination occurs at the interface between the chip and die attach and fatigue voids appear in the die attach layer, which is consistent with the findings of X-ray, scanning electron microscopy and C-mode scanning acoustic microscopy analyses. Various temperature cycling experiments are carried out to analysis cycling temperature stress to examine the influences of different junction temperature and power on device failure.