At present, LED technology is becoming more and more mature, and its longevity advantage has been one of the focuses of the public. However, in recent years, in the LED production and application, we still encountered a lot of "dead lights" phenomenon. The so-called dead light, also known as the light, is that the LED light source is not bright. Whether it is the dead light generated in production or application, it is a headache for manufacturers. It must face the loss caused by product defects and affect consumers' confidence in LED products .
Therefore, research and analysis of some common LED dead lights causes us to reduce and prevent the recurrence of LED product failures, ensure product quality and improve product competitiveness, and also provide reference for enterprise technology improvement and improvement. Enterprises create greater economic benefits.
Since the establishment of the Foshan Center of the Hong Kong University of Science and Technology since 2011, many dead lights have been accumulated. In summary, the main causes of LED dead lights are as follows:
1. Wire bond break
For the "dead light", we should first determine whether the LED is short-circuited or open. If it is open circuit, we will generally consider whether the wire inside the LED lamp is disconnected. The wire inside the LED lamp is disconnected, causing the LED to have no supply voltage, which is one of the common causes of LED dead lights. The common disconnection position of the wire has 5 places, as shown in Figure 1, points A, B, C, D, E:
Wire break position icon â–¼
Point A: the junction of the chip electrode and the gold ball;
Point B: the combination of the golden ball and the gold wire is the neck of the ball;
Point C: the range of the wire arc;
Point D: the joint between the two solder joints and the gold wire;
Point E: the joint between the two solder joints and the bracket plating.
The use of optical microscopy and scanning electron microscopy (SEM) for cross-sectional analysis of the sample or sol can be used to check the location of the wire breakage, which is helpful for further analysis. The following is a case provided by everyone, the location of the wire break and the reasons for the fracture are different.
1.1 Case 1
The failed lamp bead model is 5730. The lamp beads were dead after a 100-cycle thermal shock test. After section analysis of the failed sample, it was found that the silica gel around the first solder joint and the second solder joint of the failed sample burst, and the second solder joint D has been disconnected, as shown in FIG. 2 to FIG.
Failure sample cross-section morphology â–¼
Due to the large difference in thermal expansion coefficient between silica gel and gold wire, after 100 cycles of thermal shock test, the silica gel and gold wire continuously expand and shrink, and the bend of gold wire bond is the stress concentration point, so it is most likely to cause The silica gel around the solder joint bursts, and the cracking of the silica gel causes the weakest point D of the second solder joint of the wire to be broken, and the final sample shows a dead light.
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