Shaoxing Xinshan Science Technology Co.,Ltd
Address: Dongfangyimai, No. 2, Pujiang Road, Shaoxing, China
At present, the LED technology is increasingly mature, the lifetime of long-life advantages has always been one of the focus of the masses. But from the point of view, in recent years in LED production and application, we still encounter a lot of "dead lamp" phenomenon. The so-called death light, also called out light, LED light source is not bright. Both production and application of the death of the lamp, are also very headache problem, manufacturers should not only face the product bad losses, also affects the consumer confidence in LED products.
Therefore, study of some common LED die light reason analysis, helps to reduce and prevent the failure phenomenon recurring LED products, ensure product quality and enhance the competitiveness of their products, but also provide a reference for enterprises technical improvement and improve, so as to create greater economic benefits for the enterprise. Summary, common LED die light reason mainly has the following kinds:
1. The welding wire fracture
For "dead lamp", we should first determine the LED is a short circuit or open circuit, if it is open, we usually consider LED lights inside the welding wire is disconnected. LED lights inside welding wire broken, leading to the LED without power supply voltage, this is the LED lamp is one of the common causes of death. Common welding line disconnect position has 5 place, as shown in figure 1 A, B, C, D, E:
A: chip electrode and golden junction;
B: golden with gold thread attaches the ball neck;
C: arc welding lines in scope;
D: support two solder joints with gold thread junction;
E: stents solder joints and junction of coating.
By means of optical microscope and scanning electron microscope (SEM) after the samples section anatomy or sol can check the position of the welding wire fracture, helps to further analysis of the reasons. The following and provide the case for everyone, the position of the welding wire fracture, and the reason of fracture is different.
Failure lamp bead model for 5730. Lamp bead is hot and cold impact test after 100 cycle after the death of the lamp. After cross section analysis, the failure samples and found the failure samples first solder joint and the bursting of silica gel around the solder joint position has a second solder point D is disconnected, as shown in figure 2 ~ is shown in figure 4.
The failure samples section morphology
Because of the silica gel and gold wire thermal expansion coefficient difference is bigger, after 100 cycles after hot and cold impact test, silica gel with gold thread in constant expansion and contraction, and gold wire solder joints bend is the concentration, therefore, the most likely to cause around the solder joint blowout of silica gel, silica gel crack in welding line second solder joint is the weakest point D disconnect, eventually appear dead lamp sample.
2. Solid crystal layer stripping
For some USES vertical chip LED lamp bead, solid crystal layer at the bottom and stent coating strip is a common cause the death of the lamp.
Failure samples for upright type LED lamp bead, in the process of using the dead lamp, defective rate is 1.5%. After inspection section failure samples, we found that the gold thread solder joints are intact, as shown in figure 11 ~ shown in figure 13. But find solid crystal layer and stent coating completely, but also a stripping glass encapsulation adhesive and stent, as shown in figure 14.
ide by the above observations, the cause of lamp bead death lamp is encapsulated interface between glue and stents appear stripping phenomenon, stripping degree and regional extension with intensified use process, causing a further solid crystal glue with stents, eventually cause death within the sample lamp. May also be a bad glue adhesion caused by packaging glue and stents appear on the interface between layers.
3. The solder joint burned
In some cases, lamp bead dead lamp is not necessarily the lamp bead itself, it is possible that the use of the power supply.
Failure is lumen LED lamp bead, the LED lamp bead use after a period of time appear dead lamp. Inspection on multiple failure after the lamp bead sol, failure light bead chip found near 2 P gold wire solder electrode and electrode graphic lines have been burned, 2 N gold wire solder electrode and electrode graph line and four second spot on the stent are intact, burned or fracture has not been found, the following figure 15 and figure 16.
It is obvious that P electrode chip burned is the direct cause of lamp bead death lamp. So, what causes P electrode chip burned? Next, we made the following analysis.
We randomly selected from a few to normal light lamp bead simulated high voltage shock experiment, sample of each lamp bead 20 v instantaneous high voltage applied separately. Experimental results show that the high voltage surge back bead instantly appear dead lamp, sol examination revealed is also on the chip after P electrode lines burned in open die lamp, shown in figure 17 and 18.
Through the inspection and verification of the test, can infer that caused this batch of lamp bead lamp light bead is the root cause of death in the process of using the surge current is too large, because chip resistance value is N P area area is high, when the current concentration by P electrode, P electrode first burned and lead to death open lamp.
Lamp bead in the process of using the surge current (or voltage) is too large, probably with the driving power of lamps and lanterns in the surge current on or off, it is possible that the chip P electrode, the defective cause P electrode welds a momentary contact undesirable situation, cumulative when have more LED series high pressure on the poor contact contact cause instantaneous high current lamp bead welding wire burned and sealant was blackened.
4. The chip from corrosion
Dead lights ahead of the case is open circuit phenomenon, died for everyone to take a short circuit under the lamp case.
Failure sample for copy flow lamp bead, light beads found these lights appear in the process of aging death lamp, as well as the dim light. Sol was carried out on the defective product, check found a chip electrode area appears more corrosion and electrode flake, as shown in figure 21 and 22.
Using X-ray spectrometer (EDS) for chip corrosion area element analysis, to detect a chip electrode corrosion area were found to contain more, Na, Cl and K element is shown in figure 23 and 24.
According to the chemical composition of elements, speculated that the chip may be contamination of NaCl and KCl. When heat and water vapor corrosion chip electrode, chip electrode metal corrosion and electrode lines down, stick relay fall off and even result in local area. And electrode of solute migration can make P, N electrode lead shorting chip death lamp.