We often encounter the situation that the LED power supply does not light up. Packaging companies, application companies, and the units and individuals that use it may all encounter it. This is the dead light phenomenon that people in the industry say. The reason is nothing more than two situations:

First, the excessive leakage current of the LED causes the failure of the PN junction and the LED lamp does not light up. This situation generally does not affect the operation of other LED lamps;

Second, the internal connecting lead of the LED lamp is disconnected, causing no current to pass through the LED and causing a dead lamp. This situation will affect the normal operation of other LED lamps. The reason is that the working voltage of the LED lamp is low (red, yellow and orange LED working voltage). 1.8V-2.2V, blue, green and white LED working voltage 2.8-3.2V), generally must be connected in series and parallel to adapt to different working voltages, the more LED lights in series, the greater the impact, as long as there is one LED If the internal wiring of the lamp is open, the entire string of LED lights in the series circuit will not light up. It can be seen that this situation is much more serious than the first situation.

LED dead lights are the key to product quality and reliability. How to reduce and eliminate dead lights and improve product quality and reliability is a key issue that packaging and application companies need to solve. The following is an analysis and discussion on some of the causes of dead lights.

1. Static electricity damages the LED chip, causes the PN junction of the LED chip to fail, increases the leakage current, and becomes a resistance. Static electricity is a very harmful devil. There are countless electronic components damaged by static electricity all over the world. Economic losses of tens of millions of dollars. Therefore, preventing static electricity from damaging electronic components is a very important task in the electronics industry, and LED packaging and application companies must not take it lightly. Any problem in any link will cause damage to the LED, and cause the performance of the LED to deteriorate or even become invalid. We know that the human body (ESD) static electricity can reach about three kilovolts, which is enough to break down and damage the LED chip. In the LED packaging production line, whether the grounding resistance of various equipment meets the requirements is also very important. Generally, the grounding resistance is required to be 4 Ohm, the grounding resistance of some high-demand occasions even reach ≤ 2 ohms. These requirements are familiar to the people in the electronics industry. The key is whether they are in place and whether there is a record in actual implementation.

According to the author's understanding, the anti-static measures of general private enterprises are not in place. This is the test record of grounding resistance that most enterprises cannot find. Even if the grounding resistance test is done, it is once a year or once every few years, or there may be problems. Check the grounding resistance from time to time. Everyone knows that the grounding resistance test is a very important task, at least 4 times a year (once every quarter). In some places with high requirements, a grounding resistance test must be done every month. The soil resistance varies with the seasons. In spring and summer, there is more rain and the soil wet ground resistance is easier to achieve. In autumn and winter, the dry soil has less moisture, and the ground resistance may exceed the specified value. Recording is to preserve the original data. It will be well documented in the future. Comply with ISO2000 quality management system. You can design a form for testing grounding resistance. Both grounding resistance testing and packaging companies and LED application companies need to fill in the form for various equipment names, record the grounding resistance of each equipment, and file the tester’s signature.

Human body static electricity can also cause great damage to LEDs. Wear anti-static clothing and wear an electrostatic ring. The static ring should be well grounded. There is a kind of static ring that does not need to be grounded. The anti-static effect is not good. It is recommended not to use the strap. For this kind of product, if the staff violates the operating rules, they should receive corresponding warning education, and at the same time play the role of notifying others. The amount of static electricity in the human body is related to the clothes of different fabrics that people wear and each person's physique. It is easy to see the discharge between clothes when we take off clothes at night in autumn and winter. The voltage of this kind of electrostatic discharge is three thousand volts.

While the ESD value of silicon carbide substrate chips is only 1100 volts, the ESD value of sapphire substrate chips is even lower, only 500-600 volts. A good chip or LED, if we take it by hand (without any protective measures on the body), the result can be imagined. The chip or LED will be damaged to varying degrees. Sometimes a good device passes through our hands. It is inexplicably broken, this is the fault of static electricity. If the packaging company does not strictly follow the grounding regulations, it will be the company itself that will suffer, which will cause a decline in the product qualification rate and reduce the economic benefits of the company. If the equipment and personnel are also poorly grounded, the company that uses LEDs will also cause damage to the LED. It is inevitable. According to the requirements of the LED standard user manual, the lead of the LED should be no less than 3-5 mm away from the gel and be bent or soldered. However, most application companies have not done this, but only separated by the thickness of a PCB board (≤ 2mm) is directly soldered, which will also cause damage or damage to the LED, because too high soldering temperature will affect the chip, which will deteriorate the chip characteristics, reduce the luminous efficiency, and even damage the LED. This phenomenon is not uncommon.

Some small companies use manual soldering and use a 40-watt ordinary soldering iron. The soldering temperature cannot be controlled. The soldering iron temperature is above 300-400℃. Excessive soldering temperature can also cause dead lights. The expansion coefficient ratio of LED leads at high temperatures is about 150℃. The expansion coefficient is several times higher, and the internal gold wire solder joints will be pulled apart due to excessive thermal expansion and contraction, resulting in a dead light phenomenon.