It is often encountered that the LED lamp beads do not light up. Packaging companies, application companies, and units and individuals who use them may encounter the dead light phenomenon that people in the industry say. There are only two reasons for this: First, the leakage current of the LED lamp bead is too large, causing the PN junction to fail, so that the LED lamp bead lamp does not light up. This situation generally does not affect the work of other LED lamps; second, The internal connection lead of the LED lamp is disconnected, causing the LED to have no current passing through and producing a dead lamp. This situation will affect the normal operation of other LED lamp beads. 2.2V, blue-green-white LED working voltage 2.8-3.2V is generally connected in series and parallel to adapt to different working voltages, the more LED lights in series, the greater the impact, as long as one of the LED lights has an open circuit. , will cause the whole string of LED lights in the series circuit to not light up, which shows that this situation is much more serious than the first situation. LED dead lights are the key to affecting product quality and reliability. How to reduce and eliminate dead lights and improve Product quality and reliability, key issues that packaging and application companies need to solve. The following is some analysis and discussion of some causes of dead lights.

  1. Static electricity damages the LED chip, causing the PN junction of the LED chip to fail, increasing the leakage current and becoming a resistor. Tens of millions of dollars in economic losses. Therefore, preventing static electricity from damaging electronic components is a very important job in the electronics industry. Enterprises in LED packaging and application must not take it lightly. Any problem in any link will cause damage to the LED, making the performance of the LED worse or even invalid. Knowing the human body (ESD static electricity can reach about 3000 volts, enough to break down the LED chip, LED packaging production line, whether the grounding resistance of various equipment meets the requirements, this is also very important. The general requirement is that the grounding resistance is 4 ohms, some requirements In high places, the grounding resistance should even reach ≤ 2 ohms. These requirements are familiar to people in the electronics industry. The key is whether the actual implementation is in place and whether there is a record.

  It is understood that the general private enterprises do not take anti-static measures in place, which is why most enterprises cannot find the test records of grounding resistance. Check the grounding resistance, but the grounding resistance test is a very important job, at least 4 times a year (test once a quarter) and some places with high requirements, a grounding resistance test should be done once a month. Soil resistance will vary with the change of seasons. There is a lot of rain in spring and summer, and the soil wet grounding resistance is easier to achieve in autumn and winter. Dry soil moisture is less, and the grounding resistance may exceed the specified value. The purpose of recording is to keep the original data and achieve Evidence will be available later. In line with ISO2000 quality control system. You can design a form for testing grounding resistance, and both packaging companies and LED application companies need to do the grounding resistance test. Just fill in the names of various devices in the form, and record the grounding resistance of each device, and the tester can sign it and save it.

  The static electricity of the human body is also very harmful to the LED. When working, you should wear anti-static clothing, equipped with an electrostatic ring, and the electrostatic ring should be well grounded. There is an electrostatic ring that does not need to be grounded. The anti-static effect is not good, it is recommended not to use it. Products, if the staff violates the operating procedures, they should receive corresponding warning education, and also play the role of notifying others. The amount of static electricity in the human body is related to the different fabrics people wear and their physique. I can easily see the discharge between clothes when I take off my clothes in autumn and winter. The voltage of this electrostatic discharge is 3,000 volts.

  The ESD value of silicon carbide substrate chips is only 1100 volts, and the ESD value of sapphire substrate chips is even lower, only 500-600 volts. A good chip or LED, if I take it with my hand, the result can be imagined that the chip or LED will be damaged at different levels, and sometimes a good device is broken inexplicably after passing through my hand. This is the fault of static electricity. . If the packaging company does not strictly follow the grounding regulations, the company that suffers will reduce the product qualification rate and reduce the economic benefit of the company. Similarly, if the equipment and personnel are poorly grounded in LED companies, the LED will be damaged, and rework is inevitable. According to the requirements of the LED specification manual, the LED lead should be no less than 3-5 mm away from the gel, and the legs should be bent or welded, but most application companies have not done this, but only separated by the thickness of a PCB board (≤2 mm) directly soldered, which will also cause damage or damage to the LED, because excessive 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 °C. Excessive soldering temperature will also cause dead lights. The expansion coefficient ratio of LED leads at high temperature is about 150 °C The expansion coefficient is several times higher, and the internal gold wire solder joints will pull the solder joints apart due to excessive thermal expansion and contraction, resulting in a dead lamp phenomenon.