Analysis of the Causes of LED Dead Lights

We often encounter LEDs that don't shine. Package companies, application companies, and the units and individuals that use them are likely to come across. This is the phenomenon of dead lights in the industry. The reason is nothing more than two cases: First, the LED leakage current is too large, causing the PN junction to fail, so that the LED light does not light up, this situation generally does not affect the work of other LED lights; Second, LED lights The internal connection lead is disconnected, causing no current to pass through the LED and generating a dead light. This situation will affect the normal operation of other LED lamps, because the LED lamp has a low operating voltage (red, yellow and orange LED operating voltage is 1.8V-2.2V). , blue green white LED working voltage 2.8-3.2V), generally have to use string, parallel to connect, to adapt to different working voltage, the more LED lights in series, the greater the impact, as long as there is an LED light inside the open circuit This will cause the entire string of LEDs in the series circuit to be off, which is much more serious than the first case. LED dead lights are the key to affect product quality and reliability. How to reduce and eliminate dead lights and improve product quality and reliability is a key issue for packaging and application companies. Here are some analysis and some reasons for the cause of the dead lights.

1. damage caused by static electricity to the LED chip, the LED chip PN junction failure, leakage current increases to become a resistor

Static electricity is a very harmful devil. The world's electronic components damaged by static electricity are countless, resulting in tens of millions of dollars in economic losses. Therefore, it is an important task in the electronics industry to prevent static electricity from damaging electronic components. LED packaging and application companies should not be taken lightly. Any problem in one link will cause damage to the LED, making the LED performance deteriorate or even fail. We know that the human body (ESD) static electricity can reach about three kilovolts, which can damage the LED chip. In the LED packaging production line, the grounding resistance of all kinds of equipment meets the requirements. This is also very important. Generally, the grounding resistance is 4 Ohm, in some cases where the requirements are high, the grounding resistance should even reach ≤ 2 ohms. These requirements are familiar to people in the electronics industry. Whether the key is in place during actual execution and whether there is a record. According to the author's understanding of the general private enterprise, the anti-static measures are not in place. This is the test record that most enterprises can't find the grounding resistance. Even if the grounding resistance test is done once a year, or once a few years, or there is a problem. When checking the grounding resistance, it is a very important task to test the grounding resistance test. At least 4 times a year (tested every quarter), some places with high requirements should be grounded once a month. The soil resistance will vary with the seasons. There are many rains in spring and summer, and the soil wet grounding resistance is easy to reach. In autumn and winter, the soil moisture is less, and the grounding resistance may exceed the specified value. The record is to preserve the original data. It will be well documented in the future. Comply with ISO2000 quality management system. The test grounding resistance can be designed by itself. The grounding resistance test packaging enterprise and the LED application enterprise must do it. Just fill in the various device names in the table and measure the grounding resistance of each device. The tester's signature can be archived.

The human body static electricity is also very harmful to the LED. It should be worn with anti-static clothing when working. It should be equipped with an electrostatic ring. The electrostatic ring should be well grounded. There is an antistatic effect that does not need to be grounded. The antistatic effect is not good. It is recommended not to use the belt. This kind of product, if the staff violates the operating procedures, should receive corresponding warning education, and also play a role in notifying others. The amount of static electricity in the human body is related to the different fabrics worn by people and the physique of each person. It is easy to see the discharge between clothes in autumn and winter nights. The voltage of this electrostatic discharge is three thousand volts. . The ECD value of the silicon carbide substrate chip is only 1100 volts, and the ESD value of the sapphire substrate chip is lower, only 500-600 volts. A good chip or LED, if we take it by hand (the body does not take any protective measures), the result can be imagined, the chip or LED will be damaged to varying degrees, sometimes a good device passes our hands It is inexplicably broken, this is the fault of static electricity.

If the packaging company does not strictly follow the grounding procedures, the company will suffer losses, which will result in a decline in the product qualification rate and reduce the economic benefits of the enterprise. If the equipment and personnel are also poorly grounded, the LED will be damaged. It is inevitable. According to the requirements of the LED standard manual, the lead wire of the LED should be no less than 3-5 mm, and be bent or soldered, but most application companies do not do this, but only the thickness of a PCB board (≤ 2 mm) 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 enterprises use manual soldering, using 40 watt ordinary soldering iron, the soldering temperature can not be controlled, the soldering iron temperature is above 300-400 °C, too high soldering temperature will also cause dead light, LED lead expansion coefficient at high temperature is about 150 °C The expansion coefficient is several times higher, and the internal gold wire solder joint will open the solder joint due to excessive thermal expansion and contraction, resulting in a dead light phenomenon.

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