LED dead lights phenomenon, from packaging companies, downstream finished products to the use of units and individuals and other consumers, may encounter. The reason is nothing more than two kinds of situations: First, the leakage current of the LED is too large to form a PN junction failure, so that the LED light does not light, and that kind of situation generally does not affect the work of other LED lights; second, LED lights The internal connection leads are disconnected, forming a LED without current passing and generating a dead light. That kind of situation will affect the general work of other LED lights. The reason is that the working voltage of the LED lamp is low (red yellow orange LED working voltage 1.8V-2.2 V, blue green white LED working voltage 2.8-3.2V), generally have to use string, parallel to connect, to smooth different working voltage, the more LED lights in series, the greater the impact, only one LED light inside When the line is open, the zero-string LEDs that form the series circuit are not lit, so that the situation is much more severe than the first type. LED dead lights are the key to affecting the quantity and reliability of production. How to reduce and eliminate dead lights and increase the quantity and reliability of production is a key issue that needs to be dealt with by enterprises. Let's do some analysis and discussion on some reasons for forming dead lights.
1. The PN junction formed electrostatic damage to the LED chip, the LED chip failure, puncturing a large leakage current into a resistor
Static electricity is a kind of destructive devil. The world's electronic components damaged by static electricity are countless, resulting in tens of millions of dollars in economic loss. Therefore, it is a major task in the electronics industry to prevent static electricity from damaging electronic components. LED packaging and LED display companies should not be taken lightly. Any problem in one of the links will cause damage to the LED, causing the LED performance to deteriorate and fail. We know that the human body (ESD) static electricity can reach three thousand volts left and right, and the foot can break down the LED chip. In the LED packaging production line, whether the grounding resistance of various types of equipment can meet the requirements is also very important. Generally, the grounding resistance is required. For 4 ohms, the grounding resistance of the case where there is no high requirement is such that it is ≤ 2 ohms.
The damage of the human body static electricity to the LED is also very large. When working, when wearing anti-static clothing, with an electrostatic ring, the electrostatic ring is grounded and inferior, there is no static electricity ring that does not need to be grounded. The anti-static effect is not good, it is recommended not to If you use this type of product, if the staff violates the operating procedures, you will receive a fairly warning education and also use it to inform others. The amount of static electricity in the human body is related to the different fabrics worn by people and the volume of each person. When we undress in autumn and winter, it is very difficult to see the discharge phenomenon between the clothes. The voltage of the electrostatic discharge is no more than three thousand. Volt. The ESD value of the ruthenium carbide substrate chip is only 1100 volts, and the ESD value of the sapphire substrate chip is lower, as long as 500-600 volts. A good chip or LED, if we take it by hand (the body does not do any protective measures), the result can be imagined, the chip or LED will be damaged to varying degrees, a good device from time to time through us The hand is inexplicably broken, and that is the fault caused by static electricity.
If the packaging company does not strictly follow the grounding rules, the company will suffer losses, which will reduce the qualified rate of products and reduce the economic efficiency of the enterprise. If the equipment and personnel are also poorly grounded, the LEDs will be damaged and reworked. It is inevitable again. According to the requirements of the LED standard manual, the LED leads are not less than 3-5 mm from the colloid, and are bent or soldered, but most of the companies have not done that, but only the thickness of a PCB. ≤ 2 mm) Indirect soldering, it will also damage or damage the LED. Because the high soldering temperature will affect the chip, the chip characteristics will be deteriorated, and the luminous efficiency will be reduced, which will damage the LED. This kind of phenomenon is not uncommon. . No 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 form a dead light, LED lead is at high temperature, the expansion coefficient ratio is 150 °C The expansion coefficient of the left and left is several times higher, and the inner gold wire solder joint will open the solder joint due to excessive heat shrinkage and cold, forming a dead light phenomenon.
2. Analysis of the Causes of Dead Lights Formed by Open Connections of LED Lamps
2.1 The packaging company's production process is not complete, the incoming inspection method is backward, which is the indirect cause of the LED dead light.
Generally, the LEDs are sealed and sealed. The racks are made of copper or iron metal materials and precision stamped. Because the copper is expensive, the cost is naturally high, and the market is fiercely affected by factors, in order to reduce the formation of the system. In this case, most of the market adopts cold-rolled low-carbon steel to bring the stamped LED to the frame. The iron racks are silver-plated and silver-plated without two. One is to prevent oxidation and rust, and the other is to facilitate welding. The amount of plating in the rack is very critical. It is related to the life of the LED. The processing before electroplating is strictly carried out according to the operating procedures. The procedures of derusting, degreasing, phosphating and the like are perfunctory, and the plating should be controlled. Good current, the thickness of the silver plating layer should be well controlled, the plating layer is too thick and costly, and the thickness is too thin to affect the quantity. Since the general LED packaging enterprises do not have the ability to check the amount of plating in the rack, it gives some electroplating enterprises no gaps, so that the electroplated racks are thinned by silver plating, reducing the cost income, and the general sealing company IQC There is a lack of inspection methods for the racks, and there is no instrument for detecting the thickness and fastness of the plating plate, so it is difficult to pass through.
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