The DL light engineers summed up the reasons for the problems and solutions. First look at the causes of problems caused by led flood lights and street lights
Application companies and the use of units and individuals, may often encounter the case of LED is not lit, this is the phenomenon of dead lights in the industry. The reason is as follows: First, LED leakage current is too large to cause PN junction failure, so that the LED light does not shine, this situation will not affect the work of other LED lights; second, the disconnection of the LED light inside leads to cause death. light. Due to the low operating voltage of the LED lamp, it is generally necessary to use strings and parallel connections to adapt to different operating voltages. As long as one LED lamp is internally disconnected, all the series LED lamps will not be illuminated. There are visible LED dead lights that are the key factors affecting product quality and reliability. How to reduce and eliminate dead lights and improve product quality and reliability are key issues that package companies and application companies need to address. The following are some of the reasons for analyzing dead lights.
1. Electrostatic damage to the LED chip causes the PN junction of the LED chip to fail and the leakage current increases. Static electricity is the devil that causes major harm. Countless electrostatically-damaged electronic components around the world. Tens of millions of dollars in economic losses. Therefore, it is an important task for the electronics industry to prevent electrostatic damage to electronic components. Companies of LED packaging and application must not take it lightly. Any problem in one of the links will cause damage to the LED, leading to degradation or even degradation of the LED performance. The electrostatic discharge (ESD) of the human body can reach around 3,000 volts, which is enough to cause the LED chip to malfunction. It is also important that the grounding resistance of various devices meet the requirements of the LED packaging production line. In general, the grounding resistance is also 4 ohms, and even some highly demanding companies require that the grounding resistance must reach ≤2 ohms.
According to the understanding of the general private enterprises, anti-static measures have not been put in place. This is the test record that most companies can't find the grounding resistance. Even if they do a grounding resistance test, they are once a year, once a few years, or when there are problems. Check the grounding resistance. Everyone knows that the grounding resistance test is a very important task. At least 4 times a year (once a quarterly test), and some places with high demands, a grounding resistance test should be made once a month. The soil resistance varies with the seasons. In spring and summer, the wet ground resistance is relatively easy to reach. In the autumn and winter, the dry soil moisture is less, the grounding resistance may exceed the specified value, and the record is to save the original data. It is well documented in the future. In line with ISO2000 quality control system. Test grounding resistance can be designed on its own table, grounding resistance test packaging companies, LED application companies have to do, as long as the various device names filled in the table, measure the grounding resistance of each device is recorded on the record, the tester can save the signature.
The human body's electrostatic damage to the LED is also very large, work should wear anti-static clothing, equipped with electrostatic ring, electrostatic ring should be well grounded, there is a need to ground the static ring anti-static effect is not good, it is recommended not to use Such products, if the staff violates the operating procedures, should receive corresponding warning education, and also serve as a notice to others. The amount of static electricity in the human body is related to the different fabrics people wear and the physique of each person. In autumn and winter nights, when we undress, we can easily see the discharge between clothes. The voltage of this electrostatic discharge is 3,000 volts.
While the silicon carbide substrate chip has an ESD value of only 1100 volts, the sapphire substrate chip has a lower ESD value of 500-600 volts. A good chip or LED, if we take it by hand (the body does not make any protective measures), the result can be imagined, the chip or LED will be damaged to varying degrees, sometimes a good device passes our hand It's strangely broken. This is the scourge of static electricity. If the packaging company does not strictly follow the grounding procedures, it is the company itself that suffers from losses, which will reduce the qualified rate of the products and reduce the economic benefits of the enterprises. If the equipment and personnel of the same LED application company are grounded poorly, it will also cause damage to the LED. It is inevitable. According to the requirements of the LED standard user manual, the distance between the LED lead and the colloid should be not less than 3-5 mm, and the foot or welding should be carried out. However, most of the application companies have not done so, but only the thickness of a PCB board (≤ 2mm) is soldered directly, which can also cause damage or damage to the LED. Excessive soldering temperature will affect the chip, deteriorate the chip characteristics, reduce the luminous efficiency, and even damage the LED. This phenomenon is not uncommon. Some small businesses use manual welding, use 40 watt ordinary iron, soldering temperature can not be controlled, soldering iron temperature is above 300-400 °C, too high welding temperature will also cause dead lights, LED wire at high temperature expansion coefficient than about 150 °C The coefficient of expansion is several times higher, and the internal gold wire solder joints will open the welding point due to excessive expansion and contraction, resulting in a dead light phenomenon.
2. Analysis of Causes of Dead Lamp Phenomenon Caused by Open Connection of LED Lamp Inside Solder Joint
2.1 The packaging company's production process is not complete, and the inspection method for incoming materials is behind, which is the direct cause of LED dead lamps. LED brackets are generally used to encapsulate LEDs. Brackets are made of copper or iron metal materials and are stamped and formed from precision dies. More expensive, the cost is naturally high, subject to fierce competition in the market, in order to reduce manufacturing costs, the market mostly use cold-rolled low-carbon steel stamped LED brackets, iron bracket row through silver, silver plated two One role is to prevent oxidative rusting. The second is to facilitate welding. Plating quality of the bracket row is very critical. It is related to the life of the LED. The treatment before plating should be performed strictly in accordance with the operating procedures, rust removal, oil removal, and phosphorus. The chemical and other processes should be meticulous, the current should be controlled during plating, the thickness of the silver plating layer should be controlled well, the coating thickness is too high and the cost is too high, and the thickness is too thin to affect the quality. Because the general LED packaging companies do not have the ability to test the plating quality of the stent row, this gives some electroplating companies an opportunity to make the electroplated stent row silver plating thin, reduce costs, the general packaging company IQC on the stent row Due to the lack of inspection tools, there is no instrument for measuring the thickness and the fastness of the stent plating, so it is easier to get through.
Some stents rusted in the warehouse after being discharged for a few months. Not to mention the use, the quality of the plating was poor. The products made with such brackets are certainly not used for a long time. Don't say 30,000-30,000 hours, 10,000 hours are problems. The reason is very simple. There is a period of southerly weather every year. Such weather has high humidity in the air, which can easily cause the embroidering of poorly electroplated metal parts and make the LED components ineffective. Even if the packaged LED is too thin due to the silver plating layer, the adhesion is not strong, and the solder joint and the bracket are detached, causing a dead light phenomenon. This is why the well-used lamp that we have encountered is not bright. In fact, the internal solder joint is separated from the bracket.
2.2 Every process in the packaging process must be handled carefully. Any negligence is the cause of the dead light. In the point and die bonding process, the silver paste (for a single soldering point chip) is more or less Will return to the chip gold pad, causing a short circuit, less chip and sticky. The same is true for double-soldered chip point insulating adhesives, and more insulating adhesives will be returned to the gold pad of the chip, resulting in the occurrence of die-welding during welding and thus causing dead lights. The chip is not sticky enough, so dispensing must be just right, neither more nor less. The welding process is also very important. The pressure, time, temperature, and power of the gold wire ball welding machine must be matched with the four parameters. In addition to the fixed time, the other three parameters are adjustable, the pressure adjustment should be moderate, and the pressure should be high. It is easy to crush the chip, and too small is easy to weld. Welding temperature is generally adjusted to 280 °C as well, the power adjustment refers to the ultrasonic power adjustment, too big, too small are not good, moderate to degree, in short, the adjustment of the parameters of the gold wire ball welding machine, with a good welding Material, with a spring torque tester measuring ≥6 grams, is qualified.
Each year, the parameters of the gold ball welding machine are tested and corrected to ensure that the welding parameters are in the best condition. In addition, the arc of the welding wire is also required. The arc height of the single solder joint chip is 1.5-2 chip thickness, and the arc height of the dual solder joint chip is 2-3 chip thickness. The level of arc can also cause LED quality problems, and the arc height is high. Too low is likely to cause the phenomenon of dead lights during welding. If the arc height is too high, the impact of the current is poor.
3, the method of identifying the dead spot of the broken fuse will not light the LED lighter with a lighter to heat the LED lead to 200-300 °C, remove the lighter, with 3 volt battery button, positive and negative connection LED, if the LED light at this time Lit, but as the lead temperature decreases, the LED light changes from bright to dark, which proves that the LED light is cold. The reason why the heating energy is lighted is to use the principle of metal thermal expansion and contraction. When the LED wire is heated, the expansion elongation is connected with the internal soldering point. At this time, the power supply is turned on, the LED can emit light normally, and the LED wire shrinks as the temperature decreases. Return to the normal temperature state, disconnected with the internal solder joints, LED lights do not shine, and this method is tried and tested. Weld the two pins of the false-welding dead lamp on a metal strip and soak it with concentrated sulfuric acid to dissolve the outer colloid of the LED. After the colloid is completely dissolved, it is taken out. The welding conditions of the solder joints are observed under a magnifying glass or a microscope. It can be found out whether it is a welding or a two-welding problem. It is the wrong setting of the parameters of the gold wire ball welding machine, or other reasons, in order to improve the methods and processes to prevent the occurrence of the phenomenon of the virtual welding.
However, even if it is exhibited at the China Electronics Show, users who use LED products will encounter a phenomenon of dead lights. This is the phenomenon of dead lights after the LED products have been used for a period of time. There are two reasons for dead lights. The welding quality is not good, or there is a problem with the quality of the stent plating. The increase in the LED chip leakage current will also cause the LED lamp to fail to shine. Now many LED products do not add anti-static protection in order to reduce costs, so the phenomenon of electrostatic damage to the chip can easily occur. Thundering on rainy days is prone to high-voltage static electricity on the power supply line, and spikes on the superimposed supply line will cause LED products to suffer varying degrees of damage.
In short, there are many reasons for the dead lights, and they cannot be listed one by one. The phenomenon of dead lights may occur from packaging, application, to use, and how to improve the quality of LED products. It is the packaging companies and application companies who must attach great importance to and seriously study them. The problem, from the selection of chips, brackets, to the entire process of LED packaging, must be performed in accordance with the ISO2000 quality system. Only in this way can the product quality of LED be fully improved and long life and high reliability can be achieved. In the application of circuit design, select varistors and PPTC elements to improve the protection circuit, increase the number of parallel circuits, the use of constant current switching power supply, additional temperature protection are effective measures to improve the reliability of LED products. As long as the packaging and application companies operate in strict accordance with the ISO2000 quality system, they will surely make the LED product quality a new level.
Contact: Mr. Leon Li
Add: Room 709 Unit 5 Build 19, Ruihang Square, Airport Economic Area, Dongli Disctric Tianjin, China