First, the leakage current of the LED is too large, causing the PN junction to fail, so that the LED lamp does not light up. This situation generally does not affect the operation of other LED lamps;
Second, the internal connection lead of the LED lamp 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. The reason is that the LED lamp generally has a low operating voltage. Parallel to connect to adapt to different working voltages, the more LED lights in series, the greater the impact, as long as one of the LED lights is connected internally, the whole series of LED lights of the series circuit will not be bright, which is more obvious than this. The first situation is much more serious.
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 that packaging and application companies need to solve. LED light-emitting diodes are solid-state semiconductor devices that convert electrical energy into visible light, which convert electricity directly into light. The heart of the LED is a semiconductor wafer with one end attached to a holder, one end being the negative pole and the other end connected to the positive pole of the power supply, so that the entire wafer is encapsulated by epoxy. The following is some analysis of some of the causes of the dead lights.
1. Static electricity damages the LED chip, causing the PN junction of the LED chip to fail, and the 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 a very 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 static electricity of the human body can reach about three kilovolts, which can damage the LED chip. In the LED packaging production line, whether the grounding resistance of various types of equipment meets the requirements is also very important. Generally, the grounding resistance is 4 ohms. In the case of high requirements, 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 year, or there is a problem. When inspecting the grounding resistance, it is a very important task to test the grounding resistance test. At least 4 times a year, some places with high requirements should be tested for grounding resistance every 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 and do It will be available in the future. In line with the 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 equipment 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 a static ring that does not need to be grounded. The anti-static 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 physical fitness of each person. It is easy to see the discharge between clothes in the autumn and winter nights. The voltage of this electrostatic discharge is three thousand volts.
The silicon carbide substrate chip has an ESD value of only 1100 volts, and the sapphire substrate chip has a lower ESD value of only 500-600 volts. A good chip or LED, if we take it by hand, the result can be imagined, the chip or LED will be damaged to varying degrees, sometimes a good device is inexplicably broken by our hands, this is The trouble 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 distance of the LED should be no less than 3-5 mm for bending or soldering, but most application companies do not do this, but only the thickness of a PCB is directly Soldering, this 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.
2. Analysis of the cause of dead light caused by the opening of the internal connection of the LED lamp
2.1 The packaging company's production process is not complete, and the incoming inspection method is backward, which is the direct cause of the LED dead light.
Generally, LEDs are packaged in brackets. The brackets are made of copper or iron metal materials and precision stamped. Because copper is expensive, the cost is naturally high. Due to fierce competition in the market, in order to reduce manufacturing costs, most of the market The cold-rolled low-carbon steel is used to stamp the LED brackets. The iron brackets are silver-plated and silver-plated has two functions. One is to prevent oxidation and rust, and the other is to facilitate welding. The plating quality of the brackets is very important. It is related to the life of LED. The treatment before electroplating should be carried out strictly according to the operating procedures. The procedures of derusting, degreasing and phosphating should be meticulous. The current should be controlled during electroplating. The thickness of the silver plating layer should be controlled well. Thick and high cost, too thin to affect quality.
Because the general LED packaging companies do not have the ability to check the plating quality of the bracket row, this gives some electroplating companies the opportunity to make the electroplated bracket silver plating thinner and reduce the cost. The general packaging enterprise IQC is the bracket row. The inspection method is lacking, and there is no instrument for testing (checking and testing) the thickness and fastness of the plating of the stent, so it is easier to get away with it. I have seen some stents rust in the warehouse after a few months, not to mention the use, it can be seen how poor the quality of plating. Products made with such brackets are definitely not used for a long time. Don't say 30,000 hours, 10,000 hours are a problem.
The reason is very simple. There is a period of southerly winds every year. In such a weather, the humidity in the air is large, and it is easy to cause the metal parts of the poorly electroplated to be embroidered and the LED components to fail. Even if the packaged LED is too thin due to the silver plating layer, the adhesion is not strong, and the solder joint is separated from the bracket, causing a dead light phenomenon. This is the well-used lamp that we 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 carefully operated. Any negligence in any link is the cause of the dead light.
In the point and solid crystal process, the silver glue points are much less and less, and more glue will return to the chip gold pad, causing a short circuit, and the chip is less sticky. The same is true for the double-solder chip point insulation glue. When more points are applied, the insulating glue will return to the gold pad of the chip, causing the solder joint to cause a dead light. The point is less and the stick is not sticky, so the dispensing must be just right, neither too much nor too little.
The welding process is also critical. The four parameters of the pressure, time, temperature and power of the gold ball welder should be just right. In addition to the fixed time, the other three parameters are adjustable. The pressure should be adjusted moderately. It is easy to crush the chip, and if it is too small, it is easy to solder. Led lamp bead uses low voltage power supply, the supply voltage is between 2-4V, depending on the product, so it is a safer power supply than the use of high voltage power supply, especially suitable for public places; brightness changes with current Bright, low power LED lamp bead working current is 0-60mA, high power LED working current is above 150mA. The welding temperature is generally adjusted at 280 °C. The adjustment of the power refers to the adjustment of the ultrasonic power. Too large or too small is not good. To moderateness, in short, the adjustment of various parameters of the gold wire ball welder is good. The material is tested by ≥6 g with a spring torque tester.
Every year, the parameters of the gold ball ball welder are tested and corrected to ensure that the welding parameters are in the best condition. In addition, the arc of the bonding wire is also required. The arc height of the single pad chip (also known as the microcircuit) is 1.5-2 chip thickness, and the arc height of the double pad chip is 2-3 chip thickness. The arc height also causes the LED. The quality problem, the arc height is too low, it is easy to cause the dead light phenomenon during welding, and the arc height is too large to resist the current impact difference.
3. Method for identifying dead soldering dead lights
Use the lighter to heat the LED lead to 200-300 °C, remove the lighter, and connect the LED with the positive and negative poles with a 3 volt button battery. If the LED light can be lit at this time, but the lead temperature is lowered. The LED light changes from bright to off, which proves that the LED light is a virtual solder. The reason why the heating can be ignited is to use the principle of thermal expansion and contraction of the metal. When the LED lead is heated, the expansion elongation is connected to the internal solder joint. At this time, the LED is turned on normally, and the LED leads to shrink normally with the temperature drop. Return to the normal temperature state, disconnected from the internal solder joints, the LED light will not light up, this method is tried and tested.
The two soldered dead lights are soldered to a metal strip, soaked with concentrated sulfuric acid, so that the external colloid of the LED is dissolved, the colloid is completely dissolved, and the solder joints are observed under a magnifying glass or a microscope. It is possible to find out whether it is a welding or a second welding problem. It is the parameter setting of the gold ball ball welder, or other reasons, in order to improve the method and process to prevent the phenomenon of the virtual welding from happening again. The terminal voltage of the PN junction of the led lamp bead constitutes a certain barrier. When the forward bias voltage is applied, the barrier decreases, and the majority carriers in the P and N regions diffuse to each other. Since the electron mobility is much larger than the hole mobility, a large amount of electrons diffuse into the P region, which constitutes injection of minority carriers in the P region. These electrons recombine with the holes in the valence band, and the energy obtained during the recombination is released in the form of light energy. This is the principle of PN junction illumination.
Users who use LED products will also encounter the phenomenon of dead lights. This is the phenomenon of dead lights after using LED products for a period of time. There are two reasons for dead lights. Open circuit dead lights are not good quality, or the quality of bracket plating. There is a problem, the LED chip leakage current will also cause the LED light to not light. Nowadays, many LED products do not have antistatic protection in order to reduce the cost, so it is easy to cause damage to the chip by induced static electricity. Thundering in rainy days is prone to high-voltage static electricity on the power supply line, and the spikes on the power supply line will cause LED products to suffer different degrees of damage.
In short, there are many reasons for the death of lights. It is impossible to enumerate them. From the aspects of packaging, application, and use, there may be dead lights. How to improve the quality of LED products is a high priority and serious research for packaging companies and application companies. The problem, from chip, bracket selection, to LED packaging, the entire process must be operated in accordance with the ISO2000 quality system. Only in this way, the quality of LED products can be comprehensively improved, in order to achieve long life and high reliability. In the application circuit design, the selection of varistor and PPTC components to improve the protection circuit, increase the number of parallel circuits, the use of constant current switching power supply, the addition of temperature protection are effective measures to improve the reliability of LED products. As long as the packaging and application enterprises operate in strict accordance with the ISO2000 quality system, the quality of LED products will definitely reach a new level.
Second, the internal connection lead of the LED lamp 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. The reason is that the LED lamp generally has a low operating voltage. Parallel to connect to adapt to different working voltages, the more LED lights in series, the greater the impact, as long as one of the LED lights is connected internally, the whole series of LED lights of the series circuit will not be bright, which is more obvious than this. The first situation is much more serious.
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 that packaging and application companies need to solve. LED light-emitting diodes are solid-state semiconductor devices that convert electrical energy into visible light, which convert electricity directly into light. The heart of the LED is a semiconductor wafer with one end attached to a holder, one end being the negative pole and the other end connected to the positive pole of the power supply, so that the entire wafer is encapsulated by epoxy. The following is some analysis of some of the causes of the dead lights.
1. Static electricity damages the LED chip, causing the PN junction of the LED chip to fail, and the 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 a very 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 static electricity of the human body can reach about three kilovolts, which can damage the LED chip. In the LED packaging production line, whether the grounding resistance of various types of equipment meets the requirements is also very important. Generally, the grounding resistance is 4 ohms. In the case of high requirements, 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 year, or there is a problem. When inspecting the grounding resistance, it is a very important task to test the grounding resistance test. At least 4 times a year, some places with high requirements should be tested for grounding resistance every 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 and do It will be available in the future. In line with the 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 equipment 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 a static ring that does not need to be grounded. The anti-static 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 physical fitness of each person. It is easy to see the discharge between clothes in the autumn and winter nights. The voltage of this electrostatic discharge is three thousand volts.
The silicon carbide substrate chip has an ESD value of only 1100 volts, and the sapphire substrate chip has a lower ESD value of only 500-600 volts. A good chip or LED, if we take it by hand, the result can be imagined, the chip or LED will be damaged to varying degrees, sometimes a good device is inexplicably broken by our hands, this is The trouble 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 distance of the LED should be no less than 3-5 mm for bending or soldering, but most application companies do not do this, but only the thickness of a PCB is directly Soldering, this 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.
2. Analysis of the cause of dead light caused by the opening of the internal connection of the LED lamp
2.1 The packaging company's production process is not complete, and the incoming inspection method is backward, which is the direct cause of the LED dead light.
Generally, LEDs are packaged in brackets. The brackets are made of copper or iron metal materials and precision stamped. Because copper is expensive, the cost is naturally high. Due to fierce competition in the market, in order to reduce manufacturing costs, most of the market The cold-rolled low-carbon steel is used to stamp the LED brackets. The iron brackets are silver-plated and silver-plated has two functions. One is to prevent oxidation and rust, and the other is to facilitate welding. The plating quality of the brackets is very important. It is related to the life of LED. The treatment before electroplating should be carried out strictly according to the operating procedures. The procedures of derusting, degreasing and phosphating should be meticulous. The current should be controlled during electroplating. The thickness of the silver plating layer should be controlled well. Thick and high cost, too thin to affect quality.
Because the general LED packaging companies do not have the ability to check the plating quality of the bracket row, this gives some electroplating companies the opportunity to make the electroplated bracket silver plating thinner and reduce the cost. The general packaging enterprise IQC is the bracket row. The inspection method is lacking, and there is no instrument for testing (checking and testing) the thickness and fastness of the plating of the stent, so it is easier to get away with it. I have seen some stents rust in the warehouse after a few months, not to mention the use, it can be seen how poor the quality of plating. Products made with such brackets are definitely not used for a long time. Don't say 30,000 hours, 10,000 hours are a problem.
The reason is very simple. There is a period of southerly winds every year. In such a weather, the humidity in the air is large, and it is easy to cause the metal parts of the poorly electroplated to be embroidered and the LED components to fail. Even if the packaged LED is too thin due to the silver plating layer, the adhesion is not strong, and the solder joint is separated from the bracket, causing a dead light phenomenon. This is the well-used lamp that we 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 carefully operated. Any negligence in any link is the cause of the dead light.
In the point and solid crystal process, the silver glue points are much less and less, and more glue will return to the chip gold pad, causing a short circuit, and the chip is less sticky. The same is true for the double-solder chip point insulation glue. When more points are applied, the insulating glue will return to the gold pad of the chip, causing the solder joint to cause a dead light. The point is less and the stick is not sticky, so the dispensing must be just right, neither too much nor too little.
The welding process is also critical. The four parameters of the pressure, time, temperature and power of the gold ball welder should be just right. In addition to the fixed time, the other three parameters are adjustable. The pressure should be adjusted moderately. It is easy to crush the chip, and if it is too small, it is easy to solder. Led lamp bead uses low voltage power supply, the supply voltage is between 2-4V, depending on the product, so it is a safer power supply than the use of high voltage power supply, especially suitable for public places; brightness changes with current Bright, low power LED lamp bead working current is 0-60mA, high power LED working current is above 150mA. The welding temperature is generally adjusted at 280 °C. The adjustment of the power refers to the adjustment of the ultrasonic power. Too large or too small is not good. To moderateness, in short, the adjustment of various parameters of the gold wire ball welder is good. The material is tested by ≥6 g with a spring torque tester.
Every year, the parameters of the gold ball ball welder are tested and corrected to ensure that the welding parameters are in the best condition. In addition, the arc of the bonding wire is also required. The arc height of the single pad chip (also known as the microcircuit) is 1.5-2 chip thickness, and the arc height of the double pad chip is 2-3 chip thickness. The arc height also causes the LED. The quality problem, the arc height is too low, it is easy to cause the dead light phenomenon during welding, and the arc height is too large to resist the current impact difference.
3. Method for identifying dead soldering dead lights
Use the lighter to heat the LED lead to 200-300 °C, remove the lighter, and connect the LED with the positive and negative poles with a 3 volt button battery. If the LED light can be lit at this time, but the lead temperature is lowered. The LED light changes from bright to off, which proves that the LED light is a virtual solder. The reason why the heating can be ignited is to use the principle of thermal expansion and contraction of the metal. When the LED lead is heated, the expansion elongation is connected to the internal solder joint. At this time, the LED is turned on normally, and the LED leads to shrink normally with the temperature drop. Return to the normal temperature state, disconnected from the internal solder joints, the LED light will not light up, this method is tried and tested.
The two soldered dead lights are soldered to a metal strip, soaked with concentrated sulfuric acid, so that the external colloid of the LED is dissolved, the colloid is completely dissolved, and the solder joints are observed under a magnifying glass or a microscope. It is possible to find out whether it is a welding or a second welding problem. It is the parameter setting of the gold ball ball welder, or other reasons, in order to improve the method and process to prevent the phenomenon of the virtual welding from happening again. The terminal voltage of the PN junction of the led lamp bead constitutes a certain barrier. When the forward bias voltage is applied, the barrier decreases, and the majority carriers in the P and N regions diffuse to each other. Since the electron mobility is much larger than the hole mobility, a large amount of electrons diffuse into the P region, which constitutes injection of minority carriers in the P region. These electrons recombine with the holes in the valence band, and the energy obtained during the recombination is released in the form of light energy. This is the principle of PN junction illumination.
Users who use LED products will also encounter the phenomenon of dead lights. This is the phenomenon of dead lights after using LED products for a period of time. There are two reasons for dead lights. Open circuit dead lights are not good quality, or the quality of bracket plating. There is a problem, the LED chip leakage current will also cause the LED light to not light. Nowadays, many LED products do not have antistatic protection in order to reduce the cost, so it is easy to cause damage to the chip by induced static electricity. Thundering in rainy days is prone to high-voltage static electricity on the power supply line, and the spikes on the power supply line will cause LED products to suffer different degrees of damage.
In short, there are many reasons for the death of lights. It is impossible to enumerate them. From the aspects of packaging, application, and use, there may be dead lights. How to improve the quality of LED products is a high priority and serious research for packaging companies and application companies. The problem, from chip, bracket selection, to LED packaging, the entire process must be operated in accordance with the ISO2000 quality system. Only in this way, the quality of LED products can be comprehensively improved, in order to achieve long life and high reliability. In the application circuit design, the selection of varistor and PPTC components to improve the protection circuit, increase the number of parallel circuits, the use of constant current switching power supply, the addition of temperature protection are effective measures to improve the reliability of LED products. As long as the packaging and application enterprises operate in strict accordance with the ISO2000 quality system, the quality of LED products will definitely reach a new level.
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