2024-01-20
Science LED lamp bead damage possible cause
Science LED lamp bead damage possible cause
Causes of LED dead lights
The causes of LED dead lights are nothing more than two situations: first, LED leakage current caused by large PN junction failure, so that the LED light is not bright, this situation generally does not affect the work of other LED lights;
Second, the internal connection lead of the LED lamp is disconnected, resulting in no current passing through the LED and a dead lamp, which will affect the normal operation of other LED lights, because the LED lamp working voltage is low (red yellow orange LED working voltage 1.8V-2.2V, blue green white LED working voltage 2.8-3.2V). Generally, it is necessary to use string and parallel connection to adapt to different working voltages, the more LED lights in series, the greater the impact, as long as there is an open internal connection of the LED light, the whole series of LED lights in the series circuit will not be bright, which is more serious than the first case.
Second, the internal connection lead of the LED lamp is disconnected, resulting in no current passing through the LED and a dead lamp, which will affect the normal operation of other LED lights, because the LED lamp working voltage is low (red yellow orange LED working voltage 1.8V-2.2V, blue green white LED working voltage 2.8-3.2V). Generally, it is necessary to use string and parallel connection to adapt to different working voltages, the more LED lights in series, the greater the impact, as long as there is an open internal connection of the LED light, the whole series of LED lights in the series circuit will not be bright, which is more serious than the first case.
Analyze and discuss the causes of LED dead lights
LED dead light is the key to affect product quality and reliability, how to reduce and eliminate dead light, improve product quality and reliability, is the key issue that packaging and application enterprises need to solve. The following is some analysis of the causes of dead lights.
1, electrostatic damage to the LED chip
Static electricity causes damage to the LED chip, makes the PN junction of the LED chip fail, the leakage current increases, and becomes a resistance Static electricity is a devil of great harm, and the world is countless electronic components damaged by static electricity, causing tens of millions of dollars in economic losses. Therefore, to prevent electrostatic damage to electronic components, is a very important work in the electronics industry, LED packaging, application enterprises must not be taken lightly. Any problem in any link will cause damage to the LED, so that the LED performance deteriorates or even fails. We know that the human body (ESD) static electricity can reach about three thousand volts, enough to breakdown and damage the LED chip, in the LED packaging production line, the grounding resistance of all kinds of equipment is in line with the requirements, which is also very important, the general requirements of the grounding resistance of 4 ohms, some high requirements of the grounding resistance even to reach ≤2 ohms. These requirements are familiar to people in the electronics industry, and the key is whether they are in place and documented when they are actually implemented.
It is understood that the general private enterprises, anti-static measures are not in place, which is that most companies can not find the grounding resistance test record, even if the grounding resistance test is once a year, or several years, or when there is a problem to check the grounding resistance, but do not know that the grounding resistance test is a very important work, at least 4 times a year (quarterly test), Some places with high requirements must be tested once a month for ground resistance. Soil resistance will vary with the change of seasons, spring and summer rain, soil wet ground resistance is easier to achieve, autumn and winter dry soil moisture is less, grounding resistance may exceed the specified value, record is to preserve the original data, so that the future can be checked. Comply with ISO2000 quality control system. Test ground resistance can design their own form, ground resistance test packaging enterprises, LED application enterprises are to do, as long as the name of the various equipment filled in the form, the grounding resistance of the equipment is measured and recorded, the test person can sign the disk.
The damage of human static electricity to LED is also very great, work should wear anti-static clothing, with electrostatic ring, electrostatic ring should be grounded well, there is a need to ground electrostatic ring anti-static effect is not good, it is recommended not to use this product, if the staff violate the operating procedures, you should accept the corresponding warning education, but also play a role in notifying others. The amount of static electricity in the human body is related to the different fabrics people wear, and the physique of each person, and it is easy to see the discharge phenomenon between clothes on the night of autumn and winter, and the voltage of this electrostatic discharge is three thousand volts.
The ESD value of the silicon carbide substrate chip is only 1100 volts, and the ESD value of the sapphire substrate chip is even lower, only 500-600 volts. A good chip or LED, if we use the hand to take (the body does not do any protective measures), the result can be imagined, the chip or LED will be damaged to different degrees, sometimes a good device through our hands inexplicably bad, this is the trouble caused by static electricity. Packaging enterprises if not strictly in accordance with the grounding regulations, the loss is the enterprise itself, will cause the product pass rate to decline, reduce the economic benefits of the enterprise, the same application of LED if the equipment and personnel grounding will also cause LED damage, rework is inevitable. According to the requirements of the LED standard user manual, the lead distance of the LED colloid should be no less than 3-5 mm, for bending feet or welding, but most application companies do not do this, but only separated by the thickness of a PCB board (≤2 mm) directly welded, which will also cause damage or damage to the LED, because too high welding temperature will have an impact on the chip. Will make the chip characteristics bad, reduce the luminous efficiency, and even damage the LED, this phenomenon is not uncommon. Some small businesses use manual welding, the use of 40 watts of ordinary soldering iron, welding temperature can not be controlled, soldering iron temperature above 300-400 ° C, too high welding temperature will also cause dead lights, LED lead at high temperature expansion coefficient is several times higher than the expansion coefficient of about 150 ° C, the internal gold wire solder will be due to excessive thermal expansion and contraction of the welding point will be pulled apart, Cause dead lamp phenomenon.
It is understood that the general private enterprises, anti-static measures are not in place, which is that most companies can not find the grounding resistance test record, even if the grounding resistance test is once a year, or several years, or when there is a problem to check the grounding resistance, but do not know that the grounding resistance test is a very important work, at least 4 times a year (quarterly test), Some places with high requirements must be tested once a month for ground resistance. Soil resistance will vary with the change of seasons, spring and summer rain, soil wet ground resistance is easier to achieve, autumn and winter dry soil moisture is less, grounding resistance may exceed the specified value, record is to preserve the original data, so that the future can be checked. Comply with ISO2000 quality control system. Test ground resistance can design their own form, ground resistance test packaging enterprises, LED application enterprises are to do, as long as the name of the various equipment filled in the form, the grounding resistance of the equipment is measured and recorded, the test person can sign the disk.
The damage of human static electricity to LED is also very great, work should wear anti-static clothing, with electrostatic ring, electrostatic ring should be grounded well, there is a need to ground electrostatic ring anti-static effect is not good, it is recommended not to use this product, if the staff violate the operating procedures, you should accept the corresponding warning education, but also play a role in notifying others. The amount of static electricity in the human body is related to the different fabrics people wear, and the physique of each person, and it is easy to see the discharge phenomenon between clothes on the night of autumn and winter, and the voltage of this electrostatic discharge is three thousand volts.
The ESD value of the silicon carbide substrate chip is only 1100 volts, and the ESD value of the sapphire substrate chip is even lower, only 500-600 volts. A good chip or LED, if we use the hand to take (the body does not do any protective measures), the result can be imagined, the chip or LED will be damaged to different degrees, sometimes a good device through our hands inexplicably bad, this is the trouble caused by static electricity. Packaging enterprises if not strictly in accordance with the grounding regulations, the loss is the enterprise itself, will cause the product pass rate to decline, reduce the economic benefits of the enterprise, the same application of LED if the equipment and personnel grounding will also cause LED damage, rework is inevitable. According to the requirements of the LED standard user manual, the lead distance of the LED colloid should be no less than 3-5 mm, for bending feet or welding, but most application companies do not do this, but only separated by the thickness of a PCB board (≤2 mm) directly welded, which will also cause damage or damage to the LED, because too high welding temperature will have an impact on the chip. Will make the chip characteristics bad, reduce the luminous efficiency, and even damage the LED, this phenomenon is not uncommon. Some small businesses use manual welding, the use of 40 watts of ordinary soldering iron, welding temperature can not be controlled, soldering iron temperature above 300-400 ° C, too high welding temperature will also cause dead lights, LED lead at high temperature expansion coefficient is several times higher than the expansion coefficient of about 150 ° C, the internal gold wire solder will be due to excessive thermal expansion and contraction of the welding point will be pulled apart, Cause dead lamp phenomenon.
2. Analysis of the cause of dead lamp phenomenon caused by open welding joints inside LED lights
2.1 Packaging enterprise production process is not complete, materials inspection means backward, is the direct cause of LED dead light, the general use of bracket package LED, bracket row is made of copper or iron metal materials by precision mold stamping, because copper is more expensive, the cost is naturally high, by the market fierce competition factors, in order to reduce manufacturing costs, Most of the market uses cold-rolled low carbon steel to bring stamping LED bracket. The iron bracket row is silver plated, which has two functions, one is to prevent oxidation and rust, and the other is to facilitate welding. The plating quality of the bracket row is very key, which is related to the life of the LED. When electroplating, the current should be controlled, the thickness of the silver plating layer should be controlled, the coating is too thick, the cost is high, and the quality is too thin. Because the general LED packaging enterprises do not have the ability to test the plating quality of the support, which gives some plating enterprises the opportunity to make the plating of the support plating silver layer thinner, reduce costs, general packaging enterprises IQC lack of testing means for the support plating, there is no instrument to detect the thickness and fastness of the support plating coating, so it is easier to cheat.
Some scaffolds are rusted after a few months in the warehouse, not to say that they are used, which shows how poor the quality of electroplating is. The products made with such a bracket row are certainly not long, do not say 30-50,000 hours, 10,000 hours are a problem. The reason is very simple every year there is a period of south wind days, such weather in the air humidity is large, it is easy to cause poor electroplating metal parts embroider, so that LED components fail. Even the packaged LED will not have strong adhesion due to the thin silver plating layer, and the solder joint will be separated from the support, resulting in dead lamp phenomenon. This is what we encountered when the well-used light was not lit, in fact, the internal solder joint was separated from the support.
Some scaffolds are rusted after a few months in the warehouse, not to say that they are used, which shows how poor the quality of electroplating is. The products made with such a bracket row are certainly not long, do not say 30-50,000 hours, 10,000 hours are a problem. The reason is very simple every year there is a period of south wind days, such weather in the air humidity is large, it is easy to cause poor electroplating metal parts embroider, so that LED components fail. Even the packaged LED will not have strong adhesion due to the thin silver plating layer, and the solder joint will be separated from the support, resulting in dead lamp phenomenon. This is what we encountered when the well-used light was not lit, in fact, the internal solder joint was separated from the support.
2.2 Each process in the packaging process must be carefully operated, any link negligence is the cause of dead light in the point, solid crystal process, silver glue (for single solder joint chip) point more and less is not good, more glue will return to the chip gold pad, resulting in short circuit, less chip and sticky. Double solder joint chip point insulation glue is the same, point more insulation glue will return to the gold pad of the chip, resulting in virtual welding during welding and resulting in dead lamp. The chip is less and the glue is not strong, so the glue must be just right, neither more nor less. The welding process is also very critical, the pressure, time, temperature, power of the four parameters of the welding machine should be just right, in addition to the fixed time, the other three parameters are adjustable, the adjustment of the pressure should be moderate, the pressure is easy to crush the chip, too small is easy to virtual welding. The welding temperature is generally adjusted at 280 ° C, the power adjustment refers to the ultrasonic power adjustment, too large, too small are not good, to moderate, in short, the adjustment of the parameters of the golden ball welding machine, with the welded material, with the spring moment tester to detect ≥6 grams, that is qualified.
Every year, the parameters of the gold wire welding machine should be checked and corrected to ensure that the welding parameters are in the best state. In addition, the arc of the welding line is also required, the arc height of the single solder joint chip is 1.5-2 chip thickness, the arc height of the double solder joint chip is 2-3 chip thickness, the arc height of the LED will also cause quality problems, arc height is too low, easy to cause the dead lamp phenomenon when welding, arc height is too large, the current impact is poor.
Every year, the parameters of the gold wire welding machine should be checked and corrected to ensure that the welding parameters are in the best state. In addition, the arc of the welding line is also required, the arc height of the single solder joint chip is 1.5-2 chip thickness, the arc height of the double solder joint chip is 2-3 chip thickness, the arc height of the LED will also cause quality problems, arc height is too low, easy to cause the dead lamp phenomenon when welding, arc height is too large, the current impact is poor.
3, identify the method of virtual welding dead lamp
The LED light will not light with a lighter to heat the LED lead to 200-300 ° C, remove the lighter, and connect the LED with a 3-volt battery according to the positive and negative electrodes, if the LED light can be lit at this time, but as the lead temperature decreases the LED light from bright to not bright, which proves that the LED light is virtual welding. Heating can light up the reason is to use the principle of metal thermal expansion and contraction, LED lead heating expansion elongation and internal solder joints connected, at this time on the power supply, LED can emit normal light, with the temperature drop LED lead shrinkage returned to normal temperature state, and internal solder joints disconnected, LED light is not bright, this method has been tried repeatedly are effective. The two leads of the virtual welding of the dead lamp are welded on a metal strip, soaked with concentrated sulfuric acid, so that the external colloid of the LED is dissolved, and the colloid is removed after all dissolution, and the welding situation of the solder joints can be observed under a magnifying glass or microscope, and it can be found out whether the problem is a welding or a second welding, whether the parameter setting of the gold ball welding machine is wrong, or other reasons, in order to improve the method and process. Prevent the phenomenon of virtual welding from happening again.
However, even the exhibits at the China Electronics Exhibition, users of LED products will encounter the phenomenon of dead lights, which is the LED products after a period of time, the phenomenon of dead lights, dead lights have two reasons, open circuit dead lights are bad welding quality, or the quality of the bracket electroplating is problematic, LED chip leakage current increases will cause LED lights not to light. Now many LED products do not add anti-static protection in order to reduce costs, so it is easy to be damaged by induced static electricity. Rainy day thunder prone to high-voltage electrostatic induction of the power supply line, as well as the superimposed peak pulse of the power supply line, will cause LED products to suffer varying degrees of damage.
However, even the exhibits at the China Electronics Exhibition, users of LED products will encounter the phenomenon of dead lights, which is the LED products after a period of time, the phenomenon of dead lights, dead lights have two reasons, open circuit dead lights are bad welding quality, or the quality of the bracket electroplating is problematic, LED chip leakage current increases will cause LED lights not to light. Now many LED products do not add anti-static protection in order to reduce costs, so it is easy to be damaged by induced static electricity. Rainy day thunder prone to high-voltage electrostatic induction of the power supply line, as well as the superimposed peak pulse of the power supply line, will cause LED products to suffer varying degrees of damage.
