Industry news

2016August

Cause analysis of death lamp for LED lamp

From: www.szbako.com Data:30/08/2016

LED lamp strip lamp death cause analysis

we often encounter LED does not shine, packaging company, the enterprise application and the use of units and individuals, are likely to encounter, this is people in the industry said the dead lights. The reason is nothing more than two kinds of situations: first, through the LED leakage caused by the failure of the LED PN junction lights, is not bright, this situation generally does not affect the other LED lights work; second, the internal connection wire of LED lights off, causing LED caused death no current through the lamp, the normal work of the a LED lamp will affect the other, because the LED lamp low voltage (red and yellow orange LED working voltage of 1.8V— 2.2V, blue green and white LED working voltage 2.8— 3.2V), usually used in series and parallel to join, to adapt to different working voltage, LED lamp string with more influence the more, as long as there is a LED lamp inside line open, will cause the whole series of LED series circuit of the lamp is not lit, the situation is more serious than the first case. LED dead light is the impact of product quality, reliability of Guan Jian, how to reduce and eliminate dead lights, improve product quality and reliability, packaging and application of enterprises need to solve the key issues. Below is the lamp of death caused by some reasons are discussed,

1. Static on the LED chip damage, make LED chip of PN junction failure, leakage current increases, becomes a resistance

electrostatic is a harm great devil, all over the world because of the electrostatic damage to electronic components countless, resulting in several tens of millions of dollars in economic losses. So to prevent electrostatic damage to electronic components, electronic industry, an important work, LED packaging and application of enterprises must not be taken lightly. Any link out of the problem, will cause damage to the LED, so that the performance of LED worse or even failure. We know the human body static (ESD) can reach 3000 volts or so, can be led chip breakdown, in LED packaging production line, equipment grounding resistance whether it meets the requirements, this is also very important, general requirements for the grounding resistance is a 4 ohm, and some demanding the grounding resistance even to reach & Le; 2 ohms. These requirements are familiar to people in the electronics industry, Guan Jian is in the actual implementation is in place, whether there is a record. According to the author's understanding of private enterprises, anti electrostatic measures do not place, this is the majority of enterprises do not check to ground resistance test records, even to do contact resistance test is also a year a, or a few years, or a problem with the check grounding resistance, does not know that ground resistance test which is a very important work, at least four times a year (testing every quarter), where some of the requirements of high per month to grounding resistance test for. Soil resistance with the change of seasons and different, spring and summer rain, soil wetting contact resistance is easy to reach, autumn and winter dry soil moisture less, grounding resistance is probably exceeds a specified value, record is to preserve the original data, do well documented in the future. Accord with ISO2000 quality management system. Testing and measurement of grounding resistance can be designed table, ground resistance test packaging companies, led enterprise application to do, as long as the name of various equipment fill in this form in measured the equipment grounding resistance documented test signature can be archived.

human body electrostatic damage to the LED is also great, work should wear anti electrostatic clothing, equipped with electrostatic ring, good electrostatic ring should be grounded, a don't need grounding electrostatic ring anti electrostatic effect is not good, not recommended for use with the kinds of products, if the staff in violation of anti operation rules, accept the respective warning education, as well as to notice of others. Human body electrostatic, and people wear different clothes, fabrics, and every man's physique, autumn and winter night we undressed it was easy to see discharge phenomenon between the clothes, the electrostatic discharge voltage have 3000 volts. The silicon carbide substrate chip ESD value is only 1100 volts, the sapphire substrate chip ESD value is lower, only 500— 600 volts. A good chips, or LED, if we use hand to take (a body without any protective measures), the result it can be imagined, LED chips, or will be subject to varying degrees of damage, sometimes a good device through our hands on the inexplicable bad, this is electrostatic provoked disaster.

packaging companies if not strictly on the ground rules for work, the loss is their own business will cause products pass rate of decline, reduce the economic efficiency of enterprises, the same application of led enterprises if equipment and personnel bad grounding will cause such damage, rework is inevitable. In accordance with such standards manual requirements that lead led from the gel should be not less than 3 & mdash; 5 mm, to kink or welding, but most enterprise applications do not this, and only separated by a piece of PCB board thickness (& le; 2 mm) is directly welded, which will cause damage or damage to the LED, because of the high welding temperature will have an impact on the chip, and will become bad chip characteristics, reduce the luminous efficiency, even damage the LED. This phenomenon not uncommon. Some small businesses to use manual welding, using a 40 Watt ordinary iron, beyond the control of welding temperature, solder iron temperature in 300— more than 400 DEG C, high welding temperature will cause dead lights, LED lead at high temperature expansion coefficient than in about 150 DEG C expansion coefficient high several times, the internal wire solder joints will because of thermal expansion and contraction welding point opened, resulting in dead lights phenomenon. Analysis of the production process of

2.1 package enterprises not complete the cause of death light phenomenon

2.LED lamp internal connection spot open, incoming inspection means backward, is caused by the direct cause of LED death lights generally use the support row package LED, stent row is used copper or iron metal materials by precision die stamping, because copper is more expensive naturally, the cost is high, due to fierce market competition factors, in order to reduce manufacturing costs, the market mostly adopts cold rolled low carbon steel stamping LED stent can bring, iron bracket row to the silver, silver two for one is to prevent rust, two is convenient welding, plating quality support platoon very critical, it is related to the life of LED, in the treatment before plating should be in strict accordance with the operating rules, derusting, degreasing, phosphating processes should be strict in demands , to control the current electroplating, silver plated layer thickness to be controlled, the coating is too thick, high cost, too thin to affect the quality of the coating. Because LED encapsulation enterprises in general do not have the checking bracket electroplating quality. This gives some electroplating enterprises exploit, the plating bracket row of silver plating layer thinning, reduce costs, general packaging companies IQC to support row test means lack of, no detection supporting rack coating thickness and the fastness of the instrument, therefore easy to muddle through. I have seen some stents in the warehouse a few months after the rust, not to say that the use of the quality of the plating can be seen. With such a bracket out of the product is sure to use not long, do not say 3— 50 thousand hours, 10 thousand hours into a problem. The reason is very simple every year have southerly days for a period of time, in such weather, the air humidity is big, very easy to cause the differential plating metal parts rust, the LED component failure. Even if the package of the LED is also due to the silver plating layer is too thin adhesion, solder joints and stents from the dead light phenomenon. This is the use we encountered a good light is not bright, in fact, the solder joints and the stent is out of the.

2.2 package in the process of every working procedure must be careful operation, a part of any negligence are caused by dead lights

at the point, solid crystal process, silver glue (for single chip solder joints) points than and less will not work, the glue will return to gold chip pad, caused by a short circuit and less chip and glue rickety. Double joint chip insulating glue is the same, the insulating glue chip the gold pad on the back, causing welding the weld resulting in dead lights. A little sticky chip is not strong, so the glue must be just perfect, neither more nor less. Welding process is also critical, with gold wire bonder with pressure, time, temperature, and the power of the four parameters must be just right, in addition to the fixed time, the other three parameters is adjustable, pressure regulation should be moderate, pressure crushes easily chip, too small to weld. Welding temperature regulation in 280 DEG C for good, power regulation is that the ultrasonic power regulation, too big, too little is not good, to moderate, in short, regulation of the parameters of the gold wire ball welding machine, to the welded material and spring torque test meter detection & Ge; 6 grams, which is qualified. Each year to the gold wire ball welding machine parameters into the detection and correction, to ensure that the welding parameters in the best condition. Also welding line arc is also required. Single chip solder joints of camber is 1.5-2 chip thickness, double chip solder joints, the camber is 2-3 chip thickness, radian level will cause quality problems led, arc height is too low, easy to cause the welding when the lights die phenomenon, the camber is too large, current anti impact.
3. Identification of weld die

lamp will not light the LED lamp with a lighter will led lead wire heating to 200-300 DEG C, remove the lighter, 3 volt button cell type according to the positive pole and the negative pole is connected with the LED, if this led lamp is lit, but with the lead temperature decrease LED lamp light is not bright, which proved that the LED lights are weld. Heating can lit reason is by the expansion and contraction of the material principle, expansion of elongation and solder joints connected LED lead wire heating. At this time the power supply is switched on, LED can be normal luminescence, with temperature drop led shrinkage leads to revert back to the normal state, and solder joints is disconnected, LED lamp is not bright, try this method is efficacious. Will this weld dead lights two lead solder on a piece of metal strips, with thick sulfuric acid soaking, such external colloidal dissolved, colloidal all dissolved out, under a magnifying glass or microscope observation of each welding spot welding, is to find out a welding or welding problems is gold wire ball welding machine the parameters set incorrectly, or for other reasons, in order to improve methods and process, to prevent the recurrence of the phenomenon of weld.

use of LED products users will encounter the phenomenon of dead lights, this is a period of time a LED products, the dead light phenomena, dead lights have two reasons, open circuit of dead lights is the welding quality is not good, quality or plating rack, LED chip leakage current increases will cause led lamp does not light. Now a lot of LED products in order to reduce the cost is not anti static protection, it is easy to appear the phenomenon of induction electrostatic damage to the chip. Rainy days of thunder prone to power supply circuit of high voltage electrostatic induction, and power lines superimposed spike pulse, will make the LED products are subject to different degrees of damage.

all in all place dead lights for many reasons, not to enumerate, from package, application, to use each link are likely to appear dead lights phenomenon, how to improve the quality of LED products, packaging companies and enterprise application to attaches great importance to and earnestly study and from chip, frame selection, to the LED package according to ISO2000 quality system to carry on the operation of the entire process. Only in this way can the quality of LED products be improved, in order to achieve long life, high reliability. In the circuit design and application, selection of varistors and PPTC components to improve the protection circuit, increasing the number of parallel circuits, using constant

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