Industry news

2016August

Analysis and Discussion on the phenomenon of dead light in

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

we often encounter LED does not light the situation, packaging companies, applications and the use of units and individuals, are likely to come across, this is the industry's people say dead light phenomenon. 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, the electrostatic

1. chip on LED caused damage, make LED chip PN node failure, leakage current increase, become a harm great devil is a resistance

electrostatic, all over the world because of electrostatic damage to electronic components countless, causing 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.

2.1 packaging companies aren't the cause of death light phenomenon

2. LED lamp internal connection spot open, incoming inspection means backward, is caused by the direct cause of death LED

lamp generally use the support line package LED, support 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 more than the cold rolled low carbon steel stamping bring LED bracket Pai, iron bracket row to the silver, silver has two functions, one is to prevent rust, two is convenient welding, plating quality support platoon very critical, it is related to the life of the LED, in Before plating processing should be carried out strictly according to the operating rules, derusting, removing oil, phosphating process should be meticulous, electroplating to control current, the thickness of the silver plating layer to control the coating is too thick to high cost and too thin to affect the quality. 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 encapsulation process in each procedure must be careful operation, a part of any negligence are caused by dead lights

in solid crystal process, silver glue (for single chip solder joints) much more 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. differential weld die lamp method

will not be bright LED lights 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 can light up, but with the lead temperature decrease LED lamp light is not bright, which proved that led lamps 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 product LED, 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 the chip, frame selection, to the LED packaging the entire process according to ISO2000

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