What are the reasons for LED dead lights

We often encounter the LED does not light up the situation, packaging companies, application companies, as well as the use of units and individuals.

All may encounter, this is the industry people say the dead light phenomenon.

The reason for this is no more than two situations.

One, the LED leakage current is too large to cause the PN junction failure, so that the LED lights do not light, this situation generally does not affect the work of other LED lights; second, the LED lights of the internal connection leads disconnected, resulting in LED no current through the dead light, this situation will affect the normal work of other LED lights, the reason is that the LED lights due to low working voltage (red, yellow and orange LED working voltage 1.8V-2.2V, blue, green and white LED working voltage 2.8-3.2V), generally have to be connected in series, parallel to adapt to different working voltage, the more LED lights in series, the greater the impact, as long as one of the LED lights internal connection open circuit, will cause the series circuit of the whole string of LED lights do not light, see this situation is much more serious than the first case. LED dead light is the impact of product quality, reliability of the key.

How to reduce and eliminate dead lights, improve product quality and reliability, is the packaging, application companies need to address the key issues. The following are some of the causes of dead lights for some analysis of the discussion.

Static electricity on the LED chip damage, so that the LED chip PN junction failure, leakage current increases, into a resistance Static electricity is a very harmful devil, the world because of static damage to electronic components countless, resulting in tens of millions of dollars in economic losses. Therefore, preventing static electricity from damaging electronic components is a very important job in the electronics industry.

LED packaging, application of the enterprise should not be taken lightly. Any one of the links out of order, will cause damage to the LED, so that the LED performance deterioration or even failure. We know that the human body (ESD) static electricity can reach about three thousand volts, enough to break through the LED chip damage, in the LED packaging production line, all kinds of equipment grounding resistance is in line with the requirements, this is also very important.

This is also very important, the general requirement of grounding resistance of 4 ohms, some high requirements of the occasion of its grounding resistance even to ≤ 2 ohms. These requirements are familiar to people in the electronics industry, the key is whether the actual implementation in place, whether there are records.

According to my understanding of the general private enterprises, anti-static measures are not in place, which is the majority of enterprises can not check the grounding resistance test records, even if the grounding resistance test is once a year, or once every few years, or a problem when checking the grounding resistance, I do not know that the grounding resistance test is a very important work.

At least 4 times a year (quarterly test), some high requirements of the place, once a month to make a grounding resistance test. Soil resistance will vary with the seasonal changes, spring and summer rain, soil wet grounding resistance is easier to reach, autumn and winter dry soil moisture less, grounding resistance is likely to exceed the specified value.

To make records is to save the original data, to do later have data to check. Comply with ISO2000 quality management system. Test grounding resistance can be self-designed form, grounding resistance test packaging companies, LED application companies to do, as long as the name of various devices filled in the form, measured the grounding resistance of each device on record, the test person's signature can be archived.

Human electrostatic damage to LED is also very large, should wear anti-static clothing when working with electrostatic ring, electrostatic ring should be grounded well, there is a do not have to ground the electrostatic ring anti-static effect is not good, it is recommended not to use with the product, if the staff violates the operating procedures, it should receive the appropriate warning education, but also play the role of notice others.

The human body with the amount of static electricity, and people wearing different fabrics clothes, and each person's physique, autumn and winter darkness we can easily see the discharge between the clothes, the electrostatic discharge voltage of three thousand volts. The ESD value of the silicon carbide substrate chip is only 1100 volts, the ESD value of the sapphire substrate chip is even lower, only 500-600 volts. A good chip or LED, if we use our hands to take (the body did not make any protective measures), the results can be imagined, the chip or LED will be damaged to varying degrees, sometimes a good device through our hands is somehow bad, which is the disaster of static electricity.

Packaging enterprises if not strictly according to grounding procedures, the loss is the enterprise itself, will cause a decline in product qualification rate, reducing the economic benefits of enterprises, the same application of LED enterprises if the equipment and personnel grounding is poor, it will also cause damage to the LED, rework is inevitable. According to the requirements of the LED standard use manual, the LED lead from the colloid should be no less than 3-5 mm for bending the foot or welding, but most of the application companies are not doing this, but only the thickness of a PCB board apart (≤ 2 mm) will be directly welded, which will also cause damage or damage to the LED, because too high a welding temperature will have an impact on the chip, will make the chip characteristics become bad, reducing Luminous efficiency, and even damage LED, this phenomenon is common.

Some small businesses use manual welding, the use of 40-watt ordinary soldering iron, welding temperature can not be controlled, the temperature of the iron in the 300-400 ℃ or more, too high welding temperature will also cause dead lights, LED lead expansion coefficient at high temperatures than in the expansion coefficient of about 150 ℃ several times higher, the internal gold wire solder joints will be due to excessive thermal expansion and contraction of the solder joints will be pulled apart, resulting in the phenomenon of dead lights. 2. LED lights internal wiring solder joints open circuit caused by the dead light phenomenon of the cause analysis 2.1 packaging enterprise production process is not built complete, backward means of inspection of incoming materials, is the direct cause of LED dead light General use of bracket row packaging LED, bracket row is the use of copper or iron metal materials by precision mold stamping, due to copper is more expensive, the cost is naturally high, subject to the fierce market competition factors, in order to reduce Manufacturing costs, most of the market are used to bring cold-rolled low carbon steel stamping LED bracket hover, iron bracket row to be silver plated, silver plating has two roles, one is to prevent oxidation rust, the second is to facilitate welding, bracket row plating quality is very critical, it is related to the life of the LED, the treatment before plating should be carried out in strict accordance with the operating procedures, rust removal, oil removal, phosphating and other processes should be meticulous, plating to control Good current, the thickness of the silver layer should be controlled, the plating layer is too thick and costly, too thin to affect the quality.

Because the general LED packaging companies do not have the ability to test the quality of stent row plating, which gives some plating companies have the opportunity to take advantage of the plating of the stent row silver plating layer thinning, reducing the cost of expenditure, the general packaging companies IQC on the stent row inspection means lack of detection stent row plating thickness and fastness of the instrument, so it is easier to muddle through. I have seen some bracket row in the warehouse a few months after the rust, not to mention the use of the plating quality is very poor. With such a bracket row made out of the product is certainly not long, not to say 30-50,000 hours, 10,000 hours have become a problem. The reason is very simple every year there is a period of south windy days, such weather air humidity, it is easy to cause poor plating of metal parts embroidered, so that the LED components fail.

Even if the encapsulated LED will also be too thin silver-plated layer adhesion is not strong, solder joints and bracket detachment, resulting in dead light phenomenon. This is what we encountered the use of a good light does not light up, in fact, is the internal solder joints and bracket detachment.

Each process must be carefully operated in the packaging process, any negligence is the cause of dead lights in the point, solid crystal process, silver glue (for single solder point chip) point more and less can not be, more glue will return to the chip gold pad, resulting in short circuit, less chip and sticky not firm. Double solder point chip point insulating glue is the same, point more insulating glue will return to the chip's gold pad, resulting in soldering when the virtual solder and thus produce dead lights. Point less chip and sticky, so the point of glue must be just right, neither more nor less. Welding process is also very critical, gold wire ball welding machine pressure, time, temperature, power four parameters with the right fit, in addition to time fixed, 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 false soldering. Welding temperature is generally adjusted at 280 ℃ is good, the adjustment of power refers to the ultrasonic power adjustment, too large, too small are not good, to moderate, in short, the adjustment of the parameters of the gold wire ball welding machine to weld good material, using the spring torque test meter test ≥ 6 grams, that is, qualified. Every year, the gold wire ball welder should be tested and corrected for each parameter to ensure that the welding parameters are in the best condition. In addition, the arc of the weld line also has requirements, a single welded chip arc height of 1.5-2 chip thickness, double welded chip arc height of 2-3 chip thickness, the arc height will also cause the quality of LED problems, arc height is too low easily caused by the phenomenon of dead lights when welding, arc height is too large is poor resistance to current shocks.

 Identify the method of false welding dead lights will not light the LED lamp with a lighter to heat the LED lead to 200-300 ℃, remove the lighter, with a 3-volt buckle battery connected to the LED according to the positive and negative, if the LED lamp can be lit, but as the lead temperature decreases LED lamp from light to no light, which proves that the LED lamp is false welding. The reason for heating can light up is the use of the principle of metal thermal expansion and contraction, LED lead expansion and elongation when heated and internal solder joints connected, at this time, the power supply, L