ED chip

Second, the internal connection lead of the LED light is disconnected, causing the LED to have no current passing through and producing a dead light. This situation will affect the normal operation of other LED lights. 1.8V-2.2V, blue-green-white LED working voltage 2.8-3.2V), generally connected in series and parallel to adapt to different working voltages, the more LED lights in series, the greater the impact, as long as there is one LED The open circuit of the internal connection of the lamp will cause the entire string of LED lights in the series circuit to not light up. It can be seen that this situation is much more serious than the first situation.

LED dead lights are the key to affecting product quality and reliability. How to reduce and eliminate dead lights and improve product quality and reliability are key issues that packaging and application companies need to solve. The following is some analysis and discussion on some of the causes of dead lights:

1. Static electricity causes damage to the LED chip, which makes the PN junction of the LED chip fail, and the leakage current increases, becoming a resistor.

Static electricity is a very harmful devil. There are countless electronic components damaged by static electricity all over the world, causing economic losses of tens of millions of dollars. Therefore, preventing static electricity from damaging electronic components is a very important job in the electronics industry. Enterprises in LED packaging and application must not take it lightly. Any problem in any link will cause damage to the LED, making the LED performance worse or even invalid. We know that the static electricity of the human body (ESD) can reach about 3,000 volts, which is enough to damage the LED chip. In the LED packaging production line, it is also very important whether the grounding resistance of various equipment meets the requirements. Generally, the grounding resistance is required to be 4 Ohm, and in some occasions with high requirements, the grounding resistance should even reach ≤ 2 ohms.

These requirements are familiar to people in the electronics industry, and the key is whether they are in place when actually implemented and whether there is a record. According to the author's understanding of general private enterprises, the anti-static measures are not in place, which is why most enterprises cannot find the test records of grounding resistance. Check the grounding resistance from time to time, but the grounding resistance test is a very important job, at least 4 times a year (test once a quarter), and some places with high requirements, a grounding resistance test is required every month.

Soil resistance will vary with the change of seasons. There is a lot of rain in spring and summer, and the soil wet grounding resistance is easier to achieve. In autumn and winter, the dry soil moisture is less, and the grounding resistance may exceed the specified value. The purpose of recording is to preserve the original data. There will be evidence at a later date. In line with ISO2000 quality management system. You can design a form to test the grounding resistance, and the grounding resistance testing packaging companies and LED application companies should do it. Just fill in the names of various devices in the form, and record the grounding resistance of each device, and the tester's signature can be archived.

The damage of human body static electricity to the LED is also very large. You should wear anti-static clothing and wear an electrostatic ring when working. The electrostatic ring should be well grounded. There is an electrostatic ring that does not need to be grounded. For this kind of product, if the staff violates the operating procedures, they should receive corresponding warning education, and also play the role of notifying others. The amount of static electricity in the human body is related to the different fabrics people wear and their physique. When we take off our clothes in autumn and winter, we can easily see the discharge between clothes. The voltage of this electrostatic discharge is 3,000 volts.

The ESD value of silicon carbide substrate chips is only 1100 volts, and the ESD value of sapphire substrate chips is even lower, only 500-600 volts. A good chip or LED, if we take it with our hands (the body does not take any protective measures), the result can be imagined, the chip or LED will be damaged to varying degrees, and sometimes a good device passes through our hands. It is inexplicably broken, and this is the fault of static electricity.

If the packaging company does not strictly follow the grounding regulations, the company itself will suffer, which will cause the product qualification rate to drop and reduce the economic benefits of the company. If the equipment and personnel are poorly grounded, the LED will also be damaged. Inevitably. According to the requirements of the LED standard manual, the lead of the LED should be no less than 3-5 mm away from the glue, and the legs should be bent or welded, but most application companies have not done this, but only separated by the thickness of a PCB board (≤ 2 mm) directly soldered, which will also cause damage or damage to the LED, because excessive soldering temperature will affect the chip, make the chip characteristics worse, reduce the luminous efficiency, and even damage the LED. This phenomenon is not uncommon. Some small companies use manual soldering and use a 40-watt ordinary soldering iron. The soldering temperature cannot be controlled. The soldering iron temperature is above 300-400 °C. Excessive soldering temperature will also cause dead lights. The expansion coefficient of LED leads at high temperature is about 150 °C The expansion coefficient is several times higher, and the internal gold wire solder joints will pull the solder joints apart due to excessive thermal expansion and contraction, resulting in a dead lamp phenomenon.