Analysis:How the LED lamp inside open circuit cause a death lamp（Part 3)
1.The direct cause: The defective production process of packaging enterprise, incoming inspection means backward
Usually use stents encapsulate LED, stent is made of copper or iron materials with precision die stamping, metal materials as copper more expensive, the cost is high, affected by the market fierce competition, in order to reduce the manufacturing cost, market mostly use cold rolled low carbon steel with stamping LED stent. Iron stent has to through silver plated,it has two function, one is to prevent oxidation rust; two, it is convenient for welding, stent electric plating quality is critical, it is related to the LED span life. Before plating, it should be dealt in accordance with the procedures, such as cleaning, degreasing, phosphating process should be meticulously, need to control the current when plating, silver plating layer thickness have to control good, too thick cost high, too thin affect quality.
Because the general LED packaging enterprise does not have the ability to test the plating quality of the scaffold. It gives some electroplating enterprises the opportunity to reduce the plating and the cost. Generally, the packaging enterprise IQC is deficient in the stent inspection method, and it has no equipment to detect the thickness and fastness of the stents, so it is easy to muddle through.I have seen some of the stent emissions in the warehouse within a few months of rust, do not to use, the quality of plating is visible poor. This kind of bracket is definitely not used for long, don't about 3-50 thousand hours, 10,000 hours is a problem.
The reason is simple.Every year there is a period of south wind weather, in such weather air humidity is high, and very easy to cause electroplating poor metal parts to be embroidered, make LED element to fail. Even if the encapsulated LED is not strong because of the thin silver plating, the solder joint is detached from the bracket, resulting in the death lamp phenomenon. And this is what we always find a good light is not bright, which is that the internal solder is disconnecting from the scaffold.
2.Every process must be carefully operated in the packaging process, and any omission in the process is the cause of the death lamp
In the solid crystal process, the silver glue (for single solder point chip) is need to noted, too more, the glue will return to the chip gold pad, causing the short circuit,; too less, the chip will not adhere to the cell. It is also the same with the solder point insulating gel, too more the glue will return to the gold mat of the chip, causing the false welding to produce the dead lamp; too less, the chips are not glued together, so the glue must be just right, not too much or less.
The welding process is also critical. Gold ball welding machine’s pressure, time, temperature, four parameters are need to just right, in addition to the fixed time, the other three parameters are adjustable, the pressure should be moderate, too high, easy to crush the chip under pressure; too small, cause faulty soldering. Welding temperature at 280℃for good adjustment. The power regulation refers to the ultrasonic power regulation, it’s not good to too big and too small, moderate is better. In conclusion, the adjusted parameters of the ball welder, the spring torque test with the welding material is more than 6 grams, which means qualified.
Every year, the parameters of the ball welder are tested and calibrated to ensure that the welding parameters are in the best condition. The radian of welding line also have requirements, single chip solder joints arc height is 1.5-2 chip thickness, double arc solder chip height for 2-3 chip thickness. The arc height can also cause the quality problem of the LED, arc height too low can cause death lamp phenomenon during welding, the ability of current shock resistance of high arc height is poor.