Analysis of the problem of LED lamp bead dead light after mounting on board

In the production process, we always encounter the phenomenon that one, one string, or several strings of lamp beads cannot light up when testing after mounting on the board. Here is a summary of this phenomenon:

Dead light during welding

1. Common welding methods can be divided into electric soldering iron welding, heating platform welding and reflow soldering, etc.

A. Electric soldering is the most common, such as making samples and repairs. In order to save costs, most existing manufacturers purchase unqualified and inferior electric soldering irons, most of which are poorly grounded and have leakage. During the welding process, this is equivalent to forming a loop between the leaking soldering iron tip-the LED being soldered-the human body-the ground, which means that the voltage that is dozens to hundreds of times higher than the voltage that the lamp bead bears is applied to the LED lamp bead, which will burn it out instantly. Note: The situation will be more serious if the static belt is connected, because when the human body is connected to the static belt, the resistance of the loop formed to the ground is smaller, and the current passing through the human body to the lamp bead will be greater. This is also the problem that many people say that there are still so many damaged lamp beads even though they are wearing static belts.

B. Dead lights caused by welding on the heating platform. Due to the continuous increase in lamp sample orders, most companies use heating platforms as the best production tools to meet the needs of small batches and sample orders due to their low equipment cost, simple structure and operation. However, the use environment (for example, the temperature cannot be kept constant in places with fans) and the welding operator's proficiency and control of welding speed have become major problems causing dead lights. Another issue is the grounding condition of the heating platform equipment.

C. Reflow soldering. Generally, this soldering method is the most reliable production method and is suitable for mass production and processing. If it is not operated properly, it will cause more serious consequences of dead lights, such as unreasonable temperature adjustment, poor machine grounding, etc.

2. Improper storage causes dead light

This problem is the most common. It is caused by not paying attention to moisture-proof after unpacking. Since the sealing glue of the lamp beads is mostly made of silicone material, it has certain water absorption characteristics. After the lamp beads are attached to the board after being damp, the silicone will expand and contract due to the high-temperature welding process. The gold wire, chip, and bracket are deformed, causing the gold wire to shift and break, and the lamp will not light up. Therefore, it is recommended that: LEDs should be stored in a dry and ventilated environment, the storage temperature is -40℃- +100℃, and the relative humidity is below 85%; it is best to use the LED within 3 months under its original packaging conditions to avoid rusting of the bracket; when the LED packaging bag is opened, it should be used up as soon as possible. At this time, the storage temperature is 5℃-30℃, and the relative humidity is below 60%.

3. Chemical cleaning

Do not use unknown chemical liquids to clean LEDs, as this may damage the surface of the LED colloid or even cause cracks in the colloid. If necessary, clean it with an alcohol cotton swab in a ventilated environment at room temperature. The best time is one minute .

Since some light boards are deformed, the operators will reshape them. As the board is deformed, the lamp beads on it will also be deformed, breaking the gold wire and causing the light not to light up. It is recommended that this type of board be reshaped before production. Long production assembly and moving may also cause deformation and break the gold wire. Another cause is stacking. For convenience during the production process, the light boards are randomly stacked. Due to gravity, the lamp beads on the lower layer will be deformed by force and damage the gold wire.

5. The heat dissipation structure, power supply and light board do not match

Due to unreasonable power supply design or selection, the power supply exceeds the maximum limit that the LED can withstand (overcurrent, instantaneous impact); the heat dissipation structure of the lamp is unreasonable, which will cause dead lamps and premature light decay.

6. Factory grounding

It is necessary to check whether the factory's main grounding wire is in good condition.

7. Static electricity

Static electricity can cause LED function failure, so it is recommended to prevent ESD from damaging the LED.

A. When testing and assembling LEDs, operators must wear anti-static wrist straps and anti-static gloves.

B. Welding equipment, testing equipment, work tables, storage racks, etc. must be well grounded.

C. Use an ion fan to eliminate static electricity generated by friction during storage and assembly of LEDs.

D. The box for LED should be anti-static and the packaging bag should be anti-static bag.

E. Don't take chances and touch the LED.

LEDs damaged by ESD may experience the following abnormal phenomena:

A. Reverse leakage, in mild cases it will cause the brightness to decrease, in severe cases the light will not turn on.

B. The forward voltage value becomes smaller.

LEDs cannot emit light when driven at low current.

8. Poor welding causes the lamp to not light up.