What are common LED failures?
LED does not work after SMT or SMD assembly PCB, problem analysis Analysis of the problem of dead light after the lamp bead is pasted on the board
In the process of production, some LEDs
will always encounter the phenomenon that one, one string, or several strings of lamp beads cannot be lit when testing after mounting the board. To make a summary for this phenomenon: The lamp is dead during the welding process.
1. Common welding methods can be divided into electric soldering iron welding, heating platform welding and reflow soldering, etc.
A. Soldering with electric soldering iron is common, such as sample making and maintenance. In order to save costs, most existing manufacturers buy back soldering irons that are mostly unqualified and low-quality products. Most of them are poorly grounded and have leakage. The welding process This is equivalent to forming a circuit between the tip of the soldering iron that is leaking electricity–the soldered LED–the human body–the earth, that is to say, it is equal to tens of times-hundreds of times the voltage that the lamp bead bears is added to the LED lamp bead, instantly Burn it out. Note: The situation of connecting the electrostatic belt will be more serious, because when the human body is connected with the electrostatic belt, the resistance of the loop to the ground is smaller, and the current passing through the human body to the lamp bead will be greater. This is what many people say that there is obviously static electricity The belt still has the problem of so many lamp beads being damaged.
B. Dead lamps caused by heating platform welding. Due to the continuous sample list of lamps, most enterprises meet the needs of small batches and sample lists. Due to the advantages of low equipment cost, simple structure and operation, etc., the heating platform has become the best production tool, but , due to the use environment (such as: the temperature cannot be kept constant in places with fans) and the control of the welding operator’s proficiency and welding speed, it has become a big problem causing dead lights. In addition, there is the heating platform. Equipment grounding.
C. Reflow soldering. Generally, this soldering method is a 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 and poor grounding of the machine.
2. Improper storage causes dead lights
This kind of problem is common, because the moisture-proof problem is not paid attention to after opening the package, because the sealing glue of the lamp bead is mostly made of silica gel material, which has certain water absorption characteristics, after the damp lamp bead is attached to the board, it goes through a high-temperature welding process Silicone will expand with heat and contract with cold, and the gold wire, chip, and bracket will be deformed, causing the gold wire to shift and break, and the lamp will not light up. Therefore, it is recommended that LEDs be stored in a dry and ventilated environment, and the storage temperature is -40 ℃- +100℃, relative humidity below 85%; it is better to use the LED within 3 months in its original packaging to avoid rusting of the bracket; when the LED packaging bag is opened, it should be used up as soon as possible. The storage temperature is 5°C-30°C, and the relative humidity is below 60%.
3. Chemical cleaning
Do not use unknown chemical liquid to clean the LED, because it may damage the surface of the LED colloid, or even cause colloidal cracks. If necessary, please clean it with an alcohol cotton swab in a room temperature and ventilated environment, and the time is controlled within one minute.
4. Deformation causes dead lights
Due to the deformation of some of the lamp boards, the operator will have to reshape the board. Due to the deformation of the board, the lamp beads on it will also be deformed at the same time, and the gold wire will be broken, causing the lamp to not light up. It is recommended to have this type of board in the Shaping before production. Longer ones may be deformed and broken during production, assembly and moving. In addition, it is caused by stacking. For the convenience and smoothness of the production process, the lamp panels are stacked randomly. 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 lamp board do not match
Due to the unreasonable design or selection of the power supply, 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 lights and premature light failure
6. Factory production line grounding
It is necessary to check whether the general ground wire of the factory is in good condition.
7. Static electricity
Static electricity can cause LED function failure, it is recommended to prevent ESD damage to LED.
A. Operators must wear anti-static wristbands and anti-static gloves during LED testing and assembly.
B. Welding equipment and testing equipment, work tables, storage racks, etc. must be well grounded.
C. Use an ion fan to eliminate the static electricity generated by friction during storage and assembly of LEDs.
D. The material box for LED is anti-static material box, and the packaging bag is electrostatic bag.
E. Don’t be lucky, touch the LED casually. The abnormal phenomena that will appear in the LED damaged by ESD are:
a) Reverse leakage, the light one will cause the brightness to decrease, and the serious one will not light up.
b) The forward voltage value becomes smaller. LED cannot emit light when driven by low current.
9. Poor welding causes the lamp to not light up.