Precautions during the use of SMD LED
Time: 2018-09-13 View: 832 Author: Paul
First, the common precautions in the use of SMD LED:
1, welding conditions
Reflow soldering: Preheat at 150 ° C for 2 minutes, and heat once at 240 ° C for 5 seconds.
Soldering iron soldering: Use a temperature-controlled soldering iron of up to 25W with a tip temperature not higher than 320 ° C and soldering once within 3 seconds.
Do not apply external force to the product while welding. Do not bend the circuit board after soldering.
Since the moisture absorption of the resin causes evaporation and expansion of water during welding, the interface may be peeled off, so the purpose of the moisture-proof packaging is to ensure the lowest moisture in the package.
The product should be used within one year from the date of packaging. Before the package is unopened, it should be stored in an environment with a temperature of 5~30 °C and a relative humidity of <60%.
After the package is unpacked, the product must be welded within 24 hours. Otherwise, the product must be stored in an environment with a temperature of 5~30°C and a relative humidity of <30% for a period of less than one week. If there is any unused product, please put it back.
Moisture-proof bag sealed for preservation
If the product exceeds the above storage requirements or is damp, it must be baked at 60 ± 5 ° C for 12 hours.
The surface of the product electrode is gold-plated and is susceptible to corrosion or discoloration, which is difficult to weld. It is recommended to use it as soon as possible.
Take care to avoid rapid changes in ambient temperature, especially in humid environments.
3, static protection
High-brightness blue, green and white products are sensitive to static electricity. In use, it is necessary to pay attention to static electricity surges that will damage or destroy the product. The workbench that is in contact with the product should be grounded through a resistor with a conductive pad; the tip of the soldering iron must be Grounding is recommended; an ionizer is recommended.
Second, the 7 major reasons for the death of SMD LED welding process
1, common welding methods can be divided into electric soldering iron welding, heating platform welding and reflow soldering, etc.:
A, soldering iron welding is the most common, such as sample preparation, maintenance, because most existing manufacturers in order to save costs, the purchase of soldering iron is mostly unqualified slightly, most of the grounding is poor, there is leakage, the welding process This is equivalent to the tip of the electric iron in the leakage - the LED being welded - the human body - forming a circuit in the earth, that is to say tens of times - hundreds of times the voltage of the lamp bead is applied to the LED lamp bead, instantaneously Burn it out.
Note: The situation of connecting the static electricity belt will be more serious, because when the human body is connected to the static electricity belt, the resistance to the ground forming circuit is smaller, and the current passing through the human body to the lamp bead will be larger, which is also said by many people that there is static electricity. There are still so many problems with lamp bead damage.
B. The dead lights caused by the heating platform welding, due to the continuous sample of the lamps, most enterprises have become the best production tools in order to meet the needs of small batches and sample sheets, due to the low cost of equipment, simple structure and operation. However, due to the use environment (for example, the temperature of the fan can not be constant) and the control of the welding operator's proficiency and welding speed has become a major problem causing the dead light, in addition to heating Grounding of equipment on the platform.
C, reflow soldering, generally this welding method is the most reliable production method, suitable for mass production and processing, if improper operation, it will cause more serious dead light consequences, such as unreasonable temperature adjustment, poor machine grounding.
2, improper storage caused by dead lights:
This kind of problem is the most common. Because it does not pay attention to the moisture-proof problem after opening the package, because the sealing material of the lamp bead is mostly made of silica gel material, it has certain water absorption characteristics. After the damp after the lamp bead is attached, the high-temperature welding process The silica gel will expand and contract, and the deformation of the gold wire, chip and bracket will cause the gold wire to shift and break, and the light spot will not be bright. Therefore, it is recommended that the LED be stored in a dry and ventilated environment with a storage temperature of -40. °C-
+100 ° C, the relative humidity is below 85%; LED is used 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 as soon as possible, then store The temperature is 5 ° C - 30 ° C, and the relative humidity is below 60%.
3, chemical cleaning:
Do not use unknown chemical liquids to clean the LEDs, as this may damage the surface of the LED colloids and even cause colloidal cracks. If necessary, clean them with an alcohol swab in a normal temperature and ventilated environment. The time is best controlled in one minute.
4, deformation caused by dead lights:
Due to the deformation of some of the light panels, the operator will go to the plastic shape. Because the board is deformed, the upper light beads are also deformed together at the same time. The gold wire is broken and the light is not bright. It is recommended that this type of board is the most It is good to carry out shaping treatment before production. Longer production and assembly and moving may also cause deformation to break the gold wire. There is also the stacking, the production process for the convenience of the hand, the light board is randomly stacked, due to gravity, the lower layer of the lamp bead will be deformed by force, damage the gold wire.
5. The heat dissipation structure, power supply and lamp board do not match:
Because the power supply design or selection is unreasonable, the power supply exceeds the maximum limit that the LED can withstand (super current, instantaneous impact); the heat dissipation structure of the lamp is unreasonable, which will cause dead lights and premature light decay.
6, factory grounding:
The factory's total ground wire must be checked for goodness.
Static electricity can cause LED function failure. It is recommended to prevent ESD from damaging the LED.
A. The operator must bring an anti-static wrist strap and anti-static gloves when testing and assembling the LED.
B. Welding equipment and test equipment, work tables, storage racks, etc. must be well grounded.
C. Use an ion fan to eliminate static electricity generated by the LED during storage and assembly due to friction.
D. The box with LED is made of anti-static material box, and the bag is made of electrostatic bag.
E. Don't have a chance to touch the LED.
The anomalies that can be caused by ESD-damaged LEDs are:
A, reverse leakage, light will cause the brightness to decrease, and the light will not light.
B. The forward voltage value becomes smaller. The LED does not emit light when driven at low current.
C, poor soldering causes the lamp to not light.