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SMD LED disassembly and repair

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1 . SMD led disassembly skills

The most common method is to use a heating table to heat on the aluminum substrate. When the tin is melted, the unnecessary lamp beads can be removed. Another method is to use a hair dryer to heat the bottom surface of the aluminum substrate. 

The terminal voltage of the PN junction constitutes a certain potential barrier. When a forward bias voltage is applied, the potential barrier drops, and the majority carriers in the P and N regions diffuse to each other. Since the mobility of electrons is much greater than that of holes, a large number of electrons will diffuse to the P region, which constitutes the injection of minority carriers in the P region. These electrons recombine with the holes in the valence band, and the energy obtained during the recombination is released in the form of light energy. This is the principle of PN junction light emission.

High-power LEDs cannot be classified into SMD series. Their power and current usage are different, and their photoelectric parameters are quite different. If a single high-power LED light source is not equipped with a heat dissipation base (usually a hexagonal aluminum base), its appearance is not much different from ordinary patches. The high-power LED light source is circular, and the packaging method is basically the same as that of SMD patches. However, it is essentially different from the SMD patch in terms of use conditions, environment, and effects.


2 . LED patch replacement tips

(1) It is recommended to use reflow soldering under normal conditions and only perform manual soldering when repairing.

(2) The maximum power of the electric soldering iron used for manual welding should not exceed 30W, the welding temperature should be controlled within 300℃, and the welding time should be less than 3 seconds.

(3) Do not touch the colloid with the soldering iron tip.

(4) When the pin is heated to 85°C or higher than this temperature, it should not be pressed, otherwise the gold wire bond will be disconnected.

3. Reflow soldering

(1) Peak reflux temperature: 260℃or lower than this temperature value. (Encapsulation surface temperature)

(2) The time required for the temperature to rise above 210℃: 30 seconds or less.

(3) Times of reflows: no more than twice at most.

(4) After reflow, the LED needs to be cooled to room temperature before it can touch the colloid.

For reflow soldering, if it is an aluminum substrate, a hot plate can also be used. The soldering iron heats the aluminum substrate, but pay attention to the speed and remove it immediately after soldering.

Void-welding is easy to occur, it is the void-welding of the LED chip on the LED lamp, and the gold wire in the welding is not connected properly.

Open the steel mesh according to different styles of light bars, and the steel mesh and light bars can be consistent. Choose a good quality solder paste. Poor solder paste is easy to fall off using LED lamp beads. Solder paste is printed to the position to be soldered, and then soldered after reflow soldering.


4 . SMD LED repair

Tools/Materials: Constant temperature heating sheet PTC220V270 degrees, small tweezers,Corresponding to LED chip, low temperature solder paste


1.Connect the plug to the thermostatic PTC, and be careful not to expose the wires. (It is recommended that beginners add a power-on indicator.)

2. The constant temperature PTC is connected to the power supply, and the bottom should be insulated. I use the old electronic transformer iron shell to insulate and reduce the temperature loss. (The constant temperature PTC will heat up after power-on, so be careful not to touch it, there will be residual temperature after power-off, be careful not to touch.)

3. Put the broken LED patch board on the constant temperature heating board. When the temperature reaches the melting point of the solder paste, use tweezers to pick up the damaged LED patch and place a new one at the same time. Negative), the cost is very low, and the service life after repair is the same as the original one. It is recommended to apply some thermal silica gel when the LED patch board is installed back, so that the heat dissipation is good and the LED has a long life.