Detailed explanation of the working principles of the four desoldering methods during welding
1. Desoldering method of tin absorber
Using the negative pressure of the built-in cavity of the tin suction device, the heated and molten solder is sucked into the cavity to separate the lead wire from the pad.
2. Desoldering method of tin suction rope
The soldering rope desoldering method is to use the tinning rope to suck away the molten solder to separate the lead wire from the pad.
Coat the part of the braided wire with rosin flux, then put it on the solder joint to be desoldered, then put the electric soldering iron on the braided wire to heat the solder joint, and when the solder in the solder joint melts, it will be absorbed by the copper braided wire.
If the spot solder is not sucked up once, it can be done for the second or third time until it is sucked up. When the braided rope is full of tin, it can no longer be used, and the place that is full of solder needs to be cut off.
3. Short pin desoldering method
The empty needle desoldering method is to use an empty needle (a syringe needle can also be used) of the same size (the aperture is slightly larger than the diameter of the lead) to be placed on the lead that needs to be desoldered. When the soldering iron heats the solder and melts, quickly rotate the needle until the soldering iron is removed. It can be stopped after the solder is solidified. At this time, the needle is pulled out and the lead wire has been separated.
4. Desolder with tin-absorbing soldering iron
Tin-absorbing soldering iron is a special desoldering iron, which can absorb tin into the inner cavity while heating the solder joints, thereby completing desoldering.
Judgment of non-standard tin points
(1) False soldering: It seems that it is soldered but it is not soldered. The main reason is that the pads and pins are dirty or the flux and heating time are not enough.
(2) Short circuit: parts with feet are short-circuited by excess solder between the feet, or short-circuited due to improper operation of inspectors using tweezers, bamboo sticks, etc. Short circuit with pin.
(3) Offset: due to inaccurate positioning of the device before welding, or mistakes made during welding, the pins are not within the specified pad area.
(4) Less tin: Less tin means that the tin point is too thin to fully cover the copper skin of the part, which affects the connection and fixing effect.
(5) Too much tin: The part feet are completely covered by tin and form an outer arc, so that the shape of the part and the pad position cannot be seen, and it is impossible to determine whether the parts and pads are tinned well.
(6) Wrong parts: If the specifications or types of parts placed do not match the operation regulations or BOM and ECN, they are wrong parts.
(7) Missing parts: The position where the parts should be placed is vacant due to abnormal reasons.
(8) Solder balls and tin slag: Excess solder balls and tin slag attached to the surface of the PCB will cause small pins to short circuit.
(9) Polarity reversal: The correctness of the polarity orientation is not consistent with the processing requirements, that is, the polarity is wrong.
