PCB News - SMT patch process welding is an essential link

Welding is an indispensable link in SMT patch process. If there is a mistake in this link, it will directly affect the chip processing circuit board is unqualified or even scrapped. Therefore, it is necessary to master the correct welding method and understand the relevant matters needing attention to avoid problems during welding.

1. Before SMT processing and welding, apply flux to the solder pad and handle it with soldering iron to avoid bad tin plating or oxidation on the solder pad, resulting in poor welding. Generally, the chip does not need to be handled.

2. Carefully place the PQFP chip on the PCB board with tweezers, taking care not to damage the pin.
Align it with the solder pad to ensure that the chip is placed in the correct direction.
Set the temperature of the soldering iron to more than 300 degrees Celsius, dip the tip of the soldering iron into a small amount of solder, use the tool to press down on the chip that has been aligned, add a small amount of flux to the pins in the two diagonal positions, still press down on the chip, weld the pins in the two diagonal positions, so that the chip is fixed but cannot be moved.
Recheck the alignment of the chip position after welding the diagonal.
Adjust or remove and reposition the PCB if necessary.

3. When welding all pins, add soldering tin to the tip of the soldering iron and apply flux to all pins to keep the pins wet.
Touch the end of each pin of the chip with the tip of the soldering iron until you see the solder flow into the pin.
During welding, keep the tip of the soldering iron parallel to the welded pin to prevent overlapped soldering.

4. After welding all pins, wet all pins with flux to clean the solder.
Drain excess solder where needed to eliminate any short circuits and overlaps.
Finally, use tweezers to check for weld defects. After the inspection is completed, remove the flux from the circuit board and wipe the bristle brush with alcohol along the pin direction carefully until the flux disappears.

It is relatively easy to weld the SMT resistance and receptacle elements. You can first put some tin on a welding spot, then put one end of the element on, and then clamp the element with tweezers. After welding the end of the element, you can see whether it has been put right.
If correct, weld the other end.
To really master welding skills still need a lot of practice.