1. Before the circuit board welding, the welding agent is applied to the plate before welding. It is treated with the soldering iron to avoid the bad or oxidation of the tin plate. The chip is generally not treated.
2, use tweezers to carefully place the PQFP chip on the PCB board. Be careful not to damage the pin. Make it aligned with the pad to ensure that the chip is placed in the right direction. The temperature of the soldering iron is adjusted to more than 300 degrees Celsius, a small amount of soldering tin is attached to the tip of the soldering iron. The chip is pressed down by the tool and a small amount of flux is added to the pins of the two diagonal positions. The chip is still pressed down and the pins on the two diagonal positions are welded to make the core fixed and not move. After checking the diagonal angle, re check the position of the chip. If necessary, it can be adjusted or removed and re positioned on the PCB board.
3. When you start welding all the pins, solder solder should be added to the iron tips, and all the pins will be coated with flux to keep the pins moist. Contact the end of each pin with the tip of the soldering iron until the solder is inflow into the pin. When welding, keep the soldering iron tip parallel to the welding pin to prevent overlap due to excessive solder.
4. After welding all the pins, wet all pins with flux to clean solder. Remove excess solder to remove any short circuiting and lap joints wherever needed. Finally, use the tweezers to check whether there is any welding. After the inspection is completed, remove the flux from the circuit board, soak the hard brush on the alcohol and wipe it in the direction of the pin until the flux is lost.
5, the patch resistance element is relatively easy to weld some. You can spot tin on a solder joint first, then put one on the element, clamp the element with tweezers, and then see if it is correct. If you have put it right, then weld another head. It takes a lot of practice to really master welding skills.