How to weld SMT components by hand?

The soldering of SMT chip components should choose a temperature-regulating tip soldering iron at 200 ~ 280℃. \x0d\ Substrates of patch resistors and capacitors are mostly made of ceramic materials, which are easily broken when colliding. Therefore, it is necessary to master the skills of temperature control, preheating and light touch when welding. Temperature control means that the welding temperature should be controlled at about 200 ~ 250℃. Preheating means preheating the parts to be welded in an environment of 100℃ for 1 ~ 2 minutes to prevent the parts from being damaged due to sudden thermal expansion. Touch means that the welding head should first heat the solder joint or conductive tape of the printed board when operating, and try not to touch the components. In addition, the welding time should be controlled at about 3 seconds each time, and the circuit board should be naturally cooled at room temperature after welding. The above methods and techniques are also applicable to the welding of SMD crystal diodes and triodes. \x0d\ SMD integrated circuits have many pins, narrow spacing and low hardness. If the welding temperature is not suitable, it is easy to cause faults such as short circuit of lead solder, virtual welding or separation of printed circuit copper foil from printed board. When the SMD IC is disassembled, the temperature of the temperature regulating soldering iron can be adjusted to about 260℃. When the soldering head and the soldering suction device suck up the solder of the IC pin, gently insert the pliers with pointed ends into the bottom of the IC. While heating with a soldering iron, gently lift the IC pins one by one with pliers, so that the IC pins are gradually separated from the printed board. When lifting the integrated circuit with tweezers, it must be synchronized with the heated part of the soldering iron to prevent the circuit board from being washed out. \x0d\ Before switching to a new integrated circuit, all the solder left by the original integrated circuit should be removed to ensure that the pad is flat and clean. Then clean the pins of the integrated circuit to be soldered with fine sandpaper, evenly tin-plate, align the pins of the integrated circuit to the corresponding solder points of the printed board, gently press the pins on the surface of the integrated circuit during soldering to prevent the integrated circuit from moving, and operate the soldering iron with the other hand to dip an appropriate amount of solder to solder and fix the pins at the four corners of the integrated circuit with the circuit board, then check and confirm the model and direction of the integrated circuit again, and formally solder after it is correct, and adjust the temperature of the soldering iron to about 250℃. One hand holds the soldering iron to heat the pins of the integrated circuit, and the other hand sends the welding wire to the heating pins for welding until all the pins are heated and welded. Finally, carefully check and eliminate pin short circuit and virtual welding. After the solder joint cools naturally, use a brush dipped in absolute alcohol to clean the circuit board and solder joint again to prevent welding slag. \x0d\ Before overhauling the module circuit board, it is advisable to clean the printed circuit board with a brush dipped in anhydrous alcohol to remove impurities such as dust and welding slag, and observe whether there is virtual welding or welding slag short circuit on the original circuit board, so as to find the fault point as early as possible and save the overhaul time.