Process and precautions for manual welding of SMD components

Date：2022-03-17 15:32:00Views：1354

To weld the patch components on the self-made PCB board, similarly, two pads of the patch components should be made on the PCB board, which is the same as the factory processed PCB board. The welding of SMT chip mounted components should use 200 ~ 280 ℃ temperature regulating pointed soldering iron.

The substrates of chip mounted resistors and capacitors are mostly made of ceramic materials, which are easy to crack due to collision. Therefore, the skills of temperature control, preheating, light touch and so on should be mastered during welding. Temperature control means that the welding temperature should be controlled at about 200 ~ 250 ℃. Preheating refers to preheating the elements to be welded in an environment of about 100 ℃ for 1 ~ 2 minutes to prevent sudden thermal expansion and damage of the elements. Light touch means that the soldering iron head should first heat the solder joint or guide belt of the printed board, and try not to touch the components. In addition, the welding time should be controlled at about 3 seconds each time. After welding, let the circuit board cool naturally at room temperature. The above methods and techniques are also applicable to the welding of SMD crystal diodes and triodes.

The number of pins of SMD IC is large, the spacing is narrow and the hardness is small. If the welding temperature is improper, it is very easy to cause faults such as short circuit of pin solder, false soldering or separation of printed circuit copper foil from printed board. When disassembling the chip integrated circuit, adjust the temperature of the temperature regulating soldering iron to about 260 ℃, suck all the soldering tin of the integrated circuit pin with the soldering iron head and the tin suction device, gently insert it into the bottom of the integrated circuit with pointed nose tweezers, heat it with the soldering iron, and gently lift the integrated circuit pins one by one with tweezers to gradually separate the integrated circuit pins from the printed board. When lifting the integrated circuit with tweezers, it must be carried out synchronously with the heated part of the soldering iron to prevent damage to the circuit board.

Before replacing with a new integrated circuit, all the solder left by the original integrated circuit shall be removed to ensure the flatness and cleanness of the pad. Then polish and clean the pins of the integrated circuit to be welded with fine sandpaper and tin them evenly. Then align the pins of the integrated circuit to be welded with the corresponding solder joints of the printed board. During welding, gently press them on the surface of the integrated circuit by hand to prevent the integrated circuit from moving. With the other hand, operate the electric soldering iron and dip an appropriate amount of solder to weld and fix the pins at the four corners of the circuit with the circuit board, Check and confirm the model and direction of the integrated circuit again, and then conduct formal welding. Adjust the temperature of the soldering iron to about 250 ℃. One hand holds the soldering iron to heat the integrated circuit pins, and the other hand sends the soldering wire to the heating pins for welding until all the pins are heated and welded. Finally, carefully check and eliminate the short circuit and false welding of the pins. After the solder joint cools naturally, Clean the circuit board and solder joint again with a brush dipped in anhydrous alcohol to prevent welding slag.

Before troubleshooting the module circuit board, it is advisable to clean the printed board with a brush dipped in anhydrous alcohol, remove the dust, welding slag and other sundries on the board, observe whether the original circuit board has false welding or welding slag short circuit, and find the fault point early to save maintenance time.

Precautions for manual welding of SMD components

When welding, the temperature setting of electric soldering iron is very important. The suitable welding temperature is to make the melting point of solder temperature h on the solder joint to about 50 ℃. Due to the size of the welding object, the power and performance of the electric soldering iron, the type and model of solder, when determining the temperature of the soldering iron head, it is also necessary to increase 100 ° C on the basis of K said temperature.

① When welding or removing the following components, the temperature of the electric soldering iron shall be set to 250 ℃, 1206 to all SMT resistance, capacitance and inductance components in the factory. All resistor bars, inductor bars and capacitor bars. SMD with area less than 5mm x 5mm (including pin length) and less than 8 pins.

② The welding temperature of the above components is set at 350-370 ℃. When overhauling SMT circuit board, if there are no good welding conditions, silver paste conductive adhesive can also be used to bond the solder joints of components. This method avoids the heating of components and is simple to operate, but the connection strength is poor.

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