PCBA Tech - Soldering technology of electric soldering iron in PCB

1. Types and power of soldering irons commonly used in PCB circuit boards

Commonly used electric soldering irons are divided into internal heating type and external heating type. The soldering iron head of the internal heating type electric soldering iron is outside the heating wire, and this electric soldering iron heats up quickly and is light in weight. The soldering iron tip of the external heating electric soldering iron is inserted into the heating wire. Although it heats slowly, it is relatively strong.

The electric soldering iron is directly heated by 220V AC power supply. The power cord and the shell should be insulated, and the resistance between the power cord and the shell should be greater than 200MΩ.

Electronic hobbyists usually use 30W, 35W, 40W, 45W, 50W soldering irons. The electric soldering iron with higher power has lower electric resistance. Ohm's law derived formula: R=U/I=U2/P.

2. Precautions for the use of soldering iron

(1) Before using the newly bought soldering iron, it must be dipped in a layer of tin (power on the soldering iron, and then use the tin bar to approach the tip of the soldering iron when the soldering iron is heated to a certain level). File bright, then heat up with electricity, and dip the soldering iron tip with a little rosin. When the rosin is smoking, tin it so that the surface of the soldering iron tip is plated with a layer of tin first.

(2) The temperature of the soldering iron can be as high as 250 degrees Celsius after it is energized. It should be placed on the soldering iron stand when not in use, but the power supply should be cut off when it is not used for a long time to prevent the soldering iron tip from being burnt due to high temperature (oxidation). It is necessary to prevent the electric soldering iron from damaging other components, especially the power cord. If the insulation layer is burned by the soldering iron, carelessness will easily lead to safety accidents.

(3) Do not subject the electric soldering iron to strong vibrations, so as not to break the heating wire or lead wire inside the electric soldering iron and cause malfunctions.

(4) After the soldering iron is used for a period of time, tin scale may remain on the tip of the soldering iron. When the soldering iron is heated, we can use a damp cloth to lightly sassafras. If there are pits or oxidized blocks, apply a fine-grained file to repair the tin again. After using it for a long time, the tip of the soldering iron will be shortened to a certain extent, and the tip of the soldering iron must be replaced.

2. Welding technology

The welding technology mentioned here refers to the fusion between metal conductors and solder commonly used in the production of electronic circuits. The solder is a lead-tin alloy (Pb-Sn) with a melting point of about 183 degrees. Commercial solder is often made into strips or filaments, and some solders also contain rosin, which is more convenient to use.

1. How to hold an electric soldering iron

There are usually two ways to hold an electric soldering iron: a pen and a fist.

(1) The method of holding a pen. Suitable for lightweight soldering irons such as 25-50W internal heating type. Its soldering iron tip is straight, and the tip is filed into a bevel or conical shape, which is suitable for soldering small pads.

(2), fist method. It is suitable for high-power soldering irons. We generally do not use high-power soldering irons for electronic production (not introduced here).

2. Several methods of soldering leads on the PCB printed circuit board.

Printed circuit boards are divided into two types: single-sided and double-sided. The through-holes on it are generally non-metallized, but in order to make the components welded on the circuit board more solid and reliable, the PCB through-holes of electronic products are mostly metalized (double-sided). The method of welding the lead wire on the ordinary single board:

(1) Straight-through cutting head. The lead passes directly through the through hole. During soldering, an appropriate amount of molten solder will evenly surround the tin-dipped lead on the top of the pad to form a cone shape. After it has cooled and solidified, cut off the excess lead.

(2) Directly bury your head. The leads passing through the through holes are only exposed to an appropriate length, and the molten solder bury the lead heads in the solder joints. This kind of solder joint is approximately hemispherical. Although it is beautiful, special care should be taken to prevent false soldering.

3 Prevent poor welding

Welding technology is a basic technology that radio enthusiasts must master, and it takes a lot of practice to master it. 1. Choose suitable solder, and use low melting point solder wire for soldering electronic components. 2. Flux, use 25% rosin dissolved in 75% alcohol (weight ratio) as a flux. 3. The electric soldering iron should be tinned before use. The specific method is: heat the electric soldering iron, and when the solder can just be melted, apply the flux, and then apply the solder evenly on the tip of the soldering iron to make the tip of the soldering iron evenly eaten. One layer of tin.

4. The soldering method, polish the PCB pads and component pins with fine sandpaper, and apply flux. Dip a proper amount of solder with the tip of a soldering iron and touch the solder joints. After the solder on the solder joints are all melted and immersed in the component leads, the soldering iron tip is gently picked up along the pins of the component and away from the solder joints.

5. The soldering time should not be too long, otherwise the components will be easily burned. If necessary, use tweezers to clamp the pins to help dissipate heat. 6. The solder joints should be in the shape of sine wave peaks (steamed buns), and the surface should be bright and smooth, free of tin thorns, and a moderate amount of tin. 7. After the soldering is completed, use alcohol to clean the residual flux on the circuit board to prevent the carbonized flux from affecting the normal operation of the circuit.

8. The integrated circuit should be soldered last, and the electric soldering iron should be grounded reliably, or the residual heat should be used for welding after power failure (MOS digital integrated circuit). Or use dedicated sockets for integrated circuits, and then plug in the integrated circuits after soldering the sockets.

9. The electric soldering iron should be placed on the soldering iron stand