Soldering skills with electric soldering iron
Soldering is to solder the components that have passed the "test" to the printed circuit board or designated position as required. When welding, be sure to control the temperature of the soldering iron and the welding time. If the temperature is too low and the time is too short, the soldered tin surface will have burr-like tails, the surface will not be smooth, and may even look like tofu. It may be due to the lack of flux. After all evaporation, a certain amount of flux remains between the solder and the metal. After cooling, the solder and the metal surface are stuck to each other by the flux (rosin), and they can be pulled apart with a little force. This is the so-called false soldering.
Furthermore, when the temperature of the soldering iron is too low, you are eager to solder, and the tin on the solder joint melts very slowly. If the component to be soldered is in contact with the soldering iron for too long, excessive heat will be transferred to the component, causing the component to be soldered. Components are damaged (such as capacitor plastic melting, resistor resistance value changes due to heat, etc.), especially transistors, which will be damaged if the tube core is heated above 100°C. On the contrary, if the temperature of the soldering iron is too high and the welding time is too long, the solder surface will be oxidized and the solder flow will spread, resulting in insufficient solder in the solder joints. Only a small amount of solder will connect the component leads to the metal surface, and the contact resistance will be very low. If it is too large, it will break when pulled. This is the so-called virtual soldering. In severe cases, it will cause the copper foil strips of the printed circuit board to curl and fall off, and the components to be overheated and damaged. Whether the temperature of the electric soldering iron is suitable can be determined by experience based on the length of time the soldering iron tip takes to tin and the amount of solder attached to the tip. The length of welding time should ensure that the solder joints are smooth and bright, generally 2 to 3 seconds, and should not exceed 5 seconds for larger solder joints. When soldering consumable parts such as transistors, still use the same method as when tin plating. Use tweezers, needle-nose pliers, etc. to clamp the root of the pin to help dissipate heat.
In addition, the amount of solder should be appropriate. Do not use a large ball of solder to cover the solder joints. The outline of the lead can be vaguely distinguished from the tin surface of the solder joint. If it looks like a volcano from the side of the solder joint, it is a qualified solder joint. point. When welding with a hand-held electric soldering iron, do not rub the soldering surface back and forth or press hard with the soldering iron tip. In fact, as long as the contact area between the tinned part of the bevel of the soldering iron tip and the soldering surface is increased, the heat can be effectively directed from the soldering iron tip to the solder joint. part. It should be noted that after the soldering is completed and the soldering iron is removed, wait until the solder on the solder joints is completely solidified (4 to 5 seconds) before loosening the tweezers or hands holding the components. Otherwise, the leads of the soldered parts may come out or the surface of the solder joints may become loose. It looks like tofu dregs. After welding, if you find that the tail of the solder joint is pulled out, dip the tip of the soldering iron in the rosin and then repair the solder to eliminate it.
If there are dross edges and corners, it means that the welding time is too long, and the debris needs to be removed and welded again. The components on the printed circuit board should be suspended in the air before welding. There should be a 2-4mm gap between the component body and the circuit board surface and should not be close to the board surface. The transistor should be higher. For larger components, after inserting them into the holes of the circuit board, bend the leads 90° along the direction of the circuit copper foil strip as shown in Figure 6, leaving a length of 2mm and flatten it before welding to increase the firmness. When welding high input impedance devices such as integrated circuits, if the reliable connection between the soldering iron shell and the ground cannot be guaranteed, you can use the residual heat to weld after unplugging the soldering iron power plug. When welding a printed circuit board, you can also insert the resistor first, and after welding point by point, use offset pliers or nail clippers to cut off the excess length of the leads, then solder larger components such as capacitors, and finally solder them on. Vulnerable transistors, integrated circuits, etc. that are not heat-resistant.
