How do you understand the soldering of electric soldering iron
Welding is the process of soldering qualified components to a printed circuit board or designated location as required. When welding, it is necessary to control the temperature and welding time of the electric soldering iron. If the temperature is too low or the time is too short, the tin surface will have a burrs like tail, the surface will not be smooth, and even appear like tofu residue. It is possible that due to the incomplete evaporation of the soldering flux, there is a certain amount of flux left between the soldering tin and the metal. After cooling, the soldering flux (rosin) will stick the soldering tin to the metal surface, and it can be pulled open with a little force, which is called false soldering.
Furthermore, when the temperature of the electric soldering iron is too low, it is urgent to weld it. The tin on the soldering point melts slowly, and the soldered components come into contact with the soldering iron for too long, which can cause excessive heat to be transmitted to the components, causing damage to the components (such as melting of capacitor packaging, changing of resistor resistance due to thermal resistance, etc.), especially for transistors. When the tube core is heated above 100 ℃, it will be damaged.
On the contrary, if the temperature of the electric soldering iron is too high and the welding time is slightly longer, it will cause oxidation of the solder surface, the solder flow will be scattered, and the solder joint will not eat enough tin. Only a small amount of solder will connect the component leads to the metal surface, causing high contact resistance and breaking when pulled, which is called virtual soldering. In severe cases, it can also cause the copper foil strip on the printed circuit board to curl and fall off, and the components to be damaged due to overheating.
Whether the temperature of an electric soldering iron is suitable can be determined based on experience based on the length of soldering time of the soldering iron head and the amount of solder attached to the head. The length of welding time should ensure that the solder joints are smooth and bright, usually for 2-3 seconds, and larger solder joints should not exceed 5 seconds. Soldering transistors and other vulnerable parts, still like when tinning, uses tweezers, pointed nose pliers, etc. to clamp the root of the pins to help dissipate heat.
In addition, the amount of solder used should be appropriate, and a large ball of solder should not be used to paste the solder joint. The outline of the lead can be vaguely distinguished from the tin surface of the solder joint, and the volcanic shape seen from the side of the solder joint is a qualified solder joint. When welding with a handheld electric soldering iron, do not use the soldering iron head to rub the welding surface back and forth or forcefully touch and press. In fact, as long as the contact area between the tin plated part of the soldering iron head and the welding surface is increased, heat can be effectively transferred from the soldering iron head to the welding point.
It should be noted that after removing the soldering iron after welding, wait until the solder on the solder joint is completely solidified (4-5 seconds), and then loosen the tweezers or hands that fix the components. Otherwise, the solder lead may come out or the surface of the solder joint may appear like tofu residue. After welding, if the tail of the solder joint is pulled out, dip it in the rosin with an electric soldering iron tip, and then repair welding to eliminate it. If there are slag edges and corners, it indicates that the welding time is too long, and it is necessary to remove impurities before re welding.
The components on the printed circuit board should be suspended and welded, with a gap of 2-4mm between the component body and the circuit board surface. They should not be tightly attached to the board surface, and the crystal transistor should be higher. For larger components, after inserting them into the circuit board hole, the lead wire can be bent 90 ° along the direction of the circuit copper foil strip as shown in Figure 6, leaving a length of 2mm to be flattened and welded to increase firmness. Welding high input impedance devices such as integrated circuits, if it is not possible to ensure reliable connection between the electric soldering iron shell and the ground, can be achieved by unplugging the electric soldering iron power plug and using residual heat welding.
When welding printed circuit boards, it is also possible to insert resistors first, weld them point by point, and then cut off excess length of leads using side cutters or nail clippers. Then, solder larger components such as capacitors, and finally solder heat-resistant and vulnerable crystal transistors, integrated circuits, etc.
