The many electric soldering irons and their power options
The power of the electric soldering iron used is too large, it is easy to burn the components (generally, when the junction temperature of the diode and triode exceeds 200°C, it will burn out) and the printed wires will fall off the substrate; the power of the soldering iron used is too small, and the soldering tin cannot be fully Melting, the flux cannot volatilize, the solder joints are not smooth and firm, and it is easy to produce false welding. Generally, it is used for welding integrated circuits, printed circuit boards, CMOS circuits, decoration transistors, IC recorders, TV sets, for ordinary circuit experiments, generally 20W is appropriate, and for repairing vacuum tube machines, such as amplifiers and old instruments. , 35W is appropriate, and the external heating type is 45W. The wiring of the welding large transformer and the grounding trunk line on the metal base plate are 50W for the internal heating type and 75W for the external heating type. If you want to weld metal materials, you should use an external heating electric soldering iron above 100W. If conditions permit, amateur radio enthusiasts can be equipped with a 2OW internal heating type, a 35W internal or external heating type, and a 150W external heating type electric soldering iron, so that it can basically meet various welding needs.
The solder we use is generally divided into two types: leaded solder and lead-free solder, but the most commonly used is leaded solder, which has a composition of 63% tin, 37% lead, and a melting point of 183°C; while the composition of lead-free solder is 99% tin , The flux is about 1%, and the melting point is 227°C. Lead solder has the advantages of low melting point, easy soldering, and low price, but it is not environmentally friendly, and lead is harmful to the human body, so after soldering, you must wash your hands carefully. During the soldering process, it is best to wear a mask or place with bright light to ensure A certain distance between the head and the weldment. With the enhancement of people's awareness of environmental protection, lead-free solder is now used for machine welding in factories. Due to the high melting point of lead-free solder, it is not difficult to understand why it is sometimes difficult to melt the solder when repairing imported electrical appliances.
The electric soldering iron is an electric heating device, which can generate a high temperature of about 250°C after being energized. During the soldering process of the electric soldering iron, it is actually a process of heat conduction. When it contacts the soldering surface, the heat on the soldering iron tip is transferred to the solder. The solder absorbs the heat and melts and flows to form a bright and round solder joint under the action of surface tension. . In the process of welding heat conduction, since metals are good conductors of heat, the heat transfer is faster. During the melting process of the solder, due to the heat loss of the soldering iron tip, its temperature will drop more or less. If the solder joint has a large area, it needs to absorb more heat to make the solder on it reach the melting point. If the soldering iron tip is small in size and stores less heat, the temperature drops faster, and the heat generated due to the small power of the soldering iron core is too late to replenish the lost heat. At this time, the most intuitive phenomenon is that the solder does not melt or does not melt completely. In this case, we have to use a high-power soldering iron for welding. On the contrary, if the welded parts are small, we don't need to use high-power soldering iron; if we use high-power soldering iron, we must pay attention to the welding time, otherwise too much heat will easily cause the circuit through which the current flows, and the circuit board will be damaged. , causing the printed copper foil to fall off. The specific power of the soldering iron is suitable, and there is no specific quantitative requirement. The long-term work experience accumulation of maintenance personnel is the best way to choose a soldering iron that suits you.
