Electric soldering iron power selection Electric soldering iron power size difference
In the electrical repair process, the electric soldering iron is an indispensable tool, but many maintenance personnel who have just come into contact with the soldering iron do not know what standard is used to select the power of the electric soldering iron during the welding process, and they often go all over the world with a single soldering iron. The most direct consequence is that the welding effect is not ideal due to carelessness in selecting the power of the soldering iron.
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 solder cannot Fully melted, the flux cannot be volatilized, the solder joints are not smooth and firm, and it is easy to produce false soldering. 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.
35W is suitable for power amplifiers and old-style instruments, and 45W for external heating. For the wiring of large transformers and the grounding trunk line on the metal base plate, use 50W for internal heating and 75W for external heating. 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 20W internal heating type, - - a 35W internal heating or external heating type, - 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 tin 99 %, 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. 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 welding process of the electric soldering iron, it is actually a process of heat conduction. When it contacts the welding surface, the heat on the soldering iron tip is transferred to the solder. solder joints. 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 tip of the soldering iron, its temperature drops 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 melts incompletely. In this case, we have to use a high-power soldering iron for welding. On the contrary, if the weldment is small, we don't need to use a high-power soldering iron; if you use a high-power soldering iron, you must pay attention to the soldering time, otherwise too much heat will easily cause the circuit through which the current flows, and damage the circuit board , 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 accumulation of long-term work experience of maintenance personnel is the best way to choose a soldering iron that suits you.
Explain two common problems again, let us understand the principle of weldment more deeply. First of all, why use flux (such as rosin), in fact, to put it bluntly, the purpose of using flux is to prevent false soldering. The most direct function of flux is to make the solder easy to flow. A tiny hole; In addition, the flux also has the effect of removing the oxide layer on the surface of the weldment. Of course, some fluxes are corrosive (such as solder paste) and should be used with caution. In order to improve the welding effect and ensure the quality, rosin is added to the finished solder wire, which is more convenient to use.
