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The use of soldering iron power is too large, easy to burn components (generally diode, triode junction temperature of more than 200 degree will be burned) and make the printed wire from the substrate off; the use of soldering iron power is too small, solder can not be fully melted, flux can not be volatilized out of the soldering point is not smooth, not firm, easy to produce virtual welding. Generally, used for welding integrated circuits, printed circuit boards, CMOS circuits, decorative transistors, IC-type tape recorders, televisions, for general circuit experiments, generally 20W is appropriate, repair vacuum tube machines, such as gall bladder, old instruments, to 35W is appropriate, the external heat type is 45W, welding large transformer wiring, grounding trunks on the metal substrate, it is the use of the internal heat type 50W, external heat type 75W. If you want to weld metal materials, you should choose more than 100W external hot soldering iron. If the conditions allow, amateur radio enthusiasts can be equipped with a 2OW endothermic, a 35W endothermic or exothermic, a 150W exothermic soldering iron, so that basically meet the needs of a variety of welding.
We use the solder is generally divided into leaded and lead-free solder two kinds of solder, but the most commonly used is leaded solder, composition is 63% tin, lead 37%, melting point 183 degree : and lead-free solder composition is 99% tin, flux for about 1%, melting point 227 degree . Leaded solder has the advantage of low melting point, easy to weld, low price, but not environmentally friendly, lead is harmful to the human body, so after the completion of welding, must carefully wash their hands, in the welding process, it is best to wear a mask, or brightly lit places to ensure that the head and the weldment a certain distance. With the enhancement of people's awareness of environmental protection, now the machine welding in factories are using lead-free solder. Since the melting point of lead-free solder is higher, it is not difficult to understand why sometimes it is harder to melt the solder when repairing imported electrical appliances.
Soldering iron is a kind of electric heating device, can produce a high temperature of about 250 degree after energized. Soldering iron in the welding process, is actually a heat conduction process, in contact with the welding surface, the soldering iron head on the heat transfer to the solder, the solder absorbs the heat melting flow and under the action of surface tension, the formation of a bright rounded solder joint. In the welding heat conduction process, because the metal is a good conductor of heat, heat transfer faster. Solder melting process, due to the iron tip of the heat loss, its temperature are more or less down, if the soldering point area is larger, need to absorb more heat to make its above the solder to reach the melting point. If the soldering iron head volume is small, less heat storage, the temperature drops faster, due to the smaller power of the iron core to produce heat to supplement the loss of heat, the most intuitive phenomenon at this time is that the solder is not melted or melting is not complete. In this case, we have to choose high-power soldering iron for welding. On the contrary, if the welding piece is small, we do not need to choose a high-power soldering iron; if you use a high-power soldering iron, be sure to pay attention to the welding time, otherwise too much heat can easily cause the current flow through the road called circuit, circuit board damage, resulting in printed copper foil off. Specifically how high power soldering iron is appropriate, there is no specific quantitative requirements, maintenance personnel of the long-term work experience is the best way to choose the best way to suit their own soldering iron.
