A guide to help you choose a soldering iron
(1) Selection of soldering iron types
1. Internal heating soldering iron. Internally heated soldering irons have a simple structure, high thermal efficiency, are lightweight and flexible, and are the first choice. It consists of a connecting rod, a handle, a spring clip, a soldering iron core, and a soldering iron tip (also called a copper tip). The soldering iron core is installed inside the soldering iron head. The soldering iron core is made of nickel-chromium resistance wire wound on a porcelain tube. Generally, the resistance of a 20W soldering iron is about 2.4kΩ, and that of a 35W soldering iron is about 1.4kΩ.
2. External heating soldering iron. This kind of electric soldering iron has complex manufacturing process, low efficiency and high price. It is generally composed of a soldering iron head, a soldering iron core, a shell, a handle, a plug and other parts. The soldering iron tip is installed in the soldering iron core and is made of copper alloy material with copper as the base with good thermal conductivity.
The length of the soldering iron tip can be adjusted (the shorter the soldering iron tip, the higher the temperature of the soldering iron tip). Commonly used in practice are chisel, pointed cone, round surface, round, pointed cone and semi-circular groove shapes to adapt to the needs of different welding surfaces.
3. Constant temperature soldering iron. A magnet-type temperature controller is installed in the soldering iron head to control the power-on time, which is a constant temperature electric soldering iron. When welding components whose temperature should not be too high and whose welding time should not be too long, a constant-temperature soldering iron should be used, but it is expensive. Although the automatic constant temperature electric soldering iron has many parts, is difficult to maintain, and is expensive, it can ensure the quality of solder joints, especially when doing circuit experiments and repairing a large number of printed boards, and it works very well. The electric soldering iron used on the production line adopts the method of automatic voltage regulation and constant temperature, and the cost may be lower. In some areas, the mains power is unstable, and the soldering iron often burns without being dipped in tin, or the temperature is not enough to prevent soldering. In order to ensure the quality of soldering, the only option is to use an automatic constant temperature series soldering iron, or configure a voltage regulating system. If the temperature is just too high, a series of step-down resistors will do.
The picture shows a constant temperature soldering iron
4. Soldering iron. The desoldering iron is a desoldering tool that integrates a piston type desoldering device and an electric soldering iron. It is easy to use, flexible, and has a wide range of applications. The disadvantage is that you can only desolder one solder joint at a time.
5. Gas soldering iron. It is a soldering iron that uses liquefied gas, methane and other flammable gases to burn and heat the soldering iron tip. You can choose to use it in situations where power supply is inconvenient or AC power cannot be supplied. Due to the risk of explosion, this article does not discuss the purchase of this type of soldering iron.
(2) Soldering iron power selection
If the power of the soldering iron is too high, it is easy to burn the components (usually the junction temperature of the diode and transistor exceeds 200°C) and cause the printed wire to fall off the substrate; if the power of the soldering iron is too small, the solder cannot be fully melted. , the flux cannot evaporate, 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 radios and recorders, and televisions. It is generally used for ordinary circuit experiments. Generally, 20W is suitable for repairing vacuum tube machines, such as tube amps and old instruments. , 35W is suitable, and external heating type is 45W. For welding large transformer wiring and grounding trunk lines on metal base plates, internal heating type 50W and external heating type 75W are used. There are also some occasions with higher power.
There are various shapes of soldering iron tips. The key points of selection are that they can always maintain a certain amount of solder, can quickly and effectively melt the solder on the joints, and do not produce false solder, soldering, or hanging tin. The solder joints have no burrs and are not burned. Boards and components. If the solder joints on the machine are new and bright, the soldering iron tip can have a larger tinned cross section and use a flat or oval tip, which can transfer heat quickly and operate smoothly. The oxide layer on the tin surface is thicker, and the soldering iron tip should be relatively pointed to facilitate breakthrough.
The density of components is high, so it is necessary to use correspondingly tapered ferroalloy heads to avoid burns and soldering. When assembling and disassembling IC blocks, special-shaped soldering iron tips are often used. Sometimes, because it cannot be soldered and to avoid burning plastic parts, a curved soldering iron tip is used. Of course, it also depends on everyone's operating habits and hobbies.
(3) How to choose a soldering iron
1. Selection according to the heating mode of electric soldering iron
(1) Selection of internal heating type and external heating type: Under the same power, the temperature of internal heating type soldering iron is higher than that of external heating type soldering iron.
(2) When low-temperature welding is required, a voltage regulator should be used to control the temperature of the soldering iron. The temperature of the soldering iron is closely related to the power supply voltage. In actual use, the temperature of the soldering iron is often reduced by lowering the power supply voltage.
(3) Control the temperature by adjusting the extension length of the soldering iron tip.
(4) The main methods to stabilize the temperature of the soldering iron are as follows: install a regulated power supply to prevent changes in the power supply network; maintain a certain volume, length and shape of the soldering iron tip; use a constant-temperature soldering iron; keep the indoor temperature constant; avoid natural wind Or electric fan, etc.
2. Choose according to the power of the soldering iron
(1) When welding low-power RC components, transistors, integrated circuits, printed circuit board pads or plastic wires, it is advisable to use a 30~45W external heating or 20W internal heating soldering iron. It is best to use a 20W internal heating soldering iron for the application.
(2) When welding the welding points of general structural products, such as wire rings, wire claws, heat sinks, grounding soldering lugs, etc., a 75~100W electric soldering iron should be used.
(3) For large solder joints, such as welding metal frame tabs, soldering lugs, etc., a 100~200W electric soldering iron should be used.
