Choosing and employing an electric soldering iron
1. External heat soldering iron
The structure of the external heating electric soldering iron is shown in Figure 2.10. It is composed of soldering iron tip, soldering iron core, shell, wooden handle, power lead, plug and other parts. Because the soldering iron head is installed inside the soldering iron core, it is called an external heating type electric soldering iron.
2. Internal heating soldering iron
The appearance and internal structure of the internal heating electric soldering iron are shown in Figure 2.11. The main part is composed of a iron head, a heater, a connecting rod, and a handle. Because its heating element is installed inside the cavity of the iron head, it is called internal heating type.
3. Selection of electric soldering iron
It can be seen from the previous speed that there are many types and specifications of electric soldering irons, and the sizes of the workpieces to be welded are different. Therefore, the rational selection of the power and type of electric soldering irons has a direct relationship with improving welding quality and efficiency. If the welding is too large and the power of the electric soldering iron used is small, the welding temperature is too low, the solder will melt slowly, the flux cannot volatilize, and the solder joints will not be smooth and firm. This will inevitably lead to unqualified welding strength and appearance quality, and even the solder cannot Melted, making welding impossible.
If the power of the electric soldering iron is too high, too much heat will be transferred to the tool to be welded, and the solder joints of the components will be overheated, causing damage to the components, or causing the copper foil of the printed circuit board to fall off, and the solder will be on the soldering surface. The flow was too fast to be controlled.
The correct selection of electric soldering iron can be considered from the following aspects:
1) When soldering integrated circuits, transistors and vulnerable components due to heat, a 20-watt internal heating type or a 25-watt external heating type electric soldering iron should be used.
2) When welding wires and coaxial cables, a 45-75 watt external heating soldering iron or a 50 watt internal heating soldering iron should be used.
3) When soldering larger components, such as the lead pins of output transformers, the lead pins of large electrolytic capacitors, the grounding pads of metal chassis, etc., an electric soldering iron of more than 100 watts should be used.
4. How to use the soldering iron
(1) How to hold the soldering iron
In order to make the weldment welded firmly without burning the surrounding components and wires, depending on the position and size of the welded piece and the size of the soldering iron, it is very important to properly select the grip of the soldering iron.
There are three types of holding methods for electric soldering irons, which are suitable for small-power electric soldering irons to weld parts with small heat dissipation, such as welding printed circuit boards of radios and TVs and their maintenance. Forehand grip. The electric soldering iron used in this method is relatively large and mostly has a curved soldering iron tip. The reverse grip method is to hold the handle of the soldering iron in the palm with five fingers. This method is suitable for high-power electric soldering iron welding parts with large heat dissipation.
(2) Treatment of new soldering iron before use
A new soldering iron cannot be used immediately. The tip of the soldering iron must be treated before it can be used normally. That is to say, the tip of the soldering iron should be coated with a layer of solder before use. The specific method is: first use a file to file the tip of the soldering iron into a certain shape as required, then connect the power supply, when the temperature of the tip of the soldering iron rises to the point where it can melt tin, apply rosin on the tip of the soldering iron, and then apply it after the rosin smokes. Apply a layer of solder, and do this two to three times, so that the surface of the soldering iron tip is completely covered with a layer of tin and it can be used.
When the soldering iron is used for a period of time, an oxide film will be formed on the blade surface of the soldering iron tip and its surroundings, which will make it difficult to "eat tin". At this time, the oxide film can be removed and re-plated with solder.
(3) Adjustment of the length of the soldering iron tip
After selecting the power of the soldering iron tip, it has basically met the needs of the soldering temperature, but it still cannot fully meet the needs of the components installed in the printed circuit board. For example, when welding integrated circuits and transistors, the temperature of the soldering iron tip should not be too high, and the time should not be too long. At this time, the length of the soldering iron tip inserted on the soldering iron core can be properly adjusted to control the temperature of the soldering iron tip.
(4) Selection of soldering iron tip
There are two types of soldering iron tips, straight and curved. When the pen grip method is adopted, the electric soldering iron with a straight tip is more flexible to use, and is suitable for soldering in circuits with many components. It is more suitable to hold the electric soldering iron with curved iron head, and it is mostly used for soldering when the circuit board is vertical to the desktop.
(5) Prevent "eating tin"
It is not easy to energize the soldering iron for a long time without using it, because it is easy to accelerate the oxidation of the soldering iron core and burn it out, and it will also cause the soldering iron tip to oxidize due to prolonged heating, and even be "burned to death" and no longer "eat tin".
(6) Replace the soldering iron core
When replacing the soldering iron core, be careful not to connect the leads incorrectly, because the electric soldering iron has three terminals, one of which is grounded, and the other two are connected to the two leads of the soldering iron core (these two terminals are directly connected to the 220 through the power cord. connected to a volt AC power supply). If the 220-volt AC power cord is wrongly connected to the binding post of the ground wire, the electric soldering iron shell will be charged, and it will also be charged when being welded, so that an electric shock accident will occur.
(7) Selection of flux
When soldering an electric soldering iron, it is best to use rosin flux to protect the soldering iron tip from corrosion. Zinc oxide and acidic solder oil are more corrosive to the soldering iron tip, which will shorten the life of the soldering iron tip, so they are not commonly used.
