Correct use of soldering iron in circuit repair
The soldering iron is an essential tool for electronic repair. The correct use method, precautions and tips for using the soldering iron in instrument circuit repair. To improve your soldering skills, you must first master how to use a soldering iron.
1. How to hold the soldering iron
①How to hold the pen
The pen holding method is suitable for electric soldering irons with low power and straight tip, and is suitable for welding parts to be welded with small heat dissipation, such as printed circuit boards in welding instruments. The pen holding method is the most commonly used method by instrument workers.
②Forward grip
The upright grip method is suitable for soldering irons with relatively large and curved tips. It can be used for welding when the circuit board is vertical to the desktop.
③Reverse grip
The reverse grip method is to hold the handle of the soldering iron in the palm of your hand with your five fingers. This method is suitable for high-power electricity, soldering iron, and welding parts that dissipate large heat.
2. Choose a soldering iron according to its purpose
When welding conventional components on printed circuit boards, such as diodes, transistors, resistor-capacitor components, and integrated circuits, a 20-30W internal heating soldering iron should be used. Due to the slow welding speed, it is recommended for novices to use 20W. When welding components with thick pins or large-area grounding points on printed circuit boards or power connectors, it is advisable to use a 45-75W soldering iron to ensure the firmness between the welded components and the printed circuit board or wires. Do not use a low-power electric soldering iron to weld the solder joints of large electronic components. Due to the rapid heat dissipation and rapid temperature drop of the soldering iron tip, solder accumulation will occur, which may appear to be soldered but is actually a weak solder. Using a high-power soldering iron to solder general electronic components on a printed circuit board will often burn the copper foil lines or electronic components.
3. Master the correct welding steps
The level of welding determines the stability and reliability of the instrument being repaired. Quality problems with small solder joints may cause the entire instrument or control system to fail to work properly, and the fault point is usually extremely hidden. Therefore, mastering the correct welding steps is the key to ensuring welding quality. Here is an introduction.
① Place the soldering iron tip at the pin of the component to be soldered, and heat the solder joint first. When the solder joint reaches the appropriate temperature, place the rosin solder wire on the solder joint in time to melt it.
②After the tin melts, the soldering iron tip should be moved slightly according to the shape of the solder joint so that the solder evenly covers the soldered joint and penetrates into the gaps on the soldered surface. After the appropriate amount of solder has melted, the solder wire should be removed quickly.
③When the solder joint is nearly full of solder, the flux has not completely evaporated, the temperature is appropriate, and the solder is the brightest and most fluid, move the soldering iron tip quickly along the direction of the component pins. When you are about to leave, quickly bring it back, and at the same time Leave the solder joint to ensure that the surface of the solder joint is bright, smooth and burr-free. Finally, use diagonal pliers to cut off the excessively long component pins until the component pins are slightly exposed to the solder joints.
The operation time of the above steps ①-② should be controlled within 2-3 seconds. Beginners usually take a long time to weld. Long heating time may cause the copper foil on the printed circuit board to be damaged beyond repair. Step ③ plays a decisive role in the quality of the solder joints, and you need to practice more to understand its essentials.
4. How to protect the soldering iron tip
Before using a newly purchased electric soldering iron, the soldering iron tip needs to be tinned. For copper soldering iron tips, you can use sandpaper or a file to polish the soldering iron tip first. The color of the soldering iron tip will change after a few minutes of being connected to the power supply, indicating that the soldering iron is hot. Wait until the soldering iron tip is heated. When the temperature rises to the melting point of the solder, use it to dip the rosin solder wire. The surface of the soldering iron tip will be dipped in a layer of bright tin, and the soldering iron tip can be used. If the soldering iron tip is not dipped in tin, it will not be tinned during soldering, and it is impossible to solder.
The soldering iron tip must be kept clean. An unclean soldering iron tip will quickly oxidize and become unable to absorb tin. Over time, it will cause corroded pits on the soldering iron tip, making the welding work more difficult. If the soldering iron is left in the soldering state for a long time and the temperature is too high, it will also cause the soldering iron head to "burn out". When not welding, turn off the power supply of the soldering iron immediately. The oxides and carbides derived from the residual flux on the soldering iron tip will damage the soldering iron tip and reduce its thermal conductivity. Therefore, you should always clean the soldering iron tip with a temperature-resistant wet sponge to prevent damage to the soldering iron tip. After each use, the soldering iron tip should be wiped clean and dipped in a layer of tin to protect the soldering tip.
