The common ways to utilize an electric soldering iron and how to troubleshoot them
A. The soldering iron does not heat up after being powered on:
Measure the two ends of the plug with the ohm block of the multimeter to check whether there is an open circuit fault;
If there is no plug open circuit fault, then use a multimeter to measure the lead wires at both ends of the soldering iron core. If the needle does not move, replace it with a new soldering iron core;
If the resistance value of the two lead wires of the soldering iron core is about 2.5KΩ, it means that the soldering iron core is intact, it is very likely that the lead wires are broken, and the joint in the skewer is disconnected.
B. The tip of the soldering iron is charged
The power line is wrongly connected to the terminal of the grounding line;
The power cord falls off from the soldering iron core connection screw and then hits the grounding wire screw, causing the soldering iron head to be electrified;
Leakage caused by winding of power lead wires; leakage of power ground wire itself.
C. The tip of the soldering iron does not "eat" tin
After the iron tip is used for a long time, it will not "eat" tin due to oxidation, and a new soldering iron tip should be replaced;
The tip of the soldering iron does not heat up and does not eat tin. For the solution, please refer to "The soldering iron does not heat up after being energized".
4. Welding operation essentials
A. Preparation before welding
Materials: including direct materials and auxiliary materials, pay attention to whether the welding components have polarity requirements, whether the component feet are oxidized, oily, etc., and whether there are special requirements for welding temperature and time during welding;
Tools and utensils: depending on the welding components, there should be tin wire holders, component boxes, welding torches, soldering stations, tweezers, cutting pliers, etc. If there are anti-static requirements, anti-static tools and appliances should be used, and the operator should wear an anti-static wrist strap;
B. Implement welding
Prepare solder wire and soldering iron tip, and keep the soldering iron tip clean;
Heating the weldment (heating component feet and pads at the same time);
Melting solder: When the weldment is heated to a temperature that can melt the solder, put the tin wire on the solder joint, and the solder begins to melt and wet the solder joint;
After adding the appropriate solder to the solder joint, remove the tin wire;
When the solder has completely wetted the joint, remove the soldering iron at a roughly 45° angle.
The above process is completed in about 2 to 3 seconds for general solder joints. It should be noted that the connected components should not be shaken before the solder is completely solidified to avoid false soldering.
C. Treatment after welding
After soldering, check for missing soldering, wrong soldering (reversed polarity soldering), short circuit, virtual soldering, etc., and clean up residues on the PCBA such as: tin slag, tin chips, component feet, etc.
5. Welding of several vulnerable components
A. Welding of cast shell components
Electronic components made of thermoplastic. Such as micro-switches, connectors, etc., which cannot withstand high temperatures, if the heating time is not controlled, it is easy to cause plastic deformation, resulting in component failure or performance degradation, resulting in hidden failures. Therefore, the following items should be paid attention to when actually welding such components:
Tin the component feet in advance to facilitate soldering and shorten the soldering time;
When soldering, it is necessary to weld one foot by one foot to shorten the heating time of the component feet;
The tip of the soldering iron must not exert pressure on the component feet;
It is more appropriate to choose tin wire with a small amount of flux, and the diameter of the tin wire is ф0.6-0.8mm;
Do not touch the components before the plastic case is cold.
B, FET and integrated circuit welding
MOSFET, especially the insulated gate type component, because of its high input impedance, a little carelessness can cause its internal breakdown and fail. Bipolar integrated circuits, due to the high internal integration, but the tube isolation layer is very thin, and it is easily damaged once it is subjected to excessive heat. None of the above types of circuits can withstand a temperature of 250°C. Therefore, the following items should be paid attention to when welding:
The welding time should not exceed 3 seconds, and should be as short as possible under the premise of ensuring wetting;
Use anti-static constant temperature soldering iron, the temperature is controlled at 230 ° C ~ 250 ° C;
The power of the electric soldering iron should not exceed 20W for the internal heating type and 30W for the external heating type;
If the integrated circuit does not use a socket, when it is directly soldered to the PCB board, the safe welding sequence is ground terminal → output terminal → power terminal → input terminal.
