Causes and Solution to Cold solder joints of Components
During the soldering of electronic components, the solder seems like being successful on the surface of the solder joint, but in fact, it is not soldered firmly. Sometimes, the lead wire can be pulled out from the solder joint even by hand. Definitely,this is called dry joints or cold solder joints..
Inspection Methods of cold solder joint
1. Look: Use a magnifying glass with a high magnification to examine the bottom of the circuit board carefully. Pay more attention to components with high power and large heat generation, such as high-power resistors, three-terminal voltage regulators, transistors, chips, the power pins of integrated blocks, and the output pins of field blocks, the terminal posts of deflection coil lead-out wires, etc.Don't worry, Most of the faults can be solved by re-soldering.
2. Knock: Knock on each circuit board and plug-in box gently with a wooden stick after turning on the power.If there is a response,we can determine whether the problem lies in the power board, the scanning board, the signal board, or the plug-in box roughly.
3. Shake: After finding out where is the problem, you can shake each component gently with a wooden stick after turning on the power, and we will see which component is loose. If none of above three methods work, you have to find the circuit diagram of the device and check the DC potential of each channel carefully according to the circuit diagram to determine where the problem is. But it depends on lot of dealing experience.
Causes of Cold solder joint
1. Poor quality of solder;
2. Poor reducibility or insufficient amount of flux;
3. The soldered surface is not cleaned in advance, and the tin layer is not firm;
4. The temperature of the soldering iron tip is too high or too low, and there is an oxide layer on its surface;
5. The soldering time is too long or too short ,which is not well controlled;
6. During soldering, the solder has not solidified completely.
7. The pins of components are oxidized.
Methods to Solve Cold solder joint
1. Distribute the thimbles EVENLY to make the amount of tin even. At the same time, PLEASE confirm whether the printed scraping blade is deformed or worn, and replace the defective scraping blade on time.
2. Use the point-by-point calibration method to calibrate the mounting position of components as that they are mounted in the middle of the copper foil.
3.The deformed scraping blade needs to be reshaped before mounting. Please contact the IQC and ask the supplier to improve the oxidized components.
4. Increase the temperature and time appropriately in the re-flow preheating zone to make them fully welded.
5. Strictly control the time from printing to re-flow, and try to adopt integrated production as much as possible to reduce the direct and long-time contact of the solder with air after printing.
6. Replace the expired solder.
