Stuck boards are a common fault phenomenon in the production practice of electronic assembly (PCBA) manufacturing reflow soldering process. But for vacuum reflow soldering, the impact of stuck boards is much greater than that of ordinary reflow soldering. In this article, we will introduce why the stuck boards occurs in vacuum reflow soldering? How to avoid it? What precautions need to be taken?
Reasons for stuck boards
The phenomenon of stuck board refers to the fact that during the welding process, electronic components or PCB boards cannot move normally on the welding platform, resulting in poor welding or unstable welding quality. The main causes of the stuck board phenomenon are as follows:
1. Uneven welding platform: The surface of the welding platform is uneven or has a raised part, which will cause electronic components or PCB to be stuck on it and cannot be moved.
2. There are pollutants on the surface of the welding platform: There are pollutants such as oil and dust on the surface of the welding platform, which will also cause electronic components or PCB boards to be stuck on it and cannot be moved.
3. The temperature of the welding platform is too high: The temperature of the welding platform is too high, which will increase the adhesion between the electronic components or PCB board and the welding platform, resulting in the phenomenon of stuck board.
4. Insufficient vacuum of the welding platform: vacuum reflow soldering needs to be carried out under a certain vacuum degree, if the vacuum degree is insufficient, the adhesion between the electronic components or PCB board and the welding platform will increase, resulting in stuck board.
Consequences of stuck boards
In the reflow soldering process, the board is stuck and will cause the circuit board reflow time to be too long, which will affect the circuit board as follows:
First, the temperature is too high to damage the component, resulting in shortened component life.
Second, the PCB will soften when it exceeds the TG temperature, the higher the temperature, the more severe the softening, the more serious the deformation, and the higher the possibility of virtual soldering, offset, drop-off, circuit board bubbles and other undesirable phenomena.
Third, the more serious the oxidation is over time, the darker and blacker the solder joint, and the more empty the solder joint. The most serious defect is that if the reflux time is too long at high temperature, it may cause fire.
Treatment method for Reflow soldering stuck boards
1. If boards stuck occurs, do not send the board into the furnace again;
2. Open the furnace lid as soon as possible and take out the plate;
3. Find out the cause and take measures;
4. After the temperature reaches the requirements, continue welding.
If there is an alarm, the welding should be stopped immediately, check the cause of the alarm and deal with it in time.
1. In reflow soldering, if the power fails, do not send the plate into the furnace again. With the support of UPS backup power, mesh belts and chain guides will continue to operate. After the surface mount plates are run to the furnace mouth, remove all surface mount plates, open the furnace lid, and stop after cooling.
2. In unexpected situations, such as UPS failure, the motor square axis at the exit should be clamped with a live wrench to rotate and transfer the PCB from the furnace as soon as possible.
Precautions for reflow soldering stuck boards
In order to avoid the occurrence of stuck plates, the following precautions can be taken:
1. Keep the welding platform flat: Before using the welding platform, check whether its surface is flat, and trim it in time if there is a protruding part.
2. Keep the welding platform clean: Before using the welding platform, its surface should be cleaned to avoid the presence of pollutants such as oil and dust.
3. Control the temperature of the soldering platform: When soldering, the temperature of the soldering platform should be controlled to avoid excessive temperature leading to increased adhesion between electronic components or PCB boards and the soldering platform.
4. Improve the vacuum degree: When vacuum reflow soldering, it should be ensured that the vacuum degree of the welding platform meets the requirements to avoid the occurrence of stuck plates caused by insufficient vacuum.
5. Use appropriate welding process: When selecting the welding process, the appropriate welding process should be selected according to the characteristics of electronic components and PCB boards to avoid the occurrence of stuck board phenomenon caused by excessive soldering or insufficient welding.
Preparation and inspection before stuck boards
1. Check whether the power supply is a three-phase five-wire power supply with specified rated voltage and rated current.
2. Check whether the main power supply is connected to the machine.
3. Check whether the equipment is well grounded.
4. Check whether there are any irrelevant debris left in the electric control box, and whether the wiring sockets in the electric control box are well plugged in.
5. Check whether the emergency brake switch located at the exit and entrance end is up.
6. Check whether the UPS is working normally.
7. Ensure that the exhaust duct at the inlet and outlet of the reflow soldering machine are movably connected with the main ventilation duct of the factory.
8. Check the lubrication of each rotating shaft bearing.
9. Clean up the furnace cavity and do not put anything other than the workpiece into the machine.
Conclusion
In summary, the phenomenon of stuck plates is a common problem in vacuum reflow soldering, but it can be avoided by taking appropriate precautions. In actual production, attention should be paid to details to ensure the flatness, cleanliness and temperature control of the welding platform, and to ensure that the vacuum degree meets the requirements to improve welding quality and production efficiency.
