The principle and treatment method of PCB green oil foaming and circuit board foaming after reflow soldering
2026-03-11
In the circuit board of some electronic companies, it is often found that the PCB does not have any blistering phenomenon before soldering, but after soldering, it is found that the surface of some PCB boards is green and oily, what is the reason for this, is there a problem with the board or the soldering process? The main reasons for the green oil bubbling on the board surface are as follows:
1. The green oil quality of the circuit board itself is not good, the temperature limit value that can withstand is low, and there are phenomena such as blistering when welding at high temperatures;
2. Some additives that can destroy the solder mask are added to the flux;
3. The temperature of the tin liquid or preheating temperature is too high during soldering, which exceeds the temperature range that the solder mask of the circuit board can withstand, causing green oil bubbles.
4. After defects occur in the welding process, repeated welding will also cause undesirable conditions such as green oil bubbles on the circuit board surface.
5. When the tin immersion operation is carried out, the soldering surface of the circuit board stays on the surface of the tin liquid for too long, generally about 2-3 seconds, if the time is too long, it will also cause this undesirable situation.
Therefore, to avoid green oil bubbling after PCB board soldering, in addition to strictly controlling the quality of PCB products, it is also necessary to choose the appropriate flux and strictly control the process during the soldering process.
Blistering of the circuit board after reflow soldering generally refers to the foaming of green oil on the solder mask on the circuit board. This phenomenon is that after the reflow soldering of the printed circuit board of the component, light green bubbles will appear around individual solder joints, and in severe cases, bubbles the size of nail caps will appear, which not only affects the appearance quality, but also affects the performance in severe cases, which is one of the problems that often occur in the welding process.
The root cause of the green oil bubbling of the solder mask after reflow soldering is the presence of gas/water vapor between the solder mask and the positive substrate. Trace amounts of gas/water vapor are entrained into different processes, and when exposed to high temperatures, the gas expansion causes the solder mask to delaminate from the positive substrate. The pad temperature is relatively high during soldering, so bubbles appear around the pad first.
Now the processing process often needs to be cleaned, and then the next process is done after drying, such as after decoration, the solder mask film should be applied after drying, at this time, if the drying temperature is not enough, it will carry water vapor into the process. The storage environment before PCB processing is not good, the humidity is too high, and the drying is not done in time during soldering. In the wave soldering process, water-containing solder masks are often used, if the PCB preheating temperature is not enough, the water vapor in the flux will enter the inside of the PCB substrate along the hole wall of the through-hole, and the water vapor will first enter the solder pad around the pad, and bubbles will be generated after encountering high soldering temperatures.
The solution to the green oil foaming of the circuit board after reflow soldering is:
1. All links should be strictly controlled, and the purchased PCB should be inspected and put into storage.
2. The PCB should be stored in a ventilated and dry environment for no more than 6 months;
3. The PCB should be pre-baked in the oven for 105°C/4H~6H before soldering.
Core Advantages and Industry Impact of SMT Technology
The Soul of PCBA Processing: Demystifying the Importance of Chip Burning
SEND MESSAGE