Causes and solutions of green oil blistering after circuit board reflow soldering

 The blistering of the circuit board after reflow soldering refers to the blistering of the solder mask green oil on the circuit board. This phenomenon is that light green bubbles will appear around individual solder joints after reflow soldering on the printed circuit board with components pasted. In severe cases, there will be nail-sized bubbles, which will not only affect the appearance quality, but also affect the performance. It is one of the common problems in the welding process. The following editor will talk about the reasons for the bubbles in detail And the solution.

Reasons for blistering of green oil after reflow soldering:

1. There is gas or water vapor between the solder mask and the anode substrate. A small amount of gas or water vapor will be entrained in different processes. When encountering high temperatures, the gas expansion will cause the solder mask and the anode substrate to delamination , The temperature of the pad is relatively high during soldering, so bubbles first appear around the pad.

2. It is often necessary to clean during the processing, and then do the next process after drying. For example, after etched, solder mask should be applied after drying. At this time, if the drying temperature is not enough, moisture will be entrained into the next process.

3. The storage environment before the circuit board processing is not good, the humidity is too high, and the soldering process is not dried in time. In the wave soldering process, water-containing solder resist is often used. If the circuit board preheating temperature is not enough, the water vapor in the flux It will enter the inside of the circuit board substrate along the hole wall of the through hole. Water vapor first enters around the pad, and air bubbles will be generated in these situations when the soldering high temperature is encountered.

Solution of green oil blistering after reflow soldering:

1. All links should be strictly controlled. The purchased circuit boards should be put into storage after inspection. Normally, there should be no air bubbles under standard conditions.

2. The circuit board should be stored in a ventilated and dry environment, and the storage period should not exceed 6 months.

3. The circuit board should be pre-baked 105℃/4H～6H in an oven before soldering.