What should I do if the solder mask of the printing plate blisters after SMA soldering?
After SMA is welded, light green bubbles will appear around individual solder joints. In severe cases, there will be fingernail-sized bubbles, which not only affect the appearance quality, but also affect the performance in severe cases. This defect is also a reflow welding process. The problem often occurs in the middle, but the wave soldering time is more.
The fundamental reason for the blistering of the solder mask is the presence of gas or water vapor between the solder mask and the PCB substrate. These trace amounts of gas or water vapor will be entrained in it during different processes. When the soldering high temperature is encountered, the gas expands This leads to the delamination between the solder mask and the PCB substrate. During soldering, the temperature of the pad is relatively high, so bubbles first appear around the pad.
One of the following reasons can cause moisture to be entrained on the PCB:
① The PCB often needs to be cleaned and dried before the next process is performed. For example, the solder mask should be dried after being etched. If the drying temperature is not enough at this time, it will entrain moisture into the next process. Bubbles appear in high temperature.
② The storage environment before PCB processing is not good, the humidity is too high, and it is not dried in time during welding.
③ In the wave soldering process, water-containing flux is often used now. 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 surrounding pad. Air bubbles will be generated after welding high temperature.
① Strictly control all production links. The purchased PCB should be put into the warehouse after inspection. Usually, the PCB should not be blistered within 10s at a temperature of 260°C.
② PCB should be stored in a ventilated and dry environment, and the storage period should not exceed 6 months;
③ The PCB should be pre-baked in an oven at (120±5)℃ for 4 hours before soldering;
④ The preheating temperature in wave soldering should be strictly controlled, and it should reach 100～140℃ before entering wave soldering. If water-containing flux is used, the preheating temperature should reach 110～145℃ to ensure that the water vapor can be completely evaporated.