After wave soldering and lead wave soldering, the defective circuit board pinhole and porosity are different, from the appearance, the diameter of the pinhole is small, now on the surface, you can see the bottom. Pinhole and the porosity represents in the solder joints have bubbles, but has not yet been expanding surface, most have occurred in the bottom of the base board, porosity is larger hole on solder joint can be seen inside, it is empty normally in the pinhole internal, internal air porosity is completely jet caused by the big hole, the forming reason is solder in the gas has not been completely ruled out that has solidified, which formed a pinhole or porosity. The reasons are as follows:
The main cause of such defects is moisture in the printed circuit boards, which evaporates during welding at high temperatures. The main escape route of moisture is through the through hole of the welding pad. In particular, if the printed circuit board manufacturing process using a cheaper substrate or using a rough drilling method, the through hole in the solder pad in the storage process is more likely to absorb moisture. The solution is to dry the PCB for about 2 hours under the condition of 120C before soldering. If still unable to solve the problem, the printed circuit board tile leakage test should be carried out, and the circuit board manufacturer is recommended to increase the coating thickness at the through hole to more than 25 m.