When two solders are heated differently or one of them has oxidation layer and dirt on the surface, the molten tin will adhere to the solder pad of the solder with higher temperature and clean surface, but not to the solder with low temperature and dirty surface, so that there is still a way between the two solders.
THE FALSE WELDING:
One of the two soldered bodies has an oxide layer or impurity on its surface, and the molten tin completely covers the soldered body. The two soldered bodies appear to be well connected, but due to the separation of oxide layer and dirt, the conductivity between the two soldered bodies is extremely poor.
When two soldered bodies are heated unevenly or the surface of one of them is not very clean, the molten tin is less adhered to the solder plate with a lower temperature and not very clean; Or the welding technique is not correct, so that the molten tin is not evenly and fully attached to the two soldered bodies on the welding plate, the two soldered bodies although the conduction but poor electrical conductivity.
In the welding process, due to the low welding temperature and short welding time, the tin is not enough time to fully melt, rosin is not volatilized clean and then remove the ferrochrome, so that the connection between the two soldered bodies is not strong and the electrical conductivity is not good, the position of the mouth is dirty, there is a lot of dirt.