1. Observe whether the components have blackening and oxidizing phenomenon, and the cleanliness of components also affects the fullness of tin;
2. Observe whether the surface of the PCB is attached with grease, impurities, etc., and then wash it with a solvent. There is also a look at the circuit board is not polished particles left on the surface of the board. The storage time of the board is too long, the storage time, the surface of the substrate is improper, or the tin surface of the part is oxidized. This phenomenon can only help the tin effect by re-welding once, but it is also labor-intensive.
3, improper use of flux, such as the pressure and height required for foaming is also a very important factor, the amount of flux distribution on the surface of the circuit board, the improper storage environment or misuse of improper flux may also cause tin bad;
4, there is a preheating temperature should be appropriate, the preheating temperature does not reach the required temperature will also be the solder can not be fully melted, or the impurities in the solder too much, may cause poor tin.