1. It can't match the solder characteristics with improper setting of furnace temperature curve of reflux furnace
2, The solder paste does not match the spray tin on the surface of the PCB.
3. The furnace temperature set by the reflux furnace can't reach the lead-free tin melting point.
4. The over - furnace chain is dirty, causing the contamination of the pad.
The methods to solve the poor soldering wettability are below:
1, Adjust furnace temperature curve in the standard range and confirm the first inspection before production.
2, Match the lead-free solder paste and spray tin on the PCB surface.
3. Adjust the peak value of reflux furnace temperature to lead free tin melting point.
4. Normalizing the furnace method and using the reflow soldering top track to suspend the furnace.