Due to the lack of post-welding cleaning process, there is a risk of high surface ion content using no-clean flux. If the solder resistance film or green oil plug hole has certain defects, under the continuous electric field, the residual corrosive ions will gradually penetrate through the solder resistance film to corrode the copper layer, resulting in a series of bad lead-free solder products. Even if there is no electric field, the high surface ion residue will cause corrosion to the solder joints on the surface of PCB components, which will affect the reliability of lead-free solder strips and even all lead-free solder products. In order to prevent such failure problems, the following active preventive measures should be taken:
Ensure that PCBA cleanliness, especially ion cleanliness, meets the requirements of the specified standards.
Strengthen the control of PCB to ensure its structural integrity.
Try to use halogen-free or low halogen content of the flux, in addition to the detection of its ionic halogen, the flux should also be tested to understand its total halogen including covalent halogen, or to detect halogen ions after use.
Use cleaning solvents correctly. If rosin flux is used, it will not be corrosive normally because the active substance containing halogen is surrounded by rosin resin. However, if the improper cleaning solvent is used, it can only clean the rosin and cannot remove the halogen-containing ions, which will accelerate corrosion. It is generally recommended to use a conforming cleaning agent that contains both polar solvents and non-polar or low polarity, that is, it has a good effect on removing ionic and non-ionic residues (such as resins).