What is the cause of the corrosion of the PCBA surface

After the PCBA is soldered, the PCBA board will have tin, flux, dust and employee fingerprints, which will cause the surface of the PCBA board to be dirty, and the organic acids and ions in the flux residue will cause corrosion on the PCBA board. And the consequences of a short circuit. Residues on the PCBA board can be handled by manual cleaning and machine cleaning. After the residue is cleaned in time, there will be no corrosion of the PCBA surface.