Preventing field failures due to electrochemical migration used to be relatively easy: Use a water-soluble flux and clean the board after soldering. This solution no longer holds true, and sometimes causes more problems than it prevents.
Water-clean fluxes, also known as organic acid (OA) fluxes, are often preferred over No Clean products for high reliability applications because of their higher activity. They are more effective at removing oxides, promoting wetting and overcoming solderability variations. Problems arise when their residues are not fully cleaned form the assembly. OA fluxes are active at room temperature, and all they need to begin damaging the assembly is DC voltage and atmospheric moisture. When OA flux residues remain on a circuit assembly, the concern is not a matter of if the circuit board will fail; it is a matter of when it will fail.