Mg Chemicals 4140-400g Flux Remover for PC Boards

This pen puts out just the right amount of flux remover and it does the job.

Excellent stuff

If you're doing a lot of soldering, using a lot of flux, then this stuff will clean for you. I can't recommend anything better.

Alcohol works for most cleaning, but if you have something that alcohol doesn't clean, then this will. I cleaned off burnt flux with this while alcohol did nothing.