 Do you have to remove flux residue from a PCB? Well, not necessarily. Solder has sticky flux inside. As long as you're using no clean type solder, the flux is completely safe to leave on, and even protects your board a little from oxidation. But if a bit of flux stickiness really does bug you, you can remove most fluxes with isopropyl alcohol. And if that's not enough, you can reach for something more specialized, like, say, this flux off. That'll do it. You'll want something to help remove the flux remover, too. And the proper thing to use is an ESD safe brush, like this one. Apply flux remover, scrub gingerly, wipe clean, and enjoy your newfound sense of control.