I've been finding that ever since I switched to Inventec Amtech flux, isopropyl alcohol just doesn't cut it when trying to remove the residue. I can scrub (and even soak) a board and it'll still be sticky afterwards. Does anyone have a recommendation for a cleaner that will work better? I know there's PCB setergents designed for ultrasonic cleaners, but I'm not sure if they're suitable for spot cleaning (e.g. in a small spray bottle, used with an old toothbrush).