Utilize Flux and alcohol. Clean with alcohol utilizing a wipe-clean-wipe method. After soldering with Flux, clean off residual Flux with alcohol. Leaving Flux can promote corrosion. My phone keeps autocorrecting Flux to capitalize it, and I don’t care enough to fix it. 🤷♂️
Edit: Do not use clinical isopropyl alcohol solutions (~70% whatever). Those solutions need some water to work as a disinfectant. You want as little water as possible (>99% solution).
Believe it or not, isopropyl alcohol leaves residue behind. If you’ve ever wiped a shiny metal surface with it, you might see it looks a bit duller. Wiping after using alcohol is attempting to remove the residue to give the cleanest bonding surface possible.
I couldn’t remember what the standard industrial solution was. All I could remember is that it’s impossible to have 100% because water is introduced to the solution the moment it’s exposed to air.