and halides. The last I haven't found what is.
Halides are ionic compounds that include an element from the halide column, the most typical in fluxes being zinc chloride.
Zinc chloride dissociates at soldering temp and becomes acidic. It basically turns into hydrochloric acid. The chloride ions have the tendency to borrow the electron from neighboring water molecules and/or other agreeable hydrocarbons, increasing the probability of a free proton in any given space at any given time, which is essentially what acidity is.
Halides are among the most corrosive part of a flux. Definitely not a first choice for electrical work, although plenty of electric fluxes contain some zinc chloride. (Zinc chloride is the main ingredient in plumbers flux). These halides essentially leave salt behind in the residue, and it embeds in the pores of the metal. It cannot be effectively cleaned away. This is a problem on ferrous metals, in particular. If you have ever tried to clean rusty metal with HCl, you know this is not a good method. You will get the metal sparkly clean, but no matter how well you wash it, it will rust within days.
As for making your own flux with acid and alcohol, that is fine. But you probably ought to clean the board after. What makes rosin so special it is made from super long chain acids. The rosin is at once the acid that dissolves the metal oxides and the residue that binds the end products. It just happens that rosin is acidic enough to dissolve copper oxide, and that it is a viscous fluid which is very liquid at 150+C but essentially solid and highly insoluble in water at under 50C.
Some of the rosin-free no-cleans work on the same principle, of leaving a hard, non-hygroscopic residue. Others are deemed no-clean for having a very low solids content (and therefor also a very low activity), so that when the carrier is completely evaporated there's not enough "crap" leftover to be problematic.