@tooki: Okay great I'm gonna try the Felder then as well. For stubborn residues I've got a bottle of Kontakt WL here, do I have any advantage using Kontakt LR over WL for flux removal?
I honestly don’t know. I actually have both here, but I’m about to head out so I can’t test it right away.
I know I looked at the ingredients long ago, and Kontakt LR, WL, and LS are all very similar. (LS is the more unusual one, because it comes in a larger can with much higher pressure.)
Maybe I'm wrong, but It think that the term "no-clean" is trying to sell the obvious, i.e. standard flux meant for electronics isn't corrosive anyway.
I’d say half right. Indeed, standard RMA flux does not need to be cleaned for most applications.
No-clean liquid fluxes tend to have
far less solids content than liquid rosin fluxes: most have under 5% (often under 2%), versus the 10-30% typical of liquid rosin flux. The no-clean liquids in turn have more non-rosin agents.
The low resin content makes any residues practically invisible.
For the flux core in wire solders, as well as in pastes/gels, no-clean usually has paler residues than traditional rosin. The amount of flux is also usually slightly less.
Paste/gel and liquid no-clean also can only be considered no-clean when used for full-board reflow soldering. These fluxes must be heated to a particular temperature to neutralize the fluxing agent, and in hand soldering, it’s very common for part of the flux (at the edges) to get heated enough to activate the fluxing agents, but not hot enough to neutralize them! That leaves them in an active, corrosive state. So always thoroughly clean such fluxes when hand-soldering. (That problem doesn’t affect no-clean flux cores, since the flux is heated sufficiently by the molten solder.)
I don’t know this for sure, but my hunch is that no-clean really became more important with lead free solder, because the higher temperatures required end up burning a lot of traditional rosin fluxes. (Burnt flux could well be conductive, and it is unsightly.) It seems to me that no-clean is mostly used in a sense to indicate fluxes that can handle higher temperatures better.
But for sure, there’s a ton of overlap, and the terminology chosen
sucks.
Also, corrosive fluxes are actually common in electronics manufacturing: most water-washable fluxes are highly corrosive and need to be removed flawlessly. (And must not be used whatsoever for anything the flux wicks into, especially stranded wire.) The stringent cleaning requirements are why such fluxes are best avoided for hobbyist use.
Some traditional electronics rosin flux types (like RA) do require cleaning, because the residues are conductive and/or corrosive.