Flux conductivity

[alecto]

I'm a Beginner with a capital B...
I'm getting better at soldering...and I try to do what is supposed to be done....
I use 0.38mm multicore solder(60/40), a temperature adjustable soldering station with chisel tip(2.4mm or 3.2mm depending on what I'm soldering)
....and some cheap flux that contains zinc chloride.

Recently I had problems with little projects...on the breadboard everything was fine... then I soldered those....

and today, again... little project... breadboard ok...but once soldered...troubles!!
so I begin to check: 
-if I made a connection mistake....nope(really easy project)
-checked for bridges with a magnifier(8x with led ring)...no bridges...again with my DMM  continuity tests...no buzz but a little resistance(60~80) between two pins where it shouldn't??? so back to the magnifier and again no bridge but some flux residue...

So I scrapped the flux residue(last hope before desoldering stuff...)
and BOOM everything was fine....

can flux residue be conductive??or the flux I use?

[Rerouter]

yes, and depending on what had deposited on the board surface before hand it can be on the same roder as what you saw there,

There are different types of fluxes, but even if you use a non conductive one, the metals and oils that deposit out of the air over time, once it has a medium to move around in like molten flux tend to concentrate in, can cause exactly what you are seeing, and is part of why cleaning off the flux is a good habit to follow,

[wraper]

Zinc chloride flux is completely unsuitable for electronics and destroys soldering iron tips too.

[wraper]

As a metallurgical flux[edit]
Zinc chloride has the ability to react with metal oxides (MO) to give derivatives of the formula MZnOCl2.[30] This reaction is relevant to the utility of ZnCl2 solution as a flux for soldering — it dissolves oxide coatings exposing the clean metal surface.[30] Fluxes with ZnCl2 as an active ingredient are sometimes called "tinner's fluid". Typically this flux was prepared by dissolving zinc foil in dilute hydrochloric acid until the liquid ceased to evolve hydrogen; for this reason, such flux was once known as "killed spirits". Because of its corrosive nature, this flux is not suitable for situations where any residue cannot be cleaned away, such as electronic work. This property also leads to its use in the manufacture of magnesia cements for dental fillings and certain mouthwashes as an active ingredient.

[alecto]

first thanx for the fast replies...

so buying the only flux I found at my local hardware store ...bad Idea...ok lesson learned...

and destroys soldering iron tips too

thanx for that tip too(pun intended)
I couldn't keep their efficiency over time, but now I know why....

and also I just realized I should have search ggogle whith the terms "Zinc chloride flux"...so obvious...