How do you solder without flux?

Is it “okay” to solder without flux, sure it is, so long as you don’t demand anyone else solder without flux. Most people solder with flux on purpose, and it’s benefits outweigh any detractors. Bear in mind though, most common solder wire is rosin-core, it has one or more cores of flux inside of it.When soldering circuit boards, or other electrical / electronic devices, yes - you need to use flux. Fortunately, almost all solder for electronics use has an internal core of flux, so you usually don’t need to add more.Well you can use rosin core solder and not use any externally added flux. That's sort of “soldering without flux.”
 In a pinch you can use a solution of white vinegar and salt. This makes a mild acid. It will even shine a tarnished penny before your eyes. This can work as a flux of sorts and will allow soldering of copper or aluminum parts that you want to solder for an electrical connection.
Just make sure to clean it all off after or it will corrode your solder joint. Water works okay, but filter or pure bottled water is better as it has no or fewer minerals in it that can corrode the joint too. Not Perrier or Dasani or any other mineral water. All this is just IF you can’t get or don’t have time to get real soldering flux.
Flux is cheap and makes soldering SOOOO much easier. In fact…you will likely NOT get a good solder joint without it or something like it. This is true for electrical conductivity and mechanical strength of the joint. The solder just won’t stick to the two parts. The solder just beads up.
If you get flux-core-solder you got a hollow tube of solder around a core of flux so you are all set. This is a great option.
When you heat metals in air, they oxidize (aka rust). You might not see it but a thin thin film or layer of oxidized metal (rust or tarnish) will form super fast…in a second or less depending on the metals in the joint.. The flux keeps this oxidation from forming.The flux is required to remove oxides from the parts to be joined by soldering. If you can guarantee there are no oxides present, then you could (in theory) solder successfully in an inert (nitrogen) environment. However it is very difficult to ensure there are no oxides present ! Even in new board manufacture, wave soldering in a nitrogen environment requires the use of flux.
So for practical purposes, Yes you need flux.


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