In my magnetic stirrer project, I came across something that wasn’t very easy to solder: a braided stainless steel sheath. In this video, I’ll show you how to properly solder stainless steel.
This “no clean” flux works well with copper and brass. However, it doesn’t work with stainless steel. No matter how hard you try, the solder will not stick.
Stainless steel is an alloy of Iron,chromium, and some other metals depending on the type. It is a special group of iron alloys because each form an oxide layer that drastically reduces corrosion. It can be difficult to solder because this oxide layer keeps the solder from sticking like the teflon in a pan keeps eggs from sticking.
Trying it again with a high acidity flux results in solder wicking up into the strands of stainless steel nicely.
You must clean this flux off thoroughly with distilled water and light brushing, because the residue will conduct electricity. You can see here that it is very acidic. The no clean solder is fairly neutral, maybe slightly acidic.
Once fully dry, you have a strong electric connection ready for use.