What's the best flux liquid for soldering copper onto stainless steel, HCl or H3PO4?

Oct 2017
3
0
Indonesia
What's the best flux liquid for soldering copper onto stainless steel, HCl or H3PO4, with how many percent concentration of each ?
How's logical explanation on solder sticking process will actually work
some suggest Phosphoric acid better, actually I tried both works, ...many thanks in advance !