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Was wandering whether anyone could suggest how to solder stainless steel. I know hydrochloric acid flux is suggested to remove oxidation. Anyone could suggest a supplier in UK or who would be able to deliver to UK.

The part we have is a folded miniature box (approx. 2x4x3mm). We require to close up 2 gaps of stainless steel material by soldering the surfaces together, however conventional flux does not seem to work...

If anyone has any suggestions on technique or super aggressive flux supplier suitable for this procedure I would be most grateful for advice.

Thanks in advance.

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  • \$\begingroup\$ My intuition is that you could apply copper vitriol (hope it's called the same in English) to a region to have a copper surface on there \$\endgroup\$ – Marcus Müller Feb 27 '17 at 16:49
  • \$\begingroup\$ That must be cupric sulphate. \$\endgroup\$ – Leon Heller Feb 27 '17 at 16:56
  • \$\begingroup\$ If all else fails, silver brazing (with borax flux) works very well on stainless steel - but at about 650C. \$\endgroup\$ – user_1818839 Feb 27 '17 at 17:09
  • \$\begingroup\$ Our soldering irons go only up to 400C and this is a micro part required to be soldered under microscope, so ideally would prefer a flux. Copper sulphate is interesting idea. Any resources how to use it? \$\endgroup\$ – Tad Vaas Feb 27 '17 at 17:13
  • \$\begingroup\$ @TadVaas 1. dissolve in water. 2. apply to steel. 3. Wait for copper to deposit within a couple hours. 4. wash off residue 5. solder onto copper surface \$\endgroup\$ – Marcus Müller Feb 27 '17 at 19:33
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Stainless steel solders very well with nothing more than dilute HCl. Special flux is not required. I'm not sure this is true of all alloys, but it is of the ones I've used. Use all appropriate safety precautions and clean the soldered surface with water.

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It might be worth it to mechanically attach a contact. What about you bore a small hole, tap it, and screw a miniature brass screw into the same with enough force to ensure contact by tension?

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  • \$\begingroup\$ We have no real estate on the part to attach a screw. The soldering perimeter needs to be less than 2mm square. \$\endgroup\$ – Tad Vaas Feb 27 '17 at 19:47
  • \$\begingroup\$ you seem to be underestimating mechanical engineer's abilities to produce tiny screws. \$\endgroup\$ – Marcus Müller Feb 27 '17 at 19:48
  • \$\begingroup\$ alternatively, what about bolting something on? \$\endgroup\$ – Marcus Müller Feb 27 '17 at 19:57
  • \$\begingroup\$ The are that needs to be joined together is approx 2mm. Not sure bolting is viable. \$\endgroup\$ – Tad Vaas Mar 17 '17 at 22:16
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I used to do a fair amount of soldering of stainless with this flux -

EutecTor 157

I would imagine it's available world-wide, but I don't know for sure.

If I remember correctly, I have also used "standard" zinc chloride flux (ie, zinc and HCl) successfully, though some mechanical abrasion (brushing with a stainless steel brush) with the flux film in place is helpful in that application. It's not quite as active as the 157.

Clean up well after using either one.

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