Plating to enable soldering

[cybermaus]

So when soldering stuff like tungsten en stainless, there is typically two problem:
- Not enough heat
- Does not want to wet with solder.
I should probably try hard solder (silver) really, but I got rid of my acetylene set when I moved house.

So if I want to stick to soft solder, I was thinking to address item 2 with plating.
Chemically/Electrolytically depositing gold, silver, nickel and then soldering

Did anyone experiment with that before? Which would have the best wetting to normal solder?
Copper might be best, but most plating sets are for those other 3.

[moffy]

This might be of interest: https://advancedplatingtech.com/technical-library/plating-topics/make-solderable-deposit/

[Ian.M]

For steels, electroless copper plating works well enough.  No special plating solutions, just a few grams of copper sulphate (or at a pinch copper chloride) used a few crystals at a time to make a couple of ml of conc. solution to dip a Q-tip to brush-plate with!   You only need a 'flash' of copper over the surface so don't try to build up a thick copper layer as the adhesion will be poor and the copper is only there to get the solder to wet the surface.  It should fully dissolve in the solder leaving a good solder to steel bond.   Rinse, pat dry and immediately solder, as the copper needs to be fresh, not oxidised.

See my replies #20 onwards here: https://www.eevblog.com/forum/beginners/soldering-to-strange-metal-contacts/msg3315024/#msg3315024

[cybermaus]

Wait, so you say if I put iron (steel) in a solution designed to *desolve* copper, it will instead *deposit* it?

I assume the solution should have been saturated already first, iow, the stuff that had etched a lot already, is about to be trown out?
To be honest, it has been years I last etched something myself.

Also, if I understand what you say correctly, it may not work on all metals, depends a bit on where the metal sits on the row of metals.
Like where aluminium ionizes before zinc, ionizes before copper, ionizes before iron, with gold at the end of the chain?

---

Edit: Ok read a bit better. You also mentioned copper clorate, but advised copper sulphate. I ordered some (needed some IPA anyway)
Probably going to be a lifetime supply and then they still will bury me with most of it, but I can experiment with it.
Do need to make sure I do not spill it, I read it is really bad for the fish.

[Conrad Hoffman]

Yes, bad for fish and you. FWIW, you can get root killer, which is copper sulfate, fairly easily around here at any farm/garden store.

[T3sl4co1l]

Some acid is welcome, to dissolve surface oxides, counter water hardness if applicable, and ensure the salt fully dissolves (most non-alkali salts leave some hydroxide precipitate on dissolving, as they prefer a lower pH).

Also make sure the surface is clean -- use a detergent to remove dirt and oils, and solvent and clean wipes to further remove oils.  If it's rusty or corroded, soak in something suitable first (e.g. evaporust?), or mechanically prepare it (sand off the crud).

Plain steel can be plated easily enough, though the finish is rather weak without proper preparation and bath formulation.  Wipe-on may still be good enough for soldering purposes.  I'm not sure that it actually matters, when a fresh iron surface is also tinnable with rosin flux -- it goes a bit slower, but still isn't as bad as trying to solder nickel plating, let alone stainless.

Stainless and tungsten are quite different fish kettles. Stainless is protected with a layer of chrome oxide, which needs to be etched away with a strong enough acid.  The stronger reducing environment (Cr metal fraction) may plate Cu too aggressively, giving a flaky deposit, I don't know.  Tungsten, I'm not sure how much and in what ways it oxidizes in air at low temps (it does make WO3 at higher temps), but I imagine it's hard to tin, and may be better with a plating process, or series of platings, to get a secure bond.

There are copper-impregnated tungsten brush materials, which may prove helpful as well.

Tim

[exmadscientist]

There are fluxes from hell that can solder to stainless, even 316 (aka A4), like Superior No. 71. These are not pleasant substances and require great care to use safely. (I mean, really, HCl is the least toxic thing listed on that SDS.)

But... they do solder stainless. I've done it! They work!

[Doctorandus_P]

Recently I used silver solder with an Propane / Butane flame. One of the properties with silver solder with a high silver content is that it has a relatively low melting point and thus the high cost of the solder is justified by not needing acetylene. But still I do not understand why the stuff costs EUR3000/kg while silver is just a few hundred EUR/kg.

When soldering "difficult" materials, specialized (more aggressive) fluxes can help. A long time ago I soldered galvanized steel pipe with leaded solder and S65 flux, but it was not easy to do. There is only a small temperature range in which the flux works. When overheated, the solder don't wet anymore. I also had the solder creeping under the galvanized layer. A bit weird, but it worked.

Another method I have heard of, but not used myself is to first put oil on the metal, then use sanding paper to remove the oxide. The oil keeps oxygen away from the metal and thus prevents immediate oxidation.

[T3sl4co1l]

Zinc is a weird metal to soft solder; it's immiscible with lead, but can be convinced to alloy together with tin.  It's freely soluble with tin, but the resulting alloy oxidizes quickly, turning the surface drossy and consuming rosin fairly quickly.  So you tend to want to do solder joints quickly to avoid soaking up much, plus oxidizing the solder itself.

But, despite its protective oxide, it does indeed wet, whether by amalgamating action disturbing the oxide, or rosin dissolving it directly.  And tin and zinc are compatible metals, giving a strong joint.

Aluminum is even worse, of course, the oxide being entirely(?) insoluble in rosin, and being so reactive.  It does dissolve in tin (not lead!) so you'll see it drossing up as base metal dissolves into the solder.

Tim

[cybermaus]

Ok, I got the stuff. And it does work, though not very easy:

The layer of copper sets immediately, but is also very thin and fragile. It needs to be very clean before, and you should not even wipe it after
- after clean with acid and/or sandpaper, rinse with alcohol, don't wipe it the alcohol dry
- put it in the copper solution
- after the copper solution, rinse with alcohol, don't wipe the alcohol dry.
- add flux
- solder.

Also, it works on iron, steel, stainless. But not on this wire, not sure what it is, tungsten, whatever
I sort of expected that, but I was curious.
Now, what to do with the remainder 0.998 kg

[moffy]

Now, what to do with the remainder 0.998 kg

Yeah, leftovers.

[coppercone2]

Hmm ok, so I wanna understand this using copper as flux.


If you melt some solder on it, then flick it off, will you be left with tinned steel like you would for a soldering iron? Like actually tinned?

Or better yet, if you use a braid to wick off all the solder... you should be left with a very fine tin layer.

Does it actually happen?? Or is it some in between thing where it kinda happens?

Its so weird if this actually works good for stainless steel.

[Whales]

It probably doesn't act as a flux (reducing agent), but instead a sealant against air during the soldering process.

[coppercone2]

well ok but does it really tin that well?

I see stainless steel even resist acid brazing with silver sometimes.

[Buriedcode]

The self plating that comes from dipping more electronegative metals into copper solution tends to have poor adhesion because it reduces to copper away from the actual surface.  Add to the fact surfaces need to be "activated" (cleaned, oxides removed, and somehat etched with acid) for any kind of funcitonal plating means the above solution can indeed be hit and miss.

I would have thought copper chloride would be far better than just plain copper sulphate solution since the former can attack the steel - in way, activating it - whilst also providing copper ions to reduce on the surface.

I'll have to try this out myself. I can confirm spent Soldium Persulphate etchant - pretty blue, full of copper - doesn't plate onto steel at all, it immediately wipes off.  But its a weird etchant and not particularly powerful.

As for copper sulphate uses - without sulphuric acid to create an acid copper solution, plating will be slow, but... if you don't mind waiting, you can use plain old copper sulphate, along with a constant current source to plate onto copper, to thicken up tracks.  Without acid it'll be less conductive so much slower, but this can be an advantage since faster plating is rougher and usually requires additives like levellers and brightners, but the very slow steady plating can be finer.  It won't be "shiney" But handy if you're making your pwn PCB's and need thicker copper traces for higher current.