copper plating lead free nickel bearing solder?

[coppercone2]

I got a plating pen and made a plating solution with H2SO4/CuSO4/HCl and tarn-x (thiourea)

it works for writing on nickel silver sheet (18 percent nickel, 62 percent copper, 20 percent zinc) and also on leaded solder, quite nicely. I get a deposit of real nice shiny copper on a eutectic solder blob.

However I was trying to copper plate a nickel bearing (bridge-it, harris brand) solder joint between two pieces of copper and its just turning black.

https://www.harrisproductsgroup.com/en/Products/Alloys/Soldering/Lead-Free-Solders/Bridgit.aspx

is it the antimony in the solder or something thats preventing it from working? I don't think its the nickel because it works just fine on nickel silver and on leaded solder soldered to nickel silver sheet.

What am I missing? I did the same procedure for both work pieces, and tried fresh plating pen tips. I think its something about the metal composition thats screwing with it. Antimony stands out at me. I don't think its a problem relating to cleaning because I hardly did anything to the sample that worked, wiped the flux off with alcohol a little bit

[coppercone2]

Ok I managed to plate one of them there are a few tricks

1) put the felt or whatever it is pen into into the solution of electrolyte and pull a vacuum on it for a while to infuse it
2) get a syringe of electrolyte

So its a little like tig welding, when its a big surface you can drip the syringe on the felt periodically while making a stirring motion to get the plating to attach. I don't know why this is but it worked, maybe its getting depleted by the solder or it was doing some kind of chemical cleaning and getting depleted (maybe more HCl is required). I am tempted to hook up a pump to it to turn it into a "mig" process, perhaps it would help if the tip spun as well at slow speed. It needs a vacuum collector too to that can be stuck to the surface to collect drip, its paper towel heavy... but as usual its highly non linear so controlling the drip location with a external syringe a-la tig/acetylene is best, and I am pretty sure a tip heater would help as well. 


Very finicky procedure