Stripping Sn/Pb solder from pins

Anyone tried to do this? I'm interested in stripping solder from a nickel layer on small (say 1mm diameter) pins, without removing the
nickel barrier, so they can be replated with gold. Got a couple hundred pins to do. The parts are very expensive and cannot be shipped.
Thanks for sharing any experience or ideas
Best regards, Spehro Pefhany    
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On a sunny day (Mon, 22 Jul 2013 13:15:32 -0400) it happened Spehro Pefhany

I do not know if that works for you, but I use a paper napkin folded over many times to clean solder of parts, expecially my expensive solder iron tips. It is amazing how good paper cleans (pins have to be hot of course). For solder irons it is 100000 better than the 'wet sponge', as the moisture causes he tips to rot aways, and the sponges do not clean at all. Paper is a mysterious thing, you can even cook water in a paper cup.
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On Mon, 22 Jul 2013 17:21:18 GMT, Jan Panteltje

I want to get down to the nickel so I can brush plate gold back onto the pins wot some cretin soldered to.
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'Reverse plating' is another method. Depending upon the electrolyte and the other electrode, it can be exquisitely selective.
Lloyd
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Lloyd E. Sponenburgh schrieb:

Hello,
I think the applied voltage is more important than the other electrode material.
Bye
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Since the metals almagum (sp) with each other making an alloy you will have to de-plate it off.
I think it is a folly to try.
Sorry Martin
On 7/22/2013 3:01 PM, Spehro Pefhany wrote:

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Acetic acid and hydrogen peroxide will react with the lead to form lead acetate. That should easily wipe off. Not sure what it will do to the Ni.
tm
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tm wrote:

OK, just watch out, lead acetate is VERY easily absorbed through the skin, considered HIGHLY toxic.
Jon
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On Mon, 22 Jul 2013 13:15:32 -0400, Spehro Pefhany

I found this: <http://lanthanumkchemistry.over-blog.com/article-the-dissolving-of-lead-101037110.html I've never tried it. That leaves what it will do to nickel: <http://lanthanumkchemistry.over-blog.com/article-the-dissolving-of-nickel-101259615.html Acetic acid: 5% acetic acid is too dilute to dissolve nickel metal. Even the addition of hydrogen peroxide did not dissolve the nickel to any appreciable extent after 36 hours. It just might work...
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wrote:

Its not the dilution of the acid - that relates to the speed it works. The strength (ability to donate or accept electrons or some such) of the acid controls what it will eat away eg. Hydrochloric acid will eat away nickel at any concentration
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Although, HCl and H2SO4 are astonishingly slow when it comes to nickel. The stuff is pretty much noble (hence its popularity!).
Acidity alone doesn't determine corrosivity: if a complex is formed, metal will dissolve much faster. Copper dissolves faster in HCl + H2O2 than H2SO4 + H2O2, because it forms a green chloride complex (there is also a reduced form with a deep brown color, which is probably familiar to anyone who's used this brew to etch PCBs), while sulfuric basically does nothing special with copper.
Hydrofluoric acid isn't actually very strong, but because it forms a complex with silicon (hexafluorosilicate), it's one of the few chemicals which dissolves glass.
Oxidation potential is, of course, a big force. Electrolysis can beat the pants off any chemical, for obvious reasons. (There's literally nothing more "acidic" on Earth than the LHC -- one definition of acidity is "proton donator", and a naked proton beam at ~light speed can't really be stopped from "donating" to anything!) Among chemicals, this means zinc dissolves faster than iron faster than nickel, while copper pretty much doesn't at all (in acidic water alone). If you add an oxidizer (nitric acid, H2O2, hypochlorite, etc.), less energy is spent generating hydrogen and more doing the reaction. (Bubbling decreases or stops when an oxidizer is used, unless another gas is produced -- nitric usually gives off NO and NO2 fumes, nasty things.)
There is, of course, no chemical which is a stronger oxidizer than fluorine, which will literally burn through anything on the periodic table besides pure oxygen and the noble gasses (which, except for helium and neon, are all known to form compounds with fluorine anyway, they just take some persuading).
Tim
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On 7/23/2013 12:49 AM, Tim Williams wrote:

If you think all that is fun, read this and the comments to continue the fun. "How Not to Do It: Tertiary Butyllithium"

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I had my share of that fun with Lithium Aluminum Hydride. I was a novice chemical researcher, the only undergrad in the summer research program, so a wise and kindly grad student offered to chisel off a chunk of the concrete-like mass for me, and set it all on fire with the second blow. We just closed the fume hood door and enjoyed the bright red fireworks display. jsw
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On 7/23/2013 1:49 AM, Tim Williams wrote:

I always hated it when my professors would refer to a hydrogen ion as a "proton". Sure that's all it is, a naked proton, but there is a world of difference in terms of how it is considered. The LHC isn't trying to etch glass or any other chemically mediated reaction. Likewise etching circuit boards doesn't really demand the calculations performed when setting up a particle accelerator. Very different worlds... so why make it sound like they are merged significantly by using the nuclear term "proton" instead of calling it a hydrogen ion. All the other atoms are just clumps of protons and neutrons too, but we refer to their ions as... well, ions.
--

Rick

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Spehro Pefhany wrote:

Replace tin/lead with gold? Are you nuts? Gold is SO less reliable especially in light of the corrosion problems.
What is this "cannot be shipped" BS?
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    Hmm ... you are asking for *total* removal, which probably needs a chemical attack. And the solder wets the nickel very well, to make it more complex.
    For a first pass (perhaps to make the chemical pass whatever it is more efficient) there are various mechanical and tricky ways to do it.
    Are these used pins with solder and wire fragments in them? Onews with the wire fragments removed but lots of solder, or ones which were solder-tinned from the factory. I'll assume below that it is the middle ground above, and what I am offering will leave you somewhat close to the factory-tinned level.
    For just a few, without a solder cup for wire ends, I would grip them in a solder-free area with needle nose pliers or the like, dip in rosin flux and then in a solder pot to get it up to the melting point, and then strike the hinge part of the pliers against a wood block, thus flicking off *most* of the solder (but not all).
    With solder cups, what I would do is grip it in some kind of pin vise, and then heat with a soldering iron and either use a vacuum solder removal iron or use small braid soaked in rosin flux to wick up as much solder as possible.
    For quantities greater than your couple of hundred, the mechanical method could be a vibratory feeder to an automated pin vise Perhaps load a half dozen or more in arms fixed to a common hub, hit with a hot air flow and while hot, spin the hub so the solder at the outer ends is flipped off and collects as a film on the inside of the splash shield, and then hit with a blast of cold air before dropping them into a hopper.
    And probably OSHA will consider it a hazmat zone by the time you have all that oh so deadly lead mixed with tin scattered all over. :-)
    But -- this still leaves you with needing a chemical method. For the quantities you are talking about, it may still be less expensive to simply buy new ones with the desired gold plating.
    The cleaning methods I listed above would not be commercially cost-effective. they are what a hobby user would do to clean terminals stripped from old equipment for re-use.
    Good Luck,         DoN.
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wrote:

Hey, how about tumbling in a material softer than Ni but harder than Pb?
Find someone who reloads ammo and try it with corn cob media.
tm
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As an electronic lab tech I second all of that. If the assembly is too large or delicate to knock off the liquid solder, wiping it with a wadded-up dry paper towel works well too.
If you hold the pin vertical and heat it from the bottom with an iron, most of the solder will flow down onto the hot tip. Hit the pin with a vacuum solder sucker as you pull the iron away. The tip of the sucker will recoil into the pin when the plunger springs back so whatever supports the work should be fairly substantial. jsw
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On Tue, 23 Jul 2013 08:48:49 -0400, "Jim Wilkins"

I can get the pins relatively clean pretty easily. The goal is to have nice shiny gold plated pins again, like new, so they can be used as contact surfaces.
Right now I'm thinking mechanical abrasion to get down to the bare metal (which is relatively hard) then nickel plate, then gold plate.
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wrote:

http://www.electrochem.org/dl/ma/203/pdfs/2374.pdf
Solder dissolves gold plating quickly. http://www.eng-tips.com/viewthread.cfm?qids70
jsw
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