Stripping Sn/Pb solder from pins

On a sunny day (Mon, 22 Jul 2013 13:15:32 -0400) it happened Spehro Pefhany wrote in :

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.

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

I found this: I've never tried it. That leaves what it will do to nickel: 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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I want to get down to the nickel so I can brush plate gold back onto the pins wot some cretin soldered to.

Spehro Pefhany fired this volley in news: snipped-for-privacy@4ax.com:

'Reverse plating' is another method. Depending upon the electrolyte and the other electrode, it can be exquisitely selective.

Lloyd

OK, just watch out, lead acetate is VERY easily absorbed through the skin, considered HIGHLY toxic.

Jon

Jon Elson fired this volley in news:a4idnYGumcitOHDMnZ2dnUVZ snipped-for-privacy@giganews.com:

It's also a greate old pyrotechnic chemical, used for turning cotton string into slow match (fuse, for the uninitiated).

Lloyd

It's used in hair dye. I was looking into it to blacken brass.

Kevin Gallimore

Absolutely no experience. I guess I'd try heating and some mechancial wiping, blowing first. Do you have to get it all off? How much money can I spend? Could you heat it in a vacuum to drive the last bits off?

George H.

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

The problem with Gold is not corrosion. The problem with Gold is intermetallic embrittlement.

The 'cannot be shipped' refers to no external job. must be done in house. Justt a guess.

On Monday, July 22, 2013 1:15:32 PM UTC-4, Spehro Pefhany wrote:

From yahoo answers, looks like solubility is best way:

1) Mechanical removal is usually not practical because of static electricit y considerations, and, you can't get to all sides of the device. It should be mentioned, however, the IC leads probably could withstand bending out fl at (like gull-wings) so that you could get access to both sides, and use me chanical-abrasive methods to remove the lead (electronic grade baking soda abrasive blasting techniques for example, or residue-free CO2 ice blasting, mechanical sanding, etc.). Depends on the static sensitivity of your devic e and especially how you 'ground' the device in a custom-built enclosed fix ture to eliminate static damage. Is labor-intensive, but doable to salvage an expensive device - suitable for low volumes - can be subcontracted to lo cal shops for 'rework', but you'll have to spend time confirming that the * **very strict*** anti-static measures are implemented and adhered to on the shop floor. I don't think any post-rework electronic testing is really goi ng to catch static damaged parts (some will only be 'wounded' and will fail prematurely - short-term testing won't find this), so your only recourse i s to avoid damage in the first place. Bead-blast residues are relatively sm all and inexpensive to capture and dispose of.

2) Chemical methods would take advantage of the solubility of lead in certa in liquids at room temperature (i.e, acids). FUNDAMENTAL PROBLEM: aqueous-b ased solvents WILL be absorbed into the plastic. Further, acidic ions will remain trapped in the crevices by capillary action and migrate over time by diffusion directly into through plastic to the electronic device where cor rosion could occur. So the requirements for dissolution by acid are: Acids that would eventually cause device failure are excluded (this eliminates HC L due to chloride migration to the wirebonds and subsequent corrosion), aci ds that are difficult to rinse are excluded (sulfuric acid is notoriously d ifficult to rinse). Further, it would only make sense to encapsulate the ep oxy IC package in a protective covering to isolate the acid from the plasti c packaging in the first place (thus tooling and extra labor expense is inv olved). Acetic acid is a weak organic acid that *might* be usable, in that its diffusion through plastic is lower due to the larger molecule size comp ared to HCl. You'd have to check acetic acid against solubility of lead vs. its compatibility with gold, silicon, aluminum, copper, epoxy used in IC m anufacturing. THEN you'd need to 'tin' the leads with some other metal (ano ther expense). After rinsing, the plastic packages would need to be 'baked' to drive off the moisture (and hopefully acetic acid residues if baking te mp is above boiling point of acetic acid) - this must be done in a oven spe cially designed for removing humidity with a rechargable dessicant (an ordi nary oven won't get the dew-point low enough; you need -80°F dew point or thereabouts), and you'd need to confirm by laboratory methods the acetic a cid was gone. Acetic acid is so slow acting that I don't think you'd want t o wait around for it to work (time is money), but whatever the candidate ac id, it would be one that you could remove the traces of completely, and wou ldn't damage the device. You'll need to work with your plating shop to sele ct the ideal acid if you take this route. To confirm the effectiveness of y our rework procedure, the devices really should be tested with '85/85'-type device testing to confirm you haven't introduced a problem with the acidic removal of lead, and you'd need to confirm solderability with a soldering test to ensure the moisture introduced in cleaning was indeed removed from the epoxy and didn't affect solderability. Wet chemical methods seem like t he most logical or attractive approach at first glance, but really introduc e a host of problems that you'd need to test and confirm to ensure were avo ided by your manufacturing procedure. Hard experience shows: you could **RE ALLY** introduce problems and eventual failures in an otherwise reliable pr oduct if you don't carefully consider the impact of wet chemical methods. A nd remember, if you're not the person doing the work, the reliability is de legated to the person doing the work (you know what that means), so objecti ve testing methods and manufacturing process procedures are fundamental to making sure the parts aren't damaged in handling/treating. Also, the Pb in the dissolved acid is now a waste disposal problem and will need to be prec ipiated/concentrated before sending to a hazardous waste disposal unit (als o at great expense).

3) Solubility: One possible method worth investigating: how was the Pb appl ied in the first place? Was the Pb electro-plated on the IC leadframe? (in which case acid could not reach inside the encapsulated package to dissolve anyway), or, was it applied through a wave-solder or reflow method? Lead, like most metals, are soluble in other liquid metals (similar to mercury am algams). Depending on your devices, it might be possible to run them again through a wave-solder bath with the objective of dissolving the Pb in a wav e-solder bath that only consists of, say, tin-silver. This has the advantag e of not introducing moisture & acids into the plastic which you eventually will need to remove later at great expense, and, the packages are 'dried' by the high temperatures, and, any oxide layer that existed on the Pb-tinne d leads are now refreshed with new tin-silver tinning. Might be good idea t o package in nitrogen bags for storage if you don't anticipate using them u p right away to keep the tinned leads 'fresh' and oxide free. Only signific ant drawback: under the requirements of the law, you'd need to confirm that with your 'rework' method that the lead has indeed been dissolved to level s permitted by law; this however is basically a non-recurring expense with process monitoring (it also gets you off the hook if you show due diligence ). Further, if anyone tests the lead frames, they would only find tin-silve r on the surface of the lead frames (you'd need to dig into the fine print of the law, but traces of Pb that is buried deep in the product might be ex empt under certain instances). The only way to find the Pb would be to grin d up the IC into a fine powder and look for a Pb signature on a spectrograp h, and I don't think that is the intent of this initial RoHS initiative.

It could be some combination of the above would work for you also. Source(s):

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

Not much of a constraint. Actually, I lied, it can be shipped. Miscommunication. Apparently "welded" means something different to other people.

Probably not safe, cracking of the insulation ($$$$$$$$) and lead fumes.

Best regards, Spehro Pefhany

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Not BS. I was originally told it was welded into a big chunk of a multi-million dollar "thing", but it turns out not. Still better not shipped.

Turns out it doesn't have to be done in-situ, but still I'd hand carry the d*mn things.

Best regards, Spehro Pefhany

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Would it be an optionto machine off the sn/pb and Nickel, then replate?

Cheer

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?

In Any case give ATO a call.

They would have a better answer for sure.

Cheers

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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