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chemical solution for cleaning component leads

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LAN_403

Avalanche

Sat Oct 20 2007, 12:23PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

thought some of you chemistry guys might be able to throw some light on this one...

I have recently unearthed hundreds of perfectly good electronic components, mostly power switching transistors, but they have dirty tarnished leads that simply won't solder without manual cleaning with wire wool.

I wondered if there was something easily available that I could soak the components in to clean up the leads... I have tried carb cleaner (acetone, xylene, and methonol) but to my surprise it did absolutely nothing. It would be really nice to clean this lot up so that I can use them, it would be a shame to throw away such a lot of valuable components.

As you can tell chemistry not my area! I have some (dilute?) hydrochloric that I thought might work, but I don't really want to waste it (it's for filling motorcycle batteries!)

Thanks

ragnar

Sat Oct 20 2007, 02:31PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Are they RoHS-compliant parts that have been rotting and tarnishing for a while?

IMHO, European politicians spouted the generalizations that formed RoHS that made it illegal to use most products involving lead/mercury to get themselves into power.

Non-EU companies worldwide producing semiconductors, cadmium plated fittings and connectors, and compact fluorescent bulbs, etc, etc, etc, suddenly finding their products deemed illegal, should not subjugate themselves to the EU demands, and could probably afford to stop selling into Europe for a while...

...a while long enough for everything European to grow tin whiskers and die over the next decade, until some more politicians finally pay engineers and scientists to investigate...

But no, instead, we punish the manufacturers and engineers for the irresponsible actions of consumers who dispose of electronics where purportedly the heavy metals leech from landfill into groundwater.

Shame, I seem to have digressed.

Andy, personally I keep a pot of proper flux (the Zinc-reduced yellow acid goo with the fumes that taste foul), and a flux pen handy. Generally, swiping the leads (or circuit board traces, as appropriate) superficially with the pen is sufficient that I can get anything to whet nicely with lead-tin solder. In extreme cases, I dip them into the flux goo, then solder.

Carl Pugh

Sat Oct 20 2007, 04:39PM

Registered Member #1064 Joined: Tue Oct 16 2007, 05:04PM
Location:
Posts: 42

Some solders have much more active fluxes than other solders. Try a solder with a different flux.

Don't use solder with acid fluxes.

...

Sat Oct 20 2007, 04:52PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I would agree with matt, you just need to get a flux pen and put some decent flux in them.

Really, flux is the best cleaner you can use, because it was formulated to get rid of the corrosion you speak of, you get to use it when the surface is 600f, and you solder to the surface immediately after it cleans the surface. And its cheap

Bored Chemist

Sun Oct 21 2007, 09:36AM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

A few thoughts,
First; you don't put hydrochloric acid in batteries; my guess is it's sulphuric.

Secondly Matt's post, though interesting, doesn't actually answer the question as asked. He doesn't give some solvent that will clean up the leads.
What he does is advocate the use of a corrosive flux. The irony being that over time it will do at least as much damage as tin whiskers.
Certainly an agressive flux will help to solder dirty leads but it's really better to clean them.
Last time I saw any advice on the use of "killed spirits" as a flux it said you should boil the joint in water afterwards to remove the residues, otherwise you get corrosion problems.
I'm afraid that the best way round this is mechanical cleaning- sandpaper or a wire brush and be careful not to breathe too much of the dust. A wire brush on a "Dremmel" type tool is good, but only outside on a windy day unless you have a decent dust mask.

Incidentally re "IMHO, European politicians spouted the generalizations that formed RoHS that made it illegal to use most products involving lead/mercury to get themselves into power"
How can that make sense? Unless they were already in power they couldn't have made anything illegal. They only got into power because the people voted for them.

Sulaiman

Sun Oct 21 2007, 10:00AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

I still have components from the 70's and 80's - some quite tarnished / unable to solder reliably
these components are (of course) non-RoHS compliant, and I still use lead/tin solder
of various flux types, none seem to work - I resort to sandpaper.
SO I too would be very interrested in a simple 'solution'
Maybe I'll try "cillit-bang", seems to work on coins

(There's a bunch of cheesy adverts for a general purpose household cleaner in UK, brand "cillit-bang")

ragnar

Sun Oct 21 2007, 12:09PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Bored Chemist wrote ...

Secondly Matt's post, though interesting, doesn't actually answer the question as asked. He doesn't give some solvent that will clean up the leads.

You're right, I had a colossal axe to grind, and was grinding it at the EU's expense

If I've had a PCB made up (RoHS), and I have it shipped to my holder in the USA (before multiple packages are consolidated and shipped to me in Australia in one box), often by the time it gets here, if not well packed, it has tarnished badly. I find flux the easiest way to encourage fresh solder to take to the pads/traces, when I re-plate the board all over.

Bored Chemist wrote ...

What he does is advocate the use of a corrosive flux. The irony being that over time it will do at least as much damage as tin whiskers.

After this, I failed to mention I meticulously rinse and wipe the whole board in acetone, and this removes all flux residues, resin residues and crap from the board.

I can understand though, that this is probably impractical with soldermasked boards, and probably highly impractical with large, bulky components, which may even be attached to assemblies.

I think BC definitely has the right end of the stick with a small, powered wire-brush.

Eric

Sun Oct 21 2007, 06:35PM

Registered Member #69 Joined: Thu Feb 09 2006, 07:42AM
Location:
Posts: 116

It seems to me a dip in HCl would work. Choride attack is essentially how the aggressive flux works anyway so this is pretty much the same thing. The bonus is it should be easy to rinse away afterward. Couldn't hurt to try... I would try it with rubber gloves and a toothbrush or something to assist in removing lead oxide for really corroded parts.

Bjørn

Mon Oct 22 2007, 06:10AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Toothpaste and a brush works well on old PCBs. It might not be so practical on components.

Steve Conner

Mon Oct 22 2007, 10:17AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

How many could you have cleaned with wire wool, a fiberglass brush

or even scraped with a Stanley knife (the way I do it) in the time it took to write those posts?

Matt, I think everyone agrees RoHS was a sheer waste of time, but it's here, so get used to it! If you want something to really get worked up about, try the proposed incandescent lamp ban:

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