Soldering aluminum tabs

Hey all,

I’m going to try and solder some copper wire to aluminum pads/tabs, and have heard that that is quite difficult to do with ‘normal’ solder wire - is that true? Does anyone have any experience with soldering onto aluminum? I read that getting something called aluminum solder paste can make things a bit easier - I poked around the elab but didn’t notice any laying around. Does anyone know if we have a tube of it anywhere?

Thanks!

Not at all true. Rather it is essentially impossible with normal solder. The oxide layer on the aluminum can’t be wetted by molten lead or tin, and is an electrical insulator to a reasonable extent. Theoretically an aggressive flux might make some progress, but I’ve never read of an application for it.

Electrical connections to aluminum are nearly always made mechanically, usually submerged in dielectric grease to keep oxygen out, and often augmented with zinc whiskers to penetrate the oxide layer on the aluminum, as well as act as sacrificial anode. Noalox is one commercial dielectric and zinc whisker paste sold at home centers for the few remaining applications for aluminum wiring in residential wiring.

Is there some strongly overwhelming design constraint that prevents a mechanical connection?

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Thanks for the reply! The contacts are very short (tabs extending 1cm out of a lipo battery back) and the two tabs can’t sit tab to tab, so i think a mechanical fastener is out of the question.

Good to hear that the solder paste is sold at home centers though. do you know if we have any laying around at the space? i looking on amazon and all of the tubes appear to be in the $10+ range, so it’d be nice to not have to buy one for a single solder.

Noalox mentioned relative to home centers isn’t a flux. It is a corrosion inhibitor and conductivity enhancer for cold mechanical connections.

Are you sure your pack doesn’t have nickel tabs already attached? Those are much easier to deal with.

Also, please don’t use the stuff intended for aluminum tabs on the irons in e lab without permission from the chair. That stuff eats soldering iron tips, and without proper cleaning, will leave a residue behind that can transfer to the next few projects that can eat through expensive components/projects.

Separately, especially if they are nickel tabs, or maybe aluminum that can be spot welded to nickel tab extensions, e lab does have a battery terminal spot welder.

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Why not use the spot welder in the eLab that is made specifically for batteries? There is even a roll of nickel tape in the toolbox.

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Noted the corrosive nature of the aluminum paste, i’ll be sure to get clearance and be careful with it if I end up going that route.

I can’t make a terminal to terminal connection with a nickel strip as the bridge as the terminals are going to be about 3 inches apart and there will be far too much current running through these terminals for a nickel strip to bridge over that distance. Spot welding nickel strips to the aluminum tabs as a intermediary and then soldering a wire onto that might work though - good suggestions, I’ll have to look into that.

And honestly, no, I am not 100 percent sure that they are aluminum pads and not a thick nickel one as I haven’t actually opened the batteries up yet. From the posts online that I have seen, though, most lipo batteries appear to use aluminum because they are moving so much current (these batteries are theoretically rated for 300 amps [which I find hard to believe] and run in real world conditions of 60 amps very regularly)

https://www.amazon.com/MG-Chemicals-Two-Part-Conductive-Adhesive/dp/B008UH4DB2

Have fun paying for it.

https://www.amazon.com/Aluminum-Solder-Wire-96-5-3-5Ag/dp/B00DC3102Y/ref=sr_1_3?ie=UTF8&qid=1517852658&sr=8-3&keywords=aluminum+solder

This is what I’ve been recommended so far, but again, it’s 30 bucks and I’m just making two connections so I really don’t want to buy the entire roll if there are any alternatives.

I ended up spot welding nickel strips onto the tabs and then soldering on to those. Worked out reasonably well.

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Cool!

Glad that worked out for you! It was odd that some had aluminum and others had copper strips attached to them.

Raymond

One of the electrodes is always aluminum. Good quality cells always weld a nickel tab to it. Budget cells sometimes don’t.