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Solder to Aluminum?

Discussion in 'Electronic Design' started by Chris Carlen, Jun 14, 2005.

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  1. Chris Carlen

    Chris Carlen Guest


    I have voice coils wound with aluminum magnet wire that I need to solder
    to a flex-PCB with tin plated pads.

    Any idea on the best alloy/flux combo for that? Low melting temperature
    possible would be best to avoid harming the polyimide PCB substrate.


    Christopher R. Carlen
    Principal Laser/Optical Technologist
    Sandia National Laboratories CA USA

    NOTE, delete texts: "RemoveThis" and "BOGUS" from email address to reply.
  2. Al

    Al Guest

    Spot weld the aluminum wire to copper wire. If you don't want to spot
    weld, then use crimp hardware designed for aluminum/copper connections.
    Then solder the copper wire to whatever.

  3. mike

    mike Guest

    Depends somewhat on the size of your wire.
    There are various fluxes containing fluorides that can work on aluminum.

    There's some stuff called "solder-it" or "Kool-it brand" made by
    universal corporation. They have a lot of specialty soldering stuff.

    There's some aluminum welding rod called Welco 52. Can get it at any
    welding supply house. Made for low temperature welding of aluminum
    pieces. Also sold in hardware stores
    as no-flux aluminum solder or brazing rod.

    If your wire is big enough, you can use the Welco 52 and a torch to
    "tin" the wire. Then you can solder to the Welco 52 coating. I've used
    that technique to make aluminum resonant cavities that I could assemble
    with ordinary solder.

    Voice coil implies motion. Aluminum doesn't flex well. Make sure
    the aluminum part stays rigid.

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  4. colin

    colin Guest

    cant say if this is suitable or not, but the soldering iron tip
    wetter/flux/solder paste has an extremly active flux, ive used it to solder
    nichrome wire onto a pcb before, i did have some aluminium solder too but
    dont think i had much luck with it.

    Colin =^.^=
  5. I'd say 'forget it'. There are solders that will join aluminium to copper,
    but most involve an intermediate alloy, and some fairly nasty fluxes, and
    are usually at the higher temperature end of normal soft soldering
    temperatures. Have a look at: and look at Tra-Duct 2902. This could be ideal for the

    Best Wishes
  6. Chris Carlen

    Chris Carlen Guest

    That would be a nice way to do things, if there was enough space. But
    the coil terminations are about 4mm long, recessed in a notch in the
    aluminum coil former. I have existing coils that I wish to rebuild,
    that were soldered, so I know it can be done.

    Thanks for the input.

    Good day!

    Christopher R. Carlen
    Principal Laser/Optical Technologist
    Sandia National Laboratories CA USA

    NOTE, delete texts: "RemoveThis" and "BOGUS" from email address to reply.
  7. Robert

    Robert Guest

    There are quite a few metal filled epoxies around. Some with quite low
    resistance (the silver impregnated ones). Check the industry for those and
    then there's always:

  8. Robert Baer

    Robert Baer Guest

    JB Weld is excellent to hold things together.
    It is a darn good *insulator*.
  9. Robert Baer

    Robert Baer Guest

    Over 40 years ago, i wanted to solder to aluminum, and so bought some
    special solder for that, useable with ordinary solder irons.
    A bit problematic, as it had chromium (if i remember correctly), and
    the fumes were toxic.
    Worked *very* well; in fact, too well if the aluminum was too thin;
    the alloy crept underneath the oxide skin and leached the aluminum,
    making it thinner if one was not careful.
    The basic secret to soldering aluminim, is getting underneath or thru
    the oxide skin without allowing the aluminum to protect itself by
    creating new oxide.
    One can use ordinary electronic solder, and a rather active flux to
    break down the oxide and cover the area from oxygen.
    Once there is a break, the solder will *very* easily flow underneath
    the skin (makes it bulge as the solder flows underneath).
    The solder will quickly flow over the are wheer it is hot enough to
    keep it a liquid.
    So if you can heat a local are just enough to get that break, and
    quickly wipe the oxide off as it cools, then one can later do a quick
    solder of a copper wire to that area.
    Practice a lot on first a 1/16th inch sheet and then on similarly
    sized wires before doing the real thing!
  10. Well, I use Alusol from Multicore. It is listed for example at
    (search for Alusol). Melting point may be rather high perhaps - and the website says not suitable for electrical joints - but
    it works for me.
  11. David Lesher

    David Lesher Guest

    Solder in an inert atmosphere/vacuum, maybe?
  12. You are on the right track: don't let the Al2O3 reform.
    Instead of vacuum/inert gas, I had good luck with soldering under
    a droplet of engine oil. I was soldering to a 1mm by 1 cm Al strip, using
    a small 30 W iron; I wetted the tip with a blob of solder, and touched the
    side of the oil droplet, while scrapping the area covered by oil with a
    dental pick. Within 10-20 seconds, the solder wetted the scratched area
    under the oil.
  13. Robert Baer

    Robert Baer Guest

    No need for that extreme; most liquid fluxes stay around and keep the
    oxygen out.
  14. Robert Baer

    Robert Baer Guest

    OIL! Did not think of that.
    Forgive the pun, but that was a slick idea!
  15. Chris Carlen

    Chris Carlen Guest

    There is an alloy from Indium Corp that is 91Sn 9Zn which can solder Al
    with a flux. I'm waiting for them to get back to me.

    I can't find a US distributor of that Alusol anywhere. Thanks for the
    link, though.

    Good day!

    Christopher R. Carlen
    Principal Laser/Optical Technologist
    Sandia National Laboratories CA USA

    NOTE, delete texts: "RemoveThis" and "BOGUS" from email address to reply.
  16. Carl Ijames

    Carl Ijames Guest

    The technique I've read for soldering to aluminum with zinc alloys is to
    melt a blob of solder onto the aluminum and then to keep scratching back
    and forth at the bottom of the puddle with the soldering iron tip. This
    scratches through the aluminum oxide layer and exposes fresh aluminum
    which the solder bonds to, while the puddle of solder itself keeps
    oxygen away.
  17. Jim Thompson

    Jim Thompson Guest

    I haven't done it in years, but I recall a block of some substance
    with which you abraded the surface of the aluminum and then you could
    solder to it in a normal fashion.

    ...Jim Thompson
  18. Al

    Al Guest

    Might be sal ammoniac also known as ammonium chloride. You used to be
    able to buy them at Sears many moons ago.

  19. Here is something most folk don't know. During WWII the RAF mechanics used
    to solder plates over the bullet holes in Spitfire engines. They used a
    really hot iron and heavy engine oil. As an experiment I had a go at
    soldering aluminium and their method worked but was a bit hit or miss. You
    have to solder through a film of engine oil and keep the iron vigorously
    moving while tinning the surfaces. Yeah! I know it is not what you wanted
    but it was just a bit of history.

    Aefauldlie, (Scots word for Honestly),
    Robert, (Auld Bob), Peffers,
    Scotland, (UK).
    Web Site, "The Eck's Files":-
  20. Mike Monett

    Mike Monett Guest

    Robert Peffers wrote:

    You'd think a bullet hole would mean a ruined engine and a crashed plane.

    Where and how can you put a hole in an engine without destroying it?

    Mike Monett
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