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Lead-Free vs. 63/37 tin/lead solder

Discussion in 'Electronic Repair' started by [email protected], Jun 7, 2006.

  1. http://en.wikipedia.org/wiki/Soldering
    http://www.finishing.com/Library/flux.html
    http://www.worldwideflood.com/ark/pitch/pitch.htm

    Ignoring acid flux, the rosin fluxes come in two flavors. Water based
    and those that require some solvent to remove. Water based fluxes can
    allegedly be left on the board and will not eat the copper traces. The
    inspiration for this was not to reduce cleanup costs, but because of
    environmental and workplace regulations which proscribed the use of
    chlorinated hydrocarbon solvents for board cleaning.

    The problem is that water soluble fluxes require rather hot water to
    remove properly. They're mostly used wave solder machines and not
    hand soldering. However, we were using them on the production in
    rework stations and of course, I ended up with a few rolls of the
    stuff. That's when I discovered that if you leave the flux on the
    board for more than a few days, it turns rock hard and no amount of
    hot water will get rid of it. The residue is water soluable, but the
    big lumps left in rework are not. I experimented with some household
    cleaners and found the ammonia cleaner sorta works. It's often easier
    to scrape the ossified flux off the board than to wash it as it's
    quite brittle.

    Another fun experiment was to make my own flux. I managed to
    accidentally purchase a roll of solid core 63/37. No flux inside. I
    could purchase a tub of Kester rosin solder paste, but that's too easy
    and no fun. Rosin is just tree sap and I live in a forest with pine
    trees and lots of sticky gooey sap. I just walk outside, scrape off
    some pine sap, and I have instant rosin. I melted a big lump of the
    stuff to clean it and boil off the volatiles, and voila, instant
    sticky rosin flux.

    When testing it, I found that the soldering iron was insufficient to
    set the flux on fire, but did an adquate job of converting it into
    noxious fumes. Rosin works by vaporizing into a cloud of inert smog,
    which protects the tin and lead from oxidation. The soldered
    connections were successful, but difficult to see under the carbonized
    sticky mess. Removal required trichlorethane (auto brake cleaner) and
    some elbow grease. Once cleaned, the connections looked quite shiny
    and bright. Obviously, I missed a step in the production process, but
    in general, it worked.
     
  2. Arfa Daily

    Arfa Daily Guest

    Ah ! See ... I knew there'd be someone out there that knew about the
    chemistry of fluxes. Thanks for the info. Most interesting.

    Arfa
     
  3. g. beat

    g. beat Guest

    I'm a bit confused about the talk of not using acid fluxed solders in electronics. Just about all conventional solder wires formulated for electronic work, contain one or more cores of rosin based flux. As far as I am aware, this is a fundamentally acidic material when in its activated state, and in fact its being acidic is how it removes the tarnish and oxidation on the surfaces to be joined.

    Afra -

    In the United States, acid core (and not rosin core) was readily available for the plumbing trades (soldering copper water pipes)
    When I started in 1970, it was easier for a newcomer to walk into a hardware store and purchase this formulation instead of rosin core (referred to as Radio-TV solder it that era).

    While the problem has been greatly reduced, I still find a few amateurs commenting that they are using the same roll of solder they purchase many years ago -- for the copper water pipes in the house.

    gb
     
  4. g. beat

    g. beat Guest

    Go back to store and tell manager to fire him (or shut him up)

    gb
     
  5. It's a question of quantity.

    Both acid core and activated rosin flux contains ammonium or zinc
    chloride. When heated, these produce hydrogen chloride gas (not
    liquid) which disolves the copper, lead, and tin oxides and keeps the
    solder joint clean. The metallic oxide is converted to zinc, metal,
    and a salt. A detailed explanation can be found at:
    http://yarchive.net/metal/soldering_flux.html

    The difference is that the typical mildly activated rosin flux
    generates hydrochloric acid vapor, not liquid. There's very little
    acid in the flux and none in the residue. The bulk of the oxidation
    protection is from the abietic acid in the rosin.
    http://en.wikipedia.org/wiki/Abietic_acid
    This effectively protects the copper from oxidation, but not the lead
    or tin. That's what the hydrochloric acid smog from the activated
    flux produces.

    On the other hand, plumbers acid core flux contains the same ammonium
    or zinc chloride, but in much larger quantities. There's plenty of
    corrosive hydrochloric acid in the residue. That's the problem. Left
    on the board, the acid will corrode everything. Just using such flux
    around circuit boards will evaporate the acid, which will condense on
    nearby components, and eventually corrode them.
     
  6. Arfa Daily

    Arfa Daily Guest

    Thank you both - more good stuff on the subject !

    Arfa
     
  7. Franc Zabkar

    Franc Zabkar Guest

    I find that metho leaves a white stain on some PCBs.

    - Franc Zabkar
     
  8. Lionel

    Lionel Guest

    [cleaning flux from PCBs]
    Get out the meth's again & vigorously scrub the stained areas with an
    old toothbrush. That usually does the trick for me.

    Isopropyl alchohol is less likely to leave residue, but it costs a lot
    more.
     
  9. mc

    mc Guest

    [cleaning flux from PCBs]
    Not in the USA. 70% isopropyl alcohol (mixed with water, perfectly good for
    defluxing) is 40 cents for 500 mL at the corner pharmacy.

    How is isopropyl alcohol made and why is it so cheap and abundant in the USA
    compared to other countries?
     
  10. Arfa Daily

    Arfa Daily Guest

    The IPA normally sold for electronic purposes is very pure at 99.7% or
    better. Lower grade rubbing alcohol is also abundant and cheap over here.
    However, I have to say that the high grade stuff is not especially
    expensive, and lasts a long time. I buy it in a 1 ltr tin, and one of those
    lasts about a year in my shop. I don't use it for defluxing though. For
    this, I buy an aerosol product from Servisol called "De-Flux 160". It comes
    in a 200ml can and lasts me for a good six months. Only a tiny spray is
    required, and with a stiff toothbrush, flux and other nasty deposits
    disappear like magic.

    Arfa
     
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