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Best chemical for removing flux residue?

Discussion in 'Electronic Repair' started by [email protected], May 30, 2007.

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  1. Guest

    When repairing circuitry, its often tricky to remove flux residues
    from the PCB after rework.
    The flux remover spray I find locally in my area doesnt seem to be
    very effective.
    for this (some type of CFC). Can anyone recommend an effective flux-
    remover spray (brand) that perhaps I can order online?
  2. Ron(UK)

    Ron(UK) Guest

    A trick I used to do when I repaired boards for a commercial company,
    was to lightly brush over the newly soldered joints with a brass wire
    brush, then mop over the area with isopropanol. This smooths out the
    coating on the board and makes it virtually impossible to see which
    components have been changed.

  3. I've never bothered in many many years of DIY building stuff and never had
    problems. Might make a difference with densely packed SM technology,
  4. Smitty Two

    Smitty Two Guest

    Isopropyl alcohol works quite well, as long as it's 99% or so. Don't use
    the watered-down drugstore kind. Commercial flux thinner is mostly ethyl
    alcohol and that works, too, but it's usually more difficult to obtain
    and quite a bit more expensive. Isopropyl runs in the neighborhood of
    $25 for a five gallon can from an industrial chemical supply house.

    I don't use a spray bottle because it distributes the dissolved flux all
    over the place rather than picking it up. I buy 6" cotton swabs by the
    case (10,000 pieces) for less than $50. A Menda dispenser is handy for
    dampening the swab prior to working the flux residue. Several swabs will
    be needed and patience is more important than furious pressure and
    speed. Still it only takes a minute or two to clean up after a typical
    component replacement.
  5. James Beck

    James Beck Guest

    Why not use the watered down stuff?
    Some of the fluxes out there are water soluble and between the alcohol
    and the water I think you would have the bases covered.
    We have been using 90% for 20+ years. Seems to have worked just fine
    for us. In fact, until they changed their formula, we used a local
    industrial chemical manufacturer's "Window Cleaner" that was just
    isopropyl, water, some surfactants, and a little blue dye. 55 gallons
    drums of the stuff was pretty reasonable.

  6. Smitty Two

    Smitty Two Guest

    Good considerations, and I'm hardly in a position to disagree with your
    experience. My thinking is that if it's water soluble flux, use water.
    If not, the water just reduces drying time, reduces cleaning
    effectiveness, and helps to exacerbate the spreading of flux residue
    over an increasingly larger area of the board.

    Of course, for most repair work, that's not an issue. Perfect cosmetic
    cleanliness is demanded of me by my commercial customers, so a little
    irregularly shaped stain of flux residue, however slight, just won't
    fly. Your average consumer isn't going to notice or expect that.

    It's good to remember that rosin flux is non-corrosive and
    non-conductive and there's no real need (other than cosmetic) to clean
    it up at all, while water soluble flux is definitely corrosive and
    should be pretty thoroughly removed soon after use.
  7. Smitty Two

    Smitty Two Guest

    Uh, I meant increase, of course.
  8. Arfa Daily

    Arfa Daily Guest

    For many years I've used Servisol De-Flux 160. Just got a new can today in
    fact. Cheap, well behaved and controlled aerosol, and very effective.

  9. Jim Yanik

    Jim Yanik Guest

    The usual "rubbing" alcohol found in US drugstores is 70% alk.
  10. James Beck

    James Beck Guest

    Here, I have no problem finding 90% at our local national chain drug
    70% is the most common, but 90% is not that obscure.

  11. JeffM

    JeffM Guest

    This violates the teachings of every advisor I have ever had.
    Makes me think you don't live near a large body of water.
    When working in a Southern climate near the Atlantic Ocean,
    airborne moisture was the enemy.
    Anything that would absorb it was equally depricated.

    This report
    says that putting PCBs in a vapor degreaser made things WORSE.
    So much for intuition.
  12. In the UK? You're never that far from a large body of water. Including the
    If the sort of flux found in standard lead multicore solder was very
    hydroscopic surely it would be easy to wash off with water?

    I'm ignoring modern lead free solder and water based flux. For the rest of
    my life. ;-)
  13. DaveM

    DaveM Guest

    Rosin-based flux comes in several levels of activity. Type R (rosin) flux
    contains rosin only, with no cleaning agents. RMA flux (rosin-mildly activated)
    contains a nominal amount of cleaning agents, and RA (rosin-activated) flux
    contains a fair amount of cleaning agents. The cleaning agents act on the
    metals being soldered to remove surface contaminants and float them away so the
    metals are adequately wetted by the solder.
    The RMA and RA fluxes are corrosive if insufficient heat is applied to the
    fluxed area during solder to neutralize the cleaning agents, and over time will
    definitely cause problems if not properly cleaned after soldering.

    Water soluble fluxes are more active than any of the rosin-based fluxes.
    Organic flux is more active than RA flux and inorganic flux is the most active.
    Obviously, all fluxes need to be cleaned after soldering to avoid any
    possibility of contamination or corrosion. Mil-spec soldering requires that all
    flux residue be removed after soldering is complete.

    Dave M
    MasonDG44 at comcast dot net (Just substitute the appropriate characters in the

    Life is like a roll of toilet paper; the closer to the end, the faster it goes.
  14. Smitty Two

    Smitty Two Guest

    Kester disagrees.
  15. I've never noticed being given a choice when buying lead multicore. And I
    buy it from a large supplier, and keep four reels of different sizes on a
    dispenser. Perhaps I've simply never looked. Of course what industry uses
    for mass production can well be different from that used for one off
    construction, repair and servicing.

    The earliest PCB I have and assembled is well over 40 years old. Still
    works fine. ;-)
  16. GregS

    GregS Guest

    I use ethanol when I get it for free. You can even take a drink if you need it.
    95% is the common variety, and the higher % stuff has some nasties.

    Electronic supply houses sell the isopropal, allthough shipping can be a problem
    fo rthe high % stuff. I have also used some harsh spray cleaners, but they
    can damage components.

    We used to use Tri back in the 60's to clean boards. used to have a spigot
    at DEC for cleaning boards. Worked the best.

  17. Tim

    Tim Guest

    I use laquer thinner on a q-tip. Wrks well for me. It does leave a
    slight whit residue sometimes, but that is easy to wipe off.

    - Tim -
  18. me

    me Guest

    Acetone and a small brush works nicely.
  19. I use MEK (methyl ethyl ketone). I can pick it up in gallon sized cans at a
    paint store. Does a wonderful job with flux, just don't get it on plastic...

    Mark Z.
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