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Solder Paste Flux?

Discussion in 'Electronic Basics' started by Ron J, Feb 28, 2006.

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  1. Ron J

    Ron J Guest

    Hi all,

    I just went to local electronics hobby store and got GC Electronics
    Soldering Paste (Flux). I'm now confused. The container says Soldering
    Paste, but right above it says Flux. Did I just get a Flux material or
    does this contain solder, as well? Can I use this Soldering Paste /
    Flux material for toaster oven reflow?

  2. Chris

    Chris Guest

    Hi, Ron. Could you provide the GC part number?

  3. Ron J

    Ron J Guest

    Hi Chris,

    I can only find GC 10-202 on the container. More accurately, it says
    "Water Removable Soldering Paste" with "Solder Flux" written on top.

    The directions state:
    1). Apply Water Removable Soldering Paste
    2). Heat
    3). Then add GC's pure non-leaded solder

    So, I'm guessing this is just a flux? But if that's the case, why do I
    need to heat the paste first?

  4. Chris

    Chris Guest

    Hi, Ron. GC 10-0202 is a water cleanable, organic flux made to be used
    with a lead-free solder. I'm not sure if GC Waldom still sells that
    kind of solder. You can still use it with leaded solder, as long as it
    either has no flux core, or has an organic (water soluble) flux core.

    Look on page 16 of the Chemicals section.

    Flux is a good thing to have on the bench, because many times the
    circuit board pad has become somewhat oxidized, or the component isn't
    easily wettable for some reason. Also, extra flux usually means you
    don't have to heat as long to get a good solder joint. The small
    amount of flux in the solder wire core may not be enough to clean the
    surface of the pad.

    To use the flux manually, apply it to the circuit board or area to be
    wetted. Apply the soldering iron to the area for a brief time to heat
    up the flux (it becomes reactive at higher temperatures, and is
    relatively inert at room temperature). You usually see it bubble, or a
    small amount of smoke will come of the flux as it's heated. Then apply
    the solder to the jointand release both the solder and iron as the
    joint is formed. The flux cleans and chemically activates the metal
    surface, making it more easily wettable by the solder. Otherwise, you
    might just have a blob of solder sitting over a dirty pad or component
    wire, with either poor or no electrical connection.

    The advantage (such as it is) of organic water-soluble fluxes is, of
    course, that the residue can be cleaned after soldering without using
    banned solvents. This is something of an advantage, but organic fluxes
    are less inert than rosin at room temperature, and can cause conductive
    paths across the circuit board. Also, they can be kind of aggressive
    at elevated temperatures, causing etching of traces under SMT
    components that get hot. So, with organic water-soluble fluxes, you
    really should make sure to clean the boards in water after you're done
    (I like to use Palmolive Green in warm dishwater concentrations with a
    brush, followed by a straight hot water rinse and warming oven dry).

    Also, this is a water-soluble organic flux, so you should avoid mixing
    it with rosin-based fluxes. Neither one works as well when they're
    mixed, and you usually end up with something that doesn't work or clean
    very well. Most wire solder has a flux core, so you should check
    before you use it. If you want extra flux with a rosin core, use
    GC-10-4202 liquid solder flux.

    I hope this is the explanation you were looking for. If not, please
    post again.

  5. Ron J

    Ron J Guest

    Hi Chris,

    Thank you very much for the informative post!

    I have a Radio Shock solder that says "Silver-bearing solder." I don't
    see any indication of rosin-based flux. Will this work with the GC

    Also, to clean the board with water, do I need to use distilled water
    and not tap water?

  6. Chris

    Chris Guest

    Again, a part number would have helped. The website shows two current
    selections for "silver bearing solder". 64-035 shows rosin core on the
    webpage. The other, 64-013, doesn't show anything. It may or may not
    have a flux core.

    If the label on the package doesn't say anything, you might want to
    take a razor blade or sharp utility knife and make a non-perpendicular
    cut in the wire. If you see something that looks like a hollow core in
    the center of the wire, it has a flux core. You then should determine
    whether it's rosin or organic. Failing everything else, if you happen
    to know what standard rosin flux smells like, just touch the tip of
    your hot iron with the solder and take a sniff.

    However, it really should say on the package.

    I would doubt Radio Shack would sell solder with organic flux (it's
    quite a bit more hazardous than the rosin stuff, and they do have
    lawyers), so if it does have a flux core, you probably shouldn't use it
    with your organic flux.

    And if you're near the Radio Shack, you may want to look at Catalog #:
    64-022. It's a 2 oz. Non-Spill Rosin Soldering Paste Flux, if you have
    to have some. But as I said, most solder comes with some kind of flux
    core, and that's sufficient for most electronics work.

    By the way, if you are going to be using the Palmolive cleaning method
    (recommended by Bob Pease of National Semiconductor, along with the
    dishwasher method), plain very warm tap water should be adequate for
    most stuff. Use lots of it to rinse off any residue. Another pass
    with the brush while rinsing isn't a bad idea, either. Make sure,
    though, that everything on the board can be water-cleaned. Many
    things, such as pots, relays, switches, &c., will retain the water, and
    then cause you grief when you turn it on. Either that, or washing will
    remove lubrication, or cause oxidation. If you have these components
    on board, you have to install them after water washing.

    Good luck
  7. Ron J

    Ron J Guest

    Hi Chris,

    Thank you again!

    I found this page: Radio/Experimentation/N2PKVNA/SMT.htm

    In it, the author mentions that "the solder is 0.015 inch
    silver-bearing solder made by Radio Shack (64-035E). In general, silver
    solder is becoming more common because there is a drive underway to
    remove/reduce lead from all products. While silver-bearing solder may
    have slightly improved conductivity, and it is much stronger than pure
    tin-lead solder, it does have a slightly higher flow temperature. Note:
    this solder, and as best as I can tell, all solder of that thin
    diameter, do not have a rosin core. The solder is simply too small to
    support a core of flux."

    I have the same Radio Shack solder. However, when I search on the
    website I only found the one that you mentioned 64-035...and not
    64-035E. I wonder if they are the same. The picture on the RS website
    does have the same marking except for the extra E on the part number.
  8. Chris

    Chris Guest

    Hi, Ron. I'm not familiar with Radio Shack solder. I've got a few
    spools of Kester (a 1 pound spool will last forever), and use those.

    The 64-035 is eutectic 62%-tin, 36%-lead, 2%-silver solder, not the
    lead-free type. The silver is useful in SMT soldering to help prevent
    leaching from the component terminations, a big problem with hobbyist
    work. The 64-035 is also .015", and _does_ have a rosin flux core.
    Again, use a new razor blade to make a diagonal cut in the solder wire,
    and you should see it kind of fold in. Or just touch it to a hot
    soldering iron. If there's no flux, you won't see any wisps of smoke,
    hear any hissing when it melts, or get any smell off the solder. All
    flux is chemically active when it heats up, which means that it will
    give you an odor. I would think RS would give a different part number
    if they made a major change to a solid wire solder.

    For manual SMT work, it's better to use some kind of extra flux, if
    only to help avoid overheating of components. If that's what you've
    got, you might as well try it. But you should get a feel for using the
    different types of flux, and choose one or the other if you're going to
    be doing this regularly. I'll use Kester "44" whenever I can for
    prototype and repair work, but if you need to clean the board, common
    sense as well as consideration for the environment might lead you to
    use the water-soluble organics.

    Good luck
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