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Fast soldering techniques

Discussion in 'Electronic Basics' started by Bahremu, Dec 23, 2004.

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  1. Bahremu

    Bahremu Guest

    A while ago I was working with an older engineer developing some boards for
    my old college. He kept saying how easy it would be if we had a large
    solder pot to dip the populated boards into to solder them. I know of
    reflow and wave soldering -- not ot mention manual soldering -- but how
    would soldering with a large solder pot work? I can see it being similar to
    wave soldering, the board being in direct contact with the molten solder.
    But i keep thinking that the dross would hinder the ability for the joints
    to form well, and what about fluxing?

    Can anyone explain how static soldering works, and maybe a book about
    soldering techniques?

  2. Guest

    skim the dross off and quickly dip the prefluxed board.........
  3. John Larkin

    John Larkin Guest

    And inspect for and rework all the solder bridges.

  4. CFoley1064

    CFoley1064 Guest

    Subject: Fast soldering techniques
    I don't think you'll find a book on this subject -- this is definitely an
    inferior method of soldering. The most important flaw is that it will leave
    much more solder on the individual solder joints, which will really tend to
    cook your transistors and such. It was a fairly common method in the '60s,
    though, and it _is_ faster than soldering individual components by hand.

    If you insist on doing this, and you have a fairly small board, you first have
    to look at which components are most susceptible to heat damage, and set them
    aside to do by hand later. Actually, this may not be so bad, especially if
    you're using sockets for your ICs. Basically, your biggest problems then will
    be with semiconductors, small signal diodes and electrolytic caps.

    Once you've got that out of the way, give some serious consideration to
    clinching the leads down on the pads while you're cutting them. This will
    result in less solder in the solder joint, and less surface area of the lead in
    contact with the solder to channel heat up to the component. It also keeps the
    components from popping up when you don't want them to. You also might want to
    dab some soluble solder mask over the pads on the components you're reserving.

    You obviously need a solder pot with a surface area larger than your circuit
    board. Make sure that solder pot has a good heat control (in most cases, the
    bimetallic switch type are too crude -- you don't want the solder any hotter
    than necessary. Try a setting of about 430 degrees to start, and see if you
    get good wetting of pads. You definitely need euctectic (63-37) solder for
    lowest solder temp, filled up past the top of the tub (the meniscus of the
    solder is over the level of the top).

    Now, before you start, you need an infrared heating lamp, some liquid
    rosin-based flux (thicker is better), a paintbrush, and a fixture to hold the
    circuit board so your hands aren't too close to the heat (either that or wear
    thermal gloves). Try to use steel for the part of the fixture that clamps the
    board -- it's strong, the solder won't wet, and you can dump it in water to
    cool when you're not using it without worry. Also, ventilation is a must (you
    breathe, right?)

    Now you can begin. Clean any dross off the surface of the solder. Clinch the
    leads on the components on the board. Apply solder mask. Place your small
    board in the hand-held fixture. Get your good rosin flux, and paint the flux
    onto the bottom of the board while holding the board so the solder side is
    down. Paint strokes left-right, and forward-reverse, so as to make sure the
    flux gets into every nook and cranny. Enjoy the dripping and slop. This is
    one place a syrupy flux comes in handy. Now hold the small board (solder side
    still down) under a heat lamp to increase the surface temperature of the traces
    and flux temperature (this activates the flux and starts the chemistry before
    it hits the solder). I guess you'll have to time this. If the components get
    too hot, or if the board starts to discolor, you've gone way too far.

    Now immediately bring your handheld fixture over to the solder pot. Hold your
    eye (you ARE wearing safety glasses, right???) level with the surface of the
    pot, so you can see the surface of the solder. Not too close, OK? Now angle
    the board slightly, and then slowly set one edge of the bottom of the board
    barely touhing the solder. In about 1 second, pull the angle down so all of
    the bottom of the board is touching the solder. Now quickly push down
    slightly, so the meniscus of the solder is starting to come up on the edges of
    the board, but not enough to have the solder start pushing up through the
    holes. After a mystery time (you'll have to determine this yourself, use a
    count of four seconds as a start) leave the entire board in the solder. Now
    lift the end of the board opposite the one you put in, then take the whole
    board out of the solder. Hold the board steady and motionless once you've
    removed the board from the heat area immediately above the solder, to allow the
    solder joints to set. With a little practice, you won't have to eyeball the
    level of the solder -- you can play with the depth just by looking at the
    meniscus of the solder on the board. You can even let the level of the solder
    come down to the level of the top of the pot.

    After this, clean using totally aggressive '60s organics which are now all
    blatantly illegal, hand solder the components you held back, and moan about
    your poor yield. If you haven't left the board in the solder too long, you
    don't have issues with solder bridges and with solder flecks sticking to the PC
    board. If you have, welcome to the rookie leagues. Get out your magnifier,
    pick and soldering iron, and get to work.

    That is, if you insist. This is an ugly way to do real boards.

  5. Dmitri

    Dmitri Guest



    Dmitri Abaimov, RCDD
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