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Soldering surface mount components

Discussion in 'Electronic Basics' started by Daniel Kelly \(AKA Jack\), Jun 8, 2004.

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  1. Hi,

    I am planning a job where I need to manually solder surface mount ICs. Some
    of these ICs have pins that are only 0.5mm apart! I'm worried that this
    will be impossible to solder manually.

    I've looked on the web - people tell me it is possible to solder SMDs but
    I'm worried their talking about older SMDs with pin-to-pin distances of more
    like 1mm.

    I'm a relatively skilled soldering iron user.

    Is it possible to manually solder ICs with pins only 0.5mm apart?

    Thanks,
    Jack
     
  2. 1/ Magnification
    2/ Liquid flux and solder paste
    3/ Hot air soldering device
    4/ Practice and patience
     
  3. Mariano

    Mariano Guest

    How do you apply the solder paste manually to the IC pins or pads ? I've
    tried and the paste does not stick anywhere (before soldering). I even tried
    with a syringe and ended up clogging the needle.

    IMO this is the most critical part in SMD. It doesn't matter if your
    placement is poor, since the solder will try to align the components with
    the pads (when soldering). But you need to apply an even coat (and right
    quantity) of paste to each pad. This is were I fail.
     
  4. Ian Stirling

    Ian Stirling Guest

    To add to this, is it possible to buy smaller diameter than normal solder?
    I've found I can make my own, with a drawplate, but it is a tedious process.
    I ahven't found anywhere that stocks under .5mm multicore.
     
  5. Repzak

    Repzak Guest

    Hey

    Yearh.. i did it last week with a Tusb6250, on a home etched pcb...

    u just used some quite thin solder and a lot of flux....

    i thing my tip on the solder iron is 0,5 times 1mm ... but as long as there
    is a lot of flux and you dosent use much solder i runs nice... and maybe use
    "solder remover litze" with added flux to remove some of the solder there is
    to much...


    normally i just put litle solder on the solderiron tip and flux on the IC
    legs, and then the flux will attrack the solder to the legs...


    you could find some old computer stuff and remove some of the ic's with hot
    air and use then as test, before using an expensive ic

    Kasper
     
  6. Mjolinor

    Mjolinor Guest

    I just flatten it with pliers then cut it lengthways.
     
  7. Mark (UK)

    Mark (UK) Guest

    Hi!

    How I do it, is once the chip is removed, and you've got the bare pads,
    I then use a regular iron set to a low temp, 275-300, to go over the
    pads with fresh LMP solder and lots of flux, that tinns them up,the flux
    helps stop them joining together, and leaves solder on each pad to help
    solder the new IC legs to. Then use a hot air pencil to finally solder
    the chip in place.

    Yours, Mark.
     
  8. John Larkin

    John Larkin Guest

    Paste isn't necessary. Flux the pins (liquid, maybe diluted RMA rosin
    flux) and apply a small glob of solder to the tip of the iron. Run the
    tip down the pins, at the pin/pad junctions; solder will magically
    wick off the tip onto the pins. There are special "hoof" tips with a
    beveled flat that holds a nice little pool of solder to make this work
    better.

    Tack two corner pins first, then just run down the line. Works great.

    John
     
  9. Impmon

    Impmon Guest

    Yes it can be done, just use fine point, magnifying glass, and use
    little solder.

    It'd be easier to leave such tiny work to machines. Why do you need
    to solder them manually?
     
  10. Chuck Olson

    Chuck Olson Guest

    As mentioned, you need magnification. The first thing you should invest in
    is a binocular microscope with variable power from 7 to 30 diameters and a
    socket for a spotlight. If you can see it, you can do it. You should be
    able to find a used one for about $200, (try Ebay) (and another $25 for the
    spotlight) and it will last your whole life. You will be astounded at what
    you can see with that microscope - - from examining today's almost invisible
    electronic components to removing slivers and hangnails, and learning about
    tiny creatures. Nobody should be without one.

    The next thing you need is a soldering iron that allows your fingers to get
    within about 1.25" of where the soldering is happening so that you have as
    good control of the soldering tip as you have of the tip of a pencil when
    you write. I find the Metcal stuff works very well, and older used systems
    are available for under $100 on Ebay. Finally, you should be able to find
    some 0.020" diameter solder (try Ebay or a big electronics flea market).

    I made a surface-mount component clamp for my microscope consisting of a
    strip of springy phosphor-bronze or beryllium-copper between two standoffs
    about 3 inches apart and a piece of #12 wire soldered at the middle of the
    strip to form a "T" so it pokes almost into the field of view of the
    microscope, and finally a piece of #20 solid wire soldered at the end of the
    #12 arm and bent down so the tip of the wire presses on the component you
    want to solder right in the middle of the field of view. Just pull up on
    the spring-supported #12 arm when you want to move the assembly or lift it
    up onto another component.

    Good luck,

    Chuck
     
  11. Hi,
    I'm building a one-off design for a psychology PhD experiment. I do have
    access to University College London's Electrical Engineering department but
    I doubt they have robots for building surface mount systems.

    Oh, and I have looked long and hard for 'normal' sized chips but they just
    don't exist for the sort of application I need.

    Thanks,
    Jack
     
  12. Excellent, thanks so much for all the help, everyone.

    Jack
     
  13. Tim Auton

    Tim Auton Guest

    They will have technicians, lecturers and students who should know
    what to do though. Ask nicely and someone might give you a
    demonstration and show you the tools they have available.


    Tim
     

  14. Antex low watt iron with fine tip. Use a flux pen to paint flux onto
    pads. Using tweezers hold the I.C. in place and tack the corner pins.
    Apply just enough solder to iron tip to wet it and flick off excess.
    Apply the tip very briefly to the pin end and pad and the solder will
    wick into and between the pin and pad. When removing a chip without
    heat simply take a sharp Xacto blade and carefully apply pressure to
    the blade onto the pins as near to the chip body as possible. This
    will sever the pins from the chip body making them easier for removal
    without lifting a pad. Be careful to not exceed the pin / chip body
    with the knife or you will risk opening a trace. I have been doing
    this for years and have lost a trace or pad in over twenty years.
     
  15. Yes, good plan.

    Jack
     
  16. Gordon Youd

    Gordon Youd Guest

    I have a VHS video demonstrating METCAL Soldering Systems.

    They make SMT rework by hand look so simple, like John Larkin said "tack the
    ends and run down the line".

    Try CPC Ltd for a copy of the video, it's free.

    If you cannot get a copy I can copy mine for you.

    The site for Metcal is www.metcal.com, I could not find the video there
    but electronic wholesalers have it.

    Regards, Gordon.

    Remove the Z from my address to reply.
     
  17. I have Flux inside a syringe with a 1mm needle. Before application i
    heat the syringe and the flux with the heatgun to 80 degC or so.

    The solder past also comes in a syringe that needs to be heated before
    use. I prefer the 1mm tin wire though. Tin paste is a mess.

    Rene
     
  18. Yes. Sure.

    For magnification I recommend strong reading glasses. I use 4 dioptries.
    That let me have it as close as 15cm from my eyes.

    Then I use fluxpaste from a syringe, heated with the heatgun to make it
    more liquid.

    And medium tip iron plus 1 mm or 0.8mm tim wire.

    First come the fixng phase where two diagonal corner pins are soldered
    down. It doesn't matter whether the adjacent pins are soldered too.

    Don't even try to solder a single pins. A few of them at one is ok. The
    flux separates the tin on the pins.
    Oh, yes, having a soldermask helps.

    Rene
     
  19. Mariano

    Mariano Guest

    Can anybody point me to any flux and paste product in the US ? I checked
    Newark products and they are quite expensive. And since I have no experience
    with flux/paste, I don't want to screw up buying something useless.

    Thanks.
    Mariano
     
  20. Paul Guy

    Paul Guy Guest

    The pads MUST NOT have any applied solder on them. If they do,
    remove it all with solderwick. (the bumps from the solder will not
    allow the chip to lie flat.)
    Align the IC, solder one corner pin to hold it down. Solder the
    opposite corner down. Don't worry if the solder joins several pins.
    Make absolutely sure it's aligned properly, and all the pins are
    resting on the pads. Now apply enough solder that all the pins are
    covered, even if they are all shorted together.
    Here's the neat part: Take some "solderwick" (the braided stuff you
    use for removing solder) and remove all the solder! It doesn't really
    take it all off, it leaves the required amount underneath the "feet"
    of the pins. If you look in a microscope, you'll find that you have
    almost perfectly soldered pins. There will be trouble if the pins
    didn't all touch the pads prior to soldering. Chips intended for
    surface mount must have good co-planarity, so be very gentle handling
    them. If you bend the leads for than a few thousands of an inch, you
    can expect trouble.
    If you have a good touch with an iron, and are using good liquid
    flux (RMA type, you must remove the residual flux afterward using a
    solvent like isopropyl alcohol), you can zoom thin solder along the
    pins, and it will not short them out. I believe it's absolutely
    necessary to use the proper liquid flux in order to pull this off, and
    it does need a bit of practice. You'll need the solderwick to remove
    shorted pins. I figure if you're using solderwick anyhow, then do the
    first method and not lose any sleep over it.
    I have successfully soldered QFP80's this way, the most difficult
    part is the alignment to the pads.
    This is not a fast way to solder, but it doesn't need any fancy
    equipment.
    To show how crude you can get, instead of using our hot air reflow
    stations (several thousand $ each), I demonstrated soldering a QFP80
    using an old crappy soldering GUN, along with the solderwick removal.
    The final results were just as good, under close inspection with a
    microscope, and they easily met the IPC/EIA J-STD-001C soldering
    standards. (Don't do this with a good chip! The soldering guns can
    damage chips because of electrostatic discharge (ESD) from the
    capacitive coupling to the power line.)

    -Paul
    ...............................................................
    Paul
    Somewhere in the Nova Scotia fog
    ANTISPAM - Please remove the m's in my email address
     
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