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Solder braid: width?

Discussion in 'Electronic Basics' started by aleksa, Jul 16, 2008.

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  1. aleksa

    aleksa Guest

    I want to solder one TQFP144, but do not have
    any experience with anything more than DIP40.

    This is what I'm planning to do. I will:

    1. apply some tinnol on all the pins on the PCB
    2. remove excess tinnol with dump cloth
    3. place the chip and solder it pin by pin with solder iron

    step 3 will certanly solder several pins together which I plan to
    fix with solder braid. The question is: what width should I buy?
     
  2. ian field

    ian field Guest

    Desolder braid risks pulling up pins if you don't keep it fully and
    uniformly heated.

    Hold the board upside down but slanted with the ends of the pins downwards
    and tease the excess solder away with the tip of the iron, you need enough
    flux to prevent a skin of oxide forming.
     
  3. Ben Jackson

    Ben Jackson Guest

    I'm not sure what 'tinnol' is, but assuming it's some kind of liquid
    flux: Skip step 2. You can readily solder fine pitch parts like that
    in a puddle of flux. Fine pitch + lots of flux = easy. In fact, the
    first remedy I would suggest for almost any problem (including bridged
    pins) is to add flux and reheat it. You can often "pick up" the excess
    solder with the iron and remove it or redistribute it. With lots of
    flux, the solder will strongly prefer to stick to the pins rather than
    itself which can cure the bridge.

    If you get braid, make it very fine, and NEVER PULL IT OFF THE BOARD
    if it resists. If you do, you will remove traces, bend pins, etc. It
    can help to tin the braid as well, but it will corrode over time.
     
  4. Tony Burch

    Tony Burch Guest

    Hi,

    I would not recommend using solder braid. Please have a look at the video at
    http://www.supersolderingsecrets.com for a reliable technique for had
    soldering TQFPs.

    If you don't have a "reservoir tip" for your iron, you can just use a broad
    chisel tip.

    Kind regards,
    Anthony Burch
     
  5. aleksa

    aleksa Guest

    'tinnol' = 'solder wire'.

    What is liquid flux? SMD solder paste?
    Schukat has it, 15EUR for only 10ml of paste.

    Maybe it is possible to place the braid across
    all the pins (min 3cm), heat the whole braid and
    it will pick up all the solder at once? If the
    braid is enough heated, it won't break the traces.

    BTW, the minimum braid width at Schukat is 0.5mm, max 2mm.
     
  6. Rich Webb

    Rich Webb Guest

    For some alternative videos and tutorials (including using braid) that
    don't require a "full membership," interested parties may wish to surf
    on over to http://www.sparkfun.com/commerce/hdr.php?p=tutorials

    Disclaimer: I have no association with Sparkfun other than as a
    satisfied customer.
     
  7. Ben Jackson

    Ben Jackson Guest

    If you make a mistake and have a less-capable iron, it's easy to end
    up with the solder wick attached to so much thermal mass you can't
    remove it.

    I basically do your steps 1, 2 except I use a more moderate amount of
    solder in 2. I end up with small groups of pins bridged but not the
    whole lot.

    And for the OP, liquid flux is not solder paste or solder. It's a
    substance that cleans the pins and pads and makes it easier for solder
    to "wet". Make sure you get some designed for electronics, not plumbing.
    And if you can, choose water soluble.
     
  8. Clint Sharp

    Clint Sharp Guest

    You and me both, in fact I've used this technique to rework stuff at
    home on plenty of occasions now, the only slight difference is that I
    apply a little pressure to the chip package so the pins are pushed
    gently onto the pads whilst I solder them on.

    I've also used the puddle of solder to remove chips, using a sewing
    needle apply a little leverage between the chip body and board, drag the
    puddle of solder along the legs away from the needle, move needle to
    another corner, rinse and repeat. A little practice and a few cycles of
    this will remove chips quite easily with no board damage. Clean up with
    wick and flux remover once the chip is off before you attempt to replace
    the chip.
     
  9. Yukio YANO

    Yukio YANO Guest

    I find it very very interesting that NO ONE is talking about the cursed
    Lead-free solder !!! "Long-Live eutectic 65/37"

    Yukio YANO
     
  10. Yukio YANO

    Yukio YANO Guest

    sorry "63/37 tin/lead"
     
  11. neon

    neon

    1,325
    0
    Oct 21, 2006
    solder braid do have flux deposits in itself. adding more flux makes better addision of the solder. that is not desirable if you un-soldering pins or eyelets. a solder sucker is more desirable first it cools the pins as it extract the solder. next is break the pins loose by wiggle the pins cold solder joints are easy to break. then lift the package. solder braid is harmfull to the board and components too much heat must be applied to do the job.
     
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