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small soldering job

Discussion in 'Electronic Design' started by [email protected], May 24, 2005.

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  1. Guest

    Can someone recommend a soldering/manufacturing service that will do
    a small soldering job for me. Just 2 ICS: one TSOP 44 pin and a TQFP
    144 pins. Well there is no solder mask on the PCB, so I think they have
    to be soldered manually instead of using wave soldering.

  2. Pooh Bear

    Pooh Bear Guest

    If it's a prototype I'd hand solder it anyway.

    It's not tricky when you've had some practice.

    Don't bother with solder paste ( it ' goes off ' fast anyway ) - just use
    ultra thin cored solder ( I think mine is 0.8mm ) and a very fine tip. Pin
    down the corners of each chip carefully to locate it, then attack the other

    You *will* get 'bridging' between pins - just use good solder wick to
    remove the surplus, I recommend Chemtronics 'SODER WICK' - best wick I've
    ever come across.

    Maybe I'll post an example of what you can do this way at a.b.s.e if you're
    interested ?

  3. Do it yourself with flux gel. A wide iron, 1.5mm, with
    a drop of tin does 5 pins at once and the boiling flux
    gel removes the bridges. If you etch yourself, do yourself
    a favour and make the footprint pads at least 100 mils long.
    This would allow to wipe the tin away from the chip.

  4. Guest

    Pace make a tip with a small well to hold a blob of solder, several
    others have copied it, you just run it down the row of pins. the trick
    is to have the right amount of flux on the pins. Practice! start with
    the packages with the widest pin spacing and work down as you get the
  5. Leon Heller

    Leon Heller Guest

    Metcal makes a cartridge with a mini hoof tip for drag soldering. It works
    very well, even on parts with 0.5 mm lead spacing.

  6. Paul Olley

    Paul Olley Guest

    One such company is

    I haven't used them myself.

    Like the other posters I agree that it is quite feasible to solder it

    A good amount of flux is the thing that did the trick for me.

    For around £5 I bought a bottle of "Future 315 Low Residue Flux"
    ( I used a syringe to flood the (tinned) pads
    before placing the 80 PIN TQFP. Soldered two diagonally opposite pads
    before doing the rest. (This was the most difficult step, to get the
    alignment exactly right!) My technique was to load the soldering iron
    tip with a very small amount of solder and then to touch it to the pad
    and pin with just a little pressure. The flux has the effect of making
    the joint pretty much instantly. The flux tended to evaporate quickly,
    so I just syringed more. I used an Antex M12 soldering iron, with a
    very small tip that I had filed down a little to make a very fine
    point. A magnifying glass from a set of "helping hands" was necessary
    to make the pins clearly visible.

    As I recall I only had one solder bridge, easily removed with solder
    wick. Another popular technique is the "flood it with solder and then
    remove it with wick" approach, which I haven't tried.

    The only pins that didn't have a connection were I couple that I had
    omitted to solder!

  7. I've had some success with first wetting a corner pad with a bit of solder.
    Then, while using the soldering pencil to keep that solder melted, hold the
    component with tweezers, place it in the desired location, and finally
    remove the soldering pencil.

    That works very well on SOIC16 and smaller. I haven't tried soldering
    anything with a finer pitch than that, but I don't know why it wouldn't

    I have been tempted to try the "toaster oven reflow" technique, but the high
    price of solder paste has prevented me. (I suppose it's cheaper in larger
    quantities, but last time I looked it was going to cost something like US$65
    to purchase the smallest quantity I could find, including the syringe and
    the required overnight shipping.) Hand-soldering has proved very easy,
  8. Paul Olley

    Paul Olley Guest

    I looked into the solder paste "toaster over" scenario. I found (search for "solder paste") stocks it in a syringe for
    around £9, that's around US$16 Perhaps try at
  9. Paul Burke

    Paul Burke Guest

    SOIC16??? That's HUGE, I do those quite happily with the big tip iron
    and a pair of tweezers. It's the little buggers, 0.5mm pitch say, and
    the ones without any noticeable lead at all (the ones with a metal slab
    on the bottom too, forget the name) that make life harder. Not to
    mention BGA....

    Paul Burke
  10. Yes, the ones with the metal on the bottom (TI's PowerPad, for instance) are
    what make me think that sooner or later I'm going to have to figure out the
    toaster oven method.

    For now, I'm getting along fine with SOIC, SOT-23, etc.; all of the
    components I need to use are available in those form factors (though not DIP
    any more).
  11. Paul Burke

    Paul Burke Guest

    I've mastered the FN(?) package, though it's fiddly. When laying out,
    put a hole in the base pad, large enough to get the tip of a fine bit
    through. Flux everything. Solder blob one corner pin, and anchor the
    component in place with that. Solder the other pins (fiddly). Then
    introduce solder through the underside hole gently, so it acts to
    conduct heat to the bottom pad. When it's ready, it wicks in, and all is
    OK. I've only tried it with quite small components, the LTC2601 being
    the smallest, but it works fine for them.

    Paul Burke
  12. Hot air works okay for them too, at least for a few prototypes. I have
    not tried a QFN44 or 28 yet, but they don't look too scary.

    Best regards,
    Spehro Pefhany
  13. I'm assuming we're all talking about the same thing, chips with a heat-sink
    pad in the center that is intended to be soldered directly to a pad on the
    component side of the PCB, that in turn is connected with thermal vias to
    more copper on the other side of the PCB. The problem being that the pad is
    between PCB and chip, and therefore not accessible.

    How do you get solder to the hidden pad? And, are you applying the hot air
    from the component side or the other side?

    I like Paul's idea of leaving a hole big enough to get the solder in from
    the bottom.
  14. Fred Bartoli

    Fred Bartoli Guest

    The pad in itself won't do much for power dissipation. You have to connect
    it through a bunch of vias to some plane that'll spread heat across the PCB
    more efficiently.

    As Paul said, make one or more vias bigger so that you can solder the
    package through them.
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