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Small-volume SMD setup?

Discussion in 'CAD' started by Mike Rocket J Squirrel, Jul 21, 2006.

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  1. This is not a CAD question, my apologies to those with limited bandwidth.

    On occasion, we need to produce small runs of boards with surface-mount
    parts. We do through-hole boards by hand day in and day out, but
    surface-mount tech is a mystery to me, so we offload them to a local
    assembly house. I don't mind paying other folks to do stuff that we
    don't want to get into, like powder-coating, painting, fabbing pcbs,
    etc., but it kinda rankles me to pay to have someone build up boards
    just because I don't know how to do them myself.

    Are there turnkey SMD assembly systems for small-volume work? I assume
    we'd need a way to screen paste onto the boards, smoosh the parts on,
    then flow the solder. There -- I've shown how little I understand.

    -- mike elliott
     
  2. Boris Mohar

    Boris Mohar Guest

    Some have gone this route

    http://www.beloev.net/gbvio.html

    Google toaster oven SMD for more



    Regards,

    Boris Mohar

    Got Knock? - see:
    Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca

    void _-void-_ in the obvious place
     
  3. Paul Burke

    Paul Burke Guest


    There have been several discussions of this on sci.electronics.design.
    It's actually quite easy for everything down to 0603s (0402s are
    possible but a bit finicky) except BGA, though for FN packages you need
    to modify the footprint.


    You just need a fine tipped soldering iron, an ordinary one say 2mm
    chisel tip, fine tweezers, desoldering braid and a flux pen. Oh, and a
    little tray to put the components in. It's really as easy as through
    hole when you get used to it.

    Flux all the pads before soldering- best proceed one type at a time.

    (1) Discretes

    Put a blob of solder on one pad (best orient the board so it's the right
    pad if you're rigfht- handed). Pick the component up with the tweezers,
    melt the solder blob and position the component. I find it useful to try
    to pick the board up with the tweezers at this point- it checks the
    joint is right. When you've positioned all the components, turn the
    board round and solder the other end.

    (2) SOIC

    Put a blob on one corner pad - I use top right. Pick up the component
    with the tweezers, melt the blob and position the component. Solder the
    opposite corner, then do all the other pins.

    (3) Fine pitch packages including quads.

    Put a blob on one corner pad. Position the component and solder that pin
    down- this can take a couple of goes until you get used to it. Then
    solder down all the corners. Don't worry if pads get bridged a little.
    Then using the ordinary iron, clean the tip and put a little solder on
    it. Draw the tip gently across the pins with a smooth action. Finally
    clean up with desoldering braid- don't be too heavy or you'll lift the pads.

    (4) FN packages.

    Make a hole in the underside pad big enough to insert a fine soldering
    iron tip. Solder the component down as for SOIC or fine pitch (finicky
    as the pins don't rprotrude much) then solder the bottom down via the
    hole in the underside pad.

    Nearly everything I design these days uses fine- pitch SM, and the guys
    who build it for me hand- assembl;e using these techniques, with success
    rate approaching 100%.

    Paul Burke
     
  4. Chuck Harris

    Chuck Harris Guest

    Hi Mike,

    Yes, and no. The fully automated SMD assembly systems are too expensive
    to ever amortize with small runs. But for runs of 100, or so boards, you
    can achieve better efficiencies manually assembling SMT boards than you can
    achieve with through hole.

    Go to http://www.aoyue.com/en/ArticleShow.asp?ArticleID=331 and look at the 853A,
    quartz infrared preheating system. It can be used, in conjunction with a hot
    air rework station such as the 2738 as a small production assembly unit.

    The basic sequence of events is to apply paste to the board where the parts
    are to go, and manually place the parts using a microscope, or a Mantis
    viewer. Put the board on the preheater, and set the temperature to slightly
    above the melting point of the solder paste alloy. Watch the process
    under the scope until the solder has reflowed on all joints. If one or two
    are not flowing (usually due to having a lot of heat sink area on the part,
    connectors are the worst offenders...), apply a little hot air with the hot
    air rework station.

    It is much easier than thru hole because you don't have to prepare the parts
    in any way, and you don't have to clip leads, ...

    I import Aoyue equipment, mostly for my own use, but I do a limited amount
    of reselling, to make the equipment available at a reasonable cost to small
    companies, and hobbyists.

    -Chuck Harris
     
  5. Paul Burke

    Paul Burke Guest


    Well, c'mon...
     
  6. There are some interesting new (cheap) systems for doing BGAs too.


    Best regards,
    Spehro Pefhany
     
  7. Hal Murray

    Hal Murray Guest

    You just need a fine tipped soldering iron, an ordinary one say 2mm
    You also need good eyes. I use one of the head mounted magnifying
    glass things, half to make things bigger and half to let me focus
    closer.
     
  8. The problem with BGAs, is that there is no cheap manner to adequately
    inspect them. Even the cheaper optical devices are pricey and suffer from
    significant limitations.
     
  9. Thanks to all who replied!

    -- mike elliott
     
  10. Guest

    Could possible be done with a pick and place robot. Ie first apply small dots
    of resin. And then place components. Before reflow.
    Catch is precision I guess with 0.5 mm pitch.. ;)
     
  11. [Snipped]

    I find a "Hoof" tip works much better for SMT devices with many pins.
    SOIC, TQFP and others. One positions the device as described and
    solder two pins to keep it in place. Apply some flux, and then with
    the "hoof" tip full of solder, solder all pins on one side in one
    sweep. Surface tention and the shape of the tip prevents shorts. If
    you do end up with a few, it is easy to clean up with Solder wick.
    With this method it takes under a minute to hand solder a 208 pin TQFP
    device. One must have PCBs with soldermask though for this method to
    work.

    Regards
    Anton Erasmus
     
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