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Air pencils for SMT soldering?

Discussion in 'Electronic Design' started by Richard, Nov 29, 2004.

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  1. Richard

    Richard Guest

    Are air pencils really a lot easier for SMT assembly? Are there
    drawbacks, besides the cost? Recommendations for a good system?

    I've seen impressive demos using QFP packages, but I've also heard
    frustrations about passives getting blown off the board. (I've also
    read that ceramic chip caps shouldn't be iron-soldered because of the
    thermal stress.)

    Metcal offers a model, and Zephyrtronics does an impressive demo at
    shows - any comments on these?
    http://www.metcal.com/products/hotair_pencil.htm
    http://www.zeph.com/pencil.html


    Pre-heaters seem like a great idea - are they practical, or a gimmick?
    http://www.zeph.com/airbathseries.htm

    Thanks,
    Richard
     
  2. Paul Burke

    Paul Burke Guest

    I've found them totally useless. Maybe it's just my technique, but for
    the small quantities I do (i.e. prototypes) the soldering iron has
    proved the best bet, with a wavetip for QFPs and TSSOPs.

    Paul Burke
     
  3. Paul Burke wrote...
    We got a Zephyrtronics last June, and love it, especially for the
    really small stuff. You can turn down the air pressure to suit.
     
  4. Dave Garnett

    Dave Garnett Guest

    I agree. You are supposed to use air pencils with a hotplate to get
    everything pretty warm first, but since I have components both sides, this
    doesn't really work ...

    De-soldering is another game entirely

    Dave
     
  5. Jon Yaeger

    Jon Yaeger Guest

    ****

    I have to agree that IMHO they aren't too good for SMT work. You might be
    able to take off an 8 pin DIP or a discrete part with relative ease, but
    getting a larger part evenly heated is a lot harder.

    If you use paste with impregnated solder, you have to be careful because the
    pencil will blow little balls of molten solder all over the place.

    I have a Hart hot air station (functions like 2 hair dryers blowing at each
    other) that I used for 98% of the SMT repair work I do. I either use a
    smaller nozzle or usually mask off adjacent areas and focus the heat where I
    want it. Makes it easy to position the part just so.

    I've discovered that hot air pencils do have one good use: "precision"
    shrinking of heat-shrinkable tubing!

    Jon
     
  6. Ken Smith

    Ken Smith Guest

    I like the Zephyrtronics pre-heater. The desoldering stuff that comes
    with it is very easy to use and leaves the PCB un damaged.

    The hot-air-soldering pencil is the easiest way to solder the TQFP
    packages. You put on the paste place the chip, preheat the PCB and then
    go around the part with the hot air. If you use only modest amounts of
    paste, there is virtually never a solder bridge. Every pin gets soldered.

    Soldering SMT film caps is a job that must be left to the experts.
    Ceramic capacitors can be soldered with an iron if you are careful but it
    is not recomended for thermal stress reasons. Use the coolest most
    thermally conductive tip you can and ideally pre-heat the PCB if you are
    using an iron.

    On proto-types I often solder parts with a metcal. 0402 components are
    about as small as is practical for manual work. If you are working on
    stuff this small, you have to have non-magnetic tools. Even a slightly
    magnetized tool will pick up an 0402 part.
     
  7. It's hard to prototype QFN and other packages that have no leads
    protruding (eg. some SMT inductors) without hot air.


    Best regards,
    Spehro Pefhany
     
  8. Richard

    Richard Guest

    I've wondered about re-using the pads after their "co-metalization"
    solder is used. Does it clean off effectively, or might it taint a
    subsequent joint (and would it be an issue)? I expect it's a bit like
    Chip-Quik's product, and the ability to remove & reuse is great.

    Yep, even if I stick with the iron, it looks like I'll need a pre-heater
    for anything with power planes. While I got good results before at 225
    celsius, the large planes sink too much heat even at higher temps. I
    may try an even shorter, flatter tip to get better heat transfer at
    lower temps.

    Normal tip or the two-pronged 0402 tip? (Those seem like they're really
    for removal, not assembly - are they?)

    BTDT. I've been using 0402 for a while now with an iron with good
    results, but it takes a steady hand to hold them in place - the surface
    tension on the iron is enough to pick them up. Helluva time keeping
    flux off the tweezers too; it's just sticky enough to make things
    interesting.


    Thanks!
    Richard
     
  9. Richard

    Richard Guest

    Good feedback, thanks. Can it be set low enough to do 0402's without
    holding them in place?

    Anything special about the Zephyr unit vs. others, or just positive
    results moving to an air pencil in general? (I like that it's core to
    their product line vs. other vendors' treatment of their air pencils.)

    Thanks!
     
  10. Richard

    Richard Guest

    ?? Because the hot plate would touch the bottom-side components, or
    because they'd de-solder? (But solder shouldn't melt at the 150c
    pre-heat temp...)

    I've seen some (e.g., Metcal's) that are a flat hot element that I guess
    you'd set the PCB onto, but an air-based unit would seem to make more
    sense with bottom-mounted parts.

    A lot of our bypass caps end up on the bottom, so I'm curious if you ran
    into a particular problem.

    Thanks!
     
  11. mike

    mike Guest

    I haven't had access to a real desoldering station for a decade. Been
    using a paint stripper with some custom baffles and nozzles to do SMT.
    Second gun on the back for preheat if necessary. Small hotplate also
    works great for preheating the backside.
    Plenty of heat, but too much air. Blowed stuff around...

    My stripper bit the dust and I had a SEVERE case of sticker shock when I
    went
    looking for a real hot air pencil for soldering.
    This is the cheapest thing I found that looked decent.

    http://www.mpja.com/directview.asp?product=+15159+TL&Go.x=14&Go.y=7&Go=direct

    Anybody used one of these?

    By accident, I discovered that a Weller Portasol Butane soldering iron
    with the catalytic hot air tip works wonderfully for small jobs.
    Air flow is almost zero and there's a lot of IR going on too.

    Experimented on a laptop hard drive board. Was the best/easiest hand
    job I've ever done...
    on a circuit board.

    mike

    --
    Return address is VALID.
    500MHz Tek DSOscilloscope TDS540 $2200
    http://nm7u.tripod.com/homepage/te.html
    Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
    Bunch of stuff For Sale and Wanted at the link below.
    http://www.geocities.com/SiliconValley/Monitor/4710/
     
  12. Richard

    Richard Guest

  13. nospam

    nospam Guest

    And what comes out doesn't contain much oxygen so it doesn't oxidise the
    solder. It might even contain a bit of carbon monoxide to reduce it?
     
  14. Ken Smith

    Ken Smith Guest

    I've reused the pads with never a problem. You use those foam Q-tip like
    things to clean the area while it is still hot. Almost all of the metal
    comes off clean leaving just a tiny amount on the tined pads.

    I use the cone shaped tip. The long thin ones don't conduct heat well
    enough. There is a temperature gradient on those small tips. Solder
    always flows to the hotter place which in this case is away from the work
    and up the tip.

    I just finished replacing 3 resistors. I did the 3 with no trouble except
    for losing the part among the visual clutter of the PCB.

    The very thin wirewrp wire can be soldered to 0402 pads. I've had to add
    some circuitry to my design and this is how I hooked it in.
     
  15. Richard wrote...
    Not sure. I usually have some 2nd-hand activity.
    Not familiar with the others, but the frame and under-heat setup of
    the is Zephyrtronics is very nice. We modified it a bit to take into
    account our smaller boards. Intended for prototype work of course.
     
  16. Paul Burke

    Paul Burke Guest

    Yes, I've only limited experience with QFN. What I did there (just for
    the prototype, the great thing about PCB Pool is that you KNOW you've
    got to pay for the phototools again, so a few specials just for the
    prototype don't matter) was to make a hole - for a larger QFN I'd use
    more than one- in through to the underside pad, large enough to get the
    tip of a fine iron right through. Solder the component on "as usual"
    (hard with such little pads on the side, but possible), then flood the
    undeside with solder. Worked pretty well.

    Paul Burke
     
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