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Surface mount heck

Discussion in 'Electronic Components' started by EBG, Dec 11, 2003.

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  1. EBG

    EBG Guest

    I'm delving into my first attempt at an SMT chip and was wondering....

    (1) has anyone had success using a Weller wes50 and what....maybe an ETR
    tip? ETS? what setiing on the iron?
    12 oclock etc? (or should I just go for a 15 watt designed for SMT?)

    (2) whats the adhesive you use to hold it in place?
    MCM part number or brand?

    (3) is there such a thing as a hot air system that will actually reflow
    solder on very small areas? like a small nozzle that you point to chip pins
    (probably not, right?)

    (4) is there any kind of liquid solder out there now that is
    being used on SMT by chance?
  2. John Larkin

    John Larkin Guest

    Most any small-tip iron will work, even a cheap RatShack, although
    better is always better. Just try it.
    Most people don't glue the parts. Parts are occasionally glued to the
    bottom of the board in production applications where both sides are
    soldered in one pass. In my shop, we stencil paste,pick-n-place, and
    reflow the top, and hand-solder the bottom parts.

    For hand assembly, just solder the little buggers.

    I've heard of people applying solder paste from a syringe, placing
    parts by hand, and reflowing in a toaster over.
    Hot air usually just blows the parts around.
    Production generally uses stenciled solder paste. Most everybody hand
    solders with fine roll solder. For fine pitch ICs, smaller than 50 mil

    solder two corner pins by hand
    slosh liquid flux on remaining pins
    put a blob of solder on your tip and run it down the line of pins

    We just sent some BGAs out to be soldered and xray inspected. The
    contractor added no solder at all - just used the solder coating on
    the traces, and some flux - and it worked fine.

  3. Tim Wescott

    Tim Wescott Guest

    This matches my experience. I'm not sure of your Weller part number, but if
    you've never used on a temperature controlled soldering iron is heaven
    compared to the fixed-power ones. If you do much soldering at all it's a
    good buy.

    I've seen kits that claim to make the toaster oven method reliable, with
    little plastic cones that melt at the right temperature for calibrating your
    oven. The company is either PCB Express or Express PCB (they both exist,
    but only one sells the toaster oven reflow kits and cheap stencils).

    At my last job we had reliability problems with soldering large (600-700
    ball) BGAs with just the solder mask and flux on prototypes. On our
    production stuff we _always_ used stencils and solder paste.
  4. John Larkin

    John Larkin Guest

    Metcal! Their irons are expensive and worth it. They do show up on
    Um, then wish us luck. The guys we sent it to seem to know what
    they're doing. They did say that the time-temperature profile is
    critical, and they did xray the critters afterwards.

  5. Robert Baer

    Robert Baer Guest

    I use an old GE 25W iron and a light dimmer to keep the temperature
    down (latter not really needed if fast).
    I hold the part dowm with a toothpick and tack on one lead to start;
    go around and do the others, and return and re-fresh the first lead.
    For SOT-363 and SOT-23 5-leaded parts, i have found that if i put a
    thin film of solder on the pads first, align the part on top, i can use
    the iron on the 3 leads on one side (a bit away from the part) to heat
    up all of the traces - and cause a re-flow that is extremely satisfying.
    But i cheat: i use a flux pen and wet the traces *and* the part leads
    (bottom side) first.

    Possible problems with hot air: too much air flow will blow the part
    away (and you cannot find it in the dirt).
  6. Roger Gt

    Roger Gt Guest

    I constructed a hot air source using a 3/8 inch quartz tube with one end
    formed down to a .020 inch opening, the tube is 5 inches long and in the
    tube wound on a ceramic mandrel is forty turns of NiChrome heater wire. The
    air used is dry nitrogen and a flow regulator to set the volume. I use a
    setting of 20CC per minute. Temperature is set with a low voltage regulated
    supply. Been using this method since I needed to attach leads to quartz
    crystals, and it works great for small surface mount parts.
  7. Tim Wescott

    Tim Wescott Guest

    I'm not an expert in the process, so I'm not saying it _can't_ be done, just
    that we didn't have good luck with it ourselves -- and having 700 balls that
    all must be right increases your probability of failure. If it works for
    you then more power to you and your board assembly guys, you can always go
    to a stencil later.

    X-ray images do a good job of showing bridged solder joints, which you're
    not going to get when there isn't enough solder. It doesn't do a good job
    of showing a cold solder joint or one where the ball was just too small,
    which seemed to be the problem we were having.
  8. Roger Gt

    Roger Gt Guest

    I did not recommend using a point of hot air for a ball grid array. A wave
    with very precise control would be needed for that.

    For the SOT23 and 2 to 8 pin SMT devices the point hot air works well.
  9. EBG

    EBG Guest

    What is a good basic hot air system, not for production, just onezees and

    Anything I could pick up on Ebay? model numbers?

    Does a quality (milwaukee) hot air gun work? Has anyone done a homebrew
    adapter on one?
  10. Guest

    How much does it cost to have a BGA part soldered onto a prototype
  11. Not that much. I had two BGA256 parts replaced (one each on two
    boards) for a hundred bucks by our prototype house a while back. That
    included XRay inspection before (open balls) and after.
  12. Roger Gt

    Roger Gt Guest

    Roger Gt wrote
    When we devised this configuration, it was to produce 12,000 crystals a day
    with 24 stations. It all depends on how you apply the method. Of
    course there is only one connection made each time, but a turntable with two
    hundred crystals went pretty fast!
  13. How much does it cost to have a BGA part soldered onto a prototype
    That sounds really reasonable. May I ask who you use? And, do you do a
    lot of business with them, or is that their "walk-in customer" rate?
    I've got occasional use for mounting a few MBGAs.
  14. Mac

    Mac Guest

    I would not try to use hot air. A soldering iron works just fine for
    surface mount parts. For two-terminal devices, two irons are best. You
    place the part on the pads, then touch both sides at the same time and
    move away evenly. For fine pitch parts and small resistors/capacitors (805
    and 603) it helps to have a microscope.

    Any thermostatically controlled soldering iron should work. Hakko and
    Weller are two quality brands that aren't too expensive.

  15. Guest

    I have long used a hot-air pencil and solder paste. You have
    to hold most parts down, but it is an easy and forgiving system.
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