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SMT rework

Discussion in 'Electronic Repair' started by Herman, Aug 1, 2010.

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  1. Herman

    Herman Guest

    I am looking to buy a hot air SMT rework station. Only for occasional use.
    I like the idea of the vacuum pencil and the hot tweezers. What would be
    the recommended tips for general use for ICs and resistors etc. I do not
    need to do the PLLC size chips. Price $300 max or so.
  2. Arfa Daily

    Arfa Daily Guest

    I have recently purchased a hot air rework station. It has hot air handpiece
    with fully controllable airflow and temperature. Digital readout for temp.
    Also has conventional iron with stand, again fully controllable temp and
    digital readout. Comes with 5 round hot air nozzles. Square ones for QFPs
    etc purchased from other sources fit, I understand from a friend who also
    has one. Also 5 tips for the soldering iron, spare element for the hot air
    and spare element for the soldering iron. I paid 55UKP for it, so work that
    out in USD - about $80 maybe. Company I got it from is in China and called
    dragondirectmall. Very efficient and helpful service. Once it had been
    collected from them by DHL, arrived at my door less than 24 Hrs later. On
    their eBay site, they have a video showing a station being built, and you
    can see that for the money, it is incredible value.

    Go to eBay and put in "KADA 852D" then look for the one that says "buy now
    for £55". They have USD prices as well, as far as I recall. Very satisfied
    with mine, so far.

  3. Herman

    Herman Guest

    I was looking at that one. What do you think about the vacuum pencil and
    the hot tweezers? Seems like a good idea for resistors and diodes. Do the
    tips supplied work for small ICs? I have never used one of these stations.
  4. Arfa Daily

    Arfa Daily Guest

    I've never bothered with vacuum pencils and hot tweezers. I guess it depends
    how much you are going to be doing with it. I work with surface mount on a
    daily basis, but it's actually pretty reliable stuff, in general. When I
    need to get a resistor off a board, I just heat both ends alternately with a
    standard iron, and then 'flick' it off the pads. If I have one that is in an
    awkward place to do that, I use one of the shaped bits that I have for my
    Antex station. These are just 'standard' tips in that they fit any Antex 25
    watt iron, but have a sort of 'forked' tip, the prongs being the right
    distance apart to heat both ends simultaneously, of standard profile sm
    components. There are also tips in the same range that have an I.C. spacing
    to the forks, and are the length of an IC. Good for your standard sized 8 /
    14 / 24 etc pinned sm ICs. I have a full set of these specially shaped tips
    that I use when needed with my Antex temp controlled station. Not cheap, but
    a good investment. As for picking the devices up, I just use needle tipped
    stainless steel tweezers.

    The smallest nozzle supplied for the hot air handpiece is a couple of mm
    diameter. It easily allows removal of ICs as long as they are not too big.
    The process involves going round and round the pin rows until it's hot
    enough for the solder on all pins to stay molten long enough to flick the IC
    off the board. Obviously, if it's a very big QFP package, then that's not so
    easy to do, and a shaped nozzle to heat all four sides at once, is more

    That said, when I got my KADA hot air station, I spent a while getting a
    'feel' for it, and I removed all sizes of QFP ICs from and old mother board,
    and just to prove that you could, I even removed two BGAs that were probably
    4cm square each.

    I guess it's horses for courses, but for general use, so far, I can
    thoroughly recommend my KADA as being a good value for money tool, and
    actually, of remarkable quality and functionality, for the price.

  5. Arfa Daily

    Arfa Daily Guest

    Interesting you should ask that Jim. I've just been working on some boards
    where the use of hot air was the only option, but I was finding that I had
    to get the areas of concern up to a very high temperature in order for the
    heat that was being put in, to not be leached away by the board substrate.
    So I employed a bit of lateral thinking, and knocked up a little jig to hold
    the boards flat and level about 3 inches or so above the base (a piece of
    MDF). I then fitted two 12v 50 watt halogen lamps - the sort fitted in
    ceiling downlighters, shaped like an Apollo rocket nose cone - pointing
    upwards, and under the areas of concern. I switch these on, and leave them
    for about 5 minutes. When I come back, the board is toasty warm, and I am
    then able to carry out the soldering work using less air and temperature. So
    far, this has been 100% successful on every one that I've done.

  6. N_Cook

    N_Cook Guest

    Why the intermediary MDF? I suppose it would be a useful surface to stick
    some thermochromic stickers
  7. Arfa Daily

    Arfa Daily Guest

    Correct, Jim. The MDF is the 'base'. The boards have mounting holes along
    their edges, which take screws when they are assembled into their product.
    So I took a piece of MDF, cut a base, and two pieces about 9" long by 3" or
    so wide. I then screwed these to the base like a pair of 'walls', set the
    right distance apart so that their centres were exactly under the mounting
    holes. I then marked a couple of these holes on each side, drilled 3mm holes
    down into the 'walls', and inserted cut down pieces of laser slide rails
    from old CD decks. These have nice smooth chamfered ends on them as
    standard. This allowed me to just drop a board over the pins, which then
    served to locate it on the tops of the walls, and stop it sliding around.
    The whole thing was then modified to take the lamps under the board, by
    drilling two 17mm holes in the MDF base, and push-fitting circular ceramic
    lampholders into those holes.

    The fact that I used MDF for all this is neither here nor there really. I
    just happened to have a big enough piece laying around, and it's easy to
    work with. Because of the nature of its makeup, if you drill holes in it
    that are just under clearance sized, it will grip whatever you push into the
    hole really tightly, without it being much effort to actually push it in.
    For instance, the slide rods that I used as pins, which are actually about
    3.1 mm, and the lampholders which are actually a tad over 17mm diameter.

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