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De-soldering ICs with a hot air gun.

Discussion in 'Electronic Repair' started by N Cook, Oct 21, 2007.

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  1. N Cook

    N Cook Guest

    In response to someone who emailed me a couple of
    months back saying he did not believe it
    was possible to desolder , with a hot-air gun,
    ICs soldered in plated through hole pcb boards,
    without causing mayhem.
    And anyone else who could use the technique.
    The following is some before and after pics
    of such a board this week, with thin tracks, through pin tracks and
    a nearby via for good measure.
    http://home.graffiti.net/diverse:graffiti.net/de_sol1.jpg
    http://home.graffiti.net/diverse:graffiti.net/de_sol2.jpg
    Masked off with the thick form of plummer's PTFE
    tape to protect adjascent components from desoldering/
    flicking off.
    http://home.graffiti.net/diverse:graffiti.net/de_sol3.jpg
    http://home.graffiti.net/diverse:graffiti.net/de_sol4.jpg
    After blasting with hot-air and before cleaning
    up the holes with a needle-point probe and soldering iron.
    Usually the polyester of the pcb does not discolour, for
    normal cheap IC soldering, but the plated-through
    fixings mean more heat required than usual.
    http://home.graffiti.net/diverse:graffiti.net/de_sol5.jpg
    http://home.graffiti.net/diverse:graffiti.net/de_sol6.jpg
    The converted circlip pliers extractor tool , with a close up
    of the double joggled tips.
    Lines of bending are at B-B and the red lines.
    Graph paper is mm squares.

    The full text for the tip
    De-soldering ICs
    Use a hot-air paint-stripper,1400W,500 degree centigrade,with 2 level heat
    control to prolong element life. Activity may appear fearsome but it is no
    worse than a flow-solder bath.Pre-heat for one minute then apply to
    pcb,make extractor tool to pull ic from component side. Make an IC extractor
    from an
    old large pair,10 inch, of circlip pliers,the jaws need to open out enough
    to clip around the ends of up to 64 pin ICs with enough force to overcome
    the mechanical force of the situation where all the pins are angled relative
    to the PCB holes.Forge around both of the
    original circlip pins,one joggle at right angle to clear the heigth of the
    ICs and a slight
    inwards joggle to make purchase on the underside of the IC,grinding a wedge
    angle to the
    points helps particularly where there is no clearance between IC and pcb.
    [ Because of these joggles this tool is also useful for depressing the rear
    grippers and releasing of that type chassis mount fuseholders and switches
    when internally surrounded by other
    components ] . For awkward positions lock the pliers to the IC by wrapping
    a cable tie around the handles, tighten, slide down and
    add a couple of notches to the tie and force back along the handles.
    Use this technique for salvaging (working order) up to 64 pin ics ( when
    practised ),other
    components, sm and even repair (tracks are not dislodged).For repair work
    beware of spatter of molten solder causing solder bridges on adjascent
    compoents because if you are doing the job properly,ie not dislodging pcb
    tracks the IC must be pulled out with
    some force and the board tends to flex so possibility of flicking solder.
    Mask off surrounding areas with wide aluminium tape or thick plummer's PTFE
    tape around both sides of board to avoid unsoldering
    and flicking off nearby minor components and trap any that do.
    The secret is to be as quick as possible,idealy the body of the extracted ic
    will be just about handleable rather than too hot to touch.Try practising on
    a board with close packed TTL chips or similar and aim for an extraction
    rate of something like one every 2 seconds.Between boards keep the hot air
    gun running on low power setting (not switching off).Don't rest the gun
    against the board
    when heating as vibration seems to affect the element life also don't allow
    the board to
    flex back onto the gun for the same reason.Hold the gun so airflow is angled
    to the board as solder spat directly into the nozzle can kill the element.
    About the only components that cannot be removed with this technique are
    parts moulded in soft plastic,e.g. crystal sockets,rf coils with plastic
    former
    (IF coils usually OK) some DIP switches. Even these are desolderable intact
    if the body of the component is previously cooled with a blast of aerosol
    freezer spray.
    You definitely need a tool to pull the IC off the board as soon as the
    solder is non-solid/breaking up ie before even fully melted quite possibly.
    An old pair of long nose pliers with the ends ground down so the remnant
    tips can be bent inwards to grab the ends of the IC would probably be
    sufficient to show the method works.
    Also definitely practise on an old/scrap board first as it needs that
    confidence because otherwise pointing a glowing hot element and 300 degree C
    or more blast of hot air at a pcb is not a natural thing to do.
    SAFETY NOTE:- ensure good ventilation, use safety goggles because trapped
    water etc in the capaillary structure of glass fibre reinforced PCB can
    super-heat to steam and jet out molten solder,also it is possible to
    overlook
    small electrolytic capacitors on the solder side of the board which of
    coarse
    explode with the direct heat of the hot air gun and beware of very
    slight risk of combustion of adjascent flammable parts especially where
    components have extra (un-noticed) mechanical bonding leading to extended
    duration of heating activity.
     
  2. Baron

    Baron Guest

    FWIW A simple removal tool for use with this technique is a strip
    of .75mm thick aluminium bent in a U shape with the ends of the U
    folded under. Similar in fashion to the old keycap puller.
     
  3. hr(bob)

    hr(bob) Guest

    Norm:

    Thanx for the step by step information. Your posts are always worth-
    while. Is adjascent the UK spelling of adjacent?? <G>

    H. R. (Bob) Hofmann
     
  4. Smitty Two

    Smitty Two Guest

    Um, IC pullers are $3.50. You have to be pretty dedicated to the DIY
    approach to make your own.
     
  5. N Cook

    N Cook Guest

    If you mean the likes of
    http://www.maplin.co.uk/images/300/fd54j.jpg
    then no - not man enough even for cheapo boards, certainly not for
    plated-through extraction.
    B&D first sold a hot air gun in the UK about 1982.
    I bought one in something like 1985/6 and soon realised how useful it would
    be for IC extraction. The one I made up, in the mid 1980s, has survived
    perhaps 50,000 IC extractions. The handles were originally all black
    enamelled, now bare metal.
    Same can't be said for using the same gun - I would recomment Bosch or any
    make that uses a ceramic matrix for the element, B & D still uses mica as
    far as i know.
    I'm only guessing on 50,000 but does include about 1500 , inch diameter , 6
    inch long celluloid pill pots , on average 3/4 full of extracted, salvaged
    and sorted ICs
     
  6. Just had to tell someone - I got a bright idea to remove a flyback
    transformer using a paint stripper gun.

    AMAZING. Had that FBT out of there in about 40 seconds - no need to fight
    the thing clearing eyelets, etc.

    Done it twice now. Works great. Surely someone here has done this, But I
    work with a couple really experienced TV techs and they hadn't thought of it
    before...

    I would recommend watching out for any nearby SMD's, though...


    Mark Z.
     
  7. N Cook

    N Cook Guest

    I've always used it for LOPT and pcb mounted mains ones and near enough
    removing everything else except soft plastic enclosed components.

    I very rarely use this SMD technique for more than 16 pin DIL format but it
    does work for karger formats but I would not like to rely on any salvaged in
    such manner.
    Note the residual patterning in the solder, on the board, makes it a doddle
    for replacing with a new one. Again you have to exert quite a pull on the IC
    to keep IC heating time to a minimum. Another reason for making a strong IC
    extractor tool for the basic DIL IC format removal.

    Hint for de-soldering surface mount ICs.
    Use a hot-air paint-stripper,1400W,500 degree centigrade,with 2 level heat
    control to prolong element life.
    Form a ring of silicone covered wire around the IC{to isolate the remaing
    components on the pcb.Push a thin piece of wire
    under one side of the IC and form a loop around the IC,repeat on the other
    side;this is to remove the IC when the solder melts, tug on these wires
    while
    heating up to ensure minimum heating contact time.
    Place a slab of PTFE with right size hole cut into and
    clip pcb and slab together with clothes pegs/Bulldog clips etc.
    If the IC is for re-use then cover body of IC with heat insulating material
    or blast IC with freezer spray.Allow the hot-air gun to get up to heat{say 1
    minute}
    before applying to IC.
    For more crowded boards make "conical" shrouds to surround the IC. I used
    some PTFE strip that i had but thin paxolin or similar but drilled and wired
    together would probably do. Cut 4 small trapezoids from the PTFE
    or tin-plate and wire at the corners to form a
    truncated pyramidal frustrum.
    Fixed PTFE together with paper staples but for the smallest shroud
    for 8 pin SM had to wire together the final join.
    Tie to the PTFE/ tin-plate cone (to stop the blower blowing it off) with
    copper wire or temporarily solder to distant points.
    When practised the heated contact time should be less than
    2 seconds - no board distortion or collateral damage surprisingly.
    If you can't get the tugging wires under the IC then pass
    under a few pins at each corner.
    Because this tugging frees the IC at the earliest moment, the solder
    on the board is not fully melted and leaves a profile for localising
    the new IC in place and then solder pin by pin.
    Even for thick board and plated-through holes
    so only tips of IC leads protrude,
    very thin signal traces, traces to tiny pads on both sides of boards of same
    pin in some cases and plated vias under ICs as well. I know if i used
    "proper " vacuum assist desolder or butcher-and-remove-single-pins , many of
    those traces/pads would have dislodged.
    I had to sharpen the points of my large adapted circlip pliers to get the
    extra purchase on the ends of 14,16, and 28 pin ICs. Not one dislodged
    track using a paint-strip hot-air gun. Next time i'll have to take some
    before and after pics for the doubting thomases.
    SAFETY NOTE:- ensure good ventilation, use safety goggles,and beware of very
    slight risk of combustion.
     
  8. Baron

    Baron Guest

     
  9. Clint Sharp

    Clint Sharp Guest

    Weller instant heat soldering gun, length of heavy gauge copper wire in
    place of the normal tip bent into the outline of the pins, works
    wonderfully. As for the heat gun desoldering ICs, I recommend a Steinel
    variable heat gun, used to work on lots of expensive IBM motherboards
    using one of these to pre-heat or desolder chips.
     
  10. Baron

    Baron Guest

    I agree. That is why I made mine using 10mm wide x .75mm alloy strip.
    The other advantage is that as you squeeze the angle on the bent ends
    lifts the ic off the board. Just like the modified circlip pliers. It
    can get a little difficult if the dil's are a bit close together
    though.
     
  11. Duh! Boy do I feel stupid. We use hot air for ICs, why not a flyback.
    Thinking about all that cleaning of desoldering tools and wick over the
    years while that heat gun was sitting idle makes me sick for the time and
    money wasted. Big heavy traces and lots of solder to catch the heat. I
    read your post and had to go try it and it works great.

    Thanks Mark.

    Leonard
     
  12. Andy Cuffe

    Andy Cuffe Guest

    I bought a temperature regulated hot air gun. It cost about 3 times
    what a regular hot air gun cost, but it was worth the extra. It's
    continuously adjustable from 120-800 degrees F. While it's not as
    good as a professional hot air soldering station, it works well for
    removing components without burning, or damaging the board. It easily
    removes regular SMD ICs without damaging them, or bending the pins.
    I've even managed to remove and re-use a few small BGA chips.
    Andy Cuffe

     
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