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Salvage Components from PCBs

Discussion in 'Electronic Repair' started by Brad, Jun 2, 2004.

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  1. Brad

    Brad Guest

    Hi,

    I have a bunch of circuit boards (no SMDs) that I would love
    to find an easy way to remove the parts without unsoldering each
    one at a time. I know there is a chemical (not cheap), when
    applied, lowers the melting point of solder. Maybe I could use
    a hot air gun? Do you know a good method?

    Thanks in advance, Brad

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  2. One method I've heard of -- but not tried myself -- involves using a
    blowtorch. You heat up the solder side of the board, liquifying all of the
    solder joints at once, and then knocking the board over an empty metal
    garbage can to catch everything as it falls off.

    This may or may not work well. It depends on the manufacturer of the
    circuit board. Sometimes the parts legs are bent over or crimped after
    they've been inserted into the board, so they won't pop loose this way.
     
  3. Don Young

    Don Young Guest

    If you have one, a heat gun works great. Otherwise a torch or even a
    hotplate can do it. It just takes a little practice to get the heat right
    and you may ruin some parts. If the leads are crimped you can melt the
    solder and remove it by brushing, banging the board against something, or
    even an air blast (which can be pretty dangerous). A forked tool is best for
    uncrimping the leads.
    Don Young
     
  4. Soren Kuula

    Soren Kuula Guest

    Hot air gun works great, but the fumes are not healthy --> go outdoors.

    I used to do that, only to realize that the component you are looking
    for is much easier to find while still on the board, also because it is
    quite easy to guess what kind of device the old boards used to sit in,
    and thus on which boards you should look for a certain kind of IC,
    transistor, or whatever....

    Soren
     
  5. N Cook

    N Cook Guest

    I've used this technique for salvaging and repair for 10 years.
    Although I do own a proper vacuum assist desolder station I
    prefer to use a hot-air gun - it causes less damage to tracks etc

    De-soldering ICs etc
    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.
    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.
    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.

    SAFETY NOTE:- ensure good ventilation, use safety goggles because trapped
    water etc in the capaillary structure of glass fibre reinfiorced 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.

    other tips on
    http://homepages.tcp.co.uk/~diverse
     
  6. Art

    Art Guest

    Kind'a wonder what antistatic procedures are being implemented to actually
    produce opera devices once these procedures are completed?? IMHO I agree
    with leaving the components physically on the pcb until required for use,
    then use appropriate antistatic removal techniques to assure a component
    that may actually function in it's new enverironment. Otherwise you may have
    a few resistors and caps that end up in a pile to be sorted later, static
    sensitive devices would best be left on the boards until required for use.
     
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