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Repairing corrosion damage to PCBs

Discussion in 'Electronic Repair' started by DaveC, Apr 22, 2006.

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  1. DaveC

    DaveC Guest

    There are many web pages dedicated to emergency procedures to take if you
    spill a drink into a laptop. But I don't find any describing what to do about
    remaining corrosion.

    I was given a laptop that had coffee (no sugar, I'm told) spilled into the
    keyboard. The owner turned off the power and removed the battery and drained
    the computer as best he could, but did not take any steps to rinse out the
    coffee. Some time later the computer quit.

    There is evidence of corrosion on pc traces, SMD component and connector
    leads:

    http://www.hostmypic.info/uploads/27f71caf77.jpg

    I plan to soak the board(s) in a weak solution of dishwashing detergent and
    mineral-free h2o and dry for a few days. (Is there a more effective
    solution?)

    In preparation for examination and repair of any compromised conductors on
    the pcbs, what's the best way to remove (ie, halt) the green & black residue
    of corrosion?

    Thanks,
     
  2. Smitty Two

    Smitty Two Guest

    I'll take a shot at this, but YMMV. We clean our newly minted PWBAs in a
    somewhat corrosive mixture of saponifier and distilled water. They're
    then rinsed in fresh distilled water. Occasionally they're left in the
    soap too long, or not rinsed well, and the nice shiny new solder joints
    end up dull and dark.

    I've cleaned gold contacts with liquid silver detarnish, but the best
    thing for corroded solder is a drop of (can you believe it?) liquid
    flux, and then reflow the joint.

    If you've got actual crystals growing, or other severe surface
    contamination, a stiff brushing (I use an acid brush with bristles cut
    quite short to stiffen them) should preface the reflow work.
     
  3. n cook

    n cook Guest

    Wouldn't it be a multi-layer board with liquid conducted into the board by
    capillary action ?
     
  4. DaveC

    DaveC Guest

    Thus spake n cook:
    So, the board's toast? No reason to attempt repair?

    Opinions welcome.
     
  5. Roy L. Fuchs

    Roy L. Fuchs Guest

    You may have to bake it at 60 C for an hour or so since there are
    things on the board that were not on it when it was soldered and water
    washed. A good vacuum cycle is good for evaporating those last little
    bits of remaining water as well.
     
  6. Roy L. Fuchs

    Roy L. Fuchs Guest

    Use a fine child's tooth brush on it while you are doing the water
    wash.

    BTW, if there are any transformers on the board, all bet are off.
    You would HAVE TO bake it or vacuum it out (the water).
     
  7. Roy L. Fuchs

    Roy L. Fuchs Guest

    The material PCBs are made from, regardless of the layer count, are
    hygroscopic and will absorb water.

    If he cleans it with water, he will need to bake it out at the very
    least.
     
  8. Toast. Not because of the above but because it stopped working whilst
    powered up with the contamination in place. The odds are that
    irreversible damage has been done.
     
  9. bloggybob

    bloggybob Guest

    No...... clean it and use a conductive ink pen .. i have fixed many laptop
    keyboards and mainboards using one of these .. you basically draw a new line
    on top of the old one with the pen which is silver conductive ink ... last i
    checked MCM electronics carries them .. i still have one from years ago and
    it is still half full ... hope this helps you out

    cheers ..
     
  10. ampdoc

    ampdoc Guest

    Another factor to contend with on multilayer PCB's are the VIA's (some call
    them feed-throughs) that rout traces through the board. If the metal has
    been etched out of the VIA by corrosive action, then you have to take a very
    small drill bit and clean out the thru-hole in the board an pass a small
    wire through and solder it to the traces, meaning a lot of work if many of
    them are bad. Also if the PCB is more than 2 layers it may be impossible to
    repair.

    Also if you have heavy soil on a board or it is contaminated with Glycol
    (CRT Coolant for PJTV's) you can wash it with an ammonia based cleaner then
    rinse with distilled water. Windex works wonders :)

    Jammy
     
  11. Roy L. Fuchs

    Roy L. Fuchs Guest

    NEVER, I repeat NEVER "take a very small drill bit" to ANY of your
    vias. Adding and soldering the wire is fine. Use FLUX for that
    operation, NOT a friggin drill bit. That (drilling) would almost
    ensure that there will be detached layers.
    Drilling the fucking thing will surely produce that result.
    It's a laptop, not a CRT.
     
  12. Charlie+

    Charlie+ Guest

    underneath my scribble :

    Some actual experience:
    I did a resurrect of a Sony MZ-R30 Minidisk Recorder/Player which had
    been dropped in seawater and this had stopped working immediately!
    This unit had been unwashed and returned around the world so had had
    about a month or more to corrode, seawater is unforgiving so I wasnt
    hopeful.
    I removed the 1/32" FG PTH 4 layer boards completely, then washed
    them in hot water, then blow dried with compressed air, you have to be
    sensible with this as physical damage is possible with compressed air,
    scanned them up to X10 for inspection then warmed boards (hot to
    touch) then coated with WD40 for about 30 minutes, compressed air
    again to remove most of the WD40 then baked in a warm oven for about 4
    hours to flash off the remaining oil, repired some obviously corroded
    SM joints by flux/solder and iron reflow (under magnification!) and
    then reassembled. The point of the WD40 soak was to arrest any
    ongoing corrosive action, it is thin enough to wick anywhere the
    original liquid has gone.
    Worked like a champ ever since, about 3 years now.
    Your board has failed under power perhaps well after the event though
    and this points towards electrolytic corrosion and this may not be
    recoverable whatever you do, in a multilayered board.
    Whatever you do I would advise you against soaking a board in anything
    for a few days, imo that would be asking for trouble!
    Charlie+
     
  13. DaveC

    DaveC Guest

    Thus spake Charlie+:
    I fully appreciate your creative technique of halting the corrosion. This is
    a concern for me, and until your post, I wasn't sure how to address that
    (other than using flux + solder on accessible lead corrosion), especially
    that hidden beneath components.

    WD-40 -- while it may be effective in this application -- stinks! This is a
    laptop I'll be using (if I'm successful), which pretty much places my nose
    right above the logic board. Can't imagine smelling that awful smell for
    years.

    Can someone offer an alternative for WD-40 to arrest corrosion on PC traces
    and component leads?

    Thanks,
     
  14. GregS

    GregS Guest

    Your not going to smell it if its baked like he said until all oil is evaporated.

    By the way, I usually coat the board or anything I have sprayed with water
    with WD-40.

    Want something more aromatic, try some Bullfrog electronic
    contact cleaner.
    I think it smells pretty!

    if not, get some stuff at The Home Depot, CRC 2-26 Lubricant, almost
    no smell, its plastic safe, multi purpose, presision lubricant, improves electrical properties,
    as read on can. Really cheap too, but slightl more than WD-40.
    They also have a no residue electronic contact cleaner which is also cheap for
    a large supersized can.

    greg
     
  15. bobs

    bobs Guest

    why not soak the board for 20 minutes in DR99 solutiom at a ratio of
    5/1. After that bake the pcb for 30 minutes at 60 degrees and then, add
    a sprinkle of salt and garnish and serve with potatoes and side dish.
     
  16. DaveC

    DaveC Guest

    Thus spake GregS:
    Thanks, Greg. I think WD-40 is great for most such applications (WD, I'm
    told, stands for "water displacer"), but if there's any chance I'll be
    sniffing that smell for years, I'll try the CRC route.

    General Q: these products are water displacers. The reason these products
    stop corrosion is that they remove all traces of moisture? After that, if the
    green stuff (corrosion) is not causing a short, the corrosion should not
    continue, as long as moisture is not reintroduced?

    Thanks,
     
  17. DaveC

    DaveC Guest

    Thus spake DaveC:
    Should say:
    Then the water displacer product is evaporated (baked with high temperature).
    After that, if the green stuff (corrosion) is not causing a current path, the
    corrosion should not continue as long as moisture is not reintroduced?

    (It seems weird to post a "reply" to your own post...)
     
  18. Charlie+

    Charlie+ Guest

    LOL!
    Charlie+
     
  19. Charlie+

    Charlie+ Guest

    underneath my scribble :

    Sorry nearly missed this reply as you started a new thread!
    WD40 as well as being hygroscopic has corrosion inhibitors built in to
    a self wetting very thin liquid - that is the whole point. Also the
    point of putting the WD40 onto a preheated board is to help suck into
    any cavity as it cools. There is zero niff after baking off the
    volotiles leaving a very thin layer of inhibitors and wax behind, the
    compressed air has already removed practically all the visible WD40
    anyway. That was my thinking in doing it this way!
    The visible corrosion is not the problem, as visible areas will have
    dried out quickly after the spill, coffee is I guess not particularly
    corrosive to metals but may make insulators conductive/resistive under
    certain conditions and this is probably the reason for failure.
    Post a followup how it goes with the laptop - you will probably have
    quite a job getting it down to just the boards in any case!
    Charlie+
     
  20. GregS

    GregS Guest


    Green is most easily removed by water. WD-40 leaves a varnish like film when dry.
    Not really good for contacts. There are more products leaving a film when dry. Bullfrog
    makes a range of cleaners and evaporative film anti corrosion inhibitors. A molecular
    layer of material is deposited on metal to prevent corrosion. Many switches
    come with the piece of paper with an evaporative product.

    greg
     
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