What is causing this.

Discussion in 'General Electronics Chat' started by nerdegutta, Nov 6, 2014.

  1. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    I came across this this today, and I was wondering what caused this. The circuit is outside, but in a casing so it will not get wet by rain or water. The casing is not waterproof or air tight.

    It looks like the circuit has started to corrode or grow mold.

    DSC_0447-3.JPG DSC_0447-6.JPG
    Could it be something other than water/moisture?
     
  2. ISB123

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    May 21, 2014
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    Moisture will cause corrosion and heat will just speed up the effect of corrosion.Since that circuit has lots of components with thermal pads they could generate enough heat to keep the box warm especially if its completely closed.
     
  3. Kermit2

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    if so then the grayish brown powder is tin oxide. i absolutely Hate the solder without lead in it. harder to work with and less forgiving of cleaning. flux and time combined to create an oxidative environment which attacks the tin.
     
  4. Alec_t

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    If the box is not hermetically sealed there will always be moist air and mould spores inside. Some circuit parts will likely have just the right temperature for encouraging mould growth. Unprotected steel parts will rust.
     
  5. GopherT

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    It could be mould / mildew. It could also just be
    And, any organic materials collected adds to the mold. Water rolls off trees or leaves that blow into the box, all support the growth of mold.

    Also, a metal box in direct sunlight can get really hot and speed oxidation when moisture is present. Alternatively, lack of direct sunlight means that the overnight dew or rain never really dries and you get mold if you have any organic (a more likely scenario in the Norsk country.
     
  6. nerdegutta

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    The box is not hermetically sealed. And it is plastic. And leaves can get into the box, as well as rats and mice. They die in the box, and starts to decompose. Could the decomposion of dead animals be a boost?
     
  7. cmartinez

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    It is quite possibly the result of moisture, either causing oxidation or mould, since I've seen many of my circuits develop layers very similar to your picture. My suggestion is that you gently but thoroughly clean the circuit using a dry toothbrush, and then add a small sack of moisture absorbing silica gel (desiccant) into the enclosure, in a place where any condensation that forms later has a way to drip out of it.
     
  8. jpanhalt

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    Tin whiskers are tin, not tin oxide.

    As for being mold. Take a piece of clear Scotch tape, press it against the "mold", and look at it under a high power magnifying glass or microscope. Tin whiskers and mold hyphae look quite different (http://en.wikipedia.org/wiki/Mycelium). Any microbiologist can tell the two apart. If you have access to calcofluor white (like in laundry detergent) and a wood's lamp, it will also work. The hyphae will be brightly fluorescent.

    Also, tin whiskers are electrically conductive; mold is by comparison non-conductive.

    My guess is tin whiskers.

    John
     
  9. studiot

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  10. Alec_t

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    Many of the grey areas shown are circular, typical of mould colonies. Do tin whiskers usually form circular clusters ?
     
  11. alfacliff

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    Dec 13, 2013
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    it looks like stuff around here that has moisture intrusion. if it still works, clean it up as good as you can, and spray it with clear Krylon, that should block further corosion.
     
  12. nerdegutta

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    The circuit is dead. I've not tried to do anything with it, except applying power for a short time. Just enough time to confirm it's dead. I could not see any magic smoke or something like that. I was thinking of spraying/flooding it with some electrical spray, something like this: CRC 2-26, and then bake it in the stove at 70C for a few hours.

    Could the tin whiskers short - circuit the hole PCB? Why does tin whiskers happen? Poorly cleaning from factory?
     
  13. jpanhalt

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    Tin whiskers are an innate property of pure tin. They have nothing to do with factory defects. I suggest physically removing them, say with a toothbrush with alcohol, and then see if that helps. They do cause electrical shorts, and the circuit may still be dead from that damage.

    John
     
  14. nerdegutta

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    So I could gently use a soft toothbrush and isopropyl alcohol to remove it, and then see if it works? What about the IC's are they waterproof, to some level? The circiut has not been submerged in water. (I was kind of hoping you'd say that the PCB had not been properly cleaned from the factory... )
     
  15. jpanhalt

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    Isopropyl alcohol (IPA) will not harm the IC's. If you have some optical devices on the board (e.g., LCD's), it may fog the lenses, but I didn't see any. I don't think you need to be particularly gentle with the brushing. You are simply breaking them off, not dissolving them.

    John
     
  16. studiot

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    Brass brush may be better
     
  17. mcgyvr

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    thats NOT tin whiskers at all.. not that we would be able to see anyways..
    thats just typical corrosion/mold/dirt/contamination,etc.... could be old flux/dendritic growth,etc..
    100% expected knowing the conditions..

    sadly doesn't look like it was conformally coated either and it absolutely should have been.
     
  18. Lundwall_Paul

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    Oct 18, 2011
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    Clean it up get it running and apply a conformal coat.
     
  19. paulktreg

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    Jun 2, 2008
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    Back to the OP.

    "The casing is not waterproof or air tight."

    ?
     
  20. mcgyvr

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    I wouldn't expect anything less if I opened an electronics enclosure like that in those conditions.. in fact I think it looks fantastic for its level of exposure. It surely doesn't look like its been in service for long at all.

    I just got a picture last week of one of our products that was installed in an outside enclosure (sealed/waterproof) except for the 1/2" hole in the top of the box where the idiot installer decided he would drill to pass the 8 AWG ground wire through instead of using the conduit entering at the bottom bringing in the power supply leads.. Moron didn't even put a grommet or caulk or anything else around this wire.. Only took 1 week to fill 25% of the enclosure with rainwater causing an electrical short/flames/rust,etc...
     
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