Waterproof coating PCB's ?

Discussion in 'General Electronics Chat' started by bowlingo, Aug 27, 2013.

  1. bowlingo

    Thread Starter Member

    Jun 29, 2011
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    Hi all,

    Someone has made me some probe sensor PCBs..basically a non contact capacitive strip with a temperature sensor on them.

    This is to be pushed into soil to measure moisture and temperature..

    The top of the probe is housed in a IP65 adaptable box and contains the battery..wireless module etc

    The bottom part (probe) needs to be waterproof coated

    Any ideas on what is used to do this in marine applications etc?

    Thanks
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Anything that needs to be removed at a later date, Dielectric grease from any automotive store.
    If it is a PC board, then there is a special product called Conformal Coating.
    Very hard to remove though if repairs needed.
    Also good is Glyptal Enamel, comes in spray or 1/2l cans.
    Max.
     
  3. wayneh

    Expert

    Sep 9, 2010
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    I've seen folks use cheap fiberglass resin as potting compound. It's not great for heat dissipation and has bad thermal expansion properties, but that shouldn't be a problem for your probe. You might be able to put the probe into a test tube used as a mold, pour in the resin, and then break away the mold. Coat the inside of the mold with vaseline to allow for easy release.
     
  4. #12

    Expert

    Nov 30, 2010
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    The Krylon Clear that I use would fail instantly in a marine environment. Don't bother with a cheap, easy, spray paint. It isn't good enough.
     
  5. MaxHeadRoom

    Expert

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    My preference for potting is FibreGlass Autobody filler (Bondo), it doesn't seem to crack as easily and also is nice to shape afterwards if necessary.
    Max.
     
  6. bowlingo

    Thread Starter Member

    Jun 29, 2011
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  7. #12

    Expert

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    I think you're being unrealistic. A stainless steel probe will last a few million strokes into soil. If you want this to last 100 years instead of 50 years, pack a spare set of probes with it.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    A photo of the probe and the part that needs protection may help?
    Max.
     
  9. bowlingo

    Thread Starter Member

    Jun 29, 2011
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    Its a standard pcb...with a point on the end..
     
  10. #12

    Expert

    Nov 30, 2010
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    You want to jam a fiberglass circuit board into dirt and expect it to last? I still think you're being unrealistic.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Could the part that senses temp. and moisture be a remote from the PCB at least, but if sensing moisture then I assume you cannot cover it?
    Max.
     
  12. bowlingo

    Thread Starter Member

    Jun 29, 2011
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    Its a capacitive none contact coated sensor...works suprisingly well....
     
  13. strantor

    AAC Fanatic!

    Oct 3, 2010
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    I've seen the type of thing OP is describing. Google vegetronix if interested. Coated PCB, shoved in dirt, works. I've used a high grade 2 part potting compound from MG chemicals before to waterproof PCBs. It would probably work for you. I don't have the part number, but it's black 2 part stuff, pretty nasty. But it works very well and is flexible after curing, and penetrates all nooks and crannies. Cures better in the oven at low heat, but make sure to put a drip catcher underneath because it turns from thick tarry goop into runny drippy tarry goop before it cures.
     
  14. strantor

    AAC Fanatic!

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  15. strantor

    AAC Fanatic!

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    Following up. Did you find a suitable coating?
     
  16. bowlingo

    Thread Starter Member

    Jun 29, 2011
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    No luck so far..im in the UK...most of the ideas are US companies etc...I cant see a spray working...maybe something i can apply via a brush?
     
  17. MaxHeadRoom

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  18. bowlingo

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    Jun 29, 2011
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  19. MaxHeadRoom

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    I think you would be surprised at its durability, especially when you try to remove it down the road!.
    You can always give it a couple of coats?
    Max.
     
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