How to remove this silicone potting?

Discussion in 'The Projects Forum' started by russian, Oct 3, 2014.

  1. russian

    Thread Starter Member

    Sep 1, 2012
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    1
    I need to remove the connector from a PCB which was completely covered with soft transparent silicone (?)

    I was told heat would not really help. Any suggestions? Caulk remover? Mineral spirit? What would be the procedure - do I submerge this into the remover? For how long? I do not want to damage the plastic part which makes it tricky.

    Here is where I am at right now. So far only mechanical brute force applied:
    [​IMG]

    Here is how this stuff looked before I've started messing with it:
    [​IMG]
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    It is probably Conformal Coating, bit of a devil to remove.
    Max.
     
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,979
    744
    try acetone, or nail polish remover.
     
  4. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Referring to the colorless, grease looking stuff, if that is really conformal coating, then I agree on the use of a lacquer type solvent, e.g., acetone or lacquer thinner.

    It does not look like conformal coating to me given its thickness and apparent texture. It may well be silicone, and nothing dissolves silicone caulk. There are some ways to denature it, however.

    There are three ways I know of to remove silicone rubber caulk:
    1) Mechanical -- just pick it off
    2) Isopropyl alcohol (99%) and light mineral spirits, 2:1 (e.g. ,VM&P Naphtha, Stoddard solvent) -- requires a lot of soaking and rubbing, but eventually the mineral solvent disrupts the bond to the substrate and it comes off. I use this mixture for the final clean up when there is just a slight haze of the caulking/rubber.
    3) A type of caulking remover that contains a sulfonated, long-chain hydrocarbon : CH3(CH2)nSO3H (http://en.wikipedia.org/wiki/Sulfonic_acid). Those removers are relatively recently on the market. They denature the silicone and facilitate its removal. One brand is McKanica (http://www.acehardware.com/product/...182&KPID=2373634&kpid=2373634&pla=pla_2373634). My experience with "Motsenbockers" silicone caulk remover available at Home Depot, which I had hoped might be a bit safer and less aggressive than the sulfonic acid, was that it was a complete waste of money. The secret of the sulfonic acid appears to be that the long carbon chain facilitates penetration through the hydrophobic silicone. Then the strongly acidic sulfonic acid group denatures the silicone and disrupts the bond to the surface. The problem, of course, is that the sulfonic acid is quite a strong acid. It is in the same class as sulfuric acid (battery acid). It will not be kind to electronic parts. However, if the board under the silicone was coated with an epoxy resist or conformal coating, you might get away with using it.

    My first choice would be soaking in the IPA/Naptha and then trying mechanical remomval. Only if that failed, and I really needed to get the silicone off, would I go with the sulfonic acid.

    John
     
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  5. tom_s

    Member

    Jun 27, 2014
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    there are some commercially available 'silicone remover' products available. it actually breaks down the silicone bonding to enable removal (eg silicone in bathrooms)

    not sure whats available in the states, downunder we have http://www.selleys.com.au/sealants/silicone/remover/
     
  6. russian

    Thread Starter Member

    Sep 1, 2012
    55
    1
    Right, that's only if the once available to regular Joes in regular hardware stores are strong enough :( A bit above there is some negative experience with "Motsenbockers" silicone caulk remover which is a spray.

    I've just cut my connector in pieces (it's four housings together), and submerged one piece in liquid "Goof Off" and another piece in VM&P Naphtha. Will see how it looks in three hours from now.
     
  7. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    McKanica is available at Ace Hardware stores. If you check the link, you will probably find one in Chicago. You may need to order it shipped to store. The price is a bit steep for what it is.

    As they say:
    Easy to find
    Works
    Cheap

    Pick two out of the three. ;)

    John
     
  8. russian

    Thread Starter Member

    Sep 1, 2012
    55
    1
    40 minutes update:
    "Goof Off": silicone got a bit softer
    VM&P Naphtha: silicone has expanded x2 & got even more softer
     
  9. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,783
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    i second the vote on the naptha/kerosene soak. It will not damage most boards and components.
    Mechanical removal is still needed, a stiff nylon bristle brush works well.
    2-propanol or isopropal will remove most of the greasy residue you are left with.
     
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  10. russian

    Thread Starter Member

    Sep 1, 2012
    55
    1
    2 hours of VM&P Naphtha
    tooth brush cleanup
    2 hours of fresh VM&P Naphtha
    tooth brush cleanup & warm soapy water
    success

    Thank you!


    [​IMG]
     
  11. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    I am impressed.

    Nice work from the mess you had to start with.
     
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