Casting resin as potting compound?

Discussion in 'General Electronics Chat' started by rjjenkins, Jul 7, 2014.

  1. rjjenkins

    Thread Starter Member

    Apr 16, 2011
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    Is there any reason why I shouldn't use casting resin as a potting compound? The curing process is exothermic which would not be too good for some components, but I think that if you're prepared for a slow cure, it should be acceptable.

    The reason for considering it is that it's cheaper, it's less viscous, and I want to encapsulate the PCB into a mould with quite fine detail.
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    It really depends on the components and the properties of the resin. Dielectric constant, corrosion and thermal expansion and, therefore, mechanical stresses are just a few considerations. If it is for a hobby, then try it. If it is for mission critical aerospace components, that is another story...
     
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  3. MrChips

    Moderator

    Oct 2, 2009
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    Resin will shrink over time. If the volume of resin is not uniform on both sides of a PCB the board will warp as the resin shrinks.
     
  4. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    :eek: Could you elaborate a little? Why is that?
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I have used ordinary body filler (fibreglass resin with filler) with success and no visible downside?
    Depends on the application.
    Max.
     
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  6. rjjenkins

    Thread Starter Member

    Apr 16, 2011
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    That's good to know. Has enough time passed for problems to emerge? (eg cracking, warping, corrosion)?
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Not so far, also when you consider its original main purpose and the extremes it is exposed to, it cannot be too frail..
    Max.
     
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  8. wayneh

    Expert

    Sep 9, 2010
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    Thermal conductivity is perhaps the biggest reason to use the higher-priced potting compound. Dimensional stability is another. So if you wanted to pot a coil, for instance, that needs to fit a tight clearance and not overheat, then Bondo may not be the best choice.
     
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  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    The higher the percentage of inert filler the less the shrinkage upon curing.

    Polyester resin with no fillers shrinks badly, a couple of percent, which can warp and crack electronics and rip parts from PCBs.

    Epoxies and Polyurethanes generally shrink as a liquid before the gel point is reached, then have little shrinkage after gelling.
     
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  10. sirch2

    Well-Known Member

    Jan 21, 2013
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    Thanks RB, that's good to know
     
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