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'(OT)Encase PCB with epoxy, silicone or ??? (OT)'
2000\03\19@142023 by MEDICINTEKNIK KB

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I don't have a good answer for you, but would still like to comment that, YES, epoxy is very water absorbing. .. Bad experience...


Sven
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Från: John <spam_OUTjsandTakeThisOuTspamPIXIE.CO.ZA>
Till: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU <PICLISTspamKILLspamMITVMA.MIT.EDU>
Datum: den 19 mars 2000 19:50
Ämne: Encase PCB with epoxy, silicone or ??? (OT)


{Quote hidden}

2000\03\20@092118 by Mark Newland

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What if one was to conformal coat the PCB before encaseing it in epoxy??

MILTON MEDICINTEKNIK KB wrote:

{Quote hidden}

2000\03\20@101448 by Barry King

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> I don't have a good answer for you, but would still like to comment that,
> YES, epoxy is very water absorbing. .. Bad experience...
> Sven

No, I don't think so.

All the datasheets for the materials I have indicate < 1% water
absorption. The materials used for boats survive for decades in
marine environments and keep the core materials (usually wood)
completely dry.

For encapsulating electronics, we use two different epoxys from
Emerson & Cumming, Stycast brand.  The system we use is a 2 hour high
temp cure, but there are (slow) room-temp options.  One material is
filled with silica, pretty cheap and very good electrical properties.
The other is loaded with Aluminum oxide which gives better thermal
conductivity.  No web sites that I know of for reference :(

These are industrial chemicals, meaning you need to be very careful
about exposure to the material.  We use vent hoods when mixing and
vent the curing oven, too.

When these things are cast into epoxy like this, they will literally
run under water.  Impossible to service, however.

-Barry
------------
Barry King, KA1NLH
NRG Systems "Measuring the Wind's Energy"
http://www.nrgsystems.com
Check out the accumulated (PIC) wisdom of the ages at:
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2000\03\20@103531 by Andrew Kunz

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Hydroscopic/hydrophobic depends on the type of epoxy.  I encase my
water-immersed equipment in 3M #270.  If I need to service it, an iron tip will
cause the compound to turn into little blobs which can be blown out of the way
with air.  Then I just remove the component and re-coat with #270.

Andy











Barry King <TakeThisOuTbarryEraseMEspamspam_OUTNRGSYSTEMS.COM> on 03/20/2000 09:49:39 AM

Please respond to pic microcontroller discussion list <RemoveMEPICLISTspamTakeThisOuTMITVMA.MIT.EDU>








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Subject: Re: (OT)Encase PCB with epoxy, silicone or ??? (OT)








> I don't have a good answer for you, but would still like to comment that,
> YES, epoxy is very water absorbing. .. Bad experience...
> Sven

No, I don't think so.

All the datasheets for the materials I have indicate < 1% water
absorption. The materials used for boats survive for decades in
marine environments and keep the core materials (usually wood)
completely dry.

For encapsulating electronics, we use two different epoxys from
Emerson & Cumming, Stycast brand.  The system we use is a 2 hour high
temp cure, but there are (slow) room-temp options.  One material is
filled with silica, pretty cheap and very good electrical properties.
The other is loaded with Aluminum oxide which gives better thermal
conductivity.  No web sites that I know of for reference :(

These are industrial chemicals, meaning you need to be very careful
about exposure to the material.  We use vent hoods when mixing and
vent the curing oven, too.

When these things are cast into epoxy like this, they will literally
run under water.  Impossible to service, however.

-Barry
------------
Barry King, KA1NLH
NRG Systems "Measuring the Wind's Energy"
http://www.nrgsystems.com
Check out the accumulated (PIC) wisdom of the ages at:
PIC/PICList FAQ: http://www.piclist.com

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