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'[OT] Silicone as potting compound?'
2006\06\07@132925 by Picdude

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Anyone know if I can use silicone, such as sensor-safe silicone for potting?  The intention is not to wait until I can order/receive some, but to provide basic protection for electronics under the hood of a car during testing.  Are any types to be avoided (perhaps they are somewhat conductive, etc)?

Cheers,
-Neil.

2006\06\07@140534 by Spehro Pefhany

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At 10:29 AM 6/7/2006 -0700, you wrote:
>Anyone know if I can use silicone, such as sensor-safe silicone for
>potting?  The intention is not to wait until I can order/receive some, but
>to provide basic protection for electronics under the hood of a car during
>testing.  Are any types to be avoided (perhaps they are somewhat
>conductive, etc)?
>
>Cheers,
>-Neil.

Definitely avoid the acetic acid cure stuff (typical stuff you'll find
in DIY stores, you can smell the vinegar right off). The acid will
corrode electronics.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spam_OUTspeffTakeThisOuTspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->>Test equipment, parts OLED displys http://search.ebay.com/_W0QQsassZspeff


2006\06\08@014537 by Picdude

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At 10:29 AM 6/7/2006 -0700, you wrote:
> Definitely avoid the acetic acid cure stuff (typical stuff you'll find
> in DIY stores, you can smell the vinegar right off). The acid will
> corrode electronics.


Thanks.  Does "sensor-safe" mean that's it's free of acetic acid?  Or is there some other designation I should look for?  My range of selection will be Home Depot and Pep Boys.

Cheers,
-Neil.

2006\06\08@054649 by Bob Axtell

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Picdude wrote:
> Anyone know if I can use silicone, such as sensor-safe silicone for potting?  The intention is not to wait until I can order/receive some, but to provide basic protection for electronics under the hood of a car during testing.  Are any types to be avoided (perhaps they are somewhat conductive, etc)?
>
> Cheers,
> -Neil.
>  
I always liked silicone compound, initially called RTV. But it has an
acidic cure. To protect metal connections, we always sprayed the  PCB
with an acrylic plastic spray,
which dried quickly and sealed the metal. Then when we potted with
silicone, nothing bad happened. The silicone's curing procedure did not
affect the acrylic spray.

--Bob

2006\06\08@072128 by Spehro Pefhany

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At 10:45 PM 6/7/2006 -0700, you wrote:
>At 10:29 AM 6/7/2006 -0700, you wrote:
> > Definitely avoid the acetic acid cure stuff (typical stuff you'll find
> > in DIY stores, you can smell the vinegar right off). The acid will
> > corrode electronics.
>
>
>Thanks.  Does "sensor-safe" mean that's it's free of acetic acid?

No, apparently.
www.mightyautoparts.com/pdf/msds/permatex/6c.pdf
but they are supposed to not foul automotive oxygen sensors

>  Or is there some other designation I should look for?  My range of
>selection will be Home Depot and Pep Boys.

I keep a couple kinds of commercial conformal coating aerosol sprays
around (common types are epoxy, silicone, urethane and acrylic) for this
sort of thing. Here's a representative supplier:
http://www.techspray.com/newinfo/2102.pdf  I get them from local
electronics suppliers.

This is a bit of a PITA to figure out, since the detailed technical specs
are usually not given for retail items, and the same stuff is probably
sold with a different product number to OEMs (where they have to give all
the specs to get a sale). I spent a few minutes on it, and found this
round-up of retail Loctite products. See the chart on page 3 of the PDF.

http://www.loctite.com/int_henkel/loctite_us/binarydata/pdf/lt3770_Gasketing.pdf

The first item, Ready Gasket, has no detailed tech specifications on the
Loctite website, however by looking at the MSDS:
http://sds.loctite.com/wv.asp?A=putPDF%00&RID=F%5FPDF%5C%27EN%27%5C%27FG%27%5C%2737512%27%5C%27LOC%27%5C%27USA%27%5C%7Bts+%272006%2D04%2D07+15%3A30%3A26%27%7D

We can see that it is an alcohol (not acetic acid)- cure silicone. Similarly
for item 37464. You should be able to find something that will work.

Here is the MSDS link:
http://www.loctite.com/int_henkel/loctite_us/index.cfm?&pageid=118&layout=1

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->>Test equipment, parts OLED displys http://search.ebay.com/_W0QQsassZspeff


2006\06\08@102856 by PicDude

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On Thursday 08 June 2006 04:46, Bob Axtell wrote:
> I always liked silicone compound, initially called RTV. But it has an
> acidic cure. To protect metal connections, we always sprayed the  PCB
> with an acrylic plastic spray,
> which dried quickly and sealed the metal. Then when we potted with
> silicone, nothing bad happened. The silicone's curing procedure did not
> affect the acrylic spray.
>
> --Bob


At this point, I'm considering just using epoxy, or perhaps coat it in wax,
then fill with silicone, such that it should be removeable.

20+ years ago, I experimented with RC boats and we used regular silicone to
seal the box with the electronics.  I need to find these someday and see what
the state of the electronics is.

-Neil.

2006\06\08@105206 by Robert Young

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{Quote hidden}

Never used it for potting, only for supporting some TO220 components
mounted "upright" but MG Chemicals makes an electronics grade RTV that
does not have the acedic acid curing agent.  Safe for use around metals.
Does not dry as rigid as the cheap, clear RTV you get at the hardware
store.

MG Chemicals CAT. NO. 1036-300ml for 300ml tube that fits in a standard
caulking gun.

Rob

2006\06\08@114659 by Rolf

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PicDude wrote:
{Quote hidden}

Hmmm...

I put together a little flashing light as a security device for a
friend's car.... nothing fancy. I "potted" my dead-bug soldered 10F206
in the epoxy I use for my model planes ("6 minute epoxy"). The cure
temparature was very high... high enough to significantly impact the
internal oscilator. (I ran it while it cured....). I ended up putting it
in the freezer because it was way too hot to touch. Next time I will use
30min epoxy (cures slower and cooler).

be careful in your choice of epoxy...

Rolf

2006\06\08@132718 by Bob Axtell

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PicDude wrote:
{Quote hidden}

Mr PicDude, I'd LOVE to have a report on the state of the seal!

--Bob

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