What type of epoxy is best for electronics?
Joe
so, can you recommend some brand names that I may be able to order online or
buy at a store?
TIA,
Joe
John Popelish
What is your purpose for such a process?
--
John Popelish
John Fields
---
Depending on what your goal is for potting the circuitry, epoxy may be
a very bad choice because of its exotherm and because of its
dimensional instability as it cures. What are you trying to
accomplish?
--
John Fields
Joe
"John Fields" <jfi...@austininstruments.com> wrote in message
news:406a4898....@news.texas.net...
Hi John,
I am trying to protect a circuit board once it is in the enclosure (black
box) from things like vibration, shock, and especially moisture. I use all
my devices outdoors and the extremes of temperature and sunlight, sometimes
I can see the condensation on the inside of the box.
I thought something to weatherproof and totally encapsulate the board would
be helpful.
Joe
Joe
"John Popelish" <jpop...@rica.net> wrote in message
news:40684970...@rica.net...
Hi John,
I am trying to protect a circuit board once it is in the enclosure (black
box) from things like vibration, shock, and especially moisture. I use all
my devices outdoors and the extremes of temperature and sunlight, sometimes
I can see the condensation on the inside of the box.
I thought something to weatherproof and totally encapsulate the board would
be helpful. I remember a (very) long time ago, I worked at a local lab where
we made large capacitors for NASA. There was a potting compound we used, it
was brown in color and had to be mixed with a curing agent, then placed in a
vaccuum chamber to pull all the air bubbles out. Then we would pour it over
the circuit and let it harden. Something like that.
Joe
Joe
"DarkMatter" <DarkM...@thebarattheendoftheuniverse.org> wrote in message
news:eh3h609592t3ookfb...@4ax.com...
> On Mon, 29 Mar 2004 15:55:33 GMT, "Joe"
> use a varnish humidity barrier such as Dolph's ac-51 or ac-43.
>
> If no future servicing is expected, one can use epoxy, but one must
> remeber that such materials shrink when curing, and PCB assemblies
> will fracture parts or suffer other damage if the epoxy cross
> sectional thickness is too high.
>
> There are soft compounds we refer to as encapsulants that can be
> use. Many different formulations exist, such as RTV, and
> "PolyUrethane" types. None are cheap. Even a small pint sample will
> likely cost you up to a hundred bucks.
>
> There are also thermally conduct versions for conduction cooled
> brick designs.
>
> Since the mediums are so expensive, the industry generally only
> fully encapsulates for either security (dongle, etc) or environmental
> (HV in a vacuum, humidity, etc) type reasons.
>
> It isn't a cheap route. The varnish is the cheapest way to go.
> Bake the PCB out before any assembly, and again if aqueous cleaning is
> used, right before application of the humidity barrier.
>
> BTW, such materials, and vented type electrolytic caps don't work
> well together. You must assemble the boards without the caps before
> the last bake and clean cycle, then carefully attach the caps, hand
> cleaning each solder joint. The shellac, can seal the vent, and
> vacuum impregnation is not the greatest idea.
>
> PC Boards are hygroscopic. Good luck deciding. Dow Corning, and
> General Electric are two makers of potting compounds, though they do
> not sell directly, you must find a polymers dealer.
Thank you for the info, Dark Matter, my circuits would not need to be
serviceable, but I did not realize that some parts would possibly fracture
when the epoxy cures. I'll have to keep looking. Thanks for the references
to Dow Corning and GE. I can check into those further also.
Joe
John Fields
<nuisance...@nospamearthlink.net> wrote:
>
>I am trying to protect a circuit board once it is in the enclosure (black
>box) from things like vibration, shock, and especially moisture. I use all
>my devices outdoors and the extremes of temperature and sunlight, sometimes
>I can see the condensation on the inside of the box.
>
>I thought something to weatherproof and totally encapsulate the board would
>be helpful.
---
There are many encapsulant manufacturers, among them Master Bond and
Emerson and Cuming. I've used E&C wencapsulants in the past and was
well satisfied with them. Here's a link:
http://www.emersoncuming.com/YourSolution/index.jsp?id=1&c=167
--
John Fields
John Popelish
If you want to pour epoxy in the box you might use something like
this, though there is some risk that it will distort as it hardens and
damage some of the components. Curing it slowly (starting with it
cool) helps.
http://www.abra-electronics.com/catalog/chemicals/gc16.html
You can find key words to search out similar things like this:
http://www.crosslinktech.com/epoxies.htm
http://www.transene.com/epoxies_potting.html
http://www.magnapoxy.com/magencap.htm
http://www.emersoncuming.com/YourSolution/properties.jsp?appId=65&geoId=0
I have used this product from that last vendor, and it has the
advantage of being almost indestructible. It is pretty highly filled
with inert mineral fillers, so it seldom overheats or shrinks. When
it hardens, it is basically a rock.
http://www.emersoncuming.com/YourSolution/ProductDetails.jsp?i=77
You can also dip the board in melted paraffin wax, first, to keep the
potting epoxy from actually bonding on to the parts or board. But it
will melt in the sun. The professionals often dip the board in
silicone resin to give it an elastic coat before potting.
--
John Popelish
Bob Masta
<DarkM...@thebarattheendoftheuniverse.org> wrote:
<snip>
> There are soft compounds we refer to as encapsulants that can be
>use. Many different formulations exist, such as RTV, and
>"PolyUrethane" types. None are cheap. Even a small pint sample will
>likely cost you up to a hundred bucks.
>
Speaking of RTV, how about plain old silicone sealer,
from GE or others? It's fairly cheap, conforms well,
waterproof, and doesn't have thermal expansion problems
like epoxies. It doesn't flow on as well as the expensive
conformal coatings, so it will be a little messy to apply.
Maybe squirt it into the enclosure and force the lid on,
then wipe up whatever is squeezed out?
Just a thought...
Bob Masta
dqatechATdaqartaDOTcom
D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Joe
Thank you John, sounds like just what I was looking for
Joe
Joe
Thanks for all the links, John, it will take me awhile to sort thru them,
but the emerson cuming one sounds like the right product.
What is silicone resin? Do these same companies sell that also?
Joe
Joe
"Bob Masta" <NoS...@daqarta.com> wrote in message
news:40697376...@news.itd.umich.edu...
Hi Bob,
good suggestion, I think. Do you mean like the silicone caulking they sell
at home depot? It comes in a tube for use in a caulking gun for outdoor use
around windows and door frames. I have used it for caulking windows and
stuff, and it does dry flexible. Is that what you are referring to?
Joe
Bob Masta
The stuff I am thinking of is called "silicone sealant" and is not
the same as "silicone caulking". As DarkMatter points out,
there may be problems getting it to flow into all the little
nooks and crannies of your board. But it seems to me that
unless there is a completely open path to the outside then
this will make it perfectly waterproof nonetheless. If you
are worried about trapped humidity when potting, you
might warm it in the oven a little first. You might also
use a little stick to move and wipe it around in the case
to force it into any voids. Get the clear stuff, and you
may be able to see any voids as lighter unwetted areas.
Overfilling and forcing the lid on may also help by adding
more pressure to collapse any voids.
Might be worth an experiment, before springing for the
expensive conformal coating.
Joe
Yes, someone else suggested heating the board to about 100 degrees F, for
an hour to remove any moisture first. I am not too worried about small
voids, because doing something is better then doing nothing and just letting
the components get exposed to the raw damp moisture we have around here. So
I will google for silicone sealants and see what I can come up with. Some
other folks gave me some links to some sites that sell the right kind of
epoxies for this purpose so I may go with one of those. My first experiment
with it was going to be to just build a simple astable (555) oscillator with
a npn transistor driver output, test it, and then pot it and see if it works
afterwards. Power leads sticking out of the box, and the output from the
transistor sticking out the other end of the box. Something simple and cheap
so it won't matter too much if something bad happens to it.
Thanks again to all,
Joe
Joe
> On Tue, 30 Mar 2004 18:17:33 GMT, "Joe"
>
> >
> >"Bob Masta" <NoS...@daqarta.com> wrote in message
> >news:40697376...@news.itd.umich.edu...
> >> On Mon, 29 Mar 2004 13:09:55 -0800, DarkMatter
> >> <DarkM...@thebarattheendoftheuniverse.org> wrote:
> >>
> >> <snip>
> >>
> >> > There are soft compounds we refer to as encapsulants that can be
> >> >use. Many different formulations exist, such as RTV, and
> >> >"PolyUrethane" types. None are cheap. Even a small pint sample will
> >> >likely cost you up to a hundred bucks.
> >> >
> >>
> >> Speaking of RTV, how about plain old silicone sealer,
> >> from GE or others? It's fairly cheap, conforms well,
> >> waterproof, and doesn't have thermal expansion problems
> >> like epoxies. It doesn't flow on as well as the expensive
> >> conformal coatings, so it will be a little messy to apply.
> >> Maybe squirt it into the enclosure and force the lid on,
> >> then wipe up whatever is squeezed out?
> >>
> >> Just a thought...
> >>
>
> >
> >good suggestion, I think. Do you mean like the silicone caulking they
sell
> >at home depot? It comes in a tube for use in a caulking gun for outdoor
use
> >around windows and door frames. I have used it for caulking windows and
> >stuff, and it does dry flexible. Is that what you are referring to?
> >
> >
> compounds are very thin and runny when first mixed up, and are firm
> when cured (there are rubbery gel types too).
>
> The point is that the tube applied media will not lay into the
> cavity well, and will leave voids, or air pockets. If a moisture
> barrier is the goal here, then a void is double disaster.
Thanks DM,
I am going to explore silicone sealants on a very simple 555 oscillator
circuit (cheap and easy to build). Something that I don't mind losing if I
use the wrong stuff or screw something up. I also received some links from a
few others on the list for companies who make such epoxy compounds for this
purpose.
Joe
Rheilly Phoull
> On Mon, 29 Mar 2004 15:55:33 GMT, "Joe"
> <nuisance...@nospamearthlink.net> Gave us:
>
> use a varnish humidity barrier such as Dolph's ac-51 or ac-43.
>
> If no future servicing is expected, one can use epoxy, but one must
> remeber that such materials shrink when curing, and PCB assemblies
> will fracture parts or suffer other damage if the epoxy cross
> sectional thickness is too high.
>
> use. Many different formulations exist, such as RTV, and
> "PolyUrethane" types. None are cheap. Even a small pint sample will
> likely cost you up to a hundred bucks.
>
> brick designs.
>
> Since the mediums are so expensive, the industry generally only
> fully encapsulates for either security (dongle, etc) or environmental
> (HV in a vacuum, humidity, etc) type reasons.
>
> It isn't a cheap route. The varnish is the cheapest way to go.
> Bake the PCB out before any assembly, and again if aqueous cleaning is
> used, right before application of the humidity barrier.
>
> BTW, such materials, and vented type electrolytic caps don't work
> well together. You must assemble the boards without the caps before
> the last bake and clean cycle, then carefully attach the caps, hand
> cleaning each solder joint. The shellac, can seal the vent, and
> vacuum impregnation is not the greatest idea.
>
> PC Boards are hygroscopic. Good luck deciding. Dow Corning, and
> General Electric are two makers of potting compounds, though they do
> not sell directly, you must find a polymers dealer.
Talking specifically about "Araldite" does that shrink and apply stress to
components ??
From observation it certainly will flow into voids at moderate temps of say
40c.
--
Regards ........ Rheilly Phoull
Bob Masta
<shre...@bigpong.net> wrote:
>Talking specifically about "Araldite" does that shrink and apply stress to
>components ??
>From observation it certainly will flow into voids at moderate temps of say
>40c.
Don't know from experience on circuit boards, but I recall that
Araldite was one of the embedding epoxies used by the anatomy
lab down the hall from where I used to work. They would embed
tissue specimens, then section them for microscopy. Any distortion
would have caused problems, so I assume Araldite was fine in
this respect. I also recall them using something called Epon,
possibly together with Araldite. "Embedded with Epon and
Araldite" was a standard phrase around there.
Tim Auton
>On Thu, 8 Apr 2004 19:44:16 +0800, "Rheilly Phoull"
[snip]
>>Talking specifically about "Araldite" does that shrink and apply stress to
>>components ??
>>From observation it certainly will flow into voids at moderate temps of say
>>40c.
>
>I am not familiar with "araldite". Soft, rubbery compounds typically
>don't apply heavy stresses, and hard epoxies typically do.
Araldite is the brand name of the (formally?) most popular expoy resin
in the UK. They make other stuff; to quote their website: " The
Araldite© 2000 range comprises 18 adhesives spanning epoxy,
polyurethane and methacrylate chemistries" - but the hard epoxy is
generally what people mean by "Araldite".
Tim
--
Love is a travelator.