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Fiberglass resin as an encapsulent

T

Tony

Jan 1, 1970
0
I have used Fiberglass resin in samll ~2 x ~3 x ~1 molds fr4 boards with all
sorts of parts on them. Should I be expecting problems from my choice of
materials? So far there have been none. I also mix in a blue tint. Only
problem is a sticky residue on the top surface. Very thin but tacky.
 
M

Marc H.Popek

Jan 1, 1970
0
I used different material to encase pcb items, the key is to check the
chemistry of the compound as well as any mechanical stress evaluation from
differing thermal expansion coefficients.

The chemistry cannot be too acid nor base or it will attacks the metal
leads, etc over time.
 
R

Richard Lamb

Jan 1, 1970
0
It sounds like you are using polyester resin.
May I suggest an epoxy resin instead?
Less shrinkage during ans after the cure, for one reason.
And epoxy resins cure slick.

I've potted circuits for RC guys in epoxy/microballoon mix
to make tiny little bricks with connectors poking out of them.

Or maybe, for small projects, try clear acrylic casting resin?
Again, a smooth, slick final surface.

With ANY of these techniques, be careful how much resin you
use because the cure gives off heat. At some mass, the resin
can't dissipate the heat as fast as it is created.

Oops...
 
A

Anand Dhuru

Jan 1, 1970
0
Hi,

Automobile body workshops use a material that is used for levelling of
reshaped surfaces; here in India its called car patch material. I have
had excellent results using this material for potting. When set, it
becomes hard enough to turn on a lathe (not that that matters for this
application!)

Advantages over resin is that sets *much* faster, is much cheaper, and
I believe has an even higher impedence.

Regards,

Anand.
 
T

Tony

Jan 1, 1970
0
Our version is genericaly referred to as Bondo. I believe. It is fiber
reinforced though. Sounds messy.
 
A

AB

Jan 1, 1970
0
Fiberglass sounds shakey to me, it shrinks. It's tough stuff though
and should provide a weather barrier (if that's your goal).

I play with high voltage generators using smt parts. I can test them
without an encapsulant up to about 50 to 80 volts output. So, I screen
the boards before encasulating them. I can take the output up to 150
volts after applying 2 thin layers of clear Krylon spray paint.

After the krylon treatment, I can take the output voltages up to 300
volts, which is the limit of my components and more than twice what I
really need.

Strictly speaking, this DOES NOT protectthe edges of the board from
absorbing moisture.

But, it stands up ok over time, I have a few projects that have run
well for 10 years and still use my circa 1974 ttl keyer for my ham
radio transmitter.

Atr the time I started using Krylon, an OT (old timer) advised me I
could coat the edges of the board with peanut oil (after the krylon
layer). This prevents moisture intrusion into the edges of the board,
but I've never done this.

Lately, Krylon has become hard to find, so I am looking for an
alternative.

Regards,

Art
 
T

Tony

Jan 1, 1970
0
Well I dont know about the shrinkage. I assume if the device survives
hardening the shrinking no longer matters? I am using the encapsulation as
an anti tampering measure. Krylon was available at Home Depot last time I
looked. Cheap clear coat. I have used it to stick and or protect labels.
Tony
 
I

Ian Stirling

Jan 1, 1970
0
Tony said:
Well I dont know about the shrinkage. I assume if the device survives
hardening the shrinking no longer matters? I am using the encapsulation as
<snip quoted message incorrectly placed at bottom>

It may well matter.
As the resin shrinks, anything that doesn't shrink at the same rate is
subjected to large forces.
The outside components are pushed inwards to the center of the board.
Then, as temperature varies, they are pushed less or more, creating
almost certain failure in some cases.
If you can, decouple the board from the resin.
For example, put the board in a plastic bag with bubblewrap around
before adding the resin, so that the resin does not touch any components,
but is held off by a flexible layer.

Needless to say,

--
http://inquisitor.i.am/ | mailto:[email protected] | Ian Stirling.
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