Info on PCB potting/encapsulation?

[unknown]

I'm working on a hydraulic valve driver board for some heavy equipment, and
am toying with the idea of potting them in epoxy, pourable RTV, etc. The
main reason is mechanical in nature; I'm using two small PCB's, 90 degrees
to the main card as the user interface, potting it would make in into a
brick which would secure the small boards. This might seem overkill, but
these machines have very severe vibration and any hanging mass is vulnerable
to destruction. Also protection from moisture, hydraulic fluid, etc. is a
secondary reason. I put a drawing which might explain the setup better at:
www.ottelectronics.com/photos/valvedriver.gif

In the past, I've only done this with prototypes or one-offs using regular
epoxy. The commercially available stuff from MG Chemicals and Loctite looks
to be very good quality, and designed specifically for potting, but it's
much more expensive that I would have guessed. $100 - $150 per gallon.

I'm sure someone out there has come across this problem as well. Any hints?
Is this stuff commercially available for other applications at a better
price? Standard gallon jugs of epoxy (from the hardware or craft store)
supposedly have a lot of shrinking as they cure which can shear parts off
the board. I've read that some people "cut" the epoxy with sand to control
this and act as a cheap filler, has anyone had experience with this?

Thanks!

Chris

[Frithiof Andreas Jensen]

Post by unknown
I'm sure someone out there has come across this problem as well. Any hints?

Maybe some Urethane-compound or -foam might be cheaper and better. Or silicones.

Epoxy is frowned upon - at least round 'ere (DK) - for health and safety reasons
and that migh also be why it is expensive: It is becoming a niche product.

PS: If you *do* use epoxy it is a good idea to coat the boards in some soft
material first, silicone or urethane f.ex. otherwise the epoxy can exert
pressure on the components. I once had 1000 pulse tranformer cores loose their
magnetic properties due to compression. Worked on the bench, did not work
potted, worked un-potted ... bastard that was.

[qrk]

On Mon, 25 Sep 2006 22:27:10 -0700, "Christopher Ott" <chrisott *at*

Post by unknown
I'm working on a hydraulic valve driver board for some heavy equipment, and
am toying with the idea of potting them in epoxy, pourable RTV, etc. The
main reason is mechanical in nature; I'm using two small PCB's, 90 degrees
to the main card as the user interface, potting it would make in into a
brick which would secure the small boards. This might seem overkill, but
these machines have very severe vibration and any hanging mass is vulnerable
to destruction. Also protection from moisture, hydraulic fluid, etc. is a
www.ottelectronics.com/photos/valvedriver.gif
In the past, I've only done this with prototypes or one-offs using regular
epoxy. The commercially available stuff from MG Chemicals and Loctite looks
to be very good quality, and designed specifically for potting, but it's
much more expensive that I would have guessed. $100 - $150 per gallon.
I'm sure someone out there has come across this problem as well. Any hints?
Is this stuff commercially available for other applications at a better
price? Standard gallon jugs of epoxy (from the hardware or craft store)
supposedly have a lot of shrinking as they cure which can shear parts off
the board. I've read that some people "cut" the epoxy with sand to control
this and act as a cheap filler, has anyone had experience with this?
Thanks!
Chris

You can check Emmerson & Cumming's stycast line. Hard epoxy might
mechanically stress your circuitry. I have used silicon conformal coat
before potting in hard epoxy.

J-RTV from Dow Corning is nice to use, but pretty expensive. It's also
fun to make feelie toys with the leftovers.

Polyurethane is another possibility (http://www.conap.com). Navy uses
EN-9 and EN-7 for underwater uses.

If you use board-to-board connectors, you may want to seal off the
contact areas to prevent the potting compound from getting in the
contact areas.

You should consider conformal coating. A polyurethane conformal coat
will hold parts in place.

Don't fret about price of the potting compound! The time you spend
potting will cost more than the potting material and down time on the
equipment will cost even more.

---
Mark