Homebrew PCBs

>It's been my experience that epoxy is your friend
>against harsh environments and climates...

I've used epoxy too, and have filled potting boxes with it. However it can
raise havoc with heat producing parts, as well as creating additional
thermal and conductive paths. However if the economic conditions allow it,
its quite workable except when it comes to service.

On key thing with some epoxies is that they can cause stress related
failures, eg op amp Vos drift is exagerated with temp, and ferrite beads
really hate the stuff unless you balance their coefficient of expansion with
the epoxy.

The VCI stuff we used was in addition to conformal coatings on the pcb, and
as such protected the wire harnesses  as well.

The worst corrosion on a pcb I've ever seen was in the washdown area of a
cheese plant. While the box used liquid tight fittings and was NEMA 4X,
water vapor made inroads, and then would condense. After 6 months, the unit
died due to corroded traces.  Conformal coating was mandatory after this
problem, despite the extra cost.

The worst case of corrosion I've ever seen was on a stainless steel sensor
housing in a very nasty and proprietary chemical process. After 3 months,
the atmospheric vapors had eaten away 50% of a 0.1" stainless steel shell.
They had to go to a series of air knives to keep the nasty atmosphere away.

The underwater stuff sounds really cool. What did you have to do for cases,
as I imagine the pressure loads were really high.

Thanks
Ron