Thanks to everyone who replied to my previous question about an extremely long lasting battery/energy storage device.
I am now asking if anyone on here knows of an epoxy/epoxy like material that can be used for potting electronics, but which does not UV degrade, degrade significantly with temperature cycles etc, extremely durable basically.
Learning from my previous post I need to also include the application. I am looking for such a material to encapsulate multiple micro controllers which will be exposed to UV from the sun, and other weather effects, and last a very long time 80 years like specified in my previous post.
I am currently think that this material does not exist but I thought I would ask anyway.
Thanks
Thought: It's more cost effective to make something replaceable than make it reliable enough to never be replaced.
I agree 100% but in this case the system cannot be replaced
currently almost all materials over this time frame will suffer from differences in CTE or coefficient of expansion, e.g. there is a minute difference between the pins of a microcontroller and the package of one, its small, but its there, this will also be different to the FR4 pcb material and different again to the SMD passive packaging,
In general these will be close, but over 80 years, things will slowly tear off there joints unless you get very specialized, to clarify, BGA and QFN / DFN are out, and cannot be used, even for passives, throughole may prove better so long as you follow correct lead forming,
As for weatherproofing, you say durable, but fail to give an indication of to what extent, for this time frame I would be thinking sealed in glass with external connections welded to the pins, and have desiccant packets inside to reduce the very slow long term leakage the seals will face. the glass blower can use UV repelling glass, however I do not believe the coatings are expected to last beyond 20 years in direct exposure to sunlight.
The problem here is that the epoxy reaction will never stop.
Things that need to last that long are mounted in Aluminum or Steel blocks with glass to metal hermetic seals. Purged with high pressure argon or nitrogen, then sealed with a cold welded pinch seal used on a copper or nickel fill stem.
Refrigerator grade 30$ pinch seal tools based on vice grip pliars will not work for this task.
My pinch tool is not for sale or loan nor rental. They used to be 1100$, now ten years on they have risen to 3200$.
Steve
Seems like a good application for a die cast aluminum box except for humidity intrusion. I am not convinced that potting the entire board is better than conformal coating but in both cases, I would thoroughly clean the board and use a vacuum. We used to use a lot of gel like silicon potting compounds from Dow Corning.
We don't understand why you jumped to the conclusion that potting is the solution to "extremely durable" ("does not UV degrade, degrade significantly with temperature cycles etc") Perhaps you omitted details which might prove beneficial to responses you might collect from this question. Else it seems like a random question of limited real-world significance.
Is this for an application like undersea, intercontinental cable (which isn't potted)? Or outer-space inter-galactic deployment (which isn't potted, either)? Potting (and especially what a hard material like epoxy) seems rather unsuitable for your stated goals.
If you mount the thing in a metal box, UV won't be an issue.
Maybe beeswax? I've seen 150 instruments, etc with beeswax seals that are still good. But beeswax, being a natural substance, can be of variable quality / properties... not all bee barf is the same. There are sources of purified scientific grade beeswax. I've also seen ancient devices that used pitch for seals.
Your best modern substance might be electronic grade silicone. Urethanes tend to want to revert to their native state of promordial goo over time.
Beeswax breaths through which is acceptable for something in a climate controlled location but not so good for preventing long term damage from electrolysis. Its long term dimensional stability is not the best either.
If you can lower the exposure to UV with a stainless steel enclosure then there are many more possible solutions.
I’d be tempted to look at things that have a proven track record of surviving long periods - military gear from WWII has survived very nearly 80yrs, what seals have they used?
Look at the potting compounds used on 1950’s TV’s LOPT’s??
I like the beeswax, but what about using pitch? Could you use an oil? Does it have to be solid?
Pot your device, expect a lifetime of about 7 years based on my experience. Do what they do for aircraft, hermetic housing, gas fill, mil-spec conformal coating, after selecting parts that the coating will not egress into. I've opened forty year old avionics that looks like it was just made.
Steve
Not sure if this fits in your requirement, result from one of the member here while ago, read carefully this particular post ->
HERE 1st and then subsequent proof ->
HERE , to me its quite convincing.