Subsea Electronics to 4500psi

On Wed, 29 Oct 2003 05:08:18 +0000, Guy Macon <http://www.guymacon.com/ Gave us:>


I didn't say that that was all that it meant. Doh!
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Did you or did you not write "hermetically sealed, and that means no trapped air" ?
Hermetically sealed does NOT mean no trapped air. It means that whatever gas is inside (dry nitrogen in the case of hermetically sealed military specification integrated circuits) is sealed from the outside. In other words, trapped air is an example of being hermetically sealed.

I hope that that wasn't directed at me. As you may have noticed, I have a policy of treating everyone with respect and honor, and if someone insists on making personal comments I simply killfile them and continue the conversation with those who are willing to be civil. I am aware that you insult some other people and that they insult you back, but that's not a game I am willing to play.
Remember those of is who are smart are here to learn, not to impress, and that means admitting it when you are wrong. I think that you are among the smart. It would be a shame if I were to find out that my high opinion of you was misplaced and that you are actually one of the stupid people who never admit that they are wrong and thus never learn anything new.
--
Guy Macon, Electronics Engineer & Project Manager for hire.
Remember Doc Brown from the _Back to the Future_ movies? Do you
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On Wed, 29 Oct 2003 14:52:46 +0000, Guy Macon <http://www.guymacon.com/ Gave us:> As you may have noticed,

A rare thing, indeed.
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On Wed, 29 Oct 2003 05:08:18 +0000, Guy Macon <http://www.guymacon.com/ Gave us:>Bad advice. Many mil-spac chips have ceramic packages with large

I'm sure it would hold up better than a plastic dip, or epoxy encapsulated die. The die itself is the same relative hardness as the ceramic tablets used to cover them.
They are made SPECIFICALLY for high heat, pressure, vacuum, and other extreme conditions and would likely be the BEST choice. Especially if the completed assembly then gets encapsulated further, as they are best conditioned to conduction cooling, which is what fully potted designs are all relegated to. So, the lifespan would be extended as well. Putting something down deep, one wants the highest possible reliability, and the longest MTBF, cause service calls are a bitch!
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All true except the "high pressure" part. Mil-spec chips are made to better withstand other kinds of harsh environments and would otherwise be the logical choice, but mil-spec chips are NOT designed to withstand 4500psi of pressure. In this specific case, an otherwise inferior die attach package (you have seen them if you have opened' any modern electronic toy - it looks like a blob of epoxy on the board) would be better able to withstand the pressure because it doesn't have the nitrogen-filled void that a ceramic mil-spec chip has.
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Remember Doc Brown from the _Back to the Future_ movies? Do you
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<http://www.guymacon.com/ says...

Mil-spec parts aren't always the best alternative for commercial applications. I had a high-rel requirement for a commercial crypto product and was going to specify Mil-parts, until I got education. Ceramic, particularly the 'C' (IIRC) packages are easily damaged and will leak if the seal is cracked (easy to do with mechanical-insertion). Commercial parts were a better choice for the application.
Subjecting a cavity part to 4500PSI is simply nuts. I don't think I'd specify anything without some serious testing or well known specifications covering my donkey.
--
Keith

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On Wed, 29 Oct 2003 23:13:56 -0500, Keith R. Williams

Funny that, since they can handle 40 plus G tests for conformance to meet reqs for space applications.
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snipped-for-privacy@thebarattheendoftheuniverse.org says...

You continue to insist on advertising the fact that haven't a clue.
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Keith

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On Thu, 30 Oct 2003 21:52:21 -0500, Keith R. Williams

top chewing on your fingers. You are babbling.
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snipped-for-privacy@thebarattheendoftheuniverse.org says...

You're simply proving what an idiot you are. Mil spec parts are designed for *one* envrionment. 4500psi tain't it!
--
Keith


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On Fri, 31 Oct 2003 22:05:02 -0500, Keith R. Williams

You're a Dumbshit again, as usual.
mil spec parts are designed for a range of environmental conditions from full vacuum (space) to a specific positive number of atmospheres pressure. That's pressure. They are also able to withstand greater heat ranges than standard ICs are as well.
The word for today is range.
Go get some clues, and come back later... much later.
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Silicone liquid is more likely.

Is this just curiosity, or do you have a project? It it's just curiosity, newsgroup answers are fine. If you are making something that has to work at 10000 ft. you need expert help. Your best bet would be someone who has made several 10000 ft. ROVs Your second best bet would be someone like me - see my resume at http://www.guymacon.com to see if I am a good fit for your project.

Not always. Some have cavities, many have bubbles. If I was in charge of the project, I would consider using QuickPak ( http://www.quikicpak.com/news/200207_quicksolutions.html ) with a vacuum-based bubble remover.

Most surface mount components trap air in the attach epoxy. The problem with the boards isn't so much the vias but the blind vias. It's just that BGAs usually require blind vias.
Your fiberglass also traps air in it. I would look into Teflon PWBs

Exactly right. And it won't be easy to service, either!

Crystals don't work when encapsulated - they come in cans (or, in your case crushed cans!). I would have to research ceramic resonators. How accurate must the clock be?

You can go all ceramic.

Depends. I think the attach resin will be a problem.

Why do you think that soldering rather than using connectors isn't off the shelf? (I wonder if the mil-spec Radsok would work...)
BTW, have you thought about voids in the solder joints?

Oops! There goes your choices as far as connectors and ICs! I have never seen a PC104 CPU board without a can crystal. Have you?

Hard to tell. The power semiconductors shouldn't be a problem, but the rest? I don't know.

Have you solved any pressure related motor problems?

In an oil bath? Pretty much a non-issue.

Why you shouldn't ask for E-mail responses on Usenet: http://www.cs.tut.fi/~jkorpela/usenet/mail-responses.html
--
Guy Macon, Electronics Engineer & Project Manager for hire.
Remember Doc Brown from the _Back to the Future_ movies? Do you
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On Mon, 27 Oct 2003 01:23:41 +0000, Guy Macon <http://www.guymacon.com/ Gave us:>

Solid forms are more likely. Liquid is not likely at all.
RTV is common. Hard epoxies are even used.
NASA uses polyurethane.
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Having worked on the Space Shuttle, I can confirm that semi-solid is used in air and space. I have never done deep sea, but I can see some real problems with it if used that deep underwater. In that application, you need to fill the entire enclosure. A liquid seems like the best way to do that. A layer of semi-saolid (maybe 1/4 inch?) covering the boards would seem to be a good idea as well. These are just guesses, of course; I don't have the experience to know for sure.
--
Guy Macon, Electronics Engineer & Project Manager for hire.
Remember Doc Brown from the _Back to the Future_ movies? Do you
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On Mon, 27 Oct 2003 03:00:42 +0000, Guy Macon <http://www.guymacon.com/ Gave us:>

For LV, perhaps, but the ONLY approved encapsulant for HV devices in space, by NASA, is a polyurethane medium known as "Conap".
It is VERY expensive, and it will stop a bullet it is so tough. Literally. It cannot be sliced, diced, serviced, or anything else, once it has been cast and cured. It has the least gassing (none), and the highest adhesion available, when thermal expansions, and contractions are considered. Hard epoxies do not work as parts get sheared by the differing thermal expansion rates.
If you press on a surface, and it "gives", that does NOT make it a "semi-solid". RTV encapsulants have gel like feel to them, but are considered a solid. For it to be "wet", it has to "wet" a surface by touch.
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With such extreme pressures, even solids have a problem. The idea is to allow the pressure inside and outside the container to equalize. The forces on even a modest enclosure would squeeze pretty hard on epoxies or RTV, deforming them and the container.
Completely filling with oil (or silicone liquid) with a small 'bladder' or diaphram exposed to sea pressure works much better. As pressure rises, the diaphragm deflects a tiny amount, and a small amount of the *nearly* incompressible liquid is forced into the 'can', keeping pressure equal across the can walls. Of course if you leave an air pocket, more oil must be forced in to equalize, and if too much is needed, the diaphram deforms too much and ruptures. Now seawater is into you electronics :-(
Perhaps the best is to 'pot' the electronics so water won't affect them, then fill the free space in the enclosure with silicone liquid to keep the pressure equal. But the 'potting' has to be perfect. Any voids and it will add to the total voids the oil/diaphram have to accomodate.
daestrom
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Even potting has it's dangers as the process can displace sensitive parts and leave you with an impressive paperweight.
daestrom wrote:

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On Mon, 27 Oct 2003 23:32:34 -0500, **THE-RFI-EMI-GUY**

Hard epoxy potting, yes. One must choose a material that shrinks minimally during cure, and moves minimally during hot and cold temperature cycling.
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forces
or
the
must
the
will
Since you are the EMI guy...what is your opinion on the life span of EMI filters....just a general question....Ross
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On Mon, 27 Oct 2003 22:20:41 GMT, "daestrom"

If the encapsulant is hard epoxy, the voids you mention won't "see" the pressure. Also, the polyurethane version I mentioned is so stiff it stops bullets. Then, one can place the assembly into a hardened container that can handle the number of atmospheres it is to be subjected to with hermetic pass throughs on the conductors or cabling to and from the device. Expansion cavities, and such can be eliminated.
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