Circuits under pressure

Padded electronics survives that kind of pressure. Problems are:

1) avoid the components getting ripped off the board due to thermal contraction/expansion and mechanical stress. Especially when the padding is cured. 2) how to seal all cables and wires which have to go through the padding.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

All generalities, I hope someone here has specific experience:

I would take care to talk to each and every component vendor, and hope that their app engineers are good. I'd hesitate to trust even the PC board.

Just about any component that I can think of, I can think of a failure mechanism that you may run into by squeezing them that hard. If any one stands out it would be aluminum electrolytic caps, because they're designed to vent. After that is, well, everything -- any component with a void is going to be prone to leaking and have that void filled with oil.

I strongly suspect that before you're done you'll be testing each and every component, separately, under pressure. After your product has been in the field for a year or two you'll be doing it again, looking for long-term failure mechanisms.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

Do you mean "potted"?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

Maybe you could track down the people that make deep-water submersible craft, like the ones that got so much press during the BP spill.

Good Luck! Rich

It's common to use ceramic/metal seals and a metal container for such boards. Some packages (metal-can transistors) are likely to flex, and others (electrolytic capacitors) can be expected to turn unreliable if they aren't isolated from the pressure.

How do you make reliable insulated-wiring connections in your oil bath?

Marco Trapanese schrieb:

Hello,

all components with gas filled hollow spaces within their cases.

Bye

Thanks to all guys!

In these days I've seen a board with this feature (up to 200 bar in oil tank) that uses standard 1n4148 diodes!

I will put a board with some components into a tank under pressure to stress them.

What about a crystal for MCU? I'm pretty sure I can't use HC49 :)

Marco

--

Il 19/10/2010 18:39, Marco Trapanese ha scritto:

Use an MCU with a built-in oscillator. Some are trimmed to better than

1%.

John

John Larkin:

I guess that Marco, that probably did not tell you deals with ROVs because otherwise his employer (The Spectre) would kill him, already checked if, in his desired range of temperatures, the AVR's oscillator will keep within the desired tolerance.

OR NOT?

Marco Trapanese:

Pure tu, ti pare l'ora di stare ancora in giro?

ke?

The 1n4148 has a hermetic seal. Most components aren't sealed as well.

Discretes are interesting in that the JEDEC number describes both the electrical and physical package, unlike ICs.

snipped-for-privacy@sushi.com:

Sort of IPxx classification? What's the key?

JEDEC is pretty old. Then again, so is the 1n4148

I don't know how long the IPxx classifications were around. I only came across them for GPSs.

The way I came across the JEDEC spec-ing both the electricals and package was that I was doing a very cheap SMPS chip where they wanted to use the 1n4148. I couldn't find it in surface mount. Well you can't make a diode like the 1n4148 in surface mount and call it a 1n4148 since the spec covered both electricals and package. Now of course you can get diodes like the 1n4148 in surface mount, but under other numbers.

No, he said gas-filled -- mercury rectifiers, thyratrons and neon lights are out, but high vacuum tubes, CRTs, etc. are perfectly okay! ;-)

Okay, fine, so there's about four molecules of gas actually skipping around inside a "vacuum" tube...

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Late at night, by candle light, Uwe Hercksen penned this immortal opus:

So vacuum tubes are out, then.

- YD.

--
Remove HAT if replying by mail.

Il 27/10/2010 04:45, F. Bertolazzi ha scritto:

The Spectre isn't a problem. And the end application isn't so important. It's a general discussion.

Anyway, the temperature range is ok - let's say between 25 °C and 40 °C. I'd like to use a crystal oscillator because I need to go fast (the board will host an ARM MCU). Furthermore I'll use a lot of high-speed serials so the internal oscillator (1-4-8 MHz typ) isn't the best solution.

Marco

.

Prior to JEDEC, there were "EIA" codes, and prior to that, there were "RMA" codes.

RMA =3D Radio Manufacturer's Association, 1933. Also see "Committee on Tube Numbering".

The original variant of the JEDEC scheme (number-letter-number) began in 1942, with the 1C21, a cold-cathode triode. ("C" =3D triode... in the familiar 1N and 2N schemes "N" was at first a crystal diode and later any semiconductor). For all number-letter pairs, the second number started with 21. e.g. the first crystal diode registered was the 1N21. This minimized confusion with prior tube registrations which were also number-letter-number but rarely did the second number ever get into the teens.

Last 1N number is circa 1N6300; last 2N number is 2N6800. About that time the need for registration of part numbers kinda faded out as the semiconductor industry started moving way faster than the registration scheme ever could.

Tim.

Il 27/10/2010 04:46, snipped-for-privacy@sushi.com ha scritto:

So the key point is the hermetic seal? I was afraid the pressure around the case. For example I expect a standard 5x20 fuse will implode at such a pressure, even if it has hermetic seal.

Am I wrong?

Marco

I'm not going to make any claims or predictions, but I'd expect either of them to take a surprising amount of pressure, because of the cylindrical form. But weren't you talking about like, 9,000 psi or so?

Thanks, Rich