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Are there crystals that are tolerant of high pressure?

Or do they all have an open space in their case?

A customer wants to use our product in a submarine, immersed in high pressure oil.

I thought we'd be OK using SMD crystals, based on this Wikipedia article and based on reading the reference from the US Dept of the Navy.

Instead, under pressure, the top of the case of the crystal imploded.

enter image description here

(Picture of imploded SMD crystal after high pressure oil immersion test.)

Obviously, there's an air pocket in there.

It was suggested that we pot the crystal in epoxy. But I have some doubts that that would work: The pressure cracked the ceramic body of the SMD crystal; I doubt that epoxy can withstand what ceramic couldn't.

(Can a kind soul with 300 reputation points create a "high pressure" tag and add it to this post, please?)

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    \$\begingroup\$ Does it have to be a crystal? I.e., do you require really precise timing, or could something "lower" spec be used? \$\endgroup\$ – Majenko Jan 28 '15 at 21:12
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    \$\begingroup\$ CAN bus. So, 0.5 % over full temperature. \$\endgroup\$ – Davide Andrea Jan 28 '15 at 22:06
  • \$\begingroup\$ This is a product in high volume production. Because this is a just for a few units, just for this particular customer, we are not going to redesign the circuit. We wish to just replace the crystal with another crystal, or other component that is as accurate. \$\endgroup\$ – Davide Andrea Jan 28 '15 at 22:08
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    \$\begingroup\$ Ceramic is brittle, and I wouldn't be surprised to find an epoxy stronger than it - many are rated to be as hard as the plastic in hard-hats/helmets, I would certainly try one out as a test. \$\endgroup\$ – user2813274 Jan 28 '15 at 23:59
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    \$\begingroup\$ Can you quantify "high pressure"? I tend to agree with the prior comment, i.e. there is probably an epoxy that will do the job well. Just make sure it's fully cured before testing. \$\endgroup\$ – Scott Winder Jan 29 '15 at 0:50
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I've used solid ceramic resonators in high-pressure environments (inside oil-filled canisters at 120m below sea-level) without any trouble.
Of course as Majenko has already alluded to they're typically not quite as precise as a crystal usually is, but they quite happily clocked my PICs and were accurate enough to allow my serial comms at a few 100k-baud.

I did consider encapsulating a standard crystal in epoxy as suggested bu others, but my concern was that although many epoxies are generally tougher and harder to break than a crystal, I didn't think they would provide much protection.
My thinking was that the reason epoxy is tough & hard-to-break is that it is able to flex or deform somehow by some small amount before breaking. But this would be transferring force to the crystal - exactly what I was trying to avoid.

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Talk to your crystal manufacturer. They are more used to interacting with small customers than most component suppliers, given that they supply custom cuts and custom frequencies. If they have packaging solutions to meet your needs, they are the best equipped to answer your questions.

In the UK I could recommend IQD or Euroquartz as useful contacts; I have no suggestions for other locales.

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If you use a high compressive strength epoxy with a low dielectric constant (so that not much capacitance is added between the crystal's pins) you should be OK.

MasterBond makes some high pressure stuff that would probably work for you.

There are data sheets available but you have to jump through some hoops to get them.

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