On 12/9/18 7:08 AM, Bob kb8tq wrote:
Hi
On a normal OCXO or TCXO design you would put the product in a
package with a hermetic outer wall to keep out crud and moisture.
Per the papers cited you would put a small vent hole in a “space grade”
product. Every time I see an eBay listing with a nutty price on a “space
OCXO” I wonder if it’s been sitting “vented” on a nice humid / dusty shelf for
decades.
Actually, you could have hermetic packaging - as long as you show that
the pressure differential won't cause a problem. Tons of ceramic ICs
have hermetic packages (an a variety of XOs, as well).
It's sort of a judgement/analysis call - if it's something which is a
box with boards, probably easier to vent - if it's something tiny, and
people have been making and flying them for decades, then hermetic.
We do lots of thick and thin film hybrid circuits which are hermetic -
e-beam welding of the lids and all.
Indeed the only way to test / use product vented like that is to put it in a
thermal / vacuum chamber (or fly it to outer space). While my basement
has a reasonable selection of this and that, I don’t seem to have missed
out on picking up a thermal vac chamber ….
How different is the performance with air in the package? It turns out to
be very much a “that depends” sort of thing. Usually not as big a deal
on a TCXO as on an OCXO.
for the CSAC, apparently, gas outside the physics package affects the
heat required to keep the gas vaporized in the optical cell.
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