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Hermetic cover deflection allowed?

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biff44

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Anyone know the maximum aluminum hermetic cover deflection allowed/advised for a largish box in a vacuum environment? To keep the bowing down, I would have go to a very thick cover.

Is 0.047 inches ok for a 4 x 4 inch package? It seems like a lot
 

The 4x4 package would be in a vacuum chamber? Does the package have to be square. Can it be round, or at least rounded sides?

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And how deep a vacuum?
 

sorry, forgot I posted here.
No unfortunately it needs to be a rectangular package, which DOES cause some stress at the corners.
 

4inch is about 10cm; 4X4 is about 100cm2. Atmospheric pressure is about 10kg/cm2 and the whole weight on the Al plate is about 1000kg or about a ton (metric)

0.047 inches thickness is rather small; I need to use a calculator: about 1.2mm

Yes, you should use braces inside the plate or use some engineering alloys of Al used for strength.

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But how about a concave/convex lid that is far more resistant to deformation? But the major strain will be at the center, if I understand correctly. The stress will be rather uniform.
 
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Atmospheric pressure is about 10kg/cm2 and the whole weight on the Al plate is about 1000kg or about a ton (metric)
Fortunately only 1/10 of it, 100 kp force on the 10x10 cm surface.

I fear that 1.2 mm deflection is beyond elastic deformation.

I wonder how the sealing is made. It's not easy to keep a rectangular case hermetic.
 
Thick and/or stiff material. Kovar lids are pretty stiff but
I don't know what's used in hybrids. I have seen some
fairly large ones that have no bracing. Might look at some
of the mil / aero vendors like MS Kennedy / Anaren who
have put out some big honkin' motor drives and such, in
Class K (where you're going to get breathed on the most
about this kind of thing). You won't go far wrong by copying
the mechanical assembly info for some similar-sized and
been-qualified product.

Cobham, Teledyne, Sensitron are some others to try, don't
know whose online data is the most forthcoming about the
construction details. A 5961- SMD may also have good
drawings if the manufacturer doesn't host them on their
products pages, but calls out a SMD.
 

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