how to create a vacuum between two layers?

[var10]

Hi,

I've got two machined parts and pcb. I have recess in my part which allows the sensor on the board to fit inside. The sensor measures the pressure of whatever our customer wants to measure. So because of this I need to create a vacuum between the contact surfaces of board and machined nozzle (hardened steel). Hence need some sort of lubricant or something to achieve this. I have heard about vacuum grease, but not sure if it will cause any problems on the board's components. Any experiences? And what is the difference between high and low ones? my guess is probably a tiny bit less volatile and not long lasting? or is there anything else?

Does anyone know of anything else better? Thanks for you help!

Cheers,

V.

 

[MintJulep]

Vacuum grease does not create a vacuum.

 

[1gibson]

I am assuming by "vacuum" you just mean you need to seal the inner chamber.

Is it cost effective to make the part serviceable? Meaning, why not use a permanent adhesive? Or just silicone sealant (caulk) which isn't permanent if you really don't want it to be.

 

[IRstuff]

Generally, you should require the sensor rigidly attached to the nozzle, rather than the PCB, given the forced choice. A PCB adds to the mass load on the connection to the sensor, and makes for a less than reliable system.

TTFN
faq731-376

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[var10]

Mintjulep - you are correct, what I was trying to get at was it prevents air leakage from the inner chamber. I prefer it not to be permanently sealed as it is still at R&d and you never know what might come up after few months.

 

[MintJulep]

Grease is a lubricant. Grease is not a sealant. If it were they would call it sealant, not grease.

 

[MintJulep]

Consider:

http://www.hylomar.com/index.php?option=com_content&view=article&id=64&Itemid=55

or

http://www.dowcorning.com/content/news/iam_news32.asp

 

[IRstuff]

a gazillion years ago, we used vacuum "grease" to help out the O-ring seals on our vacuum processing chamber. The grease would allow the seal to settle in and move a bit, as well as filling in any tine voids.

TTFN
faq731-376

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[Timelord]

Vacuum grease is often used as a sealant, ground glass tapers, bell jars etc. If var10 is only after a temporary seal it may work well for him. If he presses matching surfaces together, vacuum grease will help seal the joint. Vacuum grease is about as inert as you can get, it is designed primarily for an extremely low vapor pressure (i.e. no outgassing) and is quite stiff and temperature stable. It shouldn't be a problem to the electronics.