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From: whit@milton.u.washington.edu (John Whitmore)
Newsgroups: sci.physics,sci.electronics
Subject: Re: Circuits and UHV
Message-ID: <15902@milton.u.washington.edu>
Date: 6 Feb 91 04:26:13 GMT
References: <'-^&7$|@rpi.edu>
Organization: University of Washington, Seattle
Lines: 37

In article <'-^&7$|@rpi.edu> atchan@aix01.aix.rpi.edu (Anthony C.T. Chan) writes:

>Does anyone have tips on building a UHV-compatible electronic circuits? 

>I am currently modifying a Scanning Tunneling Microscope for operation in the
>UHV and need to put the STM preamplifier in the UHV in order to minimize the
>noise.

>I understand that heat dissipation and outgassing from components could be
>a major problem. 

	UHV, for the uninitiated, is ultra-high vacuum (generally
10^-10 torr, sometimes lower).
	While I cannot say for certain, I suspect that many transistor
and some IC packages will be suitable at high vacuum; remember, the
metal-package transistors we use today are built with glass/metal
seals that were originally engineered for vacuum tubes.  If the
transistor leads are magnetic (most are), the lead material is likely
Invar (and the package will be welded steel, as likely as not).  
Glass capacitors and glazed (or wire) resistors would outgas for
a while but probably stabilize.  Ceramic circuit board material
is available for hybrids, certainly some compositions will
be vacuum compatible.
	Your main problem is likely to be characterizing the various
packages available to you; there is really no substitute to calling
up the manufacturer's reps and asking for detailed material/package
information.
	A more expensive alternative would be to weld a stainless steel
box over the circuit, and use UHV ceramic/metal feedthroughs to
get the signals and power in, making a sealed pod for the electronics
that fits inside your vacuum vessel.  I wouldn't recommend baking
it TOO hot, so you might have a long wait before the vacuum 
gets really hard.

	Hope this helps.

	John Whitmore