hi all,
first of all, I normally read the digest version, so please take that
into account if my comments are mis-timed -- or otherwise seem misguided :)
Many of the comments below have already been mentioned by John Pierce,
Lucas Wiman, Martijn, and Brian Beesley.
In my experience, cooling electronics components and circuitry presents a lot
of challenges both for the operation of the components themselves, and for the
packaging. It's certainly true that cooling chips often (but not always)
makes them perform better--generally the allowable bandwidth goes up and the
thermal noise goes down. There are limits, though, to how low one should go.
For silicon chips, the main problem (at typical material purity levels) is
carrier freezeout somewhere between 120 (deg) Kelvin and 50 K. Below the
freezeout temperature, the chips will generally not work at all. It is
certainly possible to bias the transistors so that the carriers get heated and
refrain from freezing, but then the cooling apparatus (which lowers the
temperature of the semiconductor lattice) doesn't "thermalize" the electrons,
and therefore isn't completely effective.
In some other materials, the transistor action can work all the way down to
temperatures where quantum effects become important. Examples are GaAs FETs,
which are built for speed and low-noise.
If one is careful, condensation and freezing (of water ice) can be handled.
I've never had a problem with corrosion (except in components and assemblies
that were thermally cycled often). More tricky is the cooldown from room
temperature to temperatures to e.g. 77K (Liquid Nitrogen), because the
differential contraction between dissimilar materials can break component
cases and snap wire bonds. This is true for passive garden variety components
(such as the bypass caps) on a board, and is one reason why it's undesirable
to spend a lot of resources on cooling electronics that are designed to work
at room temperature.
regards,
Doug Mar
[EMAIL PROTECTED]
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