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Hall D FDC issues
Hi,
A few FDC issues:
Strip-to-strip gap
Ed says the minimum interstrip distance that is easily manufactured is approx 3 times the
copper thickness. Thus for 1 oz copper, about 1.2 mils, 5 mils is easy to fabricate.
I don't know what sets the lower limit on this from an operating standpoint, if anything.
If the gap is too large the induced fields will leak between the gaps and couple to the
next plane, induced signal strengths on the strips will decrease, etc.
Oxidation
Normally the copper on a pc board is coated to control oxidation, etc. This can't be done
for the FDC's as the ions need to land on the bare metal in order to be neutralized. A
coating would cause a buildup of ion charge that would make the chambers stop operating
after a while.
But a non-conducting oxide layer may cause the same problem. Does the copper need to be
gold-plated? This probably isn't too expensive since the gold coating is extremely thin
(microns), and gold coating copper on pc boards is not unusual. I suspect we don't need
gold plating, but I'm not sure. Anyone have experience with this?
Skin depth
The minimum copper thickness is set by the risetime or bandwith of the induced signals on
the strips through the skin depth. If the copper is too thin higher frequencies can leak
through the strip. Recall that when a wave hits a conductor the plane wave turns into an
exponential decay with 1/e distance set by the frequency-dependent skin depth.
Mehmet...you should estimate the risetime of the induced signal and then the skin depth in
copper and verify 1 oz. copper is enough. My guess is that this is not an issue, but it
should be checked.
Sincerely,
Elliott
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"Science plays a major role in satisfying the minor needs of mankind"
"Secular man, by playing God, becomes the devil"
Elliott Wolin
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