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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
Stalag 602-11
Gulag ARC-ipelago

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