From: Robert P. Johnson [rjohnson@scipp.ucsc.edu]

Sent: Monday, March 01, 2004 14:44

To: Steve Ritz; William Atwood

Cc: Peter Michelson; Jerry Clinton; Lowell Klaisner

Subject: copper numerology

Regarding the impact of 1/2 oz copper in bias circuits instead of 1/4 oz, here
are the numbers that I come up with:

1/4 oz/square foot = 7.62E-3 g/cm2

Cu density = 8.96 g/cm3

So 1/4 oz thickness = 8.5 microns

Cu radiation length = 12.86 g/cm2

So 1/4 oz radiation lengths = 0.059%

The bias circuit has one solid ground plane. The top layer of copper has only a
very small percentage coverage (narrow traces and small pads), so the impact on
it can be neglected to first order.

Hence we can expect that the increase in radiation lengths per tray will be
about 0.12% if we go from 1/4 oz copper to 1/2 oz copper. This compares with
0.86% rad len per tray for the silicon itself.

Robert