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June 2007

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From:
Greg Triggs <[log in to unmask]>
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Date:
Wed, 27 Jun 2007 08:17:44 -0700
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Hello
 
             I know that there are not a lot of Fab Guys still out
there, but here goes. Over the years I have seen a problem with coverage
of the oxide replacement along the traces when the layers have been etch
using cupric rather than alkaline. What you see is a lack of coverage on
the fine traces with full coverage on the larger lines and ground
planes. The coverage problem is worse as the copper weight gets higher.
This seems to point to a problem that begins in the cupric etcher, and
becomes worse the longer the layer is in the etcher. If the layers are
passed thru a chem clean (acid) prior to oxide replacement the problem
goes away. Typical clean prior to oxide replacement is alkaline (dryfilm
residue). This seems to indicate that whatever is on the edge of the
trace is acid soluble. Most people seem to blame the dryfilm strip
process, but the isolated lines and ground planes don't have the
problem. I would appreciate any input. Thanks.

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