Ok, got my specifications, looking at IPC-2221A Figure 10-3, for conductor width (see section 10.1.1 also, pages 77&79); and IPC-A-600H 3.2.1 (see page 86).  It looks like "etch factor" drives how much of a trapezoid one has on any given trace, although outer layers (since they are plated) may have overhang.

What I don't see is any qualitative numbers: ie, an etch factor of y +/-z is typical for outer layers, vs w for inner layers.  Are these numbers variable from vendor to vendor; and have to be called out on any given FAB drawing, since there isn't a generic number to be pointed at?

Shawn Upton, KB1CKT
Test Engineer
Allegro MicroSystems, Inc
[log in to unmask]
603.626.2429/fax: 603.641.5336


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