etch factor can vary quite a bit from one fab to another and also the 
specific design.

At 08:52 AM 6/20/2012, Upton, Shawn wrote:
>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
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>603.626.2429/fax: 603.641.5336
>
>
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