Daan,

Don't confuse the "incident or pit" tolerance with feature acceptability.
The 20 percent rule is for fabrication.  The 12 wide copper lands coming in
at less than 10 is a function of PCB CAM being a bit out of control.  I
assume this is because you require solder mask in-between these 12 wide lands
spaced on 19.5 centers.  What I have done is 12 lands no mask in-between.  If
you are starting with 1/2 copper you can get mask between lands (not easy).
If your at one ounce prior to plating; forget it.
Call your supplier if they can't supply lands 12 wide, find someone that can.
 When these 12 footprints fall below 11.5 problems really get big in the
solder stencil department.  Lastly, this is not a function of over etch,
otherwise your 5 traces would be gone or your 6's would be 3.5, etc.

Boston Brad

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