Greg,

Here is one problem I was aware of..

Layer 1 and layer 2 both have seperate, and sometimes different aperture 
lists in X-Gerber (RS-274X).

Layer 1 defines D16 as a .010 round.
Layer 2 defines D16 as a .015 round.

The boards shop reads Layer 1 into CAM, then reads Layer 2 into CAM.  
Issue:  What is D16 defined as?

In my experience, if you printed Layer 1 as it is in CAM right now, the 
D16 traces would all be plotted as .015 lines, not .010 lines.

Some / most CAM tools flag this problem, but still require the operator 
to make a choice. 

Some time you should see a ground plane "filled" with a "80-60-15-4" 
thermal instead of a .005" round.

There are draw backs to both standard and X-gerber.  I prefer the 
X-Gerber, but still include the aperature.txt file, (or files) as if it 
were not X-Gerber.

-- 


George Franck Jr
Raytheon E-Systems
Product Assurance Engineer
Falls Church Va

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