Mike is correct unless the shop has a "Smartdrill" or equivalent. This machine can be programmed to find both global panel fiducials (any shape) and local (on each circuit) fiducials for higher accuracy of placement.
Some models even have Rout functions as long as the path is round. :)
Accuracy of placement can be less than a mil. We usually do these as Secondary drill although it doesn't matter as long as good fiducials can be had.

-----Original Message-----
From: Tony Steinke [mailto:[log in to unmask]]
Sent: Monday, November 10, 2003 12:06 PM
To: [log in to unmask]
Subject: Re: [TN] Question for Pcb fabricators


Mike,
My experience is the most accurate would be at primary drill rather than
secondary, of course
most drill machines have limitations to drill
hole size diameter, usually around .250 in. which you are forced to do a
secondary either by peck drill or routed out-you also have limitations on
resist tenting if you primary drill large diameter holes.
----- Original Message -----
From: "Mike Larson - ID" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, November 07, 2003 4:31 PM
Subject: [TN] Question for Pcb fabricators


> What is the tightest tolerance that can be held on a non-plated hole
> relative to the fine pitch artwork pattern on one of the external layers,
> this could be a dimension od around an inch to 5 inches approximately  I
am
> trying to locate a hole within +/-.0015" of a artwork pad that is sized
> .006"x.098" , this is connector pattern of around 300 to 400 pads at a
pitch
> of .31mm
>
> Which method of drilling would work best for this, primary drill operation
> or a secondary drill after the outer layer has been etched?  The pcbs are
> both rigid and rigid flex polyimide class 3 designs.
>
> Thanks in advance,
>
> Mike
>
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