> Also I believe there is an extra process step involved when you have
> pad area on a NPT hole. 

I've talked to a couple of vendors about the implications of 
PTH/NPTH holes. Their requirements are essentially that they want 
copper of the minimum annular ring outside of the hole for PTH and 
that amount of clearance inside the hole for NPTH due to drilling 
tolerance. That assumes a hole that is small enough to be masked 
by the etch resist and those holes will be drilled prior to plating (no 
cost penalty). The allowable size of the hole seems to vary quite a 
bit and isn't usually published (that I've noticed).
If the hole is bigger than that threshold, it will be done on the 
routing machine near the end of the process. Probing a bit further 
with one vendor, I found out that although the NPTH drill and the 
outline routing run on the same machine, they are two separate 
programs so the boards go through it twice. (This particular place 
was rather 'low-end' so I don't know how applicable that it to other 
fab shops).
In the case of the vanishing fiducials, the board house was getting 
so many boards with pads the same size as the holes for NPTH 
holes, they have got into the habit of removing all pads from NPTH 
drill sites. That's quite reasonable except that the CAM operator 
decided to select based on pad size and that caused my fiducials 
to fall off.

Regards,

Steve.

======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: [EMAIL PROTECTED]      fax +64 9 820-1929
======================================================

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