It's probably because most NPT's are "second drilled". That is, they are
drill after the panel has been imaged and etched rather than before. So
you are dealing not only with the DTP of the hole but also the
registration of the artwork as well as the artwork feature tolerance.
Denis Lefebvre, CID+
Sr. PCB Designer
Finisar Corporation
(408)542-3832
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Kitty Hines
Sent: Thursday, February 22, 2007 6:11 AM
To: [log in to unmask]
Subject: Re: [DC] NPTH to copper/trace clearance
We have the same clearance standards here. I don't know why, but it's
required by our manufacturing engineers to keep 15 mils away from NPT
holes.
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]]On Behalf Of ert
ert
Sent: Thursday, February 22, 2007 5:02 AM
To: [log in to unmask]
Subject: [DC] NPTH to copper/trace clearance
I got a mail from my FAB house to increase the NPTH - copper/t Hi All,
I got a mail from my FAB house to increase the NPTH - copper/trace
clearance from 0.010 inch to 0.015 inch for a NPTH hole with drill size
0.150".When my drill hole is 0.150 inch with offset tolerance of +/-
0.003, i still have 0.004 inch safer value when i use 0.010 inch
clearance value. When I questioned the FAB house i got feedback that its
their DFM rule for maximizing the production yield.
I am not satisfied with the answer, Can anyone help me understand why
NPTH to copper/trace clearance should be much higher?
thanks,
Raj.
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