I'm no expert by any means, but all pcb persons I have ever discussed this
with have always said the stated hole size is finished.  Both pcb vendors
and pcb layout persons.
It is the pcb manufacturer's responsibility to know their process and over
drill hole diameter so the finished hole size is attained after plating.
Just my $.02
Lenny Carter
Design Engineer
ERG, Inc.
www.ergpower.com


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Collins
Sent: Tuesday, July 08, 2008 11:45 AM
To: [log in to unmask]
Subject: Re: [TN] Flex specifications - tolerance on hole size

Hey guys.
Thanks for all the opinions and info.  I'm stuck in the middle, on one side
is a designer saying that it means pre-finishing size, on the other I've got
a fabricator saying it means finished hole size.  The drawing is ambiguous
on this point.  I just want parts to build things with!!!

I do agree with Werner that it does not matter as they are only vias, but
once someone had inspected and measured something it became a debate. 


regards,
 - Graham

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ken Bloomquist
Sent: Monday, July 07, 2008 7:57 PM
To: [log in to unmask]
Subject: Re: [TN] Flex specifications - tolerance on hole size

Hi Werner,

I like your thinking but... 

I'm not in the quality department, no offense to those of you who are, but I
wouldn't want to be ;-) But thinking like an inspector, how would you verify
that you got the right size holes if you don't call out a finished hole
size? I guess you could do a cross section but a pin gage is a lot simpler.

Just thinking out loud,

KennyB

-----Original Message-----
From: Werner Engelmaier /* [mailto:[log in to unmask]]
Sent: Monday, July 07, 2008 3:36 PM
To: [log in to unmask]
Subject: Re: [TN] Flex specifications - tolerance on hole size

Hi Graham,
Why do you care what the finished hole size is? Do you put component leads
into 0.028"/+- 0.003" holes, that is 25 mils minimum?
The finished hole size specifications are an anachronism harking back to the

THT-days-today they only should be specified for componet lead holes.
For vias the drilled hole diameter should be specified-it is much more
important.
Werner
Future workshops:
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Thal, Switzerland Pb-Free Soldering Processes-Survival, Quality,
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