I tend to recommend keeping the fab print to reflect the "finished" PCB
requirements. That way the inspectors have
a "black and white" document to inspect the PCBs too throughout the fab
process. If the process attributes were
specified they might change depending on which factory and where they are
made. Those could be written up in
a Customer Specification document that is separate than the fab print but
chances are there would be a series of
waivers/deviation requests between the fabricator and OEM.
Cheers,
Groovy (aka, Dave Hoover)
----- Original Message -----
From: "Barton, Ken" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, July 09, 2008 7:19 AM
Subject: Re: [TN] Flex specifications - tolerance on hole size
If we started dialing in the drill sizes for actual drill size before plate
as opposed to finished (plated) size, it would surely confuse the heck out
of our fab houses.
Ken Barton
-----Original Message-----
From: John Burke [mailto:[log in to unmask]]
Sent: Tuesday, July 08, 2008 4:28 PM
To: [log in to unmask]
Subject: Re: [TN] Flex specifications - tolerance on hole size
The hole size MUST be the drilled size. If it is NOT the drilled size you
have no control whatsoever over the design in terms of drill to copper
clearances. If you must call out a finished hole size do it separately on
the drawing for the holes concerned.
John Burke
(408) 515 4992
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Collins
Sent: Tuesday, July 08, 2008 8:45 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:
Pb-Free Soldering Processes-Survival, Quality, Reliability, July 17/18,
Thal, Switzerland Pb-Free Soldering Processes-Survival, Quality,
Reliability, July 21/22, Bad Segeberg, Germany Pb-Free Soldering
Processes-Survival, Quality, Reliability, August 18, Orlando Reliability
Issues with Lead-Free Soldering Processes, September 22, Schaumburg
Failure Mode and Root Cause Analyses Reliability (Fatigue, Brittle
Fracture,
ENIG), September 22, Schaumburg
Solder Joint Reliability: Parts 1 & 4, Oct. 9, Moscow, Russia Solder
Joint Reliability: Parts 1 & 4, Oct. 17, Timisoara, Rumania Solder Joint
Reliability: Parts 1 & 4, Oct. 22, Tallinn, Estonia
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