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July 2008

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Subject:
From:
Joe Fjelstad <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 9 Jul 2008 11:55:45 EDT
Content-Type:
text/plain
Parts/Attachments:
text/plain (222 lines)
Everyone who has commented is basically right based on their varying  
perspectives.
 
Providing a tolerance on a via is not necessary for accept or reject,  so 
long as it has the copper needed/requested but it is important to know  what is 
happening on internal layers and therein lies the rub. 
 
It is very helpful for the designer to know something about the  
manufacturing process and manufacturing tolerances to avoid painting themselves  into a 
corner (which happens more often than should be) and wasting time with  after 
the fact clarifications. 
 
Time spent with a manufacture learning about the process before  designing is 
time well spent. 
 
Joe    
 
 
In a message dated 7/9/2008 7:33:47 A.M. Pacific Daylight Time,  
[log in to unmask] writes:

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
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