Our drawings almost always have a tolerance associated for vias. As Ramon just stated, we add a "plating factor" to the specified hole size to obtain the drill size. The expectation is to finish at the nominal (middle of the tolerance) hole size.
Karl
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Dehoyos, Ramon
Sent: Friday, April 27, 2007 2:32 PM
To: [log in to unmask]
Subject: Re: [TN] "plated shut vias"
Agreed, We just went through such an exercise and the conclusion
was that the specified hole size was the final hole size. A 6, 7, 8 or 5
mils were added to find the drill size.
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Smith, Richard
Sent: Friday, April 27, 2007 10:05 AM
To: [log in to unmask]
Subject: Re: [TN] "plated shut vias"
I don't disagree but, unless I'm behind the times which is entirely
possible, the IPC used to promote the practice of specifying all plated
hole sizes as finished permitting the manufacturer to select the
appropriate drill. I'm not implying this is the best practice, but on
the other hand I've not seen a via reliability issue attributable to the
finished via hole tolerance on the drawing.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Thursday, April 26, 2007 3:23 PM
To: [log in to unmask]
Subject: Re: [TN] "plated shut vias"
Hi All,
Vias should never be specified in terms of finished hole size (there is
no
functional need for any specific finished hole diameter), but in terms
of
drilled hile diameter, because that determines all kinds of things
important to the reliability of the via interconnect structure.
Werner
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