Depends upon the need for registration assessment on the other via structures.
Robisan does not believe that 6012/2221 or 31032 requires such testing for (legal) conformance assessment.
The argument is that the thru holes provide some measure, even though it may well be from a different drill cycle.
I was there when the magic "minimum of 3 holes" verbiage went in, without the opposing corner mention. I believe that was the intent, at the time.
Several discriminating OEMs require the assessment for acceptance. However, to my knowledge, all are open minded to other assessment techniques including electrical, drill-and-look, maybe x-ray, and I would think Compunetic's novel x-sect approach. Why don't you just try to sell them that?
This is a current topic on the 6012D calls due to the amending of the tables for the A/B-R.
Chris Mahanna
Robisan Lab
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Louis Hart
Sent: 2011/11/01 7:18 PM
To: [log in to unmask]
Subject: [TN] Microsection of blind and buried vias
Technetters, my question deals with the number of microsections of blind or buried vias, per panel, required by IPC-6012.
For plated holes, one thermally stressed A/B coupon is required per panel. A second A/B coupon, from the corner opposite to that from which the thermally stressed one was taken, is required to be microsectioned in a direction perpendicular to that of the first per panel to check internal annular ring. (I have not been calling for thermal stress of the second A/B.)
Does 6012 require a second microsection coupon for blind and buried vias? (I have collected a number of opinions, and have one of my own.)
I have noticed that MIL-PRF-55110 does not require a second blind or buried vias. As I read it, the requirement is for a single coupon per panel, thermally stressed, for each blind of buried via. MIL-PRF-31032 does not, it appears to me, explicitly address the number of blind and buried microsections required.
Thanks for any comments or insight.
Louis Hart
Compunetics
Monroeville, PA
USA
[log in to unmask]<mailto:[log in to unmask]>
412-858-1272
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