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July 2006

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Subject:
From:
Orna and Yehuda - Barak <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Orna and Yehuda - Barak <[log in to unmask]>
Date:
Tue, 18 Jul 2006 22:36:11 +0300
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text/plain
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Jay,
I think that you should make clear what kind of blind via you are referring
too - sequentially laminated vs. laser ablated blind via.

Anyway, the IPC-6012 spec. does not distinguish between the various cases
when it refers to the minimum annular ring allowed. And so, officially, the
1 mil minimum requirement bounds also the case of an internal layer of a
blind via. This - when you are seeking conformance with spec.

Now, if you are a manufacturer than I cannot agree enough with Wayne. I
think that he got the laser via perfectly covered and wish to ad a word or
two about the sequentially laminated board.
In the sequential lamination, the layers go through several lamination
sequences that cause the layers to "shift" and if your annular ring in the
sub-assembly is only 1 mil, than you must be extremely good or extremely
lucky to keep this 1 mil in the final product. Therefore manufacturers try
to make the inner layer lands larger in case of blind vias (as much as the
minimum spacing allows).

Yours,
Yehuda Weisz

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Monday, July 17, 2006 4:32 PM
To: [log in to unmask]
Subject: Re: [TN] Blind Via Internal Annular Ring

No, it should be bigger!

If a blind via is made by a laser as a controlled depth job, the target
pad acts a bit like a "backstop" for the laser.  For this case
"breakout" has the most horrendous consequences:  The dielectric
adjacent to the pad is damaged (perhaps even carbonized) and may plate
during the plating step.  It may be detectable as a short right away, or
may have to wait a while to show up.  I use minimum of 3 mil annular
ring for laser blinds, and other pcb fabricators appear to be in the
same ballpark.

Wayne Thayer

>>> [log in to unmask] 7/16/2006 2:39 am >>>
IPC-6012, Class 3 requires 1 mil minimum internal annular ring for
plated through holes.  Is the internal layer of a blind via bound by
these requirements?

Jay Otts
Raytheon

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