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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