As per IPC-RB-276 section 3.2.2:
Pink Ring:  A zone around a through hole/internal layer interface
from which the oxide coating on the copper has been discolored or
chemically removed.

As per IPC-RB-276 section 3.6.2.3:
Pink Ring: No evidence exists that pink ring affects functionality.
The presence of excessive pink ring may be considered an indicator
of process or design variation but is not a cause for rejection.
The focus of concern should be the quality of the lamination bond.

I have not read in any discussions evidence that a mismatch in the
thermal expansion will cause pink ring.

Does anyone have any QUANTIFIED data (other than the empirical data
of those who have switched) on the problems and benefits of direct
connection vias to plane layers?  So far, I have heard two types of
response -- "We switched and have had no problems", and "We haven't
tried it, but you might want to watch out for <insert potential
problem here>..."

Has anyone done any mixed designs (ie: thermals on the Vcc layer and
direct connections on the GND layer) with the intention of creating
an impedence "slope" to funnel noise to the ground plane?

[log in to unmask]
Don Walker

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