Hi,
I'n in the end run of a revision to a board design which is double sided eight layers with blind vias on layers
1/2, 1/4, 5/8 and 7/8, as well as the normal through-hole 1/8 vias. Sizes are 0.3mm (12mil) for in-pad blind vias
and 0.6mm (24mil) wherever I can get away with it.

We've already had batches of Rev A boards made up with sequential lamination and with controlled depth drilling
and we're in the process of evaluating suppliers and their boards. My problem is that we are having trouble nailing
down any sort of specification for our next run. These will also be prototypes but we're getting close to volume
production and need something for QA to hang its hat on for incoming inspection.

Factors we are considering are:
a) Boards manufactured with controlled depth drilling promise to be considerably less expensive (30% on one estimate)
b) The repeatability of the depth of drilling is an unknown, from stack to stack and from batch to batch.
c) The long term reliability of a blind via defined this way is unknown to us
d) The aspect ratio of a blind hole appears to be critical, but what is optimum and what is acceptable?

and so on and on.

Can anyone help?

Thanks in advance

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