Hi Ken,
There are a couple of points regarding PTV reliability that need to be
clarified. For PTVs it is the drilled hole diameter, not the finished hole
diameter that is important. The aspect ratio is the ratio of PCB thickness to
drilled hole diameter.
This aspect ratio is a good guideline for the difficulty, or lack thereof, of
producing high quality PTVs. We are definitely looking at a moving target,
because manufacturing capabilities are constantly being improved to meet ever
increasing requirements. From a purely reliability point of view, PCB
thickness and hole diameter should be treated as independent parameters.
Smaller PTV diameters make it more dificult to for drilling and wet chemistry
processes, but do not produce significantly higher PTV barrel stresses and
produce reduced innerlayer attachment stresses.
Thicker PCBs make it more dificult to for drilling and wet chemistry
processes, and increase both the stresses on the PTV barrel and the
innerlayer interconnects.
The response from Joe Duclos is right on the money as far as your direct
questions are concerned.

Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 973-543-2747
E-mail: [log in to unmask]

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