Hi Bill,
Thanks for sharing the results. They reconfirm the results from the round
robin study that was reported in IPC-TR-579 and the conclusions based on these
results. The hierarchy of parameters influencing PTH/PTV interconnect
reliability you show is almost identical to the one I have been relating to
the attendees of my workshop since1990.
I would place copper plating thickness uniformity (dog-boning) at the 2nd
level where I also would place stress risers created by non-uniformities
resulting from rough drilling.
Your explanation on pad vs. no-pad reliability influence is fine as far as it
goes. However, the different location of barrel cracks in MLBs with and
without pads is only apparent. If you will look closely where the prepreg
layers are, you will find that the cracks will always be in tthe prepreg layer
sections of the cu barrel (of course, without pads they are much harder to
identify).
Also the difference between smaller and larger diameter PTH/PTVs may be an
artifact of the IST test method; pads will carry thermal energy into the
spaces between PTHs faster, thus resulting in a larger resin cylinder around
the PTH reaching higher temperatures (IST is not a steady-state thermal test)
and therefore more resin volume to expanding. This causes larger loads on the
PTH barrel. In larger diameter PTHs the Cu volume replacing resin and the
stiffening of the PTH barrel by the pads causes a small increase in
reliability, whereas smaller diameter PTHs are sufficiently stiff in their own
right, the pads do not significantly increase the barrel stiffness and the
increase expanding resin volume has a negative effect on reliability.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask]

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