Hi Werner,

I do so appreciate the response that you made to Bill Birch. I certainly have
seen air to air and liquid to liquid results that conflict with the IST
post-sep of small Plated vias. I did not fully rationalize why Bill was seeing
the greater failures with non-functional pads on the small holes until you so
aptly put it in perspective. I appreciate the insight.

Regards,
Les

>  From: Werner  Engelmaier <[log in to unmask]>, on 2/25/99 11:00 AM:
>  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]
>
>  ################################################################
>  TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
>  ################################################################
>  To subscribe/unsubscribe, send a message to [log in to unmask] with following
>  text in the body:
>  To subscribe:   SUBSCRIBE TechNet <your full name>
>  To unsubscribe:   SIGNOFF TechNet
>  ################################################################
>  Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section
>  for additional information.
>  For technical support contact Hugo Scaramuzza at [log in to unmask] or
>  847-509-9700 ext.312
>  ################################################################
>
>