Hi Rob,
The optimum PTV barrel plating thickness is between 1.2 and 1.5 mils. 
Thicker, and you may shift towards innerlayer separation (the old post 
separation), because the PTV barrel gets too stiff in compression and forces 
more z-direction expansion of the resin. For 17 mil holes in a 255 mil thick 
MLB your vendor should also plate significantly slower than 1 mil Cu per 
hour. You need spezialized solutions for this; and of course more plating 
time is more expensive. But this plating thickness is not the whole story, 
you also want plating uniformity (no dog-boning), which is also an indication 
of better Cu deposit properties (strength, ductility) in the PTV center, and 
good drilling (no localized stress risers).
Use only high Tg resin and specify E3 (HTE) foil for all layers. 
Also, make sure, your MLBs do not see any manual soldering processes—even 
HASL may be too high a temperature excursion.
You should have been at my IPC Expo workshop on the subject. Absent that, 
take a look at IPC-D-279, Appendix B. 

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], Website: www.engelmaier.com 

################################################################
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
################################################################