Hi Charlie,
Specifications are for the most part somebody's guess of what might work
based on prior experience with a different design in a different application.
For something a little more directly applicable, you might want to look at
IPC-D-279, Design Guidelines for Reliable Surface Mount Technology Printed
Board Assemblies, Appendix B. This will let you assess the consequences of
reduced PTV barrel plating thickness as well as plating non-uniformity as to
reduced reliability for your application.

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