Hi Phil,
The problem for the most part is the integrity of the PTH/PTV
interconnects--barrel cracks and post separation. This 'Rule of Thumb' is based on
experience--but remember, that experience was gained with simpler PCBs, lower Tg
materials, lower quality ED copper plating, Sn/Pb soldering processes, etc. Some
things improve(d)/worsenthe propensity for PCB interconnect failure.
But it is a 'Rule of Thumb.'
You may want to look at IPC-D-279 and/or attend my workshop on the subject to
get a more technical understanding.

Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com


---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------