I'd like to add to the via cracking discussion.  If the elongation values
are adequate or even excellent, say 20%+, the possibility of cracking still
exists and can increase dramatically, especially if the thickness of the
deposit in the via is below spec.  Copper plating thickness uniformity can
be notoriously bad, especially with certain designs.

Elongation values, as I remember them from IPC documents, are arrived at
using a specified thickness on test coupons.  It used to be 2 mils.  Thus,
if the via deposit thickness is less than this, the elongation of the
thinner deposit can decrease.  I've heard engineers discuss this saying they
have excellent elongation values and can't understand how copper cracking
occurs.

---------------------------------------------------
Technet Mail List provided as a free 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/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------