Hi Bob,
As Werner mentioned, cross-sectioning to evaluate what's going on inside the
PTHs is paramount. One additional point I'd like to make regarding the
reliability of PTHs is drill hole quality. You don't want a rough drill
hole, as this can lead to plating folds, barrel cracks, etc.... The rough
drill quality is typically seen more in the smaller DHSizes, but "it
depends" on the board shop....
Kind regards,
Garry Morand
Symmetrix Hardware Engineering
EMC2
176 South Street
Hopkinton, MA 01748-9103
' 508-249-4329
* mailto:[log in to unmask]
Pager: 888-377-9799 or mailto:[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]
Sent: Monday, January 16, 2006 8:41 PM
To: [log in to unmask]
Subject: Re: [TN] Drill and plated hole callouts
Hi Bob,
The call out of finished hole size is an anachronism left over from the
through-hole technology era. In modern high-density PCBs you should specify
the
drilled hole size (no tolerance) with a minimum plating thickness in the
hole to
be verified by cross-sectiong of coupons.
The reliability of your vias depends on PCB thickness, drilled hole size, Cu
plating thickness, Cu plating quality (verified by testing co-plated mandrel
foils for tensile strength and ductiolity--not elongation). Your friend is
right,
electrical test is not enough. You should have coupons either IST or
HATS-tested. This will be even more important with LF-soldering
temperatures. You then
might want to specify not only Tg, but Td and CTE(z) as well.
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
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