As usual all good sound stuff from Werner. I would always specify the
drill size as that is what the aspect ratio is calculated from and hence
(all other things being equal) the via hole reliability. However, in the
case of for example a press-fit connector, then you need to specify a
tight tolerance finished hole size. Another classic case of "it depends"

Regards
Ian Fox
Goodrich ECS

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: 17 January 2006 01:41
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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