The symptoms sound exactly like a barrel crack from Z-expansion. 

Something to look for... If inner layers are planes, were non-functional
pads retained to minimize resin-rich stack-up around PTH's?  

Denis Lefebvre, CID+
Sr. PCB Designer
Finisar Corporation
(408)542-3832

-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Tom
Parkinson
Sent: Tuesday, June 05, 2007 7:14 AM
To: [log in to unmask]
Subject: [DC] Via Open

Tech Net & Designer Net

Greetings. We are running into a situation on Lead Free processed PCBs.
Failure mode is finding open vias during unit testing (fully populated).

Boards are Tg170, Material type EM320, 0.063" thick boards.  
6 layers of 1 oz copper. ENIG 3~5u"

Suspect vias go from top layer to bottom layer only.

After running through reflow, we have found vias open. No visual signs
of delamination, however when ohming out the via, if we press on the via
we get continuity - thus we suspect the vias are opening during the
process.

Anyone out there having these problems, or information concerning this
failure mode?  Z-expansion failure?


Tom Parkinson
Quality System Manager - CIT
WinTronics, Inc.
Phone: 724-981-5770 - extension 235

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