This appears to be contaminants creating voids inside of the vias. I do
not think it is from outside applications of solder, such as from wave
soldering, as the voids appear to be concentrated within the via and are
not seen in the solder joints on the surface of the board. This appears
to be caused by ablation or plating residues left inside the vias after
fabrication. These contaminants will also cause the blistering seen near
the surface. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Tuesday, May 24, 2005 3:08 PM
To: [log in to unmask]
Subject: Re: [TN] Solder Joint Anomaly

Hi All,
This is why people tent or fill their vias with soft polymer. These
voids create stress risers at the Cu barrel walls--not a real problem
for benign operating environments, but the death knell in severe
conditions.



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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