Nee hao GA Tan,
You do not need T-shock to break the SJs, they are already broken.What you are observing is the fact that the fractured SJs separate at elevated T's giving you electrical opens, but make contact at room temperature giving you continuity.
All you have to do to get the opens is heating the assemblies, maybe to about 80 to 100C.
Regards,
Werner Engelmaier
可靠性先生
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com
-----Original Message-----
From: Tan Geok Ang <[log in to unmask]>
To: [log in to unmask]
Sent: Wed, 22 Oct 2008 9:29 pm
Subject: [TN] Underfill, Cause
Hi All,
A) Does anyone use Sunstar reworkable underfill 991U (reworkable)
before?
http://www.eleshow.com/contents/sunster/rewunderfill/enindex.html
Recently, I used this material to underfill a dummy Pb-free BGA (1156
balls on ENIG) which showed a number of "open circuit" during ESS
testing. Post measurement showed that the "open circuit" solder joints
closed back, hence was not able to determine the cause of the problem
(Pending cross-section).
Intend to use thermal shock (-45 to 85 oC) to "break" the joint
permanently, is it the right way?
Any suggestion what might be the cause?
Thank in advance...
Regards
GA Tan
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