Hi Chris,
The undamaged holes adjacent to the failure site should demonstrate similar material conditions to the failure site. If crazing, adhesive delamination or cohesive failure is in the area that is a strong indicator that the failure site had the same condition.
It has been suggested that on occasion CAF can force a path, as it were, in the epoxy around the glass fibers, not only a path between glass and epoxy interface. If CAF is self propagating then it is not necessary that the path be present before CAF grows.
Using one of our delamination coupons we would look for material degradation after preconditioning and at the end of thermal cycle testing (150°C). Armed with this information you can determine if the material will be insulted by assembly and rework and would have a tendency to degrade in the end use environment. Adhesive delamination, cohesive failure and crazing all produce a change in capacitance in a coupon designed to "see" those changes. In this way at least you could say that a path is produced down which CAF could propagate. Then all you need is a little moisture, ionic contaminate (did someone say bromine) and a potential between adjacent traces, holes or planes.
Sincerely,
Paul Reid
Program Coordinator
PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario
Canada, K2H 9C1
613 596 4244 ext. 229
Skype paul_reid_pwb
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna
Sent: January 19, 2010 11:13 AM
To: [log in to unmask]
Subject: [TN] TI MSP Early Life Failure?
Hello Technet,
We are working on a failure analysis of a battery operated remote sensing device. Failure is linked to 500ohm short power/ground. The assembly experiences at least (2) 255C reflow thermal excursions. Failure manifests at ~6 months.
Slicing/dicing isolation yielded: breakdown between two vias (17 mil spacing) and/or MSP input impedance. Beyond that, original evidence is lost.
We are working the CAF theory, however reproduction of the problem is proving difficult, possibly due to the low number of opportunities on the actual board.
For those of you who know that I'm pushing for placement of (the new) CAF coupons on panels, yes this is our most recent example of the problem.
I would like to get feedback on the possibility that it was the microcontroller instead...
TI MSP430F1612
Level-3-260C-168 HR
Thanks!
Chris Mahanna
Robisan Laboratory Inc.
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