Steve -
It appears that the registration of the PCB is out somewhat - being 14
layers is possible that via came to close to a utility.
Jeffrey Bush
Director, Quality Assurance and Technical Support
76 Technology Drive - POB 1890
Brattleboro, Vermont 05302-1890
Tel. 802.257.4571.21 Fax. 802.257.0011
[log in to unmask]
http://www.vtcircuits.com
-----Original Message-----
From: Bev Christian [mailto:[log in to unmask]]
Sent: Tuesday, April 27, 2004 3:50 PM
To: [log in to unmask]
Subject: Re: [TN] Interesting Occurence...
Steve,
I wonder if this might have been a case of CAF? Were there buried
traces, PTHs, vias in the are with different potentials?
And as a stickler and a former employee of Owens Corning Fiberglas, I
bet your tech did not smell "burnt fiber glass", but burnt epoxy resin
from the board, which might smell a little like the phenolic binder used
in fiber glass batts. regards, Bev
-----Original Message-----
From: Steve Gregory [mailto:[log in to unmask]]
Sent: April 27, 2004 2:08 PM
To: [log in to unmask]
Subject: [TN] Interesting Occurance...
Hi All!
Just had an interesting occurance that I thought I'd share with you. We
build this 14-layer assembly here that has 10 Altera FLEX 240-pin QFP's
on it...4 on one side, 6 on the other. We've been building this assembly
for some time now with no problems.
After SMT, the board goes through AOI, gets some connectors hand
soldered on, then goes to ICT. After ICT it goes into a Thermotron for
some power-on thermal cycling for eight hours.
Last week, after a cycle was done, the test technician went to retrieve
the boards from the oven. Upon opening the oven door, he noticed this
funky smell....kinda like burnt fiber glass. At one of the twelve
positions in the test rack he found this:
Go to http://www.stevezeva.homestead.com and look at "Smoking Hole" and
"Smoking Hole 2" (NOTE: DUE TO THE GRAPHIC NATURE OF THESE IMAGES,
PARENTAL DISCRETION IS ADVISED)
We don't have a clue how this happened. ICT on this assembly was fine,
there were no problems found in the test fixture position in the oven
(other assemblies have gone through the temp cycle in the same position
without a problem). And supposedly, there is only 5V and 3.3V being
applied during the thermal cycle.
Obviously there had to be more voltage than that to cause the kind of
damage you see in the pictures, but nobody knows where it came from.
Smoking Hole is a QFP on one side of the board, and Smoking Hole 2 is on
the other. The leads are vaporized in the pictures. This only happened
to one board, and the fixture was loaded up with another 11-assemblies.
I don't expect we'll ever figure out what happened unless it somehow
happens again. I know one thing, if it does, I don't want to be anywhere
near the oven!
Thought you might find the pictures interesting...these are $4000
images.
-Steve Gregory-
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