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Reply To: | (Combined Forum of D-33a and 7-31a Subcommittees) |
Date: | Fri, 30 Oct 2009 10:04:25 -0500 |
Content-Type: | text/plain |
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-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of
[log in to unmask]
Sent: Friday, October 30, 2009 9:34 AM
To: [log in to unmask]
Subject: [IPC-600-6012] Latent defects on PWA
All:
I have run into an anomaly that I am having trouble understanding. I am
including a couple cross section pictures to show the anomaly.
After as few as one thermal cycle (-55 to +60C) the boards are failing.
The failure is a reduced resistance between isolated circuits. The
board shown in the pictures was 160 ohms.
I had the failed connection cross sectioned (both horizontal and
vertical views) and it revealed a crack in the prepreg. This is a 14
layer board and the crack is showing up between layers 7 and 8 - it is
B-stage that is cracking. The laminate is polyimide.
As seen in the cross section pictures it appears to me that the crack is
happening after plating - most likely during my thermal cycle. I see no
evidence of plating or any contamination in the crack.
So, my question boils down to why is the crack manifesting itself as a
short or reduced resistance? Has anyone ever come across something like
this or have an explanation?
Thanks for your help.
Pete Menuez
Supplier Quality Engineering Manager
L-3 Communications Cincinnati Electronics 7500 Innovation Way Mason,
Ohio 45040 [log in to unmask]
513-573-6401 Voice
513-573-6767 Fax
<<Cross section.jpg>>
<<Z axis view.jpg>>
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