Karen,
Are you sure this is migration? They might very well be plain shorts from excess of solder or manual component realignment before reflow. Has the assembler checked the components under X-Ray before the conditioning, just to make sure everything is clean at the exit of the oven?
Just a thought,
Ioan Tempea, ing.
t : 450-967-7100 ext : 244
[log in to unmask]
www.digico.cc
P N'imprimer que si nécessaire - Print only if you must
----- Forwarded by Karen Tellefsen/AlphaMetalsUS/Cookson on 06/12/2009
10:47 AM -----
Karen
Tellefsen/AlphaMe
talsUS/Cookson To
[log in to unmask]
06/12/2009 10:26 cc
AM
Subject
Strange tin "migration" under OFN
soldered with no-clean SAC305
solder paste
One of our technical service engineers asked me about a strange migration phenomenon one of our customers observed under passives and QFN's that have been soldered with one of our no-clean SAC305 solder pastes. I've attached an X-ray picture of a QFN exhibiting this strange failure, but I don't know how it can be posted so you can look at it.. Further analysis after removing the component showed that the shadows in the X-ray picture is caused by a black material containing tin. The boards were conditioned 85°C 85%RH for 500 hr, but no voltage was applied. This phenomenon was not observed under QFPs (not surprising), and seems to be independent of reflow profile used. Additionally, the customer has not seen anything like this with tin lead solder paste, however, the tin-lead solder pastes would have
a different fluxes. The tin "migration" is coming from both adjacent
solder joints, and there is no voltage applied, so it seems to be a corrosion problem. Certainly QFN and big passives are good at trapping and retaining water in the flux residue underneath them.
I've never seen anything like this; has anyone else out in TechNet land seen this or have any ideas what caused this?
Thanks
Karen Tellefsen - Electrical Testing
[log in to unmask]
908-791-3069
(See attached file: Strange tin migration.JPG)
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