I agreed with Ioan that it plain excess solder for on QFP.
Karen, do you have a picture of passive parts? Yours customer is using SAC305 WS process?
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Karen Tellefsen
Sent: Saturday, 13 June 2009 1:19 AM
To: [log in to unmask]
Subject: Re: [TN] Strange tin "migration" under OFN soldered with no-clean SAC305 solder paste
More information from our tech service engineer:
There is no hand soldering.
The board is Ni-Au
The boards are clean... no issue with Sn Pb
Could it be galvanic corrosion with exposed Ni or Au acting as a cathode,
allowing the tin in the solder joint to corrode? Maybe there is some metal
surface on the QFN that can act as a cathode.
There's no externally applied voltage, maybe there is a battery somewhere
on the board.
Karen Tellefsen - Electrical Testing
[log in to unmask]
908-791-3069
Dave Hillman wrote:
Hi Karen - you should attempt to determine if any ionic contamination is
present - you could just have a typical electrochemical migration issue to
due contamination.
Dave Hillman
Rockwell Collins
[log in to unmask]
Karen Tellefsen <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
06/12/2009 11:12 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Karen Tellefsen <[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [TN] Strange tin "migration" under OFN soldered with no-clean SAC305
solder paste
I'm not sure; I'm getting my information second hand.
Thanks
-------------------
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]
Enthone GmbH Geschäftsführer: Knut Balzer, Luc de Croo, Jürgen Dietrich Amtsgericht Düsseldorf HRB 45276
USt-Id-Nr. DE 811 205 946
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