What is the surface finish on the QFN and what is t
Karen,
What is the surface finish on the QFN and what is the PCB surface finish?
Regards,
George
George M. Wenger
Andrew Solutions
Senior Principal FMA / Reliability Engineer
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 [Office] (732) 309-8964 [Cell]
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Karen Tellefsen
Sent: Friday, June 12, 2009 11:10 AM
To: [log in to unmask]
Subject: Re: [TN] Strange tin "migration" under OFN soldered with no-clean SAC305 solder paste
I though of creep corrosion also, but flux contains no sulfur of halide.
That doesn't mean that there is no source of sulfur, but I don't know about
it.
Karen Tellefsen - Electrical Testing
[log in to unmask]
908-791-3069
fabrice pires <[log in to unmask]:
It make me think about creep corrosion phenomena. Is there any sulfur in
the residues?
Just an idea.
Karen Tellefsen a écrit :
> 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
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