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June 2009

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Subject:
From:
Karen Tellefsen <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Karen Tellefsen <[log in to unmask]>
Date:
Fri, 12 Jun 2009 12:38:35 -0400
Content-Type:
text/plain
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text/plain (100 lines)
I asked the tech service engineer, but he didn't know.  Immersion silver is
particularly succeptable to creep corrosion.  I'll ask him to get more
information about the QFN.  It also happens under ceramic passives.

Thanks

Karen Tellefsen - Electrical Testing
[log in to unmask]
908-791-3069

George M. Wenger wrote:

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]
[log in to unmask]


-----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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