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December 1999

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Subject:
From:
Martin Christie <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 17 Dec 1999 08:38:00 +0000
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text/plain
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Ed,

Where do these failures tend to manifest themselves...post reflow, final
inspection?

If you were to cross section through the failed joints what type of solder
fillet would you see?

I've seen similar failures on solder mask defined pads where excessive
solder has caused an effective wetting angle greater than  90Deg. This then
acts as a stress raiser and failures can then occur during mechanical
handling / thermal stress.

Other than that, the only other time I've seen this failure is during
thermal cycling.

Martin

===== Original Message from [log in to unmask] (TechNet E-Mail Forum.) at
12/17/99 12:22 am
>Hi everyone ... I have been looking at solder joint failures for quite a
>while and have stumbled on something new to me.  I hope someone has seen
>this and can give me some insights.  Here it is ...
>
>*  the failures occur on a number of different component types including
>SOICs, QFPs, SMT caps (not chip caps)
>*  the failure is complete interfacial failure of the mounting pad at
>the copper/IMC interface (i.e the solder, Cu6Sn5 and Cu3Sn layers stay
>with the component lead)
>*  the board finish was HASL and the IMC layer appears normal (i.e. ~
>1-2 microns total thickness)
>*  the copper is heavily oxidized.  However, I believe this is because
>the crack existed for a long period of time (perhaps?)
>*  I see no convincing evidence of contamination at the failed interface
>
>*  the failure does not appear to be related to an electroplated copper
>interface
>
>Based on past experience, this type of thing seems to be caused by gross
>thermal shock!?!  Have any of you seen the type of failure I have
>described?  If so, what was the conclusion as to cause?
>
>Best regards,
>Ed Hare
>VP SEM Lab, Inc.
>
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