My recommendation is to conduct a metallurgical cross-section (which is
going to not be a simple task). There are a number of possible root causes
but understanding if there is a defect in the base material (your CuSn6) or
a defect in the plating structures is going to only be resolved by a
cross-sectional analysis.

Dave Hillman
Rockwell Collins
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On Tue, Oct 18, 2016 at 6:31 AM, Deng RongJun <[log in to unmask]> wrote:

> Hello All,
>
> I have got a problem that about pin insertion on PCB. It seems something
> oxidized on pin surface and will effect soldering at customer site, and
> this been found  several month later after SMT assembly.
> Pin base material is CuSn6, and plating is: 1-2um Ni under 3-5um Sn 100.
> What is problem on pin surface? Any one of you have experience on this case?
>
> Pictures and SEM result:
> https://goo.gl/photos/GkZGsjRCQj16BW5V8
>
>
>
>
> Best regards
>
> Deng
>