Hi Julie - well, that's a new one to me. I am skeptical that the lead frame
is really "pure iron" but can't think of a reason having that configuration
(pure iron/copper/ Sn5Bi) would cause an issue. The Sn5Bi surface finish is
also somewhat unique.  You might want to cross section a lead and do a
quick SEM assessment.

Dave Hillman
Rockwell Collins
[log in to unmask]


On Tue, Nov 7, 2017 at 7:40 PM, Julie Silk <[log in to unmask]> wrote:

> Have you heard of component terminations made of “pure iron”?  Not an
> alloy.  Any concerns that I should know about?  Seems like the CTE is low,
> although not as low as alloy 42.  These are plated with copper then Sn5Bi.
> Rather odd...
>
> Comments from our materials engineer:
> Per existing guidelines, Alloy 42 is a high risk in SMT because of CTE
> mismatches with Sn.
> CTE of pure Fe is 11.7 ppm/C
> CTE of Cu or alloys ranges from 16.2 to 17.8 ppm/C
> CTE of Sn is  23.5 ppm/C
> CTE of pure Alloy 42  is  4.6 ppm/C
>