Hi Bob! I have used tin/lead HASL (yea, I know its not Pbfree but I wanted
a baseline), immersion tin, immersion silver, and ENIG pwb surface finishes
in a variety of Pbfree soldering process investigations. All of the
finishes performed adequately. Keep in mind that Pbfree soldering processes
are going to be running a minimum of 34C hotter than typical thus
anticipate that you will experience increased surface finish thermal
exposure degradation (loss of solderability, discoloration, etc.). Inert
atmospheres (e.g. nitrogen) can help open up the process window but are not
absolutely necessary. My personal preference is immersion silver. Good
Luck.

Dave Hillman
Rockwell Collins
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             Robert Walker
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Hi All,

I'm doing my first PCB design that will use lead-free components and I need
to change my board finish from what I've always used.....HASL. I'm looking
for
 any recommendations or comments on the best board finish to use.

The components used on the design will be a mixture of tin-lead and
lead-free (SAC), so I'm not sure if there is a preferred finish to use in
this  type
of situation. I work in a prototype environment where the boards may be
reworked (BGA removal/replaced) a number of times, so I'm concerned about
the
ability of the finish being able to handle being  reworked/reflowed a
number of
times.

I'd also welcome any recommendations on the type of board material to use
since it will see an elevated temperature of up to 260C. I've always just
specified FR4 in the past.

Thanx in advance for any feedback.

Regards,
Bob Walker
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