Immersion silver.
Flat.
May tarnish slightly after each reflow, but does not affect
solderability. Can easily withstand several reflow cycles.
Allows you to form IMF with copper, not nickel.
Very few plating issues seen.
Good shelf life when properly packaged from vendor.
Much cheaper than Electroless nickel/immersion gold.
No issues with nickel oxides continuing to grow during subsequent heat
cycles after plating. (Process cycles and service cycles).
Requires shorter time/less heat to properly dissolve copper into
intermetallic formation than is needed for nickel.
Provides better performance on high-frequency/high-impedance circuits.


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Walker
Sent: Wednesday, January 18, 2006 11:39 AM
To: [log in to unmask]
Subject: [TN] RoHS board finish

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
[log in to unmask] (mailto:[log in to unmask])

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