First suggestion is that you search the archives of the IPC LeadFree
forum - you can get to them off the IPC.org site.  There is tons of info
on that forum.  To a lesser extent, search the archives of this forum as
well (Technet).
You will see many heated arguments about the pros and cons of ENIG, Imm
Ag, Imm Sn, and maybe even a little about OSP.
Why are you using SnPb components if you are doing a design for Pb free?

Talk to your board supplier about recommendations for Pb free FR4 - I'm
sure they have options available.  Td and Tg are the main factors to
look into.
If this is supposed to be RoHS compliant, you may need to verify that
your soldermask is RoHS compliant as well.

Good luck.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Walker
Sent: 18-Jan-06 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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