Hi Doug,

The Massachusetts Lead Free Consortium has tested five LF surface
finishes: solder mask over bare copper with hot air solder leveling
(SMOBC/HASL) (pure tin), matte tin, immersion silver (Ag), organic
solder preservative (OSP), and electroless nickel immersion gold (ENIG).
As you've probably guessed, there is no drop in substitute, and thus the
choice involves weighing various trade-offs. A short summary of tradeoffs:

- We found significantly more visual defects with lead free SMOBC/HASL
than the other finishes we tested.
- ENIG gives good coplanarity and solderability, but is more costly, can
cause black pad and is not appropriate for press fit.
- Immersion Sn is cost-effective, has relatively good solderability, but
opens up the whiskering issue and can grow intermetallics with Cu during
storage.
- OSP is cost effective, but is susceptible to various processing
defects and constraints.

Weighing these and other trade-offs, and based on our test results, our
belief is that ENIG and immersion Sn will be the most widely adopted LF
board finishes.

You can find some of our results in papers and presentations at:
http://www.turi.org/content/content/view/full/460

Regards,
Todd



Doug Barnhard wrote:

>Could I get some direction on some of the board surface finishes the
>designers have gone to in order to get away from the HASL process which
>contains lead. Also any explanation of problems or issues with whatever
>you are using would be helpful.
>
>
>
>Thanks
>
>Doug
>
>

*:-.,_,.-:*'``'*:-.,_,.-:*'``'*:-.,_,.-:*'``'*:*:-.,_,.-:*'*:-.,_
Todd MacFadden
Project Manager
Toxics Use Reduction Institute
University of Massachusetts Lowell
One University Ave
Lowell, MA 01854

978.934.3391
978.934.3050 (fax)

[log in to unmask]
www.turi.org

Because not everyone can live upstream.
,.-:*'``'*:-.,_,.-:*'``'*:-.,_,.-:*'``'*:*:-.,_,.-:*'*:-.,_,.-:*'

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