In a message dated 13/04/99  03:09:43PM, you write:

>
>  Hello Technetters!!
>
>  My company is seriously considering moving to the use of Sn/Ag solder on
all
> of our products.  My question concerns the interaction of this solder with
> the amount of Sn/Pb normally coated on the pads of our PWB's, then HASLed.
> Can anyone give me some feedback?  Is this something ignorable, or is there
> reason for further investigation?
>
....

You don't explain your motivation for wanting to increase your material
costs. A first step to lead free or maybe for higher operating temperatures
in service or what?

If in service operating temperature is a concern then be aware that you are
going to have joints made of variable amounts of tin, lead and silver
contributed from the solder and lead finishes. The lowest melting point
combination of these metals is 179C (plays 183 for Sn/Pb) so there is no
benefit in switching.
Tin lead silver solders are stable in a variety of combinations and I am not
imediately aware of any life issues arising from what you propose, but I
haven't looked. Your alloy combinations will be "more rigid" than Sn/Pb and
there could be implications in life testing and possibly also in service
environments involving wide temperture swings. This area is one which for me
is close to theology and I will leave further comment to better informed
Technetters.
There has been considerable discussion on Technet on lead free issues of late
and Sn/Ag is a candidate alloy.[ As this discussion mostly took place under
the title "European Union" you may have ignored it.] You should be able to
find some useful info amongst the references in that.


Mike Fenner.

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