In a previous life I worked for a place that made thousands of tin boards.
The customer (Texas Instruments) specified nickel as a migration barrier 
between the copper and tin.  There is no reason you can't use bright acid 
tin as a surface finish.  The one caveat we encountered was that using 
tin nickel as an etch resist tended to give very sharp edges to the lines
where the etchant undercuts the nickel.  Operators can cut their hands 
and if you overetch and get slivers they are like little razors.

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On Wed, 27 Sep 1995 [log in to unmask] wrote:

> Does anyone have any experience soldering surface mount devices to
> Electrolytic Tin plating as opposed to Tin/Lead reflow or HAL?  We have a
> customer that is interested in this but wants us to ensure that they'll be
> able to solder the boards.  They are using a BTU convection oven for
> reflowing the boards after assembly.  Thanks in advance for any
> correspondence.
> 
>