Tracy, IBM and other companies have tried in the past with TIN plating for
PCB and as a contact finish. However there are severe reliability problems as
mentiuoned by Don. That was also the case with contact reliability where gold
vs tin or tinlead is not recommended. There is plenty of literature on this
subject from  companies like AMP, Bell Labs etc. Tinlead finish for contact
works when high contact force ie greater than 120 gms/contact is assured and
mating/unmating are a small number ie less than 5.

You can contact Dr Roger Sandwall at IBM Raleigh, North Carolina for more
information on this subject.