Suspect that you may face a loss of solderability over 3-4 week hold time as
the Tin forms intermetallic with Copper, and loses solderability.   Immersion
Tin can be Thin (35 microinches, or 1 micron) to very thin (10 microinches,
or .25 micron), even thickest would have trouble meeting one month storage,
especially if storage temp were above usual room temp.

There are two common immersion Tin systems, a salt based system, that must be
used hot, and a more common liquid based system that is normally used at room
temp.
Only the hot one has even a prayer, and not much of one.

Rudy Sedlak
RD Chemical Company

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