MOTM

>Sorry if this is really basic but could any one please tell me if I
>need to be concerned about tarnished finishes on RoHS pcb's. The ones
>in question are about 6 months old and not soldered yet but have been
>stored in airtight bags. I do avoid touching the surfaces with my
>fingers but are they still usable? Also, even once soldered do RoHS
>pcbs become tarnished once exposed to air.

They are still usable. I haven't noticed any difference in soldering 
lightly tarnished RoHS PCBs, but I guess it depends on how badly they 
have tarnished. If you have any concerns, run an abrasive (like steel 
wool) over the pads just prior to soldering. I used to have to do 
that with Paia circuit boards back in the 80s; they were plain copper 
and oxidized very quickly.