The likelihood of electrolytic corrosion on a silver/copper couple is 
really negligible, because the EMF difference is only 0.485 V, referred 
to hydrogen equals 0 V. This is insufficient to dissociate most ions.

On 23/04/2015 15:59, MacFadden, Todd wrote:
> Hello Technet friends,
>
> We are usually asked by our PCB suppliers to add teardrops (track expansion) to thin traces (<=5mil) at soldermask openings. We understand the impetus for this on immersion silver boards, where there is a risk of galvanic corrosion due to Cu-Ag couple at the soldermask/Cu interface of SMT pads.
>
> But some suppliers also ask for track expansion on OSP boards. What would be the motivation in this case? My understanding is the risk of corrosion at the soldermask interface on OSP boards is low, even if the soldermask undercut is severe. So is there perhaps some other reliability advantage to having wider copper at trace/pad interfaces on otherwise thin traces? Do others get this question as well?
>
> Thanks in advance for any thoughts or insight.
>
> Todd MacFadden
>
>
>
>
>
>
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