On gold-plated contacts, I used to prescribe 4-5 µm Ni as a barrier, but 
that was also to provide a mechanical robustness. If there is no 
mechanical stress, I would say that 1 µm should be ample as a migration 
barrier.

Brian

Crepeau, Phil (Space Technology) wrote:
> hi,
> 
> forgetting about ipc spec requirements, what is the minimum nickel plating thickness over copper on a printed wiring board that you would feel comfortable with as a barrier against copper migration.
> 
> thanks,
> 
> phil
> 
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