Depends on material, construction build, assembly process and product end 
use. Some PCB suppliers will have recommended bake regimes prior to 
assembly for all product they supply which you ignore at your own peril even 
though they seem overkill.

See also for example:

http://www.parkelectro.com/parkelectro/images/cm_qna.pdf

which recommends 120C for 2 hrs min.

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