Here you can specify any requirements/instructions specific to the manufacturing of the bare PCBs that you would like to be followed. You should also enter any parameters that fall outside our default specifications as these require custom quotes. Some examples are:
Via in pad
Non default stackup requirements
Inclusion of additional layers on the silkscreen, eg Eagle tDoc/bDoc layers
If these requirements are already listed in a board layer, you can simply point us to it.
Note, do not use this field to specify custom assembly instructions. See How can I specify custom assembly instructions for this purpose. Adding non bare board related requirements to this section may result in a delay in quoting.