PCB manufacture

When do fabricators apply the gold on an ENIG board?

ENIG can be applied before or after solder mask. There are advantages/disadvantages to both. BEFORE GOLD: Applying solder mask then gold is typically cheaper since less gold plating is involved. The biggest potential drawback is the solder mask can be attacked by the nickel-plating bath. The extent of the attack is dependent on the solder mask used, some masks are more susceptible than others. AFTER GOLD: Applying gold then solder mask can cause solder mask adhesion problems to the gold surface. Solder mask residues can also be left on the gold, resulting in solderability issues during assembly.

Finally [on this topic], recognize that some dry films are simply not made to withstand the harsh gold plating environment. So, you should choose one that is designed specifically for gold plating, or, a good universal plating film.

When do fabricators apply the OSP on a board?

Where HASL occurs in the panel form (i.e., prior to the boards being excised), the OSP coating is typically applied after rout and test. In terms of processing sequence, however, both technologies share many of the same steps.

OSP: Preclean => Rinse => OSP Coat => Rinse => Dry Hot Air Solder Level: Preclean => Rinse => Flux Coat => Solder Coat => Hot Air Level => Cool => Soft Brush => Post Clean Rinse => Dry

Look here http://www.epa.gov/opptintr/dfe/pubs/pwb/ctsasurf/download/pdf/ch2.pdf

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