Several online PCB fabrication quote forms offer SMOBC as a surface finish along with HASL, Ni/AU, etc. How does one specifify SMOBC for traces and untented vias, and elctroless Ni/Au for smt pads? Are these processes mutually exclusive? Or can I get both as desired?
Actually they are complimentary. SMOBC describes how the solder mask shall be applied (but not the type, surface finish, color, etc). The other terms describe the type of surface protective finish applied to the solderable surfaces. You need to specify both attributes. You can find more information in the archives.