Through-hole, Secondary, and Mechanical Services
Some boards after SMT may have only a few through-hole components to be added to the board. These can be placed on a slide line and soldered in by a selective soldering machine.
Other assemblies can have their parts prepped and dropped into the board where the populated board then goes through the appropriate wave solder machine (shown above), either lead or lead-free.
Some through-hole boards have large parts and require hand-soldering followed by visual inspection.