For correct production of your printed circuit board, it must have a label in the copper of the top and bottom layer, for multilayer additionally on the inner layers.
In German, it was once common practice to label the Bestückungsseite (assembly side) with BS, and the Lötseite (solder side) with LS. With SMD assembly this is no longer appropriate, and even worse, in a technical environment where English is more common, the abbreviation “BS” may be misunderstood as “bottom side”! We therefore recommend a uniform inscription using TOP and BOT (for ALL languages!), to indicate the upper and lower sides.
Please NOTE: missing or incorrect labelling is the most frequent cause of problems, since many Layout programs permit mirrored data output! For this reason, please label your circuit boards always with TOP and BOT in the copper! Correct labelling with TOP and BOT in the circuit board’s copper provides information about the layer definition, and also for the layer orientation!
layer definition = unique labelling of top and bottom layers.
layer orientation = labelling to avoid mirrored layers.
