There is a misperception that copper weights offer certain exact thicknesses and that these do not reduce during the production of a PCB. For example 1 oz. = 35um or ½ oz. = 18um. However IPC-6012 detailed the acceptable minimum thickness of both copper foils and foils after plating based upon allowable tolerances of copper foils and reductions of plating copper during subsequant processing. Below shows some of the more standard copper weights and allowable finished thickness.
As such it is critical to understand what you need and specify correctly – if not then you may under-specify or you may over-specifiy which can lead to excess costs being built into the design. For more information, please consult our technicians.