Exactly: it tells an computer controlled pick and place machine on an automated PCB assembly line precisely where and in what orientation to place the components on the PCB. https://en.wikipedia.org/wiki/SMT_placement_equipment

hi, i would like to know how to transfer the prefixes of the components and their packages to the bottom layer and remain with copper traces on the top layer

@MAYLD, Please do not hijack threads. Your question, whilst being perfectly valid, has nothing to do with the OP's question. If you have any more questions, please post them as a new thread. However, to answer your question: Select the part; **Footprint Attributes > Layer** ![enter image description here][1] You will find this very helpful: https://easyeda.com/andyfierman/Welcome_to_EasyEDA-31e1288f882e49e582699b8eb7fe9b1f :) [1]: /editor/20180206/5a78b8f245317.png