​ The engineering library of the PCB is the same as the schematic engineering library. The engineering library is all the device libraries currently placed in the project, including symbols, footprints and multiplexing blocks. Adding devices and special symbols to the project can be displayed in the engineering library. , the device engineering library deleted in the project will not be deleted, it will be kept in the engineering library, make a historical record, record the devices placed in this project, and can also click to use or modify again, and modify it in the engineering library The device can only be used in the current project and has no effect on the component library, but the device that has been placed in the project cannot be deleted from the project library.