IPC-4556 is a specific standard related to "Specification for Performance Requirements of Metallic Coated Printed Boards for High-Frequency and High-Speed Applications".
I'm assuming you're looking for the full article or document related to "IPC-4556 PDF". IPC stands for Institute for Printed Circuits, which is now known as IPC, a trade association that develops standards and guidelines for the electronics industry. ipc-4556 pdf
Would you like more information on how IPC standards are structured or how to navigate the IPC website? Or perhaps there's another way I can assist you related to IPC-4556 or similar topics? IPC-4556 is a specific standard related to "Specification