Issue link: https://iconnect007.uberflip.com/i/1537475
10 DESIGN007 MAGAZINE I JULY 2025 • Material analysis: This is an investigation of any special materials that may be needed, such as RF materials, flex materials, etc. These all have an impact on the stackup of the PCB and often lead to routing restric- tions. For instance, you can only route the RF signals on the RF layers, or you have fewer routing layers available in the flex sections vs. the rigid sections of a rigid-flex board, lim- iting your ability to route signals from one rigid section to the next. Designers often say that setting constraints cor- rectly is a delicate balance of trade-offs. What are some of these trade-offs? One that comes to mind is mass vs. SI vs. cost. For example, from an SI point of view, we want two plane layers for every two signal layers so that we can have the proper controlled impedance struc- tures in our design, but this often leads to addi- tional layers added to the board, which increases both mass and cost. Another example is the copper weight trade-off. As we design evermore highly integrated prod- ucts, we run into the situation of wanting power generation, even if it's relatively low power, on the same board layer as our digital devices. As the digi- tal devices are made in increasingly smaller pack- ages, the pitch of the devices is in the sub-1-mm range. This often requires the use of very thin copper to etch these fine features. The use of the thin copper limits the total cross-sectional area of the power traces and features due to the pitch and other limits of the power devices. In turn, this affects the induc- tance of the PDN and can have other manufactur- ing impacts as well. What are the biggest challenges to setting PCB design constraints? It's understanding what analyses need to be done and the impact to the design if they are not com- pleted prior to start of routing. Which IPC standards or documents are useful in setting constraints? Understanding the interplay and impacts between the IPC-222X (design) series and the correspond- ing IPC-601X (Qualification and Performance, aka fabrication) series, as well as the IPC-2141 High- Speed digital design and the IPC-J-STD-001 Workmanship (aka assembly standards), is the most critical. In addition to these standards, it is also beneficial to understand the various materi- als standards such as IPC-4101 and the others in the IPC-4000 group. The Global Electronics Association (formerly known as IPC) is setting up a database of DFM profiles for participating fabricators, which would provide much of the info needed while setting your constraints. Have you used any of these DFM profiles? Yes. I am on the team that helped define and cre- ate these profiles. These take the relevant infor- mation from several of the standards, such as the ones I've just mentioned, and create a profile that takes the Global Electronics Association class and producibility levels into account, along with data on fabricator limitations, to provide a profile that will incorporate all of these principles into a more complete understanding of the design. Is there anything else you would like to add? With the ever-increasing complexity of mod- ern designs that incorporate higher speed digi- tal devices and signals, understanding and imple- menting proper constraints is a critical step to suc- cessful board and product design. DESIGN007 Kris Moyer