Issue link: https://iconnect007.uberflip.com/i/1530269
16 DESIGN007 MAGAZINE I DECEMBER 2024 asked the fabricator and assembler all the right questions. e things that are called out are somewhat customizable per fabricator, and using these specs will help you get consistent answers and fabrication price quotes. Hole sizes and aspect ratios, component pin spacing, and product sizes are getting smaller all the time. How can we navigate the demands of these conditions with the existing manufac- turing processes that exist out there? Speaking of rules, more and more people are using AI as a starting point for their ideas, so I asked AI for an overview for PCB stackups. As you might guess, AI doesn't get everything right. I've listed the AI rules (in italics) fol- lowed by my comments and corrections along with a few other tidbits: Sequential layer arrangement: Alternate lay- ers of signal, ground, and power planes to reduce electromagnetic interference (EMI). EMI is noise. So, this is a good start. However, many designs don't have a power plane due to the multiple power levels in the same IC. If you find there is one power level that is common to all ICs, then use that as a power plane. Otherwise: • Convert one or more signal layers into a power puddle layer. • Take a little time to group components with similar power levels in the same gen- eral areas. • Really look at all signal return paths. e power puddle layer(s) cannot be used as a return path. It's now a signal layer. • Add more GND layers if needed. • Flood ground on the signal layers and add stitching vias. Signal layer placement: Place signal layers below the ground plane for tight coupling. Keep high-speed signals close to the ground plane to reduce noise. is is not quite right. It really doesn't mat- ter if the signal is above or below the ground plane, just keep the distance as close as possible to reduce noise (EMI). In a four-layer board, keep the planes close to the signals, not each other. You won't get enough capacitance from them anyway. Use them to dampen the EMI. Power and ground planes: Maintain a mini- mum distance between power and ground planes. Don't split the power plane. Yes, this is true in any situation. If you have to split the power plane, don't use it for a signal return layer, or don't run your signal across the split on an adjacent layer. Symmetry: Build a symmetrical stackup of the top and bottom layers. is is not quite right. e more accurate statement would be to build a symmetri- cal stack-up from the center of the stackup toward the top and bottom of the board. Sometimes this is not possible due to the electrical requirements. For uneven stackups,