Issue link: https://iconnect007.uberflip.com/i/1534120
40 DESIGN007 MAGAZINE I APRIL 2025 solder and unsolder. ese pins should only connect to the planes as needed, with as few connections as possible. • Shielding vias: I have some suggestions about placing vias in the GND plane around a signal on the same layer. › ese vias eat up space on every layer of your board. Start thinking in 3D. If I'm isolating signals on Layer 1, my GND should be on Layer 2 or 3. Use a blind via for these. is not only frees up routing space on the other layers but also pre- vents the spreading of the noise (like an antenna) to all the other layers. › Find the signal λ for spacing the vias properly. Place these appropriately. • Component issues: › Parts too close together or sharing foot- print pads violates the IPC "one pin, one pad" rule found in IPC-2221, 8-2. It also creates less solder for both components. Most assembly shops consider this an error when using AOI systems to check for solder faults. It reads as a short. › Component tolerances are not in the "ideal" range. You may have to have tight tolerances on the parts you purchase or have them measured and "binned" before assembly. › Component substitutions and dual foot- prints can cause havoc with the "real" cir- cuit. Be sure to follow the three Fs—func- tion, fit, and form—for all substitutions. • Materials and layer stackup: › Unbalanced layer stackups are common in RF designs. is doesn't create too many issues in fabrication, but it really does at assembly. Bow and twist gets out of hand. ¤ If you can plan on inserting stiffeners in the layer stackup, this will help. ¤ Adding metal bars or plates and have them be a part of the fabrication process. ¤ Adding a thick copper plane or copper- invar-copper. › Discuss all possibilities with your fabri- cator and assembler. is will probably need some special handling, pre-drilling, and special materials. › Material specifications in core and pre- preg can differ from batch to batch and from supplier to supplier. e tighter your "ideal" circuit has to be, the more picky you have to with your "real" material. › Really work with your fabricator to be able to have enough of the same batch of materials you'll need for your product, even if they need to store it for you. • Multiple power and ground connections: › Placement of components under these conditions is vital. Keep all components with the same power and ground refer- ences together. Spreading them out will create noise and poor signal integrity. › Don't break the loop. RF is everywhere now, and it behooves today's PCB designers to learn all they can about this technology, and why it's not really "black magic" aer all. I hope this article helps you design better RF boards. I would also advise you to read as many books and articles on RF PCB design as you can and watch a few videos by the above-mentioned experts. DESIGN007 Cherie Litson is the founder of Litson1 Consulting and an instructor with EPTAC.