Issue link: https://iconnect007.uberflip.com/i/1522641
82 PCB007 MAGAZINE I JUNE 2024 Article by Alex Knowles RoBAT While we've long known the importance of impedance control in PCB design, with the increase in frequencies, the decrease in SNR (NRZ to PAM4), and the continual reduction in device size, the impact of signal integrity on poor impedance control of transmission lines is even more significant. What Affects Impedance in a PCB? Obviously, the critical elements include the design of trace width/separation, copper thick- ness, dielectric, stackup, glass weave, routing/ snaking, and via placement. ere are many helpful products to simulate and simplify this process, but theoretical simulation and exper- imental measurement are two different ball- games. Now we must look past our perfectly ideal design and get it manufactured. All PCB fabricators have their own carefully guarded methods of modifying their process to achieve the desired controlled impedance specification. When you start considering the techniques and processes in PCB manufactur- ing, the list seems endless: etching, high layer counts, feature density, pressing, layer registra- tion, material storage, and expansion/contrac- tion. With so many contributing factors, who can blame them for playing their cards close to the vest? us, how well can these manufacturing pro- cesses produce a match to the original design, and how well will the result match the the- Pushing the Limits of PCB Impedance Control