Pushing the Limits of PCB Impedance Control
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 thickness, dielectric, stackup, glass weave, routing/snaking, and via placement. There are many helpful products to simulate and simplify this process, but theoretical simulation and experimental measurement are two different ballgames. 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 manufacturing, the list seems endless: etching, high layer counts, feature density, pressing, layer registration, material storage, and expansion/contraction. With so many contributing factors, who can blame them for playing their cards close to the vest?
Thus, how well can these manufacturing processes produce a match to the original design, and how well will the result match the theory? As Einstein said, “A theory is something nobody believes in except the person who made it. An experiment is something everybody believes, except the person who made it.”
Original link: https://iconnect007.com/article/141436/pushing-the-limits-of-pcb-impedance-control/141433/pcb
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