Why Do Vias Drag Down High-Speed Signals? Starting with Impedance — Parasitics, Stubs, and Return Path

Last Wednesday afternoon, I had a technical sync with a customer who builds servers. The board was 16 layers, 3.2 mm thick, main signals at 25G, with a few pairs running 56G. About halfway through, the SI engineer on the other side put the simulation plot on the screen and asked: for these vias that […]