Synchronous buck converters generate broadband noise typically in 50 - 300 MHz range. In this paper, the root cause of this broadband noise and possible coupling mechanisms are analysed. Then, a list of EMC design guideline for minimizing the broadband noise is presented. The guideline contains circuit level guideline which involves input filtering, component selection, and an effective snubber strategy using a parallel resistor and inductor. The guideline also contains layout level guideline, which involves decoupling capacitor placement, layer stackup, and minimizing exposed phase voltage area. For each suggested guideline item, an example illustrates the impact of the particular strategy through experimental results or SPICE simulations, leading to a strong reduction of broadband noise from the synchronous buck converter.