Embodiments herein describe a high-speed communication channel in a PCB that includes a dielectric waveguide sandwiched between two ground layers. The dielectric waveguide includes a core and a cladding where the material of the core has a higher dielectric constant than the material of the cladding. Thus, electromagnetic signals propagating in the core are internally reflected at the interface between the core and cladding such that the electromagnetic signals are primary contained in the core.