An apparatus includes an IC package comprising a substrate having a first metal layer, a second metal layer, and a dielectric layer disposed between the first and second metal layers. The IC package further comprises an IC die disposed at a surface of the substrate and comprising RF circuitry. The first metal layer comprises a microstrip feedline extending from a pin of the IC die. The microstrip feedline includes a conductive trace having a probe element at a tip distal from the pin. The first metal layer further comprises a waveguide opening comprising a region surrounding the probe element, the region being substantially devoid of conductive material. The substrate further comprises a plurality of metal vias disposed at the perimeter of the region, the metal vias extending from the first metal layer to the second metal layer.