Circuit board (1) and method of producing thereof, the circuit board having a cavity for microstrip to waveguide transition means (2) defined by a hollow space on the walls of which a protection layer (21) is provided. A microelectronic substrate (33) is placed upon an adhesive film (31) adhered onto a surface of the circuit board (1), the adhesive film being pre-cut in selected areas (32) thereof providing openings therethrough. A metal layer (5) is disposed on the resulting structure, wherein a selected part (51) of the metal layer (5) present on a surface of microelectronics substrate (33), facing the hollow space defined by the cavity for microstrip to waveguide transition means (2) is removed.