Shelf unit for electronic communication devices

A shelf unit (10) for packing therein printed circuit boards in electronic communication devices, to be put one upon another in a cabinet, wherein said shelf unit (10) comprises hollow side plates (15) which are provided, on their outer faces, with air inlet openings (18), and atop plate (13) which is connected to the side plates and which comprises an inclined heat diffusion plate which defines thereon an air introduction space (22), the side plates being provided, on their innerfaces, with openings (19) communicating with the air introduction space.