A protected electrical device having at least one electrical sub-assembly (1) to be protected comprises on at least one (11) of upper and lower surfaces (11, 12), at least a screening layer (2) against the electromagnetic (EM) and radiofrequency (RF) fields emitted by the electrical sub-assembly (1). The screening layer (2) comprises at least a first layer made of soft magnetic material with a high relative permeability (µr) larger than 500. The screening layer (2) is placed on substantially the whole surface of said at least one (11) of the upper and lower surfaces (11, 12), except on predetermined regions (1a) of limited area, the electrical connections (8, 9) with external devices being located on at least some of the predetermined regions of limited area.