Printed circuit board having outer power planes

A multi-layer printed circuit board (PCB) routes signal traces on internal signal layer(s) and includes power planes on the two outermost layers. The outer layers are maintained at the same non-ground voltage level, and are electrically connected by a series of vias that circumscribe signal traces on the internal layer(s). With a preferred maximum spacing of one-tenth the wavelength of electromagnetic energy generated by the signal traces, the vias, together with the outer power planes, contain electromagnetic energy within the PCB. One or more of the outer planes may include a second power plane area maintained at a different voltage. The two power plane areas are connected by decoupling capacitors, located proximate underlying signal traces that traverse the two power plane areas.