Reduction of radiated emissions from semiconductor by using absorbent materials

Semiconductors performing digital clocking are a main source of radiated emission noise. Therefore, the most secure method of reducing emission noise is to reduce emission radiated from semiconductors; an application of an absorber to the surface of the semiconductors is one of these methods, too. However, in reality, it is difficult to achieve as much effect of noise reduction as expected by using only an absorber. It is confirmed by experiment that a loop area within the chip has no correlation with radiated emission noise and it is clarified why the existing absorber fails to achieve a satisfactory effect of emission noise reduction. Besides, a new type of chip coating absorber has been developed which can cover up to the semiconductor out lead by using a ferrite coating material of a ferrite/epoxy acrylate substance using only permeability loss out of electronic wave reduction characteristics of materials. As a result of evaluating the radiated emission noise by applying this coating absorber to a semiconductor device, it could be confirmed that the emission noise decreased from about 3 dB up to 20 dB depending on frequency.