Reduction of Electromagnetic Emission from ICs Using Soft Flexible Ferrite Sheets

Soft ferrite sheets are widely used to reduce e.g. unwanted electromagnetic emissions from electronic systems. Based on standardized measurement procedures, the attenuation properties of different materials and thicknesses of such ferrite sheets can be investigated over a wide frequency range. The results of the measurements can be used to find the right ferrite plates for targeted reduction of electromagnetic interferences. In this paper, we characterize different ferrite sheets by measuring the coupling between two antennas according to a standardized measurement procedure as defined in IEC 62333. Furthermore, these ferrite sheets are applied to the surface of an IC package and various IC-level measurements are used to demonstrate the real electromagnetic emission reduction that can be achieved with such ferrite sheets. Thereby reduction of the near E- and H-field is measured with near-field probes. Additionally, the reduction of the emissions obtained with the TEM-cell and the IC stripline method are considered. Finally, we will also discuss the influence of ferrite sheets on the conducted emission of an IC.