Radiation Reduction from Heatsinks by a PMC Surface

The radiation from IC heatsink is a major concern in the sub-GHz range as well as at few GHz due to the ever-increasing operating frequencies and complexity of digital, analog, and mixed signal systems developed as Systems on Chip (SoC), Systems in Package (SiP), and based on 3D technology. The heatsink is usually larger than the IC package, thus the heatsink bottom plate can guide EM noise from the IC source building up an effective PCB-heatsink radiator. The application of an artificial perfect magnetic conductor (PMC) surface below the heatsink is demonstrated in this paper to effectively reduce the radiation from the heatsink within a well-defined band whose limits can be analytically computed. The use of dielectric material with high permittivity are shown to be effective for lowering the bandgap to the desired frequency band; if the dielectric material is of absorber type, thus with a high loss factor, the combination of pins and absorbing material can lead to several tens of dB of radiation reduction.