Study on the reduction of heatsink radiation by combining grounding pins and absorbing materials

This paper describes a study on the effectiveness of grounding pins and high-frequency absorbers to reduce the emissions of heatsinks up to 20 GHz. The study considers four different types of excitations, namely a direct excitation, an excitation by a patch antenna, an excitation by a microstrip below the center of the heatsink, and an excitation by a microstrip that was off-set with respect to the center of the heatsink. Grounding post are positioned equidistantly along the edges of the heatsink and the number of grounding pins per side is varied. Adding grounding pins significantly reduces the emission of the heatsink below 1–2 GHz. At higher frequencies, they lose their capability to reduce the heatsink emission and even introduce extra resonance frequencies where the emission is higher compared to the ungrounded heatsink. Three different possible arrangements for the application of absorbing material were considered, namely a thin flat absorber just below the heatsink, a ring absorber between the heatsink and the PCB, and a collar absorber around the heatsink. The absorber succeeds in reducing the heatsink´s emission above 1–2 GHz, but has little of no positive effect on the emissions below 1–2 GHz. Only by the combination of the grounding pins and the absorber material, a reduction of the heatsink´s emission is achieved over the full frequency range.