Radiated Emissions from Proximity Coupled Oversized Heat-Sinks

Radiated emission characteristics of oversized heat sinks that have surface area substantially larger than the top contact surface of the IC package are investigated. The oversized heat sinks are found to radiate higher levels at the frequencies that are present in components and traces in the proximity of the heat sink than the frequencies contained within the IC package itself. In this paper, oversized heat sinks are modeled as proximity coupled patch antennas with a short-circuited stub. Patch antenna characteristics such as input impedance (that varies with the feed positions) and resonance frequencies are applied in analyzing the radiated emissions characteristics of oversized heat sinks. Radiated emissions measured from a physical proximity coupled patch antenna model and a highly integrated PCB with oversized heat sink is presented and results discussed. An oversized heat sink is defined as heat sink mounted to the top IC package that has a planar area substantially (> 2 times) larger than the contact area of the IC package.