Mitigation of Unintentional Radiated Emissions from Tall VLSI Heatsinks Using Ground Posts

When a heatsink is mounted on an integrated circuit (IC) package above a printed circuit board (PCB), noise from the IC can be coupled to the board-heatsink structure causing radiated emissions. One method to reduce these emissions is to connect the heatsink to the PCB using shorting posts. This paper examines the effectiveness of shorting posts for reducing the radiated emissions from tall heatsinks, based on the partial inductance of the posts. A closed-form expression is derived for calculating the reduction in emissions that is obtained by shorting posts mounted symmetrically around the perimeter of the heatsink. The effectiveness of connecting the posts to the board through a resistance to damp resonant peaks is also discussed.